Simultaneous dual contrast weighting using double echo rapid acquisition with relaxation enhancement (RARE) imaging.

PubMed

Fuchs, Katharina; Hezel, Fabian; Klix, Sabrina; Mekle, Ralf; Wuerfel, Jens; Niendorf, Thoralf

2014-12-01

This work proposes a dual contrast rapid acquisition with relaxation enhancement (RARE) variant (2in1-RARE), which provides simultaneous proton density (PD) and T2 * contrast in a single acquisition. The underlying concept of 2in1-RARE is the strict separation of spin echoes and stimulated echoes. This approach offers independent weighting of spin echoes and stimulated echoes. 2in1-RARE was evaluated in phantoms including signal-to-noise ratio (SNR) and point spread function assessment. 2in1-RARE was benchmarked versus coherent RARE and a split-echo RARE variant. The applicability of 2in1-RARE for brain imaging was demonstrated in a small cohort of healthy subjects (n = 10) and, exemplary, a multiple sclerosis patient at 3 Tesla as a precursor to a broader clinical study. 2in1-RARE enables the simultaneous acquisition of dual contrast weighted images without any significant image degradation and without sacrificing SNR versus split-echo RARE. This translates into a factor of two speed gain over multi-contrast, sequential split-echo RARE. A 15% broadening of the point spread function was observed in 2in1-RARE. T1 relaxation effects during the mixing time can be neglected for brain tissue. 2in1-RARE offers simultaneous acquisition of images of anatomical (PD) and functional (T2 *) contrast. It presents an alternative to address scan time constraints frequently encountered during sequential acquisition of T2 * or PD-weighted RARE. © 2013 Wiley Periodicals, Inc.

Increasing sensitivity of pulse EPR experiments using echo train detection schemes.

PubMed

Mentink-Vigier, F; Collauto, A; Feintuch, A; Kaminker, I; Tarle, V; Goldfarb, D

2013-11-01

Modern pulse EPR experiments are routinely used to study the structural features of paramagnetic centers. They are usually performed at low temperatures, where relaxation times are long and polarization is high, to achieve a sufficient Signal/Noise Ratio (SNR). However, when working with samples whose amount and/or concentration are limited, sensitivity becomes an issue and therefore measurements may require a significant accumulation time, up to 12h or more. As the detection scheme of practically all pulse EPR sequences is based on the integration of a spin echo--either primary, stimulated or refocused--a considerable increase in SNR can be obtained by replacing the single echo detection scheme by a train of echoes. All these echoes, generated by Carr-Purcell type sequences, are integrated and summed together to improve the SNR. This scheme is commonly used in NMR and here we demonstrate its applicability to a number of frequently used pulse EPR experiments: Echo-Detected EPR, Davies and Mims ENDOR (Electron-Nuclear Double Resonance), DEER (Electron-Electron Double Resonance|) and EDNMR (Electron-Electron Double Resonance (ELDOR)-Detected NMR), which were combined with a Carr-Purcell-Meiboom-Gill (CPMG) type detection scheme at W-band. By collecting the transient signal and integrating a number of refocused echoes, this detection scheme yielded a 1.6-5 folds SNR improvement, depending on the paramagnetic center and the pulse sequence applied. This improvement is achieved while keeping the experimental time constant and it does not introduce signal distortion. Copyright © 2013 Elsevier Inc. All rights reserved.

A Spiral Spin-Echo MR Imaging Technique for Improved Flow Artifact Suppression in T1-Weighted Postcontrast Brain Imaging: A Comparison with Cartesian Turbo Spin-Echo.

PubMed

Li, Z; Hu, H H; Miller, J H; Karis, J P; Cornejo, P; Wang, D; Pipe, J G

2016-04-01

A challenge with the T1-weighted postcontrast Cartesian spin-echo and turbo spin-echo brain MR imaging is the presence of flow artifacts. Our aim was to develop a rapid 2D spiral spin-echo sequence for T1-weighted MR imaging with minimal flow artifacts and to compare it with a conventional Cartesian 2D turbo spin-echo sequence. T1-weighted brain imaging was performed in 24 pediatric patients. After the administration of intravenous gadolinium contrast agent, a reference Cartesian TSE sequence with a scanning time of 2 minutes 30 seconds was performed, followed by the proposed spiral spin-echo sequence with a scanning time of 1 minutes 18 seconds, with similar spatial resolution and volumetric coverage. The results were reviewed independently and blindly by 3 neuroradiologists. Scores from a 3-point scale were assigned in 3 categories: flow artifact reduction, subjective preference, and lesion conspicuity, if any. The Wilcoxon signed rank test was performed to evaluate the reviewer scores. The t test was used to evaluate the SNR. The Fleiss κ coefficient was calculated to examine interreader agreement. In 23 cases, spiral spin-echo was scored over Cartesian TSE in flow artifact reduction (P < .001). In 21 cases, spiral spin-echo was rated superior in subjective preference (P < .001). Ten patients were identified with lesions, and no statistically significant difference in lesion conspicuity was observed between the 2 sequences. There was no statistically significant difference in SNR between the 2 techniques. The Fleiss κ coefficient was 0.79 (95% confidence interval, 0.65-0.93). The proposed spiral spin-echo pulse sequence provides postcontrast images with minimal flow artifacts at a faster scanning time than its Cartesian TSE counterpart. © 2016 by American Journal of Neuroradiology.

Value of a single-shot turbo spin-echo pulse sequence for assessing the architecture of the subarachnoid space and the constitutive nature of cerebrospinal fluid.

PubMed

Pease, Anthony; Sullivan, Stacey; Olby, Natasha; Galano, Heather; Cerda-Gonzalez, Sophia; Robertson, Ian D; Gavin, Patrick; Thrall, Donald

2006-01-01

Three case history reports are presented to illustrate the value of the single-shot turbo spin-echo pulse sequence for assessment of the subarachnoid space. The use of the single-shot turbo spin-echo pulse sequence, which is a heavily T2-weighted sequence, allows for a rapid, noninvasive evaluation of the subarachnoid space by using the high signal from cerebrospinal fluid. This sequence can be completed in seconds rather than the several minutes required for a T2-fast spin-echo sequence. Unlike the standard T2-fast spin-echo sequence, a single-shot turbo spin-echo pulse sequence also provides qualitative information about the protein and the cellular content of the cerebrospinal fluid, such as in patients with inflammatory debris or hemorrhage in the cerebrospinal fluid. Although the resolution of the single-shot turbo spin-echo pulse sequence images is relatively poor compared with more conventional sequences, the qualitative information about the subarachnoid space and cerebrospinal fluid and the rapid acquisition time, make it a useful sequence to include in standard protocols of spinal magnetic resonance imaging.

Strong-coupling induced damping of spin-echo modulations in magic-angle-spinning NMR: Implications for J coupling measurements in disordered solids

NASA Astrophysics Data System (ADS)

Guerry, Paul; Brown, Steven P.; Smith, Mark E.

2017-10-01

In the context of improving J coupling measurements in disordered solids, strong coupling effects have been investigated in the spin-echo and refocused INADEQUATE spin-echo (REINE) modulations of three- and four-spin systems under magic-angle-spinning (MAS), using density matrix simulations and solid-state NMR experiments on a cadmium phosphate glass. Analytical models are developed for the different modulation regimes, which are shown to be distinguishable in practice using Akaike's information criterion. REINE modulations are shown to be free of the damping that occurs for spin-echo modulations when the observed spin has the same isotropic chemical shift as its neighbour. Damping also occurs when the observed spin is bonded to a strongly-coupled pair. For mid-chain units, the presence of both direct and relayed damping makes both REINE and spin-echo modulations impossible to interpret quantitatively. We nonetheless outline how a qualitative comparison of the modulation curves can provide valuable information on disordered networks, possibly also pertaining to dynamic effects therein.

Rabi oscillation and electron-spin-echo envelope modulation of the photoexcited triplet spin system in silicon

NASA Astrophysics Data System (ADS)

Akhtar, Waseem; Sekiguchi, Takeharu; Itahashi, Tatsumasa; Filidou, Vasileia; Morton, John J. L.; Vlasenko, Leonid; Itoh, Kohei M.

2012-09-01

We report on a pulsed electron paramagnetic resonance (EPR) study of the photoexcited triplet state (S=1) of oxygen-vacancy centers in silicon. Rabi oscillations between the triplet sublevels are observed using coherent manipulation with a resonant microwave pulse. The Hahn echo and stimulated echo decay profiles are superimposed with strong modulations known as electron-spin-echo envelope modulation (ESEEM). The ESEEM spectra reveal a weak but anisotropic hyperfine coupling between the triplet electron spin and a 29Si nuclear spin (I=1/2) residing at a nearby lattice site, that cannot be resolved in conventional field-swept EPR spectra.

Isotropic 3-D T2-weighted spin-echo for abdominal and pelvic MRI in children.

PubMed

Dias, Sílvia Costa; Ølsen, Oystein E

2012-11-01

MRI has a fundamental role in paediatric imaging. The T2-weighted fast/turbo spin-echo sequence is important because it has high signal-to-noise ratio compared to gradient-echo sequences. It is usually acquired as 2-D sections in one or more planes. Volumetric spin-echo has until recently only been possible with very long echo times due to blurring of the soft-tissue contrast with long echo trains. A new 3-D spin-echo sequence uses variable flip angles to overcome this problem. It may reproduce useful soft-tissue contrast, with improved spatial resolution. Its isotropic capability allows subsequent reconstruction in standard, curved or arbitrary planes. It may be particularly useful for visualisation of small lesions, or if large lesions distort the usual anatomical relations. We present clinical examples, describe the technical parameters and discuss some potential artefacts and optimisation of image quality.

Polarisation in spin-echo experiments: Multi-point and lock-in measurements

NASA Astrophysics Data System (ADS)

Tamtögl, Anton; Davey, Benjamin; Ward, David J.; Jardine, Andrew P.; Ellis, John; Allison, William

2018-02-01

Spin-echo instruments are typically used to measure diffusive processes and the dynamics and motion in samples on ps and ns time scales. A key aspect of the spin-echo technique is to determine the polarisation of a particle beam. We present two methods for measuring the spin polarisation in spin-echo experiments. The current method in use is based on taking a number of discrete readings. The implementation of a new method involves continuously rotating the spin and measuring its polarisation after being scattered from the sample. A control system running on a microcontroller is used to perform the spin rotation and to calculate the polarisation of the scattered beam based on a lock-in amplifier. First experimental tests of the method on a helium spin-echo spectrometer show that it is clearly working and that it has advantages over the discrete approach, i.e., it can track changes of the beam properties throughout the experiment. Moreover, we show that real-time numerical simulations can perfectly describe a complex experiment and can be easily used to develop improved experimental methods prior to a first hardware implementation.

Electrical detection of nuclear spin-echo signals in an electron spin injection system

NASA Astrophysics Data System (ADS)

Lin, Zhichao; Rasly, Mahmoud; Uemura, Tetsuya

2017-06-01

We demonstrated spin echoes of nuclear spins in a spin injection device with a highly polarized spin source by nuclear magnetic resonance (NMR). Efficient spin injection into GaAs from a half-metallic spin source of Co2MnSi enabled efficient dynamic nuclear polarization (DNP) and sensitive detection of NMR signals even at a low magnetic field of ˜0.1 T and a relatively high temperature of 4.2 K. The intrinsic coherence time T2 of 69Ga nuclear spins was evaluated from the spin-echo signals. The relation between T2 and the decay time of the Rabi oscillation suggests that the inhomogeneous effects in our system are not obvious. This study provides an all-electrical NMR system for nuclear-spin-based qubits.

[The use of the T2-weighted turbo-spin-echo sequence in studying the neurocranium. A comparison with the conventional T2-weighted spin-echo sequence].

PubMed

Siewert, C; Hosten, N; Felix, R

1994-07-01

T2-weighted spin-echo imaging is the standard screening procedure in MR imaging of the neurocranium. We evaluated fast spin-echo T2-weighted imaging (TT2) of the neurocranium in comparison to conventional spin-echo T2-weighted imaging (T2). Signal-to-noise and contrast-to-noise ratio of normal brain tissues (basal ganglia, grey and white matter, CSF fluid) and different pathologies were calculated. Signal-to-noise ratio and contrast-to-noise ratio were significantly higher in TT2 than in T2 (with the exception of gray-to-white matter contrast). Tissues with increased content of water protons (mobile protons) showed the highest contrast to surrounding tissues. The increased signal intensity of fat must be given due attention in fatty lesions. Because the contrast-to-noise ratio between white matter and basal ganglia is less in TT2, Parkinson patients have to be examined by conventional T2. If these limitations are taken into account, fast spin-echo T2-weighted imaging is well appropriate for MR imaging of the neurocranium, resulting in heavy T2-weighting achieved in a short acquisition time.

Detection of malignant hepatic tumors with ferumoxides-enhanced MRI: comparison of five gradient-recalled echo sequences with different TEs.

PubMed

Matsuo, Masayuki; Kanematsu, Masayuki; Itoh, Kyo; Murakami, Takamichi; Maetani, Yoji; Kondo, Hiroshi; Goshima, Satoshi; Kako, Nobuo; Hoshi, Hiroaki; Konishi, Junji; Moriyama, Noriyuki; Nakamura, Hironobu

2004-01-01

The purpose of our study was to compare the detectability of malignant hepatic tumors on ferumoxides-enhanced MRI using five gradient-recalled echo sequences at different TEs. Ferumoxides-enhanced MRIs obtained in 31 patients with 50 malignant hepatic tumors (33 hepatocellular carcinomas, 17 metastases) were reviewed retrospectively by three independent offsite radiologists. T1-weighted gradient-recalled echo images with TEs of 1.4 and 4.2 msec; T2*-weighted gradient-recalled echo images with TEs of 6, 8, and 10 msec; and T2-weighted fast spin-echo images of livers were randomly reviewed on a segment-by-segment basis. Observer performance was tested using the McNemar test and receiver operating characteristic analysis for the clustered data. Lesion-to-liver contrast-to-noise ratio was also assessed. Mean lesion-to-liver contrast-to-noise ratios were negative and lower with gradient-recalled echo at 1.4 msec than with the other sequences. Sensitivity was higher (p < 0.05) with gradient-recalled echo at 6, 8, and 10 msec and fast spin-echo sequences (75-83%) than with gradient-recalled echo sequences at 1.4 and 4.2 msec (46-48%), and was higher (p < 0.05) with gradient-recalled echo sequence at 8 msec (83%) than with gradient-recalled echo at 6 msec and fast spin-echo sequences (75-78%). Specificity was comparably high with all sequences (95-98%). The area under the receiver operating characteristic curve (A(z)) was greater (p < 0.05) with gradient-recalled echo at 6, 8, and 10 msec and fast spin-echo sequences (A(z) = 0.91-0.93) than with gradient-recalled echo sequences at 1.4 and 4.2 msec (A(z) = 0.82-0.85). In the detection of malignant hepatic tumors, gradient-recalled echo sequences at 8 msec showed the highest sensitivity and had an A(z) value and lesion-to-liver contrast-to-noise ratio comparable with values from gradient-recalled echo sequences at 6 and 10 msec and fast spin-echo sequences.

Reduction of respiratory ghosting motion artifacts in conventional two-dimensional multi-slice Cartesian turbo spin-echo: which k-space filling order is the best?

PubMed

Inoue, Yuuji; Yoneyama, Masami; Nakamura, Masanobu; Takemura, Atsushi

2018-06-01

The two-dimensional Cartesian turbo spin-echo (TSE) sequence is widely used in routine clinical studies, but it is sensitive to respiratory motion. We investigated the k-space orders in Cartesian TSE that can effectively reduce motion artifacts. The purpose of this study was to demonstrate the relationship between k-space order and degree of motion artifacts using a moving phantom. We compared the degree of motion artifacts between linear and asymmetric k-space orders. The actual spacing of ghost artifacts in the asymmetric order was doubled compared with that in the linear order in the free-breathing situation. The asymmetric order clearly showed less sensitivity to incomplete breath-hold at the latter half of the imaging period. Because of the actual number of partitions of the k-space and the temporal filling order, the asymmetric k-space order of Cartesian TSE was superior to the linear k-space order for reduction of ghosting motion artifacts.

Computer simulation of magnetic resonance spectra employing homotopy.

PubMed

Gates, K E; Griffin, M; Hanson, G R; Burrage, K

1998-11-01

Multidimensional homotopy provides an efficient method for accurately tracing energy levels and hence transitions in the presence of energy level anticrossings and looping transitions. Herein we describe the application and implementation of homotopy to the analysis of continuous wave electron paramagnetic resonance spectra. The method can also be applied to electron nuclear double resonance, electron spin echo envelope modulation, solid-state nuclear magnetic resonance, and nuclear quadrupole resonance spectra. Copyright 1998 Academic Press.

3D GRASE PROPELLER: improved image acquisition technique for arterial spin labeling perfusion imaging.

PubMed

Tan, Huan; Hoge, W Scott; Hamilton, Craig A; Günther, Matthias; Kraft, Robert A

2011-07-01

Arterial spin labeling is a noninvasive technique that can quantitatively measure cerebral blood flow. While traditionally arterial spin labeling employs 2D echo planar imaging or spiral acquisition trajectories, single-shot 3D gradient echo and spin echo (GRASE) is gaining popularity in arterial spin labeling due to inherent signal-to-noise ratio advantage and spatial coverage. However, a major limitation of 3D GRASE is through-plane blurring caused by T(2) decay. A novel technique combining 3D GRASE and a periodically rotated overlapping parallel lines with enhanced reconstruction trajectory (PROPELLER) is presented to minimize through-plane blurring without sacrificing perfusion sensitivity or increasing total scan time. Full brain perfusion images were acquired at a 3 × 3 × 5 mm(3) nominal voxel size with pulsed arterial spin labeling preparation sequence. Data from five healthy subjects was acquired on a GE 1.5T scanner in less than 4 minutes per subject. While showing good agreement in cerebral blood flow quantification with 3D gradient echo and spin echo, 3D GRASE PROPELLER demonstrated reduced through-plane blurring, improved anatomical details, high repeatability and robustness against motion, making it suitable for routine clinical use. Copyright © 2011 Wiley-Liss, Inc.

On the application of magic echo cycles for quadrupolar echo spectroscopy of spin-1 nuclei.

PubMed

Mananga, E S; Roopchand, R; Rumala, Y S; Boutis, G S

2007-03-01

Magic echo cycles are introduced for performing quadrupolar echo spectroscopy of spin-1 nuclei. An analysis is performed via average Hamiltonian theory showing that the evolution under chemical shift or static field inhomogeneity can be refocused simultaneously with the quadrupolar interaction using these cycles. Due to the higher convergence in the Magnus expansion, with sufficient RF power, magic echo based quadrupolar echo spectroscopy outperforms the conventional two pulse quadrupolar echo in signal to noise. Experiments highlighting a signal to noise enhancement over the entire bandwidth of the quadrupolar pattern of a powdered sample of deuterated polyethelene are shown.

Electrical detection of electron-spin-echo envelope modulations in thin-film silicon solar cells

NASA Astrophysics Data System (ADS)

Fehr, M.; Behrends, J.; Haas, S.; Rech, B.; Lips, K.; Schnegg, A.

2011-11-01

Electrically detected electron-spin-echo envelope modulations (ED-ESEEM) were employed to detect hyperfine interactions between nuclear spins and paramagnetic sites, determining spin-dependent transport processes in multilayer thin-film microcrystalline silicon solar cells. Electrical detection in combination with a modified Hahn-echo sequence was used to measure echo modulations induced by 29Si, 31P, and 1H nuclei weakly coupled to electron spins of paramagnetic sites in the amorphous and microcrystalline solar cell layers. In the case of CE centers in the μc-Si:H i-layer, the absence of 1H ESEEM modulations indicates that the adjacencies of CE centers are depleted from hydrogen atoms. On the basis of this result, we discuss several models for the microscopic origin of the CE center and conclusively assign those centers to coherent twin boundaries inside of crystalline grains in μc-Si:H.

Effect of low refocusing angle in T1-weighted spin echo and fast spin echo MRI on low-contrast detectability: a comparative phantom study at 1.5 and 3 Tesla.

PubMed

Sarkar, Subhendra N; Mangosing, Jason L; Sarkar, Pooja R

2013-01-01

MRI tissue contrast is not well preserved at high field. In this work, we used a phantom with known, intrinsic contrast (3.6%) for model tissue pairs to test the effects of low angle refocusing pulses and magnetization transfer from adjacent slices on intrinsic contrast at 1.5 and 3 Tesla. Only T1-weighted spin echo sequences were tested since for such sequences the contrast loss, tissue heating, and image quality degradation at high fields seem to present significant diagnostic and quality issues. We hypothesized that the sources of contrast loss could be attributed to low refocusing angles that do not fulfill the Hahn spin echo conditions or to magnetization transfer effects from adjacent slices in multislice imaging. At 1.5 T the measured contrast was 3.6% for 180° refocusing pulses and 2% for 120° pulses, while at 3 T, it was 4% for 180° and only 1% for 120° refocusing pulses. There was no significant difference between single slice and multislice imaging suggesting little or no role played by magnetization transfer in the phantom chosen. Hence, one may conclude that low angle refocusing pulses not fulfilling the Hahn spin echo conditions are primarily responsible for significant deterioration of T1-weighted spin echo image contrast in high-field MRI.

Neutron resonance spin echo with longitudinal DC fields

NASA Astrophysics Data System (ADS)

Krautloher, Maximilian; Kindervater, Jonas; Keller, Thomas; Häußler, Wolfgang

2016-12-01

We report on the design, construction, and performance of a neutron resonance spin echo (NRSE) instrument employing radio frequency (RF) spin flippers combining RF fields with DC fields, the latter oriented parallel (longitudinal) to the neutron propagation direction (longitudinal NRSE (LNRSE)). The advantage of the longitudinal configuration is the inherent homogeneity of the effective magnetic path integrals. In the center of the RF coils, the sign of the spin precession phase is inverted by a π flip of the neutron spins, such that non-uniform spin precession at the boundaries of the RF flippers is canceled. The residual inhomogeneity can be reduced by Fresnel- or Pythagoras-coils as in the case of conventional spin echo instruments (neutron spin echo (NSE)). Due to the good intrinsic homogeneity of the B0 coils, the current densities required for the correction coils are at least a factor of three less than in conventional NSE. As the precision and the current density of the correction coils are the limiting factors for the resolution of both NSE and LNRSE, the latter has the intrinsic potential to surpass the energy resolution of present NSE instruments. Our prototype LNRSE spectrometer described here was implemented at the resonance spin echo for diverse applications (RESEDA) beamline at the MLZ in Garching, Germany. The DC fields are generated by B0 coils, based on resistive split-pair solenoids with an active shielding for low stray fields along the beam path. One pair of RF flippers at a distance of 2 m generates a field integral of ˜0.5 Tm. The LNRSE technique is a future alternative for high-resolution spectroscopy of quasi-elastic excitations. In addition, it also incorporates the MIEZE technique, which allows to achieve spin echo resolution for spin depolarizing samples and sample environments. Here we present the results of numerical optimization of the coil geometry and first data from the prototype instrument.

Optimization of transversal relaxation of nitroxides for pulsed electron-electron double resonance spectroscopy in phospholipid membranes.

PubMed

Dastvan, Reza; Bode, Bela E; Karuppiah, Muruga Poopathi Raja; Marko, Andriy; Lyubenova, Sevdalina; Schwalbe, Harald; Prisner, Thomas F

2010-10-28

Pulsed electron-electron double resonance (PELDOR) spectroscopy is increasingly applied to spin-labeled membrane proteins. However, after reconstitution into liposomes, spin labels often exhibit a much faster transversal relaxation (T(m)) than in detergent micelles, thus limiting application of the method in lipid bilayers. In this study, the main reasons for enhanced transversal relaxation in phospholipid membranes were investigated systematically by use of spin-labeled derivatives of stearic acid and phosphatidylcholine as well as spin-labeled derivatives of the channel-forming peptide gramicidin A under the conditions typically employed for PELDOR distance measurements. Our results clearly show that dephasing due to instantaneous diffusion that depends on dipolar interaction among electron spins is an important contributor to the fast echo decay in cases of high local concentrations of spin labels in membranes. The main difference between spin labels in detergent micelles and membranes is their local concentration. Consequently, avoiding spin clustering and suppressing instantaneous diffusion is the key step for maximizing PELDOR sensitivity in lipid membranes. Even though proton spin diffusion is an important relaxation mechanism, only in samples of low local concentrations does deuteration of acyl chains and buffer significantly prolong T(m). In these cases, values of up to 7 μs have been achieved. Furthermore, our study revealed that membrane composition and labeling position in the membrane can also affect T(m), either by promoting the segregation of spin-labeled species or by altering their exposure to matrix protons. Effects of other experimental parameters including temperature (<50 K), presence of oxygen, and cryoprotectant type are negligible under our experimental conditions.

Polaron spin echo envelope modulations in an organic semiconducting polymer

DOE PAGES

Mkhitaryan, V. V.; Dobrovitski, V. V.

2017-06-01

Here, we present a theoretical analysis of the electron spin echo envelope modulation (ESEEM) spectra of polarons in semiconducting π -conjugated polymers. We show that the contact hyperfine coupling and the dipolar interaction between the polaron and the proton spins give rise to different features in the ESEEM spectra. Our theory enables direct selective probe of different groups of nuclear spins, which affect the polaron spin dynamics. Namely, we demonstrate how the signal from the distant protons (coupled to the polaron spin via dipolar interactions) can be distinguished from the signal coming from the protons residing on the polaron sitemore » (coupled to the polaron spin via contact hyperfine interaction). We propose a method for directly probing the contact hyperfine interaction, that would enable detailed study of the polaron orbital state and its immediate environment. Lastly, we also analyze the decay of the spin echo modulation, and its connection to the polaron transport.« less

Coherent Spin Control at the Quantum Level in an Ensemble-Based Optical Memory.

PubMed

Jobez, Pierre; Laplane, Cyril; Timoney, Nuala; Gisin, Nicolas; Ferrier, Alban; Goldner, Philippe; Afzelius, Mikael

2015-06-12

Long-lived quantum memories are essential components of a long-standing goal of remote distribution of entanglement in quantum networks. These can be realized by storing the quantum states of light as single-spin excitations in atomic ensembles. However, spin states are often subjected to different dephasing processes that limit the storage time, which in principle could be overcome using spin-echo techniques. Theoretical studies suggest this to be challenging due to unavoidable spontaneous emission noise in ensemble-based quantum memories. Here, we demonstrate spin-echo manipulation of a mean spin excitation of 1 in a large solid-state ensemble, generated through storage of a weak optical pulse. After a storage time of about 1 ms we optically read-out the spin excitation with a high signal-to-noise ratio. Our results pave the way for long-duration optical quantum storage using spin-echo techniques for any ensemble-based memory.

Access to long-term optical memories using photon echoes retrieved from electron spins in semiconductor quantum wells

NASA Astrophysics Data System (ADS)

Poltavtsev, S. V.; Langer, L.; Yugova, I. A.; Salewski, M.; Kapitonov, Y. V.; Yakovlev, D. R.; Karczewski, G.; Wojtowicz, T.; Akimov, I. A.; Bayer, M.

2016-10-01

We use spontaneous (two-pulse) and stimulated (three-pulse) photon echoes for studying the coherent evolution of optically excited ensemble of trions which are localized in semiconductor CdTe/CdMgTe quantum well. Application of transverse magnetic field leads to the Larmor precession of the resident electron spins, which shuffles optically induced polarization between optically accessible and inaccessible states. This results in several spectacular phenomena. First, magnetic field induces oscillations of spontaneous photon echo amplitude. Second, in three-pulse excitation scheme, the photon echo decay is extended by several orders of magnitude. In this study, short-lived optical excitation which is created by the first pulse is coherently transferred into a long-lived electron spin state using the second optical pulse. This coherent spin state of electron ensemble persists much longer than any optical excitation in the system, preserving information on initial optical field, which can be retrieved as a photon echo by means of third optical pulse.

Singleshot T1 Mapping using Simultaneous Acquisitions of Spin- and STimulated-Echo Planar Imaging (2D ss-SESTEPI)

PubMed Central

Shi, Xianfeng; Kim, Seong-Eun; Jeong, Eun-Kee

2011-01-01

The conventional stimulated-echo NMR sequence only measures the longitudinal component, while discarding the transverse component, after tipping up the prepared magnetization. This transverse magnetization can be used to measure a spin-echo, in addition to the stimulated-echo. 2D ss-SESTEPI is an EPI-based singleshot imaging technique that simultaneously acquires a spin-echo-planar image (SEPI) and a stimulated-echo-planar image (STEPI) after a single RF excitation. The magnitudes of SEPI and STEPI differ by T1 decay and diffusion weighting for perfect 90° RF, and thus can be used to rapidly measure T1. However, the spatial variation of B1 amplitude induces un-even splitting of the transverse magnetization for SEPI and STEPI within the imaging FOV. Correction for B1 inhomogeneity is therefore critical for 2D ss-SESTEPI to be used for T1 measurement. We developed a method for B1 inhomogeneity correction by acquiring an additional STEPI with minimal mixing time, calculating the difference between the spin-echo and the stimulated-echo and multiplying the STEPI by the inverse functional map. Diffusion-induced decay is corrected by measuring the average diffusivity during the prescanning. Rapid singleshot T1 mapping may be useful for various applications, such as dynamic T1 mapping for real-time estimation of the concentration of contrast agent in DCE-MRI. PMID:20564579

Operating Spin Echo in the Quantum Regime for an Atomic-Ensemble Quantum Memory

NASA Astrophysics Data System (ADS)

Rui, Jun; Jiang, Yan; Yang, Sheng-Jun; Zhao, Bo; Bao, Xiao-Hui; Pan, Jian-Wei

2015-09-01

Spin echo is a powerful technique to extend atomic or nuclear coherence times by overcoming the dephasing due to inhomogeneous broadenings. However, there are disputes about the feasibility of applying this technique to an ensemble-based quantum memory at the single-quanta level. In this experimental study, we find that noise due to imperfections of the rephasing pulses has both intense superradiant and weak isotropic parts. By properly arranging the beam directions and optimizing the pulse fidelities, we successfully manage to operate the spin echo technique in the quantum regime by observing nonclassical photon-photon correlations as well as the quantum behavior of retrieved photons. Our work for the first time demonstrates the feasibility of harnessing the spin echo method to extend the lifetime of ensemble-based quantum memories at the single-quanta level.

Solvent signal suppression for high-resolution MAS-DNP

NASA Astrophysics Data System (ADS)

Lee, Daniel; Chaudhari, Sachin R.; De Paëpe, Gaël

2017-05-01

Dynamic nuclear polarization (DNP) has become a powerful tool to substantially increase the sensitivity of high-field magic angle spinning (MAS) solid-state NMR experiments. The addition of dissolved hyperpolarizing agents usually results in the presence of solvent signals that can overlap and obscure those of interest from the analyte. Here, two methods are proposed to suppress DNP solvent signals: a Forced Echo Dephasing experiment (FEDex) and TRAnsfer of Populations in DOuble Resonance Echo Dephasing (TRAPDORED) NMR. These methods reintroduce a heteronuclear dipolar interaction that is specific to the solvent, thereby forcing a dephasing of recoupled solvent spins and leaving acquired NMR spectra free of associated resonance overlap with the analyte. The potency of these methods is demonstrated on sample types common to MAS-DNP experiments, namely a frozen solution (of L-proline) and a powdered solid (progesterone), both containing deuterated glycerol as a DNP solvent. The proposed methods are efficient, simple to implement, compatible with other NMR experiments, and extendable past spectral editing for just DNP solvents. The sensitivity gains from MAS-DNP in conjunction with FEDex or TRAPDORED then permits rapid and uninterrupted sample analysis.

Adjustable shunt valve-induced magnetic resonance imaging artifact: a comparative study.

PubMed

Toma, Ahmed K; Tarnaris, Andrew; Grieve, Joan P; Watkins, Laurence D; Kitchen, Neil D

2010-07-01

In this paper, the authors' goal was to compare the artifact induced by implanted (in vivo) adjustable shunt valves in spin echo, diffusion weighted (DW), and gradient echo MR imaging pulse sequences. The MR images obtained in 8 patients with proGAV and 6 patients with Strata II adjustable shunt valves were assessed for artifact areas in different planes as well as the total volume for different pulse sequences. Artifacts induced by the Strata II valve were significantly larger than those induced by proGAV valve in spin echo MR imaging pulse sequence (29,761 vs 2450 mm(3) on T2-weighted fast spin echo, p = 0.003) and DW images (100,138 vs 38,955 mm(3), p = 0.025). Artifacts were more marked on DW MR images than on spin echo pulse sequence for both valve types. Adjustable valve-induced artifacts can conceal brain pathology on MR images. This should influence the choice of valve implantation site and the type of valve used. The effect of artifacts on DW images should be highlighted pending the development of less MR imaging artifact-inducing adjustable shunt valves.

A controlled ac Stark echo for quantum memories.

PubMed

Ham, Byoung S

2017-08-09

A quantum memory protocol of controlled ac Stark echoes (CASE) based on a double rephasing photon echo scheme via controlled Rabi flopping is proposed. The double rephasing scheme of photon echoes inherently satisfies the no-population inversion requirement for quantum memories, but the resultant absorptive echo remains a fundamental problem. Herein, it is reported that the first echo in the double rephasing scheme can be dynamically controlled so that it does not affect the second echo, which is accomplished by using unbalanced ac Stark shifts. Then, the second echo is coherently controlled to be emissive via controlled coherence conversion. Finally a near perfect ultralong CASE is presented using a backward echo scheme. Compared with other methods such as dc Stark echoes, the present protocol is all-optical with advantages of wavelength-selective dynamic control of quantum processing for erasing, buffering, and channel multiplexing.

Sudden transition and sudden change from open spin environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Zheng-Da; School of Science, Jiangnan University, Wuxi 214122; Xu, Jing-Bo, E-mail: xujb@zju.edu.cn

2014-11-15

We investigate the necessary conditions for the existence of sudden transition or sudden change phenomenon for appropriate initial states under dephasing. As illustrative examples, we study the behaviors of quantum correlation dynamics of two noninteracting qubits in independent and common open spin environments, respectively. For the independent environments case, we find that the quantum correlation dynamics is closely related to the Loschmidt echo and the dynamics exhibits a sudden transition from classical to quantum correlation decay. It is also shown that the sudden change phenomenon may occur for the common environment case and stationary quantum discord is found at themore » high temperature region of the environment. Finally, we investigate the quantum criticality of the open spin environment by exploring the probability distribution of the Loschmidt echo and the scaling transformation behavior of quantum discord, respectively. - Highlights: • Sudden transition or sudden change from open spin baths are studied. • Quantum discord is related to the Loschmidt echo in independent open spin baths. • Steady quantum discord is found in a common open spin bath. • The probability distribution of the Loschmidt echo is analyzed. • The scaling transformation behavior of quantum discord is displayed.« less

Improved Spin-Echo-Edited NMR Diffusion Measurements

NASA Astrophysics Data System (ADS)

Otto, William H.; Larive, Cynthia K.

2001-12-01

The need for simple and robust schemes for the analysis of ligand-protein binding has resulted in the development of diffusion-based NMR techniques that can be used to assay binding in protein solutions containing a mixture of several ligands. As a means of gaining spectral selectivity in NMR diffusion measurements, a simple experiment, the gradient modified spin-echo (GOSE), has been developed to reject the resonances of coupled spins and detect only the singlets in the 1H NMR spectrum. This is accomplished by first using a spin echo to null the resonances of the coupled spins. Following the spin echo, the singlet magnetization is flipped out of the transverse plane and a dephasing gradient is applied to reduce the spectral artifacts resulting from incomplete cancellation of the J-coupled resonances. The resulting modular sequence is combined here with the BPPSTE pulse sequence; however, it could be easily incorporated into any pulse sequence where additional spectral selectivity is desired. Results obtained with the GOSE-BPPSTE pulse sequence are compared with those obtained with the BPPSTE and CPMG-BPPSTE experiments for a mixture containing the ligands resorcinol and tryptophan in a solution of human serum albumin.

The aluminum ordering in aluminosilicates: a dipolar 27Al NMR spectroscopy study.

PubMed

Gee, Becky A

2004-01-01

The spatial ordering of aluminum atoms in CsAl(SiO3)2 and 3Al2O3.2SiO2 was probed by 27Al dipolar solid-state NMR spectroscopy. The 27Al response to a Hahn spin-echo pulse sequence in a series of aluminum-containing model crystalline compounds demonstrates that quantitative 27Al homonuclear dipolar second moments can be obtained to within +/-20% of the theoretical values, if evaluation of the spin-echo response curve is limited to short evolution periods (2t1 < or = 0.10 ms). Additionally, selective excitation of the central transition m = 1/2 --> -1/2 is necessary in order to ensure quantitative results. Restriction of spin exchange affecting the dephasing of the magnetization may decelerate the spin-echo decay at longer evolution periods. Considering these restraints, the method was used to probe the spatial distribution of aluminum atoms among the tetrahedral sites in two aluminosilicate materials. Experimental 27Al spin-echo response data for the aluminosilicates CsAl(SiO3)2 (synthetic pollucite) and 3Al2O3.2SiO2 (mullite) are compared with theoretical data based on (I) various degrees of aluminum-oxygen-aluminum bond formation among tetrahedrally coordinated aluminum atoms (Al(T(d) )-O-Al(T(d) )) and (II) the maximum avoidance of Al(T(d) )-O-Al(T(d) ) bonding. Analysis of the second moment values and resulting echo decay responses suggests that partial suppression of spin exchange among aluminum atoms in crystallographically distinct sites may contribute to the 27Al spin echo decay in 3Al2O3.2SiO2, thus complicating quantitative analysis of the data. Silicon-29 and aluminum-27 magic angle spinning (MAS) NMR spectra of 3Al2O3.2SiO2 are consistent with those previously reported. The experimental 27Al spin-echo response behavior of CsAl(SiO3)2 differs from the theoretical response behavior based on the maximum avoidance of Al-O-Al bonding between tetrahedral aluminum sites in CsAl(SiO3)2. A single unresolved resonance is observed in both the silicon-29 and aluminum-27 MAS spectra of CsAl(SiO3)2. Copyright 2003 John Wiley & Sons, Ltd.

Sine-squared shifted pulses for recoupling interactions in solid-state NMR

NASA Astrophysics Data System (ADS)

Jain, Mukul G.; Rajalakshmi, G.; Equbal, Asif; Mote, Kaustubh R.; Agarwal, Vipin; Madhu, P. K.

2017-06-01

Rotational-Echo DOuble-Resonance (REDOR) is a versatile experiment for measuring internuclear distance between two heteronuclear spins in solid-state NMR. At slow to intermediate magic-angle spinning (MAS) frequencies, the measurement of distances between strongly coupled spins is challenging due to rapid dephasing of magnetisation. This problem can be remedied by employing the pulse-shifted version of REDOR known as Shifted-REDOR (S-REDOR) that scales down the recoupled dipolar coupling. In this study, we propose a new variant of the REDOR sequence where the positions of the π pulses are determined by a sine-squared function. This new variant has scaling properties similar to S-REDOR. We use theory, numerical simulations, and experiments to compare the dipolar recoupling efficiencies and the experimental robustness of the three REDOR schemes. The proposed variant has advantages in terms of radiofrequency field requirements at fast MAS frequencies.

Cardiovascular magnetic resonance physics for clinicians: part I.

PubMed

Ridgway, John P

2010-11-30

There are many excellent specialised texts and articles that describe the physical principles of cardiovascular magnetic resonance (CMR) techniques. There are also many texts written with the clinician in mind that provide an understandable, more general introduction to the basic physical principles of magnetic resonance (MR) techniques and applications. There are however very few texts or articles that attempt to provide a basic MR physics introduction that is tailored for clinicians using CMR in their daily practice. This is the first of two reviews that are intended to cover the essential aspects of CMR physics in a way that is understandable and relevant to this group. It begins by explaining the basic physical principles of MR, including a description of the main components of an MR imaging system and the three types of magnetic field that they generate. The origin and method of production of the MR signal in biological systems are explained, focusing in particular on the two tissue magnetisation relaxation properties (T1 and T2) that give rise to signal differences from tissues, showing how they can be exploited to generate image contrast for tissue characterisation. The method most commonly used to localise and encode MR signal echoes to form a cross sectional image is described, introducing the concept of k-space and showing how the MR signal data stored within it relates to properties within the reconstructed image. Before describing the CMR acquisition methods in detail, the basic spin echo and gradient pulse sequences are introduced, identifying the key parameters that influence image contrast, including appearances in the presence of flowing blood, resolution and image acquisition time. The main derivatives of these two pulse sequences used for cardiac imaging are then described in more detail. Two of the key requirements for CMR are the need for data acquisition first to be to be synchronised with the subject's ECG and to be fast enough for the subject to be able to hold their breath. Methods of ECG synchronisation using both triggering and retrospective gating approaches, and accelerated data acquisition using turbo or fast spin echo and gradient echo pulse sequences are therefore outlined in some detail. It is shown how double inversion black blood preparation combined with turbo or fast spin echo pulse sequences acquisition is used to achieve high quality anatomical imaging. For functional cardiac imaging using cine gradient echo pulse sequences two derivatives of the gradient echo pulse sequence; spoiled gradient echo and balanced steady state free precession (bSSFP) are compared. In each case key relevant imaging parameters and vendor-specific terms are defined and explained.

Cardiovascular magnetic resonance physics for clinicians: part I

PubMed Central

2010-01-01

There are many excellent specialised texts and articles that describe the physical principles of cardiovascular magnetic resonance (CMR) techniques. There are also many texts written with the clinician in mind that provide an understandable, more general introduction to the basic physical principles of magnetic resonance (MR) techniques and applications. There are however very few texts or articles that attempt to provide a basic MR physics introduction that is tailored for clinicians using CMR in their daily practice. This is the first of two reviews that are intended to cover the essential aspects of CMR physics in a way that is understandable and relevant to this group. It begins by explaining the basic physical principles of MR, including a description of the main components of an MR imaging system and the three types of magnetic field that they generate. The origin and method of production of the MR signal in biological systems are explained, focusing in particular on the two tissue magnetisation relaxation properties (T1 and T2) that give rise to signal differences from tissues, showing how they can be exploited to generate image contrast for tissue characterisation. The method most commonly used to localise and encode MR signal echoes to form a cross sectional image is described, introducing the concept of k-space and showing how the MR signal data stored within it relates to properties within the reconstructed image. Before describing the CMR acquisition methods in detail, the basic spin echo and gradient pulse sequences are introduced, identifying the key parameters that influence image contrast, including appearances in the presence of flowing blood, resolution and image acquisition time. The main derivatives of these two pulse sequences used for cardiac imaging are then described in more detail. Two of the key requirements for CMR are the need for data acquisition first to be to be synchronised with the subject's ECG and to be fast enough for the subject to be able to hold their breath. Methods of ECG synchronisation using both triggering and retrospective gating approaches, and accelerated data acquisition using turbo or fast spin echo and gradient echo pulse sequences are therefore outlined in some detail. It is shown how double inversion black blood preparation combined with turbo or fast spin echo pulse sequences acquisition is used to achieve high quality anatomical imaging. For functional cardiac imaging using cine gradient echo pulse sequences two derivatives of the gradient echo pulse sequence; spoiled gradient echo and balanced steady state free precession (bSSFP) are compared. In each case key relevant imaging parameters and vendor-specific terms are defined and explained. PMID:21118531

Optimal MR Plaque Imaging for Cervical Carotid Artery Stenosis in Predicting the Development of Microembolic Signals during Exposure of Carotid Arteries in Endarterectomy: Comparison of 4 T1-Weighted Imaging Techniques.

PubMed

Sato, Y; Ogasawara, K; Narumi, S; Sasaki, M; Saito, A; Tsushima, E; Namba, T; Kobayashi, M; Yoshida, K; Terayama, Y; Ogawa, A

2016-06-01

Preoperative identification of plaque vulnerability may allow improved risk stratification for patients considered for carotid endarterectomy. The present study aimed to determine which plaque imaging technique, cardiac-gated black-blood fast spin-echo, magnetization-prepared rapid acquisition of gradient echo, source image of 3D time-of-flight MR angiography, or noncardiac-gated spin-echo, most accurately predicts development of microembolic signals during exposure of carotid arteries in carotid endarterectomy. Eighty patients with ICA stenosis (≥70%) underwent the 4 sequences of preoperative MR plaque imaging of the affected carotid bifurcation and then carotid endarterectomy under transcranial Doppler monitoring of microembolic signals in the ipsilateral middle cerebral artery. The contrast ratio of the carotid plaque was calculated by dividing plaque signal intensity by sternocleidomastoid muscle signal intensity. Microembolic signals during exposure of carotid arteries were detected in 23 patients (29%), 3 of whom developed new neurologic deficits postoperatively. Those deficits remained at 24 hours after surgery in only 1 patient. The area under the receiver operating characteristic curve to discriminate between the presence and absence of microembolic signals during exposure of the carotid arteries was significantly greater with nongated spin-echo than with black-blood fast spin-echo (difference between areas, 0.258; P < .0001), MPRAGE (difference between areas, 0.106; P = .0023), or source image of 3D time-of-flight MR angiography (difference between areas, 0.128; P = .0010). Negative binomial regression showed that in the 23 patients with microembolic signals, the contrast ratio was associated with the number of microembolic signals only in nongated spin-echo (risk ratio, 1.36; 95% confidence interval, 1.01-1.97; P < .001). Nongated spin-echo may predict the development of microembolic signals during exposure of the carotid arteries in carotid endarterectomy more accurately than other MR plaque imaging techniques. © 2016 by American Journal of Neuroradiology.

Turboprop: improved PROPELLER imaging.

PubMed

Pipe, James G; Zwart, Nicholas

2006-02-01

A variant of periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) MRI, called turboprop, is introduced. This method employs an oscillating readout gradient during each spin echo of the echo train to collect more lines of data per echo train, which reduces the minimum scan time, motion-related artifact, and specific absorption rate (SAR) while increasing sampling efficiency. It can be applied to conventional fast spin-echo (FSE) imaging; however, this article emphasizes its application in diffusion-weighted imaging (DWI). The method is described and compared with conventional PROPELLER imaging, and clinical images collected with this PROPELLER variant are shown. Copyright 2006 Wiley-Liss, Inc.

Rapid Gradient-Echo Imaging

PubMed Central

Hargreaves, Brian

2012-01-01

Gradient echo sequences are widely used in magnetic resonance imaging (MRI) for numerous applications ranging from angiography to perfusion to functional MRI. Compared with spin-echo techniques, the very short repetition times of gradient-echo methods enable very rapid 2D and 3D imaging, but also lead to complicated “steady states.” Signal and contrast behavior can be described graphically and mathematically, and depends strongly on the type of spoiling: fully balanced (no spoiling), gradient spoiling, or RF-spoiling. These spoiling options trade off between high signal and pure T1 contrast while the flip angle also affects image contrast in all cases, both of which can be demonstrated theoretically and in image examples. As with spin-echo sequences, magnetization preparation can be added to gradient-echo sequences to alter image contrast. Gradient echo sequences are widely used for numerous applications such as 3D perfusion imaging, functional MRI, cardiac imaging and MR angiography. PMID:23097185

A comparison of multi-echo spin-echo and triple-echo steady-state T2 mapping for in vivo evaluation of articular cartilage.

PubMed

Juras, Vladimir; Bohndorf, Klaus; Heule, Rahel; Kronnerwetter, Claudia; Szomolanyi, Pavol; Hager, Benedikt; Bieri, Oliver; Zbyn, Stefan; Trattnig, Siegfried

2016-06-01

To assess the clinical relevance of T2 relaxation times, measured by 3D triple-echo steady-state (3D-TESS), in knee articular cartilage compared to conventional multi-echo spin-echo T2-mapping. Thirteen volunteers and ten patients with focal cartilage lesions were included in this prospective study. All subjects underwent 3-Tesla MRI consisting of a multi-echo multi-slice spin-echo sequence (CPMG) as a reference method for T2 mapping, and 3D TESS with the same geometry settings, but variable acquisition times: standard (TESSs 4:35min) and quick (TESSq 2:05min). T2 values were compared in six different regions in the femoral and tibial cartilage using a Wilcoxon signed ranks test and the Pearson correlation coefficient (r). The local ethics committee approved this study, and all participants gave written informed consent. The mean quantitative T2 values measured by CPMG (mean: 46±9ms) in volunteers were significantly higher compared to those measured with TESS (mean: 31±5ms) in all regions. Both methods performed similarly in patients, but CPMG provided a slightly higher difference between lesions and native cartilage (CPMG: 90ms→61ms [31%],p=0.0125;TESS 32ms→24ms [24%],p=0.0839). 3D-TESS provides results similar to those of a conventional multi-echo spin-echo sequence with many benefits, such as shortening of total acquisition time and insensitivity to B1 and B0 changes. • 3D-TESS T 2 mapping provides clinically comparable results to CPMG in shorter scan-time. • Clinical and investigational studies may benefit from high temporal resolution of 3D-TESS. • 3D-TESS T 2 values are able to differentiate between healthy and damaged cartilage.

Spectral narrowing and spin echo for localized carriers with heavy-tailed L evy distribution of hopping times

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yue, Z.; Mkhitaryan, Vagharsh; Raikh, M. E.

2016-02-02

We study analytically the free induction decay and the spin echo decay originating from the localized carriers moving between the sites which host random magnetic fields. Due to disorder in the site positions and energies, the on-site residence times, , are widely spread according to the L evy distribution. The power-law tail ∝ τ -1-∝ in the distribution of does not affect the conventional spectral narrowing for α > 2, but leads to a dramatic acceleration of the free induction decay in the domain 2 > α > 1. The next abrupt acceleration of the decay takes place as becomesmore » smaller than 1. In the latter domain the decay does not follow a simple-exponent law. To capture the behavior of the average spin in this domain, we solve the evolution equation for the average spin using the approach different from the conventional approach based on the Laplace transform. Unlike the free induction decay, the tail in the distribution of the residence times leads to the slow decay of the spin echo. The echo is dominated by realizations of the carrier motion for which the number of sites, visited by the carrier, is minimal.« less

On the analysis of time-of-flight spin-echo modulated dark-field imaging data

NASA Astrophysics Data System (ADS)

Sales, Morten; Plomp, Jeroen; Bouwman, Wim G.; Tremsin, Anton S.; Habicht, Klaus; Strobl, Markus

2017-06-01

Spin-Echo Modulated Small Angle Neutron Scattering with spatial resolution, i.e. quantitative Spin-Echo Dark Field Imaging, is an emerging technique coupling neutron imaging with spatially resolved quantitative small angle scattering information. However, the currently achieved relatively large modulation periods of the order of millimeters are superimposed to the images of the samples. So far this required an independent reduction and analyses of the image and scattering information encoded in the measured data and is involving extensive curve fitting routines. Apart from requiring a priori decisions potentially limiting the information content that is extractable also a straightforward judgment of the data quality and information content is hindered. In contrast we propose a significantly simplified routine directly applied to the measured data, which does not only allow an immediate first assessment of data quality and delaying decisions on potentially information content limiting further reduction steps to a later and better informed state, but also, as results suggest, generally better analyses. In addition the method enables to drop the spatial resolution detector requirement for non-spatially resolved Spin-Echo Modulated Small Angle Neutron Scattering.

(Charge separation in photoredox reactions). Informal annual technical progress report, October 1, 1981-October 1, 1982. [N,N,N',N'tetramethylbenzidine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kevan, L.

1982-10-21

During this period work has focused on the structural aspects of photoinduced charge separation in micellar media with initial forays into vesicular media. The primary techniques utilized are electron spin resonance and electron spin echo spectrometry. The analysis of electron spin echo modulation gives a unique handle on very weak hyperfine interactions thus providing a new structural tool for this general problem. Electron spin resonance and electron spin echo studies of the photoionization of N,N,N',N'tetramethylbenzidine (TMB) to give the cation radical have been carried out in anionic, cationic and nonionic micellar solutions frozen to 77/sup 0/K. The photoionization efficiency ofmore » TMB has also been studied in micelles with varying alkyl chain lengths of the surfactant. Stearic acid nitroxide spin probes have also been used to determine some structural aspects of the location of the neutral TMB molecule in anionic micelles before photoionization. The nitroxide work in which the nitroxide is acting as an electron acceptor also shows that a suitable electron acceptor can be located within the micellar structure. The effect of inorganic solutes on the efficiency of the photoionization of TMB in frozen micelles has also been studied. A series of electron scavenger studies have been initiated to study the effect on TMB photoionization efficiency. Electron spin echo detection of laser photogenerated TMB cation in liquid sodium dodecyl sulfate solutions at room temperature has recently been observed.« less

SNR-optimized phase-sensitive dual-acquisition turbo spin echo imaging: a fast alternative to FLAIR.

PubMed

Lee, Hyunyeol; Park, Jaeseok

2013-07-01

Phase-sensitive dual-acquisition single-slab three-dimensional turbo spin echo imaging was recently introduced, producing high-resolution isotropic cerebrospinal fluid attenuated brain images without long inversion recovery preparation. Despite the advantages, the weighted-averaging-based technique suffers from noise amplification resulting from different levels of cerebrospinal fluid signal modulations over the two acquisitions. The purpose of this work is to develop a signal-to-noise ratio-optimized version of the phase-sensitive dual-acquisition single-slab three-dimensional turbo spin echo. Variable refocusing flip angles in the first acquisition are calculated using a three-step prescribed signal evolution while those in the second acquisition are calculated using a two-step pseudo-steady state signal transition with a high flip-angle pseudo-steady state at a later portion of the echo train, balancing the levels of cerebrospinal fluid signals in both the acquisitions. Low spatial frequency signals are sampled during the high flip-angle pseudo-steady state to further suppress noise. Numerical simulations of the Bloch equations were performed to evaluate signal evolutions of brain tissues along the echo train and optimize imaging parameters. In vivo studies demonstrate that compared with conventional phase-sensitive dual-acquisition single-slab three-dimensional turbo spin echo, the proposed optimization yields 74% increase in apparent signal-to-noise ratio for gray matter and 32% decrease in imaging time. The proposed method can be a potential alternative to conventional fluid-attenuated imaging. Copyright © 2012 Wiley Periodicals, Inc.

Ultrafast NMR diffusion measurements exploiting chirp spin echoes.

PubMed

Ahola, Susanna; Mankinen, Otto; Telkki, Ville-Veikko

2017-04-01

Standard diffusion NMR measurements require the repetition of the experiment multiple times with varying gradient strength or diffusion delay. This makes the experiment time-consuming and restricts the use of hyperpolarized substances to boost sensitivity. We propose a novel single-scan diffusion experiment, which is based on spatial encoding of two-dimensional data, employing the spin-echoes created by two successive adiabatic frequency-swept chirp π pulses. The experiment is called ultrafast pulsed-field-gradient spin-echo (UF-PGSE). We present a rigorous derivation of the echo amplitude in the UF-PGSE experiment, justifying the theoretical basis of the method. The theory reveals also that the standard analysis of experimental data leads to a diffusion coefficient value overestimated by a few per cent. Although the overestimation is of the order of experimental error and thus insignificant in many practical applications, we propose that it can be compensated by a bipolar gradient version of the experiment, UF-BP-PGSE, or by corresponding stimulated-echo experiment, UF-BP-pulsed-field-gradient stimulated-echo. The latter also removes the effect of uniform background gradients. The experiments offer significant prospects for monitoring fast processes in real time as well as for increasing the sensitivity of experiments by several orders of magnitude by nuclear spin hyperpolarization. Furthermore, they can be applied as basic blocks in various ultrafast multidimensional Laplace NMR experiments. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Eddy current compensated double diffusion encoded (DDE) MRI.

PubMed

Mueller, Lars; Wetscherek, Andreas; Kuder, Tristan Anselm; Laun, Frederik Bernd

2017-01-01

Eddy currents might lead to image distortions in diffusion-weighted echo planar imaging. A method is proposed to reduce their effects on double diffusion encoding (DDE) MRI experiments and the thereby derived microscopic fractional anisotropy (μFA). The twice-refocused spin echo scheme was adapted for DDE measurements. To assess the effect of individual diffusion encodings on the image distortions, measurements of a grid of plastic rods in water were performed. The effect of eddy current compensation on μFA measurements was evaluated in the brains of six healthy volunteers. The use of an eddy current compensation reduced the signal variation. As expected, the distortions caused by the second encoding were larger than those of the first encoding, entailing a stronger need to compensate for them. For an optimal result, however, both encodings had to be compensated. The artifact reduction strongly improved the measurement of the μFA in ventricles and gray matter by reducing the overestimation. An effect of the compensation on absolute μFA values in white matter was not observed. It is advisable to compensate both encodings in DDE measurements for eddy currents. Magn Reson Med 77:328-335, 2017. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.

Coherence rephasing combined with spin-wave storage using chirped control pulses

NASA Astrophysics Data System (ADS)

Demeter, Gabor

2014-06-01

Photon-echo based optical quantum memory schemes often employ intermediate steps to transform optical coherences to spin coherences for longer storage times. We analyze a scheme that uses three identical chirped control pulses for coherence rephasing in an inhomogeneously broadened ensemble of three-level Λ systems. The pulses induce a cyclic permutation of the atomic populations in the adiabatic regime. Optical coherences created by a signal pulse are stored as spin coherences at an intermediate time interval, and are rephased for echo emission when the ensemble is returned to the initial state. Echo emission during a possible partial rephasing when the medium is inverted can be suppressed with an appropriate choice of control pulse wave vectors. We demonstrate that the scheme works in an optically dense ensemble, despite control pulse distortions during propagation. It integrates conveniently the spin-wave storage step into memory schemes based on a second rephasing of the atomic coherences.

MRI of gallstones with different compositions.

PubMed

Tsai, Hong-Ming; Lin, Xi-Zhang; Chen, Chiung-Yu; Lin, Pin-Wen; Lin, Jui-Che

2004-06-01

Gallstones are usually recognized on MRI as filling defects of hypointensity. However, they sometimes may appear as hyperintensities on T1-weighted imaging. This study investigated how gallstones appear on MRI and how their appearance influences the detection of gallstones. Gallstones from 24 patients who had MRI performed before the removal of the gallstones were collected for study. The gallstones were classified either as cholesterol gallstone (n = 4) or as pigment gallstone (n = 20) according to their gross appearance and based on analysis by Fourier transform infrared spectroscopy. MRI included three sequences: single-shot fast spin-echo T2-weighted imaging, 3D fast spoiled gradient-echo T1-weighted imaging, and in-phase fast spoiled gradient-echo T1-weighted imaging. The signal intensity and the detection rate of gallstones on MRI were further correlated with the character of the gallstones. On T1-weighted 3D fast spoiled gradient-echo images, most of the pigment gallstones (18/20) were hyperintense and all the cholesterol gallstones (4/4) were hypointense. The mean ratio of the signal intensity of gallstone to bile was (+/- standard deviation) 3.36 +/- 1.88 for pigment gallstone and 0.24 +/- 0.10 for cholesterol gallstone on the 3D fast spoiled gradient-echo sequence (p < 0.001). Combining the 3D fast spoiled gradient-echo and single-shot fast spin-echo sequences achieved the highest gallstone detection rate (96.4%). Based on the differences of signal intensity of gallstones, the 3D fast spoiled gradient-echo T1-weighted imaging was able to diagnose the composition of gallstones. Adding the 3D fast spoiled gradient-echo imaging to the single-shot fast spin-echo T2-weighted sequence can further improve the detection rate of gallstones.

Contrast-enhanced T1-weighted fluid-attenuated inversion-recovery BLADE magnetic resonance imaging of the brain: an alternative to spin-echo technique for detection of brain lesions in the unsedated pediatric patient?

PubMed

Alibek, Sedat; Adamietz, Boris; Cavallaro, Alexander; Stemmer, Alto; Anders, Katharina; Kramer, Manuel; Bautz, Werner; Staatz, Gundula

2008-08-01

We compared contrast-enhanced T1-weighted magnetic resonance (MR) imaging of the brain using different types of data acquisition techniques: periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER, BLADE) imaging versus standard k-space sampling (conventional spin-echo pulse sequence) in the unsedated pediatric patient with focus on artifact reduction, overall image quality, and lesion detectability. Forty-eight pediatric patients (aged 3 months to 18 years) were scanned with a clinical 1.5-T whole body MR scanner. Cross-sectional contrast-enhanced T1-weighted spin-echo sequence was compared to a T1-weighted dark-fluid fluid-attenuated inversion-recovery (FLAIR) BLADE sequence for qualitative and quantitative criteria (image artifacts, image quality, lesion detectability) by two experienced radiologists. Imaging protocols were matched for imaging parameters. Reader agreement was assessed using the exact Bowker test. BLADE images showed significantly less pulsation and motion artifacts than the standard T1-weighted spin-echo sequence scan. BLADE images showed statistically significant lower signal-to-noise ratio but higher contrast-to-noise ratios with superior gray-white matter contrast. All lesions were demonstrated on FLAIR BLADE imaging, and one false-positive lesion was visible in spin-echo sequence images. BLADE MR imaging at 1.5 T is applicable for central nervous system imaging of the unsedated pediatric patient, reduces motion and pulsation artifacts, and minimizes the need for sedation or general anesthesia without loss of relevant diagnostic information.

All-optical control of long-lived nuclear spins in rare-earth doped nanoparticles.

PubMed

Serrano, D; Karlsson, J; Fossati, A; Ferrier, A; Goldner, P

2018-05-29

Nanoscale systems that coherently couple to light and possess spins offer key capabilities for quantum technologies. However, an outstanding challenge is to preserve properties, and especially optical and spin coherence lifetimes, at the nanoscale. Here, we report optically controlled nuclear spins with long coherence lifetimes (T 2 ) in rare-earth-doped nanoparticles. We detect spins echoes and measure a spin coherence lifetime of 2.9 ± 0.3 ms at 5 K under an external magnetic field of 9 mT, a T 2 value comparable to those obtained in bulk rare-earth crystals. Moreover, we achieve spin T 2 extension using all-optical spin dynamical decoupling and observe high fidelity between excitation and echo phases. Rare-earth-doped nanoparticles are thus the only nano-material in which optically controlled spins with millisecond coherence lifetimes have been reported. These results open the way to providing quantum light-atom-spin interfaces with long storage time within hybrid architectures.

Skew Projection of Echo-Detected EPR Spectra for Increased Sensitivity and Resolution

PubMed Central

Bowman, Michael K.; Krzyaniak, Matthew D.; Cruce, Alex A.; Weber, Ralph T.

2013-01-01

The measurement of EPR spectra during pulsed EPR experiments is commonly accomplished by recording the integral of the electron spin echo as the applied magnetic field is stepped through the spectrum. This approach to echo-detected EPR spectral measurement (ED-EPR) limits sensitivity and spectral resolution and can cause gross distortions in the resulting spectra because some of the information present in the electron spin echo is discarded in such measurements. However, Fourier Transformation of echo shapes measured at a series of magnetic field values followed by skew projection onto either a magnetic field or resonance frequency axis can increase both spectral resolution and sensitivity without the need to trade one against the other. Examples of skew-projected spectra with single crystals, glasses and powders show resolution improvements as large as a factor of seven with sensitivity increases of as much as a factor of five. PMID:23644351

Skew projection of echo-detected EPR spectra for increased sensitivity and resolution

NASA Astrophysics Data System (ADS)

Bowman, Michael K.; Krzyaniak, Matthew D.; Cruce, Alex A.; Weber, Ralph T.

2013-06-01

The measurement of EPR spectra during pulsed EPR experiments is commonly accomplished by recording the integral of the electron spin echo as the applied magnetic field is stepped through the spectrum. This approach to echo-detected EPR spectral measurement (ED-EPR) limits sensitivity and spectral resolution and can cause gross distortions in the resulting spectra because some of the information present in the electron spin echo is discarded in such measurements. However, Fourier transformation of echo shapes measured at a series of magnetic field values followed by skew projection onto either a magnetic field or resonance frequency axis can increase both spectral resolution and sensitivity without the need to trade one against the other. Examples of skew-projected spectra with single crystals, glasses and powders show resolution improvements as large as a factor of seven with sensitivity increases of as much as a factor of five.

Observation of Gravitationally Induced Vertical Striation of Polarized Ultracold Neutrons by Spin-Echo Spectroscopy

NASA Astrophysics Data System (ADS)

Afach, S.; Ayres, N. J.; Ban, G.; Bison, G.; Bodek, K.; Chowdhuri, Z.; Daum, M.; Fertl, M.; Franke, B.; Griffith, W. C.; Grujić, Z. D.; Harris, P. G.; Heil, W.; Hélaine, V.; Kasprzak, M.; Kermaidic, Y.; Kirch, K.; Knowles, P.; Koch, H.-C.; Komposch, S.; Kozela, A.; Krempel, J.; Lauss, B.; Lefort, T.; Lemière, Y.; Mtchedlishvili, A.; Musgrave, M.; Naviliat-Cuncic, O.; Pendlebury, J. M.; Piegsa, F. M.; Pignol, G.; Plonka-Spehr, C.; Prashanth, P. N.; Quéméner, G.; Rawlik, M.; Rebreyend, D.; Ries, D.; Roccia, S.; Rozpedzik, D.; Schmidt-Wellenburg, P.; Severijns, N.; Thorne, J. A.; Weis, A.; Wursten, E.; Wyszynski, G.; Zejma, J.; Zenner, J.; Zsigmond, G.

2015-10-01

We describe a spin-echo method for ultracold neutrons (UCNs) confined in a precession chamber and exposed to a |B0|=1 μ T magnetic field. We have demonstrated that the analysis of UCN spin-echo resonance signals in combination with knowledge of the ambient magnetic field provides an excellent method by which to reconstruct the energy spectrum of a confined ensemble of neutrons. The method takes advantage of the relative dephasing of spins arising from a gravitationally induced striation of stored UCNs of different energies, and also permits an improved determination of the vertical magnetic-field gradient with an exceptional accuracy of 1.1 pT /cm . This novel combination of a well-known nuclear resonance method and gravitationally induced vertical striation is unique in the realm of nuclear and particle physics and should prove to be invaluable for the assessment of systematic effects in precision experiments such as searches for an electric dipole moment of the neutron or the measurement of the neutron lifetime.

DOE Office of Scientific and Technical Information (OSTI.GOV)

van den Berg, R.; Brandino, G. P.; El Araby, O.

In this study, we introduce an integrability-based method enabling the study of semiconductor quantum dot models incorporating both the full hyperfine interaction as well as a mean-field treatment of dipole-dipole interactions in the nuclear spin bath. By performing free induction decay and spin echo simulations we characterize the combined effect of both types of interactions on the decoherence of the electron spin, for external fields ranging from low to high values. We show that for spin echo simulations the hyperfine interaction is the dominant source of decoherence at short times for low fields, and competes with the dipole-dipole interactions atmore » longer times. On the contrary, at high fields the main source of decay is due to the dipole-dipole interactions. In the latter regime an asymmetry in the echo is observed. Furthermore, the non-decaying fraction previously observed for zero field free induction decay simulations in quantum dots with only hyperfine interactions, is destroyed for longer times by the mean-field treatment of the dipolar interactions.« less

Competing interactions in semiconductor quantum dots

DOE PAGES

van den Berg, R.; Brandino, G. P.; El Araby, O.; ...

2014-10-14

In this study, we introduce an integrability-based method enabling the study of semiconductor quantum dot models incorporating both the full hyperfine interaction as well as a mean-field treatment of dipole-dipole interactions in the nuclear spin bath. By performing free induction decay and spin echo simulations we characterize the combined effect of both types of interactions on the decoherence of the electron spin, for external fields ranging from low to high values. We show that for spin echo simulations the hyperfine interaction is the dominant source of decoherence at short times for low fields, and competes with the dipole-dipole interactions atmore » longer times. On the contrary, at high fields the main source of decay is due to the dipole-dipole interactions. In the latter regime an asymmetry in the echo is observed. Furthermore, the non-decaying fraction previously observed for zero field free induction decay simulations in quantum dots with only hyperfine interactions, is destroyed for longer times by the mean-field treatment of the dipolar interactions.« less

Optimization of diffusion-weighted single-refocused spin-echo EPI by reducing eddy-current artifacts and shortening the echo time.

PubMed

Shrestha, Manoj; Hok, Pavel; Nöth, Ulrike; Lienerth, Bianca; Deichmann, Ralf

2018-03-30

The purpose of this work was to optimize the acquisition of diffusion-weighted (DW) single-refocused spin-echo (srSE) data without intrinsic eddy-current compensation (ECC) for an improved performance of ECC postprocessing. The rationale is that srSE sequences without ECC may yield shorter echo times (TE) and thus higher signal-to-noise ratios (SNR) than srSE or twice-refocused spin-echo (trSE) schemes with intrinsic ECC. The proposed method employs dummy scans with DW gradients to drive eddy currents into a steady state before data acquisition. Parameters of the ECC postprocessing algorithm were also optimized. Simulations were performed to obtain minimum TE values for the proposed sequence and sequences with intrinsic ECC. Experimentally, the proposed method was compared with standard DW-trSE imaging, both in vitro and in vivo. Simulations showed substantially shorter TE for the proposed method than for methods with intrinsic ECC when using shortened echo readouts. Data of the proposed method showed a marked increase in SNR. A dummy scan duration of at least 1.5 s improved performance of the ECC postprocessing algorithm. Changes proposed for the DW-srSE sequence and for the parameter setting of the postprocessing ECC algorithm considerably reduced eddy-current artifacts and provided a higher SNR.

In vivo imaging of cortical pathology in multiple sclerosis using ultra-high field MRI

PubMed Central

Mainero, C; Benner, T; Radding, A; van der Kouwe, A; Jensen, R; Rosen, B R.; Kinkel, R P.

2009-01-01

Objective: We used ultra-high field MRI to visualize cortical lesion types described by neuropathology in 16 patients with multiple sclerosis (MS) compared with 8 age-matched controls; to characterize the contrast properties of cortical lesions including T2*, T2, T1, and phase images; and to investigate the relationship between cortical lesion types and clinical data. Methods: We collected, on a 7-T scanner, 2-dimensional fast low-angle shot (FLASH)-T2*-weighted spoiled gradient-echo, T2-weighted turbo spin-echo (TSE) images (0.33 × 033 × 1 mm3), and a 3-dimensional magnetization-prepared rapid gradient echo. Results: Overall, 199 cortical lesions were detected in patients on both FLASH-T2* and T2-TSE scans. Seven-tesla MRI allowed for characterization of cortical plaques into type I (leukocortical), type II (intracortical), and type III/IV (subpial extending partly or completely through the cortical width) lesions as described histopathologically. Types III and IV were the most frequent type of cortical plaques (50.2%), followed by type I (36.2%) and type II (13.6%) lesions. Each lesion type was more frequent in secondary progressive than in relapsing–remitting MS. This difference, however, was significant only for type III/IV lesions. T2*-weighted images showed the highest, while phase images showed the lowest, contrast-to-noise ratio for all cortical lesion types. In patients, the number of type III/IV lesions was associated with greater disability (p < 0.02 by Spearman test) and older age (p < 0.04 by Spearman test). Conclusions: Seven-tesla MRI detected different histologic cortical lesion types in our small multiple sclerosis (MS) sample, suggesting, if validated in a larger population, that it may prove a valuable tool to assess the contribution of cortical MS pathology to clinical disability. GLOSSARY ANOVA = analysis of variance; BN = background noise; CNR = contrast-to-noise ratio; DIR = double-inversion recovery; EDSS = Expanded Disability Status Scale; FLAIR = fluid-attenuated inversion recovery; FLASH = fast low-angle shot; GM = gray matter; MPRAGE = magnetization-prepared rapid gradient echo; MR = magnetic resonance; MS = multiple sclerosis; NACGM = normal-appearing cortical gray matter; RF = radiofrequency; ROI = region of interest; RRMS = relapsing–remitting multiple sclerosis; SNR = signal-to-noise ratio; SPMS = secondary progressive multiple sclerosis; TA = time of acquisition; TE = echo time; TR = repetition time; TSE = turbo spin-echo; WM = white matter. PMID:19641168

Concepts and Engineering Aspects of a Neutron Resonance Spin-Echo Spectrometer for the National Institute of Standards and Technology Center for Neutron Research

PubMed Central

Cook, Jeremy C.

2014-01-01

Following a brief introduction, the Neutron Resonance Spin-Echo (NRSE) principle is discussed classically in Sec. 2. In Sec. 3, two idealized 4-coil NRSE spectrometers are discussed (one using single π-flipper coil units and one using paired “bootstrap” coils); some idealized (exact π-flip) expressions are given for the spin-echo signal and some theoretical limitations are discussed. A more quantum mechanical discussion of NRSE is presented in Sec. 4 and additional theory related to the spin-echo signal, including wavelength-dependence, is given is Sec. 5. Factors affecting the instrumental resolution are discussed in Sec. 6. In Sec. 7, a variety of engineering issues are assessed in the context of challenging performance goals for a NIST Center for Neutron Research (NCNR) NRSE spectrometer. In Sec. 8, some Monte Carlo simulations are presented that examine the combined influences of spectrometer imperfections on the NRSE signal. These are compared with analytical predictions developed in previous sections. In Sec. 9, possible alternatives for a NCNR NRSE spectrometer configuration are discussed together with a preliminary assessment of the spectrometer neutron guide requirements. A summary of some of the useful formulas is given in Appendix A. PMID:26601027

ENDOR with band-selective shaped inversion pulses

NASA Astrophysics Data System (ADS)

Tait, Claudia E.; Stoll, Stefan

2017-04-01

Electron Nuclear DOuble Resonance (ENDOR) is based on the measurement of nuclear transition frequencies through detection of changes in the polarization of electron transitions. In Davies ENDOR, the initial polarization is generated by a selective microwave inversion pulse. The rectangular inversion pulses typically used are characterized by a relatively low selectivity, with full inversion achieved only for a limited number of spin packets with small resonance offsets. With the introduction of pulse shaping to EPR, the rectangular inversion pulses can be replaced with shaped pulses with increased selectivity. Band-selective inversion pulses are characterized by almost rectangular inversion profiles, leading to full inversion for spin packets with resonance offsets within the pulse excitation bandwidth and leaving spin packets outside the excitation bandwidth largely unaffected. Here, we explore the consequences of using different band-selective amplitude-modulated pulses designed for NMR as the inversion pulse in ENDOR. We find an increased sensitivity for small hyperfine couplings compared to rectangular pulses of the same bandwidth. In echo-detected Davies-type ENDOR, finite Fourier series inversion pulses combine the advantages of increased absolute ENDOR sensitivity of short rectangular inversion pulses and increased sensitivity for small hyperfine couplings of long rectangular inversion pulses. The use of pulses with an almost rectangular frequency-domain profile also allows for increased control of the hyperfine contrast selectivity. At X-band, acquisition of echo transients as a function of radiofrequency and appropriate selection of integration windows during data processing allows efficient separation of contributions from weakly and strongly coupled nuclei in overlapping ENDOR spectra within a single experiment.

Brainstem Cavernous Angioma

MedlinePlus

... echo” (as opposed to spin-echo or proton beam) imaging. Gradient-echo MRI is most efficient at ... radiosurgery for cavernous malformations: Kjellberg's experience with proton beam therapy in 98 cases at the Harvard Cyclotron. ...

Control of photon storage time using phase locking.

PubMed

Ham, Byoung S

2010-01-18

A photon echo storage-time extension protocol is presented by using a phase locking method in a three-level backward propagation scheme, where phase locking serves as a conditional stopper of the rephasing process in conventional two-pulse photon echoes. The backward propagation scheme solves the critical problems of extremely low retrieval efficiency and pi rephasing pulse-caused spontaneous emission noise in photon echo based quantum memories. The physics of the storage time extension lies in the imminent population transfer from the excited state to an auxiliary spin state by a phase locking control pulse. We numerically demonstrate that the storage time is lengthened by spin dephasing time.

A fast random walk algorithm for computing the pulsed-gradient spin-echo signal in multiscale porous media.

PubMed

Grebenkov, Denis S

2011-02-01

A new method for computing the signal attenuation due to restricted diffusion in a linear magnetic field gradient is proposed. A fast random walk (FRW) algorithm for simulating random trajectories of diffusing spin-bearing particles is combined with gradient encoding. As random moves of a FRW are continuously adapted to local geometrical length scales, the method is efficient for simulating pulsed-gradient spin-echo experiments in hierarchical or multiscale porous media such as concrete, sandstones, sedimentary rocks and, potentially, brain or lungs. Copyright © 2010 Elsevier Inc. All rights reserved.

Optimization of identity operation in NMR spectroscopy via genetic algorithm: Application to the TEDOR experiment

NASA Astrophysics Data System (ADS)

Manu, V. S.; Veglia, Gianluigi

2016-12-01

Identity operation in the form of π pulses is widely used in NMR spectroscopy. For an isolated single spin system, a sequence of even number of π pulses performs an identity operation, leaving the spin state essentially unaltered. For multi-spin systems, trains of π pulses with appropriate phases and time delays modulate the spin Hamiltonian to perform operations such as decoupling and recoupling. However, experimental imperfections often jeopardize the outcome, leading to severe losses in sensitivity. Here, we demonstrate that a newly designed Genetic Algorithm (GA) is able to optimize a train of π pulses, resulting in a robust identity operation. As proof-of-concept, we optimized the recoupling sequence in the transferred-echo double-resonance (TEDOR) pulse sequence, a key experiment in biological magic angle spinning (MAS) solid-state NMR for measuring multiple carbon-nitrogen distances. The GA modified TEDOR (GMO-TEDOR) experiment with improved recoupling efficiency results in a net gain of sensitivity up to 28% as tested on a uniformly 13C, 15N labeled microcrystalline ubiquitin sample. The robust identity operation achieved via GA paves the way for the optimization of several other pulse sequences used for both solid- and liquid-state NMR used for decoupling, recoupling, and relaxation experiments.

Feedback-tuned, noise resilient gates for encoded spin qubits

NASA Astrophysics Data System (ADS)

Bluhm, Hendrik

Spin 1/2 particles form native two level systems and thus lend themselves as a natural qubit implementation. However, encoding a single qubit in several spins entails benefits, such as reducing the resources necessary for qubit control and protection from certain decoherence channels. While several varieties of such encoded spin qubits have been implemented, accurate control remains challenging, and leakage out of the subspace of valid qubit states is a potential issue. Optimal performance typically requires large pulse amplitudes for fast control, which is prone to systematic errors and prohibits standard control approaches based on Rabi flopping. Furthermore, the exchange interaction typically used to electrically manipulate encoded spin qubits is inherently sensitive to charge noise. I will discuss all-electrical, high-fidelity single qubit operations for a spin qubit encoded in two electrons in a GaAs double quantum dot. Starting from a set of numerically optimized control pulses, we employ an iterative tuning procedure based on measured error syndromes to remove systematic errors.Randomized benchmarking yields an average gate fidelity exceeding 98 % and a leakage rate into invalid states of 0.2 %. These gates exhibit a certain degree of resilience to both slow charge and nuclear spin fluctuations due to dynamical correction analogous to a spin echo. Furthermore, the numerical optimization minimizes the impact of fast charge noise. Both types of noise make relevant contributions to gate errors. The general approach is also adaptable to other qubit encodings and exchange based two-qubit gates.

Dynamics of 4-oxo-TEMPO-d16-15N nitroxide-propylene glycol system studied by ESR and ESE in liquid and glassy state in temperature range 10-295 K

NASA Astrophysics Data System (ADS)

Goslar, Janina; Hoffmann, Stanislaw K.; Lijewski, Stefan

2016-08-01

ESR spectra and electron spin relaxation of nitroxide radical in 4-oxo-TEMPO-d16-15N in propylene glycol were studied at X-band in the temperature range 10-295 K. The spin-lattice relaxation in the liquid viscous state determined from the resonance line shape is governed by three mechanisms occurring during isotropic molecular reorientations. In the glassy state below 200 K the spin-lattice relaxation, phase relaxation and electron spin echo envelope modulations (ESEEM) were studied by pulse spin echo technique using 2-pulse and 3-pulse induced signals. Electron spin-lattice relaxation is governed by a single non-phonon relaxation process produced by localized oscillators of energy 76 cm-1. Electron spin dephasing is dominated by a molecular motion producing a resonance-type peak in the temperature dependence of the dephasing rate around 120 K. The origin of the peak is discussed and a simple method for the peak shape analysis is proposed, which gives the activation energy of a thermally activated motion Ea = 7.8 kJ/mol and correlation time τ0 = 10-8 s. The spin echo amplitude is strongly modulated and FT spectrum contains a doublet of lines centered around the 2D nuclei Zeeman frequency. The splitting into the doublet is discussed as due to a weak hyperfine coupling of nitroxide unpaired electron with deuterium of reorienting CD3 groups.

High Efficiency, Low Distortion 3D Diffusion Tensor Imaging with Variable Density Spiral Fast Spin Echoes (3D DW VDS RARE)

PubMed Central

Frank, Lawrence R.; Jung, Youngkyoo; Inati, Souheil; Tyszka, J. Michael; Wong, Eric C.

2009-01-01

We present an acquisition and reconstruction method designed to acquire high resolution 3D fast spin echo diffusion tensor images while mitigating the major sources of artifacts in DTI - field distortions, eddy currents and motion. The resulting images, being 3D, are of high SNR, and being fast spin echoes, exhibit greatly reduced field distortions. This sequence utilizes variable density spiral acquisition gradients, which allow for the implementation of a self-navigation scheme by which both eddy current and motion artifacts are removed. The result is that high resolution 3D DTI images are produced without the need for eddy current compensating gradients or B0 field correction. In addition, a novel method for fast and accurate reconstruction of the non-Cartesian data is employed. Results are demonstrated in the brains of normal human volunteers. PMID:19778618

Noncontrast Peripheral MRA with Spiral Echo Train Imaging

PubMed Central

Fielden, Samuel W.; Mugler, John P.; Hagspiel, Klaus D.; Norton, Patrick T.; Kramer, Christopher M.; Meyer, Craig H.

2015-01-01

Purpose To develop a spin echo train sequence with spiral readout gradients with improved artery–vein contrast for noncontrast angiography. Theory Venous T2 becomes shorter as the echo spacing is increased in echo train sequences, improving contrast. Spiral acquisitions, due to their data collection efficiency, facilitate long echo spacings without increasing scan times. Methods Bloch equation simulations were performed to determine optimal sequence parameters, and the sequence was applied in five volunteers. In two volunteers, the sequence was performed with a range of echo times and echo spacings to compare with the theoretical contrast behavior. A Cartesian version of the sequence was used to compare contrast appearance with the spiral sequence. Additionally, spiral parallel imaging was optionally used to improve image resolution. Results In vivo, artery–vein contrast properties followed the general shape predicted by simulations, and good results were obtained in all stations. Compared with a Cartesian implementation, the spiral sequence had superior artery–vein contrast, better spatial resolution (1.2 mm2 versus 1.5 mm2), and was acquired in less time (1.4 min versus 7.5 min). Conclusion The spiral spin echo train sequence can be used for flow-independent angiography to generate threedimensional angiograms of the periphery quickly and without the use of contrast agents. PMID:24753164

Noncontrast peripheral MRA with spiral echo train imaging.

PubMed

Fielden, Samuel W; Mugler, John P; Hagspiel, Klaus D; Norton, Patrick T; Kramer, Christopher M; Meyer, Craig H

2015-03-01

To develop a spin echo train sequence with spiral readout gradients with improved artery-vein contrast for noncontrast angiography. Venous T2 becomes shorter as the echo spacing is increased in echo train sequences, improving contrast. Spiral acquisitions, due to their data collection efficiency, facilitate long echo spacings without increasing scan times. Bloch equation simulations were performed to determine optimal sequence parameters, and the sequence was applied in five volunteers. In two volunteers, the sequence was performed with a range of echo times and echo spacings to compare with the theoretical contrast behavior. A Cartesian version of the sequence was used to compare contrast appearance with the spiral sequence. Additionally, spiral parallel imaging was optionally used to improve image resolution. In vivo, artery-vein contrast properties followed the general shape predicted by simulations, and good results were obtained in all stations. Compared with a Cartesian implementation, the spiral sequence had superior artery-vein contrast, better spatial resolution (1.2 mm(2) versus 1.5 mm(2) ), and was acquired in less time (1.4 min versus 7.5 min). The spiral spin echo train sequence can be used for flow-independent angiography to generate three-dimensional angiograms of the periphery quickly and without the use of contrast agents. © 2014 Wiley Periodicals, Inc.

Rapid myelin water imaging in human cervical spinal cord.

PubMed

Ljungberg, Emil; Vavasour, Irene; Tam, Roger; Yoo, Youngjin; Rauscher, Alexander; Li, David K B; Traboulsee, Anthony; MacKay, Alex; Kolind, Shannon

2017-10-01

Myelin water imaging (MWI) using multi-echo T 2 relaxation is a quantitative MRI technique that can be used as an in vivo biomarker for myelin in the central nervous system. MWI using a multi-echo spin echo sequence currently takes more than 20 min to acquire eight axial slices (5 mm thickness) in the cervical spinal cord, making spinal cord MWI impractical for implementation in clinical studies. In this study, an accelerated gradient and spin echo sequence (GRASE), previously validated for brain MWI, was adapted for spinal cord MWI. Ten healthy volunteers were scanned with the GRASE sequence (acquisition time 8.5 min) and compared with the multi-echo spin echo sequence (acquisition time 23.5 min). Using region of interest analysis, myelin estimates obtained from the two sequences were found to be in good agreement (mean difference = -0.0092, 95% confidence interval =  - 0.0092 ± 0.061; regression slope = 1.01, ρ = 0.9). MWI using GRASE was shown to be highly reproducible with an average coefficient of variation of 6.1%. The results from this study show that MWI can be performed in the cervical spinal cord in less than 10 min, allowing for practical implementation in multimodal clinical studies. Magn Reson Med 78:1482-1487, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Characterization of brain tumours with spin-spin relaxation: pilot case study reveals unique T 2 distribution profiles of glioblastoma, oligodendroglioma and meningioma.

PubMed

Laule, Cornelia; Bjarnason, Thorarin A; Vavasour, Irene M; Traboulsee, Anthony L; Wayne Moore, G R; Li, David K B; MacKay, Alex L

2017-11-01

Prolonged spin-spin relaxation times in tumour tissue have been observed since some of the earliest nuclear magnetic resonance investigations of the brain. Over the last three decades, numerous studies have sought to characterize tumour morphology and malignancy using quantitative assessment of T 2 relaxation times, although attempts to categorize and differentiate tumours have had limited success. However, previous work must be interpreted with caution as relaxation data were typically acquired using a variety of multiple echo sequences with a range of echoes and T 2 decay curves and were frequently fit with monoexponential analysis. We defined the distribution of T 2 components in three different human brain tumours (glioblastoma, oligodendroglioma, meningioma) using a multi-echo sequence with a greater number of echoes and a longer acquisition window than previously used (48 echoes, data collection out to 1120 ms) with no a priori assumptions about the number of exponential components contributing to the T 2 decay. T 2 relaxation times were increased in tumour tissue and each tumour showed a distinct T 2 distribution profile. Tumours have complex and unique compartmentalization characteristics. Quantitative assessment of T 2 relaxation in brain cancer may be useful in evaluating different grades of brain tumours on the basis of their T 2 distribution profile, and has the potential to be a non-invasive diagnostic tool which may also be useful in monitoring therapy. Further study with a larger sample size and varying grades of tumours is warranted.

Observation of Gravitationally Induced Vertical Striation of Polarized Ultracold Neutrons by Spin-Echo Spectroscopy.

PubMed

Afach, S; Ayres, N J; Ban, G; Bison, G; Bodek, K; Chowdhuri, Z; Daum, M; Fertl, M; Franke, B; Griffith, W C; Grujić, Z D; Harris, P G; Heil, W; Hélaine, V; Kasprzak, M; Kermaidic, Y; Kirch, K; Knowles, P; Koch, H-C; Komposch, S; Kozela, A; Krempel, J; Lauss, B; Lefort, T; Lemière, Y; Mtchedlishvili, A; Musgrave, M; Naviliat-Cuncic, O; Pendlebury, J M; Piegsa, F M; Pignol, G; Plonka-Spehr, C; Prashanth, P N; Quéméner, G; Rawlik, M; Rebreyend, D; Ries, D; Roccia, S; Rozpedzik, D; Schmidt-Wellenburg, P; Severijns, N; Thorne, J A; Weis, A; Wursten, E; Wyszynski, G; Zejma, J; Zenner, J; Zsigmond, G

2015-10-16

We describe a spin-echo method for ultracold neutrons (UCNs) confined in a precession chamber and exposed to a |B0|=1  μT magnetic field. We have demonstrated that the analysis of UCN spin-echo resonance signals in combination with knowledge of the ambient magnetic field provides an excellent method by which to reconstruct the energy spectrum of a confined ensemble of neutrons. The method takes advantage of the relative dephasing of spins arising from a gravitationally induced striation of stored UCNs of different energies, and also permits an improved determination of the vertical magnetic-field gradient with an exceptional accuracy of 1.1  pT/cm. This novel combination of a well-known nuclear resonance method and gravitationally induced vertical striation is unique in the realm of nuclear and particle physics and should prove to be invaluable for the assessment of systematic effects in precision experiments such as searches for an electric dipole moment of the neutron or the measurement of the neutron lifetime.

Phase modulation in dipolar-coupled A 2 spin systems: effect of maximum state mixing in 1H NMR in vivo

NASA Astrophysics Data System (ADS)

Schröder, Leif; Schmitz, Christian; Bachert, Peter

2004-12-01

Coupling constants of nuclear spin systems can be determined from phase modulation of multiplet resonances. Strongly coupled systems such as citrate in prostatic tissue exhibit a more complex modulation than AX connectivities, because of substantial mixing of quantum states. An extreme limit is the coupling of n isochronous spins (A n system). It is observable only for directly connected spins like the methylene protons of creatine and phosphocreatine which experience residual dipolar coupling in intact muscle tissue in vivo. We will demonstrate that phase modulation of this "pseudo-strong" system is quite simple compared to those of AB systems. Theory predicts that the spin-echo experiment yields conditions as in the case of weak interactions, in particular, the phase modulation depends linearly on the line splitting and the echo time.

Quantum decoherence dynamics of divacancy spins in silicon carbide

DOE PAGES

Seo, Hosung; Falk, Abram L.; Klimov, Paul V.; ...

2016-09-29

Long coherence times are key to the performance of quantum bits (qubits). Here, we experimentally and theoretically show that the Hahn-echo coherence time of electron spins associated with divacancy defects in 4H-SiC reaches 1.3 ms, one of the longest Hahn-echo coherence times of an electron spin in a naturally isotopic crystal. Using a first-principles microscopic quantum-bath model, we find that two factors determine the unusually robust coherence. First, in the presence of moderate magnetic fields (30mT and above), the 29Si and 13C paramagnetic nuclear spin baths are decoupled. In addition, because SiC is a binary crystal, homo-nuclear spin pairs aremore » both diluted and forbidden from forming strongly coupled, nearest-neighbour spin pairs. Longer neighbour distances result in fewer nuclear spin flip-flops, a less fluctuating intra-crystalline magnetic environment, and thus a longer coherence time. Lastly, our results point to polyatomic crystals as promising hosts for coherent qubits in the solid state.« less

Quantum decoherence dynamics of divacancy spins in silicon carbide.

PubMed

Seo, Hosung; Falk, Abram L; Klimov, Paul V; Miao, Kevin C; Galli, Giulia; Awschalom, David D

2016-09-29

Long coherence times are key to the performance of quantum bits (qubits). Here, we experimentally and theoretically show that the Hahn-echo coherence time of electron spins associated with divacancy defects in 4H-SiC reaches 1.3 ms, one of the longest Hahn-echo coherence times of an electron spin in a naturally isotopic crystal. Using a first-principles microscopic quantum-bath model, we find that two factors determine the unusually robust coherence. First, in the presence of moderate magnetic fields (30 mT and above), the 29 Si and 13 C paramagnetic nuclear spin baths are decoupled. In addition, because SiC is a binary crystal, homo-nuclear spin pairs are both diluted and forbidden from forming strongly coupled, nearest-neighbour spin pairs. Longer neighbour distances result in fewer nuclear spin flip-flops, a less fluctuating intra-crystalline magnetic environment, and thus a longer coherence time. Our results point to polyatomic crystals as promising hosts for coherent qubits in the solid state.

High resolution neutron Larmor diffraction using superconducting magnetic Wollaston prisms

DOE PAGES

Li, Fankang; Feng, Hao; Thaler, Alexander N.; ...

2017-04-13

The neutron Larmor diffraction technique has been implemented using superconducting magnetic Wollaston prisms in both single-arm and double-arm configurations. Successful measurements of the coefficient of thermal expansion of a single-crystal copper sample demonstrates that the method works as expected. Our experiment involves a new method of tuning by varying the magnetic field configurations in the device and the tuning results agree well with previous measurements. The difference between single-arm and double-arm configurations has been investigated experimentally. Here, we conclude that this measurement benchmarks the applications of magnetic Wollaston prisms in Larmor diffraction and shows in principle that the setup canmore » be used for inelastic phonon line-width measurements. The achievable resolution for Larmor diffraction is comparable to that using Neutron Resonance Spin Echo (NRSE) coils. Furthermore, the use of superconducting materials in the prisms allows high neutron polarization and transmission efficiency to be achieved.« less

Dedicated phantom to study susceptibility artifacts caused by depth electrode in magnetic resonance imaging

NASA Astrophysics Data System (ADS)

Garcia, J.; Hidalgo, S. S.; Solis, S. E.; Vazquez, D.; Nuñez, J.; Rodriguez, A. O.

2012-10-01

The susceptibility artifacts can degrade of magnetic resonance image quality. Electrodes are an important source of artifacts when performing brain imaging. A dedicated phantom was built using a depth electrode to study the susceptibility effects under different pulse sequences. T2-weighted images were acquired with both gradient-and spin-echo sequences. The spin-echo sequences can significantly attenuate the susceptibility artifacts allowing a straightforward visualization of the regions surrounding the electrode.

Diffusion-prepared stimulated-echo turbo spin echo (DPsti-TSE): An eddy current-insensitive sequence for three-dimensional high-resolution and undistorted diffusion-weighted imaging.

PubMed

Zhang, Qinwei; Coolen, Bram F; Versluis, Maarten J; Strijkers, Gustav J; Nederveen, Aart J

2017-07-01

In this study, we present a new three-dimensional (3D), diffusion-prepared turbo spin echo sequence based on a stimulated-echo read-out (DPsti-TSE) enabling high-resolution and undistorted diffusion-weighted imaging (DWI). A dephasing gradient in the diffusion preparation module and rephasing gradients in the turbo spin echo module create stimulated echoes, which prevent signal loss caused by eddy currents. Near to perfect agreement of apparent diffusion coefficient (ADC) values between DPsti-TSE and diffusion-weighted echo planar imaging (DW-EPI) was demonstrated in both phantom transient signal experiments and phantom imaging experiments. High-resolution and undistorted DPsti-TSE was demonstrated in vivo in prostate and carotid vessel wall. 3D whole-prostate DWI was achieved with four b values in only 6 min. Undistorted ADC maps of the prostate peripheral zone were obtained at low and high imaging resolutions with no change in mean ADC values [(1.60 ± 0.10) × 10 -3 versus (1.60 ± 0.02) × 10 -3  mm 2 /s]. High-resolution 3D DWI of the carotid vessel wall was achieved in 12 min, with consistent ADC values [(1.40 ± 0.23) × 10 -3  mm 2 /s] across different subjects, as well as slice locations through the imaging volume. This study shows that DPsti-TSE can serve as a robust 3D diffusion-weighted sequence and is an attractive alternative to the traditional two-dimensional DW-EPI approaches. Copyright © 2017 John Wiley & Sons, Ltd.

On the lorentzian versus Gaussian character of time-domain spin-echo signals from the brain as sampled by means of gradient-echoes: Implications for quantitative transverse relaxation studies.

PubMed

Mulkern, Robert V; Balasubramanian, Mukund; Mitsouras, Dimitrios

2014-07-30

To determine whether Lorentzian or Gaussian intra-voxel frequency distributions are better suited for modeling data acquired with gradient-echo sampling of single spin-echoes for the simultaneous characterization of irreversible and reversible relaxation rates. Clinical studies (e.g., of brain iron deposition) using such acquisition schemes have typically assumed Lorentzian distributions. Theoretical expressions of the time-domain spin-echo signal for intra-voxel Lorentzian and Gaussian distributions were used to fit data from a human brain scanned at both 1.5 Tesla (T) and 3T, resulting in maps of irreversible and reversible relaxation rates for each model. The relative merits of the Lorentzian versus Gaussian model were compared by means of quality of fit considerations. Lorentzian fits were equivalent to Gaussian fits primarily in regions of the brain where irreversible relaxation dominated. In the multiple brain regions where reversible relaxation effects become prominent, however, Gaussian fits were clearly superior. The widespread assumption that a Lorentzian distribution is suitable for quantitative transverse relaxation studies of the brain should be reconsidered, particularly at 3T and higher field strengths as reversible relaxation effects become more prominent. Gaussian distributions offer alternate fits of experimental data that should prove quite useful in general. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc. © 2014 Wiley Periodicals, Inc.

Accelerated Radiation-Damping for Increased Spin Equilibrium (ARISE)

PubMed Central

Huang, Susie Y.; Witzel, Thomas; Wald, Lawrence L.

2008-01-01

Control of the longitudinal magnetization in fast gradient echo sequences is an important factor enabling the high efficiency of balanced Steady State Free Precession (bSSFP) sequences. We introduce a new method for accelerating the return of the longitudinal magnetization to the +z-axis that is independent of externally applied RF pulses and shows improved off-resonance performance. The Accelerated Radiation damping for Increased Spin Equilibrium (ARISE) method uses an external feedback circuit to strengthen the Radiation Damping (RD) field. The enhanced RD field rotates the magnetization back to the +z-axis at a rate faster than T1 relaxation. The method is characterized in gradient echo phantom imaging at 3T as a function of feedback gain, phase, and duration and compared with results from numerical simulations of the Bloch equations incorporating RD. A short period of feedback (10ms) during a refocused interval of a crushed gradient echo sequence allowed greater than 99% recovery of the longitudinal magnetization when very little T2 relaxation has time to occur. Appropriate applications might include improving navigated sequences. Unlike conventional flip-back schemes, the ARISE “flip-back” is generated by the spins themselves, thereby offering a potentially useful building block for enhancing gradient echo sequences. PMID:18956463

High-Resolution Magnetic Resonance Imaging Enhanced With Superparamagnetic Nanoparticles Measures Macrophage Burden in Atherosclerosis

PubMed Central

Morishige, Kunio; Kacher, Daniel F.; Libby, Peter; Josephson, Lee; Ganz, Peter; Weissleder, Ralph; Aikawa, Masanori

2010-01-01

Background Macrophages contribute to the progression and acute complications of atherosclerosis. Macrophage imaging may serve as a biomarker to identify subclinical inflamed lesions, to predict future risk, and to aid in the assessment of novel therapies. Methods and Results To test the hypothesis that nanoparticle-enhanced, high-resolution magnetic resonance imaging (MRI) can measure plaque macrophage accumulation, we used 3-T MRI with a macrophage-targeted superparamagnetic nanoparticle preparation (monocrystalline iron oxide nanoparticles-47 [MION-47]) in cholesterol-fed New Zealand White rabbits 6 months after balloon injury. In vivo MRI visualized thickened abdominal aortas on both T1- and T2-weighted spin-echo images (T1 spin echo, 20 axial slices per animal; T2 spin echo, 28 slices per animal). Seventy-two hours after MION-47 injection, aortas exhibited lower T2 signal intensity compared with before contrast imaging (signal intensity ratio, aortic wall/muscle: before, 1.44±0.26 versus after, 0.95±0.22; 164 slices; P<0.01), whereas T1 spin echo images showed no significant change. MRI on ex vivo specimens provided similar results. Histological studies colocalized iron accumulation with immunoreactive macrophages in atheromata. The magnitude of signal intensity reduction on T2 spin echo in vivo images further correlated with macrophage areas in situ (150 slices; r=0.73). Treatment with rosuvastatin for 3 months yielded diminished macrophage content (P<0.05) and reversed T2 signal intensity changes (P<0.005). Signal changes in rosuvastatin-treated rabbits correlated with reduced macrophage burden (r=0.73). In vitro validation studies showed concentration-dependent MION-47 uptake by human primary macrophages. Conclusion The magnitude of T2 signal intensity reduction in high-resolution MRI after administration of superparamagnetic phagocytosable nanoparticles can assess macrophage burden in atheromata, providing a clinically translatable tool to identify inflamed plaques and to monitor therapy-mediated changes in plaque inflammation. PMID:20937980

MRI T2 Mapping of the Knee Articular Cartilage Using Different Acquisition Sequences and Calculation Methods at 1.5 Tesla.

PubMed

Mars, Mokhtar; Bouaziz, Mouna; Tbini, Zeineb; Ladeb, Fethi; Gharbi, Souha

2018-06-12

This study aims to determine how Magnetic Resonance Imaging (MRI) acquisition techniques and calculation methods affect T2 values of knee cartilage at 1.5 Tesla and to identify sequences that can be used for high-resolution T2 mapping in short scanning times. This study was performed on phantom and twenty-nine patients who underwent MRI of the knee joint at 1.5 Tesla. The protocol includes T2 mapping sequences based on Single Echo Spin Echo (SESE), Multi-Echo Spin Echo (MESE), Fast Spin Echo (FSE) and Turbo Gradient Spin Echo (TGSE). The T2 relaxation times were quantified and evaluated using three calculation methods (MapIt, Syngo Offline and monoexponential fit). Signal to Noise Ratios (SNR) were measured in all sequences. All statistical analyses were performed using the t-test. The average T2 values in phantom were 41.7 ± 13.8 ms for SESE, 43.2 ± 14.4 ms for MESE, 42.4 ± 14.1 ms for FSE and 44 ± 14.5 ms for TGSE. In the patient study, the mean differences were 6.5 ± 8.2 ms, 7.8 ± 7.6 ms and 8.4 ± 14.2 ms for MESE, FSE and TGSE compared to SESE respectively; these statistical results were not significantly different (p > 0.05). The comparison between the three calculation methods showed no significant difference (p > 0.05). t-Test showed no significant difference between SNR values for all sequences. T2 values depend not only on the sequence type but also on the calculation method. None of the sequences revealed significant differences compared to the SESE reference sequence. TGSE with its short scanning time can be used for high-resolution T2 mapping. ©2018The Author(s). Published by S. Karger AG, Basel.

Can a single-shot black-blood T2-weighted spin-echo echo-planar imaging sequence with sensitivity encoding replace the respiratory-triggered turbo spin-echo sequence for the liver? An optimization and feasibility study.

PubMed

Hussain, Shahid M; De Becker, Jan; Hop, Wim C J; Dwarkasing, Soendersing; Wielopolski, Piotr A

2005-03-01

To optimize and assess the feasibility of a single-shot black-blood T2-weighted spin-echo echo-planar imaging (SSBB-EPI) sequence for MRI of the liver using sensitivity encoding (SENSE), and compare the results with those obtained with a T2-weighted turbo spin-echo (TSE) sequence. Six volunteers and 16 patients were scanned at 1.5T (Philips Intera). In the volunteer study, we optimized the SSBB-EPI sequence by interactively changing the parameters (i.e., the resolution, echo time (TE), diffusion weighting with low b-values, and polarity of the phase-encoding gradient) with regard to distortion, suppression of the blood signal, and sensitivity to motion. The influence of each change was assessed. The optimized SSBB-EPI sequence was applied in patients (N = 16). A number of items, including the overall image quality (on a scale of 1-5), were used for graded evaluation. In addition, the signal-to-noise ratio (SNR) of the liver was calculated. Statistical analysis was carried out with the use of Wilcoxon's signed rank test for comparison of the SSBB-EPI and TSE sequences, with P = 0.05 considered the limit for significance. The SSBB-EPI sequence was improved by the following steps: 1) less frequency points than phase-encoding steps, 2) a b-factor of 20, and 3) a reversed polarity of the phase-encoding gradient. In patients, the mean overall image quality score for the optimized SSBB-EPI (3.5 (range: 1-4)) and TSE (3.6 (range: 3-4)), and the SNR of the liver on SSBB-EPI (mean +/- SD = 7.6 +/- 4.0) and TSE (8.9 +/- 4.6) were not significantly different (P > .05). Optimized SSBB-EPI with SENSE proved to be feasible in patients, and the overall image quality and SNR of the liver were comparable to those achieved with the standard respiratory-triggered T2-weighted TSE sequence. (c) 2005 Wiley-Liss, Inc.

Evaluation of the Chondromalacia Patella Using a Microscopy Coil: Comparison of the Two-Dimensional Fast Spin Echo Techniques and the Three-Dimensional Fast Field Echo Techniques

PubMed Central

Kim, Hyun-joo; Kang, Chang Ho; Ryu, Jeong Ah; Shin, Myung Jin; Cho, Kyung-Ja; Cho, Woo Shin

2011-01-01

Objective We wanted to compare the two-dimensional (2D) fast spin echo (FSE) techniques and the three-dimensional (3D) fast field echo techniques for the evaluation of the chondromalacia patella using a microscopy coil. Materials and Methods Twenty five patients who underwent total knee arthroplasty were included in this study. Preoperative MRI evaluation of the patella was performed using a microscopy coil (47 mm). The proton density-weighted fast spin echo images (PD), the fat-suppressed PD images (FS-PD), the intermediate weighted-fat suppressed fast spin echo images (iw-FS-FSE), the 3D balanced-fast field echo images (B-FFE), the 3D water selective cartilage scan (WATS-c) and the 3D water selective fluid scan (WATS-f) were obtained on a 1.5T MRI scanner. The patellar cartilage was evaluated in nine areas: the superior, middle and the inferior portions that were subdivided into the medial, central and lateral facets in a total of 215 areas. Employing the Noyes grading system, the MRI grade 0-I, II and III lesions were compared using the gross and microscopic findings. The sensitivity, specificity and accuracy were evaluated for each sequence. The significance of the differences for the individual sequences was calculated using the McNemar test. Results The gross and microscopic findings demonstrated 167 grade 0-I lesions, 40 grade II lesions and eight grade III lesions. Iw-FS-FSE had the highest accuracy (sensitivity/specificity/accuracy = 88%/98%/96%), followed by FS-PD (78%/98%/93%, respectively), PD (76%/98%/93%, respectively), B-FFE (71%/100%/93%, respectively), WATS-c (67%/100%/92%, respectively) and WATS-f (58%/99%/89%, respectively). There were statistically significant differences for the iw-FS-FSE and WATS-f and for the PD-FS and WATS-f (p < 0.01). Conclusion The iw-FS-FSE images obtained with a microscopy coil show best diagnostic performance among the 2D and 3D GRE images for evaluating the chondromalacia patella. PMID:21228943

Evaluation of the chondromalacia patella using a microscopy coil: comparison of the two-dimensional fast spin echo techniques and the three-dimensional fast field echo techniques.

PubMed

Kim, Hyun-joo; Lee, Sang Hoon; Kang, Chang Ho; Ryu, Jeong Ah; Shin, Myung Jin; Cho, Kyung-Ja; Cho, Woo Shin

2011-01-01

We wanted to compare the two-dimensional (2D) fast spin echo (FSE) techniques and the three-dimensional (3D) fast field echo techniques for the evaluation of the chondromalacia patella using a microscopy coil. Twenty five patients who underwent total knee arthroplasty were included in this study. Preoperative MRI evaluation of the patella was performed using a microscopy coil (47 mm). The proton density-weighted fast spin echo images (PD), the fat-suppressed PD images (FS-PD), the intermediate weighted-fat suppressed fast spin echo images (iw-FS-FSE), the 3D balanced-fast field echo images (B-FFE), the 3D water selective cartilage scan (WATS-c) and the 3D water selective fluid scan (WATS-f) were obtained on a 1.5T MRI scanner. The patellar cartilage was evaluated in nine areas: the superior, middle and the inferior portions that were subdivided into the medial, central and lateral facets in a total of 215 areas. Employing the Noyes grading system, the MRI grade 0-I, II and III lesions were compared using the gross and microscopic findings. The sensitivity, specificity and accuracy were evaluated for each sequence. The significance of the differences for the individual sequences was calculated using the McNemar test. The gross and microscopic findings demonstrated 167 grade 0-I lesions, 40 grade II lesions and eight grade III lesions. Iw-FS-FSE had the highest accuracy (sensitivity/specificity/accuracy = 88%/98%/96%), followed by FS-PD (78%/98%/93%, respectively), PD (76%/98%/93%, respectively), B-FFE (71%/100%/93%, respectively), WATS-c (67%/100%/92%, respectively) and WATS-f (58%/99%/89%, respectively). There were statistically significant differences for the iw-FS-FSE and WATS-f and for the PD-FS and WATS-f (p < 0.01). The iw-FS-FSE images obtained with a microscopy coil show best diagnostic performance among the 2D and 3D GRE images for evaluating the chondromalacia patella.

Electron spin echo envelope modulation studies of the Cu(II)-substituted derivative of isopenicillin N synthase: A structural and spectroscopic model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng Jiang; Peisach, J.; Lijune Ming

Electron spin echo envelope modulation spectroscopy (ESEEM) was used to study the active site structure of isopenicillin N synthase (IPNS) from Cephalosporium acremonium with Cu(II) as a spectroscopic probe. Fourier transform of the simulated electron spin-echo envelope for the Cu(II)-substituted enzyme, Cu(II)IPNS, revealed two nearly magnetically equivalent, equatorially coordinated His imidazoles. The superhyperfine coupling constant, A{sub iso}, for the remote {sup 14}N of each imidazole was 1.65 MHz. The binding of substrate to the enzyme altered the magnetic coupling so that A{sub iso} is 1.30 MHz for one nitrogen and 2.16 MHz for the other. From a comparison of themore » ESSEM of Cu(II)IPNS in D{sub 2}O and H{sub 2}O, it is suggested that water is a ligand of Cu(II) and this is displaced upon the addition of substrate.« less

A spin echo sequence with a single-sided bipolar diffusion gradient pulse to obtain snapshot diffusion weighted images in moving media

NASA Astrophysics Data System (ADS)

Freidlin, R. Z.; Kakareka, J. W.; Pohida, T. J.; Komlosh, M. E.; Basser, P. J.

2012-08-01

In vivo MRI data can be corrupted by motion. Motion artifacts are particularly troublesome in Diffusion Weighted MRI (DWI), since the MR signal attenuation due to Brownian motion can be much less than the signal loss due to dephasing from other types of complex tissue motion, which can significantly degrade the estimation of self-diffusion coefficients, diffusion tensors, etc. This paper describes a snapshot DWI sequence, which utilizes a novel single-sided bipolar diffusion sensitizing gradient pulse within a spin echo sequence. The proposed method shortens the diffusion time by applying a single refocused bipolar diffusion gradient on one side of a refocusing RF pulse, instead of a set of diffusion sensitizing gradients, separated by a refocusing RF pulse, while reducing the impact of magnetic field inhomogeneity by using a spin echo sequence. A novel MRI phantom that can exhibit a range of complex motions was designed to demonstrate the robustness of the proposed DWI sequence.

Comparison of axial T1 spin-echo and T1 fat-saturation magnetic resonance imaging techniques in the diagnosis of chondromalacia patellae.

PubMed

Vanarthos, W J; Pope, T L; Monu, J U

1994-12-01

To test the diagnostic value of T1 spin-echo and T1 fat-saturated magnetic resonance images (MRIs), we reviewed axial T1-weighted images with and without fat saturation in 20 patients with clinically suspected chondromalacia of the patella. All scans were obtained on 1.5-MR units. The scans were randomly ordered and reviewed independently at different times by two radiologists without knowledge of the arthroscopy results. The sensitivity of the individual techniques for detecting grade 3 or 4 chondromalacia patellae was 92% for fat-saturated axial T1-weighted images alone, and 67% for axial T1-weighted images without fat saturation. The sensitivity of the combined techniques was 100% for grades 3 and 4 and 90% for all grades (0 to 4). Chondromalacia patellae is diagnosed more accurately by using T1 fat saturation than by using T1 spin-echo images. With a combination of the two techniques, accuracy is 90% to 100%.

Development of a Double-Gauss Lens Based Setup for Optoacoustic Applications

PubMed Central

Choi, Hojong; Ryu, Jae-Myung; Yeom, Jung-Yeol

2017-01-01

In optoacoustic (photoacoustic) systems, different echo signal intensities such as amplitudes, center frequencies, and bandwidths need to be compensated by utilizing variable gain or time-gain compensation amplifiers. However, such electronic components can increase system complexities and signal noise levels. In this paper, we introduce a double-Gauss lens to generate a large field of view with uniform light intensity due to the low chromatic aberrations of the lens, thus obtaining uniform echo signal intensities across the field of view of the optoacoustic system. In order to validate the uniformity of the echo signal intensities in the system, an in-house transducer was placed at various positions above a tissue sample and echo signals were measured and compared with each other. The custom designed double-Gauss lens demonstrated negligible light intensity variation (±1.5%) across the illumination field of view (~2 cm diameter). When the transducer was used to measure echo signal from an eye of a bigeye tuna within a range of ±1 cm, the peak-to-peak amplitude, center frequency, and their −6 dB bandwidth variations were less than 2 mV, 1 MHz, and 6%, respectively. The custom designed double-Gauss lens can provide uniform light beam across a wide area while generating insignificant echo signal variations, and thus can lower the burden of the receiving electronics or signal processing in the optoacoustic system. PMID:28273794

Application of Medical Magnetic Resonance Imaging for Particle Concentration Measurement

NASA Astrophysics Data System (ADS)

Borup, Daniel; Elkins, Christopher; Eaton, John

2014-11-01

Particle transport and deposition in internal flows is important in a range of applications such as dust aggregation in turbine engines and aerosolized medicine deposition in human airways. Unlike optical techniques, Magnetic Resonance Imaging (MRI) is well suited for complex applications in which optical access is not possible. Here we present efforts to measure 3D particle concentration distribution using MRI. Glass particles dispersed in water flow reduce MRI signal from a spin-echo or gradient-echo scanning sequence by decreasing spin density and dephasing the spins present in the fluid. A preliminary experiment was conducted with a particle streak injected at the centerline of a turbulent round pipe flow with a U bend. Measurements confirmed that signal strength was related to particle concentration and showed the effects of gravitational settling and turbulent dispersion. Next, measurements of samples in a mixing chamber were taken. Particle volume fraction was varied and sensitivity to particle/fluid velocity was investigated. These results give a relationship between MRI signal, particle volume fraction, MRI sequence echo time, and spin relaxation parameters that can be used to measure local particle volume fraction in other turbulent flows of interest.

A model-based reconstruction for undersampled radial spin echo DTI with variational penalties on the diffusion tensor

PubMed Central

Knoll, Florian; Raya, José G; Halloran, Rafael O; Baete, Steven; Sigmund, Eric; Bammer, Roland; Block, Tobias; Otazo, Ricardo; Sodickson, Daniel K

2015-01-01

Radial spin echo diffusion imaging allows motion-robust imaging of tissues with very low T2 values like articular cartilage with high spatial resolution and signal-to-noise ratio (SNR). However, in vivo measurements are challenging due to the significantly slower data acquisition speed of spin-echo sequences and the less efficient k-space coverage of radial sampling, which raises the demand for accelerated protocols by means of undersampling. This work introduces a new reconstruction approach for undersampled DTI. A model-based reconstruction implicitly exploits redundancies in the diffusion weighted images by reducing the number of unknowns in the optimization problem and compressed sensing is performed directly in the target quantitative domain by imposing a Total Variation (TV) constraint on the elements of the diffusion tensor. Experiments were performed for an anisotropic phantom and the knee and brain of healthy volunteers (3 and 2 volunteers, respectively). Evaluation of the new approach was conducted by comparing the results to reconstructions performed with gridding, combined parallel imaging and compressed sensing, and a recently proposed model-based approach. The experiments demonstrated improvement in terms of reduction of noise and streaking artifacts in the quantitative parameter maps as well as a reduction of angular dispersion of the primary eigenvector when using the proposed method, without introducing systematic errors into the maps. This may enable an essential reduction of the acquisition time in radial spin echo diffusion tensor imaging without degrading parameter quantification and/or SNR. PMID:25594167

Electron density distribution in BaPb{sub 1-x}Sb{sub x}O{sub 3} superconducting oxides studied by double nuclear magnetic resonance methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piskunov, Yu. V., E-mail: piskunov@imp.uran.ru; Ogloblichev, V. V.; Arapova, I. Yu.

2011-11-15

The effect of charge disorder on the formation of an inhomogeneous state of the electron system in the conduction band in BaPb{sub 1-x}Sb{sub x}O{sub 3} superconducting oxides is investigated experimentally by NMR methods. The NMR spectra of {sup 17}O are measured systematically, and the contributions from {sup 17}O atoms with different cation nearest surroundings are identified. It is found that microscopic regions with an elevated spin density of charge carriers are formed within two coordination spheres near antimony ions. Nuclei of the superconducting phase of the oxide (regions with an elevated antimony concentration) microscopically distributed over the sample are detectedmore » in compounds with x = 0.25 and 0.33. Experiments in which a double resonance signal of the spin echo of {sup 17}O-{sup 207}Pb and {sup 17}O-{sup 121}Sb are measured in the metal phase of BaPb{sub 1-x}Sb{sub x}O{sub 3} oxides are carried out for the first time. The constants of indirect heteronuclear spin-spin {sup 17}O-{sup 207}Pb interaction are determined as functions of the local Knight shift {sub 207}Ks. The estimates of the constants of the indirect interaction between the nuclei of the nearest neighbors (O-Pb and Pb-Pb atoms) and analysis of evolution of the NMR spectra of {sup 17}O upon a change in the antimony concentration are convincing evidence in favor of the development of a microscopically inhomogeneous state of the electron system in the metal phase of BaPb{sub 1-x}Sb{sub x}O{sub 3} oxides.« less

Transient radical pairs studied by time-resolved EPR.

PubMed

Bittl, Robert; Weber, Stefan

2005-02-25

Photogenerated short-lived radical pairs (RP) are common in biological photoprocesses such as photosynthesis and enzymatic DNA repair. They can be favorably probed by time-resolved electron paramagnetic resonance (EPR) methods with adequate time resolution. Two EPR techniques have proven to be particularly useful to extract information on the working states of photoinduced biological processes that is only difficult or sometimes even impossible to obtain by other types of spectroscopy. Firstly, transient EPR yields crucial information on the chemical nature and the geometry of the individual RP halves in a doublet-spin pair generated by a short laser pulse. This time-resolved method is applicable in all magnetic field/microwave frequency regimes that are used for continuous-wave EPR, and is nowadays routinely utilized with a time resolution reaching about 10 ns. Secondly, a pulsed EPR method named out-of-phase electron spin echo envelope modulation (OOP-ESEEM) is increasingly becoming popular. By this pulsed technique, the mutual spin-spin interaction between the RP halves in a doublet-spin pair manifests itself as an echo modulation detected as a function of the microwave-pulse spacing of a two-pulse echo sequence subsequent to a laser pulse. From the dipolar coupling, the distance between the radicals is readily derived. Since the spin-spin interaction parameters are typically not observable by transient EPR, the two techniques complement each other favorably. Both EPR methods have recently been applied to a variety of light-induced RPs in photobiology. This review summarizes the results obtained from such studies in the fields of plant and bacterial photosynthesis and DNA repair mediated by the enzyme DNA photolyase.

Frequency selective detection of nuclear quadrupole resonance (NQR) spin echoes

NASA Astrophysics Data System (ADS)

Somasundaram, Samuel D.; Jakobsson, Andreas; Smith, John A. S.; Althoefer, Kaspar A.

2006-05-01

Nuclear Quadrupole Resonance (NQR) is a radio frequency (RF) technique that can be used to detect the presence of quadrupolar nuclei, such as the 14N nucleus prevalent in many explosives and narcotics. The technique has been hampered by low signal-to-noise ratios and is further aggravated by the presence of RF interference (RFI). To ensure accurate detection, proposed detectors should exploit the rich form of the NQR signal. Furthermore, the detectors should also be robust to any remaining residual interference, left after suitable RFI mitigation has been employed. In this paper, we propose a new NQR data model, particularly for the realistic case where multiple pulse sequences are used to generate trains of spin echoes. Furthermore, we refine two recently proposed approximative maximum likelihood (AML) detectors, enabling the algorithm to optimally exploit the data model of the entire echo train and also incorporate knowledge of the temperature dependent spin-echo decay time. The AML-based detectors ensure accurate detection and robustness against residual RFI, even when the temperature of the sample is not precisely known, by exploiting the dependencies of the NQR resonant lines on temperature. Further robustness against residual interference is gained as the proposed detector is frequency selective; exploiting only those regions of the spectrum where the NQR signal is expected. Extensive numerical evaluations based on both simulated and measured NQR data indicate that the proposed Frequency selective Echo Train AML (FETAML) detector offers a significant improvement as compared to other existing detectors.

Multifrequency Pulsed EPR Studies of Biologically Relevant Manganese(II) Complexes

PubMed Central

Stich, T. A.; Lahiri, S.; Yeagle, G.; Dicus, M.; Brynda, M.; Gunn, A.; Aznar, C.; DeRose, V. J.; Britt, R. D.

2011-01-01

Electron paramagnetic resonance studies at multiple frequencies (MF EPR) can provide detailed electronic structure descriptions of unpaired electrons in organic radicals, inorganic complexes, and metalloenzymes. Analysis of these properties aids in the assignment of the chemical environment surrounding the paramagnet and provides mechanistic insight into the chemical reactions in which these systems take part. Herein, we present results from pulsed EPR studies performed at three different frequencies (9, 31, and 130 GHz) on [Mn(II)(H2O)6]2+, Mn(II) adducts with the nucleotides ATP and GMP, and the Mn(II)-bound form of the hammerhead ribozyme (MnHH). Through line shape analysis and interpretation of the zero-field splitting values derived from successful simulations of the corresponding continuous-wave and field-swept echo-detected spectra, these data are used to exemplify the ability of the MF EPR approach in distinguishing the nature of the first ligand sphere. A survey of recent results from pulsed EPR, as well as pulsed electron-nuclear double resonance and electron spin echo envelope modulation spectroscopic studies applied to Mn(II)-dependent systems, is also presented. PMID:22190766

Pulsed EPR measurements on reaction rate constants for addition of photo-generated radicals to double bonds of diethyl fumarate and diethyl maleate

NASA Astrophysics Data System (ADS)

Takahashi, Hirona; Hagiwara, Kenta; Kawai, Akio

2016-11-01

Addition reaction of photo-generated radicals to double bonds of diethyl fumarate (deF) and diethyl maleate (deM), which are geometrical isomers, was studied by means of time-resolved- (TR-) and pulsed-electron paramagnetic resonance (EPR). Analysis of TR-EPR spectra indicates that adduct radicals from deF and deM should have the same structure. The double bonds of these monomers are converted to single ones by addition reaction, which allows hindered internal rotation to give the same structure of adduct radical. The rate constants for addition reaction of photo-generated radicals were determined by Stern-Volmer analysis of the decay time of electron spin-echo intensity of these radicals measured by the pulsed EPR method. Rate constants for deF were found to be larger than those for deM. This relation is in good consistent with efficiency of polymerisation of deF and deM. Experimentally determined rate constants were evaluated by introducing the addition reaction model on the basis of two important factors enthalpy and polar effects.

Contrast-enhanced Magnetic Resonance Imaging of Pelvic Bone Metastases at 3.0 T: Comparison Between 3-dimensional T1-weighted CAIPIRINHA-VIBE Sequence and 2-dimensional T1-weighted Turbo Spin-Echo Sequence.

PubMed

Yoon, Min A; Hong, Suk-Joo; Lee, Kyu-Chong; Lee, Chang Hee

2018-06-12

This study aimed to compare 3-dimensional T1-weighted gradient-echo sequence (CAIPIRINHA-volumetric interpolated breath-hold examination [VIBE]) with 2-dimensional T1-weighted turbo spin-echo sequence for contrast-enhanced magnetic resonance imaging (MRI) of pelvic bone metastases at 3.0 T. Thirty-one contrast-enhanced MRIs of pelvic bone metastases were included. Two contrast-enhanced sequences were evaluated for the following parameters: overall image quality, sharpness of pelvic bone, iliac vessel clarity, artifact severity, and conspicuity and edge sharpness of the smallest metastases. Quantitative analysis was performed by calculating signal-to-noise ratio and contrast-to-noise ratio of the smallest metastases. Significant differences between the 2 sequences were assessed. CAIPIRINHA-VIBE had higher scores for overall image quality, pelvic bone sharpness, iliac vessel clarity, and edge sharpness of the metastatic lesions, and had less artifacts (all P < 0.05). There was no significant difference in conspicuity, signal-to-noise ratio, or contrast-to-noise ratio of the smallest metastases (P > 0.05). Our results suggest that CAIPIRINHA-VIBE may be superior to turbo spin-echo for contrast-enhanced MRI of pelvic bone metastases at 3.0 T.

Accelerated Slice Encoding for Metal Artifact Correction

PubMed Central

Hargreaves, Brian A.; Chen, Weitian; Lu, Wenmiao; Alley, Marcus T.; Gold, Garry E.; Brau, Anja C. S.; Pauly, John M.; Pauly, Kim Butts

2010-01-01

Purpose To demonstrate accelerated imaging with artifact reduction near metallic implants and different contrast mechanisms. Materials and Methods Slice-encoding for metal artifact correction (SEMAC) is a modified spin echo sequence that uses view-angle tilting and slice-direction phase encoding to correct both in-plane and through-plane artifacts. Standard spin echo trains and short-TI inversion recovery (STIR) allow efficient PD-weighted imaging with optional fat suppression. A completely linear reconstruction allows incorporation of parallel imaging and partial Fourier imaging. The SNR effects of all reconstructions were quantified in one subject. 10 subjects with different metallic implants were scanned using SEMAC protocols, all with scan times below 11 minutes, as well as with standard spin echo methods. Results The SNR using standard acceleration techniques is unaffected by the linear SEMAC reconstruction. In all cases with implants, accelerated SEMAC significantly reduced artifacts compared with standard imaging techniques, with no additional artifacts from acceleration techniques. The use of different contrast mechanisms allowed differentiation of fluid from other structures in several subjects. Conclusion SEMAC imaging can be combined with standard echo-train imaging, parallel imaging, partial-Fourier imaging and inversion recovery techniques to offer flexible image contrast with a dramatic reduction of metal-induced artifacts in scan times under 11 minutes. PMID:20373445

Accelerated slice encoding for metal artifact correction.

PubMed

Hargreaves, Brian A; Chen, Weitian; Lu, Wenmiao; Alley, Marcus T; Gold, Garry E; Brau, Anja C S; Pauly, John M; Pauly, Kim Butts

2010-04-01

To demonstrate accelerated imaging with both artifact reduction and different contrast mechanisms near metallic implants. Slice-encoding for metal artifact correction (SEMAC) is a modified spin echo sequence that uses view-angle tilting and slice-direction phase encoding to correct both in-plane and through-plane artifacts. Standard spin echo trains and short-TI inversion recovery (STIR) allow efficient PD-weighted imaging with optional fat suppression. A completely linear reconstruction allows incorporation of parallel imaging and partial Fourier imaging. The signal-to-noise ratio (SNR) effects of all reconstructions were quantified in one subject. Ten subjects with different metallic implants were scanned using SEMAC protocols, all with scan times below 11 minutes, as well as with standard spin echo methods. The SNR using standard acceleration techniques is unaffected by the linear SEMAC reconstruction. In all cases with implants, accelerated SEMAC significantly reduced artifacts compared with standard imaging techniques, with no additional artifacts from acceleration techniques. The use of different contrast mechanisms allowed differentiation of fluid from other structures in several subjects. SEMAC imaging can be combined with standard echo-train imaging, parallel imaging, partial-Fourier imaging, and inversion recovery techniques to offer flexible image contrast with a dramatic reduction of metal-induced artifacts in scan times under 11 minutes. (c) 2010 Wiley-Liss, Inc.

Optical and Magnetic Resonance Investigations of 3d Ions in Single Crystal Hosts: Candidates for Tunable Solid-State Lasers

DTIC Science & Technology

1994-04-25

Resonance Spectroscopy of Chromium-Doped Lanthanum Lutetium Gallium Garnet, M. H. Whitmore and D.J. Singel 8. 51V modulation of Mn5+ electron spin echoes in...Doped Lanthanum Lutetium Gallium Garnet Chapter 9 Characterization of Optical Centers in Mn.Ba3(VO4)2 178 by Spin-Echo EPR Spectroscopy I I ! I ii I i I I...previously unpublished EPR results on Cr:gehlenites (Chapter 6) and Cr:LLGG (lanthanum lutetium gallium garnet) (Chapter 8). The gehlenite spectra do

Observation of a new coherent transient in NMR -- nutational two-pulse stimulated echo in the angular distribution of γ-radiation from oriented nuclei

NASA Astrophysics Data System (ADS)

Shakhmuratova, L. N.; Hutchison, W. D.; Isbister, D. J.; Chaplin, D. H.

1997-07-01

A new coherent transient in pulsed NMR, the two-pulse nutational stimulated echo, is reported for the ferromagnetic system 60CoFe using resonant perturbations on the directional emission of anisotropic γ-radiation from thermally oriented nuclei. The new spin echo is a result of non-linear nuclear spin dynamics due to large Larmor inhomogeneity active during radiofrequency pulse application. It is made readily observable through the gross detuning between NMR radiofrequency excitation and gamma radiation detection, and inhomogeneity in the Rabi frequency caused by metallic skin-effect. The method of concatenation of perturbation factors in a statistical tensor formalism is quantitatively applied to successfully predict and then fit in detail the experimental time-domain data.

High-speed multislice T1 mapping using inversion-recovery echo-planar imaging.

PubMed

Ordidge, R J; Gibbs, P; Chapman, B; Stehling, M K; Mansfield, P

1990-11-01

Tissue contrast in MR images is a strong function of spin-lattice (T1) and spin-spin (T2) relaxation times. However, the T1 relaxation time is rarely quantified because of the long scan time required to produce an accurate T1 map of the subject. In a standard 2D FT technique, this procedure may take up to 30 min. Modifications of the echo-planar imaging (EPI) technique which incorporate the principle of inversion recovery (IR) enable multislice T1 maps to be produced in total scan times varying from a few seconds up to a minute. Using IR-EPI, rapid quantification of T1 values may thus lead to better discrimination between tissue types in an acceptable scan time.

Multiple Locations of Peptides in the Hydrocarbon Core of Gel-Phase Membranes Revealed by Peptide 13C to Lipid 2H Rotational-Echo Double-Resonance Solid-State Nuclear Magnetic Resonance

PubMed Central

2015-01-01

Membrane locations of peptides and proteins are often critical to their functions. Solid-state rotational-echo double-resonance (REDOR) nuclear magnetic resonance is applied to probe the locations of two peptides via peptide 13CO to lipid 2H distance measurements. The peptides are KALP, an α-helical membrane-spanning peptide, and HFP, the β-sheet N-terminal fusion peptide of the HIV gp41 fusion protein that plays an important role in HIV–host cell membrane fusion. Both peptides are shown to have at least two distinct locations within the hydrocarbon core of gel-phase membranes. The multiple locations are attributed to snorkeling of lysine side chains for KALP and to the distribution of antiparallel β-sheet registries for HFP. The relative population of each location is also quantitated. To the best of our knowledge, this is the first clear experimental support of multiple peptide locations within the membrane hydrocarbon core. These data are for gel-phase membranes, but the approach should work for liquid-ordered membranes containing cholesterol and may be applicable to liquid-disordered membranes with appropriate additional analysis to take into account protein and lipid motion. This paper also describes the methodological development of 13CO–2H REDOR using the lyophilized I4 peptide that is α-helical and 13CO-labeled at A9 and 2Hα-labeled at A8. The I4 spins are well-approximated as an ensemble of isolated 13CO–2H spin pairs each separated by 5.0 Å with a 37 Hz dipolar coupling. A pulse sequence with rectangular 100 kHz 2H π pulses results in rapid and extensive buildup of REDOR (ΔS/S0) with a dephasing time (τ). The buildup is well-fit by a simple exponential function with a rate of 24 Hz and an extent close to 1. These parameter values reflect nonradiative transitions between the 2H spin states during the dephasing period. Each spin pair spends approximately two-thirds of its time in the 13CO–2H (m = ±1) states and approximately one-third of its time in the 13CO–2H (m = 0) state and contributes to the ΔS/S0 buildup during the former but not the latter time segments. PMID:25531389

The value of non-echo planar HASTE diffusion-weighted MR imaging in the detection, localisation and prediction of extent of postoperative cholesteatoma.

PubMed

Khemani, S; Lingam, R K; Kalan, A; Singh, A

2011-08-01

To evaluate the diagnostic performance of half-Fourier-acquisition single-shot turbo-spin-echo (HASTE) diffusion-weighted magnetic resonance imaging in the detection, localisation and prediction of extent of cholesteatoma following canal wall up mastoid surgery. Prospective blinded observational study. University affiliated teaching hospital. Forty-eight patients undergoing second-look surgery after previous canal wall up mastoid surgery for primary acquired cholesteatoma. All patients underwent non-echo planar HASTE diffusion-weighted imaging prior to being offered 'second-look' surgery. Radiological findings were correlated with second-look intra-operative findings in 38 cases with regard to presence, location and maximum dimensions of cholesteatoma. Half-Fourier-acquisition single-shot turbo-spin-echo diffusion-weighted imaging accurately predicted the presence of cholesteatoma in 23 of 28 cases, and it correctly excluded in nine of 10 cases. Five false negatives were caused by keratin pearls of <2 mm and in one case 5 mm. Overall sensitivity and specificity for detection of cholesteatoma were 82% (95% confidence interval [CI] 62-94%) and 90% (CI 55-100%), respectively. Positive predictive value and negative predictive value were 96% (CI 79-100%) and 64% (CI 35-87%), respectively. Overall accuracy for detection of cholesteatoma was 84% (CI 69-94%). Half-Fourier-acquisition single-shot turbo-spin-echo diffusion-weighted imaging has good performance in localising cholesteatoma to a number of anatomical sub-sites within the middle ear and mastoid (sensitivity ranging from 75% to 88% and specificity ranging from 94% to 100%). There was no statistically significant difference in the size of cholesteatoma detected radiologically and that found during surgery (paired t-test, P = 0.16). However, analysis of size agreement suggests possible radiological underestimation of size when using HASTE diffusion-weighted imaging (mean difference -0.6 mm, CI -5.3 to 4.6 mm). Half-Fourier-acquisition single-shot turbo-spin-echo diffusion-weighted imaging performs reasonably well in predicting the presence and location of postoperative cholesteatoma but may miss small foci of disease and may underestimate the true size of cholesteatoma. © 2011 Blackwell Publishing Ltd.

Improved imaging of cochlear nerve hypoplasia using a 3-Tesla variable flip-angle turbo spin-echo sequence and a 7-cm surface coil.

PubMed

Giesemann, Anja M; Raab, Peter; Lyutenski, Stefan; Dettmer, Sabine; Bültmann, Eva; Frömke, Cornelia; Lenarz, Thomas; Lanfermann, Heinrich; Goetz, Friedrich

2014-03-01

Magnetic resonance imaging of the temporal bone has an important role in decision making with regard to cochlea implantation, especially in children with cochlear nerve deficiency. The purpose of this study was to evaluate the usefulness of the combination of an advanced high-resolution T2-weighted sequence with a surface coil in a 3-Tesla magnetic resonance imaging scanner in cases of suspected cochlear nerve aplasia. Prospective study. Seven patients with cochlear nerve hypoplasia or aplasia were prospectively examined using a high-resolution three-dimensional variable flip-angle turbo spin-echo sequence using a surface coil, and the images were compared with the same sequence in standard resolution using a standard head coil. Three neuroradiologists evaluated the magnetic resonance images independently, rating the visibility of the nerves in diagnosing hypoplasia or aplasia. Eight ears in seven patients with hypoplasia or aplasia of the cochlear nerve were examined. The average age was 2.7 years (range, 9 months-5 years). Seven ears had accompanying malformations. The inter-rater reliability in diagnosing hypoplasia or aplasia was greater using the high-resolution three-dimensional variable flip-angle turbo spin-echo sequence (fixed-marginal kappa: 0.64) than with the same sequence in lower resolution (fixed-marginal kappa: 0.06). Examining cases of suspected cochlear nerve aplasia using the high-resolution three-dimensional variable flip-angle turbo spin-echo sequence in combination with a surface coil shows significant improvement over standard methods. © 2013 The American Laryngological, Rhinological and Otological Society, Inc.

Oscillating and pulsed gradient diffusion magnetic resonance microscopy over an extended b-value range: implications for the characterization of tissue microstructure.

PubMed

Portnoy, S; Flint, J J; Blackband, S J; Stanisz, G J

2013-04-01

Oscillating gradient spin-echo (OGSE) pulse sequences have been proposed for acquiring diffusion data with very short diffusion times, which probe tissue structure at the subcellular scale. OGSE sequences are an alternative to pulsed gradient spin echo measurements, which typically probe longer diffusion times due to gradient limitations. In this investigation, a high-strength (6600 G/cm) gradient designed for small-sample microscopy was used to acquire OGSE and pulsed gradient spin echo data in a rat hippocampal specimen at microscopic resolution. Measurements covered a broad range of diffusion times (TDeff = 1.2-15.0 ms), frequencies (ω = 67-1000 Hz), and b-values (b = 0-3.2 ms/μm2). Variations in apparent diffusion coefficient with frequency and diffusion time provided microstructural information at a scale much smaller than the imaging resolution. For a more direct comparison of the techniques, OGSE and pulsed gradient spin echo data were acquired with similar effective diffusion times. Measurements with similar TDeff were consistent at low b-value (b < 1 ms/μm(2) ), but diverged at higher b-values. Experimental observations suggest that the effective diffusion time can be helpful in the interpretation of low b-value OGSE data. However, caution is required at higher b, where enhanced sensitivity to restriction and exchange render the effective diffusion time an unsuitable representation. Oscillating and pulsed gradient diffusion techniques offer unique, complementary information. In combination, the two methods provide a powerful tool for characterizing complex diffusion within biological tissues. Copyright © 2012 Wiley Periodicals, Inc.

Repeatability of magnetic resonance fingerprinting T1 and T2 estimates assessed using the ISMRM/NIST MRI system phantom.

PubMed

Jiang, Yun; Ma, Dan; Keenan, Kathryn E; Stupic, Karl F; Gulani, Vikas; Griswold, Mark A

2017-10-01

The purpose of this study was to evaluate accuracy and repeatability of T 1 and T 2 estimates of a MR fingerprinting (MRF) method using the ISMRM/NIST MRI system phantom. The ISMRM/NIST MRI system phantom contains multiple compartments with standardized T 1 , T 2 , and proton density values. Conventional inversion-recovery spin echo and spin echo methods were used to characterize the T 1 and T 2 values in the phantom. The phantom was scanned using the MRF-FISP method over 34 consecutive days. The mean T 1 and T 2 values were compared with the values from the spin echo methods. The repeatability was characterized as the coefficient of variation of the measurements over 34 days. T 1 and T 2 values from MRF-FISP over 34 days showed a strong linear correlation with the measurements from the spin echo methods (R 2  = 0.999 for T 1 ; R 2  = 0.996 for T 2 ). The MRF estimates over the wide ranges of T 1 and T 2 values have less than 5% variation, except for the shortest T 2 relaxation times where the method still maintains less than 8% variation. MRF measurements of T 1 and T 2 are highly repeatable over time and across wide ranges of T 1 and T 2 values. Magn Reson Med 78:1452-1457, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Liver imaging at 3.0 T: diffusion-induced black-blood echo-planar imaging with large anatomic volumetric coverage as an alternative for specific absorption rate-intensive echo-train spin-echo sequences: feasibility study.

PubMed

van den Bos, Indra C; Hussain, Shahid M; Krestin, Gabriel P; Wielopolski, Piotr A

2008-07-01

Institutional Review Board approval and signed informed consent were obtained by all participants for an ongoing sequence optimization project at 3.0 T. The purpose of this study was to evaluate breath-hold diffusion-induced black-blood echo-planar imaging (BBEPI) as a potential alternative for specific absorption rate (SAR)-intensive spin-echo sequences, in particular, the fast spin-echo (FSE) sequences, at 3.0 T. Fourteen healthy volunteers (seven men, seven women; mean age +/- standard deviation, 32.7 years +/- 6.8) were imaged for this purpose. Liver coverage (20 cm, z-axis) was always performed in one 25-second breath hold. Imaging parameters were varied interactively with regard to echo time, diffusion b value, and voxel size. Images were evaluated and compared with fat-suppressed T2-weighted FSE images for image quality, liver delineation, geometric distortions, fat suppression, suppression of the blood signal, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR). An optimized short- (25 msec) and long-echo (80 msec) BBEPI provided full anatomic, single breath-hold liver coverage (100 and 50 sections, respectively), with resulting voxel sizes of 3.3 x 2.7 x 2.0 mm and 3.3 x 2.7 x 4.0 mm, respectively. Repetition time was 6300 msec, matrix size was 160 x 192, and an acceleration factor of 2.00 was used. b Values of more than 20 sec/mm(2) showed better suppression of the blood signal but b values of 10 sec/mm(2) provided improved volume coverage and signal consistency. Compared with fat-suppressed T2-weighted FSE, the optimized BBEPI sequence provided (a) comparable image quality and liver delineation, (b) acceptable geometric distortions, (c) improved suppression of fat and blood signals, and (d) high CNR and SNR. BBEPI is feasible for fast, low-SAR, thin-section morphologic imaging of the entire liver in a single breath hold at 3.0 T. (c) RSNA, 2008.

Wavelength-independent constant period spin-echo modulated small angle neutron scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sales, Morten, E-mail: lsp260@alumni.ku.dk; Plomp, Jeroen; Bouwman, Wim

2016-06-15

Spin-Echo Modulated Small Angle Neutron Scattering (SEMSANS) in Time-of-Flight (ToF) mode has been shown to be a promising technique for measuring (very) small angle neutron scattering (SANS) signals and performing quantitative Dark-Field Imaging (DFI), i.e., SANS with 2D spatial resolution. However, the wavelength dependence of the modulation period in the ToF spin-echo mode has so far limited the useful modulation periods to those resolvable with the limited spatial resolution of the detectors available. Here we present our results of an approach to keep the period of the induced modulation constant for the wavelengths utilised in ToF. This is achieved bymore » ramping the magnetic fields in the coils responsible for creating the spatially modulated beam in synchronisation with the neutron pulse, thus keeping the modulation period constant for all wavelengths. Such a setup enables the decoupling of the spatial detector resolution from the resolution of the modulation period by the use of slits or gratings in analogy to the approach in grating-based neutron DFI.« less

Inner-volume echo volumar imaging (IVEVI) for robust fetal brain imaging.

PubMed

Nunes, Rita G; Ferrazzi, Giulio; Price, Anthony N; Hutter, Jana; Gaspar, Andreia S; Rutherford, Mary A; Hajnal, Joseph V

2018-07-01

Fetal functional MRI studies using conventional 2-dimensional single-shot echo-planar imaging sequences may require discarding a large data fraction as a result of fetal and maternal motion. Increasing the temporal resolution using echo volumar imaging (EVI) could provide an effective alternative strategy. Echo volumar imaging was combined with inner volume (IV) imaging (IVEVI) to locally excite the fetal brain and acquire full 3-dimensional images, fast enough to freeze most fetal head motion. IVEVI was implemented by modifying a standard multi-echo echo-planar imaging sequence. A spin echo with orthogonal excitation and refocusing ensured localized excitation. To introduce T2* weighting and to save time, the k-space center was shifted relative to the spin echo. Both single and multi-shot variants were tested. Acoustic noise was controlled by adjusting the amplitude and switching frequency of the readout gradient. Image-based shimming was used to minimize B 0 inhomogeneities within the fetal brain. The sequence was first validated in an adult. Eight fetuses were scanned using single-shot IVEVI at a 3.5 × 3.5 × 5.0 mm 3 resolution with a readout duration of 383 ms. Multishot IVEVI showed reduced geometric distortions along the second phase-encode direction. Fetal EVI remains challenging. Although effective echo times comparable to the T2* values of fetal cortical gray matter at 3 T could be achieved, controlling acoustic noise required longer readouts, leading to substantial distortions in single-shot images. Although multishot variants enabled us to reduce susceptibility-induced geometric distortions, sensitivity to motion was increased. Future studies should therefore focus on improvements to multishot variants. Magn Reson Med 80:279-285, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Structural and mechanical properties of cardiolipin lipid bilayers determined using neutron spin echo, small angle neutron and X-ray scattering, and molecular dynamics simulations

DOE PAGES

Pan, Jianjun; Cheng, Xiaolin; Sharp, Melissa; ...

2014-10-29

We report that the detailed structural and mechanical properties of a tetraoleoyl cardiolipin (TOCL) bilayer were determined using neutron spin echo (NSE) spectroscopy, small angle neutron and X-ray scattering (SANS and SAXS, respectively), and molecular dynamics (MD) simulations. We used MD simulations to develop a scattering density profile (SDP) model, which was then utilized to jointly refine SANS and SAXS data. In addition to commonly reported lipid bilayer structural parameters, component distributions were obtained, including the volume probability, electron density and neutron scattering length density.

Dynamics of polymers in elongational flow studied by the neutron spin-echo technique

NASA Astrophysics Data System (ADS)

Rheinstädter, Maikel C.; Sattler, Rainer; Häußler, Wolfgang; Wagner, Christian

2010-09-01

The nanoscale fluctuation dynamics of semidilute high molecular weight polymer solutions of polyethylenoxide (PEO) in D 2O under non-equilibrium flow conditions were studied by the neutron spin-echo technique. The sample cell was in contraction flow geometry and provided a pressure driven flow with a high elongational component that stretched the polymers most efficiently. Neutron scattering experiments in dilute polymer solutions are challenging because of the low polymer concentration and corresponding small quasi-elastic signals. A relaxation process with relaxation times of about 10 ps was observed, which shows anisotropic dynamics with applied flow.

Measuring restriction sizes using diffusion weighted magnetic resonance imaging: a review.

PubMed

Martin, Melanie

2013-01-01

This article reviews a new concept in magnetic resonance as applied to cellular and biological systems. Diffusion weighted magnetic resonance imaging can be used to infer information about restriction sizes of samples being measured. The measurements rely on the apparent diffusion coefficient changing with diffusion times as measurements move from restricted to free diffusion regimes. Pulsed gradient spin echo (PGSE) measurements are limited in the ability to shorten diffusion times and thus are limited in restriction sizes which can be probed. Oscillating gradient spin echo (OGSE) measurements could provide shorter diffusion times so smaller restriction sizes could be probed.

T1 weighted fat/water separated PROPELLER acquired with dual bandwidths.

PubMed

Rydén, Henric; Berglund, Johan; Norbeck, Ola; Avventi, Enrico; Skare, Stefan

2018-04-24

To describe a fat/water separated dual receiver bandwidth (rBW) spin echo PROPELLER sequence that eliminates the dead time associated with single rBW sequences. A nonuniform noise whitening by regularization of the fat/water inverse problem is proposed, to enable dual rBW reconstructions. Bipolar, flyback, and dual spin echo sequences were developed. All sequences acquire two echoes with different rBW without dead time. Chemical shift displacement was corrected by performing the fat/water separation in k-space, prior to gridding. The proposed sequences were compared to fat saturation, and single rBW sequences, in terms of SNR and CNR efficiency, using clinically relevant acquisition parameters. The impact of motion was investigated. Chemical shift correction greatly improved the image quality, especially at high resolution acquired with low rBW, and also improved motion estimates. SNR efficiency of the dual spin echo sequence was up to 20% higher than the single rBW acquisition, while CNR efficiency was 50% higher for the bipolar acquisition. Noise whitening was deemed necessary for all dual rBW acquisitions, rendering high image quality with strong and homogenous fat suppression. Dual rBW sequences eliminate the dead time present in single rBW sequences, which improves SNR efficiency. In combination with the proposed regularization, this enables highly efficient T1-weighted PROPELLER images without chemical shift displacement. © 2018 International Society for Magnetic Resonance in Medicine.

Magnetic resonance imaging of pulmonary infection in immunocompromised children: comparison with multidetector computed tomography.

PubMed

Ozcan, H Nursun; Gormez, Ayşegul; Ozsurekci, Yasemin; Karakaya, Jale; Oguz, Berna; Unal, Sule; Cetin, Mualla; Ceyhan, Mehmet; Haliloglu, Mithat

2017-02-01

Computed tomography (CT) is commonly used to detect pulmonary infection in immunocompromised children. To compare MRI and multidetector CT findings of pulmonary abnormalities in immunocompromised children. Seventeen neutropaenic children (6 girls; ages 2-18 years) were included. Non-contrast-enhanced CT was performed with a 64-detector CT scanner. Axial and coronal non-enhanced thoracic MRI was performed using a 1.5-T scanner within 24 h of the CT examination (true fast imaging with steady-state free precession, fat-saturated T2-weighted turbo spin echo with motion correction, T2-weighted half-Fourier single-shot turbo spin echo [HASTE], fat-saturated T1-weighted spoiled gradient echo). Pulmonary abnormalities (nodules, consolidations, ground glass opacities, atelectasis, pleural effusion and lymph nodes) were evaluated and compared among MRI sequences and between MRI and CT. The relationship between MRI sequences and nodule sizes was examined by chi- square test. Of 256 CT lesions, 207 (81%, 95% confidence interval [CI] 76-85%) were detected at MRI. Of 202 CT-detected nodules, 157 (78%, 95% CI 71-83%) were seen at motion-corrected MRI. Of the 1-5-mm nodules, 69% were detected by motion-corrected T2-weighted MRI and 38% by HASTE MRI. Sensitivity of MRI (both axial fat-saturated T2-weighted turbo spin echo with variable phase encoding directions (BLADE) images and HASTE sequences) to detect pulmonary abnormalities is promising.

ADRF experiments using near n.pi pulse strings. [Adiabatic Demagnetization due to Radio Frequency pulses

NASA Technical Reports Server (NTRS)

Rhim, W. K.; Burum, D. P.; Elleman, D. D.

1977-01-01

Adiabatic demagnetization (ADRF) can be achieved in a dipolar coupled nuclear spin system in solids by applying a string of short RF pulses and gradually modulating the pulse amplitudes or pulse angles. This letter reports an adiabatic inverse polarization effect in solids and a rotary spin echo phenomenon observed in liquids when the pulse angle is gradually changed across integral multiples of pi during a string of RF pulses. The RF pulse sequence used is illustrated along with the NMR signal from a CaF2 single crystal as observed between the RF pulses and the rotary spin echo signal observed in liquid C6F6 for n = 2. The observed effects are explained qualitatively on the basis of average Hamiltonian theory.

Accelerated Fast Spin-Echo Magnetic Resonance Imaging of the Heart Using a Self-Calibrated Split-Echo Approach

PubMed Central

Klix, Sabrina; Hezel, Fabian; Fuchs, Katharina; Ruff, Jan; Dieringer, Matthias A.; Niendorf, Thoralf

2014-01-01

Purpose Design, validation and application of an accelerated fast spin-echo (FSE) variant that uses a split-echo approach for self-calibrated parallel imaging. Methods For self-calibrated, split-echo FSE (SCSE-FSE), extra displacement gradients were incorporated into FSE to decompose odd and even echo groups which were independently phase encoded to derive coil sensitivity maps, and to generate undersampled data (reduction factor up to R = 3). Reference and undersampled data were acquired simultaneously. SENSE reconstruction was employed. Results The feasibility of SCSE-FSE was demonstrated in phantom studies. Point spread function performance of SCSE-FSE was found to be competitive with traditional FSE variants. The immunity of SCSE-FSE for motion induced mis-registration between reference and undersampled data was shown using a dynamic left ventricular model and cardiac imaging. The applicability of black blood prepared SCSE-FSE for cardiac imaging was demonstrated in healthy volunteers including accelerated multi-slice per breath-hold imaging and accelerated high spatial resolution imaging. Conclusion SCSE-FSE obviates the need of external reference scans for SENSE reconstructed parallel imaging with FSE. SCSE-FSE reduces the risk for mis-registration between reference scans and accelerated acquisitions. SCSE-FSE is feasible for imaging of the heart and of large cardiac vessels but also meets the needs of brain, abdominal and liver imaging. PMID:24728341

Forward masking as a mechanism of automatic gain control in odontocete biosonar: a psychophysical study.

PubMed

Supin, Alexander Ya; Nachtigall, Paul E; Breese, Marlee

2008-07-01

In a false killer whale Pseudorca crassidens, echo perception thresholds were measured using a go/no-go psychophysical paradigm and one-up-one-down staircase procedure. Computer controlled echoes were electronically synthesized pulses that were played back through a transducer and triggered by whale emitted biosonar pulses. The echo amplitudes were proportional to biosonar pulse amplitudes; echo levels were specified in terms of the attenuation of the echo sound pressure level near the animal's head relative to the source level of the biosonar pulses. With increasing echo delay, the thresholds (echo attenuation factor) decreased from -49.3 dB at 2 ms to -79.5 dB at 16 ms, with a regression slope of -9.5 dB per delay doubling (-31.5 dB per delay decade). At the longer delays, the threshold remained nearly constant around -80.4 dB. Levels of emitted pulses slightly increased with delay prolongation (threshold decrease), with a regression slope of 3.2 dB per delay doubling (10.7 dB per delay decade). The echo threshold dependence on delay is interpreted as a release from forward masking by the preceding emitted pulse. This release may compensate for the echo level decrease with distance, thus keeping the echo sensation level for the animal near constant within a certain distance range.

Experimental quantification of decoherence via the Loschmidt echo in a many spin system with scaled dipolar Hamiltonians

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buljubasich, Lisandro; Dente, Axel D.; Levstein, Patricia R.

2015-10-28

We performed Loschmidt echo nuclear magnetic resonance experiments to study decoherence under a scaled dipolar Hamiltonian by means of a symmetrical time-reversal pulse sequence denominated Proportionally Refocused Loschmidt (PRL) echo. The many-spin system represented by the protons in polycrystalline adamantane evolves through two steps of evolution characterized by the secular part of the dipolar Hamiltonian, scaled down with a factor |k| and opposite signs. The scaling factor can be varied continuously from 0 to 1/2, giving access to a range of complexity in the dynamics. The experimental results for the Loschmidt echoes showed a spreading of the decay rates thatmore » correlate directly to the scaling factors |k|, giving evidence that the decoherence is partially governed by the coherent dynamics. The average Hamiltonian theory was applied to give an insight into the spin dynamics during the pulse sequence. The calculations were performed for every single radio frequency block in contrast to the most widely used form. The first order of the average Hamiltonian numerically computed for an 8-spin system showed decay rates that progressively decrease as the secular dipolar Hamiltonian becomes weaker. Notably, the first order Hamiltonian term neglected by conventional calculations yielded an explanation for the ordering of the experimental decoherence rates. However, there is a strong overall decoherence observed in the experiments which is not reflected by the theoretical results. The fact that the non-inverted terms do not account for this effect is a challenging topic. A number of experiments to further explore the relation of the complete Hamiltonian with this dominant decoherence rate are proposed.« less

Loschmidt echo as a robust decoherence quantifier for many-body systems

NASA Astrophysics Data System (ADS)

Zangara, Pablo R.; Dente, Axel D.; Levstein, Patricia R.; Pastawski, Horacio M.

2012-07-01

We employ the Loschmidt echo, i.e., the signal recovered after the reversal of an evolution, to identify and quantify the processes contributing to decoherence. This procedure, which has been extensively used in single-particle physics, is employed here in a spin ladder. The isolated chains have 1/2 spins with XY interaction and their excitations would sustain a one-body-like propagation. One of them constitutes the controlled system S whose reversible dynamics is degraded by the weak coupling with the uncontrolled second chain, i.e., the environment E. The perturbative SE coupling is swept through arbitrary combinations of XY and Ising-like interactions, that contain the standard Heisenberg and dipolar ones. Different time regimes are identified for the Loschmidt echo dynamics in this perturbative configuration. In particular, the exponential decay scales as a Fermi golden rule, where the contributions of the different SE terms are individually evaluated and analyzed. Comparisons with previous analytical and numerical evaluations of decoherence based on the attenuation of specific interferences show that the Loschmidt echo is an advantageous decoherence quantifier at any time, regardless of the S internal dynamics.

Spin echo SPI methods for quantitative analysis of fluids in porous media.

PubMed

Li, Linqing; Han, Hui; Balcom, Bruce J

2009-06-01

Fluid density imaging is highly desirable in a wide variety of porous media measurements. The SPRITE class of MRI methods has proven to be robust and general in their ability to generate density images in porous media, however the short encoding times required, with correspondingly high magnetic field gradient strengths and filter widths, and low flip angle RF pulses, yield sub-optimal S/N images, especially at low static field strength. This paper explores two implementations of pure phase encode spin echo 1D imaging, with application to a proposed new petroleum reservoir core analysis measurement. In the first implementation of the pulse sequence, we modify the spin echo single point imaging (SE-SPI) technique to acquire the k-space origin data point, with a near zero evolution time, from the free induction decay (FID) following a 90 degrees excitation pulse. Subsequent k-space data points are acquired by separately phase encoding individual echoes in a multi-echo acquisition. T(2) attenuation of the echo train yields an image convolution which causes blurring. The T(2) blur effect is moderate for porous media with T(2) lifetime distributions longer than 5 ms. As a robust, high S/N, and fast 1D imaging method, this method will be highly complementary to SPRITE techniques for the quantitative analysis of fluid content in porous media. In the second implementation of the SE-SPI pulse sequence, modification of the basic measurement permits fast determination of spatially resolved T(2) distributions in porous media through separately phase encoding each echo in a multi-echo CPMG pulse train. An individual T(2) weighted image may be acquired from each echo. The echo time (TE) of each T(2) weighted image may be reduced to 500 micros or less. These profiles can be fit to extract a T(2) distribution from each pixel employing a variety of standard inverse Laplace transform methods. Fluid content 1D images are produced as an essential by product of determining the spatially resolved T(2) distribution. These 1D images do not suffer from a T(2) related blurring. The above SE-SPI measurements are combined to generate 1D images of the local saturation and T(2) distribution as a function of saturation, upon centrifugation of petroleum reservoir core samples. The logarithm mean T(2) is observed to shift linearly with water saturation. This new reservoir core analysis measurement may provide a valuable calibration of the Coates equation for irreducible water saturation, which has been widely implemented in NMR well logging measurements.

Atomic-resolution structure of the CAP-Gly domain of dynactin on polymeric microtubules determined by magic angle spinning NMR spectroscopy.

PubMed

Yan, Si; Guo, Changmiao; Hou, Guangjin; Zhang, Huilan; Lu, Xingyu; Williams, John Charles; Polenova, Tatyana

2015-11-24

Microtubules and their associated proteins perform a broad array of essential physiological functions, including mitosis, polarization and differentiation, cell migration, and vesicle and organelle transport. As such, they have been extensively studied at multiple levels of resolution (e.g., from structural biology to cell biology). Despite these efforts, there remain significant gaps in our knowledge concerning how microtubule-binding proteins bind to microtubules, how dynamics connect different conformational states, and how these interactions and dynamics affect cellular processes. Structures of microtubule-associated proteins assembled on polymeric microtubules are not known at atomic resolution. Here, we report a structure of the cytoskeleton-associated protein glycine-rich (CAP-Gly) domain of dynactin motor on polymeric microtubules, solved by magic angle spinning NMR spectroscopy. We present the intermolecular interface of CAP-Gly with microtubules, derived by recording direct dipolar contacts between CAP-Gly and tubulin using double rotational echo double resonance (dREDOR)-filtered experiments. Our results indicate that the structure adopted by CAP-Gly varies, particularly around its loop regions, permitting its interaction with multiple binding partners and with the microtubules. To our knowledge, this study reports the first atomic-resolution structure of a microtubule-associated protein on polymeric microtubules. Our approach lays the foundation for atomic-resolution structural analysis of other microtubule-associated motors.

Fluorescent triplex-forming DNA oligonucleotides labeled with a thiazole orange dimer unit

PubMed Central

Ikeda, Shuji; Yanagisawa, Hiroyuki; Yuki, Mizue; Okamoto, Akimitsu

2013-01-01

Fluorescent probes for the detection of a double-stranded DNA were prepared by labeling a triplex-forming DNA oligonucleotide with a thiazole orange (TO) dimer unit. They belong to ECHO (exciton-controlled hybridization-sensitive fluorescent oligonucleotide) probes which we have previously reported. The excitonic interaction between the two TO molecules was expected to effectively suppress the background fluorescence of the probes. The applicability of the ECHO probes for the detection of double-stranded DNA was confirmed by examining the thermal stability and photophysical and kinetic properties of the DNA triplexes formed by the ECHO probes. PMID:23445822

Light Echos in Kerr Geometry: A Source of High Frequency QPOs from Random X-ray Bursts

NASA Technical Reports Server (NTRS)

Fukumura, K.; Kazanas, D.

2008-01-01

We propose that high frequency quasi-periodic oscillations (HFQPOs) can be produced from randomly-formed X-ray bursts (flashes) by plasma interior to the ergosphere of a rapidly-rotating black hole. We show by direct computation of their orbits that the photons comprising the observed X-ray light curves, if due to a multitude of such flashes, are affected significantly by the black hole's dragging of inertial frames; the photons of each such burst arrive to an observer at infinity in multiple (double or triple), distinct 'bunches' separated by a roughly constant time lag of t/M approximately equal to 14, regardless of the bursts' azimuthal position. We argue that every other such 'bunch' represents photons that follow trajectories with an additional orbit around the black hole at the photon circular orbit radius (a photon 'echo'). The presence of this constant lag in the response function of the system leads to a QPO feature in its power density spectra, even though the corresponding light curve consists of a totally stochastic signal. This effect is by and large due to the black hole spin and is shown to gradually diminish as the spin parameter a decreases or the radial position of the burst moves outside the static limit surface (ergosphere). Our calculations indicate that for a black hole with Kerr parameter of a/M=0.99 and mass of M=10*Msun the QPO is expected at a frequency of approximately 1.3-1.4 kHz. We discuss the plausibility and observational implications of our model/results as well as its limitations.

Morphology effects on spin-dependent transport and recombination in polyfluorene thin films

NASA Astrophysics Data System (ADS)

Miller, Richards; van Schooten, K. J.; Malissa, H.; Joshi, G.; Jamali, S.; Lupton, J. M.; Boehme, C.

2016-12-01

We have studied the role of spin-dependent processes on conductivity in polyfluorene (PFO) thin films by preforming continuous wave (cw) electrically detected magnetic resonance (EDMR) spectroscopy at temperatures between 10 K and room temperature using microwave frequencies between about 1 GHz and 20 GHz, as well as pulsed EDMR at the X band (10 GHz). Variable frequency EDMR allows us to establish the role of spin-orbit coupling in spin-dependent processes whereas pulsed EDMR allows for the observation of coherent spin motion effects. We used PFO for this study in order to allow for the investigation of the effects of microscopic morphological ordering since this material can adopt two distinct intrachain morphologies: an amorphous (glassy) phase, in which monomer units are twisted with respect to each other, and an ordered (β) phase, where all monomers lie within one plane. In thin films of organic light-emitting diodes, the appearance of a particular phase can be controlled by deposition parameters and solvent vapor annealing, and is verified by electroluminescence spectroscopy. Under bipolar charge-carrier injection conditions, we conducted multifrequency cw EDMR, electrically detected Rabi spin-beat experiments, and Hahn echo and inversion-recovery measurements. Coherent echo spectroscopy reveals electrically detected electron-spin-echo envelope modulation due to the coupling of the carrier spins to nearby nuclear spins. Our results demonstrate that, while conformational disorder can influence the observed EDMR signals, including the sign of the current changes on resonance as well as the magnitudes of local hyperfine fields and charge-carrier spin-orbit interactions, it does not qualitatively affect the nature of spin-dependent transitions in this material. In both morphologies, we observe the presence of at least two different spin-dependent recombination processes. At room temperature and 10 K, polaron-pair recombination through weakly spin-spin coupled intermediate charge-carrier pair states is dominant, while at low temperatures, additional signatures of spin-dependent charge transport through the interaction of polarons with triplet excitons are seen in the half-field resonance of a triplet spin-1 species. This additional contribution arises since triplet lifetimes are increased at lower temperatures. We tentatively conclude that spectral broadening induced by hyperfine coupling is slightly weaker in the more ordered β-phase than in the glassy phase since protons are more evenly spaced, whereas broadening effects due to spin-orbit coupling, which impacts the distribution of g -factors, appear to be somewhat more significant in the β-phase.

Metastable Defect Formation at Microvoids Identified as a Source of Light-Induced Degradation in a-Si :H

NASA Astrophysics Data System (ADS)

Fehr, M.; Schnegg, A.; Rech, B.; Astakhov, O.; Finger, F.; Bittl, R.; Teutloff, C.; Lips, K.

2014-02-01

Light-induced degradation of hydrogenated amorphous silicon (a-Si :H), known as the Staebler-Wronski effect, has been studied by time-domain pulsed electron-paramagnetic resonance. Electron-spin echo relaxation measurements in the annealed and light-soaked state revealed two types of defects (termed type I and II), which can be discerned by their electron-spin echo relaxation. Type I exhibits a monoexponential decay related to indirect flip-flop processes between dipolar coupled electron spins in defect clusters, while the phase relaxation of type II is dominated by H1 nuclear spin dynamics and is indicative for isolated spins. We propose that defects are either located at internal surfaces of microvoids (type I) or are isolated and uniformly distributed in the bulk (type II). The concentration of both defect type I and II is significantly higher in the light-soaked state compared to the annealed state. Our results indicate that in addition to isolated defects, defects on internal surfaces of microvoids play a role in light-induced degradation of device-quality a-Si :H.

Electrical control of a long-lived spin qubit in a Si/SiGe quantum dot.

PubMed

Kawakami, E; Scarlino, P; Ward, D R; Braakman, F R; Savage, D E; Lagally, M G; Friesen, Mark; Coppersmith, S N; Eriksson, M A; Vandersypen, L M K

2014-09-01

Nanofabricated quantum bits permit large-scale integration but usually suffer from short coherence times due to interactions with their solid-state environment. The outstanding challenge is to engineer the environment so that it minimally affects the qubit, but still allows qubit control and scalability. Here, we demonstrate a long-lived single-electron spin qubit in a Si/SiGe quantum dot with all-electrical two-axis control. The spin is driven by resonant microwave electric fields in a transverse magnetic field gradient from a local micromagnet, and the spin state is read out in the single-shot mode. Electron spin resonance occurs at two closely spaced frequencies, which we attribute to two valley states. Thanks to the weak hyperfine coupling in silicon, a Ramsey decay timescale of 1 μs is observed, almost two orders of magnitude longer than the intrinsic timescales in GaAs quantum dots, whereas gate operation times are comparable to those reported in GaAs. The spin echo decay time is ~40 μs, both with one and four echo pulses, possibly limited by intervalley scattering. These advances strongly improve the prospects for quantum information processing based on quantum dots.

Notch filtering the nuclear environment of a spin qubit.

PubMed

Malinowski, Filip K; Martins, Frederico; Nissen, Peter D; Barnes, Edwin; Cywiński, Łukasz; Rudner, Mark S; Fallahi, Saeed; Gardner, Geoffrey C; Manfra, Michael J; Marcus, Charles M; Kuemmeth, Ferdinand

2017-01-01

Electron spins in gate-defined quantum dots provide a promising platform for quantum computation. In particular, spin-based quantum computing in gallium arsenide takes advantage of the high quality of semiconducting materials, reliability in fabricating arrays of quantum dots and accurate qubit operations. However, the effective magnetic noise arising from the hyperfine interaction with uncontrolled nuclear spins in the host lattice constitutes a major source of decoherence. Low-frequency nuclear noise, responsible for fast (10 ns) inhomogeneous dephasing, can be removed by echo techniques. High-frequency nuclear noise, recently studied via echo revivals, occurs in narrow-frequency bands related to differences in Larmor precession of the three isotopes 69 Ga, 71 Ga and 75 As (refs 15,16,17). Here, we show that both low- and high-frequency nuclear noise can be filtered by appropriate dynamical decoupling sequences, resulting in a substantial enhancement of spin qubit coherence times. Using nuclear notch filtering, we demonstrate a spin coherence time (T 2 ) of 0.87 ms, five orders of magnitude longer than typical exchange gate times, and exceeding the longest coherence times reported to date in Si/SiGe gate-defined quantum dots.

Effects of off-resonance spins on the performance of the modulated gradient spin echo sequence.

PubMed

Serša, Igor; Bajd, Franci; Mohorič, Aleš

2016-09-01

Translational molecular dynamics in various materials can also be studied by diffusion spectra. These can be measured by a constant gradient variant of the modulated gradient spin echo (MGSE) sequence which is composed of a CPMG RF pulse train superimposed to a constant magnetic field gradient. The application of the RF train makes the effective gradient oscillating thus enabling measurements of diffusion spectra in a wide range of frequencies. However, seemingly straightforward implementation of the MGSE sequence proved to be complicated and can give overestimated results for diffusion if not interpreted correctly. In this study, unrestricted diffusion in water and other characteristic materials was analyzed by the MGSE sequence in the frequency range 50-3000Hz using a 6T/m diffusion probe. First, it was shown that the MGSE echo train acquired from the entire sample decays faster than the train acquired only from a narrow band at zero frequency of the sample. Then, it was shown that the decay rate is dependent on the band's off-resonance characterized by the ratio Δω0/ω1 and that with higher off-resonances the decay is faster. The faster decay therefore corresponds to a higher diffusion coefficient if the diffusion is calculated using standard Stejskal-Tanner formula. The result can be explained by complex coherence pathways contributing to the MGSE echo signals when |Δω0|/ω1>0. In a magnetic field gradient, all the pathways are more diffusion attenuated than the direct coherence pathway and therefore decay faster, which leads to an overestimation of the diffusion coefficient. A solution to this problem was found in an efficient off-resonance signal reduction by using only zero frequency filtered MGSE echo train signals. Copyright © 2016 Elsevier Inc. All rights reserved.

A fast screening protocol for carotid plaques imaging using 3D multi-contrast MRI without contrast agent.

PubMed

Zhang, Na; Zhang, Lei; Yang, Qi; Pei, Anqi; Tong, Xiaoxin; Chung, Yiu-Cho; Liu, Xin

2017-06-01

To implement a fast (~15min) MRI protocol for carotid plaque screening using 3D multi-contrast MRI sequences without contrast agent on a 3Tesla MRI scanner. 7 healthy volunteers and 25 patients with clinically confirmed transient ischemic attack or suspected cerebrovascular ischemia were included in this study. The proposed protocol, including 3D T1-weighted and T2-weighted SPACE (variable-flip-angle 3D turbo spin echo), and T1-weighted magnetization prepared rapid acquisition gradient echo (MPRAGE) was performed first and was followed by 2D T1-weighted and T2-weighted turbo spin echo, and post-contrast T1-weighted SPACE sequences. Image quality, number of plaques, and vessel wall thicknesses measured at the intersection of the plaques were evaluated and compared between sequences. Average examination time of the proposed protocol was 14.6min. The average image quality scores of 3D T1-weighted, T2-weighted SPACE, and T1-weighted magnetization prepared rapid acquisition gradient echo were 3.69, 3.75, and 3.48, respectively. There was no significant difference in detecting the number of plaques and vulnerable plaques using pre-contrast 3D images with or without post-contrast T1-weighted SPACE. The 3D SPACE and 2D turbo spin echo sequences had excellent agreement (R=0.96 for T1-weighted and 0.98 for T2-weighted, p<0.001) regarding vessel wall thickness measurements. The proposed protocol demonstrated the feasibility of attaining carotid plaque screening within a 15-minute scan, which provided sufficient anatomical coverage and critical diagnostic information. This protocol offers the potential for rapid and reliable screening for carotid plaques without contrast agent. Copyright © 2016. Published by Elsevier Inc.

T2‐Weighted intracranial vessel wall imaging at 7 Tesla using a DANTE‐prepared variable flip angle turbo spin echo readout (DANTE‐SPACE)

PubMed Central

Viessmann, Olivia; Li, Linqing; Benjamin, Philip

2016-01-01

Purpose To optimize intracranial vessel wall imaging (VWI) at 7T for sharp wall depiction and high boundary contrast. Methods A variable flip angle turbo spin echo scheme (SPACE) was optimized for VWI. SPACE provides black‐blood contrast, but has less crushing effect on cerebrospinal fluid (CSF). However, a delay alternating with nutation for tailored excitation (DANTE) preparation suppresses the signal from slowly moving spins of a few mm per second. Therefore, we optimized a DANTE‐preparation module for 7T. Signal‐to‐noise ratio (SNR), contrast‐to‐noise ratio (CNR), and signal ratio for vessel wall, CSF, and lumen were calculated for SPACE and DANTE‐SPACE in 11 volunteers at the middle cerebral artery (MCA). An exemplar MCA stenosis patient was scanned with DANTE‐SPACE. Results The 7T‐optimized SPACE sequence improved the vessel wall point‐spread function by 17%. The CNR between the wall and CSF was doubled (12.2 versus 5.6) for the DANTE‐SPACE scans compared with the unprepared SPACE. This increase was significant in the right hemisphere (P = 0.016), but not in the left (P = 0.090). The CNR between wall and lumen was halved, but remained at a high value (24.9 versus 56.5). Conclusion The optimized SPACE sequence improves VWI at 7T. Additional DANTE preparation increases the contrast between the wall and CSF. Increased outer boundary contrast comes at the cost of reduced inner boundary contrast. Magn Reson Med 77:655–663, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. PMID:26890988

T2-Weighted intracranial vessel wall imaging at 7 Tesla using a DANTE-prepared variable flip angle turbo spin echo readout (DANTE-SPACE).

PubMed

Viessmann, Olivia; Li, Linqing; Benjamin, Philip; Jezzard, Peter

2017-02-01

To optimize intracranial vessel wall imaging (VWI) at 7T for sharp wall depiction and high boundary contrast. A variable flip angle turbo spin echo scheme (SPACE) was optimized for VWI. SPACE provides black-blood contrast, but has less crushing effect on cerebrospinal fluid (CSF). However, a delay alternating with nutation for tailored excitation (DANTE) preparation suppresses the signal from slowly moving spins of a few mm per second. Therefore, we optimized a DANTE-preparation module for 7T. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and signal ratio for vessel wall, CSF, and lumen were calculated for SPACE and DANTE-SPACE in 11 volunteers at the middle cerebral artery (MCA). An exemplar MCA stenosis patient was scanned with DANTE-SPACE. The 7T-optimized SPACE sequence improved the vessel wall point-spread function by 17%. The CNR between the wall and CSF was doubled (12.2 versus 5.6) for the DANTE-SPACE scans compared with the unprepared SPACE. This increase was significant in the right hemisphere (P = 0.016), but not in the left (P = 0.090). The CNR between wall and lumen was halved, but remained at a high value (24.9 versus 56.5). The optimized SPACE sequence improves VWI at 7T. Additional DANTE preparation increases the contrast between the wall and CSF. Increased outer boundary contrast comes at the cost of reduced inner boundary contrast. Magn Reson Med 77:655-663, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

Spin-echo based diagonal peak suppression in solid-state MAS NMR homonuclear chemical shift correlation spectra

NASA Astrophysics Data System (ADS)

Wang, Kaiyu; Zhang, Zhiyong; Ding, Xiaoyan; Tian, Fang; Huang, Yuqing; Chen, Zhong; Fu, Riqiang

2018-02-01

The feasibility of using the spin-echo based diagonal peak suppression method in solid-state MAS NMR homonuclear chemical shift correlation experiments is demonstrated. A complete phase cycling is designed in such a way that in the indirect dimension only the spin diffused signals are evolved, while all signals not involved in polarization transfer are refocused for cancellation. A data processing procedure is further introduced to reconstruct this acquired spectrum into a conventional two-dimensional homonuclear chemical shift correlation spectrum. A uniformly 13C, 15N labeled Fmoc-valine sample and the transmembrane domain of a human protein, LR11 (sorLA), in native Escherichia coli membranes have been used to illustrate the capability of the proposed method in comparison with standard 13C-13C chemical shift correlation experiments.

Decoherence and spin echo in biological systems.

PubMed

Nesterov, Alexander I; Berman, Gennady P

2015-05-01

The spin-echo approach is extended to include biocomplexes for which the interaction with dynamical noise, produced by the protein environment, is strong. Significant restoration of the free induction decay signal due to homogeneous (decoherence) and inhomogeneous (dephasing) broadening is demonstrated analytically and numerically for both an individual dimer of interacting chlorophylls and for an ensemble of dimers. Our approach does not require the use of small interaction constants between the electron states and the protein fluctuations. It is based on an exact and closed system of ordinary differential equations that can be easily solved for a wide range of parameters that are relevant for bioapplications.

Copper ESEEM and HYSCORE through ultra-wideband chirp EPR spectroscopy.

PubMed

Segawa, Takuya F; Doll, Andrin; Pribitzer, Stephan; Jeschke, Gunnar

2015-07-28

The main limitation of pulse electron paramagnetic resonance (EPR) spectroscopy is its narrow excitation bandwidth. Ultra-wideband (UWB) excitation with frequency-swept chirp pulses over several hundreds of megahertz overcomes this drawback. This allows to excite electron spin echo envelope modulation (ESEEM) from paramagnetic copper centers in crystals, whereas up to now, only ESEEM of ligand nuclei like protons or nitrogens at lower frequencies could be detected. ESEEM spectra are recorded as two-dimensional correlation experiments, since the full digitization of the electron spin echo provides an additional Fourier transform EPR dimension. Thus, UWB hyperfine-sublevel correlation experiments generate a novel three-dimensional EPR-correlated nuclear modulation spectrum.

Decoherence and spin echo in biological systems

NASA Astrophysics Data System (ADS)

Nesterov, Alexander I.; Berman, Gennady P.

2015-05-01

The spin-echo approach is extended to include biocomplexes for which the interaction with dynamical noise, produced by the protein environment, is strong. Significant restoration of the free induction decay signal due to homogeneous (decoherence) and inhomogeneous (dephasing) broadening is demonstrated analytically and numerically for both an individual dimer of interacting chlorophylls and for an ensemble of dimers. Our approach does not require the use of small interaction constants between the electron states and the protein fluctuations. It is based on an exact and closed system of ordinary differential equations that can be easily solved for a wide range of parameters that are relevant for bioapplications.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brasch, R.C.; Wesbey, G.E.; Gooding, C.A.

Tissue deposits of hemosiderin, a paramagnetic iron-protein complex, resulted in marked abnormalities of magnetic resonance (MR) spin-echo signal intensity within the viscera of three children with transfusional hemosiderosis and thalassemia major. In all patients the liver and bone marrow demonstrated abnormally low spin-echo intensities and the kidneys and muscles had abnormally high intensities. These observations correlate with in vitro MR observation of ferric (Fe/sup +3/) solutions, in which concentrations of ferric salts greater than 20 mmol yielded higher intensities than did water alone. MR imaging is sensitive to the tissue deposition of hemosiderin, and MR intensity appears to provide amore » rough measure of the amount of iron deposited.« less

Removal of intensity bias in magnitude spin-echo MRI images by nonlinear diffusion filtering

NASA Astrophysics Data System (ADS)

Samsonov, Alexei A.; Johnson, Chris R.

2004-05-01

MRI data analysis is routinely done on the magnitude part of complex images. While both real and imaginary image channels contain Gaussian noise, magnitude MRI data are characterized by Rice distribution. However, conventional filtering methods often assume image noise to be zero mean and Gaussian distributed. Estimation of an underlying image using magnitude data produces biased result. The bias may lead to significant image errors, especially in areas of low signal-to-noise ratio (SNR). The incorporation of the Rice PDF into a noise filtering procedure can significantly complicate the method both algorithmically and computationally. In this paper, we demonstrate that inherent image phase smoothness of spin-echo MRI images could be utilized for separate filtering of real and imaginary complex image channels to achieve unbiased image denoising. The concept is demonstrated with a novel nonlinear diffusion filtering scheme developed for complex image filtering. In our proposed method, the separate diffusion processes are coupled through combined diffusion coefficients determined from the image magnitude. The new method has been validated with simulated and real MRI data. The new method has provided efficient denoising and bias removal in conventional and black-blood angiography MRI images obtained using fast spin echo acquisition protocols.

Setting the magic angle for fast magic-angle spinning probes.

PubMed

Penzel, Susanne; Smith, Albert A; Ernst, Matthias; Meier, Beat H

2018-06-15

Fast magic-angle spinning, coupled with 1 H detection is a powerful method to improve spectral resolution and signal to noise in solid-state NMR spectra. Commercial probes now provide spinning frequencies in excess of 100 kHz. Then, one has sufficient resolution in the 1 H dimension to directly detect protons, which have a gyromagnetic ratio approximately four times larger than 13 C spins. However, the gains in sensitivity can quickly be lost if the rotation angle is not set precisely. The most common method of magic-angle calibration is to optimize the number of rotary echoes, or sideband intensity, observed on a sample of KBr. However, this typically uses relatively low spinning frequencies, where the spinning of fast-MAS probes is often unstable, and detection on the 13 C channel, for which fast-MAS probes are typically not optimized. Therefore, we compare the KBr-based optimization of the magic angle with two alternative approaches: optimization of the splitting observed in 13 C-labeled glycine-ethylester on the carbonyl due to the Cα-C' J-coupling, or optimization of the H-N J-coupling spin echo in the protein sample itself. The latter method has the particular advantage that no separate sample is necessary for the magic-angle optimization. Copyright © 2018. Published by Elsevier Inc.

J-Refocused Coherence Transfer Spectroscopic Imaging at 7 T in Human Brain

PubMed Central

Pan, J.W.; Avdievich, N.; Hetherington, H.P.

2013-01-01

Short echo spectroscopy is commonly used to minimize signal modulation due to J-evolution of the cerebral amino acids. However, short echo acquisitions suffer from high sensitivity to macromolecules which make accurate baseline determination difficult. In this report, we describe implementation at 7 T of a double echo J-refocused coherence transfer sequence at echo time (TE) of 34 msec to minimize J-modulation of amino acids while also decreasing interfering macromolecule signals. Simulation of the pulse sequence at 7 T shows excellent resolution of glutamate, glutamine, and N-acetyl aspartate. B1 sufficiency at 7 T for the double echo acquisition is achieved using a transceiver array with radiofrequency (RF) shimming. Using an alternate RF distribution to minimize receiver phase cancellation in the transceiver, accurate phase determination for the coherence transfer is achieved with rapid single scan calibration. This method is demonstrated in spectroscopic imaging mode with n = 5 healthy volunteers resulting in metabolite values consistent with literature and in a patient with epilepsy. PMID:20648684

Breast cancer detection using double reading of unenhanced MRI including T1-weighted, T2-weighted STIR, and diffusion-weighted imaging: a proof of concept study.

PubMed

Trimboli, Rubina M; Verardi, Nicola; Cartia, Francesco; Carbonaro, Luca A; Sardanelli, Francesco

2014-09-01

The purpose of this study was to investigate the diagnostic performance of unenhanced MRI in detecting breast cancer and to assess the impact of double reading. A total of 116 breasts of 67 women who were 36-89 years old were studied at 1.5 T using an unenhanced protocol including axial T1-weighted gradient-echo, T2-weighted STIR, and echo-planar diffusion-weighted imaging (DWI). Two blinded readers (R1 and R2) independently evaluated unenhanced images using the BIRADS scale. A combination of pathology and negative follow-up served as the reference standard. McNemar and kappa statistics were used. Per-breast cancer prevalence was 37 of 116 (32%): 30 of 37 (81%) invasive ductal carcinoma, five of 37 (13%) ductal carcinoma in situ, and two of 37 (6%) invasive lobular carcinoma. Per-breast sensitivity of unenhanced MRI was 29 of 37 (78%) for R1, 28 of 37 (76%) for R2, and 29 of 37 (78%) for double reading. Specificity was 71 of 79 (90%) for both R1 and R2 and 69 of 79 (87%) for double reading. Double reading did not provide a significant increase in sensitivity. Interobserver agreement was almost perfect (Cohen κ = 0.873). An unenhanced breast MRI protocol composed of T1-weighted gradient echo, T2-weighted STIR, and echo-planar DWI enabled breast cancer detection with sensitivity of 76-78% and specificity of 90% without a gain in sensitivity from double reading.

Site-resolved multiple-quantum filtered correlations and distance measurements by magic-angle spinning NMR: Theory and applications to spins with weak to vanishing quadrupolar couplings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eliav, U., E-mail: amirgo@tau.ac.il, E-mail: eliav@tau.ac.il; Haimovich, A.; Goldbourt, A., E-mail: amirgo@tau.ac.il, E-mail: eliav@tau.ac.il

2016-01-14

We discuss and analyze four magic-angle spinning solid-state NMR methods that can be used to measure internuclear distances and to obtain correlation spectra between a spin I = 1/2 and a half-integer spin S > 1/2 having a small quadrupolar coupling constant. Three of the methods are based on the heteronuclear multiple-quantum and single-quantum correlation experiments, that is, high rank tensors that involve the half spin and the quadrupolar spin are generated. Here, both zero and single-quantum coherence of the half spins are allowed and various coherence orders of the quadrupolar spin are generated, and filtered, via active recoupling ofmore » the dipolar interaction. As a result of generating coherence orders larger than one, the spectral resolution for the quadrupolar nucleus increases linearly with the coherence order. Since the formation of high rank tensors is independent of the existence of a finite quadrupolar interaction, these experiments are also suitable to materials in which there is high symmetry around the quadrupolar spin. A fourth experiment is based on the initial quadrupolar-driven excitation of symmetric high order coherences (up to p = 2S, where S is the spin number) and subsequently generating by the heteronuclear dipolar interaction higher rank (l + 1 or higher) tensors that involve also the half spins. Due to the nature of this technique, it also provides information on the relative orientations of the quadrupolar and dipolar interaction tensors. For the ideal case in which the pulses are sufficiently strong with respect to other interactions, we derive analytical expressions for all experiments as well as for the transferred echo double resonance experiment involving a quadrupolar spin. We show by comparison of the fitting of simulations and the analytical expressions to experimental data that the analytical expressions are sufficiently accurate to provide experimental {sup 7}Li–{sup 13}C distances in a complex of lithium, glycine, and water. Discussion of the regime for which such an approach is valid is given.« less

Generation of Light with Multimode Time-Delayed Entanglement Using Storage in a Solid-State Spin-Wave Quantum Memory.

PubMed

Ferguson, Kate R; Beavan, Sarah E; Longdell, Jevon J; Sellars, Matthew J

2016-07-08

Here, we demonstrate generating and storing entanglement in a solid-state spin-wave quantum memory with on-demand readout using the process of rephased amplified spontaneous emission (RASE). Amplified spontaneous emission (ASE), resulting from an inverted ensemble of Pr^{3+} ions doped into a Y_{2}SiO_{5} crystal, generates entanglement between collective states of the praseodymium ensemble and the output light. The ensemble is then rephased using a four-level photon echo technique. Entanglement between the ASE and its echo is confirmed and the inseparability violation preserved when the RASE is stored as a spin wave for up to 5  μs. RASE is shown to be temporally multimode with almost perfect distinguishability between two temporal modes demonstrated. These results pave the way for the use of multimode solid-state quantum memories in scalable quantum networks.

T2 shuffling: Sharp, multicontrast, volumetric fast spin-echo imaging.

PubMed

Tamir, Jonathan I; Uecker, Martin; Chen, Weitian; Lai, Peng; Alley, Marcus T; Vasanawala, Shreyas S; Lustig, Michael

2017-01-01

A new acquisition and reconstruction method called T 2 Shuffling is presented for volumetric fast spin-echo (three-dimensional [3D] FSE) imaging. T 2 Shuffling reduces blurring and recovers many images at multiple T 2 contrasts from a single acquisition at clinically feasible scan times (6-7 min). The parallel imaging forward model is modified to account for temporal signal relaxation during the echo train. Scan efficiency is improved by acquiring data during the transient signal decay and by increasing echo train lengths without loss in signal-to-noise ratio (SNR). By (1) randomly shuffling the phase encode view ordering, (2) constraining the temporal signal evolution to a low-dimensional subspace, and (3) promoting spatio-temporal correlations through locally low rank regularization, a time series of virtual echo time images is recovered from a single scan. A convex formulation is presented that is robust to partial voluming and radiofrequency field inhomogeneity. Retrospective undersampling and in vivo scans confirm the increase in sharpness afforded by T 2 Shuffling. Multiple image contrasts are recovered and used to highlight pathology in pediatric patients. A proof-of-principle method is integrated into a clinical musculoskeletal imaging workflow. The proposed T 2 Shuffling method improves the diagnostic utility of 3D FSE by reducing blurring and producing multiple image contrasts from a single scan. Magn Reson Med 77:180-195, 2017. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

A TEMPORAL MAP IN GEOSTATIONARY ORBIT: THE COVER ETCHING ON THE EchoStar XVI ARTIFACT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weisberg, Joel M., E-mail: jweisber@carleton.edu; Paglen, Trevor, E-mail: trevor@paglen.com

Geostationary satellites are unique among orbital spacecraft in that they experience no appreciable atmospheric drag. After concluding their respective missions, geostationary spacecraft remain in orbit virtually in perpetuity. As such, they represent some of human civilization's longest lasting artifacts. With this in mind, the EchoStar XVI satellite, to be launched in fall 2012, will play host to a time capsule intended as a message for the deep future. Inspired in part by the Pioneer Plaque and Voyager Golden Records, the EchoStar XVI Artifact is a pair of gold-plated aluminum jackets housing a small silicon disk containing 100 photographs. The Covermore » Etching, the subject of this paper, is etched onto one of the two jackets. It is a temporal map consisting of a star chart, pulsar timings, and other information describing the epoch from which EchoStar XVI came. The pulsar sample consists of 13 rapidly rotating objects, 5 of which are especially stable, having spin periods <10 ms and extremely small spin-down rates. In this paper, we discuss our approach to the time map etched onto the cover and the scientific data shown on it, and we speculate on the uses that future scientists may have for its data. The other portions of the EchoStar XVI Artifact will be discussed elsewhere.« less

Copper ESEEM and HYSCORE through ultra-wideband chirp EPR spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Segawa, Takuya F.; Doll, Andrin; Pribitzer, Stephan

2015-07-28

The main limitation of pulse electron paramagnetic resonance (EPR) spectroscopy is its narrow excitation bandwidth. Ultra-wideband (UWB) excitation with frequency-swept chirp pulses over several hundreds of megahertz overcomes this drawback. This allows to excite electron spin echo envelope modulation (ESEEM) from paramagnetic copper centers in crystals, whereas up to now, only ESEEM of ligand nuclei like protons or nitrogens at lower frequencies could be detected. ESEEM spectra are recorded as two-dimensional correlation experiments, since the full digitization of the electron spin echo provides an additional Fourier transform EPR dimension. Thus, UWB hyperfine-sublevel correlation experiments generate a novel three-dimensional EPR-correlated nuclearmore » modulation spectrum.« less

Single-shot turbo spin echo acquisition for in vivo cardiac diffusion MRI.

PubMed

Edalati, Masoud; Lee, Gregory R; Hui Wang; Taylor, Michael D; Li, Yu Y

2016-08-01

Diffusion MRI offers the ability to noninvasively characterize the microstructure of myocardium tissue and detect disease related pathology in cardiovascular examination. This study investigates the feasibility of in vivo cardiac diffusion MRI under free-breathing condition. A high-speed imaging technique, correlation imaging, is used to enable single-shot turbo spin echo for free-breathing cardiac data acquisition. The obtained in vivo cardiac diffusion-weighted images illustrate robust image quality and minor geometry distortions. The resultant diffusion scalar maps show reliable quantitative values consistent with those previously published in the literature. It is demonstrated that this technique has the potential for in vivo free-breathing cardiac diffusion MRI.

Fully refocused multi-shot spatiotemporally encoded MRI: robust imaging in the presence of metallic implants.

PubMed

Ben-Eliezer, Noam; Solomon, Eddy; Harel, Elad; Nevo, Nava; Frydman, Lucio

2012-12-01

An approach has been recently introduced for acquiring arbitrary 2D NMR spectra or images in a single scan, based on the use of frequency-swept RF pulses for the sequential excitation and acquisition of the spins response. This spatiotemporal-encoding (SPEN) approach enables a unique, voxel-by-voxel refocusing of all frequency shifts in the sample, for all instants throughout the data acquisition. The present study investigates the use of this full-refocusing aspect of SPEN-based imaging in the multi-shot MRI of objects, subject to sizable field inhomogeneities that complicate conventional imaging approaches. 2D MRI experiments were performed at 7 T on phantoms and on mice in vivo, focusing on imaging in proximity to metallic objects. Fully refocused SPEN-based spin echo imaging sequences were implemented, using both Cartesian and back-projection trajectories, and compared with k-space encoded spin echo imaging schemes collected on identical samples under equal bandwidths and acquisition timing conditions. In all cases assayed, the fully refocused spatiotemporally encoded experiments evidenced a ca. 50 % reduction in signal dephasing in the proximity of the metal, as compared to analogous results stemming from the k-space encoded spin echo counterparts. The results in this study suggest that SPEN-based acquisition schemes carry the potential to overcome strong field inhomogeneities, of the kind that currently preclude high-field, high-resolution tissue characterizations in the neighborhood of metallic implants.

X-ray Echo Spectroscopy

NASA Astrophysics Data System (ADS)

Shvyd'ko, Yuri

2016-02-01

X-ray echo spectroscopy, a counterpart of neutron spin echo, is being introduced here to overcome limitations in spectral resolution and weak signals of the traditional inelastic x-ray scattering (IXS) probes. An image of a pointlike x-ray source is defocused by a dispersing system comprised of asymmetrically cut specially arranged Bragg diffracting crystals. The defocused image is refocused into a point (echo) in a time-reversal dispersing system. If the defocused beam is inelastically scattered from a sample, the echo signal acquires a spatial distribution, which is a map of the inelastic scattering spectrum. The spectral resolution of the echo spectroscopy does not rely on the monochromaticity of the x rays, ensuring strong signals along with a very high spectral resolution. Particular schemes of x-ray echo spectrometers for 0.1-0.02 meV ultrahigh-resolution IXS applications (resolving power >108 ) with broadband ≃5 - 13 meV dispersing systems are introduced featuring more than 103 signal enhancement. The technique is general, applicable in different photon frequency domains.

Propagation of error from parameter constraints in quantitative MRI: Example application of multiple spin echo T2 mapping.

PubMed

Lankford, Christopher L; Does, Mark D

2018-02-01

Quantitative MRI may require correcting for nuisance parameters which can or must be constrained to independently measured or assumed values. The noise and/or bias in these constraints propagate to fitted parameters. For example, the case of refocusing pulse flip angle constraint in multiple spin echo T 2 mapping is explored. An analytical expression for the mean-squared error of a parameter of interest was derived as a function of the accuracy and precision of an independent estimate of a nuisance parameter. The expression was validated by simulations and then used to evaluate the effects of flip angle (θ) constraint on the accuracy and precision of T⁁2 for a variety of multi-echo T 2 mapping protocols. Constraining θ improved T⁁2 precision when the θ-map signal-to-noise ratio was greater than approximately one-half that of the first spin echo image. For many practical scenarios, constrained fitting was calculated to reduce not just the variance but the full mean-squared error of T⁁2, for bias in θ⁁≲6%. The analytical expression derived in this work can be applied to inform experimental design in quantitative MRI. The example application to T 2 mapping provided specific cases, depending on θ⁁ accuracy and precision, in which θ⁁ measurement and constraint would be beneficial to T⁁2 variance or mean-squared error. Magn Reson Med 79:673-682, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Short-echo 3D H-1 Magnetic Resonance Spectroscopic Imaging of patients with glioma at 7T for characterization of differences in metabolite levels

PubMed Central

Li, Yan; Larson, Peder; Chen, Albert P.; Lupo, Janine M.; Ozhinsky, Eugene; Kelley, Douglas; Chang, Susan M.; Nelson, Sarah J.

2014-01-01

Purpose The purpose of this study was to evaluate the feasibility of using a short echo time, 3D H-1 magnetic resonance spectroscopic imaging (MRSI) sequence at 7T to assess the metabolic signature of lesions for patients with glioma. Materials and Methods 29 patients with glioma were studied. MRSI data were obtained using CHESS water suppression, spectrally-selective adiabatic inversion-recovery pulses and automatically prescribed outer-volume-suppression for lipid suppression, and spin echo slice selection (TE=30ms). An interleaved flyback echo-planar trajectory was applied to shorten the total acquisition time (~10min). Relative metabolite ratios were estimated in tumor and in normal-appearing white and gray matter (NAWM, GM). Results Levels of glutamine, myo-inositol, glycine and glutathione relative to total creatine (tCr) were significantly increased in the T2 lesions for all tumor grades compared to those in the NAWM (p < 0.05), while N-acetyl aspartate to tCr were significantly decreased (p < 0.05). In grade 2 gliomas, level of total choline-containing-compounds to tCr was significantly increased (p = 0.0137), while glutamate to tCr was significantly reduced (p = 0.0012). Conclusion The improved sensitivity of MRSI and the increased number of metabolites that can be evaluated using 7T MR scanners is of interest for evaluating patients with glioma. This study has successfully demonstrated the application of a short-echo spin-echo MRSI sequence to detect characteristic differences in regions of tumor versus normal appearing brain. PMID:24935758

Dual-pathway multi-echo sequence for simultaneous frequency and T2 mapping

NASA Astrophysics Data System (ADS)

Cheng, Cheng-Chieh; Mei, Chang-Sheng; Duryea, Jeffrey; Chung, Hsiao-Wen; Chao, Tzu-Cheng; Panych, Lawrence P.; Madore, Bruno

2016-04-01

Purpose: To present a dual-pathway multi-echo steady state sequence and reconstruction algorithm to capture T2, T2∗ and field map information. Methods: Typically, pulse sequences based on spin echoes are needed for T2 mapping while gradient echoes are needed for field mapping, making it difficult to jointly acquire both types of information. A dual-pathway multi-echo pulse sequence is employed here to generate T2 and field maps from the same acquired data. The approach might be used, for example, to obtain both thermometry and tissue damage information during thermal therapies, or susceptibility and T2 information from a same head scan, or to generate bonus T2 maps during a knee scan. Results: Quantitative T2, T2∗ and field maps were generated in gel phantoms, ex vivo bovine muscle, and twelve volunteers. T2 results were validated against a spin-echo reference standard: A linear regression based on ROI analysis in phantoms provided close agreement (slope/R2 = 0.99/0.998). A pixel-wise in vivo Bland-Altman analysis of R2 = 1/T2 showed a bias of 0.034 Hz (about 0.3%), as averaged over four volunteers. Ex vivo results, with and without motion, suggested that tissue damage detection based on T2 rather than temperature-dose measurements might prove more robust to motion. Conclusion: T2, T2∗ and field maps were obtained simultaneously, from the same datasets, in thermometry, susceptibility-weighted imaging and knee-imaging contexts.

Evaluation of Magnetic Resonance Imaging-Compatible Needles and Interactive Sequences for Musculoskeletal Interventions Using an Open High-Field Magnetic Resonance Imaging Scanner

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wonneberger, Uta, E-mail: uta.wonneberger@charite.d; Schnackenburg, Bernhard, E-mail: bernhard.schnackenburg@philips.co; Streitparth, Florian, E-mail: florian.streitparth@charite.de

2010-04-15

In this article, we study in vitro evaluation of needle artefacts and image quality for musculoskeletal laser-interventions in an open high-field magnetic resonance imaging (MRI) scanner at 1.0T with vertical field orientation. Five commercially available MRI-compatible puncture needles were assessed based on artefact characteristics in a CuSO4 phantom (0.1%) and in human cadaveric lumbar spines. First, six different interventional sequences were evaluated with varying needle orientation to the main magnetic field B0 (0{sup o} to 90{sup o}) in a sequence test. Artefact width, needle-tip error, and contrast-to-noise ratio (CNR) were calculated. Second, a gradient-echo sequence used for thermometric monitoring wasmore » assessed and in varying echo times, artefact width, tip error, and signal-to-noise ratio (SNR) were measured. Artefact width and needle-tip error correlated with needle material, instrument orientation to B0, and sequence type. Fast spin-echo sequences produced the smallest needle artefacts for all needles, except for the carbon fibre needle (width <3.5 mm, tip error <2 mm) at 45{sup o} to B0. Overall, the proton density-weighted spin-echo sequences had the best CNR (CNR{sub Muscle/Needle} >16.8). Concerning the thermometric gradient echo sequence, artefacts remained <5 mm, and the SNR reached its maximum at an echo time of 15 ms. If needle materials and sequences are accordingly combined, guidance and monitoring of musculoskeletal laser interventions may be feasible in a vertical magnetic field at 1.0T.« less

Light Echoes in Kerr Geometry: A Source of High Frequency QPOs from Random X-ray Bursts

NASA Technical Reports Server (NTRS)

Fukumura, Keigo; Kazanas, Demosthenes

2008-01-01

We propose that high frequency quasi-periodic oscillations (HFQPOs) can be produced from randomly-formed X-ray bursts (flashes) by plasma interior to the ergosphere of a rapidly-rotating black hole. We show by direct computation of their orbits that the photons comprising the observed X-ray light curves, if due to a multitude of such flashes, are affected significantly by the black hole's dragging of inertial frames; the photons of each such burst arrive to an observer at infinity in multiple (double or triple), distinct "bunches" separated by a roughly constant time lag of Deltat(t(sub lag))/M approx. 14, regardless of the bursts' azimuthal position. We argue that every other such "bunch" represents photons that follow trajectories with an additional orbit around the black hole at the photon circular orbit radius (a photon "echo"). The presence of this constant lag in the response function of the system leads to a QPO feature in its power density spectra, even though the corresponding light curve consists of a totally stochastic signal. This effect is by and large due to the black hole spin and is shown to gradually diminish as the spin parameter a decreases or the radial position of the burst moves outside the static limit surface (ergosphere). Our calculations indicate that for a black hole with Kerr parameter of a/M = 0.99 and mass of M = 10Stellar Mass the QPO is expected at a frequency of v(sub QPO) approx. 1.3 - 1.4 kHz. We discuss the plausibility and observational implications of our model/results as well as its limitations. Subject headings: accretion, accretion disks - black hole physics - X-rays: galaxies - stars: oscillations

Electron spin resonance and electron spin echo modulation studies of N,N,N prime ,N prime -tetramethylbenzidine photoionization adsorbed at the interface of polymeric latices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baglioni, P.; Rivara-Minten, E.; Kevan, L.

1989-02-23

Electron spin resonance (ESR) and electron spin echo modulation (ESEM) of photoionized N,N,N{prime},N{prime}-tetramethylbenzidine (TMB) cation adsorbed at the interface of butadiene-acrylonitrile-methacrylic acid and butadiene-styrene-acrylic acid polymeric latices have been studied as a function of sodium dodecyl sulfate (SDS) concentration adsorbed at the latex interface. The photoionization yield of TMB in frozen latices mainly depends on the strength of TMB{sup +}-water interactions, which are enhanced by added SDS as measured by ESEM. An increase in the negative surface potential of the latex particles, due to the adsorption of SDS at the latex surface, does not affect the photoionization yield, showing thatmore » the particle surface potential has, for negatively charged systems, a secondary role in promoting the photoionization yield. Differences in the TMB{sup +} yield are found for the two polymeric latices and are attributed to the different latex compositions and/or different interfacial structures.« less

Photoionization of N,N,N',N'-tetramethylbenzidine in anionic-cationic mixed micelles of sodium dodecyl sulfate-dodecyltrimethylammonium chloride: electron spin resonance and electron spin echo modulation studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rivara-Minten, E.; Baglioni, P.; Kevan, L.

1988-05-05

Electron spin echo modulation (ESEM) and electron spin resonance (ESR) spectra of the photogenerated N,N,N',N'-tetramethylbenzidine cation radical (TMB/sup +/) in frozen mixed micelles of dodecyltrimethylammonium chloride (DTAC) and sodium dodecyl sulfate (SDS) have been studied as a function of the mixed micelle composition. ESEM effects due to TMB/sup +/ interactions with deuterium in D/sub 2/O show a decrease of the TMB/sup +/-water interaction that depends on the SDS-DTAC mixed micelle composition and reaches a minimum for the equimolar mixed micelle. The efficiency of charge separation upon photoionization of TMB to produce TMB/sup +/ measured by ESR correlates with the degreemore » of water penetration into the micelle. ESEM effects due to interaction of x-doxylstearic acid nitroxide probes with deuterium in D/sub 2/O show that the decrease of water penetration is due to higher surface packing due to electrostatic attraction among the polar headgroups of the two surfactants.« less

Cavernous malformations of the brainstem: three-dimensional-constructive interference in steady-state magnetic resonance imaging for improvement of surgical approach and clinical results.

PubMed

Zausinger, Stefan; Yousry, Indra; Brueckmann, Hartmut; Schmid-Elsaesser, Robert; Tonn, Joerg-Christian

2006-02-01

The indications for resection of cavernous malformations (CMs) of the brainstem include neurological deficits, (recurrent) hemorrhage, and surgically accessible location. In particular, knowledge of the thickness of the parenchymal layer and of the CM's spatial relation to nuclei, tracts, cranial nerves, and vessels is critical for planning the surgical approach. We reviewed the operative treatment of 13 patients with 14 brainstem CMs, with special regard to refined three-dimensional (3D)-constructive interference in steady-state (CISS) magnetic resonance imaging (MRI). Patients were evaluated neurologically and by conventional spin-echo/fast spin-echo and 3D-CISS MRI. Surgery was performed with the use of microsurgical techniques and neurophysiological monitoring. Eleven CMs were located in the pons/pontomedullary region; 10 of the 11 were operated on via the lateral suboccipital approach. Three CMs were located near the floor of the fourth ventricle and operated on via the median suboccipital approach, with total removal of all CMs. Results were excellent or good in 10 patients; one patient transiently required tracheostomy, and two patients developed new hemipareses/ataxia with subsequent improvement. Not only did 3D-CISS sequences allow improved judgment of the thickness of the parenchymal layer over the lesion compared with spin-echo/fast spin-echo MRI, but 3D-CISS imaging also proved particularly superior in demonstrating the spatial relation of the lesion to fairly "safe" entry zones (e.g., between the trigeminal nerve and the VIIth and VIIIth nerve groups) by displaying the cranial nerves and vessels within the cerebellopontine cistern more precisely. Surgical treatment of brainstem CMs is recommended in symptomatic patients. Especially in patients with lesions situated ventrolaterally, the 3D-CISS sequence seems to be a valuable method for identifying the CM's relation to safe entry zones, thereby facilitating the surgical approach.

Dynamic half Fourier acquisition, single shot turbo spin-echo magnetic resonance imaging for evaluating the female pelvis.

PubMed

Gousse, A E; Barbaric, Z L; Safir, M H; Madjar, S; Marumoto, A K; Raz, S

2000-11-01

We assessed the merit of dynamic half Fourier acquisition, single shot turbo spin-echo sequence T2-weighted magnetic resonance imaging (MRI) for evaluating pelvic organ prolapse and all other female pelvic pathology by prospectively correlating clinical with imaging findings. From September 1997 to April 1998, 100 consecutive women 23 to 88 years old with (65) and without (35) pelvic organ prolapse underwent half Fourier acquisition, single shot turbo spin-echo sequence dynamic pelvic T2-weighted MRI at our institution using a 1.5 Tesla magnet with phased array coils. Mid sagittal and parasagittal views with the patient supine, relaxed and straining were obtained using no pre-examination preparation or instrumentation. We evaluated the anterior vaginal wall, bladder, urethra, posterior vaginal wall, rectum, pelvic floor musculature, perineum, uterus, vaginal cuff, ovaries, ureters and intraperitoneal organs for all pathological conditions, including pelvic prolapse. Patients underwent a prospective physical examination performed by a female urologist, and an experienced radiologist blinded to pre-imaging clinical findings interpreted all studies. Physical examination, MRI and intraoperative findings were statistically correlated. Total image acquisition time was 2.5 minutes, room time 10 minutes and cost American $540. Half Fourier acquisition, single shot turbo spin-echo T2-weighted MRI revealed pathological entities other than pelvic prolapse in 55 cases, including uterine fibroids in 11, ovarian cysts in 9, bilateral ureteronephrosis in 3, nabothian cyst in 7, Bartholin's gland cyst in 4, urethral diverticulum in 3, polytetrafluoroethylene graft abscess in 3, bladder diverticulum in 2, sacral spinal abnormalities in 2, bladder tumor in 1, sigmoid diverticulosis in 1 and other in 9. Intraoperative findings were considered the gold standard against which physical examination and MRI were compared. Using these criteria the sensitivity, specificity and positive predictive value of MRI were 100%, 83% and 97% for cystocele; 100%, 75% and 94% for urethrocele; 100%, 54% and 33% for vaginal vault prolapse; 83%, 100% and 100% for uterine prolapse; 87%, 80% and 91% for enterocele; and 76%, 50% and 96% for rectocele. Dynamic half Fourier acquisition, single shot turbo spin-echo MRI appears to be an important adjunct in the comprehensive evaluation of the female pelvis. Except for rectocele, pelvic floor prolapse is accurately staged and pelvic organ pathology reliably detected. The technique is rapid, noninvasive and cost-effective, and it allows the clinician to visualize the whole pelvis using a single dynamic study that provides superb anatomical detail.

Selective Optical Addressing of Nuclear Spins through Superhyperfine Interaction in Rare-Earth Doped Solids.

PubMed

Car, B; Veissier, L; Louchet-Chauvet, A; Le Gouët, J-L; Chanelière, T

2018-05-11

In Er^{3+}:Y_{2}SiO_{5}, we demonstrate the selective optical addressing of the ^{89}Y^{3+} nuclear spins through their superhyperfine coupling with the Er^{3+} electronic spins possessing large Landé g factors. We experimentally probe the electron-nuclear spin mixing with photon echo techniques and validate our model. The site-selective optical addressing of the Y^{3+} nuclear spins is designed by adjusting the magnetic field strength and orientation. This constitutes an important step towards the realization of long-lived solid-state qubits optically addressed by telecom photons.

Selective Optical Addressing of Nuclear Spins through Superhyperfine Interaction in Rare-Earth Doped Solids

NASA Astrophysics Data System (ADS)

Car, B.; Veissier, L.; Louchet-Chauvet, A.; Le Gouët, J.-L.; Chanelière, T.

2018-05-01

In Er3 +:Y2SiO5 , we demonstrate the selective optical addressing of the Y89 3 + nuclear spins through their superhyperfine coupling with the Er3 + electronic spins possessing large Landé g factors. We experimentally probe the electron-nuclear spin mixing with photon echo techniques and validate our model. The site-selective optical addressing of the Y3 + nuclear spins is designed by adjusting the magnetic field strength and orientation. This constitutes an important step towards the realization of long-lived solid-state qubits optically addressed by telecom photons.

7T MRI-Histologic Correlation Study of Low Specific Absorption Rate T2-Weighted GRASE Sequences in the Detection of White Matter Involvement in Multiple Sclerosis.

PubMed

Bagnato, Francesca; Hametner, Simon; Pennell, David; Dortch, Richard; Dula, Adrienne N; Pawate, Siddharama; Smith, Seth A; Lassmann, Hans; Gore, John C; Welch, Edward B

2015-01-01

The high value of the specific absorption rate (SAR) of radio-frequency (RF) energy arising from the series of RF refocusing pulses in T2-weighted (T2-w) turbo spin echo (TSE) MRI hampers its clinical application at 7.0 Tesla (7T). T2-w gradient and spin echo (GRASE) uses the speed from gradient refocusing in combination with the chemical-shift/static magnetic field (B0) inhomogeneity insensitivity from spin-echo refocusing to acquire T2-w images with a limited number of refocusing RF pulses, thus reducing SAR. To investigate whether low SAR T2-w GRASE could replace T2-w TSE in detecting white matter (WM) disease in MS patients imaged at 7T. The .7 mm3 isotropic T2-w TSE and T2-w GRASE images with variable echo times (TEs) and echo planar imaging (EPI) factors were obtained on a 7T scanner from postmortem samples of MS brains. These samples were derived from brains of 3 female MS patients. WM lesions (WM-Ls) and normal-appearing WM (NAWM) signal intensity, WM-Ls/NAWM contrast-to-noise ratio (CNR) and MRI/myelin staining sections comparisons were obtained. GRASE sequences with EPI factor/TE = 3/50 and 3/75 ms were comparable to the SE technique for measures of CNR in WM-Ls and NAWM and for detection of WM-Ls. In all sequences, however, identification of areas with remyelination, Wallerian degeneration, and gray matter demyelination, as depicted by myelin staining, was not possible. T2-w GRASE images may replace T2-w TSE for clinical use. However, even at 7T, both sequences fail in detecting and characterizing MS disease beyond visible WM-Ls. Copyright © 2015 by the American Society of Neuroimaging.

Evoked-potential recovery during double click stimulation in a beluga whale: implications for biosonar gain control.

PubMed

Supin, Alexander Ya; Popov, Vladimir V

2015-05-01

Auditory evoked potentials (AEPs) were recorded in a beluga whale Delphinapterus leucas using a double-pulse stimulation paradigm, specifically measuring the recovery (release from masking) of the second (test) response as a function of delay after the first (conditioning) pulse at various levels of the conditioning and test stimuli. The conditioning/test stimulus level ratio influenced the recovery time (the higher the ratio, the longer the recovery). This interrelation was used to evaluate the intensity/time trade in release from forward masking. Trade was evaluated as 32.2 dB per time decade. Data were considered as simulating interactions between the transmitted pulse and echo during echolocation, assuming that a transmitted sonar pulse produces forward masking of the echo response. With increased target distance, the attenuation of the echo may be compensated by the release from masking. According to the model, the compensation results in substantial stabilization of the echo response even if the intensity/time trade of release from masking is not precisely equal to the rate of echo attenuation with distance.

Theory and optical design of x-ray echo spectrometers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shvyd'ko, Yuri

X-ray echo spectroscopy, a space-domain counterpart of neutron spin echo, is a recently proposed inelastic x-ray scattering (IXS) technique. X-ray echo spectroscopy relies on imaging IXS spectra and does not require x-ray monochromatization. Due to this, the echo-type IXS spectrometers are broadband, and thus have a potential to simultaneously provide dramatically increased signal strength, reduced measurement times, and higher resolution compared to the traditional narrow-band scanning-type IXS spectrometers. The theory of x-ray echo spectrometers presented earlier [Yu. Shvyd'ko, Phys. Rev. Lett. 116, 080801 (2016)] is developed here further with a focus on questions of practical importance, which could facilitate opticalmore » design and assessment of the feasibility and performance of the echo spectrometers. Among others, the following questions are addressed: spectral resolution, refocusing condition, echo spectrometer tolerances, refocusing condition adjustment, effective beam size on the sample, spectral window of imaging and scanning range, impact of the secondary source size on the spectral resolution, angular dispersive optics, focusing and collimating optics, and detector's spatial resolution. In conclusion, examples of optical designs and characteristics of echo spectrometers with 1-meV and 0.1-meV resolutions are presented.« less

Theory and optical design of x-ray echo spectrometers

DOE PAGES

Shvyd'ko, Yuri

2017-08-02

X-ray echo spectroscopy, a space-domain counterpart of neutron spin echo, is a recently proposed inelastic x-ray scattering (IXS) technique. X-ray echo spectroscopy relies on imaging IXS spectra and does not require x-ray monochromatization. Due to this, the echo-type IXS spectrometers are broadband, and thus have a potential to simultaneously provide dramatically increased signal strength, reduced measurement times, and higher resolution compared to the traditional narrow-band scanning-type IXS spectrometers. The theory of x-ray echo spectrometers presented earlier [Yu. Shvyd'ko, Phys. Rev. Lett. 116, 080801 (2016)] is developed here further with a focus on questions of practical importance, which could facilitate opticalmore » design and assessment of the feasibility and performance of the echo spectrometers. Among others, the following questions are addressed: spectral resolution, refocusing condition, echo spectrometer tolerances, refocusing condition adjustment, effective beam size on the sample, spectral window of imaging and scanning range, impact of the secondary source size on the spectral resolution, angular dispersive optics, focusing and collimating optics, and detector's spatial resolution. In conclusion, examples of optical designs and characteristics of echo spectrometers with 1-meV and 0.1-meV resolutions are presented.« less

Note: A new design for a low-temperature high-intensity helium beam source

NASA Astrophysics Data System (ADS)

Lechner, B. A. J.; Hedgeland, H.; Allison, W.; Ellis, J.; Jardine, A. P.

2013-02-01

A high-intensity supersonic beam source is a key component of any atom scattering instrument, affecting the sensitivity and energy resolution of the experiment. We present a new design for a source which can operate at temperatures as low as 11.8 K, corresponding to a beam energy of 2.5 meV. The new source improves the resolution of the Cambridge helium spin-echo spectrometer by a factor of 5.5, thus extending the accessible timescales into the nanosecond range. We describe the design of the new source and discuss experiments characterizing its performance. Spin-echo measurements of benzene/Cu(100) illustrate its merit in the study of a typical slow-moving molecular adsorbate species.

Renal ablation using magnetic resonance-guided high intensity focused ultrasound: Magnetic resonance imaging and histopathology assessment.

PubMed

Saeed, Maythem; Krug, Roland; Do, Loi; Hetts, Steven W; Wilson, Mark W

2016-03-28

To use magnetic resonance-guided high intensity focused ultrasound (MRg-HIFU), magnetic resonance imaging (MRI) and histopathology for noninvasively ablating, quantifying and characterizing ablated renal tissue. Six anesthetized/mechanically-ventilated pigs underwent single/double renal sonication (n = 24) using a 3T-MRg-HIFU (1.1 MHz frequency and 3000J-4400J energies). T2-weighted fast spin echo (T2-W), perfusion saturation recovery gradient echo and contrast enhanced (CE) T1-weighted (T1-W) sequences were used for treatment planning, temperature monitoring, lesion visualization, characterization and quantification, respectively. Histopathology was conducted in excised kidneys to quantify and characterize cellular and vascular changes. Paired Student's t-test was used and a P-value < 0.05 was considered statistically significant. Ablated renal parenchyma could not be differentiated from normal parenchyma on T2-W or non-CE T1-W sequences. Ablated renal lesions were visible as hypoenhanced regions on perfusion and CE T1-W MRI sequences, suggesting perfusion deficits and necrosis. Volumes of ablated parenchyma on CE T1-W images in vivo (0.12-0.36 cm(3) for single sonication 3000J, 0.50-0.84 cm(3), for double 3000J, 0.75-0.78 cm(3) for single 4400J and 0.12-2.65 cm(3) for double 4400J) and at postmortem (0.23-0.52 cm(3), 0.25-0.82 cm(3), 0.45-0.68 cm(3) and 0.29-1.80 cm(3), respectively) were comparable. The ablated volumes on 3000J and 4400J double sonication were significantly larger than single (P < 0.01), thus, the volume and depth of ablated tissue depends on the applied energy and number of sonication. Macroscopic and microscopic examinations confirmed the locations and presence of coagulation necrosis, vascular damage and interstitial hemorrhage, respectively. Contrast enhanced MRI provides assessment of MRg-HIFU renal ablation. Histopathology demonstrated coagulation necrosis, vascular damage and confirmed the volume of damage seen on MRI.

Experimental limits on the fidelity of adiabatic geometric phase gates in a single solid-state spin qubit

DOE PAGES

Zhang, Kai; Nusran, N. M.; Slezak, B. R.; ...

2016-05-17

While it is often thought that the geometric phase is less sensitive to fluctuations in the control fields, a very general feature of adiabatic Hamiltonians is the unavoidable dynamic phase that accompanies the geometric phase. The effect of control field noise during adiabatic geometric quantum gate operations has not been probed experimentally, especially in the canonical spin qubit system that is of interest for quantum information. We present measurement of the Berry phase and carry out adiabatic geometric phase gate in a single solid-state spin qubit associated with the nitrogen-vacancy center in diamond. We manipulate the spin qubit geometrically bymore » careful application of microwave radiation that creates an effective rotating magnetic field, and observe the resulting Berry phase signal via spin echo interferometry. Our results show that control field noise at frequencies higher than the spin echo clock frequency causes decay of the quantum phase, and degrades the fidelity of the geometric phase gate to the classical threshold after a few (~10) operations. This occurs in spite of the geometric nature of the state preparation, due to unavoidable dynamic contributions. In conclusion, we have carried out systematic analysis and numerical simulations to study the effects of the control field noise and imperfect driving waveforms on the quantum phase gate.« less

Experimental limits on the fidelity of adiabatic geometric phase gates in a single solid-state spin qubit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Kai; Nusran, N. M.; Slezak, B. R.

While it is often thought that the geometric phase is less sensitive to fluctuations in the control fields, a very general feature of adiabatic Hamiltonians is the unavoidable dynamic phase that accompanies the geometric phase. The effect of control field noise during adiabatic geometric quantum gate operations has not been probed experimentally, especially in the canonical spin qubit system that is of interest for quantum information. We present measurement of the Berry phase and carry out adiabatic geometric phase gate in a single solid-state spin qubit associated with the nitrogen-vacancy center in diamond. We manipulate the spin qubit geometrically bymore » careful application of microwave radiation that creates an effective rotating magnetic field, and observe the resulting Berry phase signal via spin echo interferometry. Our results show that control field noise at frequencies higher than the spin echo clock frequency causes decay of the quantum phase, and degrades the fidelity of the geometric phase gate to the classical threshold after a few (~10) operations. This occurs in spite of the geometric nature of the state preparation, due to unavoidable dynamic contributions. In conclusion, we have carried out systematic analysis and numerical simulations to study the effects of the control field noise and imperfect driving waveforms on the quantum phase gate.« less

Electron spin relaxation of synthetic melanin and melanin-containing human tissues as studied by electron spin echo and electron spin resonance.

PubMed

Okazaki, M; Kuwata, K; Miki, Y; Shiga, S; Shiga, T

1985-10-01

Electron spin lattice relaxation times (T1) and the phase memory times (Tm) were obtained for the synthetic melanin system from 3-hydroxytyrosine (dopa) by means of electron spin echo spectroscopy at 77 degrees K. Saturation behavior of the ESR spectra of melanins in melanin-containing tissue and of the synthetic melanin was also determined at the same temperature. The spin lattice relaxation time and the spectral diffusion time of the synthetic melanin are very long (4.3 ms and 101 microseconds, respectively, in the solid state), and the ESR signal saturates readily at low microwave powers. On the other hand, ESR spectra of natural melanins from the tissues chosen for this study, as well as those of synthetic melanins which contain Fe3+ of g = 4.3 and Mn2+ of g = 2, are relatively difficult to saturate compared with samples without such metal ions. These results show clearly that a large part of those two metal ions in sites responsible for the ESR spectral components with these particular g values are coordinated to melanin in melanin-containing tissue, and modify the magnetic relaxation behavior of the melanin. Accumulations of these metal ions in melanins are different from system to system, and they increase in the order: hair (black), retina and choroid (brown), malignant melanoma of eye and skin, and lentigo and nevus of skin.

A Ku band pulsed electron paramagnetic resonance spectrometer using an arbitrary waveform generator for quantum control experiments at millikelvin temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yap, Yung Szen, E-mail: yungszen@utm.my; Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor; Tabuchi, Yutaka

2015-06-15

We present a 17 GHz (Ku band) arbitrary waveform pulsed electron paramagnetic resonance spectrometer for experiments down to millikelvin temperatures. The spectrometer is located at room temperature, while the resonator is placed either in a room temperature magnet or inside a cryogen-free dilution refrigerator; the operating temperature range of the dilution unit is from ca. 10 mK to 8 K. This combination provides the opportunity to perform quantum control experiments on electron spins in the pure-state regime. At 0.6 T, spin echo experiments were carried out using γ-irradiated quartz glass from 1 K to 12.3 mK. With decreasing temperatures, wemore » observed an increase in spin echo signal intensities due to increasing spin polarizations, in accordance with theoretical predictions. Through experimental data fitting, thermal spin polarization at 100 mK was estimated to be at least 99%, which was almost pure state. Next, to demonstrate the ability to create arbitrary waveform pulses, we generate a shaped pulse by superposing three Gaussian pulses of different frequencies. The resulting pulse was able to selectively and coherently excite three different spin packets simultaneously—a useful ability for analyzing multi-spin system and for controlling a multi-qubit quantum computer. By applying this pulse to the inhomogeneously broadened sample, we obtain three well-resolved excitations at 8 K, 1 K, and 14 mK.« less

gr-MRI: A software package for magnetic resonance imaging using software defined radios

NASA Astrophysics Data System (ADS)

Hasselwander, Christopher J.; Cao, Zhipeng; Grissom, William A.

2016-09-01

The goal of this work is to develop software that enables the rapid implementation of custom MRI spectrometers using commercially-available software defined radios (SDRs). The developed gr-MRI software package comprises a set of Python scripts, flowgraphs, and signal generation and recording blocks for GNU Radio, an open-source SDR software package that is widely used in communications research. gr-MRI implements basic event sequencing functionality, and tools for system calibrations, multi-radio synchronization, and MR signal processing and image reconstruction. It includes four pulse sequences: a single-pulse sequence to record free induction signals, a gradient-recalled echo imaging sequence, a spin echo imaging sequence, and an inversion recovery spin echo imaging sequence. The sequences were used to perform phantom imaging scans with a 0.5 Tesla tabletop MRI scanner and two commercially-available SDRs. One SDR was used for RF excitation and reception, and the other for gradient pulse generation. The total SDR hardware cost was approximately 2000. The frequency of radio desynchronization events and the frequency with which the software recovered from those events was also measured, and the SDR's ability to generate frequency-swept RF waveforms was validated and compared to the scanner's commercial spectrometer. The spin echo images geometrically matched those acquired using the commercial spectrometer, with no unexpected distortions. Desynchronization events were more likely to occur at the very beginning of an imaging scan, but were nearly eliminated if the user invoked the sequence for a short period before beginning data recording. The SDR produced a 500 kHz bandwidth frequency-swept pulse with high fidelity, while the commercial spectrometer produced a waveform with large frequency spike errors. In conclusion, the developed gr-MRI software can be used to develop high-fidelity, low-cost custom MRI spectrometers using commercially-available SDRs.

Evolution of multiple quantum coherences with scaled dipolar Hamiltonian

NASA Astrophysics Data System (ADS)

Sánchez, Claudia M.; Buljubasich, Lisandro; Pastawski, Horacio M.; Chattah, Ana K.

2017-08-01

In this article, we introduce a pulse sequence which allows the monitoring of multiple quantum coherences distribution of correlated spin states developed with scaled dipolar Hamiltonian. The pulse sequence is a modification of our previous Proportionally Refocused Loschmidt echo (PRL echo) with phase increment, in order to verify the accuracy of the weighted coherent quantum dynamics. The experiments were carried out with different scaling factors to analyze the evolution of the total magnetization, the time dependence of the multiple quantum coherence orders, and the development of correlated spins clusters. In all cases, a strong dependence between the evolution rate and the weighting factor is observed. Remarkably, all the curves appeared overlapped in a single trend when plotted against the self-time, a new time scale that includes the scaling factor into the evolution time. In other words, the spin system displayed always the same quantum evolution, slowed down as the scaling factor decreases, confirming the high performance of the new pulse sequence.

X-ray echo spectroscopy (Conference Presentation)

NASA Astrophysics Data System (ADS)

Shvyd'ko, Yuri V.

2016-09-01

X-ray echo spectroscopy, a counterpart of neutron spin-echo, was recently introduced [1] to overcome limitations in spectral resolution and weak signals of the traditional inelastic x-ray scattering (IXS) probes. An image of a point-like x-ray source is defocused by a dispersing system comprised of asymmetrically cut specially arranged Bragg diffracting crystals. The defocused image is refocused into a point (echo) in a time-reversal dispersing system. If the defocused beam is inelastically scattered from a sample, the echo signal acquires a spatial distribution, which is a map of the inelastic scattering spectrum. The spectral resolution of the echo spectroscopy does not rely on the monochromaticity of the x-rays, ensuring strong signals along with a very high spectral resolution. Particular schemes of x-ray echo spectrometers for 0.1-meV and 0.02-meV ultra-high-resolution IXS applications (resolving power > 10^8) with broadband 5-13 meV dispersing systems will be presented featuring more than 1000-fold signal enhancement. The technique is general, applicable in different photon frequency domains. [1.] Yu. Shvyd'ko, Phys. Rev. Lett. 116, accepted (2016), arXiv:1511.01526.

Removing the echoes from terahertz pulse reflection system and sample

NASA Astrophysics Data System (ADS)

Liu, Haishun; Zhang, Zhenwei; Zhang, Cunlin

2018-01-01

Due to the echoes both from terahertz (THz) pulse reflection system and sample, the THz primary pulse will be distorted. The system echoes include two types. One preceding the main peak probably is caused by ultrafast laser pulse and the other at the back of the primary pulse is caused by the Fabry-Perot (F-P) etalon effect of detector. We attempt to remove the corresponding echoes by using two kinds of deconvolution. A Si wafer of 400μm was selected as the tested sample. Firstly, the method of double Gaussian filter (DGF) decnvolution was used to remove the systematic echoes, and then another deconvolution technique was employed to eliminate the two obvious echoes of the sample. The ultimate results indicated: although the combination of two deconvolution techniques could not entirely remove the echoes of sample and system, the echoes were largely reduced.

Electrical control of a long-lived spin qubit in a Si/SiGe quantum dot

NASA Astrophysics Data System (ADS)

Kawakami, Erika

2015-03-01

Electron spins in Si/SiGe quantum dots are one of the most promising candidates for a quantum bit for their potential to scale up and their long dephasing time. We realized coherent control of single electron spin in a single quantum dot (QD) defined in a Si/SiGe 2D electron gas. Spin rotations are achieved by applying microwave excitation to one of the gates, which oscillates the electron wave function back and forth in the gradient field produced by cobalt micromagnets fabricated near the dot. The electron spin is read out in single-shot mode via spin-to-charge conversion and a QD charge sensor. In earlier work, both the fidelity of single-spin rotations and the spin echo decay time were limited by a small splitting of the lowest two valleys. By changing the direction and magnitude of the external magnetic field as well as the gate voltages that define the dot potential, we were able to increase the valley splitting and also the difference in Zeeman splittings associated with these two valleys. This has resulted in considerable improvements in the gate fidelity and spin echo decay times. Thanks to the long intrinsic dephasing time T2* = 900 ns and Rabi frequency of 1.4 MHz, we now obtain an average single qubit gate fidelity of an electron spin in a Si/SiGe quantum dot of 99 percent, measured via randomized benchmarking. The dephasing time is extended to 70 us for the Hahn echo and up to 400 us with CPMG80. From the dynamical decoupling data, we extract the noise spectral density in the range of 30 kHz-3 MHz. We will discuss the mechanism that induces this noise and is responsible for decoherence. In parallel, we also realized electron spin resonance and coherent single-spin control by second harmonic generation, which means we can drive an electron spin at half the Larmor frequency. Finally, we observe not only single-spin transitions but also transitions whereby both the spin and the valley state are flipped. Altogether, these measurements have significantly increased our understanding and raised the prospects of spin qubits in Si/SiGe quantum dots. This work has been done in collaboration with T.M. J. Jullien, P. Scarlino, V.V. Dobrovitski, D.R. Ward, D. E. Savage, M. G. Lagally, Mark Friesen, S. N. Coppersmith, M. A. Eriksson, and L. M. K. Vandersypen. This work was supported in part by the Army Research Office (ARO) (W911NF-12-0607), the Foundation for Fundamental Research on Matter (FOM) and the European Research Council (ERC). Development and maintenance of the growth facilities used for fabricating samples was supported by the Department of Energy (DOE) (DE-FG02-03ER46028). E.K. was supported by a fellowship from the Nakajima Foundation. This research utilized NSF-supported shared facilities at the University of Wisconsin-Madison.

3D hybrid profile order technique in a single breath-hold 3D T2-weighted fast spin-echo sequence: Usefulness in diagnosis of small liver lesions.

PubMed

Hirata, Kenichiro; Nakaura, Takeshi; Okuaki, Tomoyuki; Tsuda, Noriko; Taguchi, Narumi; Oda, Seitaro; Utsunomiya, Daisuke; Yamashita, Yasuyuki

2018-01-01

We compared the efficacy of three-dimensional (3D) isotropic T2-weighted fast spin-echo imaging using a 3D hybrid profile order technique with a single-breath-hold (3D-Hybrid BH) with a two-dimensional (2D) T2-weighted fast spin-echo conventional respiratory-gated (2D-Conventional RG) technique for visualising small liver lesions. This study was approved by our institutional review board. The requirement to obtain written informed consent was waived. Fifty patients with small (≤15mm) hepatocellular carcinomas (HCC) (n=26), or benign cysts (n=24), had undergone hepatic MRI including both 2D-Conventional RG and 3D-Hybrid BH. We calculated the signal-to-noise ratio (SNR) and tumour-to-liver contrast (TLC). The diagnostic performance of the two protocols was analysed. The image acquisition time was 89% shorter with the 3D-Hybrid BH than with 2D-Conventional RG. There was no significant difference in the SNR between the two protocols. The area under the curve (AUC) of the TLC was significantly higher on 3D-Hybrid BH than on 2D-Conventional RG. The 3D-Hybrid BH sequence significantly improved diagnostic performance for small liver lesions with a shorter image acquisition time without sacrificing accuracy. Copyright © 2017. Published by Elsevier B.V.

MRI image plane nonuniformity in evaluation of ferrous sulphate dosimeter gel (FeGel) by means of T1-relaxation time.

PubMed

Magnusson, P; Bäck, S A; Olsson, L E

1999-11-01

MR image nonuniformity can vary significantly with the spin-echo pulse sequence repetition time. When MR images with different nonuniformity shapes are used in a T1-calculation the resulting T1-image becomes nonuniform. As shown in this work the uniformity TR-dependence of the spin-echo pulse sequence is a critical property for T1 measurements in general and for ferrous sulfate dosimeter gel (FeGel) applications in particular. The purpose was to study the characteristics of the MR image plane nonuniformity in FeGel evaluation. This included studies of the possibility of decreasing nonuniformities by selecting uniformity optimized repetition times, studies of the transmitted and received RF-fields and studies of the effectiveness of the correction methods background subtraction and quotient correction. A pronounced MR image nonuniformity variation with repetition and T1 relaxation time was observed, and was found to originate from nonuniform RF-transmission in combination with the inherent differences in T1 relaxation for different repetition times. The T1 calculation itself, the uniformity optimized repetition times, nor none of the correction methods studied could sufficiently correct the nonuniformities observed in the T1 images. The nonuniformities were found to vary considerably less with inversion time for the inversion-recovery pulse sequence, than with repetition time for the spin-echo pulse sequence, resulting in considerably lower T1 image nonuniformity levels.

Frequency bandwidth extension by use of multiple Zeeman field offsets for electron spin-echo EPR oxygen imaging of large objects

PubMed Central

Seifi, Payam; Epel, Boris; Sundramoorthy, Subramanian V.; Mailer, Colin; Halpern, Howard J.

2011-01-01

Purpose: Electron spin-echo (ESE) oxygen imaging is a new and evolving electron paramagnetic resonance (EPR) imaging (EPRI) modality that is useful for physiological in vivo applications, such as EPR oxygen imaging (EPROI), with potential application to imaging of multicentimeter objects as large as human tumors. A present limitation on the size of the object to be imaged at a given resolution is the frequency bandwidth of the system, since the location is encoded as a frequency offset in ESE imaging. The authors’ aim in this study was to demonstrate the object size advantage of the multioffset bandwidth extension technique.Methods: The multiple-stepped Zeeman field offset (or simply multi-B) technique was used for imaging of an 8.5-cm-long phantom containing a narrow single line triaryl methyl compound (trityl) solution at the 250 MHz imaging frequency. The image is compared to a standard single-field ESE image of the same phantom.Results: For the phantom used in this study, transverse relaxation (T2e) electron spin-echo (ESE) images from multi-B acquisition are more uniform, contain less prominent artifacts, and have a better signal to noise ratio (SNR) compared to single-field T2e images.Conclusions: The multi-B method is suitable for imaging of samples whose physical size restricts the applicability of the conventional single-field ESE imaging technique. PMID:21815379

Inter-Vendor Reproducibility of Pseudo-Continuous Arterial Spin Labeling at 3 Tesla

PubMed Central

Mutsaerts, Henri J. M. M.; Steketee, Rebecca M. E.; Heijtel, Dennis F. R.; Kuijer, Joost P. A.; van Osch, Matthias J. P.; Majoie, Charles B. L. M.; Smits, Marion; Nederveen, Aart J.

2014-01-01

Purpose Prior to the implementation of arterial spin labeling (ASL) in clinical multi-center studies, it is important to establish its status quo inter-vendor reproducibility. This study evaluates and compares the intra- and inter-vendor reproducibility of pseudo-continuous ASL (pCASL) as clinically implemented by GE and Philips. Material and Methods 22 healthy volunteers were scanned twice on both a 3T GE and a 3T Philips scanner. The main difference in implementation between the vendors was the readout module: spiral 3D fast spin echo vs. 2D gradient-echo echo-planar imaging respectively. Mean and variation of cerebral blood flow (CBF) were compared for the total gray matter (GM) and white matter (WM), and on a voxel-level. Results Whereas the mean GM CBF of both vendors was almost equal (p = 1.0), the mean WM CBF was significantly different (p<0.01). The inter-vendor GM variation did not differ from the intra-vendor GM variation (p = 0.3 and p = 0.5 for GE and Philips respectively). Spatial inter-vendor CBF and variation differences were observed in several GM regions and in the WM. Conclusion These results show that total GM CBF-values can be exchanged between vendors. For the inter-vendor comparison of GM regions or WM, these results encourage further standardization of ASL implementation among vendors. PMID:25090654

Inter-vendor reproducibility of pseudo-continuous arterial spin labeling at 3 Tesla.

PubMed

Mutsaerts, Henri J M M; Steketee, Rebecca M E; Heijtel, Dennis F R; Kuijer, Joost P A; van Osch, Matthias J P; Majoie, Charles B L M; Smits, Marion; Nederveen, Aart J

2014-01-01

Prior to the implementation of arterial spin labeling (ASL) in clinical multi-center studies, it is important to establish its status quo inter-vendor reproducibility. This study evaluates and compares the intra- and inter-vendor reproducibility of pseudo-continuous ASL (pCASL) as clinically implemented by GE and Philips. 22 healthy volunteers were scanned twice on both a 3T GE and a 3T Philips scanner. The main difference in implementation between the vendors was the readout module: spiral 3D fast spin echo vs. 2D gradient-echo echo-planar imaging respectively. Mean and variation of cerebral blood flow (CBF) were compared for the total gray matter (GM) and white matter (WM), and on a voxel-level. Whereas the mean GM CBF of both vendors was almost equal (p = 1.0), the mean WM CBF was significantly different (p<0.01). The inter-vendor GM variation did not differ from the intra-vendor GM variation (p = 0.3 and p = 0.5 for GE and Philips respectively). Spatial inter-vendor CBF and variation differences were observed in several GM regions and in the WM. These results show that total GM CBF-values can be exchanged between vendors. For the inter-vendor comparison of GM regions or WM, these results encourage further standardization of ASL implementation among vendors.

A rapid method for direct detection of metabolic conversion and magnetization exchange with application to hyperpolarized substrates

NASA Astrophysics Data System (ADS)

Larson, Peder E. Z.; Kerr, Adam B.; Leon Swisher, Christine; Pauly, John M.; Vigneron, Daniel B.

2012-12-01

In this work, we present a new MR spectroscopy approach for directly observing nuclear spins that undergo exchange, metabolic conversion, or, generally, any frequency shift during a mixing time. Unlike conventional approaches to observe these processes, such as exchange spectroscopy (EXSY), this rapid approach requires only a single encoding step and thus is readily applicable to hyperpolarized MR in which the magnetization is not replenished after T1 decay and RF excitations. This method is based on stimulated-echoes and uses phase-sensitive detection in conjunction with precisely chosen echo times in order to separate spins generated during the mixing time from those present prior to mixing. We are calling the method Metabolic Activity Decomposition Stimulated-echo Acquisition Mode or MAD-STEAM. We have validated this approach as well as applied it in vivo to normal mice and a transgenic prostate cancer mouse model for observing pyruvate-lactate conversion, which has been shown to be elevated in numerous tumor types. In this application, it provides an improved measure of cellular metabolism by separating [1-13C]-lactate produced in tissue by metabolic conversion from [1-13C]-lactate that has flowed into the tissue or is in the blood. Generally, MAD-STEAM can be applied to any system in which spins undergo a frequency shift.

Pseudo Steady-State Free Precession for MR-Fingerprinting.

PubMed

Assländer, Jakob; Glaser, Steffen J; Hennig, Jürgen

2017-03-01

This article discusses the signal behavior in the case the flip angle in steady-state free precession sequences is continuously varied as suggested for MR-fingerprinting sequences. Flip angle variations prevent the establishment of a steady state and introduce instabilities regarding to magnetic field inhomogeneities and intravoxel dephasing. We show how a pseudo steady state can be achieved, which restores the spin echo nature of steady-state free precession. Based on geometrical considerations, relationships between the flip angle, repetition and echo time are derived that suffice to the establishment of a pseudo steady state. The theory is tested with Bloch simulations as well as phantom and in vivo experiments. A typical steady-state free precession passband can be restored with the proposed conditions. The stability of the pseudo steady state is demonstrated by comparing the evolution of the signal of a single isochromat to one resulting from a spin ensemble. As confirmed by experiments, magnetization in a pseudo steady state can be described with fewer degrees of freedom compared to the original fingerprinting and the pseudo steady state results in more reliable parameter maps. The proposed conditions restore the spin-echo-like signal behavior typical for steady-state free precession in fingerprinting sequences, making this approach more robust to B 0 variations. Magn Reson Med 77:1151-1161, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

The Effect of Concomitant Fields in Fast Spin Echo Acquisition on Asymmetric MRI Gradient Systems

PubMed Central

Tao, Shengzhen; Weavers, Paul T.; Trzasko, Joshua D.; Huston, John; Shu, Yunhong; Gray, Erin M.; Foo, Thomas K.F.; Bernstein, Matt A.

2017-01-01

Purpose To investigate the effect of the asymmetric gradient concomitant fields (CF) with zeroth and first-order spatial dependence on fast/turbo spin-echo acquisitions, and to demonstrate the effectiveness of their real-time compensation. Methods After briefly reviewing the CF produced by asymmetric gradients, the effects of the additional zeroth and first-order CFs on these systems are investigated using extended-phase graph simulations. Phantom and in vivo experiments are performed to corroborate the simulation. Experiments are performed before and after the real-time compensations using frequency tracking and gradient pre-emphasis to demonstrate their effectiveness in correcting the additional CFs. The interaction between the CFs and prescan-based correction to compensate for eddy currents is also investigated. Results It is demonstrated that, unlike the second-order CFs on conventional gradients, the additional zeroth/first-order CFs on asymmetric gradients cause substantial signal loss and dark banding in fast spin-echo acquisitions within a typical brain-scan field of view. They can confound the prescan correction for eddy currents and degrade image quality. Performing real-time compensation successfully eliminates the artifacts. Conclusions We demonstrate that the zeroth/first-order CFs specific to asymmetric gradients can cause substantial artifacts, including signal loss and dark bands for brain imaging. These effects can be corrected using real-time compensation. PMID:28643408

A rapid method for direct detection of metabolic conversion and magnetization exchange with application to hyperpolarized substrates.

PubMed

Larson, Peder E Z; Kerr, Adam B; Swisher, Christine Leon; Pauly, John M; Vigneron, Daniel B

2012-12-01

In this work, we present a new MR spectroscopy approach for directly observing nuclear spins that undergo exchange, metabolic conversion, or, generally, any frequency shift during a mixing time. Unlike conventional approaches to observe these processes, such as exchange spectroscopy (EXSY), this rapid approach requires only a single encoding step and thus is readily applicable to hyperpolarized MR in which the magnetization is not replenished after T(1) decay and RF excitations. This method is based on stimulated-echoes and uses phase-sensitive detection in conjunction with precisely chosen echo times in order to separate spins generated during the mixing time from those present prior to mixing. We are calling the method Metabolic Activity Decomposition Stimulated-echo Acquisition Mode or MAD-STEAM. We have validated this approach as well as applied it in vivo to normal mice and a transgenic prostate cancer mouse model for observing pyruvate-lactate conversion, which has been shown to be elevated in numerous tumor types. In this application, it provides an improved measure of cellular metabolism by separating [1-(13)C]-lactate produced in tissue by metabolic conversion from [1-(13)C]-lactate that has flowed into the tissue or is in the blood. Generally, MAD-STEAM can be applied to any system in which spins undergo a frequency shift. Copyright © 2012 Elsevier Inc. All rights reserved.

Parallel MR imaging: a user's guide.

PubMed

Glockner, James F; Hu, Houchun H; Stanley, David W; Angelos, Lisa; King, Kevin

2005-01-01

Parallel imaging is a recently developed family of techniques that take advantage of the spatial information inherent in phased-array radiofrequency coils to reduce acquisition times in magnetic resonance imaging. In parallel imaging, the number of sampled k-space lines is reduced, often by a factor of two or greater, thereby significantly shortening the acquisition time. Parallel imaging techniques have only recently become commercially available, and the wide range of clinical applications is just beginning to be explored. The potential clinical applications primarily involve reduction in acquisition time, improved spatial resolution, or a combination of the two. Improvements in image quality can be achieved by reducing the echo train lengths of fast spin-echo and single-shot fast spin-echo sequences. Parallel imaging is particularly attractive for cardiac and vascular applications and will likely prove valuable as 3-T body and cardiovascular imaging becomes part of standard clinical practice. Limitations of parallel imaging include reduced signal-to-noise ratio and reconstruction artifacts. It is important to consider these limitations when deciding when to use these techniques. (c) RSNA, 2005.

Non-destructive analysis of sensory traits of dry-cured loins by MRI-computer vision techniques and data mining.

PubMed

Caballero, Daniel; Antequera, Teresa; Caro, Andrés; Ávila, María Del Mar; G Rodríguez, Pablo; Perez-Palacios, Trinidad

2017-07-01

Magnetic resonance imaging (MRI) combined with computer vision techniques have been proposed as an alternative or complementary technique to determine the quality parameters of food in a non-destructive way. The aim of this work was to analyze the sensory attributes of dry-cured loins using this technique. For that, different MRI acquisition sequences (spin echo, gradient echo and turbo 3D), algorithms for MRI analysis (GLCM, NGLDM, GLRLM and GLCM-NGLDM-GLRLM) and predictive data mining techniques (multiple linear regression and isotonic regression) were tested. The correlation coefficient (R) and mean absolute error (MAE) were used to validate the prediction results. The combination of spin echo, GLCM and isotonic regression produced the most accurate results. In addition, the MRI data from dry-cured loins seems to be more suitable than the data from fresh loins. The application of predictive data mining techniques on computational texture features from the MRI data of loins enables the determination of the sensory traits of dry-cured loins in a non-destructive way. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry.

Simultaneous pH-sensitive and oxygen-sensitive MRI of human gliomas at 3 T using multi-echo amine proton chemical exchange saturation transfer spin-and-gradient echo echo-planar imaging (CEST-SAGE-EPI).

PubMed

Harris, Robert J; Yao, Jingwen; Chakhoyan, Ararat; Raymond, Catalina; Leu, Kevin; Liau, Linda M; Nghiemphu, Phioanh L; Lai, Albert; Salamon, Noriko; Pope, Whitney B; Cloughesy, Timothy F; Ellingson, Benjamin M

2018-04-06

To introduce a new pH-sensitive and oxygen-sensitive MRI technique using amine proton CEST echo spin-and-gradient echo (SAGE) EPI (CEST-SAGE-EPI). pH-weighting was obtained using CEST estimations of magnetization transfer ratio asymmetry (MTR asym ) at 3 ppm, and oxygen-weighting was obtained using R2' measurements. Glutamine concentration, pH, and relaxation rates were varied in phantoms to validate simulations and estimate relaxation rates. The values of MTR asym and R2' in normal-appearing white matter, T 2 hyperintensity, contrast enhancement, and macroscopic necrosis were measured in 47 gliomas. Simulation and phantom results confirmed an increase in MTR asym with decreasing pH. The CEST-SAGE-EPI estimates of R 2 , R2*, and R2' varied linearly with gadolinium diethylenetriamine penta-acetic acid concentration (R 2  = 6.2 mM -1 ·sec -1 and R2* = 6.9 mM -1 ·sec -1 ). The CEST-SAGE-EPI and Carr-Purcell-Meiboom-Gill estimates of R 2 (R 2  = 0.9943) and multi-echo gradient-echo estimates of R2* (R 2  = 0.9727) were highly correlated. T 2 lesions had lower R2' and higher MTR asym compared with normal-appearing white matter, suggesting lower hypoxia and high acidity, whereas contrast-enhancement tumor regions had elevated R2' and MTR asym , indicating high hypoxia and acidity. The CEST-SAGE-EPI technique provides simultaneous pH-sensitive and oxygen-sensitive image contrasts for evaluation of the brain tumor microenvironment. Advantages include fast whole-brain acquisition, in-line B 0 correction, and simultaneous estimation of CEST effects, R 2 , R2*, and R2' at 3 T. © 2018 International Society for Magnetic Resonance in Medicine.

Optimization image of magnetic resonance imaging (MRI) T2 fast spin echo (FSE) with variation echo train length (ETL) on the rupture tendon achilles case

NASA Astrophysics Data System (ADS)

Muzamil, Akhmad; Haries Firmansyah, Achmad

2017-05-01

The research was done the optimization image of Magnetic Resonance Imaging (MRI) T2 Fast Spin Echo (FSE) with variation Echo Train Length (ETL) on the Rupture Tendon Achilles case. This study aims to find the variations Echo Train Length (ETL) from the results of ankle’s MRI image and find out how the value of Echo Train Length (ETL) works on the MRI ankle to produce optimal image. In this research, the used ETL variations were 12 and 20 with the interval 2 on weighting T2 FSE sagittal. The study obtained the influence of Echo Train Length (ETL) on the quality of ankle MRI image sagittal using T2 FSE weighting and analyzed in 25 images of five patients. The data analysis has done quantitatively with the Region of Interest (ROI) directly on computer MRI image planes which conducted statistical tests Signal to Noise Ratio (SNR) and Contras to Noise Ratio (CNR). The Signal to Noise Ratio (SNR) was the highest finding on fat tissue, while the Contras to Noise Ratio (CNR) on the Tendon-Fat tissue with ETL 12 found in two patients. The statistics test showed the significant SNR value of the 0.007 (p<0.05) of Tendon tissue, 0.364 (p>0.05) of the Fat, 0.912 (p>0.05) of the Fibula, and 0.436 (p>0.05) of the Heel Bone. For the contrast to noise ratio (CNR) of the Tendon-FAT tissue was about 0.041 (p>0.05). The results of the study showed that ETL variation with T2 FSE sagittal weighting had difference at Tendon tissue and Tendon-Fat tissue for MRI imaging quality. SNR and CNR were an important aspect on imaging optimization process to give the diagnose information.

Infrared, Raman and Magnetic Resonance Spectroscopic Study of SiO2:C Nanopowders.

PubMed

Savchenko, Dariya; Vorliček, Vladimir; Kalabukhova, Ekaterina; Sitnikov, Aleksandr; Vasin, Andrii; Kysil, Dmytro; Sevostianov, Stanislav; Tertykh, Valentyn; Nazarov, Alexei

2017-12-01

Optical and magnetic properties of SiO 2 :C nanopowders obtained by chemical and thermal modification of fumed silica were studied by Fourier transform infrared spectroscopy, Raman, continuous wave (CW) electron paramagnetic resonance (EPR), echo-detected EPR and pulsed electron nuclear double resonance (ENDOR) spectroscopy. Two overlapping signals of Lorentzian lineshape were detected in CW EPR spectra of the initial SiO 2 :C. The EPR signal at g = 2.0055(3) is due to the silicon dangling bonds, which vanishes after thermal annealing, and the second EPR signal at g = 2.0033(3) was attributed to the carbon-related defect (CRD). The annealing of the SiO 2 :C samples gives rise to the increase of the CRD spin density and shift to the higher g-values due to the appearance of the oxygen in the vicinity of the CRD. Based on the temperature-dependent behavior of the CRD EPR signal intensity, linewidth and resonance field position we have attributed it to the spin system with non-localized electrons hopping between neighboring carbon dangling bonds, which undergo a strong exchange interaction with a localized spin system of carbon nanodots. The observed motional narrowing of the CRD EPR signal in the temperature interval from 4 to 20 K indicates that electrons are mobile at 4 K which can be explained by a quantum character of the conductivity in the vicinity of the carbon layer. The electrons trapped in quantum wells move from one carbon nanodot to another by hopping process through the energy barrier. The fact that echo-detected EPR signal at g = 2.0035(3) was observed in SiO 2 :C sample annealed at T ann  ≥ 700 °C serves as evidence that non-localized electrons coexist with localized electrons that have the superhyperfine interaction with surrounding 13 C and 29 Si nuclei located at the SiO 2 :C interface. The presence of the superhyperfine interaction of CRD with 1 H nuclei indicates the existence of hydrogenated regions in SiO 2 :C sample.

Optical absorption, electron spin resonance, and electron spin echo studies of the photoionization of tetramethylbenzidine in cationic and anionic synthetic vesicles: comparison with analogous micellar systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, A.S.W.; Kevan, L.

1983-09-07

The photoionization of N,N,N',N'-tetramethylbenzidine (TMB) in dihexadecylphosphate anionic vesicles and in dioctadecyldimethylammonium chloride cationic vesicles has been studied by optical absorption and electron spin resonance in liquid and frozen solutions. The TMB cation has been observed to be stabilized in both types of vesicles. The photoionization efficiency is about twofold greater in the cationic vesicles compared to the anionic vesicles. Shifts in the optical absorption maximum between micellar and vesicle solutions indicate that TMB is in a less polar environment in the vesicle systems. Electron spin echo modulation spectrometry has been used to detect TMB cation-water interactions that are foundmore » to be weaker than in previously studied micellar solutions. This is consistent with the optical absorption results and with an asymmetric solubilization site for TMB and TMB/sup +/ within the vesicular structure. A new absorption in the photoionized vesicles is assigned to a nonparamagnetic diamine-diimine charge-transfer complex between two TMB cations in the same vesicle. This complex is not formed in micellar systems. 5 figures.« less

High-resolution diffusion and relaxation-edited magic angle spinning 1H NMR spectroscopy of intact liver tissue.

PubMed

Rooney, O M; Troke, J; Nicholson, J K; Griffin, J L

2003-11-01

High-resolution magic angle spinning (HRMAS) (1)H NMR spectroscopy is ideal for monitoring the metabolic environment within tissues, particularly when spectra are weighted by physical properties such as T(1) and T(2) relaxation times and apparent diffusion coefficients (ADCs). In this study, spectral-editing using T(1) and T(2) relaxation times and ADCs at variable diffusion times was used in conjunction with HRMAS (1)H NMR spectroscopy at 14.1 T in liver tissue. To enhance the sensitivity of ADC measurements to low molecular weight metabolites a T(2) spin echo was included in a standard stimulated gradient spin-echo sequence. Fatty liver induced in rats by chronic orotic acid feeding was investigated using this modified sequence. An increase in the combined ADC for the co-resonant peaks glucose, betaine, and TMAO during fatty liver disease was detected (ADCs = 0.60 +/- 0.11 and 0.35 +/- 0.1 * 10(-9) m(2)s(-1) (n = 3) for rats fed with and without orotic acid), indicative of a reduction in glucose and betaine and an increase in TMAO. Copyright 2003 Wiley-Liss, Inc.

Towards homonuclear J solid-state NMR correlation experiments for half-integer quadrupolar nuclei: experimental and simulated 11B MAS spin-echo dephasing and calculated 2J(BB) coupling constants for lithium diborate.

PubMed

Barrow, Nathan S; Yates, Jonathan R; Feller, Steven A; Holland, Diane; Ashbrook, Sharon E; Hodgkinson, Paul; Brown, Steven P

2011-04-07

Magic-angle spinning (MAS) NMR spin-echo dephasing is systematically investigated for the spin I = 3/2 (11)B nucleus in lithium diborate, Li(2)O·2B(2)O(3). A clear dependence on the quadrupolar frequency (ω(Q)(PAS)/2π = 3C(Q)/[4I(2I- 1)]) is observed: the B3 (larger C(Q)) site dephases more slowly than the B4 site at all investigated MAS frequencies (5 to 20 kHz) at 14.1 T. Increasing the MAS frequency leads to markedly slower dephasing for the B3 site, while there is a much less evident effect for the B4 site. Considering samples at 5, 25, 80 (natural abundance) and 100% (11)B isotopic abundance, dephasing becomes faster for both sites as the (11)B isotopic abundance increases. The experimental behaviour is rationalised using density matrix simulations for two and three dipolar-coupled (11)B nuclei. The experimentally observed slower dephasing for the larger C(Q) (B3) site is reproduced in all simulations and is explained by the reintroduction of the dipolar coupling by the so-called "spontaneous quadrupolar-driven recoupling mechanism" having a different dependence on the MAS frequency for different quadrupolar frequencies. Specifically, isolated spin-pair simulations show that the spontaneous quadrupolar-driven recoupling mechanism is most efficient when the quadrupolar frequency is equal to twice the MAS frequency. While for isolated spin-pair simulations, increasing the MAS frequency leads to faster dephasing, agreement with experiment is observed for three-spin simulations which additionally include the homogeneous nature of the homonuclear dipolar coupling network. First-principles calculations, using the GIPAW approach, of the (2)J(11B-11B) couplings in lithium diborate, metaborate and triborate are presented: a clear trend is revealed whereby the (2)J(11B-11B) couplings increase with increasing B-O-B bond angle and B-B distance. However, the calculated (2)J(11B-11B) couplings are small (0.95, 1.20 and 2.65 Hz in lithium diborate), thus explaining why no zero crossing due to J modulation is observed experimentally, even for the sample at 25% (11)B where significant spin-echo intensity remains out to durations of ∼200 ms.

Basic physics of nuclear magnetic resonance.

PubMed

Patz, S

1986-01-01

This review of basic physics of nuclear magnetic resonance (NMR) discusses precession of magnetic nuclei in a static external field, introduces the concept of the rotating frame, and describes excitation of nuclei by an RF field. Treats subject of T1 and T2 relaxation from the dual viewpoints of (1) phenomena of relaxation times for both the longitudinal and transverse magnetization and (2) relaxation resulting from local field fluctuations. It describes practical ways in which T1 and T2 are measured (i.e., inversion recovery and spin-echo) and gives the value of the nuclear magnetization in thermodynamic equilibrium with a static external field. It discusses the reduction of NMR signal resulting from saturation. These concepts are related to clinical use with a set of four spin-echo images of a human head.

Instrument developments and recent scientific highlights at the J-NSE

NASA Astrophysics Data System (ADS)

Ivanova, Oxana; Pasini, Stefano; Monkenbusch, Michael; Holderer, Olaf

2017-06-01

The J-NSE neutron spin echo spectrometer faces now 10 years of successful user operation at the FRM II research reactor at the Heinz Maier-Leibnitz Zentrum (MLZ). We present scientific highlights and instrumental developments of the last decade, for example the development of grazing incidence neutron spin echo spectroscopy (GINSES) at the J-NSE and investigations of the dynamics at solid-liquid interfaces with this new option. Polymers in confinement have been a prominent topic, as well as the internal dynamics of proteins. The scientific questions also triggered instrumental developments such as a new polarizer and a new neutron guide concept. Finally, the future of the J-NSE will be addressed with a short presentation of the current upgrade program with superconducting main coils with reduced intrinsic field integral inhomogeneity.

NMR-based conformational analysis of perezone and analogues.

PubMed

Zepeda, L Gerardo; Burgueño-Tapia, Eleuterio; Pérez-Hernández, Nury; Cuevas, Gabriel; Joseph-Nathan, Pedro

2013-04-01

Complete assignment of the (1)H NMR chemical shift and coupling constant values of perezone (1), O-methylperezone (2) and 6-hydroxyperezone (3) was carried out by total-line-shape-fitting calculations using the PERCH iterative spectra analysis software (PERCH Solutions Ltd., Kuopio, Finland). The resulting simulated spectra for the three compounds showed strong similarity to their corresponding experimental spectra. Particularly, all vicinal, allylic and homoallylic coupling constant values for the side chain of the three compounds were very similar, thus revealing that the conformation of these three molecules in solution is indeed almost identical. This fact is in agreement with extended side chain conformations over folded chain conformations because 1, 2 and 3 undergo completely different intramolecular cycloaddition reactions. In addition, results of double pulsed field gradient spin echo NOESY 1D experiments performed on perezone (1) were unable to provide evidence for folded conformers. Copyright © 2013 John Wiley & Sons, Ltd.

Rapid NMR method for the quantification of organic compounds in thin stillage.

PubMed

Ratanapariyanuch, Kornsulee; Shen, Jianheng; Jia, Yunhua; Tyler, Robert T; Shim, Youn Young; Reaney, Martin J T

2011-10-12

Thin stillage contains organic and inorganic compounds, some of which may be valuable fermentation coproducts. This study describes a thorough analysis of the major solutes present in thin stillage as revealed by NMR and HPLC. The concentration of charged and neutral organic compounds in thin stillage was determined by excitation sculpting NMR methods (double pulse field gradient spin echo). Compounds identified by NMR included isopropanol, ethanol, lactic acid, 1,3-propanediol, acetic acid, succinic acid, glycerophosphorylcholine, betaine, glycerol, and 2-phenylethanol. The concentrations of lactic and acetic acid determined with NMR were comparable to those determined using HPLC. HPLC and NMR were complementary, as more compounds were identified using both methods. NMR analysis revealed that stillage contained the nitrogenous organic compounds betaine and glycerophosphorylcholine, which contributed as much as 24% of the nitrogen present in the stillage. These compounds were not observed by HPLC analysis.

Design and implementation of a hybrid sub-band acoustic echo canceller (AEC)

NASA Astrophysics Data System (ADS)

Bai, Mingsian R.; Yang, Cheng-Ken; Hur, Ker-Nan

2009-04-01

An efficient method is presented for implementing an acoustic echo canceller (AEC) that makes use of hybrid sub-band approach. The hybrid system is comprised of a fixed processor and an adaptive filter in each sub-band. The AEC aims at reducing the echo resulting from the acoustic feedback in loudspeaker-enclosure-microphone (LEM) systems such as teleconferencing and hands-free systems. In order to cancel the acoustical echo efficiently, various processing architectures including fixed filters, hybrid processors, and sub-band structure are investigated. A double-talk detector is incorporated into the proposed AEC to prevent the adaptive filter from diverging in double-talk situations. A de-correlation filter is also used alongside sub-band processing in order to enhance the performance and efficiency of AEC. All algorithms are implemented and verified on the platform of a fixed-point digital signal processor (DSP). The AECs are evaluated in terms of cancellation performance and computation complexity. In addition, listening tests are conducted to assess the subjective performance of the AECs. From the results, the proposed hybrid sub-band AEC was found to be the most effective among all methods in terms of echo reduction and timbral quality.

19F Magnetic resonance imaging of perfluorooctanoic acid encapsulated in liposome for biodistribution measurement.

PubMed

Kimura, Atsuomi; Narazaki, Michiko; Kanazawa, Yoko; Fujiwara, Hideaki

2004-07-01

The tissue distribution of perfluorooctanoic acid (PFOA), which is known to show unique biological responses, has been visualized in female mice by (19)F magnetic resonance imaging (MRI) incorporated with the recent advances in microimaging technique. The chemical shift selected fast spin-echo method was applied to acquire in vivo (19)F MR images of PFOA. The in vivo T(1) and T(2) relaxation times of PFOA were proven to be extremely short, which were 140 (+/- 20) ms and 6.3 (+/- 2.2) ms, respectively. To acquire the in vivo (19)F MR images of PFOA, it was necessary to optimize the parameters of signal selection and echo train length. The chemical shift selection was effectively performed by using the (19)F NMR signal of CF(3) group of PFOA without the signal overlapping because the chemical shift difference between the CF(3) and neighbor signals reaches to 14 kHz. The most optimal echo train length to obtain (19)F images efficiently was determined so that the maximum echo time (TE) value in the fast spin-echo sequence was comparable to the in vivo T(2) value. By optimizing these parameters, the in vivo (19)F MR image of PFOA was enabled to obtain efficiently in 12 minutes. As a result, the time course of the accumulation of PFOA into the mouse liver was clearly pursued in the (19)F MR images. Thus, it was concluded that the (19)F MRI becomes the effective method toward the future pharmacological and toxicological studies of perfluorocarboxilic acids.

Longitudinal analysis of MR spin-spin relaxation times (T2) in medial femorotibial cartilage of adolescent vs mature athletes: dependence of deep and superficial zone properties on sex and age.

PubMed

Wirth, W; Eckstein, F; Boeth, H; Diederichs, G; Hudelmaier, M; Duda, G N

2014-10-01

Cartilage spin-spin magnetic resonance imaging (MRI) relaxation time (T2) represents a promising imaging biomarker of "early" osteoarthritis (OA) known to be associated with cartilage composition (collagen integrity, orientation, and hydration). However, no longitudinal imaging studies have been conducted to examine cartilage maturation in healthy subjects thus far. Therefore, we explore T2 change in the deep and superficial cartilage layers at the end of adolescence. Twenty adolescent and 20 mature volleyball athletes were studied (each 10 men and 10 women). Multi-echo spin-echo (MESE) images were acquired at baseline and 2-year follow-up. After segmentation, cartilage T2 was calculated in the deep and superficial cartilage layers of the medial tibial (MT) and the central, weight-bearing part of the medial femoral condyle (cMF), using five echoes (TE 19.4-58.2 ms). 16 adolescent (6 men, 10 women, baseline age 15.8 ± 0.5 years) and 17 mature (nine men, eight women, age 46.5 ± 5.2 years) athletes had complete baseline and follow-up images of sufficient quality to compute T2. In adolescents, a longitudinal decrease in T2 was observed in the deep layers of MT (-2.0 ms; 95% confidence interval (CI): [-3.4, -0.6] ms; P < 0.01) and cMF (-1.3 ms; [-2.4, -0.3] ms; P < 0.05), without obvious differences between males and females. No significant change was observed in the superficial layers, or in the deep or superficial layers of the mature athletes. In this first pilot study on quantitative imaging of cartilage maturation in healthy, athletic subjects, we find evidence of cartilage compositional change in deep cartilage layers of the medial femorotibial compartment in adolescents, most likely related to organizational changes in the collagen matrix. Copyright © 2014 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

3D isotropic T2-weighted fast spin echo (VISTA) versus 2D T2-weighted fast spin echo in evaluation of the calcaneofibular ligament in the oblique coronal plane.

PubMed

Park, H J; Lee, S Y; Choi, Y J; Hong, H P; Park, S J; Park, J H; Kim, E

2017-02-01

To investigate whether the image quality of three-dimensional (3D) volume isotropic fast spin echo acquisition (VISTA) magnetic resonance imaging (MRI) of the calcaneofibular ligament (CFL) view is comparable to that of 2D fast spin echo T2-weighted images (2D T2 FSE) for the evaluation of the CFL, and whether 3D VISTA can replace 2D T2 FSE for the evaluation of CFL injuries. This retrospective study included 76 patients who underwent ankle MRI with CFL views of both 2D T2 FSE MRI and 3D VISTA. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of both techniques were measured. The anatomical identification score and diagnostic performances were evaluated by two readers independently. The diagnostic performances of 3D VISTA and 2D T2 FSE were analysed by sensitivity, specificity, and accuracy for diagnosing CFL injury with reference standards of surgically or clinically confirmed diagnoses. Surgical correlation was performed in 29% of the patients, and clinical examination was used in those who did not have surgery (71%). The SNRs and CNRs of 3D VISTA were significantly higher than those of 2D T2 FSE. The anatomical identification scores on 3D VISTA were inferior to those on 2D T2 FSE, and the differences were statistically significant (p<0.05). There were no significant differences in diagnostic performance between the two sequences when diagnoses were classified as normal or abnormal. Although the image quality of 3D VISTA MRI of the CFL view is not equal to that of 2D T2 FSE for the anatomical evaluation of CFL, 3D VISTA has a diagnostic performance comparable to that of 2D T2 FSE for the diagnosis of CFL injuries. Copyright © 2016 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Zeeman perturbed nuclear quadrupole spin echo envelope modulations for spin 3/2 nuclei in polycrystalline specimens

NASA Astrophysics Data System (ADS)

Ramachandran, R.; Narasimhan, P. T.

The results of theoretical and experimental studies of Zeeman-perturbed nuclear quadrupole spin echo envelope modulations (ZSEEM) for spin 3/2 nuclei in polycrystalline specimens are presented. The response of the Zeeman-perturbed spin ensemble to resonant two pulse excitations has been calculated using the density matrix formalism. The theoretical calculation assumes a parallel orientation of the external r.f. and static Zeeman fields and an arbitrary orientation of these fields to the principal axes system of the electric field gradient. A numerical powder averaging procedure has been adopted to simulate the response of the polycrystalline specimens. Using a coherent pulsed nuclear quadrupole resonance spectrometer the ZSEEM patterns of the 35Cl nuclei have been recorded in polycrystalline specimens of potassium chlorate, barium chlorate, mercuric chloride (two sites) and antimony trichloride (two sites) using the π/2-τ-π/2 sequence. The theoretical and experimental ZSEEM patterns have been compared. In the case of mercuric chloride, the experimental 35Cl ZSEEM patterns are found to be nearly identical for the two sites and correspond to a near-zero value of the asymmetry parameter, η, of the electric field gradient tensor. The difference in the η values for the two 35Cl sites (η ˜0·06 and η˜0·16) in antimony trichloride is clearly reflected in the experimental and theoretical ZSEEM patterns. The present study indicates the feasibility of evaluating η for spin 3/2 nuclei in polycrystalline specimens from ZSEEM investigations.

Spectroscopic sampling of the left side of long-TE spin echoes: a free lunch?

PubMed

Mulkern, Robert V; Balasubramanian, Mukund

2018-04-01

Use of spectroscopically-acquired spin echoes typically involves Fourier transformation of the right side of the echo while largely neglecting the left side. For sufficiently long echo times, the left side may have enough spectral resolution to offer some utility. Since the acquisition of this side is "free", we deemed it worthy of attention and investigated the spectral properties and information content of this data. Theoretical expressions for left- and right-side spectra were derived assuming Lorentzian frequency distributions. For left-side spectra, three regimes were identified based upon the relative magnitudes of reversible and irreversible transverse relaxation rates, R 2 ' and R 2 , respectively. Point-resolved spectroscopy (PRESS) data from muscle, fat deposit and bone marrow were acquired at 1.5 T to test aspects of the theoretical expressions. For muscle water or methylene marrow resonances, left-side signals were substantially or moderately larger than right-side signals but were similar in magnitude for muscle choline and creatine resonances. Left- versus right-side spectral-peak amplitude ratios depend sensitively on the relative values of R 2 and R 2 ' , which can be estimated given this ratio and a right-side linewidth measurement. Left-side spectra can be used to augment signal-to-noise and to estimate spectral R 2 and R 2 ' values under some circumstances.

The Alzheimer's Disease Neuroimaging Initiative (ADNI): MRI Methods

PubMed Central

Jack, Clifford R.; Bernstein, Matt A.; Fox, Nick C.; Thompson, Paul; Alexander, Gene; Harvey, Danielle; Borowski, Bret; Britson, Paula J.; Whitwell, Jennifer L.; Ward, Chadwick; Dale, Anders M.; Felmlee, Joel P.; Gunter, Jeffrey L.; Hill, Derek L.G.; Killiany, Ron; Schuff, Norbert; Fox-Bosetti, Sabrina; Lin, Chen; Studholme, Colin; DeCarli, Charles S.; Krueger, Gunnar; Ward, Heidi A.; Metzger, Gregory J.; Scott, Katherine T.; Mallozzi, Richard; Blezek, Daniel; Levy, Joshua; Debbins, Josef P.; Fleisher, Adam S.; Albert, Marilyn; Green, Robert; Bartzokis, George; Glover, Gary; Mugler, John; Weiner, Michael W.

2008-01-01

The Alzheimer's Disease Neuroimaging Initiative (ADNI) is a longitudinal multisite observational study of healthy elders, mild cognitive impairment (MCI), and Alzheimer's disease. Magnetic resonance imaging (MRI), (18F)-fluorode-oxyglucose positron emission tomography (FDG PET), urine serum, and cerebrospinal fluid (CSF) biomarkers, as well as clinical/psychometric assessments are acquiredat multiple time points. All data will be cross-linked and made available to the general scientific community. The purpose of this report is to describe the MRI methods employed in ADNI. The ADNI MRI core established specifications thatguided protocol development. A major effort was devoted toevaluating 3D T1-weighted sequences for morphometric analyses. Several options for this sequence were optimized for the relevant manufacturer platforms and then compared in a reduced-scale clinical trial. The protocol selected for the ADNI study includes: back-to-back 3D magnetization prepared rapid gradient echo (MP-RAGE) scans; B1-calibration scans when applicable; and an axial proton density-T2 dual contrast (i.e., echo) fast spin echo/turbo spin echo (FSE/TSE) for pathology detection. ADNI MRI methods seek to maximize scientific utility while minimizing the burden placed on participants. The approach taken in ADNI to standardization across sites and platforms of the MRI protocol, postacquisition corrections, and phantom-based monitoring of all scanners could be used as a model for other multisite trials. PMID:18302232

Neuroperformance Imaging

DTIC Science & Technology

2012-10-01

EMBC10.1722. 10. Mitra, P.P., Halperin, B.I.: Effects of finite gradient-pulse widths in pulsed- field - gradient diffusion measurements . Journal of Magnetic ...December 2011 ABSTRACT: The addition of a pair of magnetic field gradient pulses had initially enabled the measurement of spin motion to nuclear mag- netic...introduced a pair of (homogenous) magnetic field gradients into the spin echo experi- ment with the purpose of accurately measuring the scalar diffusion

Theoretical proposal for a magnetic resonance study of charge transport in organic semiconductors

NASA Astrophysics Data System (ADS)

Mkhitaryan, Vagharsh

Charge transport in disordered organic semiconductors occurs via carrier incoherent hops in a band of localized states. In the framework of continuous-time random walk the carrier on-site waiting time distribution (WTD) is one of the basic characteristics of diffusion. Besides, WTD is fundamentally related to the density of states (DOS) of localized states, which is a key feature of a material determining the optoelectric properties. However, reliable first-principle calculations of DOS in organic materials are not yet available and experimental characterization of DOS and WTD is desirable. We theoretically study the spin dynamics of hopping carriers and propose measurement schemes directly probing WTD, based on the zero-field spin relaxation and the primary (Hahn) spin echo. The proposed schemes are possible because, as we demonstrate, the long-time behavior of the zero-field relaxation and the primary echo is determined by WTD, both for the hyperfine coupling dominated and the spin-orbit coupling dominated spin dynamics. We also examine the dispersive charge transport, which is a non-Markovian sub-diffusive process characterized by non-stationarity. We show that the proposed schemes unambiguously capture the effects of non-stationarity, e.g., the aging behavior of random walks. This work was supported by the Department of Energy-Basic Energy Sciences under Contract No. DE-AC02-07CH11358.

Short-scan-time multi-slice diffusion MRI of the mouse cervical spinal cord using echo planar imaging.

PubMed

Callot, Virginie; Duhamel, Guillaume; Cozzone, Patrick J; Kober, Frank

2008-10-01

Mouse spinal cord (SC) diffusion-weighted imaging (DWI) provides important information on tissue morphology and structural changes that may occur during pathologies such as multiple sclerosis or SC injury. The acquisition scheme of the commonly used DWI techniques is based on conventional spin-echo encoding, which is time-consuming. The purpose of this work was to investigate whether the use of echo planar imaging (EPI) would provide good-quality diffusion MR images of mouse SC, as well as accurate measurements of diffusion-derived metrics, and thus enable diffusion tensor imaging (DTI) and highly resolved DWI within reasonable scan times. A four-shot diffusion-weighted spin-echo EPI (SE-EPI) sequence was evaluated at 11.75 T on a group of healthy mice (n = 10). SE-EPI-derived apparent diffusion coefficients of gray and white matter were compared with those obtained using a conventional spin-echo sequence (c-SE) to validate the accuracy of the method. To take advantage of the reduction in acquisition time offered by the EPI sequence, multi-slice DTI acquisitions were performed covering the cervical segments (six slices, six diffusion-encoding directions, three b values) within 30 min (vs 2 h for c-SE). From these measurements, fractional anisotropy and mean diffusivities were calculated, and fiber tracking along the C1 to C6 cervical segments was performed. In addition, high-resolution images (74 x 94 microm(2)) were acquired within 5 min per direction. Clear delineation of gray and white matter and identical apparent diffusion coefficient values were obtained, with a threefold reduction in acquisition time compared with c-SE. While overcoming the difficulties associated with high spatially and temporally resolved DTI measurements, the present SE-EPI approach permitted identification of reliable quantitative parameters with a reproducibility compatible with the detection of pathologies. The SE-EPI method may be particularly valuable when multiple sets of images from the SC are needed, in cases of rapidly evolving conditions, to decrease the duration of anesthesia or to improve MR exploration by including additional MR measurements. Copyright (c) 2008 John Wiley & Sons, Ltd.

The Fourier Transform in Chemistry-NMR, Part 3. Multiple-Pulse Experiments.

ERIC Educational Resources Information Center

Williams, Kathryn R.; King, Roy W.

1990-01-01

Described are six multipulse experiments with an emphasis on their application to common problems in chemistry. Exercises in relaxation time measurement, spin echoes, and polarization transfer are proposed. (CW)

Image domain propeller fast spin echo.

PubMed

Skare, Stefan; Holdsworth, Samantha J; Lilja, Anders; Bammer, Roland

2013-04-01

A new pulse sequence for high-resolution T2-weighted (T2-w) imaging is proposed - image domain propeller fast spin echo (iProp-FSE). Similar to the T2-w PROPELLER sequence, iProp-FSE acquires data in a segmented fashion, as blades that are acquired in multiple TRs. However, the iProp-FSE blades are formed in the image domain instead of in the k-space domain. Each iProp-FSE blade resembles a single-shot fast spin echo (SSFSE) sequence with a very narrow phase-encoding field of view (FOV), after which N rotated blade replicas yield the final full circular FOV. Our method of combining the image domain blade data to a full FOV image is detailed, and optimal choices of phase-encoding FOVs and receiver bandwidths were evaluated on phantom and volunteers. The results suggest that a phase FOV of 15-20%, a receiver bandwidth of ±32-63 kHz and a subsequent readout time of about 300 ms provide a good tradeoff between signal-to-noise ratio (SNR) efficiency and T2 blurring. Comparisons between iProp-FSE, Cartesian FSE and PROPELLER were made on single-slice axial brain data, showing similar T2-w tissue contrast and SNR with great anatomical conspicuity at similar scan times - without colored noise or streaks from motion. A new slice interleaving order is also proposed to improve the multislice capabilities of iProp-FSE. Copyright © 2013 Elsevier Inc. All rights reserved.

Evaluation of thermometric monitoring for intradiscal laser ablation in an open 1.0 T MR scanner.

PubMed

Wonneberger, Uta; Schnackenburg, Bernhard; Wlodarczyk, Waldemar; Rump, Jens; Walter, Thula; Streitparth, Florian; Teichgräber, Ulf Karl Mart

2010-01-01

The purpose of this study was to evaluate different methods of magnetic resonance thermometry (MRTh) for the monitoring of intradiscal laser ablation therapy in an open 1.0 Tesla magnetic resonance (MR) scanner. MRTh methods based on the two endogenous MR temperature indicators of spin-lattice relaxation time T1 and water proton resonance frequency (PRF) shift were optimised and compared in vitro. For the latter, we measured the effective spin-spin relaxation times T2* in intervertebral discs of volunteers. Then we compared four gradient echo-based imaging techniques to monitor laser ablations in human disc specimens. Criteria of assessment were outline of anatomic detail, immunity against needle artefacts, signal-to-noise ratio (SNR) and accuracy of the calculated temperature. T2* decreased in an inverse and almost linear manner with the patients' age (r = 0.9) from 70 to 30 ms (mean of 49 ms). The optimum image quality (anatomic details, needle artefacts, SNR) and temperature accuracy (+/-1.09 degrees C for T1-based and +/-1.11 degrees C for PRF-based MRTh) was achieved with a non-spoiled gradient-echo sequence with an echo time of TE = 10 ms. Combination of anatomic and thermometric non-invasive monitoring of laser ablations in the lumbar spine is feasible. The temperature accuracy of the investigated T1- and PRF-based MRTh methods in vitro is high enough and promises to be reliable in vivo as well.

[Imaging characteristics of PROPELLER T2-weighted imaging].

PubMed

Goto, Masami; Aoki, Shigeki; Hayashi, Naoto; Mori, Harushi; Watanabe, Yasushi; Ino, Kenji; Satake, Yoshirou; Nishida, Katuji; Sato, Haruo; Iida, Kyouhito; Mima, Kazuo; Ohtomo, Kuni

2004-11-01

As the PROPELLER sequence is a combination of the radial scan and fast-spin-echo (FSE) sequence, it can be considered an FSE sequence with a motion correlation. However, there are some differences between PROPELLER and FSE owing to differences in k-space trajectory. We clarified the imaging characteristics of PROPELLER T2-weighted imaging (T2WI) for different parameters in comparison with usual FSE T2WI. When the same parameters were used, PROPELLER T2WI showed a higher signal-to-noise ratio (SNR) and lower spatial resolution than usual FSE. Effective echo time (TE) changed with different echo train lengths (ETL) or different bandwidths on PROPELLER, and imaging contrast changed accordingly to be more effective.

New Imaging Strategies Using a Motion-Resistant Liver Sequence in Uncooperative Patients

PubMed Central

Kim, Bong Soo; Lee, Kyung Ryeol; Goh, Myeng Ju

2014-01-01

MR imaging has unique benefits for evaluating the liver because of its high-resolution capability and ability to permit detailed assessment of anatomic lesions. In uncooperative patients, motion artifacts can impair the image quality and lead to the loss of diagnostic information. In this setting, the recent advances in motion-resistant liver MR techniques, including faster imaging protocols (e.g., dual-echo magnetization-prepared rapid-acquisition gradient echo (MP-RAGE), view-sharing technique), the data under-sampling (e.g., gradient recalled echo (GRE) with controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA), single-shot echo-train spin-echo (SS-ETSE)), and motion-artifact minimization method (e.g., radial GRE with/without k-space-weighted image contrast (KWIC)), can provide consistent, artifact-free images with adequate image quality and can lead to promising diagnostic performance. Understanding of the different motion-resistant options allows radiologists to adopt the most appropriate technique for their clinical practice and thereby significantly improve patient care. PMID:25243115

Automatic correction of echo-planar imaging (EPI) ghosting artifacts in real-time interactive cardiac MRI using sensitivity encoding.

PubMed

Kim, Yoon-Chul; Nielsen, Jon-Fredrik; Nayak, Krishna S

2008-01-01

To develop a method that automatically corrects ghosting artifacts due to echo-misalignment in interleaved gradient-echo echo-planar imaging (EPI) in arbitrary oblique or double-oblique scan planes. An automatic ghosting correction technique was developed based on an alternating EPI acquisition and the phased-array ghost elimination (PAGE) reconstruction method. The direction of k-space traversal is alternated at every temporal frame, enabling lower temporal-resolution ghost-free coil sensitivity maps to be dynamically estimated. The proposed method was compared with conventional one-dimensional (1D) phase correction in axial, oblique, and double-oblique scan planes in phantom and cardiac in vivo studies. The proposed method was also used in conjunction with two-fold acceleration. The proposed method with nonaccelerated acquisition provided excellent suppression of ghosting artifacts in all scan planes, and was substantially more effective than conventional 1D phase correction in oblique and double-oblique scan planes. The feasibility of real-time reconstruction using the proposed technique was demonstrated in a scan protocol with 3.1-mm spatial and 60-msec temporal resolution. The proposed technique with nonaccelerated acquisition provides excellent ghost suppression in arbitrary scan orientations without a calibration scan, and can be useful for real-time interactive imaging, in which scan planes are frequently changed with arbitrary oblique orientations.

Electron spin-echo envelope modulation (ESEEM) reveals water and phosphate interactions with the KcsA potassium channel.

PubMed

Cieslak, John A; Focia, Pamela J; Gross, Adrian

2010-02-23

Electron spin-echo envelope modulation (ESEEM) spectroscopy is a well-established technique for the study of naturally occurring paramagnetic metal centers. The technique has been used to study copper complexes, hemes, enzyme mechanisms, micellar water content, and water permeation profiles in membranes, among other applications. In the present study, we combine ESEEM spectroscopy with site-directed spin labeling (SDSL) and X-ray crystallography in order to evaluate the technique's potential as a structural tool to describe the native environment of membrane proteins. Using the KcsA potassium channel as a model system, we demonstrate that deuterium ESEEM can detect water permeation along the lipid-exposed surface of the KcsA outer helix. We further demonstrate that (31)P ESEEM is able to identify channel residues that interact with the phosphate headgroup of the lipid bilayer. In combination with X-ray crystallography, the (31)P data may be used to define the phosphate interaction surface of the protein. The results presented here establish ESEEM as a highly informative technique for SDSL studies of membrane proteins.

WE-DE-206-04: MRI Pulse Sequences - Spin Echo, Gradient Echo, EPI, Non-Cartesia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pooley, R.

Magnetic resonance imaging (MRI) has become an essential part of clinical imaging due to its ability to render high soft tissue contrast. Instead of ionizing radiation, MRI use strong magnetic field, radio frequency waves and field gradients to create diagnostic useful images. It can be used to image the anatomy and also functional and physiological activities within the human body. Knowledge of the basic physical principles underlying MRI acquisition is vitally important to successful image production and proper image interpretation. This lecture will give an overview of the spin physics, imaging principle of MRI, the hardware of the MRI scanner,more » and various pulse sequences and their applications. It aims to provide a conceptual foundation to understand the image formation process of a clinical MRI scanner. Learning Objectives: Understand the origin of the MR signal and contrast from the spin physics level. Understand the main hardware components of a MRI scanner and their purposes Understand steps for MR image formation including spatial encoding and image reconstruction Understand the main kinds of MR pulse sequences and their characteristics.« less

Localized one-dimensional single voxel magnetic resonance spectroscopy without J coupling modulations.

PubMed

Lin, Yanqin; Lin, Liangjie; Wei, Zhiliang; Zhong, Jianhui; Chen, Zhong

2016-12-01

To acquire single voxel localized one-dimensional 1 H magnetic resonance spectroscopy (MRS) without J coupling modulations, free from amplitude and phase distortions. A pulse sequence, named PRESSIR, is developed for volume localized MRS without J modulations at arbitrary echo time (TE). The J coupling evolution is suppressed by the J-refocused module that uses a 90° pulse at the midpoint of a double spin echo. The localization performance of the PRESSIR sequence was tested with a two-compartment phantom. The proposed sequence shows similar voxel localization accuracy as PRESS. Both PRESSIR and PRESS sequences were performed on MRS brain phantom and pig brain tissue. PRESS spectra suffer from amplitude and phase distortions due to J modulations, especially under moderate and long TEs, while PRESSIR spectra are almost free from distortions. The PRESSIR sequence proposed herein enables the acquisition of single voxel in-phase MRS within a single scan. It allows an enhanced signal intensity of J coupling metabolites and reducing undesired broad resonances with short T2s while suppressing J modulations. Moreover, it provides an approach for direct measurement of nonoverlapping J coupling peaks and of transverse relaxation times T2s. Magn Reson Med 76:1661-1667, 2016. © 2015 International Society for Magnetic Resonance in Medicine. © 2015 International Society for Magnetic Resonance in Medicine.

Enhanced spin-torque in double tunnel junctions using a nonmagnetic-metal spacer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, C. H.; Cheng, Y. H.; Ko, C. W.

2015-10-12

This study proposes an enhancement in the spin-transfer torque of a magnetic tunnel junction (MTJ) designed with double-barrier layer structure using a nonmagnetic metal spacer, as a replacement for the ferromagnetic material, which is traditionally used in these double-barrier stacks. Our calculation results show that the spin-transfer torque and charge current density of the proposed double-barrier MTJ can be as much as two orders of magnitude larger than the traditional double-barrier one. In other words, the proposed double-barrier MTJ has a spin-transfer torque that is three orders larger than that of the single-barrier stack. This improvement may be attributed tomore » the quantum-well states that are formed in the nonmagnetic metal spacer and the resonant tunneling mechanism that exists throughout the system.« less

Arterial spin labeled perfusion imaging using three-dimensional turbo spin echo with a distributed spiral-in/out trajectory.

PubMed

Li, Zhiqiang; Schär, Michael; Wang, Dinghui; Zwart, Nicholas R; Madhuranthakam, Ananth J; Karis, John P; Pipe, James G

2016-01-01

The three-dimensional (3D) spiral turbo spin echo (TSE) sequence is one of the preferred readout methods for arterial spin labeled (ASL) perfusion imaging. Conventional spiral TSE collects the data using a spiral-out readout on a stack of spirals trajectory. However, it may result in suboptimal image quality and is not flexible in protocol design. The goal of this study is to provide a more robust readout technique without such limitation. The proposed technique incorporates a spiral-in/out readout into 3D TSE, and collects the data on a distributed spirals trajectory. The data set is split into the spiral-in and -out subsets that are reconstructed separately and combined after image deblurring. The volunteer results acquired with the proposed technique show no geometric distortion or signal pileup, as is present with GRASE, and no signal loss, as is seen with conventional spiral TSE. Examples also demonstrate the flexibility in changing the imaging parameters to satisfy various criteria. The 3D TSE with a distributed spiral-in/out trajectory provides a robust readout technique and allows for easy protocol design, thus is a promising alternative to GRASE or conventional spiral TSE for ASL perfusion imaging. © 2015 Wiley Periodicals, Inc.

[Contrastive analysis of artifacts produced by metal dental crowns in 3.0 T magnetic resonance imaging with six sequences].

PubMed

Lan, Gao; Yunmin, Lian; Pu, Wang; Haili, Huai

2016-06-01

This study aimed to observe and evaluate six 3.0 T sequences of metallic artifacts produced by metal dental crowns. Dental crowns fabricated with four different materials (Co-Gr, Ni-Gr, Ti alloy and pure Ti) were evaluated. A mature crossbreed dog was used as the experimental animal, and crowns were fabricated for its upper right second premolar. Each crown was examined through head MRI (3.0 T) with six sequences, namely, T₁ weighted-imaging of spin echo (T₁W/SE), T₂ weighted-imaging of inversion recovery (T₂W/IR), T₂ star gradient echo (T₂*/GRE), T2 weighted-imaging of fast spin echo (T₂W/FSE), T₁ weighted-imaging of fluid attenuate inversion recovery (T₂W/FLAIR), and T₂ weighted-imaging of propeller (T₂W/PROP). The largest area and layers of artifacts were assessed and compared. The artifact in the T₂*/GRE sequence was significantly wider than those in the other sequences (P < 0.01), whose artifact extent was not significantly different (P > 0.05). T₂*/GRE exhibit the strongest influence on the artifact, whereas the five other sequences contribute equally to artifact generation.

Magnetic resonance imaging metallic artifact of commonly encountered surgical implants and foreign material.

PubMed

Sutherland-Smith, James; Tilley, Brenda

2012-01-01

Magnetic resonance imaging (MRI) artifacts secondary to metallic implants and foreign bodies are well described. Herein, we provide quantitative data from veterinary implants including total hip arthroplasty implants, cranial cruciate repair implants, surgical screws, a skin staple, ligation clips, an identification microchip, ameroid constrictor, and potential foreign bodies including air gun and BB projectiles and a sewing needle. The objects were scanned in a gelatin phantom with plastic grid using standardized T2-weighted turbo-spin echo (TSE), T1-weighted spin echo, and T2*-weighted gradient recalled echo (GRE) image acquisitions at 1.5 T. Maximum linear dimensions and areas of signal voiding and grid distortion were calculated using a DICOM workstation for each sequence and object. Artifact severity was similar between the T2-weighted TSE and T1-weighted images, while the T2*-weighted images were most susceptible to artifact. Metal type influenced artifact size with the largest artifacts arising from steel objects followed by surgical stainless steel, titanium, and lead. For animals with metallic surgical implants or foreign bodies, the quantification of the artifact size will help guide clinicians on the viability of MRI. © 2012 Veterinary Radiology & Ultrasound.

In Vivo Visualization of Alzheimer’s Amyloid Plaques by MRI in Transgenic Mice Without a Contrast Agent

PubMed Central

Jack, Clifford R.; Garwood, Michael; Wengenack, Thomas M.; Borowski, Bret; Curran, Geoffrey L.; Lin, Joseph; Adriany, Gregor; Grohn, Olli H.J.; Grimm, Roger; Poduslo, Joseph F.

2009-01-01

One of the cardinal pathologic features of Alzheimer’s disease (AD) is formation of senile, or amyloid, plaques. Transgenic mice have been developed that express one or more of the genes responsible for familial AD in humans. Doubly transgenic mice develop “human-like” plaques, providing a mechanism to study amyloid plaque biology in a controlled manner. Imaging of labeled plaques has been accomplished with other modalities, but only MRI has sufficient spatial and contrast resolution to visualize individual plaques non-invasively. Methods to optimize visualization of plaques in vivo in transgenic mice at 9.4 T using a spin echo sequence based on adiabatic pulses are described. Preliminary results indicate that a spin echo acquisition more accurately reflects plaque size, while a T2* weighted gradient echo sequence reflects plaque iron content not plaque size. In vivo MRI – ex vivo MRI – in vitro histological correlations are provided. Histologically verified plaques as small as 50 μm in diameter were visualized in the living animal. To our knowledge this work represents the first demonstration of non-invasive in vivo visualization of individual AD plaques without the use of a contrast agent. PMID:15562496

Optimized, unequal pulse spacing in multiple echo sequences improves refocusing in magnetic resonance.

PubMed

Jenista, Elizabeth R; Stokes, Ashley M; Branca, Rosa Tamara; Warren, Warren S

2009-11-28

A recent quantum computing paper (G. S. Uhrig, Phys. Rev. Lett. 98, 100504 (2007)) analytically derived optimal pulse spacings for a multiple spin echo sequence designed to remove decoherence in a two-level system coupled to a bath. The spacings in what has been called a "Uhrig dynamic decoupling (UDD) sequence" differ dramatically from the conventional, equal pulse spacing of a Carr-Purcell-Meiboom-Gill (CPMG) multiple spin echo sequence. The UDD sequence was derived for a model that is unrelated to magnetic resonance, but was recently shown theoretically to be more general. Here we show that the UDD sequence has theoretical advantages for magnetic resonance imaging of structured materials such as tissue, where diffusion in compartmentalized and microstructured environments leads to fluctuating fields on a range of different time scales. We also show experimentally, both in excised tissue and in a live mouse tumor model, that optimal UDD sequences produce different T(2)-weighted contrast than do CPMG sequences with the same number of pulses and total delay, with substantial enhancements in most regions. This permits improved characterization of low-frequency spectral density functions in a wide range of applications.

3D Ultrashort TE MRI for Evaluation of Cartilaginous Endplate of Cervical Disk In Vivo: Feasibility and Correlation With Disk Degeneration in T2-Weighted Spin-Echo Sequence.

PubMed

Kim, Yeo Ju; Cha, Jang Gyu; Shin, Yoon Sang; Chaudhari, Akshay S; Suh, Young Ju; Hwan Yoon, Seung; Gold, Garry E

2018-05-01

The purpose of this study was to evaluate the feasibility of 3D ultrashort TE (UTE) MRI in depicting the cartilaginous endplate (CEP) and its abnormalities and to investigate the association between CEP abnormalities and disk degeneration on T2-weighted spin-echo (SE) MR images in cervical disks in vivo. Eight healthy volunteers and 70 patients were examined using 3-T MRI with the 3D UTE cones trajectory technique (TR/TE, 16.1/0.032, 6.6). In the volunteer study, quantitative and qualitative assessments of CEP depiction were conducted for the 3D UTE and T2-weighted SE imaging. In the patient study, CEP abnormalities were analyzed. Intersequence agreement between the images obtained with the first-echo 3D UTE sequence and the images created by subtracting the second-echo from the first-echo 3D UTE sequence (subtracted 3D UTE) and the intraobserver and interobserver agreements for 3D UTE overall were also tested. The CEP abnormalities on the 3D UTE images correlated with the Miyazaki grading of the T2-weighted SE images. In the volunteer study, the CEP was well visualized on 3D UTE images but not on T2-weighted SE images (p < 0.001). In the patient study, for evaluation of CEP abnormalities, intersequence agreements were substantial to almost perfect, intraobserver agreements were substantial to almost perfect, and interobserver agreements were moderate to substantial (p < 0.001). All of the CEP abnormalities correlated with the Miyazaki grade with statistical significance (p < 0.001). Three-dimensional UTE MRI feasibly depicts the CEP and CEP abnormalities, which may be associated with the severity of disk degeneration on T2-weighted SE MRI.

Quantification of nonenhancing tumor burden in gliomas using effective T2 maps derived from dual echo turbo spin echo MRI

PubMed Central

Ellingson, Benjamin M.; Lai, Albert; Nguyen, Huytram N.; Nghiemphu, Phioanh L.; Pope, Whitney B.; Cloughesy, Timothy F.

2015-01-01

Purpose Evaluation of nonenhancing tumor (NET) burden is an important, yet challenging part of brain tumor response assessment. The current study focuses on using dual echo turbo spin echo MRI as a means of quickly estimating tissue T2, which can be used to objectively define NET burden. Experimental Design A series of experiments were performed to establish the use of T2 maps for defining NET burden. First, variation in T2 was determined using ACR water phantoms in 16 scanners evaluated over 3 years. Next, sensitivity and specificity of T2 maps for delineating NET from other tissues was examined. Then, T2-defined NET was used to predict survival in separate subsets of glioblastoma patients treated with radiation therapy, concurrent radiation and chemotherapy, or bevacizumab at recurrence. Results Variability in T2 in the ACR phantom was 3-5%. In training data, ROC analysis suggested that 125ms < T2 < 250ms could delineate NET with a sensitivity >90% and specificity >65%. Using this criterion, NET burden after completion of radiation therapy alone, or concurrent radiation therapy and chemotherapy, was shown to be predictive of survival (Cox, P<0.05), and the change in NET volume before and after bevacizumab therapy in recurrent glioblastoma was also a predictive of survival (P<0.05). Conclusions T2 maps using dual echo data are feasible, stable, and can be used to objectively define NET burden for use in brain tumor characterization, prognosis, and response assessment. The use of effective T2 maps for defining NET burden should be validated in a randomized clinical trial. PMID:25901082

Evaluation of Chondrocalcinosis and Associated Knee Joint Degeneration Using MR Imaging: Data from the Osteoarthritis Initiative.

PubMed

Gersing, Alexandra S; Schwaiger, Benedikt J; Heilmeier, Ursula; Joseph, Gabby B; Facchetti, Luca; Kretzschmar, Martin; Lynch, John A; McCulloch, Charles E; Nevitt, Michael C; Steinbach, Lynne S; Link, Thomas M

2017-06-01

To evaluate the ability of different MRI sequences to detect chondrocalcinosis within knee cartilage and menisci, and to analyze the association with joint degeneration. Subjects with radiographic knee chondrocalcinosis (n = 90, age 67.7 ± 7.3 years, 50 women) were selected from the Osteoarthritis Initiative and matched to controls without radiographic chondrocalcinosis (n = 90). Visualization of calcium-containing crystals (CaC) was compared between 3D T1-weighted gradient-echo (T1GE), 3D dual echo steady-state (DESS), 2D intermediate-weighted (IW), and proton density (PD)-weighted fast spin-echo (FSE) sequences obtained with 3T MRI and correlated with a semiquantitative CaC score obtained from radiographs. Structural abnormalities were assessed using Whole-Organ MRI Score (WORMS) and logistic regression models were used to compare cartilage compartments with and without CaC. Correlations between CaC counts of MRI sequences and degree of radiographic calcifications were highest for GE (r T1GE  = 0.73, P < 0.001; r DESS  = 0.68, P < 0.001) compared to other sequences (P > 0.05). Meniscus WORMS was significantly higher in subjects with chondrocalcinosis compared to controls (P = 0.005). Cartilage defects were significantly more frequent in compartments with CaC than without (patella: P = 0.006; lateral tibia: P < 0.001; lateral femur condyle: P = 0.017). Gradient-echo sequences were most useful for the detection of chondrocalcinosis and presence of CaC was associated with higher prevalence of cartilage and meniscal damage. • Magnetic resonance imaging is useful for assessing burden of calcium-containing crystals (CaC). • Gradient-echo sequences are superior to fast spin echo sequences for CaC imaging. • Presence of CaC is associated with meniscus and cartilage degradation.

Protocol for generating multiphoton entangled states from quantum dots in the presence of nuclear spin fluctuations

NASA Astrophysics Data System (ADS)

Denning, Emil V.; Iles-Smith, Jake; McCutcheon, Dara P. S.; Mork, Jesper

2017-12-01

Multiphoton entangled states are a crucial resource for many applications in quantum information science. Semiconductor quantum dots offer a promising route to generate such states by mediating photon-photon correlations via a confined electron spin, but dephasing caused by the host nuclear spin environment typically limits coherence (and hence entanglement) between photons to the spin T2* time of a few nanoseconds. We propose a protocol for the deterministic generation of multiphoton entangled states that is inherently robust against the dominating slow nuclear spin environment fluctuations, meaning that coherence and entanglement is instead limited only by the much longer spin T2 time of microseconds. Unlike previous protocols, the present scheme allows for the generation of very low error probability polarization encoded three-photon GHZ states and larger entangled states, without the need for spin echo or nuclear spin calming techniques.

Small-amplitude backbone motions of the spin-labeled lipopeptide trichogin GA IV in a lipid membrane as revealed by electron spin echo.

PubMed

Syryamina, Victoria N; Isaev, Nikolay P; Peggion, Cristina; Formaggio, Fernando; Toniolo, Claudio; Raap, Jan; Dzuba, Sergei A

2010-09-30

Trichogin GA IV is a lipopeptide antibiotic of fungal origin, which is known to be able to modify the membrane permeability. TOAC nitroxide spin-labeled analogues of this membrane active peptide were investigated in hydrated bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) by electron spin echo (ESE) spectroscopy. Because the TOAC nitroxide spin label is rigidly attached to the peptide backbone, it may report on the backbone orientational dynamics. The ESE signal in this system is observed below ∼150 K. Previously, three-pulse stimulated ESE was found to be sensitive to two types of orientational motion of spin-labeled POPC lipid bilayers at these temperatures. The first type is fast stochastic librations, with a correlation time on the nanosecond scale (which also manifests itself in a two-pulse primary ESE experiment). The second type is slow millisecond inertial rotations. In the present work, we find that at low molar peptide to lipid ratio (1:200), where the individual peptide molecules are randomly distributed at the membrane surface, the spin labels show only a fast type of motion. At the high molar peptide to lipid ratio (1:20), a slow motion is also observed. Because at this high concentration trichogin GA IV is known to change its orientation from the in-plane topology to the transmembrane disposition, the observed onset of a slow motion may be safely attributed to the dynamics of peptides, which are elongated along the lipid molecules of the membrane. The possible interrelation between this backbone rotational motion of the peptide antibiotic and the membrane leakage is discussed.

Musculoskeletal MRI at 3.0 T and 7.0 T: a comparison of relaxation times and image contrast.

PubMed

Jordan, Caroline D; Saranathan, Manojkumar; Bangerter, Neal K; Hargreaves, Brian A; Gold, Garry E

2013-05-01

The purpose of this study was to measure and compare the relaxation times of musculoskeletal tissues at 3.0 T and 7.0 T, and to use these measurements to select appropriate parameters for musculoskeletal protocols at 7.0 T. We measured the T₁ and T₂ relaxation times of cartilage, muscle, synovial fluid, bone marrow and subcutaneous fat at both 3.0 T and 7.0 T in the knees of five healthy volunteers. The T₁ relaxation times were measured using a spin-echo inversion recovery sequence with six inversion times. The T₂ relaxation times were measured using a spin-echo sequence with seven echo times. The accuracy of both the T₁ and T₂ measurement techniques was verified in phantoms at both magnetic field strengths. We used the measured relaxation times to help design 7.0 T musculoskeletal protocols that preserve the favorable contrast characteristics of our 3.0 T protocols, while achieving significantly higher resolution at higher SNR efficiency. The T₁ relaxation times in all tissues at 7.0 T were consistently higher than those measured at 3.0 T, while the T₂ relaxation times at 7.0 T were consistently lower than those measured at 3.0 T. The measured relaxation times were used to help develop high resolution 7.0 T protocols that had similar fluid-to-cartilage contrast to that of the standard clinical 3.0 T protocols for the following sequences: proton-density-weighted fast spin-echo (FSE), T₂-weighted FSE, and 3D-FSE-Cube. The T₁ and T₂ changes were within the expected ranges. Parameters for musculoskeletal protocols at 7.0 T can be optimized based on these values, yielding improved resolution in musculoskeletal imaging with similar contrast to that of standard 3.0 T clinical protocols. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

gr-MRI: A software package for magnetic resonance imaging using software defined radios.

PubMed

Hasselwander, Christopher J; Cao, Zhipeng; Grissom, William A

2016-09-01

The goal of this work is to develop software that enables the rapid implementation of custom MRI spectrometers using commercially-available software defined radios (SDRs). The developed gr-MRI software package comprises a set of Python scripts, flowgraphs, and signal generation and recording blocks for GNU Radio, an open-source SDR software package that is widely used in communications research. gr-MRI implements basic event sequencing functionality, and tools for system calibrations, multi-radio synchronization, and MR signal processing and image reconstruction. It includes four pulse sequences: a single-pulse sequence to record free induction signals, a gradient-recalled echo imaging sequence, a spin echo imaging sequence, and an inversion recovery spin echo imaging sequence. The sequences were used to perform phantom imaging scans with a 0.5Tesla tabletop MRI scanner and two commercially-available SDRs. One SDR was used for RF excitation and reception, and the other for gradient pulse generation. The total SDR hardware cost was approximately $2000. The frequency of radio desynchronization events and the frequency with which the software recovered from those events was also measured, and the SDR's ability to generate frequency-swept RF waveforms was validated and compared to the scanner's commercial spectrometer. The spin echo images geometrically matched those acquired using the commercial spectrometer, with no unexpected distortions. Desynchronization events were more likely to occur at the very beginning of an imaging scan, but were nearly eliminated if the user invoked the sequence for a short period before beginning data recording. The SDR produced a 500kHz bandwidth frequency-swept pulse with high fidelity, while the commercial spectrometer produced a waveform with large frequency spike errors. In conclusion, the developed gr-MRI software can be used to develop high-fidelity, low-cost custom MRI spectrometers using commercially-available SDRs. Copyright © 2016. Published by Elsevier Inc.

T2-Weighted Dixon Turbo Spin Echo for Accelerated Simultaneous Grading of Whole-Body Skeletal Muscle Fat Infiltration and Edema in Patients With Neuromuscular Diseases.

PubMed

Schlaeger, Sarah; Klupp, Elisabeth; Weidlich, Dominik; Cervantes, Barbara; Foreman, Sarah C; Deschauer, Marcus; Schoser, Benedikt; Katemann, Christoph; Kooijman, Hendrik; Rummeny, Ernst J; Zimmer, Claus; Kirschke, Jan S; Karampinos, Dimitrios C

2018-04-02

The assessment of fatty infiltration and edema in the musculature of patients with neuromuscular diseases (NMDs) typically requires the separate performance of T1-weighted and fat-suppressed T2-weighted sequences. T2-weighted Dixon turbo spin echo (TSE) enables the generation of T2-weighted fat- and water-separated images, which can be used to assess both pathologies simultaneously. The present study examines the diagnostic performance of T2-weighted Dixon TSE compared with the standard sequences in 10 patients with NMDs and 10 healthy subjects. Whole-body magnetic resonance imaging was performed including T1-weighted Dixon fast field echo, T2-weighted short-tau inversion recovery, and T2-weighted Dixon TSE. Fatty infiltration and intramuscular edema were rated by 2 radiologists using visual semiquantitative rating scales. To assess intermethod and interrater agreement, weighted Cohen's κ coefficients were calculated. The ratings of fatty infiltration showed high intermethod and high interrater agreement (T1-weighted Dixon fast field echo vs T2-weighted Dixon TSE fat image). The evaluation of edematous changes showed high intermethod and good interrater agreement (T2-weighted short-tau inversion recovery vs T2-weighted Dixon TSE water image). T2-weighted Dixon TSE imaging is an alternative for accelerated simultaneous grading of whole-body skeletal muscle fat infiltration and edema in patients with NMDs.

A homonuclear spin-pair filter for solid-state NMR based on adiabatic-passage techniques

NASA Astrophysics Data System (ADS)

Verel, René; Baldus, Marc; Ernst, Matthias; Meier, Beat H.

1998-05-01

A filtering scheme for the selection of spin pairs (and larger spin clusters) under fast magic-angle spinning is proposed. The scheme exploits the avoided level crossing in spin pairs during an adiabatic amplitude sweep through the so-called HORROR recoupling condition. The advantages over presently used double-quantum filters are twofold. (i) The maximum theoretical filter efficiency is, due to the adiabatic variation, 100% instead of 73% as for transient methods. (ii) Since the filter does not rely on the phase-cycling properties of the double-quantum coherence, there is no need to obtain the full double-quantum intensity for all spins in the sample at one single point in time. The only important requirement is that all coupled spins pass through a two-spin state during the amplitude sweep. This makes the pulse scheme robust with respect to rf-amplitude missetting, rf-field inhomogeneity and chemical-shift offset.

76 FR 67200 - Prospective Grant of Exclusive License: Electron Paramagnetic Resonance Devices and Systems for...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-10-31

... that is a unique combination of: (1) multi-gradient Single Point Imaging involving global phase...-encoding gradients. The combination approach of single point imaging with the spin-echo signal detection...

Access to long-term optical memories using photon echoes retrieved from semiconductor spins

NASA Astrophysics Data System (ADS)

Langer, L.; Poltavtsev, S. V.; Yugova, I. A.; Salewski, M.; Yakovlev, D. R.; Karczewski, G.; Wojtowicz, T.; Akimov, I. A.; Bayer, M.

2014-11-01

The ability to store optical information is important for both classical and quantum communication. Achieving this in a comprehensive manner (converting the optical field into material excitation, storing this excitation, and releasing it after a controllable time delay) is greatly complicated by the many, often conflicting, properties of the material. More specifically, optical resonances in semiconductor quantum structures with high oscillator strength are inevitably characterized by short excitation lifetimes (and, therefore, short optical memory). Here, we present a new experimental approach to stimulated photon echoes by transferring the information contained in the optical field into a spin system, where it is decoupled from the optical vacuum field and may persist much longer. We demonstrate this for an n-doped CdTe/(Cd,Mg)Te quantum well, the storage time of which could be increased by more than three orders of magnitude, from the picosecond range up to tens of nanoseconds.

Phase incremented echo train acquisition applied to magnetic resonance pore imaging

NASA Astrophysics Data System (ADS)

Hertel, S. A.; Galvosas, P.

2017-02-01

Efficient phase cycling schemes remain a challenge for NMR techniques if the pulse sequences involve a large number of rf-pulses. Especially complex is the Carr Purcell Meiboom Gill (CPMG) pulse sequence where the number of rf-pulses can range from hundreds to several thousands. Our recent implementation of Magnetic Resonance Pore Imaging (MRPI) is based on a CPMG rf-pulse sequence in order to refocus the effect of internal gradients inherent in porous media. While the spin dynamics for spin- 1 / 2 systems in CPMG like experiments are well understood it is still not straight forward to separate the desired pathway from the spectrum of unwanted coherence pathways. In this contribution we apply Phase Incremented Echo Train Acquisition (PIETA) to MRPI. We show how PIETA offers a convenient way to implement a working phase cycling scheme and how it allows one to gain deeper insights into the amplitudes of undesired pathways.

MRI Artifacts of a Metallic Stent Derived From a Human Aorta Specimen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soto, M. E.; Flores, P.; Marrufo, O.

Magnetic resonance imaging has proved to be a useful technique to get images of the whole body. However, the presence of ferromagnetic material can cause susceptibility artifacts, which result from microscopic gradients that occur near the boundaries between areas displaying different magnetic susceptibility. These gradients cause dephasing of spins and frequency shifts in the surrounding tissues. Intravoxel dephasing and spatial mis-registration can degrade image quality. An aorta with a metallic stent was preserved in formaldehyde at 10% inside acrylic cylinders and used to obtain MR images. We tested pulsed spin echo and gradient echo sequences to improve image quality. Allmore » experiments were performed on a 7T/21 cm Varian system (Varian, Inc, Palo Alto, CA) equipped with Direct Drive technology and a 16-rung birdcage coil transceiver. The presence of metallic stents produces a lack of signal that might give falsely reassuring appearances within the vessel lumen.« less

Feasibility and applications of the spin-echo modulation option for a small angle neutron scattering instrument at the European Spallation Source

NASA Astrophysics Data System (ADS)

Kusmin, A.; Bouwman, W. G.; van Well, A. A.; Pappas, C.

2017-06-01

We describe theoretical and practical aspects of spin-echo modulated small-angle neutron scattering (SEMSANS) as well as the potential combination with SANS. Based on the preliminary technical designs of SKADI (a SANS instrument proposed for the European Spallation Source) and a SEMSANS add-on, we assess the practicability, feasibility and scientific merit of a combined SANS and SEMSANS setup by calculating tentative SANS and SEMSANS results for soft matter, geology and advanced material samples that have been previously studied by scattering methods. We conclude that lengths from 1 nm up to 0.01 mm can be observed simultaneously in a single measurement. Thus, the combination of SANS and SEMSANS instrument is suited for the simultaneous observation of a wide range of length scales, e.g. for time-resolved studies of kinetic processes in complex multiscale systems.

Electron spin-echo techniques for the study of protein motion

NASA Astrophysics Data System (ADS)

Kar, Leela; Johnson, Michael E.; Bowman, Michael K.

Electron spin-echo (ESE) spectroscopy has been used to make the first direct measurements of spin-spin relaxation times of a spin-labeled protein at physiological temperatures. Results from experiments using maleimide-labeled deoxygenated hemoglobin (dHb) from individuals homozygous for sickle cell anemia (dHbS) have been compared with those from control experiments using dHb from normal adults (dHbA). Hb "immobilized" by ammonium sulfate precipitation and by siloxane polymer entrapment have been studied for a suitable "rigid" reference. Two-dimensional ESE (2D-ESE) experiments have been performed using all of these systems. The 2D contour plots show that 2D-ESE is sensitive to the slow motion of dHbS polymers and can differentiate it from both that of immobilized Hb and of HbA molecules in solution at the same temperature and concentration. More importantly, the 2D-ESE technique enables one to select for slower motion and thereby extract the dHbS polymer signal from the total signal generated by the heterogeneous system containing dHbS molecules in solution as well as in the polymer. Computer simulations using current slow motional theories show that detailed motional and structural information may be obtained by such studies. The considerable potential of 2D-ESE spectroscopy in the study of macromolecular motion is illustrated by comparing 2D-ESE with the nonlinear technique of saturation transfer electron paramagnetic resonance.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kardash, Maria E.; Dzuba, Sergei A., E-mail: dzuba@kinetics.nsc.ru

Lipid-cholesterol interactions are responsible for different properties of biological membranes including those determining formation in the membrane of spatial inhomogeneities (lipid rafts). To get new information on these interactions, electron spin echo (ESE) spectroscopy, which is a pulsed version of electron paramagnetic resonance (EPR), was applied to study 3β-doxyl-5α-cholestane (DCh), a spin-labeled analog of cholesterol, in phospholipid bilayer consisted of equimolecular mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dioleoyl-sn-glycero-3-phosphocholine. DCh concentration in the bilayer was between 0.1 mol.% and 4 mol.%. For comparison, a reference system containing a spin-labeled 5-doxyl-stearic acid (5-DSA) instead of DCh was studied as well. The effects of “instantaneousmore » diffusion” in ESE decay and in echo-detected (ED) EPR spectra were explored for both systems. The reference system showed good agreement with the theoretical prediction for the model of spin labels of randomly distributed orientations, but the DCh system demonstrated remarkably smaller effects. The results were explained by assuming that neighboring DCh molecules are oriented in a correlative way. However, this correlation does not imply the formation of clusters of cholesterol molecules, because conventional continuous wave EPR spectra did not show the typical broadening due to aggregation of spin labels and the observed ESE decay was not faster than in the reference system. So the obtained data evidence that cholesterol molecules at low concentrations in biological membranes can interact via large distances of several nanometers which results in their orientational self-ordering.« less

Coherent Two-Dimensional Terahertz Magnetic Resonance Spectroscopy of Collective Spin Waves.

PubMed

Lu, Jian; Li, Xian; Hwang, Harold Y; Ofori-Okai, Benjamin K; Kurihara, Takayuki; Suemoto, Tohru; Nelson, Keith A

2017-05-19

We report a demonstration of two-dimensional (2D) terahertz (THz) magnetic resonance spectroscopy using the magnetic fields of two time-delayed THz pulses. We apply the methodology to directly reveal the nonlinear responses of collective spin waves (magnons) in a canted antiferromagnetic crystal. The 2D THz spectra show all of the third-order nonlinear magnon signals including magnon spin echoes, and 2-quantum signals that reveal pairwise correlations between magnons at the Brillouin zone center. We also observe second-order nonlinear magnon signals showing resonance-enhanced second-harmonic and difference-frequency generation. Numerical simulations of the spin dynamics reproduce all of the spectral features in excellent agreement with the experimental 2D THz spectra.

Highly selective detection of individual nuclear spins with rotary echo on an electron spin probe

PubMed Central

Mkhitaryan, V. V.; Jelezko, F.; Dobrovitski, V. V.

2015-01-01

We consider an electronic spin, such as a nitrogen-vacancy center in diamond, weakly coupled to a large number of nuclear spins, and subjected to the Rabi driving with a periodically alternating phase. We show that by switching the driving phase synchronously with the precession of a given nuclear spin, the interaction to this spin is selectively enhanced, while the rest of the bath remains decoupled. The enhancement is of resonant character. The key feature of the suggested scheme is that the width of the resonance is adjustable, and can be greatly decreased by increasing the driving strength. Thus, the resonance can be significantly narrowed, by a factor of 10–100 in comparison with the existing detection methods. Significant improvement in selectivity is explained analytically and confirmed by direct numerical many-spin simulations. The method can be applied to a wide range of solid-state systems. PMID:26497777

Thermal properties of spin-S Kitaev-Heisenberg model on a honeycomb lattice

NASA Astrophysics Data System (ADS)

Suzuki, Takafumi; Yamaji, Youhei

2018-05-01

Temperature (T) dependence of heat capacity C (T) in the S = 1 / 2 Kitaev honeycomb model shows a double-peak structure resulting from fractionalization of spins into two kinds of Majorana fermions. Recently it has been discussed that the double-peak structure in C (T) is also observed in magnetic ordered phases of the S = 1 / 2 Kitaev-Heisenberg (KH) model on a honeycomb lattice when the system is located in the vicinity of the Kitaev's spin liquid phase. In addition to the S = 1 / 2 spin case, similar double-peak structure has been confirmed in the KH honeycomb model for classical Heisenberg spins, where spin S is regarded as S → ∞ . We investigate spin-S dependence of C (T) for the KH honeycomb models by using thermal pure quantum state. We also perform classical Monte Carlo calculations to obtain C (T) for the classical KH model. From obtained results, we find that the origin of the high-temperature peak is different between the quantum spin case with small Ss and the classical Heisenberg spin case. Furthermore, the high-temperature peak in the quantum spin case, which is one of the clues for fractionalization of spins, disappears for S > 1 .

Satellite transitions acquired in real time by magic angle spinning (STARTMAS): ``Ultrafast'' high-resolution MAS NMR spectroscopy of spin I =3/2 nuclei

NASA Astrophysics Data System (ADS)

Thrippleton, Michael J.; Ball, Thomas J.; Wimperis, Stephen

2008-01-01

The satellite transitions acquired in real time by magic angle spinning (STARTMAS) NMR experiment combines a train of pulses with sample rotation at the magic angle to refocus the first- and second-order quadrupolar broadening of spin I =3/2 nuclei in a series of echoes, while allowing the isotropic chemical and quadrupolar shifts to evolve. The result is real-time isotropic NMR spectra at high spinning rates using conventional MAS equipment. In this paper we describe in detail how STARTMAS data can be acquired and processed with ease on commercial equipment. We also discuss the advantages and limitations of the approach and illustrate the discussion with numerical simulations and experimental data from four different powdered solids.

Spin current and second harmonic generation in non-collinear magnetic systems: the hydrodynamic model

NASA Astrophysics Data System (ADS)

Karashtin, E. A.; Fraerman, A. A.

2018-04-01

We report a theoretical study of the second harmonic generation in a noncollinearly magnetized conductive medium with equilibrium spin current. The hydrodynamic model is used to unravel the mechanism of a novel effect of the double frequency signal generation that is attributed to the spin current. According to our calculations, this second harmonic response appears due to the ‘non-adiabatic’ spin polarization of the conduction electrons induced by the oscillations in the non-uniform magnetization forced by the electric field of the electromagnetic wave. Together with the linear velocity response this leads to the generation of the double frequency spin current. This spin current is converted to the electric current via the inverse spin Hall effect, and the double-frequency electric current emits the second harmonic radiation. Possible experiment for detection of the new second harmonic effect is proposed.

EPR and ESE of CuS4 complex in Cu(dmit)2: g-Factor and hyperfine splitting correlation in tetrahedral Cu-sulfur complexes

NASA Astrophysics Data System (ADS)

Hoffmann, Stanisław K.; Goslar, Janina; Lijewski, Stefan; Zalewska, Alina

2013-11-01

Pseudotetrahedral CuS4 complexes of Cu(dmit)2 compound in DMF solution were studied by EPR, UV-Vis and electron spin echo methods. After rapid freezing at 77 K a good glassy state is formed and the CuS4 complex has a D2d symmetry of a compressed tetrahedron with xy ground state and spin-Hamiltonian parameters g|| = 2.089, g⊥ = 2.026, A|| = 146 × 10-4 cm-1 and A⊥ = 30 × 10-4 cm-1. The complex is not deformed in the glassy state and is very rigid as indicated by the echo detected spectrum and by electron spin relaxation which is governed by reorientations of methyl groups of surrounding DMF molecules as shown by electron spin echo envelope modulation (ESEEM) spectrum. The g|| and A|| of Cu(dmit)2 and other CuS4 complexes collected in Peisach-Blumberg correlation diagram were analyzed using extended Molecular Orbital theory. We explain why the correlation line for copper-sulfur complexes has larger slope compared to the CuO4 and CuN4 tetrahedra. Along the correlation line the delocalization of unpaired electron density onto ligand is constant and varies from β = 0.78-0.83 for g|| in the range 2.06-2.10 of correlation diagram. The slope of the line is determined by the product of MO-coefficients αc1, where α is a parameter characterizing delocalization of unpaired electron in x2-y2 and c1 < 1 is a mixing parameter decreasing when 4p contribution grows. We found, unexpectedly, that αc1≈0.7 for all CuS4 complexes suggesting a correlation between degree of tetrahedral deformation and MO-parameters. MO-coefficients for Cu(dmit)2 are α = 0.753, β = 0.752 and c1 = 0.930 confirming a strong delocalization of unpaired electron in xy and x2-y2 orbitals.

Comparison of 250 MHz electron spin echo and continuous wave oxygen EPR imaging methods for in vivo applications

PubMed Central

Epel, Boris; Sundramoorthy, Subramanian V.; Barth, Eugene D.; Mailer, Colin; Halpern, Howard J.

2011-01-01

Purpose: The authors compare two electron paramagnetic resonance imaging modalities at 250 MHz to determine advantages and disadvantages of those modalities for in vivo oxygen imaging. Methods: Electron spin echo (ESE) and continuous wave (CW) methodologies were used to obtain three-dimensional images of a narrow linewidth, water soluble, nontoxic oxygen-sensitive trityl molecule OX063 in vitro and in vivo. The authors also examined sequential images obtained from the same animal injected intravenously with trityl spin probe to determine temporal stability of methodologies. Results: A study of phantoms with different oxygen concentrations revealed a threefold advantage of the ESE methodology in terms of reduced imaging time and more precise oxygen resolution for samples with less than 70 torr oxygen partial pressure. Above∼100 torr, CW performed better. The images produced by both methodologies showed pO2 distributions with similar mean values. However, ESE images demonstrated superior performance in low pO2 regions while missing voxels in high pO2 regions. Conclusions: ESE and CW have different areas of applicability. ESE is superior for hypoxia studies in tumors. PMID:21626937

Electron paramagnetic resonance of a 10B-containing heterocyclic radical

NASA Astrophysics Data System (ADS)

Eaton, Sandra S.; Ngendahimana, Thacien; Eaton, Gareth R.; Jupp, Andrew R.; Stephan, Douglas W.

2018-05-01

Electron paramagnetic resonance measurements for a 10B-containing heterocyclic phenanthrenedione radical, (C6F5)2B(O2C14H8), were made at X-band in 9:1 toluene:dichloromethane from 10 to 293 K and in toluene from 180 to 293 K. In well-deoxygenated 0.1 mM toluene solution at room temperature hyperfine couplings to 10B, four pairs of protons and five pairs of fluorines contribute to a continuous wave spectrum with many resolved lines. Hyperfine couplings were adjusted to provide the best fit for spectra of the radical enriched in 10B and the analogous radical synthesized with 10,11B in natural abundance, resulting in small refinements of the hyperfine coupling constants previously reported for the natural abundance sample. Electron spin relaxation rates at temperatures between 15 and 293 K were similar for samples containing 10B and natural isotope abundance. Analysis of electron spin echo envelope modulation and hyperfine correlation spectroscopy data at 80 K found Axx = -7.5 ± 0.3, Ayy = -8.5 ± 0.3, and Azz = -10.8 ± 0.3 MHz for 11B, which indicates small spin density on the boron. The spin echo and hyperfine spectroscopy data for the 10B -containing radical are consistent with the factor of 2.99 smaller hyperfine values for 10B than for 11B.

Optimization of a double inversion recovery sequence for noninvasive synovium imaging of joint effusion in the knee.

PubMed

Jahng, Geon-Ho; Jin, Wook; Yang, Dal Mo; Ryu, Kyung Nam

2011-05-01

We wanted to optimize a double inversion recovery (DIR) sequence to image joint effusion regions of the knee, especially intracapsular or intrasynovial imaging in the suprapatellar bursa and patellofemoral joint space. Computer simulations were performed to determine the optimum inversion times (TI) for suppressing both fat and water signals, and a DIR sequence was optimized based on the simulations for distinguishing synovitis from fluid. In vivo studies were also performed on individuals who showed joint effusion on routine knee MR images to demonstrate the feasibility of using the DIR sequence with a 3T whole-body MR scanner. To compare intracapsular or intrasynovial signals on the DIR images, intermediate density-weighted images and/or post-enhanced T1-weighted images were acquired. The timings to enhance the synovial contrast from the fluid components were TI1 = 2830 ms and TI2 = 254 ms for suppressing the water and fat signals, respectively. Improved contrast for the intrasynovial area in the knees was observed with the DIR turbo spin-echo pulse sequence compared to the intermediate density-weighted sequence. Imaging contrast obtained noninvasively with the DIR sequence was similar to that of the post-enhanced T1-weighted sequence. The DIR sequence may be useful for delineating synovium without using contrast materials.

SAR and scan-time optimized 3D whole-brain double inversion recovery imaging at 7T.

PubMed

Pracht, Eberhard D; Feiweier, Thorsten; Ehses, Philipp; Brenner, Daniel; Roebroeck, Alard; Weber, Bernd; Stöcker, Tony

2018-05-01

The aim of this project was to implement an ultra-high field (UHF) optimized double inversion recovery (DIR) sequence for gray matter (GM) imaging, enabling whole brain coverage in short acquisition times ( ≈5 min, image resolution 1 mm 3 ). A 3D variable flip angle DIR turbo spin echo (TSE) sequence was optimized for UHF application. We implemented an improved, fast, and specific absorption rate (SAR) efficient TSE imaging module, utilizing improved reordering. The DIR preparation was tailored to UHF application. Additionally, fat artifacts were minimized by employing water excitation instead of fat saturation. GM images, covering the whole brain, were acquired in 7 min scan time at 1 mm isotropic resolution. SAR issues were overcome by using a dedicated flip angle calculation considering SAR and SNR efficiency. Furthermore, UHF related artifacts were minimized. The suggested sequence is suitable to generate GM images with whole-brain coverage at UHF. Due to the short total acquisition times and overall robustness, this approach can potentially enable DIR application in a routine setting and enhance lesion detection in neurological diseases. Magn Reson Med 79:2620-2628, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Solid-state NMR spin-echo investigation of the metalloproteins parvalbumin, concanavalin A, and pea and lentil lectins, substituted with cadmium-113

NASA Astrophysics Data System (ADS)

Marchetti, Paul S.; Bhattacharyya, Lokesh; Ellis, Paul D.; Brewer, C. Fred

Solid-state 113Cd NMR spectroscopy of static powder samples of 113Cd-substituted metalloproteins, parvalbumin, concanavalin A, and pea and lentil lectins, was carried out. Cross polarization followed by application of a train of uniformly spaced π pulses was employed to investigate the origin of residual cadmium NMR linewidths observed previously in these proteins. Fourier transformation of the resulting spin-echo train yielded spectra consisting of uniformly spaced lines having linewidths of the order of 1-2 ppm. The observed linewidths were not influenced by temperature as low as -50°C or by extent of protein hydration. Since the echo-train pulse sequence is able to eliminate inhomogeneous but not homogeneous contributions to the linewidths, there is a predominant inhomogeneous contribution to cadmium linewidths in the protein CP/MAS spectra. However, significant changes in spectral intensities were observed with change in temperature and extent of protein hydration. These intensity changes are attributed for parvalbumin and concanavalin A to changes in cross-polarization efficiency with temperature and hydration. For pea and lentil lectins, this effect is attributed to the elimination of static disorder at the pea and lentil S2 metal-ion sites due to sugar binding.

Contrast-Enhanced Magnetic Resonance Cholangiography: Practical Tips and Clinical Indications for Biliary Disease Management.

PubMed

Palmucci, Stefano; Roccasalva, Federica; Piccoli, Marina; Fuccio Sanzà, Giovanni; Foti, Pietro Valerio; Ragozzino, Alfonso; Milone, Pietro; Ettorre, Giovanni Carlo

2017-01-01

Since its introduction, MRCP has been improved over the years due to the introduction of several technical advances and innovations. It consists of a noninvasive method for biliary tree representation, based on heavily T2-weighted images. Conventionally, its protocol includes two-dimensional single-shot fast spin-echo images, acquired with thin sections or with multiple thick slabs. In recent years, three-dimensional T2-weighted fast-recovery fast spin-echo images have been added to the conventional protocol, increasing the possibility of biliary anatomy demonstration and leading to a significant benefit over conventional 2D imaging. A significant innovation has been reached with the introduction of hepatobiliary contrasts, represented by gadoxetic acid and gadobenate dimeglumine: they are excreted into the bile canaliculi, allowing the opacification of the biliary tree. Recently, 3D interpolated T1-weighted spoiled gradient echo images have been proposed for the evaluation of the biliary tree, obtaining images after hepatobiliary contrast agent administration. Thus, the acquisition of these excretory phases improves the diagnostic capability of conventional MRCP-based on T2 acquisitions. In this paper, technical features of contrast-enhanced magnetic resonance cholangiography are briefly discussed; main diagnostic tips of hepatobiliary phase are showed, emphasizing the benefit of enhanced cholangiography in comparison with conventional MRCP.

Music-based magnetic resonance fingerprinting to improve patient comfort during MRI examinations.

PubMed

Ma, Dan; Pierre, Eric Y; Jiang, Yun; Schluchter, Mark D; Setsompop, Kawin; Gulani, Vikas; Griswold, Mark A

2016-06-01

Unpleasant acoustic noise is a drawback of almost every MRI scan. Instead of reducing acoustic noise to improve patient comfort, we propose a technique for mitigating the noise problem by producing musical sounds directly from the switching magnetic fields while simultaneously quantifying multiple important tissue properties. MP3 music files were converted to arbitrary encoding gradients, which were then used with varying flip angles and repetition times in a two- and three-dimensional magnetic resonance fingerprinting (MRF) examination. This new acquisition method, named MRF-Music, was used to quantify T1 , T2 , and proton density maps simultaneously while providing pleasing sounds to the patients. MRF-Music scans improved patient comfort significantly during MRI examinations. The T1 and T2 values measured from phantom are in good agreement with those from the standard spin echo measurements. T1 and T2 values from the brain scan are also close to previously reported values. MRF-Music sequence provides significant improvement in patient comfort compared with the MRF scan and other fast imaging techniques such as echo planar imaging and turbo spin echo scans. It is also a fast and accurate quantitative method that quantifies multiple relaxation parameters simultaneously. Magn Reson Med 75:2303-2314, 2016. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.

Gadolinium-DTPA enhanced magnetic resonance imaging of bone cysts in patients with rheumatoid arthritis.

PubMed Central

Gubler, F M; Algra, P R; Maas, M; Dijkstra, P F; Falke, T H

1993-01-01

OBJECTIVES--To examine the contents of intraosseous cysts in patients with rheumatoid arthritis (RA) through the signal intensity characteristics on gadolinium-DTPA (Gd-DTPA) enhanced magnetic resonance imaging. METHODS--The hand or foot joints of nine patients with the cystic form of RA (where the initial radiological abnormality consisted of intraosseous cysts without erosions) were imaged before and after intravenous administration of Gd-DTPA. A 0.6 unit, T1 weighted spin echo and T2* weighted gradient echo were used to obtain images in at least two perpendicular planes. RESULTS--Most cysts showed a low signal intensity on the non-enhanced T1 weighted (spin echo) images and a high signal intensity on the T2* weighted (gradient echo) images, consistent with a fluid content. No cyst showed an enhancement of signal intensity on the T1 weighted images after intravenous administration of Gd-DTPA, whereas synovium hyperplasia at the site of bony erosions did show an increased signal intensity after Gd-DTPA. Magnetic resonance imaging detected more cysts (as small as 2 mm) than plain films, and the cysts were located truly intraosseously. In six patients no other joint abnormalities were identified by magnetic resonance imaging; the three other patients also showed, after Gd-DTPA administration, an enhanced synovium at the site of bony erosions. CONCLUSIONS--It is suggested that intraosseous bone cysts in patients with RA do not contain hyperaemic synovial proliferation. The bone cysts in patients with the cystic form of RA may be the only joint abnormality. Images PMID:8257207

In vitro determination of biomechanical properties of human articular cartilage in osteoarthritis using multi-parametric MRI

NASA Astrophysics Data System (ADS)

Juras, Vladimir; Bittsansky, Michal; Majdisova, Zuzana; Szomolanyi, Pavol; Sulzbacher, Irene; Gäbler, Stefan; Stampfl, Jürgen; Schüller, Georg; Trattnig, Siegfried

2009-03-01

The objective of this study was to evaluate the correlations between MR parameters and the biomechanical properties of naturally degenerated human articular cartilage. Human cartilage explants from the femoral condyles of patients who underwent total knee replacement were evaluated on a micro-imaging system at 3 T. To quantify glycosaminoglycan (GAG) content, delayed gadolinium-enhanced MRI of the cartilage (dGEMRIC) was used. T2 maps were created by using multi-echo, multi-slice spin echo sequences with six echoes: 15, 30, 45, 60, 75, and 90 ms. Data for apparent diffusion constant (ADC) maps were obtained from pulsed gradient spin echo (PGSE) sequences with five b-values: 10.472, 220.0, 627.0, 452.8, 724.5, and 957.7. MR parameters were correlated with mechanical parameters (instantaneous ( I) and equilibrium ( Eq) modulus and relaxation time ( τ)), and the OA stage of each cartilage specimen was determined by histological evaluation of hematoxylin-eosin stained slices. For some parameters, a high correlation was found: the correlation of T1Gd vs Eq ( r = 0.8095), T1Gd vs I/ Eq ( r = -0.8441) and T1Gd vs τ ( r = 0.8469). The correlation of T2 and ADC with selected biomechanical parameters was not statistically significant. In conclusion, GAG content measured by dGEMRIC is highly related to the selected biomechanical properties of naturally degenerated articular cartilage. In contrast, T2 and ADC were unable to estimate these properties. The results of the study imply that some MR parameters can non-invasively predict the biomechanical properties of degenerated articular cartilage.

Age-related apparent diffusion coefficient changes in the normal brain.

PubMed

Watanabe, Memi; Sakai, Osamu; Ozonoff, Al; Kussman, Steven; Jara, Hernán

2013-02-01

To measure the mean diffusional age-related changes of the brain over the full human life span by using diffusion-weighted spin-echo single-shot echo-planar magnetic resonance (MR) imaging and sequential whole-brain apparent diffusion coefficient (ADC) histogram analysis and, secondarily, to build mathematical models of these normal age-related changes throughout human life. After obtaining institutional review board approval, a HIPAA-compliant retrospective search was conducted for brain MR imaging studies performed in 2007 for various clinical indications. Informed consent was waived. The brain data of 414 healthy subjects (189 males and 225 females; mean age, 33.7 years; age range, 2 days to 89.3 years) were obtained with diffusion-weighted spin-echo single-shot echo-planar MR imaging. ADC histograms of the whole brain were generated. ADC peak values, histogram widths, and intracranial volumes were plotted against age, and model parameters were estimated by using nonlinear regression. Four different stages were identified for aging changes in ADC peak values, as characterized by specific mathematical terms: There were age-associated exponential decays for the maturation period and the development period, a constant term for adulthood, and a linear increase for the senescence period. The age dependency of ADC peak value was simulated by using four-term six-coefficient function, including biexponential and linear terms. This model fit the data very closely (R(2) = 0.91). Brain diffusivity as a whole demonstrated age-related changes through four distinct periods of life. These results could contribute to establishing an ADC baseline of the normal brain, covering the full human life span.

A quantitative experimental phantom study on MRI image uniformity.

PubMed

Felemban, Doaa; Verdonschot, Rinus G; Iwamoto, Yuri; Uchiyama, Yuka; Kakimoto, Naoya; Kreiborg, Sven; Murakami, Shumei

2018-05-23

Our goal was to assess MR image uniformity by investigating aspects influencing said uniformity via a method laid out by the National Electrical Manufacturers Association (NEMA). Six metallic materials embedded in a glass phantom were scanned (i.e. Au, Ag, Al, Au-Ag-Pd alloy, Ti and Co-Cr alloy) as well as a reference image. Sequences included spin echo (SE) and gradient echo (GRE) scanned in three planes (i.e. axial, coronal, and sagittal). Moreover, three surface coil types (i.e. head and neck, Brain, and temporomandibular joint coils) and two image correction methods (i.e. surface coil intensity correction or SCIC, phased array uniformity enhancement or PURE) were employed to evaluate their effectiveness on image uniformity. Image uniformity was assessed using the National Electrical Manufacturers Association peak-deviation non-uniformity method. Results showed that temporomandibular joint coils elicited the least uniform image and brain coils outperformed head and neck coils when metallic materials were present. Additionally, when metallic materials were present, spin echo outperformed gradient echo especially for Co-Cr (particularly in the axial plane). Furthermore, both SCIC and PURE improved image uniformity compared to uncorrected images, and SCIC slightly surpassed PURE when metallic metals were present. Lastly, Co-Cr elicited the least uniform image while other metallic materials generally showed similar patterns (i.e. no significant deviation from images without metallic metals). Overall, a quantitative understanding of the factors influencing MR image uniformity (e.g. coil type, imaging method, metal susceptibility, and post-hoc correction method) is advantageous to optimize image quality, assists clinical interpretation, and may result in improved medical and dental care.

The detectability of brain metastases using contrast-enhanced spin-echo or gradient-echo images: a systematic review and meta-analysis.

PubMed

Suh, Chong Hyun; Jung, Seung Chai; Kim, Kyung Won; Pyo, Junhee

2016-09-01

This study aimed to compare the detectability of brain metastases using contrast-enhanced spin-echo (SE) and gradient-echo (GRE) T1-weighted images. The Ovid-MEDLINE and EMBASE databases were searched for studies on the detectability of brain metastases using contrast-enhanced SE or GRE images. The pooled proportions for the detectability of brain metastases were assessed using random-effects modeling. Heterogeneity among studies was determined using χ (2) statistics for the pooled estimates and the inconsistency index, I (2) . To overcome heterogeneity, subgroup analyses according to slice thickness and lesion size were performed. A total of eight eligible studies, which included a sample size of 252 patients and 1413 brain metastases, were included. The detectability of brain metastases using SE images (89.2 %) was higher than using GRE images (81.6 %; adjusted 84.0 %), but this difference was not statistically significant (p = 0.2385). In subgroup analysis of studies with 1-mm-thick slices and small metastases (<5 mm in diameter), 3-dimensional (3D) SE images demonstrated a higher detectability in comparison to 3D GRE images (93.7 % vs 73.1 % in 1-mm-thick slices; 89.5 % vs 59.4 % for small metastases) (p < 0.0001). Although both SE or GRE images are acceptable for detecting brain metastases, contrast-enhanced 3D SE images using 1-mm-thick slices are preferred for detecting brain metastases, especially small lesions (<5 mm in diameter).

Forward-masking based gain control in odontocete biosonar: an evoked-potential study.

PubMed

Supin, Alexander Ya; Nachtigall, Paul E; Breese, Marlee

2009-04-01

Auditory evoked potentials (AEPs) were recorded during echolocation in a false killer whale Pseudorca crassidens. An electronically synthesized and played-back ("phantom") echo was used. Each electronic echo was triggered by an emitted biosonar pulse. The echo had a spectrum similar to that of the emitted biosonar clicks, and its intensity was proportional to that of the emitted click. The attenuation of the echo relative to the emitted click and its delay was controlled by the experimenter. Four combinations of echo attenuation and delay were tested (-31 dB, 2 ms), (-40 dB, 4 ms), (-49 dB, 8 ms), and (-58 dB, 16 ms); thus, attenuation and delay were associated with a rate of 9 dB of increased attenuation per delay doubling. AEPs related to emitted clicks displayed a regular amplitude dependence on the click level. Echo-related AEPs did not feature amplitude dependence on echo attenuation or emitted click levels, except in a few combinations of the lowest values of these two variables. The results are explained by a hypothesis that partial forward masking of the echoes by the preceding emitted sonar pulses serves as a kind of automatic gain control in the auditory system of echolocating odontocetes.

Exchange-mediated spin-lattice relaxation of Fe3+ ions in borate glasses.

PubMed

Misra, Sushil K; Pilbrow, John R

2007-03-01

Spin-lattice relaxation times (T1) of two borate glasses doped with different concentrations of Fe2O3 were measured using the Electron Spin-Echo (ESE) technique at X-band (9.630 GHz) in the temperature range 2-6K. In comparison with a previous investigation of Fe3+-doped silicate glasses, the relaxation rates were comparable and differed by no more than a factor of two. The data presented here extend those previously reported for borate glasses in the 10-250K range but measured using the amplitude-modulation technique. The T1 values were found to depend on temperature (T) as T(n) with n approximately 1 for the 1% and 0.1% Fe2O3-doped glass samples. These results are consistent with spin-lattice relaxation as effected by exchange interaction of a Fe3+ spin exchange-coupled to another Fe3+ spin in an amorphous material.

Role of Echocardiograghy in Treating a Case of Double Chamber Right Ventricle with Delayed Presentation.

PubMed

Barik, Ramachandra

2017-01-01

The clinical diagnosis of double chamber right ventricle (DCRV) is not straightforward. Clinical history, clinical examination, 12-lead electrocardiogram, chest X-ray, and Echocardiography (echo) contribute to morphological diagnosis. Cardiac catheterization is essential for hemodynamic evaluation. A thorough presurgical workup helps the cardiac surgeon to choose the appropriate surgical approach and timing of surgery in an individual case. We present a case of a DCRV who presented to us in the fifth decade of life. Echo confirmed the morphological diagnosis and cardiac catheterization complemented the exact pull back gradient across the obstruction in the right ventricle. This patient was suggested muscle bundle resection and ventricular septal defect closure using right atrial approach.

Multiband multi-echo imaging of simultaneous oxygenation and flow timeseries for resting state connectivity.

PubMed

Cohen, Alexander D; Nencka, Andrew S; Lebel, R Marc; Wang, Yang

2017-01-01

A novel sequence has been introduced that combines multiband imaging with a multi-echo acquisition for simultaneous high spatial resolution pseudo-continuous arterial spin labeling (ASL) and blood-oxygenation-level dependent (BOLD) echo-planar imaging (MBME ASL/BOLD). Resting-state connectivity in healthy adult subjects was assessed using this sequence. Four echoes were acquired with a multiband acceleration of four, in order to increase spatial resolution, shorten repetition time, and reduce slice-timing effects on the ASL signal. In addition, by acquiring four echoes, advanced multi-echo independent component analysis (ME-ICA) denoising could be employed to increase the signal-to-noise ratio (SNR) and BOLD sensitivity. Seed-based and dual-regression approaches were utilized to analyze functional connectivity. Cerebral blood flow (CBF) and BOLD coupling was also evaluated by correlating the perfusion-weighted timeseries with the BOLD timeseries. These metrics were compared between single echo (E2), multi-echo combined (MEC), multi-echo combined and denoised (MECDN), and perfusion-weighted (PW) timeseries. Temporal SNR increased for the MECDN data compared to the MEC and E2 data. Connectivity also increased, in terms of correlation strength and network size, for the MECDN compared to the MEC and E2 datasets. CBF and BOLD coupling was increased in major resting-state networks, and that correlation was strongest for the MECDN datasets. These results indicate our novel MBME ASL/BOLD sequence, which collects simultaneous high-resolution ASL/BOLD data, could be a powerful tool for detecting functional connectivity and dynamic neurovascular coupling during the resting state. The collection of more than two echoes facilitates the use of ME-ICA denoising to greatly improve the quality of resting state functional connectivity MRI.

Interaction of emitted sonar pulses and simulated echoes in a false killer whale: an evoked-potential study.

PubMed

Supin, Alexander Ya; Nachtigall, Paul E; Breese, Marlee

2011-09-01

Auditory evoked potentials (AEP) were recorded during echolocation in a false killer whale Pseudorca crassidens. An electronically synthesized and played-back (simulated) echo was triggered by an emitted biosonar pulse, and its intensity was proportional to that of the emitted click. The delay and transfer factor of the echo relative to the emitted click was controlled by the operator. The echo delay varied from 2 to 16 ms (by two-fold steps), and the transfer factor varied within ranges from -45 to -30 dB at the 2-ms delay to -60 to -45 dB at the 16-ms delay. Echo-related AEPs featured amplitude dependence both on echo delay at a constant transfer factor (the longer the delay, the higher amplitude) and on echo transfer factor at a constant delay (the higher transfer factor, the higher amplitude). Conjunctional variation of the echo transfer factor and delay kept the AEP amplitude constant when the delay to transfer factor trade was from -7.1 to -8.4 dB per delay doubling. The results confirm the hypothesis that partial forward masking of the echoes by the preceding emitted sonar pulses serves as a time-varying automatic gain control in the auditory system of echolocating odontocetes. © 2011 Acoustical Society of America

Fourier Analysis and Structure Determination. Part II: Pulse NMR and NMR Imaging.

ERIC Educational Resources Information Center

Chesick, John P.

1989-01-01

Uses simple pulse NMR experiments to discuss Fourier transforms. Studies the generation of spin echoes used in the imaging procedure. Shows that pulse NMR experiments give signals that are additions of sinusoids of differing amplitudes, frequencies, and phases. (MVL)

Suppression of nuclear spin bath fluctuations in self-assembled quantum dots induced by inhomogeneous strain

PubMed Central

Chekhovich, E.A.; Hopkinson, M.; Skolnick, M.S.; Tartakovskii, A.I.

2015-01-01

Interaction with nuclear spins leads to decoherence and information loss in solid-state electron-spin qubits. One particular, ineradicable source of electron decoherence arises from decoherence of the nuclear spin bath, driven by nuclear–nuclear dipolar interactions. Owing to its many-body nature nuclear decoherence is difficult to predict, especially for an important class of strained nanostructures where nuclear quadrupolar effects have a significant but largely unknown impact. Here, we report direct measurement of nuclear spin bath coherence in individual self-assembled InGaAs/GaAs quantum dots: spin-echo coherence times in the range 1.2–4.5 ms are found. Based on these values, we demonstrate that strain-induced quadrupolar interactions make nuclear spin fluctuations much slower compared with lattice-matched GaAs/AlGaAs structures. Our findings demonstrate that quadrupolar effects can potentially be used to engineer optically active III-V semiconductor spin-qubits with a nearly noise-free nuclear spin bath, previously achievable only in nuclear spin-0 semiconductors, where qubit network interconnection and scaling are challenging. PMID:25704639

53Cr NMR study of CuCrO2 multiferroic

NASA Astrophysics Data System (ADS)

Smol'nikov, A. G.; Ogloblichev, V. V.; Verkhovskii, S. V.; Mikhalev, K. N.; Yakubovskii, A. Yu.; Kumagai, K.; Furukawa, Y.; Sadykov, A. F.; Piskunov, Yu. V.; Gerashchenko, A. P.; Barilo, S. N.; Shiryaev, S. V.

2015-11-01

The magnetically ordered phase of the CuCrO2 single crystal has been studied by the nuclear magnetic resonance (NMR) method on 53Cr nuclei in the absence of an external magnetic field. The 53Cr NMR spectrum is observed in the frequency range νres = 61-66 MHz. The shape of the spectrum depends on the delay tdel between pulses in the pulse sequence τπ/2- t del-τπ- t del-echo. The spin-spin and spin-lattice relaxation times have been measured. Components of the electric field gradient, hyperfine fields, and the magnetic moment on chromium atoms have been estimated.

Zero-field optical magnetic resonance study of phosphorus donors in 28-silicon

NASA Astrophysics Data System (ADS)

Morse, Kevin J.; Dluhy, Phillip; Huber, Julian; Salvail, Jeff Z.; Saeedi, Kamyar; Riemann, Helge; Abrosimov, Nikolay V.; Becker, Peter; Pohl, Hans-Joachim; Simmons, S.; Thewalt, M. L. W.

2018-03-01

Donor spins in silicon are some of the most promising qubits for upcoming solid-state quantum technologies. The nuclear spins of phosphorus donors in enriched silicon have among the longest coherence times of any solid-state system as well as simultaneous high fidelity qubit initialization, manipulation, and readout. Here we characterize the phosphorus in silicon system in the regime of "zero" magnetic field, where a singlet-triplet spin clock transition can be accessed, using laser spectroscopy and magnetic resonance methods. We show the system can be optically hyperpolarized and has ˜10 s Hahn echo coherence times, even for applied static magnetic fields below Earth's field.

Lock-in detection for pulsed electrically detected magnetic resonance

NASA Astrophysics Data System (ADS)

Hoehne, Felix; Dreher, Lukas; Behrends, Jan; Fehr, Matthias; Huebl, Hans; Lips, Klaus; Schnegg, Alexander; Suckert, Max; Stutzmann, Martin; Brandt, Martin S.

2012-04-01

We show that in pulsed electrically detected magnetic resonance (pEDMR) signal modulation in combination with a lock-in detection scheme can reduce the low-frequency noise level by one order of magnitude and in addition removes the microwave-induced non-resonant background. This is exemplarily demonstrated for spin-echo measurements in phosphorus-doped silicon. The modulation of the signal is achieved by cycling the phase of the projection pulse used in pEDMR for the readout of the spin state.

Preoperative detection of malignant liver tumors: Comparison of 3D-T2-weighted sequences with T2-weighted turbo spin-echo and single shot T2 at 1.5 T.

PubMed

Barat, Maxime; Soyer, Philippe; Dautry, Raphael; Pocard, Marc; Lo-Dico, Rea; Najah, Haythem; Eveno, Clarisse; Cassinotto, Christophe; Dohan, Anthony

2018-03-01

To assess the performances of three-dimensional (3D)-T2-weighted sequences compared to standard T2-weighted turbo spin echo (T2-TSE), T2-half-Fourier acquisition single-shot turbo spin-echo (T2-HASTE), diffusion weighted imaging (DWI) and 3D-T1-weighted VIBE sequences in the preoperative detection of malignant liver tumors. From 2012 to 2015, all patients of our institution undergoing magnetic resonance imaging (MRI) examination for suspected malignant liver tumors were prospectively included. Patients had contrast-enhanced 3D-T1-weighted, DWI, 3D-T2-SPACE, T2-HASTE and T2-TSE sequences. Imaging findings were compared with those obtained at follow-up, surgery and histopathological analysis. Sensitivities for the detection of malignant liver tumors were compared for each sequence using McNemar test. A subgroup analysis was conducted for HCCs. Image artifacts were analyzed and compared using Wilcoxon paired signed rank-test. Thirty-three patients were included: 13 patients had 40 hepatocellular carcinomas (HCC) and 20 had 54 liver metastases. 3D-T2-weighted sequences had a higher sensitivity than T2-weighted TSE sequences for the detection of malignant liver tumors (79.8% versus 68.1%; P < 0.001). The difference did not reach significance for HCC. T1-weighted VIBE and DWI had a higher sensitivity than T2-weighted sequences. 3D-T2-weighted-SPACE sequences showed significantly less artifacts than T2-weitghted TSE. 3D-T2-weighted sequences show very promising performances for the detection of liver malignant tumors compared to T2-weighted TSE sequences. Copyright © 2018 Elsevier B.V. All rights reserved.

Contrast-enhanced fluid-attenuated inversion recovery vs. contrast-enhanced spin echo T1-weighted brain imaging.

PubMed

Falzone, Cristian; Rossi, Federica; Calistri, Maurizio; Tranquillo, Massimo; Baroni, Massimo

2008-01-01

In humans, contrast-enhanced fluid-attenuated inversion recovery (FLAIR) imaging plays an important role in detecting brain disease. The aim of this study was to define the clinical utility of contrast-enhanced FLAIR imaging by comparing the results with those with contrast-enhanced spin echo T1-weighted images (SE T1WI) in animals with different brain disorders. Forty-one dogs and five cats with a clinical suspicion of brain disease and 30 normal animals (25 dogs and five cats) were evaluated using a 0.2 T permanent magnet. Before contrast medium injection, spin echo T1-weighted, SE T1WI, and FLAIR sequences were acquired in three planes. SE T1WI and FLAIR images were also acquired after gadolinium injection. Sensitivity in detecting the number, location, margin, and enhancement pattern and rate were evaluated. No lesions were found in a normal animal. In affected animals, 48 lesions in 34 patients were detected in contrast-enhanced SE T1WI whereas 81 lesions in 44 patients were detected in contrast-enhanced FLAIR images. There was no difference in the characteristics of the margins or enhancement pattern of the detected lesions. The objective enhancement rate, the mean value between lesion-to-white matter ratio and lesion-to-gray matter ratio, although representing an overlap of T1 and T2 effects and not pure contrast medium shortening of T1 relaxation, was better in contrast-enhanced FLAIR images. These results suggest a superiority of contrast-enhanced FLAIR images as compared with contrast-enhanced SE T1WI in detecting enhancing brain lesions.

Measuring small compartment dimensions by probing diffusion dynamics via Non-uniform Oscillating-Gradient Spin-Echo (NOGSE) NMR.

PubMed

Shemesh, Noam; Alvarez, Gonzalo A; Frydman, Lucio

2013-12-01

Noninvasive measurements of microstructure in materials, cells, and in biological tissues, constitute a unique capability of gradient-assisted NMR. Diffusion-diffraction MR approaches pioneered by Callaghan demonstrated this ability; Oscillating-Gradient Spin-Echo (OGSE) methodologies tackle the demanding gradient amplitudes required for observing diffraction patterns by utilizing constant-frequency oscillating gradient pairs that probe the diffusion spectrum, D(ω). Here we present a new class of diffusion MR experiments, termed Non-uniform Oscillating-Gradient Spin-Echo (NOGSE), which dynamically probe multiple frequencies of the diffusion spectral density at once, thus affording direct microstructural information on the compartment's dimension. The NOGSE methodology applies N constant-amplitude gradient oscillations; N-1 of these oscillations are spaced by a characteristic time x, followed by a single gradient oscillation characterized by a time y, such that the diffusion dynamics is probed while keeping (N-1)x+y≡TNOGSE constant. These constant-time, fixed-gradient-amplitude, multi-frequency attributes render NOGSE particularly useful for probing small compartment dimensions with relatively weak gradients - alleviating difficulties associated with probing D(ω) frequency-by-frequency or with varying relaxation weightings, as in other diffusion-monitoring experiments. Analytical descriptions of the NOGSE signal are given, and the sequence's ability to extract small compartment sizes with a sensitivity towards length to the sixth power, is demonstrated using a microstructural phantom. Excellent agreement between theory and experiments was evidenced even upon applying weak gradient amplitudes. An MR imaging version of NOGSE was also implemented in ex vivo pig spinal cords and mouse brains, affording maps based on compartment sizes. The effects of size distributions on NOGSE are also briefly analyzed. Copyright © 2013 Elsevier Inc. All rights reserved.

Evaluation of a multiple spin- and gradient-echo (SAGE) EPI acquisition with SENSE acceleration: applications for perfusion imaging in and outside the brain.

PubMed

Skinner, Jack T; Robison, Ryan K; Elder, Christopher P; Newton, Allen T; Damon, Bruce M; Quarles, C Chad

2014-12-01

Perfusion-based changes in MR signal intensity can occur in response to the introduction of exogenous contrast agents and endogenous tissue properties (e.g. blood oxygenation). MR measurements aimed at capturing these changes often implement single-shot echo planar imaging (ssEPI). In recent years ssEPI readouts have been combined with parallel imaging (PI) to allow fast dynamic multi-slice imaging as well as the incorporation of multiple echoes. A multiple spin- and gradient-echo (SAGE) EPI acquisition has recently been developed to allow measurement of transverse relaxation rate (R2 and R2(*)) changes in dynamic susceptibility contrast (DSC)-MRI experiments in the brain. With SAGE EPI, the use of PI can influence image quality, temporal resolution, and achievable echo times. The effect of PI on dynamic SAGE measurements, however, has not been evaluated. In this work, a SAGE EPI acquisition utilizing SENSE PI and partial Fourier (PF) acceleration was developed and evaluated. Voxel-wise measures of R2 and R2(*) in healthy brain were compared using SAGE EPI and conventional non-EPI multiple echo acquisitions with varying SENSE and PF acceleration. A conservative SENSE factor of 2 with PF factor of 0.73 was found to provide accurate measures of R2 and R2(*) in white (WM) (rR2=[0.55-0.79], rR2*=[0.47-0.71]) and gray (GM) matter (rR2=[0.26-0.59], rR2*=[0.39-0.74]) across subjects. The combined use of SENSE and PF allowed the first dynamic SAGE EPI measurements in muscle, with a SENSE factor of 3 and PF factor of 0.6 providing reliable relaxation rate estimates when compared to multi-echo methods. Application of the optimized SAGE protocol in DSC-MRI of high-grade glioma patients provided T1 leakage-corrected estimates of CBV and CBF as well as mean vessel diameter (mVD) and simultaneous measures of DCE-MRI parameters K(trans) and ve. Likewise, application of SAGE in a muscle reperfusion model allowed dynamic measures of R2', a parameter that has been shown to correlate with muscle oxy-hemoglobin saturation. Copyright © 2014 Elsevier Inc. All rights reserved.

Autoregressive moving average modeling for spectral parameter estimation from a multigradient echo chemical shift acquisition

PubMed Central

Taylor, Brian A.; Hwang, Ken-Pin; Hazle, John D.; Stafford, R. Jason

2009-01-01

The authors investigated the performance of the iterative Steiglitz–McBride (SM) algorithm on an autoregressive moving average (ARMA) model of signals from a fast, sparsely sampled, multiecho, chemical shift imaging (CSI) acquisition using simulation, phantom, ex vivo, and in vivo experiments with a focus on its potential usage in magnetic resonance (MR)-guided interventions. The ARMA signal model facilitated a rapid calculation of the chemical shift, apparent spin-spin relaxation time (T2*), and complex amplitudes of a multipeak system from a limited number of echoes (≤16). Numerical simulations of one- and two-peak systems were used to assess the accuracy and uncertainty in the calculated spectral parameters as a function of acquisition and tissue parameters. The measured uncertainties from simulation were compared to the theoretical Cramer–Rao lower bound (CRLB) for the acquisition. Measurements made in phantoms were used to validate the T2* estimates and to validate uncertainty estimates made from the CRLB. We demonstrated application to real-time MR-guided interventions ex vivo by using the technique to monitor a percutaneous ethanol injection into a bovine liver and in vivo to monitor a laser-induced thermal therapy treatment in a canine brain. Simulation results showed that the chemical shift and amplitude uncertainties reached their respective CRLB at a signal-to-noise ratio (SNR)≥5 for echo train lengths (ETLs)≥4 using a fixed echo spacing of 3.3 ms. T2* estimates from the signal model possessed higher uncertainties but reached the CRLB at larger SNRs and∕or ETLs. Highly accurate estimates for the chemical shift (<0.01 ppm) and amplitude (<1.0%) were obtained with ≥4 echoes and for T2* (<1.0%) with ≥7 echoes. We conclude that, over a reasonable range of SNR, the SM algorithm is a robust estimator of spectral parameters from fast CSI acquisitions that acquire ≤16 echoes for one- and two-peak systems. Preliminary ex vivo and in vivo experiments corroborated the results from simulation experiments and further indicate the potential of this technique for MR-guided interventional procedures with high spatiotemporal resolution ∼1.6×1.6×4 mm3 in ≤5 s. PMID:19378736

Steer-PROP: a GRASE-PROPELLER sequence with interecho steering gradient pulses.

PubMed

Srinivasan, Girish; Rangwala, Novena; Zhou, Xiaohong Joe

2018-05-01

This study demonstrates a novel PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) pulse sequence, termed Steer-PROP, based on gradient and spin echo (GRASE), to reduce the imaging times and address phase errors inherent to GRASE. The study also illustrates the feasibility of using Steer-PROP as an alternative to single-shot echo planar imaging (SS-EPI) to produce distortion-free diffusion images in all imaging planes. Steer-PROP uses a series of blip gradient pulses to produce N (N = 3-5) adjacent k-space blades in each repetition time, where N is the number of gradient echoes in a GRASE sequence. This sampling strategy enables a phase correction algorithm to systematically address the GRASE phase errors as well as the motion-induced phase inconsistency. Steer-PROP was evaluated on phantoms and healthy human subjects at both 1.5T and 3.0T for T 2 - and diffusion-weighted imaging. Steer-PROP produced similar image quality as conventional PROPELLER based on fast spin echo (FSE), while taking only a fraction (e.g., 1/3) of the scan time. The robustness against motion in Steer-PROP was comparable to that of FSE-based PROPELLER. Using Steer-PROP, high quality and distortion-free diffusion images were obtained from human subjects in all imaging planes, demonstrating a considerable advantage over SS-EPI. The proposed Steer-PROP sequence can substantially reduce the scan times compared with FSE-based PROPELLER while achieving adequate image quality. The novel k-space sampling strategy in Steer-PROP not only enables an integrated phase correction method that addresses various sources of phase errors, but also minimizes the echo spacing compared with alternative sampling strategies. Steer-PROP can also be a viable alternative to SS-EPI to decrease image distortion in all imaging planes. Magn Reson Med 79:2533-2541, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Application of Modified Spin-Echo–based Sequences for Hepatic MR Elastography: Evaluation, Comparison with the Conventional Gradient-Echo Sequence, and Preliminary Clinical Experience

PubMed Central

Mariappan, Yogesh K.; Dzyubak, Bogdan; Glaser, Kevin J.; Venkatesh, Sudhakar K.; Sirlin, Claude B.; Hooker, Jonathan; McGee, Kiaran P.

2017-01-01

Purpose To (a) evaluate modified spin-echo (SE) magnetic resonance (MR) elastographic sequences for acquiring MR images with improved signal-to-noise ratio (SNR) in patients in whom the standard gradient-echo (GRE) MR elastographic sequence yields low hepatic signal intensity and (b) compare the stiffness values obtained with these sequences with those obtained with the conventional GRE sequence. Materials and Methods This HIPAA-compliant retrospective study was approved by the institutional review board; the requirement to obtain informed consent was waived. Data obtained with modified SE and SE echo-planar imaging (EPI) MR elastographic pulse sequences with short echo times were compared with those obtained with the conventional GRE MR elastographic sequence in two patient cohorts, one that exhibited adequate liver signal intensity and one that exhibited low liver signal intensity. Shear stiffness values obtained with the three sequences in 130 patients with successful GRE-based examinations were retrospectively tested for statistical equivalence by using a 5% margin. In 47 patients in whom GRE examinations were considered to have failed because of low SNR, the SNR and confidence level with the SE-based sequences were compared with those with the GRE sequence. Results The results of this study helped confirm the equivalence of SE MR elastography and SE-EPI MR elastography to GRE MR elastography (P = .0212 and P = .0001, respectively). The SE and SE-EPI MR elastographic sequences provided substantially improved SNR and stiffness inversion confidence level in 47 patients in whom GRE MR elastography had failed. Conclusion Modified SE-based MR elastographic sequences provide higher SNR MR elastographic data and reliable stiffness measurements; thus, they enable quantification of stiffness in patients in whom the conventional GRE MR elastographic sequence failed owing to low signal intensity. The equivalence of the three sequences indicates that the current diagnostic thresholds are applicable to SE MR elastographic sequences for assessing liver fibrosis. © RSNA, 2016 PMID:27509543

Detection of single electron spin resonance in a double quantum dota)

NASA Astrophysics Data System (ADS)

Koppens, F. H. L.; Buizert, C.; Vink, I. T.; Nowack, K. C.; Meunier, T.; Kouwenhoven, L. P.; Vandersypen, L. M. K.

2007-04-01

Spin-dependent transport measurements through a double quantum dot are a valuable tool for detecting both the coherent evolution of the spin state of a single electron, as well as the hybridization of two-electron spin states. In this article, we discuss a model that describes the transport cycle in this regime, including the effects of an oscillating magnetic field (causing electron spin resonance) and the effective nuclear fields on the spin states in the two dots. We numerically calculate the current flow due to the induced spin flips via electron spin resonance, and we study the detector efficiency for a range of parameters. The experimental data are compared with the model and we find a reasonable agreement.

Highly selective detection of individual nuclear spins with rotary echo on an electron spin probe

DOE PAGES

Mkhitaryan, V. V.; Jelezko, F.; Dobrovitski, V. V.

2015-10-26

We consider an electronic spin, such as a nitrogen-vacancy center in diamond, weakly coupled to a large number of nuclear spins, and subjected to the Rabi driving with a periodically alternating phase. We show that by switching the driving phase synchronously with the precession of a given nuclear spin, the interaction to this spin is selectively enhanced, while the rest of the bath remains decoupled. The enhancement is of resonant character. The key feature of the suggested scheme is that the width of the resonance is adjustable, and can be greatly decreased by increasing the driving strength. Thus, the resonancemore » can be significantly narrowed, by a factor of 10–100 in comparison with the existing detection methods. Significant improvement in selectivity is explained analytically and confirmed by direct numerical many-spin simulations. As a result, the method can be applied to a wide range of solid-state systems.« less

Neutron spin-echo studies on dynamic and static fluctuations in two types of poly(vinyl alcohol) gels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kanaya, T.; Takahashi, N.; Nishida, K.

2005-01-01

We report neutron spin-echo measurements on two types of poly(vinyl alcohol) (PVA) gels. The first is PVA gel in a mixture of dimethyl sulfoxide (DMSO) and water with volume ratio 60/40, and the second is PVA gel in an aqueous borax solution. The observed normalized intermediate scattering functions I(Q,t)/I(Q,0) are very different between them. The former I(Q,t)/I(Q,0) shows a nondecaying component in addition to a fast decay, but the latter does not have the nondecaying one. This clearly indicates that the fluctuations in the former PVA gel consist of static and dynamic fluctuations whereas the latter PVA gel does includemore » only the dynamic fluctuations. The dynamic fluctuations of the former and latter gels have been analyzed in terms of a restricted motion in the network and Zimm motion, respectively, and the origins of these motions will be discussed.« less

Dynamic and static fluctuations in polymer gels studied by neutron spin-echo

NASA Astrophysics Data System (ADS)

Kanaya, T.; Takahashi, N.; Nishida, K.; Seto, H.; Nagao, M.; Takeba, Y.

2006-11-01

We report neutron spin-echo measurements on three types of poly(vinyl alcohol) (PVA) gels. The first is PVA gel in a mixture of dimethyl sulfoxide (DMSO) and water with volume ratio 60/40, the second is PVA gel in an aqueous borax solution and the third is chemically cross-linked PVA gel. The observed normalized intermediate scattering functions I( Q, t)/ I( Q,0) were very different among them. The I( Q, t)/ I( Q,0) of the first and third gels showed a non-decaying component in addition to a decaying component, but the second one did not have the non-decaying one. This clearly indicates that the fluctuations in the first and third PVA gels consist of static and dynamic fluctuations whereas the second PVA gel does include only the dynamic fluctuations. The dynamic and static fluctuations of the PVA gels were analyzed in terms of a restricted motion in the gel network and the Zimm motion, respectively.

Motion Correction in PROPELLER and Turboprop-MRI

PubMed Central

Tamhane, Ashish A.; Arfanakis, Konstantinos

2009-01-01

PROPELLER and Turboprop-MRI are characterized by greatly reduced sensitivity to motion, compared to their predecessors, fast spin-echo and gradient and spin-echo, respectively. This is due to the inherent self-navigation and motion correction of PROPELLER-based techniques. However, it is unknown how various acquisition parameters that determine k-space sampling affect the accuracy of motion correction in PROPELLER and Turboprop-MRI. The goal of this work was to evaluate the accuracy of motion correction in both techniques, to identify an optimal rotation correction approach, and determine acquisition strategies for optimal motion correction. It was demonstrated that, blades with multiple lines allow more accurate estimation of motion than blades with fewer lines. Also, it was shown that Turboprop-MRI is less sensitive to motion than PROPELLER. Furthermore, it was demonstrated that the number of blades does not significantly affect motion correction. Finally, clinically appropriate acquisition strategies that optimize motion correction were discussed for PROPELLER and Turboprop-MRI. PMID:19365858

Classical analogs for Rabi-oscillations, Ramsey-fringes, and spin-echo in Josephson junctions

NASA Astrophysics Data System (ADS)

Marchese, J. E.; Cirillo, M.; Grønbech-Jensen, N.

2007-08-01

We investigate the results of recently published experiments on the quantum behavior of Josephson circuits in terms of the classical modeling based on the resistively and capacitively-shunted (RCSJ) junction model. Our analysis shows evidence for a close analogy between the nonlinear behavior of a pulsed microwave-driven Josephson junction at low temperature and low dissipation and the experimental observations reported for the Josephson circuits. Specifically, we demonstrate that Rabi-oscillations, Ramsey-fringes, and spin-echo observations are not phenomena with a unique quantum interpretation. In fact, they are natural consequences of transients to phase-locking in classical nonlinear dynamics and can be observed in a purely classical model of a Josephson junction when the experimental recipe for the application of microwaves is followed and the experimental detection scheme followed. We therefore conclude that classical nonlinear dynamics can contribute to the understanding of relevant experimental observations of Josephson response to various microwave perturbations at very low temperature and low dissipation.

Universality of the helimagnetic transition in cubic chiral magnets: Small angle neutron scattering and neutron spin echo spectroscopy studies of FeCoSi

NASA Astrophysics Data System (ADS)

Bannenberg, L. J.; Kakurai, K.; Falus, P.; Lelièvre-Berna, E.; Dalgliesh, R.; Dewhurst, C. D.; Qian, F.; Onose, Y.; Endoh, Y.; Tokura, Y.; Pappas, C.

2017-04-01

We present a comprehensive small angle neutron scattering and neutron spin echo spectroscopy study of the structural and dynamical aspects of the helimagnetic transition in Fe1 -xCoxSi with x =0.30 . In contrast to the sharp transition observed in the archetype chiral magnet MnSi, the transition in Fe1 -xCoxSi is gradual, and long-range helimagnetic ordering coexists with short-range correlations over a wide temperature range. The dynamics are more complex than in MnSi and involve long relaxation times with a stretched exponential relaxation which persists even under magnetic field. These results in conjunction with an analysis of the hierarchy of the relevant length scales show that the helimagnetic transition in Fe1 -xCoxSi differs substantially from the transition in MnSi and question the validity of a universal approach to the helimagnetic transition in chiral magnets.

Self-diffusion imaging by spin echo in Earth's magnetic field.

PubMed

Mohoric, A; Stepisnik, J; Kos, M; Planinsi

1999-01-01

The NMR of the Earth's magnetic field is used for diffusion-weighted imaging of phantoms. Due to a weak Larmor field, care needs to be taken regarding the use of the usual high field assumption in calculating the effect of the applied inhomogeneous magnetic field. The usual definition of the magnetic field gradient must be replaced by a generalized formula valid when the strength of a nonuniform magnetic field and a Larmor field are comparable (J. Stepisnik, Z. Phys. Chem. 190, 51-62 (1995)). It turns out that the expression for spin echo attenuation is identical to the well-known Torrey formula only when the applied nonuniform field has a proper symmetry. This kind of problem may occur in a strong Larmor field as well as when the slow diffusion rate of particles needs an extremely strong gradient to be applied. The measurements of the geomagnetic field NMR demonstrate the usefulness of the method for diffusion and flow-weighted imaging. Copyright 1999 Academic Press.

Anomalous Diffusion Measured by a Twice-Refocused Spin Echo Pulse Sequence: Analysis Using Fractional Order Calculus

PubMed Central

2011-01-01

Purpose To theoretically develop and experimentally validate a formulism based on a fractional order calculus (FC) diffusion model to characterize anomalous diffusion in brain tissues measured with a twice-refocused spin-echo (TRSE) pulse sequence. Materials and Methods The FC diffusion model is the fractional order generalization of the Bloch-Torrey equation. Using this model, an analytical expression was derived to describe the diffusion-induced signal attenuation in a TRSE pulse sequence. To experimentally validate this expression, a set of diffusion-weighted (DW) images was acquired at 3 Tesla from healthy human brains using a TRSE sequence with twelve b-values ranging from 0 to 2,600 s/mm2. For comparison, DW images were also acquired using a Stejskal-Tanner diffusion gradient in a single-shot spin-echo echo planar sequence. For both datasets, a Levenberg-Marquardt fitting algorithm was used to extract three parameters: diffusion coefficient D, fractional order derivative in space β, and a spatial parameter μ (in units of μm). Using adjusted R-squared values and standard deviations, D, β and μ values and the goodness-of-fit in three specific regions of interest (ROI) in white matter, gray matter, and cerebrospinal fluid were evaluated for each of the two datasets. In addition, spatially resolved parametric maps were assessed qualitatively. Results The analytical expression for the TRSE sequence, derived from the FC diffusion model, accurately characterized the diffusion-induced signal loss in brain tissues at high b-values. In the selected ROIs, the goodness-of-fit and standard deviations for the TRSE dataset were comparable with the results obtained from the Stejskal-Tanner dataset, demonstrating the robustness of the FC model across multiple data acquisition strategies. Qualitatively, the D, β, and μ maps from the TRSE dataset exhibited fewer artifacts, reflecting the improved immunity to eddy currents. Conclusion The diffusion-induced signal attenuation in a TRSE pulse sequence can be described by an FC diffusion model at high b-values. This model performs equally well for data acquired from the human brain tissues with a TRSE pulse sequence or a conventional Stejskal-Tanner sequence. PMID:21509877

Anomalous diffusion measured by a twice-refocused spin echo pulse sequence: analysis using fractional order calculus.

PubMed

Gao, Qing; Srinivasan, Girish; Magin, Richard L; Zhou, Xiaohong Joe

2011-05-01

To theoretically develop and experimentally validate a formulism based on a fractional order calculus (FC) diffusion model to characterize anomalous diffusion in brain tissues measured with a twice-refocused spin-echo (TRSE) pulse sequence. The FC diffusion model is the fractional order generalization of the Bloch-Torrey equation. Using this model, an analytical expression was derived to describe the diffusion-induced signal attenuation in a TRSE pulse sequence. To experimentally validate this expression, a set of diffusion-weighted (DW) images was acquired at 3 Tesla from healthy human brains using a TRSE sequence with twelve b-values ranging from 0 to 2600 s/mm(2). For comparison, DW images were also acquired using a Stejskal-Tanner diffusion gradient in a single-shot spin-echo echo planar sequence. For both datasets, a Levenberg-Marquardt fitting algorithm was used to extract three parameters: diffusion coefficient D, fractional order derivative in space β, and a spatial parameter μ (in units of μm). Using adjusted R-squared values and standard deviations, D, β, and μ values and the goodness-of-fit in three specific regions of interest (ROIs) in white matter, gray matter, and cerebrospinal fluid, respectively, were evaluated for each of the two datasets. In addition, spatially resolved parametric maps were assessed qualitatively. The analytical expression for the TRSE sequence, derived from the FC diffusion model, accurately characterized the diffusion-induced signal loss in brain tissues at high b-values. In the selected ROIs, the goodness-of-fit and standard deviations for the TRSE dataset were comparable with the results obtained from the Stejskal-Tanner dataset, demonstrating the robustness of the FC model across multiple data acquisition strategies. Qualitatively, the D, β, and μ maps from the TRSE dataset exhibited fewer artifacts, reflecting the improved immunity to eddy currents. The diffusion-induced signal attenuation in a TRSE pulse sequence can be described by an FC diffusion model at high b-values. This model performs equally well for data acquired from the human brain tissues with a TRSE pulse sequence or a conventional Stejskal-Tanner sequence. Copyright © 2011 Wiley-Liss, Inc.

Field tuning the g factor in InAs nanowire double quantum dots.

PubMed

Schroer, M D; Petersson, K D; Jung, M; Petta, J R

2011-10-21

We study the effects of magnetic and electric fields on the g factors of spins confined in a two-electron InAs nanowire double quantum dot. Spin sensitive measurements are performed by monitoring the leakage current in the Pauli blockade regime. Rotations of single spins are driven using electric-dipole spin resonance. The g factors are extracted from the spin resonance condition as a function of the magnetic field direction, allowing determination of the full g tensor. Electric and magnetic field tuning can be used to maximize the g-factor difference and in some cases altogether quench the electric-dipole spin resonance response, allowing selective single spin control. © 2011 American Physical Society

The Spin-Plane Double Probe Electric Field Instrument for MMS

NASA Astrophysics Data System (ADS)

Lindqvist, P.-A.; Olsson, G.; Torbert, R. B.; King, B.; Granoff, M.; Rau, D.; Needell, G.; Turco, S.; Dors, I.; Beckman, P.; Macri, J.; Frost, C.; Salwen, J.; Eriksson, A.; Åhlén, L.; Khotyaintsev, Y. V.; Porter, J.; Lappalainen, K.; Ergun, R. E.; Wermeer, W.; Tucker, S.

2016-03-01

The Spin-plane double probe instrument (SDP) is part of the FIELDS instrument suite of the Magnetospheric Multiscale mission (MMS). Together with the Axial double probe instrument (ADP) and the Electron Drift Instrument (EDI), SDP will measure the 3-D electric field with an accuracy of 0.5 mV/m over the frequency range from DC to 100 kHz. SDP consists of 4 biased spherical probes extended on 60 m long wire booms 90∘ apart in the spin plane, giving a 120 m baseline for each of the two spin-plane electric field components. The mechanical and electrical design of SDP is described, together with results from ground tests and calibration of the instrument.

Double line groups: structure, irreducible representations and spin splitting of the bands

NASA Astrophysics Data System (ADS)

Lazić, N.; Milivojević, M.; Vuković, T.; Damnjanović, M.

2018-06-01

Double line groups are derived, structurally examined and classified within 13 infinite families. Their irreducible representations, found and tabulated, single out the complete set of conserved quantum numbers in fermionic quasi-one-dimensional systems possessing either translational periodicity or incommensurate helical symmetry. Spin–orbit interaction is analyzed: the induced orbital band splitting and the consequent removal of the spin degeneracy are completely explained. Being incompatible with vertical mirror symmetry, as well as with simultaneous invariance under time-reversal and horizontal (roto)reflections, spin splitting and spin polarized currents may occur only in the systems with the first and the fifth family double line group symmetry. The effects are illustrated on carbon nanotubes.

Application of phase consistency to improve time efficiency and image quality in dual echo black-blood carotid angiography.

PubMed

Kholmovski, Eugene G; Parker, Dennis L

2005-07-01

There is a considerable similarity between proton density-weighted (PDw) and T2-weighted (T2w) images acquired by dual echo fast spin-echo (FSE) sequences. The similarity manifests itself not only in image space as correspondence between intensities of PDw and T2w images, but also in phase space as consistency between phases of PDw and T2w images. Methods for improving the imaging efficiency and image quality of dual echo FSE sequences based on this feature have been developed. The total scan time of dual echo FSE acquisition may be reduced by as much as 25% by incorporating an estimate of the image phase from a fully sampled PDw image when reconstructing partially sampled T2w images. The quality of T2w images acquired using phased array coils may be significantly improved by using the developed noise reduction reconstruction scheme, which is based on the correspondence between the PDw and T2w image intensities and the consistency between the PDw and T2w image phases. Studies of phantom and human subject MRI data were performed to evaluate the effectiveness of the techniques.

X-PROP: a fast and robust diffusion-weighted propeller technique.

PubMed

Li, Zhiqiang; Pipe, James G; Lee, Chu-Yu; Debbins, Josef P; Karis, John P; Huo, Donglai

2011-08-01

Diffusion-weighted imaging (DWI) has shown great benefits in clinical MR exams. However, current DWI techniques have shortcomings of sensitivity to distortion or long scan times or combinations of the two. Diffusion-weighted echo-planar imaging (EPI) is fast but suffers from severe geometric distortion. Periodically rotated overlapping parallel lines with enhanced reconstruction diffusion-weighted imaging (PROPELLER DWI) is free of geometric distortion, but the scan time is usually long and imposes high Specific Absorption Rate (SAR) especially at high fields. TurboPROP was proposed to accelerate the scan by combining signal from gradient echoes, but the off-resonance artifacts from gradient echoes can still degrade the image quality. In this study, a new method called X-PROP is presented. Similar to TurboPROP, it uses gradient echoes to reduce the scan time. By separating the gradient and spin echoes into individual blades and removing the off-resonance phase, the off-resonance artifacts in X-PROP are minimized. Special reconstruction processes are applied on these blades to correct for the motion artifacts. In vivo results show its advantages over EPI, PROPELLER DWI, and TurboPROP techniques. Copyright © 2011 Wiley-Liss, Inc.

Echoes from the abyss: Tentative evidence for Planck-scale structure at black hole horizons

NASA Astrophysics Data System (ADS)

Abedi, Jahed; Dykaar, Hannah; Afshordi, Niayesh

2017-10-01

In classical general relativity (GR), an observer falling into an astrophysical black hole is not expected to experience anything dramatic as she crosses the event horizon. However, tentative resolutions to problems in quantum gravity, such as the cosmological constant problem, or the black hole information paradox, invoke significant departures from classicality in the vicinity of the horizon. It was recently pointed out that such near-horizon structures can lead to late-time echoes in the black hole merger gravitational wave signals that are otherwise indistinguishable from GR. We search for observational signatures of these echoes in the gravitational wave data released by the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), following the three black hole merger events GW150914, GW151226, and LVT151012. In particular, we look for repeating damped echoes with time delays of 8 M log M (+spin corrections, in Planck units), corresponding to Planck-scale departures from GR near their respective horizons. Accounting for the "look elsewhere" effect due to uncertainty in the echo template, we find tentative evidence for Planck-scale structure near black hole horizons at false detection probability of 1% (corresponding to 2.5 σ

Quantification of glutathione transverse relaxation time T2 using echo time extension with variable refocusing selectivity and symmetry in the human brain at 7 Tesla

NASA Astrophysics Data System (ADS)

Swanberg, Kelley M.; Prinsen, Hetty; Coman, Daniel; de Graaf, Robin A.; Juchem, Christoph

2018-05-01

Glutathione (GSH) is an endogenous antioxidant implicated in numerous biological processes, including those associated with multiple sclerosis, aging, and cancer. Spectral editing techniques have greatly facilitated the acquisition of glutathione signal in living humans via proton magnetic resonance spectroscopy, but signal quantification at 7 Tesla is still hampered by uncertainty about the glutathione transverse decay rate T2 relative to those of commonly employed quantitative references like N-acetyl aspartate (NAA), total creatine, or water. While the T2 of uncoupled singlets can be derived in a straightforward manner from exponential signal decay as a function of echo time, similar estimation of signal decay in GSH is complicated by a spin system that involves both weak and strong J-couplings as well as resonances that overlap those of several other metabolites and macromolecules. Here, we extend a previously published method for quantifying the T2 of GABA, a weakly coupled system, to quantify T2 of the strongly coupled spin system glutathione in the human brain at 7 Tesla. Using full density matrix simulation of glutathione signal behavior, we selected an array of eight optimized echo times between 72 and 322 ms for glutathione signal acquisition by J-difference editing (JDE). We varied the selectivity and symmetry parameters of the inversion pulses used for echo time extension to further optimize the intensity, simplicity, and distinctiveness of glutathione signals at chosen echo times. Pairs of selective adiabatic inversion pulses replaced nonselective pulses at three extended echo times, and symmetry of the time intervals between the two extension pulses was adjusted at one extended echo time to compensate for J-modulation, thereby resulting in appreciable signal-to-noise ratio and quantifiable signal shapes at all measured points. Glutathione signal across all echo times fit smooth monoexponential curves over ten scans of occipital cortex voxels in nine subjects. The T2 of glutathione was calculated to be 145.0 ± 20.1 ms (mean ± standard deviation); this result was robust within one standard deviation to changes in metabolite fitting baseline corrections and removal of individual data points on the signal decay curve. The measured T2 of NAA (222.1 ± 24.7 ms) and total creatine (153.0 ± 19.9 ms) were both higher than that calculated for GSH. Apparent glutathione concentration quantified relative to both reference metabolites increased by up to 32% and 6%, respectively, upon correction with calculated T2 values, emphasizing the importance of considering T2 relaxation differences in the spectroscopic measurement of these metabolites, especially at longer echo times.

Quantification of glutathione transverse relaxation time T2 using echo time extension with variable refocusing selectivity and symmetry in the human brain at 7 Tesla.

PubMed

Swanberg, Kelley M; Prinsen, Hetty; Coman, Daniel; de Graaf, Robin A; Juchem, Christoph

2018-05-01

Glutathione (GSH) is an endogenous antioxidant implicated in numerous biological processes, including those associated with multiple sclerosis, aging, and cancer. Spectral editing techniques have greatly facilitated the acquisition of glutathione signal in living humans via proton magnetic resonance spectroscopy, but signal quantification at 7 Tesla is still hampered by uncertainty about the glutathione transverse decay rate T 2 relative to those of commonly employed quantitative references like N-acetyl aspartate (NAA), total creatine, or water. While the T 2 of uncoupled singlets can be derived in a straightforward manner from exponential signal decay as a function of echo time, similar estimation of signal decay in GSH is complicated by a spin system that involves both weak and strong J-couplings as well as resonances that overlap those of several other metabolites and macromolecules. Here, we extend a previously published method for quantifying the T 2 of GABA, a weakly coupled system, to quantify T 2 of the strongly coupled spin system glutathione in the human brain at 7 Tesla. Using full density matrix simulation of glutathione signal behavior, we selected an array of eight optimized echo times between 72 and 322 ms for glutathione signal acquisition by J-difference editing (JDE). We varied the selectivity and symmetry parameters of the inversion pulses used for echo time extension to further optimize the intensity, simplicity, and distinctiveness of glutathione signals at chosen echo times. Pairs of selective adiabatic inversion pulses replaced nonselective pulses at three extended echo times, and symmetry of the time intervals between the two extension pulses was adjusted at one extended echo time to compensate for J-modulation, thereby resulting in appreciable signal-to-noise ratio and quantifiable signal shapes at all measured points. Glutathione signal across all echo times fit smooth monoexponential curves over ten scans of occipital cortex voxels in nine subjects. The T 2 of glutathione was calculated to be 145.0 ± 20.1 ms (mean ± standard deviation); this result was robust within one standard deviation to changes in metabolite fitting baseline corrections and removal of individual data points on the signal decay curve. The measured T 2 of NAA (222.1 ± 24.7 ms) and total creatine (153.0 ± 19.9 ms) were both higher than that calculated for GSH. Apparent glutathione concentration quantified relative to both reference metabolites increased by up to 32% and 6%, respectively, upon correction with calculated T 2 values, emphasizing the importance of considering T 2 relaxation differences in the spectroscopic measurement of these metabolites, especially at longer echo times. Copyright © 2018 Elsevier Inc. All rights reserved.

GRE T2∗-Weighted MRI: Principles and Clinical Applications

PubMed Central

Tang, Meng Yue; Chen, Tian Wu; Zhang, Xiao Ming; Huang, Xiao Hua

2014-01-01

The sequence of a multiecho gradient recalled echo (GRE) T2*-weighted imaging (T2*WI) is a relatively new magnetic resonance imaging (MRI) technique. In contrast to T2 relaxation, which acquires a spin echo signal, T2* relaxation acquires a gradient echo signal. The sequence of a GRE T2*WI requires high uniformity of the magnetic field. GRE T2*WI can detect the smallest changes in uniformity in the magnetic field and can improve the rate of small lesion detection. In addition, the T2* value can indirectly reflect changes in tissue biochemical components. Moreover, it can be used for the early diagnosis and quantitative diagnosis of some diseases. This paper reviews the principles and clinical applications as well as the advantages and disadvantages of GRE T2*WI. PMID:24987676

Effect of the δ-potential on spin-dependent electron tunneling in double barrier semiconductor heterostructure

NASA Astrophysics Data System (ADS)

Chandrasekar, L. Bruno; Gnanasekar, K.; Karunakaran, M.

2018-06-01

The effect of δ-potential was studied in GaAs/Ga0.6Al0·4As double barrier heterostructure with Dresselhaus spin-orbit interaction. The role of barrier height and position of the δ- potential in the well region was analysed on spin-dependent electron tunneling using transfer matrix method. The spin-separation between spin-resonances on energy scale depends on both height and position of the δ- potential, whereas the tunneling life time of electrons highly influenced by the position of the δ- potential and not on the height. These results might be helpful for the fabrication of spin-filters.

Quadratic integrand double-hybrid made spin-component-scaled

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brémond, Éric, E-mail: eric.bremond@iit.it; Savarese, Marika; Sancho-García, Juan C.

2016-03-28

We propose two analytical expressions aiming to rationalize the spin-component-scaled (SCS) and spin-opposite-scaled (SOS) schemes for double-hybrid exchange-correlation density-functionals. Their performances are extensively tested within the framework of the nonempirical quadratic integrand double-hybrid (QIDH) model on energetic properties included into the very large GMTKN30 benchmark database, and on structural properties of semirigid medium-sized organic compounds. The SOS variant is revealed as a less computationally demanding alternative to reach the accuracy of the original QIDH model without losing any theoretical background.

Quantum memory operations in a flux qubit - spin ensemble hybrid system

NASA Astrophysics Data System (ADS)

Saito, S.; Zhu, X.; Amsuss, R.; Matsuzaki, Y.; Kakuyanagi, K.; Shimo-Oka, T.; Mizuochi, N.; Nemoto, K.; Munro, W. J.; Semba, K.

2014-03-01

Superconducting quantum bits (qubits) are one of the most promising candidates for a future large-scale quantum processor. However for larger scale realizations the currently reported coherence times of these macroscopic objects (superconducting qubits) has not yet reached those of microscopic systems (electron spins, nuclear spins, etc). In this context, a superconductor-spin ensemble hybrid system has attracted considerable attention. The spin ensemble could operate as a quantum memory for superconducting qubits. We have experimentally demonstrated quantum memory operations in a superconductor-diamond hybrid system. An excited state and a superposition state prepared in the flux qubit can be transferred to, stored in and retrieved from the NV spin ensemble in diamond. From these experiments, we have found the coherence time of the spin ensemble is limited by the inhomogeneous broadening of the electron spin (4.4 MHz) and by the hyperfine coupling to nitrogen nuclear spins (2.3 MHz). In the future, spin echo techniques could eliminate these effects and elongate the coherence time. Our results are a significant first step in utilizing the spin ensemble as long-lived quantum memory for superconducting flux qubits. This work was supported by the FIRST program and NICT.

Role of Echocardiograghy in Treating a Case of Double Chamber Right Ventricle with Delayed Presentation

PubMed Central

Barik, Ramachandra

2017-01-01

The clinical diagnosis of double chamber right ventricle (DCRV) is not straightforward. Clinical history, clinical examination, 12-lead electrocardiogram, chest X-ray, and Echocardiography (echo) contribute to morphological diagnosis. Cardiac catheterization is essential for hemodynamic evaluation. A thorough presurgical workup helps the cardiac surgeon to choose the appropriate surgical approach and timing of surgery in an individual case. We present a case of a DCRV who presented to us in the fifth decade of life. Echo confirmed the morphological diagnosis and cardiac catheterization complemented the exact pull back gradient across the obstruction in the right ventricle. This patient was suggested muscle bundle resection and ventricular septal defect closure using right atrial approach. PMID:28465983

High Slew-Rate Head-Only Gradient for Improving Distortion in Echo Planar Imaging: Preliminary Experience

PubMed Central

Tan, Ek T.; Lee, Seung-Kyun; Weavers, Paul T.; Graziani, Dominic; Piel, Joseph E.; Shu, Yunhong; Huston, John; Bernstein, Matt A.; Foo, Thomas K.F.

2016-01-01

Purpose To investigate the effects on echo planar imaging (EPI) distortion of using high gradient slew rates (SR) of up to 700 T/m/s for in-vivo human brain imaging, with a dedicated, head-only gradient coil. Materials and Methods Simulation studies were first performed to determine the expected echo spacing and distortion reduction in EPI. A head gradient of 42-cm inner diameter and with asymmetric transverse coils was then installed in a whole-body, conventional 3T MRI system. Human subject imaging was performed on five subjects to determine the effects of EPI on echo spacing and signal dropout at various gradient slew rates. The feasibility of whole-brain imaging at 1.5 mm-isotropic spatial resolution was demonstrated with gradient-echo and spin-echo diffusion-weighted EPI. Results As compared to a whole-body gradient coil, the EPI echo spacing in the head-only gradient coil was reduced by 48%. Simulation and in vivo results, respectively, showed up to 25-26% and 19% improvement in signal dropout. Whole-brain imaging with EPI at 1.5 mm spatial resolution provided good whole-brain coverage, spatial linearity, and low spatial distortion effects. Conclusion Our results of human brain imaging with EPI using the compact head gradient coil at slew rates higher than in conventional whole-body MR systems demonstrate substantially improved image distortion, and point to a potential for benefits to non-EPI pulse sequences. PMID:26921117

Colorectal carcinoma: Ex vivo evaluation using 3-T high-spatial-resolution quantitative T2 mapping and its correlation with histopathologic findings.

PubMed

Yamada, Ichiro; Yoshino, Norio; Hikishima, Keigo; Miyasaka, Naoyuki; Yamauchi, Shinichi; Uetake, Hiroyuki; Yasuno, Masamichi; Saida, Yukihisa; Tateishi, Ukihide; Kobayashi, Daisuke; Eishi, Yoshinobu

2017-05-01

In this study, we aimed to evaluate the feasibility of determining the mural invasion depths of colorectal carcinomas using high-spatial-resolution (HSR) quantitative T2 mapping on a 3-T magnetic resonance (MR) scanner. Twenty colorectal specimens containing adenocarcinomas were imaged on a 3-T MR system equipped with a 4-channel phased-array surface coil. HSR quantitative T2 maps were acquired using a spin-echo sequence with a repetition time/echo time of 7650/22.6-361.6ms (16 echoes), 87×43.5-mm field of view, 2-mm section thickness, 448×224 matrix, and average of 1. HSR fast-spin-echo T2-weighted images were also acquired. Differences between the T2 values (ms) of the tumor tissue, colorectal wall layers, and fibrosis were measured, and the MR images and histopathologic findings were compared. In all specimens (20/20, 100%), the HSR quantitative T2 maps clearly depicted an 8-layer normal colorectal wall in which the T2 values of each layer differed from those of the adjacent layer(s) (P<0.001). Using this technique, fibrosis (73.6±9.4ms) and tumor tissue (104.2±6.4ms) could also be clearly differentiated (P<0.001). In 19 samples (95%), the HSR quantitative T2 maps and histopathologic data yielded the same findings regarding the tumor invasion depth. Our results indicate that 3-T HSR quantitative T2 mapping is useful for distinguishing colorectal wall layers and differentiating tumor and fibrotic tissues. Accordingly, this technique could be used to determine mural invasion by colorectal carcinomas with a high level of accuracy. Copyright © 2017 Elsevier Inc. All rights reserved.

Volume interpolated 3D-spoiled gradient echo sequence is better than dynamic contrast spin echo sequence for MRI detection of corticotropin secreting pituitary microadenomas.

PubMed

Kasaliwal, Rajeev; Sankhe, Shilpa S; Lila, Anurag R; Budyal, Sweta R; Jagtap, Varsha S; Sarathi, Vijaya; Kakade, Harshal; Bandgar, Tushar; Menon, Padmavathy S; Shah, Nalini S

2013-06-01

Various techniques have been attempted to increase the yield of magnetic resonance imaging (MRI) for localization of pituitary microadenomas in corticotropin (ACTH)-dependent Cushing's syndrome (CS). To compare the performance of dynamic contrast spin echo (DC-SE) and volume interpolated 3D-spoiled gradient echo (VI-SGE) MR sequences in the diagnostic evaluation of ACTH-dependent CS. Data was analysed retrospectively from a series of ACTH-dependent CS patients treated over 2-year period at a tertiary care referral centre (2009-2011). Thirty-six patients (24 female and 12 male) were diagnosed to have ACTH-dependent CS during the study period. All patients underwent MRI by both sequences during a single examination. Cases with negative and equivocal pituitary MR imaging underwent corticotropin-releasing hormone (CRH) stimulated bilateral inferior petrosal sinus sampling (BIPSS) to confirm pituitary origin of ACTH excess state. Thirty patients were finally diagnosed to have Cushing's disease (CD) [based on histopathology proof of adenoma and/or remission (partial/complete) of hypercortisolism postsurgery]. Six patients were diagnosed to have histopathologically proven ectopic CS. Of 30 patients with CD, 24 patients had microadenomas and 6 patients had macroadenomas. DC-SE MRI sequence was able to identify microadenomas in 16 of 24 patients, whereas postcontrast VI-SGE sequence was able to identify microadenomas in 21 of 24 patients. All six patients of ectopic CS had negative pituitary MR imaging by both techniques (specificity: 100%). VI-SGE MR sequence was better for localization of pituitary microadenomas particularly when DC-SE MR sequence is negative or equivocal and should be used in addition to DC-SE MR sequence for the evaluation of ACTH-dependent CS. © 2012 John Wiley & Sons Ltd.

Fundamental Study of Three-dimensional Fast Spin-echo Imaging with Spoiled Equilibrium Pulse.

PubMed

Ogawa, Masashi; Kaji, Naoto; Tsuchihashi, Toshio

2017-01-01

Three-dimensional fast spin-echo (3D FSE) imaging with variable refocusing flip angle has been recently applied to pre- or post-enhanced T 1 -weighted imaging. To reduce the acquisition time, this sequence requires higher echo train length (ETL), which potentially causes decreased T 1 contrast. Spoiled equilibrium (SpE) pulse consists of a resonant +90° radiofrequency (RF) pulse and is applied at the end of the echo train. This +90° RF pulse brings residual transverse magnetization to the negative longitudinal axis, which makes it possible to increase T 1 contrast. The purpose of our present study was to examine factors that influence the effect of spoiled equilibrium pulse and the relationship between T 1 contrast improvement and imaging parameters and to understand the characteristics of spoiled equilibrium pulse. Phantom studies were conducted using an magnetic resonance imaging (MRI) phantom made of polyvinyl alcohol gel. To evaluate the effect of spoiled equilibrium pulse with changes in repetition time (TR), ETL, and refocusing flip angle, we measured the signal-to-noise ratio and contrast-to-noise ratio (CNR). The effect of spoiled equilibrium pulse was evaluated by calculating the enhancement rate of CNR. The factors that influence the effect of spoiled equilibrium pulse are TR, ETL, and relaxation time of tissues. Spoiled equilibrium pulse is effective with increasing TR and decreasing ETL. The shorter the T 1 value, the better the spoiled equilibrium pulse functions. However, for tissues in which the T 1 value is long (>600 ms), at a TR of 600 ms, improvement in T 1 contrast by applying spoiled equilibrium pulse cannot be expected.

MRI of the knees in asymptomatic adolescent soccer players: A case-control study.

PubMed

Matiotti, Simone B; Soder, Ricardo B; Becker, Rafaela G; Santos, Francisco S; Baldisserotto, Matteo

2017-01-01

To determine the range of asymptomatic abnormal findings in adolescent soccer players at 3.0T MRI of the knee. In all, 87 knees of asymptomatic 14-17-year-old male adolescents were evaluated at 3T, using a standardized examination protocol comprising four sequences: two fat-suppressed T 2 -weighted fast spin-echo sequences (T 2 FSE), in the sagittal (repetition time / echo time [TR/TE], 5.300/71, echo train length [ETL] 17) and coronal planes (TR/TE, 4234/70, ETL 17), one fat-suppressed proton density (PD) sequence in the axial plane (TR/TE, 2.467/40, ETL 9), and one T 1 -weighted spin-echo (T 1 SE) sequence in the sagittal plane (TR/TE, 684/12.5). Soccer players (46 knees) were paired with controls (41 knees) by age and weight. Bone marrow, articular cartilage, meniscus, tendons, ligaments, fat pad abnormalities, and joint fluid were assessed. One or more abnormalities were detected in 31 knees (67.4%) in the soccer player group, compared to 20 knees (48.8%) in the control group. The prevalence of bone marrow edema was higher in the soccer group (19 knees, 41.3%) than in the control group (3 knees, 7.3%), P = 0.001. Other abnormalities found in this sample (joint effusion, cartilage lesions, tendinopathy, ganglion cysts, and infrapatellar fat pat edema) were not significantly different between the two study groups. Asymptomatic adolescents had a high prevalence of abnormal findings on knee imaging, especially bone marrow edema. This prevalence was higher among soccer players. 4 J. Magn. Reson. Imaging 2017;45:59-65. © 2016 International Society for Magnetic Resonance in Medicine.

Quantum teleportation from a propagating photon to a solid-state spin qubit

NASA Astrophysics Data System (ADS)

Gao, W. B.; Fallahi, P.; Togan, E.; Delteil, A.; Chin, Y. S.; Miguel-Sanchez, J.; Imamoğlu, A.

2013-11-01

A quantum interface between a propagating photon used to transmit quantum information and a long-lived qubit used for storage is of central interest in quantum information science. A method for implementing such an interface between dissimilar qubits is quantum teleportation. Here we experimentally demonstrate transfer of quantum information carried by a photon to a semiconductor spin using quantum teleportation. In our experiment, a single photon in a superposition state is generated using resonant excitation of a neutral dot. To teleport this photonic qubit, we generate an entangled spin-photon state in a second dot located 5 m away and interfere the photons from the two dots in a Hong-Ou-Mandel set-up. Thanks to an unprecedented degree of photon-indistinguishability, a coincidence detection at the output of the interferometer heralds successful teleportation, which we verify by measuring the resulting spin state after prolonging its coherence time by optical spin-echo.

Quantum teleportation from a propagating photon to a solid-state spin qubit.

PubMed

Gao, W B; Fallahi, P; Togan, E; Delteil, A; Chin, Y S; Miguel-Sanchez, J; Imamoğlu, A

2013-01-01

A quantum interface between a propagating photon used to transmit quantum information and a long-lived qubit used for storage is of central interest in quantum information science. A method for implementing such an interface between dissimilar qubits is quantum teleportation. Here we experimentally demonstrate transfer of quantum information carried by a photon to a semiconductor spin using quantum teleportation. In our experiment, a single photon in a superposition state is generated using resonant excitation of a neutral dot. To teleport this photonic qubit, we generate an entangled spin-photon state in a second dot located 5 m away and interfere the photons from the two dots in a Hong-Ou-Mandel set-up. Thanks to an unprecedented degree of photon-indistinguishability, a coincidence detection at the output of the interferometer heralds successful teleportation, which we verify by measuring the resulting spin state after prolonging its coherence time by optical spin-echo.

Effect of disease progression on liver apparent diffusion coefficient and T2 values in a murine model of hepatic fibrosis at 11.7 Tesla MRI.

PubMed

Anderson, Stephan W; Jara, Hernan; Ozonoff, Al; O'Brien, Michael; Hamilton, James A; Soto, Jorge A

2012-01-01

To evaluate the effects of hepatic fibrosis on ADC and T(2) values of ex vivo murine liver specimens imaged using 11.7 Tesla (T) MRI. This animal study was IACUC approved. Seventeen male, C57BL/6 mice were divided into control (n = 2) and experimental groups (n = 15), the latter fed a 3, 5-dicarbethoxy-1, 4-dihydrocollidine (DDC) supplemented diet, inducing hepatic fibrosis. Ex vivo liver specimens were imaged using an 11.7T MRI scanner. Spin-echo pulsed field gradient and multi-echo spin-echo acquisitions were used to generate parametric ADC and T(2) maps, respectively. Degrees of fibrosis were determined by the evaluation of a pathologist as well as digital image analysis. Scatterplot graphs comparing ADC and T(2) to degrees of fibrosis were generated and correlation coefficients were calculated. Strong correlation was found between degrees of hepatic fibrosis and ADC with higher degrees of fibrosis associated with lower hepatic ADC values. Moderate correlation between hepatic fibrosis and T(2) values was seen with higher degrees of fibrosis associated with lower T(2) values. Inverse relationships between degrees of fibrosis and both ADC and T(2) are seen, highlighting the utility of these parameters in the ongoing development of an MRI methodology to quantify hepatic fibrosis. Copyright © 2011 Wiley Periodicals, Inc.

Skin age testing criteria: characterization of human skin structures by 500 MHz MRI multiple contrast and image processing.

PubMed

Sharma, Rakesh

2010-07-21

Ex vivo magnetic resonance microimaging (MRM) image characteristics are reported in human skin samples in different age groups. Human excised skin samples were imaged using a custom coil placed inside a 500 MHz NMR imager for high-resolution microimaging. Skin MRI images were processed for characterization of different skin structures. Contiguous cross-sectional T1-weighted 3D spin echo MRI, T2-weighted 3D spin echo MRI and proton density images were compared with skin histopathology and NMR peaks. In all skin specimens, epidermis and dermis thickening and hair follicle size were measured using MRM. Optimized parameters TE and TR and multicontrast enhancement generated better MRI visibility of different skin components. Within high MR signal regions near to the custom coil, MRI images with short echo time were comparable with digitized histological sections for skin structures of the epidermis, dermis and hair follicles in 6 (67%) of the nine specimens. Skin % tissue composition, measurement of the epidermis, dermis, sebaceous gland and hair follicle size, and skin NMR peaks were signatures of skin type. The image processing determined the dimensionality of skin tissue components and skin typing. The ex vivo MRI images and histopathology of the skin may be used to measure the skin structure and skin NMR peaks with image processing may be a tool for determining skin typing and skin composition.

Skin age testing criteria: characterization of human skin structures by 500 MHz MRI multiple contrast and image processing

NASA Astrophysics Data System (ADS)

Sharma, Rakesh

2010-07-01

Ex vivo magnetic resonance microimaging (MRM) image characteristics are reported in human skin samples in different age groups. Human excised skin samples were imaged using a custom coil placed inside a 500 MHz NMR imager for high-resolution microimaging. Skin MRI images were processed for characterization of different skin structures. Contiguous cross-sectional T1-weighted 3D spin echo MRI, T2-weighted 3D spin echo MRI and proton density images were compared with skin histopathology and NMR peaks. In all skin specimens, epidermis and dermis thickening and hair follicle size were measured using MRM. Optimized parameters TE and TR and multicontrast enhancement generated better MRI visibility of different skin components. Within high MR signal regions near to the custom coil, MRI images with short echo time were comparable with digitized histological sections for skin structures of the epidermis, dermis and hair follicles in 6 (67%) of the nine specimens. Skin % tissue composition, measurement of the epidermis, dermis, sebaceous gland and hair follicle size, and skin NMR peaks were signatures of skin type. The image processing determined the dimensionality of skin tissue components and skin typing. The ex vivo MRI images and histopathology of the skin may be used to measure the skin structure and skin NMR peaks with image processing may be a tool for determining skin typing and skin composition.

MR imaging of the inner ear: comparison of a three-dimensional fast spin-echo sequence with use of a dedicated quadrature-surface coil with a gadolinium-enhanced spoiled gradient-recalled sequence.

PubMed

Naganawa, S; Ito, T; Fukatsu, H; Ishigaki, T; Nakashima, T; Ichinose, N; Kassai, Y; Miyazaki, M

1998-09-01

To prospectively evaluate the sensitivity and specificity of magnetic resonance (MR) imaging in the inner ear with a long echo train, three-dimensional (3D), asymmetric Fourier-transform, fast spin-echo (SE) sequence with use of a dedicated quadrature-surface phased-array coil to detect vestibular schwannoma in the cerebellopontine angle and the internal auditory canal. In 205 patients (410 ears) with ear symptoms, 1.5-T MR imaging was performed with unenhanced 3D asymmetric fast SE and gadolinium-enhanced 3D gradient-recalled (SPGR) sequences with use of a quadrature surface phased-array coil. The 3D asymmetric fast SE images were reviewed by two radiologists, with the gadolinium-enhanced 3D SPGR images used as the standard of reference. Nineteen lesions were detected in the 410 ears (diameter range, 2-30 mm; mean, 10.5 mm +/- 6.4 [standard deviation]; five lesions were smaller than 5 mm). With 3D asymmetric fast SE, sensitivity, specificity, and accuracy, respectively, were 100%, 99.5%, and 99.5% for observer 1 and 100%, 99.7%, and 99.8% for observer 2. The unenhanced 3D asymmetric fast SE sequence with a quadrature-surface phased-array coli allows the reliable detection of vestibular schwannoma in the cerebellopontine angle and internal auditory canal.

Evaluation of pleural and pericardial effusions by magnetic resonance imaging.

PubMed

Tscholakoff, D; Sechtem, U; de Geer, G; Schmidt, H; Higgins, C B

1987-08-01

MR examinations of 36 patients with pleural and/or pericardial effusions were retrospectively evaluated. The purpose of this study was to determine of MR imaging is capable of differentiating between pleural and pericardial effusions of different compositions using standard electrocardiogram (ECG)-gated and non-gated spin echo pulse sequences. Additional data was obtained from experimental pleural effusions in 10 dogs. The results of this study indicate that old hemorrhages into the pleural or pericardial space can be differentiated from other pleural or pericardial effusions. However, further differentiation between transudates, exudates and sanguinous effusions is not possible on MR images acquired with standard spin echo pulse sequences. Respiratory and cardiac motion are responsible for signal loss, particularly on first echo images. This was documented in experiments in dogs with induced effusions of known composition; "negative" T2 values consistent with fluid motion during imaging sequences were observed in 80% of cases. However, postmortem studies of the dogs with experimental effusions showed differences between effusions with low protein concentrations and higher protein concentrations. We conclude from our study that characterization of pleural and pericardial effusions on standard ECG-gated and non-gated MR examinations is limited to the positive identification of hemorrhage. Motion of the fluid due to cardiac and respiratory activity causes artifactual and unpredictable changes in intensity values negating the more subtle differences in intensity associated with increasing protein content.

An MRI system for imaging neonates in the NICU: initial feasibility study.

PubMed

Tkach, Jean A; Hillman, Noah H; Jobe, Alan H; Loew, Wolfgang; Pratt, Ron G; Daniels, Barret R; Kallapur, Suhas G; Kline-Fath, Beth M; Merhar, Stephanie L; Giaquinto, Randy O; Winter, Patrick M; Li, Yu; Ikegami, Machiko; Whitsett, Jeffrey A; Dumoulin, Charles L

2012-11-01

Transporting premature infants from a neonatal intensive care unit (NICU) to a radiology department for MRI has medical risks and logistical challenges. To develop a small 1.5-T MRI system for neonatal imaging that can be easily installed in the NICU and to evaluate its performance using a sheep model of human prematurity. A 1.5-T MRI system designed for orthopedic use was adapted for neonatal imaging. The system was used for MRI examinations of the brain, chest and abdomen in 12 premature lambs during the first hours of life. Spin-echo, fast spin-echo and gradient-echo MR images were evaluated by two pediatric radiologists. All animals remained physiologically stable throughout the imaging sessions. Animals were imaged at two or three time points. Seven brain MRI examinations were performed in seven different animals, 23 chest examinations in 12 animals and 19 abdominal examinations in 11 animals. At each anatomical location, high-quality images demonstrating good spatial resolution, signal-to-noise ratio and tissue contrast were routinely obtained within 30 min using standard clinical protocols. Our preliminary experience demonstrates the feasibility and potential of the neonatal MRI system to provide state-of-the-art MRI capabilities within the NICU. Advantages include overall reduced cost and site demands, lower acoustic noise, improved ease of access and reduced medical risk to the neonate.

Study on spin filtering and switching action in a double-triangular network chain

NASA Astrophysics Data System (ADS)

Zhang, Yongmei

2018-04-01

Spin transport properties of a double-triangular quantum network with local magnetic moment on backbones and magnetic flux penetrating the network plane are studied. Numerical simulation results show that such a quantum network will be a good candidate for spin filter and spin switch. Local dispersion and density of states are considered in the framework of tight-binding approximation. Transmission coefficients are calculated by the method of transfer matrix. Spin transmission is regulated by substrate magnetic moment and magnetic flux piercing those triangles. Experimental realization of such theoretical research will be conducive to designing of new spintronic devices.

Charge instability in double quantum dots in Ge/Si core/shell nanowires

NASA Astrophysics Data System (ADS)

Zarassi, Azarin; Su, Zhaoen; Schwenderling, Jens; Frolov, Sergey M.; Hocevar, Moïra; Nguyen, Binh-Minh; Yoo, Jinkyoung; Dayeh, Shadi A.

Controlling dephasing times are of great challenge in the studies of spin qubit. Reported long spin coherence time and predicted strong spin-orbit interaction of holes in Ge/Si core/shell nanowires, as well as their weak coupling to very few nuclear spins of these group IV semiconductors, persuade electrical spin control. We have established Pauli spin blockade in gate-tunable quantum dots formed in these nanowires. The g-factor has been measured and evidence of spin-orbit interaction has been observed in the presence of magnetic field. However, electrical control of spins requires considerable stability in the double dot configuration, and imperfectly these dots suffer from poor stability. We report on fabrication modifications on Ge/Si core/shell nanowires, as well as measurement techniques to suppress the charge instabilities and ease the way to study spin-orbit coupling and resolve electric dipole spin resonance.

OPTESIM, a Versatile Toolbox for Numerical Simulation of Electron Spin Echo Envelope Modulation (ESEEM) that Features Hybrid Optimization and Statistical Assessment of Parameters

PubMed Central

Sun, Li; Hernandez-Guzman, Jessica; Warncke, Kurt

2009-01-01

Electron spin echo envelope modulation (ESEEM) is a technique of pulsed-electron paramagnetic resonance (EPR) spectroscopy. The analyis of ESEEM data to extract information about the nuclear and electronic structure of a disordered (powder) paramagnetic system requires accurate and efficient numerical simulations. A single coupled nucleus of known nuclear g value (gN) and spin I=1 can have up to eight adjustable parameters in the nuclear part of the spin Hamiltonian. We have developed OPTESIM, an ESEEM simulation toolbox, for automated numerical simulation of powder two- and three-pulse one-dimensional ESEEM for arbitrary number (N) and type (I, gN) of coupled nuclei, and arbitrary mutual orientations of the hyperfine tensor principal axis systems for N>1. OPTESIM is based in the Matlab environment, and includes the following features: (1) a fast algorithm for translation of the spin Hamiltonian into simulated ESEEM, (2) different optimization methods that can be hybridized to achieve an efficient coarse-to-fine grained search of the parameter space and convergence to a global minimum, (3) statistical analysis of the simulation parameters, which allows the identification of simultaneous confidence regions at specific confidence levels. OPTESIM also includes a geometry-preserving spherical averaging algorithm as default for N>1, and global optimization over multiple experimental conditions, such as the dephasing time ( ) for three-pulse ESEEM, and external magnetic field values. Application examples for simulation of 14N coupling (N=1, N=2) in biological and chemical model paramagnets are included. Automated, optimized simulations by using OPTESIM lead to a convergence on dramatically shorter time scales, relative to manual simulations. PMID:19553148

Sex- and Age-Dependence of Region- and Layer-Specific Knee Cartilage Composition (Spin-Spin-Relaxation Time) in Healthy Reference Subjects

PubMed Central

Wirth, Wolfgang; Maschek, Susanne; Eckstein, Felix

2016-01-01

SUMMARY Compositional measures of articular cartilage are accessible in vivo by magnetic resonance imaging (MRI) based relaxometry and cartilage spin-spin transverse relaxation time (T2) has been related to tissue hydration, collagen content and orientation, and mechanical (functional) properties of articular cartilage. The objective of the current study was therefore to evaluate subregional variation, and sex- and age-differences, in laminar (deep and superficial) femorotibial cartilage T2 relaxation time in healthy adults. To this end, we studied the right knees of 92 healthy subjects from the Osteoarthritis Initiative reference cohort (55 women, 37 men; age range 45–78 years; BMI 24.4±3.1) without knee pain, radiographic signs, or risk factors of knee osteoarthritis in either knee. T2 of the deep and superficial femorotibial cartilages was determined in 16 femorotibial subregions, using a multi-echo spin-echo (MESE) MRI sequence. Significant subregional variation in femorotibial cartilage T2 was observed for the superficial and for the deep (both p<0.001) cartilage layer (Friedman test). Yet, layer- and region-specific femorotibial T2 did not differ between men and women, or between healthy adults below and above the median age (54y). In conclusion, this first study to report subregional (layer-specific) compositional variation of femorotibial cartilage T2 in healthy adults identifies significant differences in both superficial and deep cartilage T2 between femorotibial subregions. However, no relevant sex- or age-dependence of cartilage T2 was observed between age 45–78y. The findings suggest that a common, non-sex-specific set of layer-and region-specific T2 reference values can be used to identify compositional pathology in joint disease for this age group. PMID:27836800

Spin-orbit coupling and electric-dipole spin resonance in a nanowire double quantum dot.

PubMed

Liu, Zhi-Hai; Li, Rui; Hu, Xuedong; You, J Q

2018-02-02

We study the electric-dipole transitions for a single electron in a double quantum dot located in a semiconductor nanowire. Enabled by spin-orbit coupling (SOC), electric-dipole spin resonance (EDSR) for such an electron can be generated via two mechanisms: the SOC-induced intradot pseudospin states mixing and the interdot spin-flipped tunneling. The EDSR frequency and strength are determined by these mechanisms together. For both mechanisms the electric-dipole transition rates are strongly dependent on the external magnetic field. Their competition can be revealed by increasing the magnetic field and/or the interdot distance for the double dot. To clarify whether the strong SOC significantly impact the electron state coherence, we also calculate relaxations from excited levels via phonon emission. We show that spin-flip relaxations can be effectively suppressed by the phonon bottleneck effect even at relatively low magnetic fields because of the very large g-factor of strong SOC materials such as InSb.

Double-quantum homonuclear rotary resonance: Efficient dipolar recovery in magic-angle spinning nuclear magnetic resonance

NASA Astrophysics Data System (ADS)

Nielsen, N. C.; Bildsøe, H.; Jakobsen, H. J.; Levitt, M. H.

1994-08-01

We describe an efficient method for the recovery of homonuclear dipole-dipole interactions in magic-angle spinning NMR. Double-quantum homonuclear rotary resonance (2Q-HORROR) is established by fulfilling the condition ωr=2ω1, where ωr is the sample rotation frequency and ω1 is the nutation frequency around an applied resonant radio frequency (rf) field. This resonance can be used for double-quantum filtering and measurement of homonuclear dipolar interactions in the presence of magic-angle spinning. The spin dynamics depend only weakly on crystallite orientation allowing good performance for powder samples. Chemical shift effects are suppressed to zeroth order. The method is demonstrated for singly and doubly 13C labeled L-alanine.

High-Resolution Bistatic Radar Imaging of Near-Earth Asteroids in 2015 using New Capabilities of Goldstone and Green Bank Telescopes

NASA Astrophysics Data System (ADS)

Naidu, S.; Benner, L.; Brozovic, M.; Giorgini, J. D.; Jao, J. S.; Lee, C. G.; Busch, M.; Ghigo, F. D.; Ford, A.; Kobelski, A.; Marshall, S.

2015-12-01

We present new results from bistatic Goldstone to Green Bank Telescope (GBT) high-resolution radar imaging of near-Earth asteroids (NEAs). Previously, most radar observations used either the 305-m Arecibo radar or the 70-m DSS-14 radar at Goldstone. Following the installation of new data-taking equipment at the GBT in late 2014, the number of bistatic Goldstone/GBT observations has increased substantially. Receiving Goldstone radar echoes at the 100-m GBT improves the signal-to-noise ratios (SNRs) two- to three-fold relative to monostatic reception at DSS-14. The higher SNRs allow us to obtain higher resolution images than is possible with DSS-14 both transmitting and receiving. Thus far in 2015, we have used the GBT receiver in combination with the 450 kW DSS-14 antenna and a new low-power 80kW transmitter on the 34-m DSS-13 antenna at the Goldstone complex to image five and two NEAs respectively. Asteroids 2005 YQ96, 2004 BL86, and 1994 AW1 are binary systems. 2011 UW158 has a spin period of 36 minutes that is unusually fast among asteroids its size (~500 m). 1999 JD6 is a deeply bifurcated double-lobed object. 2015 HM10 is an elongated 80 m asteroid with a spin period of 22 minutes. Our best images of these objects resolve the surface with resolutions of 3.75 m and reveal numerous features. Such images are useful to estimate the 3D shape, spin state, and other physical and dynamical properties of the objects. This knowledge is of particular interest for spacecraft mission planning, impact threat assessment, and resource utilization. Over the long term, such observations will help answer fundamental questions regarding the origin of the diversity in asteroid morphologies, the importance of spin-up mechanisms and collisional influences, the interior structure and thermal properties of asteroids, and the variety of dynamical states.

Spin Qubits in Germanium Structures with Phononic Gap

NASA Technical Reports Server (NTRS)

Smelyanskiy, V. N.; Vasko, F. T.; Hafiychuk, V. V.; Dykman, M. I.; Petukhov, A. G.

2014-01-01

We propose qubits based on shallow donor electron spins in germanium structures with phononic gap. We consider a phononic crystal formed by periodic holes in Ge plate or a rigid cover / Ge layer / rigid substrate structure with gaps approximately a few GHz. The spin relaxation is suppressed dramatically, if the Zeeman frequency omegaZ is in the phononic gap, but an effective coupling between the spins of remote donors via exchange of virtual phonons remains essential. If omegaZ approaches to a gap edge in these structures, a long-range (limited by detuning of omegaZ) resonant exchange interaction takes place. We estimate that ratio of the exchange integral to the longitudinal relaxation rate exceeds 10(exp 5) and lateral scale of resonant exchange 0.1 mm. The exchange contribution can be verified under microwave pumping through oscillations of spin echo signal or through the differential absorption measurements. Efficient manipulation of spins due to the Rabi oscillations opens a new way for quantum information applications.

Quantum measurement and orientation tracking of fluorescent nanodiamonds inside living cells

NASA Astrophysics Data System (ADS)

McGuinness, L. P.; Yan, Y.; Stacey, A.; Simpson, D. A.; Hall, L. T.; MacLaurin, D.; Prawer, S.; Mulvaney, P.; Wrachtrup, J.; Caruso, F.; Scholten, R. E.; Hollenberg, L. C. L.

2011-06-01

Fluorescent particles are routinely used to probe biological processes. The quantum properties of single spins within fluorescent particles have been explored in the field of nanoscale magnetometry, but not yet in biological environments. Here, we demonstrate optically detected magnetic resonance of individual fluorescent nanodiamond nitrogen-vacancy centres inside living human HeLa cells, and measure their location, orientation, spin levels and spin coherence times with nanoscale precision. Quantum coherence was measured through Rabi and spin-echo sequences over long (>10 h) periods, and orientation was tracked with effective 1° angular precision over acquisition times of 89 ms. The quantum spin levels served as fingerprints, allowing individual centres with identical fluorescence to be identified and tracked simultaneously. Furthermore, monitoring decoherence rates in response to changes in the local environment may provide new information about intracellular processes. The experiments reported here demonstrate the viability of controlled single spin probes for nanomagnetometry in biological systems, opening up a host of new possibilities for quantum-based imaging in the life sciences.

Phase diagram and quench dynamics of the cluster-XY spin chain

NASA Astrophysics Data System (ADS)

Montes, Sebastián; Hamma, Alioscia

2012-08-01

We study the complete phase space and the quench dynamics of an exactly solvable spin chain, the cluster-XY model. In this chain, the cluster term and the XY couplings compete to give a rich phase diagram. The phase diagram is studied by means of the quantum geometric tensor. We study the time evolution of the system after a critical quantum quench using the Loschmidt echo. The structure of the revivals after critical quantum quenches presents a nontrivial behavior depending on the phase of the initial state and the critical point.

Phase diagram and quench dynamics of the cluster-XY spin chain.

PubMed

Montes, Sebastián; Hamma, Alioscia

2012-08-01

We study the complete phase space and the quench dynamics of an exactly solvable spin chain, the cluster-XY model. In this chain, the cluster term and the XY couplings compete to give a rich phase diagram. The phase diagram is studied by means of the quantum geometric tensor. We study the time evolution of the system after a critical quantum quench using the Loschmidt echo. The structure of the revivals after critical quantum quenches presents a nontrivial behavior depending on the phase of the initial state and the critical point.

Basic spin physics.

PubMed

Pipe, J G

1999-11-01

Magnetic resonance imaging is fundamentally a measurement of the magnetism inherent in some nuclear isotopes; of these the proton, or hydrogen atom, is of particular interest for clinical applications. The magnetism in each nucleus is often referred to as spin. A strong, static magnetic field B0 is used to align spins, forming a magnetic density within the patient. A second, rotating magnetic field B1 (RF pulse) is applied for a short duration, which rotates the spins away from B0 in a process called excitation. After the spins are rotated away from B0, the RF pulse is turned off, and the spins precess about B0. As long as the spins are all pointing in the same direction at any one time (have phase coherence), they act in concert to create rapidly oscillating magnetic fields. These fields in turn create a current in an appropriately placed receiver coil, in a manner similar to that of an electrical generator. The precessing magnetization decays rapidly in a duration roughly given by the T2 time constant. At the same time, but at a slower rate, magnetization forms again along the direction of B0; the duration of this process is roughly expressed by the T1 time constant. The precessional frequency of each spin is proportional to the magnetic field experienced at the nucleus. Small variations in this magnetic field can have dramatic effects on the MR image, caused in part by loss of phase coherence. These magnetic field variations can arise because of magnet design, the magnetic properties (susceptibility) of tissues and other materials, and the nuclear environment unique to various sites within any given molecule. The loss of phase coherence can be effectively eliminated by the use of RF refocusing pulses. Conventional MR imaging experiments can be characterized as either gradient echo or spin echo, the latter indicating the use of a RF refocusing pulse, and by the parameters TR, TE, and flip angle alpha. Tissues, in turn, are characterized by their individual spin density, M0, and by the T1, T2, and T2* time constants. Knowledge of these parameters allows one to calculate the resulting signal from a given tissue for a given MR imaging experiment.

Electron spin resonance and spin-valley physics in a silicon double quantum dot.

PubMed

Hao, Xiaojie; Ruskov, Rusko; Xiao, Ming; Tahan, Charles; Jiang, HongWen

2014-05-14

Silicon quantum dots are a leading approach for solid-state quantum bits. However, developing this technology is complicated by the multi-valley nature of silicon. Here we observe transport of individual electrons in a silicon CMOS-based double quantum dot under electron spin resonance. An anticrossing of the driven dot energy levels is observed when the Zeeman and valley splittings coincide. A detected anticrossing splitting of 60 MHz is interpreted as a direct measure of spin and valley mixing, facilitated by spin-orbit interaction in the presence of non-ideal interfaces. A lower bound of spin dephasing time of 63 ns is extracted. We also describe a possible experimental evidence of an unconventional spin-valley blockade, despite the assumption of non-ideal interfaces. This understanding of silicon spin-valley physics should enable better control and read-out techniques for the spin qubits in an all CMOS silicon approach.

Probing Silica-Biomolecule Interactions by Solid-State NMR and Molecular Dynamics Simulations.

PubMed

Brückner, Stephan Ingmar; Donets, Sergii; Dianat, Arezoo; Bobeth, Manfred; Gutiérrez, Rafael; Cuniberti, Gianaurelio; Brunner, Eike

2016-11-08

Understanding the molecular interactions between inorganic phases such as silica and organic material is fundamental for chromatographic applications, for tailoring silica-enzyme interactions, and for elucidating the mechanisms of biomineralization. The formation, structure, and properties of the organic/inorganic interface is crucial in this context. Here, we investigate the interaction of selectively 13 C-labeled choline with 29 Si-labeled monosilicic acid/silica at the molecular level. Silica/choline nanocomposites were analyzed by solid-state NMR spectroscopy in combination with extended molecular dynamics (MD) simulations to understand the silica/organic interface. Cross-polarization magic angle spinning (CP MAS)-based NMR experiments like 1 H- 13 C CP-REDOR (rotational-echo double resonance), 1 H- 13 C HETCOR (heteronuclear correlation), and 1 H- 29 Si- 1 H double CP are employed to determine spatial parameters. The measurement of 29 Si- 13 C internuclear distances for selectively 13 C-labeled choline provides an experimental parameter that allows the direct verification of MD simulations. Atomistic modeling using classical MD methodologies is performed using the INTERFACE force field. The modeling results are in excellent agreement with the experimental data and reveal the relevant molecular conformations as well as the nature and interplay of the interactions between the choline cation and the silica surface. Electrostatic interactions and hydrogen bonding are both important and depend strongly on the hydration level as well as the charge state of the silica surface.

Strong spin-photon coupling in silicon

NASA Astrophysics Data System (ADS)

Samkharadze, N.; Zheng, G.; Kalhor, N.; Brousse, D.; Sammak, A.; Mendes, U. C.; Blais, A.; Scappucci, G.; Vandersypen, L. M. K.

2018-03-01

Long coherence times of single spins in silicon quantum dots make these systems highly attractive for quantum computation, but how to scale up spin qubit systems remains an open question. As a first step to address this issue, we demonstrate the strong coupling of a single electron spin and a single microwave photon. The electron spin is trapped in a silicon double quantum dot, and the microwave photon is stored in an on-chip high-impedance superconducting resonator. The electric field component of the cavity photon couples directly to the charge dipole of the electron in the double dot, and indirectly to the electron spin, through a strong local magnetic field gradient from a nearby micromagnet. Our results provide a route to realizing large networks of quantum dot–based spin qubit registers.

Longitudinal Double-Spin Asymmetry for Inclusive Jet Production in p→+p→ Collisions at s=200GeV

NASA Astrophysics Data System (ADS)

Abelev, B. I.; Aggarwal, M. M.; Ahammed, Z.; Anderson, B. D.; Arkhipkin, D.; Averichev, G. S.; Bai, Y.; Balewski, J.; Barannikova, O.; Barnby, L. S.; Baudot, J.; Baumgart, S.; Belaga, V. V.; Bellingeri-Laurikainen, A.; Bellwied, R.; Benedosso, F.; Betts, R. R.; Bhardwaj, S.; Bhasin, A.; Bhati, A. K.; Bichsel, H.; Bielcik, J.; Bielcikova, J.; Bland, L. C.; Blyth, S.-L.; Bombara, M.; Bonner, B. E.; Botje, M.; Bouchet, J.; Brandin, A. V.; Burton, T. P.; Bystersky, M.; Cai, X. Z.; Caines, H.; Calderón de La Barca Sánchez, M.; Callner, J.; Catu, O.; Cebra, D.; Cervantes, M. C.; Chajecki, Z.; Chaloupka, P.; Chattopadhyay, S.; Chen, H. F.; Chen, J. H.; Chen, J. Y.; Cheng, J.; Cherney, M.; Chikanian, A.; Christie, W.; Chung, S. U.; Clarke, R. F.; Codrington, M. J. M.; Coffin, J. P.; Cormier, T. M.; Cosentino, M. R.; Cramer, J. G.; Crawford, H. J.; Das, D.; Dash, S.; Daugherity, M.; de Moura, M. M.; Dedovich, T. G.; Dephillips, M.; Derevschikov, A. A.; Didenko, L.; Dietel, T.; Djawotho, P.; Dogra, S. M.; Dong, X.; Drachenberg, J. L.; Draper, J. E.; Du, F.; Dunin, V. B.; Dunlop, J. C.; Dutta Mazumdar, M. R.; Edwards, W. R.; Efimov, L. G.; Elhalhuli, E.; Emelianov, V.; Engelage, J.; Eppley, G.; Erazmus, B.; Estienne, M.; Fachini, P.; Fatemi, R.; Fedorisin, J.; Feng, A.; Filip, P.; Finch, E.; Fine, V.; Fisyak, Y.; Fu, J.; Gagliardi, C. A.; Gaillard, L.; Ganti, M. S.; Garcia-Solis, E.; Ghazikhanian, V.; Ghosh, P.; Gorbunov, Y. N.; Gos, H.; Grebenyuk, O.; Grosnick, D.; Grube, B.; Guertin, S. M.; Guimaraes, K. S. F. F.; Gupta, A.; Gupta, N.; Haag, B.; Hallman, T. J.; Hamed, A.; Harris, J. W.; He, W.; Heinz, M.; Henry, T. W.; Heppelmann, S.; Hippolyte, B.; Hirsch, A.; Hjort, E.; Hoffman, A. M.; Hoffmann, G. W.; Hofman, D. J.; Hollis, R. S.; Horner, M. J.; Huang, H. Z.; Hughes, E. W.; Humanic, T. J.; Igo, G.; Iordanova, A.; Jacobs, P.; Jacobs, W. W.; Jakl, P.; Jones, P. G.; Judd, E. G.; Kabana, S.; Kang, K.; Kapitan, J.; Kaplan, M.; Keane, D.; Kechechyan, A.; Kettler, D.; Khodyrev, V. Yu.; Kiryluk, J.; Kisiel, A.; Kislov, E. M.; Klein, S. R.; Knospe, A. G.; Kocoloski, A.; Koetke, D. D.; Kollegger, T.; Kopytine, M.; Kotchenda, L.; Kouchpil, V.; Kowalik, K. L.; Kravtsov, P.; Kravtsov, V. I.; Krueger, K.; Kuhn, C.; Kulikov, A. I.; Kumar, A.; Kurnadi, P.; Kuznetsov, A. A.; Lamont, M. A. C.; Landgraf, J. M.; Lange, S.; Lapointe, S.; Laue, F.; Lauret, J.; Lebedev, A.; Lednicky, R.; Lee, C.-H.; Lehocka, S.; Levine, M. J.; Li, C.; Li, Q.; Li, Y.; Lin, G.; Lin, X.; Lindenbaum, S. J.; Lisa, M. A.; Liu, F.; Liu, H.; Liu, J.; Liu, L.; Ljubicic, T.; Llope, W. J.; Longacre, R. S.; Love, W. A.; Lu, Y.; Ludlam, T.; Lynn, D.; Ma, G. L.; Ma, J. G.; Ma, Y. G.; Mahapatra, D. P.; Majka, R.; Mangotra, L. K.; Manweiler, R.; Margetis, S.; Markert, C.; Martin, L.; Matis, H. S.; Matulenko, Yu. A.; McShane, T. S.; Meschanin, A.; Millane, J.; Miller, M. L.; Minaev, N. G.; Mioduszewski, S.; Mischke, A.; Mitchell, J.; Mohanty, B.; Morozov, D. A.; Munhoz, M. G.; Nandi, B. K.; Nattrass, C.; Nayak, T. K.; Nelson, J. M.; Nepali, C.; Netrakanti, P. K.; Nogach, L. V.; Nurushev, S. B.; Odyniec, G.; Ogawa, A.; Okorokov, V.; Olson, D.; Pachr, M.; Pal, S. K.; Panebratsev, Y.; Pavlinov, A. I.; Pawlak, T.; Peitzmann, T.; Perevoztchikov, V.; Perkins, C.; Peryt, W.; Phatak, S. C.; Planinic, M.; Pluta, J.; Poljak, N.; Porile, N.; Poskanzer, A. M.; Potekhin, M.; Potrebenikova, E.; Potukuchi, B. V. K. S.; Prindle, D.; Pruneau, C.; Pruthi, N. K.; Putschke, J.; Qattan, I. A.; Raniwala, R.; Raniwala, S.; Ray, R. L.; Relyea, D.; Ridiger, A.; Ritter, H. G.; Roberts, J. B.; Rogachevskiy, O. V.; Romero, J. L.; Rose, A.; Roy, C.; Ruan, L.; Russcher, M. J.; Sahoo, R.; Sakrejda, I.; Sakuma, T.; Salur, S.; Sandweiss, J.; Sarsour, M.; Sazhin, P. S.; Schambach, J.; Scharenberg, R. P.; Schmitz, N.; Seger, J.; Selyuzhenkov, I.; Seyboth, P.; Shabetai, A.; Shahaliev, E.; Shao, M.; Sharma, M.; Shen, W. Q.; Shimanskiy, S. S.; Sichtermann, E. P.; Simon, F.; Singaraju, R. N.; Skoby, M. J.; Smirnov, N.; Snellings, R.; Sorensen, P.; Sowinski, J.; Speltz, J.; Spinka, H. M.; Srivastava, B.; Stadnik, A.; Stanislaus, T. D. S.; Staszak, D.; Stock, R.; Strikhanov, M.; Stringfellow, B.; Suaide, A. A. P.; Suarez, M. C.; Subba, N. L.; Sumbera, M.; Sun, X. M.; Sun, Z.; Surrow, B.; Symons, T. J. M.; Szanto de Toledo, A.; Takahashi, J.; Tang, A. H.; Tarnowsky, T.; Thomas, J. H.; Timmins, A. R.; Timoshenko, S.; Tokarev, M.; Trainor, T. A.; Tram, V. N.; Trentalange, S.; Tribble, R. E.; Tsai, O. D.; Ulery, J.; Ullrich, T.; Underwood, D. G.; van Buren, G.; van der Kolk, N.; van Leeuwen, M.; Vander Molen, A. M.; Varma, R.; Vasilevski, I. M.; Vasiliev, A. N.; Vernet, R.; Vigdor, S. E.; Viyogi, Y. P.; Vokal, S.; Voloshin, S. A.; Wada, M.; Waggoner, W. T.; Wang, F.; Wang, G.; Wang, J. S.; Wang, X. L.; Wang, Y.; Webb, J. C.; Westfall, G. D.; Whitten, C., Jr.; Wieman, H.; Wissink, S. W.; Witt, R.; Wu, J.; Wu, Y.; Xu, N.; Xu, Q. H.; Xu, Z.; Yepes, P.; Yoo, I.-K.; Yue, Q.; Yurevich, V. I.; Zawisza, M.; Zhan, W.; Zhang, H.; Zhang, W. M.; Zhang, Y.; Zhang, Z. P.; Zhao, Y.; Zhong, C.; Zhou, J.; Zoulkarneev, R.; Zoulkarneeva, Y.; Zubarev, A. N.; Zuo, J. X.

2008-06-01

We report a new STAR measurement of the longitudinal double-spin asymmetry ALL for inclusive jet production at midrapidity in polarized p+p collisions at a center-of-mass energy of s=200GeV. The data, which cover jet transverse momenta 5

Evoked-potential recovery during double click stimulation in a whale: a possibility of biosonar automatic gain control.

PubMed

Supin, Alexander Ya; Nachtigall, Paul E; Breese, Marlee

2007-01-01

False killer whale Pseudorca crassidens auditory brainstem responses (ABR) were recorded using a double-click stimulation paradigm specifically measuring the recovery of the second response (to the test click) as a function of the inter-click interval (ICI) at various levels of the conditioning and test click. At all click intensities, the slopes of recovery functions were almost constant: 0.6-0.8 microV per ICI decade. Therefore, even when the conditioning-to-test-click level ratio was kept constant, the duration of recovery was intensity-dependent: The higher intensity the longer the recovery. The conditioning-to-test-click level ratio strongly influenced the recovery time: The higher the ratio, the longer the recovery. The dependence was almost linear using a logarithmic ICI scale with a rate of 25-30 dB per ICI decade. These data were used for modeling the interaction between the emitted click and the echo during echolocation, assuming that the two clicks simulated the transmitted and echo clicks. This simulation showed that partial masking of the echo by the preceding emitted click may explain the independence of echo-response amplitude of target distance. However, the distance range where this mechanism is effective depends on the emitted click level: The higher the level, the greater the range. @ 2007 Acoustical Society of America.

Exact infinite-time statistics of the Loschmidt echo for a quantum quench.

PubMed

Campos Venuti, Lorenzo; Jacobson, N Tobias; Santra, Siddhartha; Zanardi, Paolo

2011-07-01

The equilibration dynamics of a closed quantum system is encoded in the long-time distribution function of generic observables. In this Letter we consider the Loschmidt echo generalized to finite temperature, and show that we can obtain an exact expression for its long-time distribution for a closed system described by a quantum XY chain following a sudden quench. In the thermodynamic limit the logarithm of the Loschmidt echo becomes normally distributed, whereas for small quenches in the opposite, quasicritical regime, the distribution function acquires a universal double-peaked form indicating poor equilibration. These findings, obtained by a central limit theorem-type result, extend to completely general models in the small-quench regime.

Unravelling electronic and structural requisites of triplet-triplet energy transfer by advanced electron paramagnetic resonance and density functional theory

NASA Astrophysics Data System (ADS)

Di Valentin, M.; Salvadori, E.; Barone, V.; Carbonera, D.

2013-10-01

Advanced electron paramagnetic resonance (EPR) techniques, in combination with Density Functional theory (DFT), have been applied to the comparative study of carotenoid triplet states in two major photosynthetic antenna complexes, the Peridinin-chlorophyll a-protein of dinoflagellates and the light-harvesting complex II of higher plants. Carotenoid triplet states are populated by triplet-triplet energy transfer (TTET) from chlorophyll molecules to photoprotect the system from singlet oxygen formation under light-stress conditions. The TTET process is strongly dependent on the relative arrangement and on the electronic properties of the triplet states involved. The proposed spectroscopic approach exploits the concept of spin conservation during TTET, which leads to recognisable spin polarisation effects in the time-resolved and field-swept echo-detected EPR spectra. The electron spin polarisation produced at the carotenoid acceptor site depends on the initial polarisation of the chlorophyll donor and on the relative geometrical arrangement of the donor-acceptor zero-field splitting axes. We have demonstrated that a proper analysis of the spectra in the framework of spin angular momentum conservation allows to derive the pathways of TTET and to gain insight into the structural requirements of this mechanism for those antenna complexes, whose X-ray structure is available. We have further proved that this method, developed for natural antenna complexes of known X-ray structure, can be extended to systems lacking structural information in order to derive the relative arrangement of the partners in the energy transfer process. The structural requirements for efficient TTET, obtained from time-resolved and pulse EPR, have been complemented by a detailed description of the electronic structure of the carotenoid triplet state, provided by pulse Electron-Nuclear DOuble Resonance (ENDOR) experiments. Triplet-state hyperfine couplings of the α- and β-protons of the carotenoid conjugated chain have been assigned with the aid of quantum chemical calculation. DFT predictions of the electronic structure of the carotenoid triplet state, in terms of spin density distribution, frontier orbital description and orbital excitation represent suitable building blocks toward a deeper understanding of electronic requirements for efficient TTET.

Staphylococcus aureus Peptidoglycan Stem Packing by Rotational-Echo Double Resonance NMR Spectroscopy

PubMed Central

Kim, Sung Joon; Singh, Manmilan; Preobrazhenskaya, Maria; Schaefer, Jacob

2013-01-01

Staphylococcus aureus grown in the presence of an alanine-racemase inhibitor was labeled with D-[1-13C]alanine and L-[15N]alanine to characterize some details of the peptidoglycan tertiary structure. Rotational-echo double-resonance NMR of intact whole cells was used to measure internuclear distances between 13C and 15N of labeled amino acids incorporated in the peptidoglycan, and from those labels to 19F of a glycopeptide drug specifically bound to the peptidoglycan. The observed 13C-15N average distance of 4.1 to 4.4 Å between D- and L-alanines in nearest-neighbor peptide stems is consistent with a local, tightly packed, parallel-stem architecture for a repeating structural motif within the peptidoglycan of S. aureus. PMID:23617832

Robust MR assessment of cerebral blood volume and mean vessel size using SPION-enhanced ultrashort echo acquisition.

PubMed

Han, S H; Cho, J H; Jung, H S; Suh, J Y; Kim, J K; Kim, Y R; Cho, G; Cho, H

2015-05-15

Intravascular superparamagnetic iron oxide nanoparticles (SPION)-enhanced MR transverse relaxation rates (∆R2(⁎) and ∆R2) are widely used to investigate in vivo vascular parameters, such as the cerebral blood volume (CBV), microvascular volume (MVV), and mean vessel size index (mVSI, ∆R2(⁎)/∆R2). Although highly efficient, regional comparison of vascular parameters acquired using gradient-echo based ∆R2(⁎) is hampered by its high sensitivity to magnetic field perturbations arising from air-tissue interfaces and large vessels. To minimize such demerits, we took advantage of the dual contrast property of SPION and both theoretically and experimentally verified the direct benefit of replacing gradient-echo based ∆R2(⁎) measurement with ultra-short echo time (UTE)-based ∆R1 contrast to generate the robust CBV and mVSI maps. The UTE acquisition minimized the local measurement errors from susceptibility perturbations and enabled dose-independent CBV measurement using the vessel/tissue ∆R1 ratio, while independent spin-echo acquisition enabled simultaneous ∆R2 measurement and mVSI calculation of the cortex, cerebellum, and olfactory bulb, which are animal brain regions typified by significant susceptibility-associated measurement errors. Copyright © 2015 Elsevier Inc. All rights reserved.

Spin-echo Echo-planar Imaging MR Elastography versus Gradient-echo MR Elastography for Assessment of Liver Stiffness in Children and Young Adults Suspected of Having Liver Disease.

PubMed

Serai, Suraj D; Dillman, Jonathan R; Trout, Andrew T

2017-03-01

Purpose To compare two-dimensional (2D) gradient-recalled echo (GRE) and 2D spin-echo (SE) echo-planar imaging (EPI) magnetic resonance (MR) elastography for measurement of hepatic stiffness in pediatric and young adult patients suspected of having liver disease. Materials and Methods In this institutional review board-approved, HIPAA-compliant study, 58 patients underwent both 2D GRE and 2D SE-EPI MR elastography at 1.5 T during separate breath holds. Liver stiffness (mean of means; in kilopascals) was measured by five blinded reviewers. Pooled mean liver stiffness and region-of-interest (ROI) size were compared by using paired t tests. Intraclass correlation coefficients (ICCs) were used to assess agreement between techniques. Respiratory motion artifacts were compared across sequences by using the Fisher exact test. Results Mean patient age was 14.7 years ± 5.2 (standard deviation; age range, 0.7-20.5 years), and 55.2% (32 of 58) of patients were male. Mean liver stiffness was 2.92 kPa ± 1.29 measured at GRE MR elastography and 2.76 kPa ± 1.39 at SE-EPI MR elastography (n = 290; P = .15). Mean ROI sizes were 8495 mm 2 ± 4482 for 2D GRE MR elastography and 15 176 mm 2 ± 7609 for 2D SE-EPI MR elastography (n = 290; P < .001). Agreement was excellent for measured stiffness between five reviewers for both 2D GRE (ICC, 0.97; 95% confidence interval: 0.95, 0.98) and 2D SE-EPI (ICC, 0.98; 95% confidence interval: 0.96, 0.99). Mean ICC (n = 5) for agreement between 2D GRE and 2D SE-EPI MR elastography was 0.93 (range, 0.91-0.95). Moderate or severe breathing artifacts were observed on 27.5% (16 of 58) of 2D GRE images versus 0% 2D SE-EPI images (P < .001). Conclusion There is excellent agreement on measured hepatic stiffness between 2D GRE and 2D SE-EPI MR elastography across multiple reviewers. SE-EPI MR elastography allowed for stiffness measurement across larger areas of the liver and can be performed in a single breath hold. © RSNA, 2016.

High slew-rate head-only gradient for improving distortion in echo planar imaging: Preliminary experience.

PubMed

Tan, Ek T; Lee, Seung-Kyun; Weavers, Paul T; Graziani, Dominic; Piel, Joseph E; Shu, Yunhong; Huston, John; Bernstein, Matt A; Foo, Thomas K F

2016-09-01

To investigate the effects on echo planar imaging (EPI) distortion of using high gradient slew rates (SR) of up to 700 T/m/s for in vivo human brain imaging, with a dedicated, head-only gradient coil. Simulation studies were first performed to determine the expected echo spacing and distortion reduction in EPI. A head gradient of 42-cm inner diameter and with asymmetric transverse coils was then installed in a whole-body, conventional 3T magnetic resonance imaging (MRI) system. Human subject imaging was performed on five subjects to determine the effects of EPI on echo spacing and signal dropout at various gradient slew rates. The feasibility of whole-brain imaging at 1.5 mm-isotropic spatial resolution was demonstrated with gradient-echo and spin-echo diffusion-weighted EPI. As compared to a whole-body gradient coil, the EPI echo spacing in the head-only gradient coil was reduced by 48%. Simulation and in vivo results, respectively, showed up to 25-26% and 19% improvement in signal dropout. Whole-brain imaging with EPI at 1.5 mm spatial resolution provided good whole-brain coverage, spatial linearity, and low spatial distortion effects. Our results of human brain imaging with EPI using the compact head gradient coil at slew rates higher than in conventional whole-body MR systems demonstrate substantially improved image distortion, and point to a potential for benefits to non-EPI pulse sequences. J. Magn. Reson. Imaging 2016;44:653-664. © 2016 International Society for Magnetic Resonance in Medicine.

Photoionization of N,N,N[prime],N[prime]-tetramethylbenzidine in a mixed micelle of ionic and nonionic surfactants: Electron spin-echo modulation and electron spin resonance studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baglioni, P.; Rivara-Minten, E.; Stenland, C.

1991-11-28

Electron spin-echo modulation (ESEM) and electron spin resonance (ESR) spectra of the photogenerated N,N,N[prime],N[prime]-tetramethylbenzidine (TMB) cation radical in frozen mixed micelles of sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium chloride (DTAC) and hexakis(ethylene glycol) monododecyl ether (C[sub 12]E[sub 6]), selectively deuterated along the poly(ethylene glycol) group (C[sub 12]D[sub 6]) or along the alkyl chain ((CD)[sub 12]E[sub 6]), have been studied as a function of the mixed-micelle composition in H[sub 2]O and D[sub 2]O. ESEM effects due to TMB[sup +] interactions with deuterium in D[sub 2]O show a decrease of the TMB[sup +]-water interactions for the system DTAC/C[sub 12]E[sub 6] and anmore » increase for the system SDS/C[sub 12]E[sub 6] that depend on the composition of the mixed micelle. The location of TMB[sup +] in the mixed micelles, deduced by comparing the modulation effects due to interactions of the photocation with water deuteriums or deuteriums of deuterated surfactants, is reported for the SDS/C[sub 12]E[sub 6] and DTAC/C[sub 12]E[sub 6] mixed micelles. The efficiency of charge separation upon the photoionization of TMB to produce TMB[sup +] measured by ESR correlates with the surface charge and with the degree of water penetration into the mixed micelle.« less

Electron spin resonance and electron spin echo modulation of n-doxylstearic acid and N,N,N',N'-tetramethylbenzidine photoionization in sodium versus lithium dodecyl sulfate micellar solutions: effect of 15-crown-5 and 18-crown-6 ether addition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baglioni, P.; Rivara-Minten, E.; Kevan, L.

1988-08-11

Electron spin echo modulation and electron spin resonance spectra of photogenerated N,N,N',N'-tetramethylbenzidine (TMB) cation radical and n-doxylstearic acids (n-DSA) in frozen micellar solutions of sodium and lithium dodecyl sulfate containing 15-crown-5 and 18-crown-6 ethers in D/sub 2/O have been studied as a function of crown ether concentration. Modulation effects due to N-DSA with water deuteriums give direct evidence that both crown ethers are mainly located at the micellar interface and that this causes a decrease of the hydration of the micellar interface. Crown ether complexation constants for sodium and lithium micellar counterions are reported and show that 18-crown-6 > 15-crown-5more » for sodium counterion and 15-crown-5 > 18-crown-6 for lithium counterion. Modulation effects from TMB/sup +/ interaction with water deuteriums indicate that the TMB molecule moves toward the micelle interfacial region when sodium or lithium cations are complexed by crown ethers. The TMB/sup +/ yield upon TMB photoionization increases by about 10% with crown ether addition for SDS and LDS micellar systems, but it is greater if the absolute values for the LDS system are compared to those for the SDS micellar system. This behavior correlates with the strength of TMB/sup +/-water interactions and suggests that the main factor in the photoionization efficiency is the photocation-water interaction.« less

Spin qubit transport in a double quantum dot

NASA Astrophysics Data System (ADS)

Zhao, Xinyu; Hu, Xuedong

Long distance spin communication is a crucial ingredient to scalable quantum computer architectures based on electron spin qubits. One way to transfer spin information over a long distance on chip is via electron transport. Here we study the transport of an electron spin qubit in a double quantum dot by tuning the interdot detuning voltage. We identify a parameter regime where spin relaxation hot-spots can be avoided and high-fidelity spin transport is possible. Within this parameter space, the spin transfer fidelity is determined by the operation speed and the applied magnetic field. In particular, near zero detuning, a proper choice of operation speed is essential to high fidelity. In addition, we also investigate the modification of the effective g-factor by the interdot detuning, which could lead to a phase error between spin up and down states. The results presented in this work could be a useful guidance for experimentally achieving high-fidelity spin qubit transport. We thank financial support by US ARO via Grant W911NF1210609.

Magnetic resonance imaging of water content across the Nafion membrane in an operational PEM fuel cell.

PubMed

Zhang, Ziheng; Martin, Jonathan; Wu, Jinfeng; Wang, Haijiang; Promislow, Keith; Balcom, Bruce J

2008-08-01

Water management is critical to optimize the operation of polymer electrolyte membrane fuel cells. At present, numerical models are employed to guide water management in such fuel cells. Accurate measurements of water content variation in polymer electrolyte membrane fuel cells are required to validate these models and to optimize fuel cell behavior. We report a direct water content measurement across the Nafion membrane in an operational polymer electrolyte membrane fuel cell, employing double half k-space spin echo single point imaging techniques. The MRI measurements with T2 mapping were undertaken with a parallel plate resonator to avoid the effects of RF screening. The parallel plate resonator employs the electrodes inherent to the fuel cell to create a resonant circuit at RF frequencies for MR excitation and detection, while still operating as a conventional fuel cell at DC. Three stages of fuel cell operation were investigated: activation, operation and dehydration. Each profile was acquired in 6 min, with 6 microm nominal resolution and a SNR of better than 15.

Input-output theory for spin-photon coupling in Si double quantum dots

NASA Astrophysics Data System (ADS)

Benito, M.; Mi, X.; Taylor, J. M.; Petta, J. R.; Burkard, Guido

2017-12-01

The interaction of qubits via microwave frequency photons enables long-distance qubit-qubit coupling and facilitates the realization of a large-scale quantum processor. However, qubits based on electron spins in semiconductor quantum dots have proven challenging to couple to microwave photons. In this theoretical work we show that a sizable coupling for a single electron spin is possible via spin-charge hybridization using a magnetic field gradient in a silicon double quantum dot. Based on parameters already shown in recent experiments, we predict optimal working points to achieve a coherent spin-photon coupling, an essential ingredient for the generation of long-range entanglement. Furthermore, we employ input-output theory to identify observable signatures of spin-photon coupling in the cavity output field, which may provide guidance to the experimental search for strong coupling in such spin-photon systems and opens the way to cavity-based readout of the spin qubit.

Motion correction in periodically-rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) and turboprop MRI.

PubMed

Tamhane, Ashish A; Arfanakis, Konstantinos

2009-07-01

Periodically-rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) and Turboprop MRI are characterized by greatly reduced sensitivity to motion, compared to their predecessors, fast spin-echo (FSE) and gradient and spin-echo (GRASE), respectively. This is due to the inherent self-navigation and motion correction of PROPELLER-based techniques. However, it is unknown how various acquisition parameters that determine k-space sampling affect the accuracy of motion correction in PROPELLER and Turboprop MRI. The goal of this work was to evaluate the accuracy of motion correction in both techniques, to identify an optimal rotation correction approach, and determine acquisition strategies for optimal motion correction. It was demonstrated that blades with multiple lines allow more accurate estimation of motion than blades with fewer lines. Also, it was shown that Turboprop MRI is less sensitive to motion than PROPELLER. Furthermore, it was demonstrated that the number of blades does not significantly affect motion correction. Finally, clinically appropriate acquisition strategies that optimize motion correction are discussed for PROPELLER and Turboprop MRI. (c) 2009 Wiley-Liss, Inc.

Clustering Effects on Dynamics in Ionomer Solutions: A Neutron Spin Echo Insight

NASA Astrophysics Data System (ADS)

Perahia, Dvora; Wijesinghe, Sidath; Senanayake, Manjula; Wickramasinghe, Anuradhi; Mohottalalage, Supun S.; Ohl, Michael

Ionizable blocks in ionomers associate into aggregates serving as physical cross-links and concurrently form transport pathways. The dynamics of ionomers underline their functionality. Incorporating small numbers of ionic groups into polymers significantly constraint their dynamics. Recent computational studies demonstrated a direct correlation between ionic cluster morphology and polymer dynamics. Here using neutron spin echo, we probe the segmental dynamics of polystyrene sulfonate (PSS) as the degree of sulfonation of the PSS and the solution dielectrics are varied. Specifically, 20Wt% PSS of 11,000 g/mol with polydispersity of 1.02 with 3% and 9% sulfonation were studies in toluene (dielectric constant ɛ = 2.8), a good solvent for polystyrene, and with 5Wt% of ethanol (ɛ = 24.3l) added. The dynamic structure factor S(q,t) was analyzed with a single exponential except for a limited q range where two time constants associated with constraint and mobile segments were detected. S(q,t) exhibits several distinctive time and length scales for the dynamics with a crossover appearing at the length scale of the ionic clusters. NSF DMR 1611136.

Probing the oxygen environment in UO(2)(2+) by solid-state 17O nuclear magnetic resonance spectroscopy and relativistic density functional calculations.

PubMed

Cho, Herman; de Jong, Wibe A; Soderquist, Chuck Z

2010-02-28

A combined theoretical and solid-state (17)O nuclear magnetic resonance (NMR) study of the electronic structure of the uranyl ion UO(2)(2+) in (NH(4))(4)UO(2)(CO(3))(3) and rutherfordine (UO(2)CO(3)) is presented, the former representing a system with a hydrogen-bonding environment around the uranyl oxygens and the latter exemplifying a uranyl environment without hydrogens. Relativistic density functional calculations reveal unique features of the U-O covalent bond, including the finding of (17)O chemical shift anisotropies that are among the largest for oxygen ever reported (>1200 ppm). Computational results for the oxygen electric field gradient tensor are found to be consistently larger in magnitude than experimental solid-state (17)O NMR measurements in a 7.05 T magnetic field indicate. A modified version of the Solomon theory of the two-spin echo amplitude for a spin-5/2 nucleus is developed and applied to the analysis of the (17)O echo signal of U (17)O(2)(2+).

Study of translational dynamics in molten polymer by variation of gradient pulse-width of PGSE.

PubMed

Stepišnik, Janez; Lahajnar, Gojmir; Zupančič, Ivan; Mohorič, Aleš

2013-11-01

Pulsed gradient spin echo is a method of measuring molecular translation. Changing Δ makes it sensitive to diffusion spectrum. Spin translation effects the buildup of phase structure during the application of gradient pulses as well. The time scale of the self-diffusion measurement shortens if this is taken into account. The method of diffusion spectrometry with variable δ is also less sensitive to artifacts caused by spin relaxation and internal gradient fields. Here the method is demonstrated in the case of diffusion spectrometry of molten polyethylene. The results confirm a model of constraint release in a system of entangled polymer chains as a sort of tube Rouse motion. Copyright © 2013 Elsevier Inc. All rights reserved.

Modeling of the N-terminal Section and the Lumenal Loop of Trimeric Light Harvesting Complex II (LHCII) by Using EPR*

PubMed Central

Fehr, Niklas; Dietz, Carsten; Polyhach, Yevhen; von Hagens, Tona; Jeschke, Gunnar; Paulsen, Harald

2015-01-01

The major light harvesting complex II (LHCII) of green plants plays a key role in the absorption of sunlight, the regulation of photosynthesis, and in preventing photodamage by excess light. The latter two functions are thought to involve the lumenal loop and the N-terminal domain. Their structure and mobility in an aqueous environment are only partially known. Electron paramagnetic resonance (EPR) has been used to measure the structure of these hydrophilic protein domains in detergent-solubilized LHCII. A new technique is introduced to prepare LHCII trimers in which only one monomer is spin-labeled. These heterogeneous trimers allow to measure intra-molecular distances within one LHCII monomer in the context of a trimer by using double electron-electron resonance (DEER). These data together with data from electron spin echo envelope modulation (ESEEM) allowed to model the N-terminal protein section, which has not been resolved in current crystal structures, and the lumenal loop domain. The N-terminal domain covers only a restricted area above the superhelix in LHCII, which is consistent with the “Velcro” hypothesis to explain thylakoid grana stacking (Standfuss, J., van Terwisscha Scheltinga, A. C., Lamborghini, M., and Kühlbrandt, W. (2005) EMBO J. 24, 919–928). The conformation of the lumenal loop domain is surprisingly different between LHCII monomers and trimers but not between complexes with and without neoxanthin bound. PMID:26316535

B0 concomitant field compensation for MRI systems employing asymmetric transverse gradient coils.

PubMed

Weavers, Paul T; Tao, Shengzhen; Trzasko, Joshua D; Frigo, Louis M; Shu, Yunhong; Frick, Matthew A; Lee, Seung-Kyun; Foo, Thomas K-F; Bernstein, Matt A

2018-03-01

Imaging gradients result in the generation of concomitant fields, or Maxwell fields, which are of increasing importance at higher gradient amplitudes. These time-varying fields cause additional phase accumulation, which must be compensated for to avoid image artifacts. In the case of gradient systems employing symmetric design, the concomitant fields are well described with second-order spatial variation. Gradient systems employing asymmetric design additionally generate concomitant fields with global (zeroth-order or B 0 ) and linear (first-order) spatial dependence. This work demonstrates a general solution to eliminate the zeroth-order concomitant field by applying the correct B 0 frequency shift in real time to counteract the concomitant fields. Results are demonstrated for phase contrast, spiral, echo-planar imaging (EPI), and fast spin-echo imaging. A global phase offset is reduced in the phase-contrast exam, and blurring is virtually eliminated in spiral images. The bulk image shift in the phase-encode direction is compensated for in EPI, whereas signal loss, ghosting, and blurring are corrected in the fast-spin echo images. A user-transparent method to compensate the zeroth-order concomitant field term by center frequency shifting is proposed and implemented. This solution allows all the existing pulse sequences-both product and research-to be retained without any modifications. Magn Reson Med 79:1538-1544, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Retinotopic mapping with Spin Echo BOLD at 7 Tesla

PubMed Central

Olman, Cheryl A.; Van de Moortele, Pierre-Francois; Schumacher, Jennifer F.; Guy, Joe; Uğurbil, Kâmil; Yacoub, Essa

2010-01-01

For blood oxygenation level-dependent (BOLD) functional MRI experiments, contrast-to-noise ratio (CNR) increases with increasing field strength for both gradient echo (GE) and spin echo (SE) BOLD techniques. However, susceptibility artifacts and non-uniform coil sensitivity profiles complicate large field-of-view fMRI experiments (e.g., experiments covering multiple visual areas instead of focusing on a single cortical region). Here, we use SE BOLD to acquire retinotopic mapping data in early visual areas, testing the feasibility of SE BOLD experiments spanning multiple cortical areas at 7 Tesla. We also use a recently developed method for normalizing signal intensity in T1-weighted anatomical images to enable automated segmentation of the cortical gray matter for scans acquired at 7T with either surface or volume coils. We find that the CNR of the 7T GE data (average single-voxel, single-scan stimulus coherence: 0.41) is almost twice that of the 3T GE BOLD data (average coherence: 0.25), with the CNR of the SE BOLD data (average coherence: 0.23) comparable to that of the 3T GE data. Repeated measurements in individual subjects find that maps acquired with 1.8 mm resolution at 3T and 7T with GE BOLD and at 7T with SE BOLD show no systematic differences in either the area or the boundary locations for V1, V2 and V3, demonstrating the feasibility of high-resolution SE BOLD experiments with good sensitivity throughout multiple visual areas. PMID:20656431

Carr-Purcell-Meiboom-Gill (CPMG) Imaging of Prostate Cancer: Quantitative T2 Values for Cancer Discrimination

PubMed Central

Roebuck, Joseph R.; Haker, Steven J.; Mitsouras, Dimitris; Rybicki, Frank J.; Tempany, Clare M.; Mulkern, Robert V.

2009-01-01

Quantitative, apparent T2 values of suspected prostate cancer and healthy peripheral zone tissue in men with prostate cancer were measured using a Carr-Purcell-Meiboom-Gill (CPMG) imaging sequence in order to assess the cancer discrimination potential of tissue T2 values. The CPMG imaging sequence was used to image the prostates of 18 men with biopsy proven prostate cancer. Whole gland coverage with nominal voxel volumes of 0.54 × 1.1 × 4 mm3 was obtained in 10.7 minutes, resulting in data sets suitable for generating high quality images with variable T2-weighting and for evaluating quantitative T2 values on a pixel-by-pixel basis. Region-of-interest analysis of suspected healthy peripheral zone tissue and suspected cancer, identified on the basis of both T1- and T2-weighted signal intensities and available histopathology reports, yielded significantly (p < 0.0001) longer apparent T2 values in suspected healthy tissue (193 ± 49 ms) vs. suspected cancer (100 ± 26 ms), suggesting potential utility of this method as a tissue specific discrimination index for prostate cancer. We conclude that CPMG imaging of the prostate can be performed in reasonable scan times and can provide advantages over T2-weighted fast spin echo imaging alone, including quantitative T2 values for cancer discrimination as well as proton density maps without the point spread function degradation associated with short effective echo time fast spin echo (FSE) sequences. PMID:18823731

Loschmidt echo in many-spin systems: a quest for intrinsic decoherence and emergent irreversibility

NASA Astrophysics Data System (ADS)

Zangara, Pablo R.; Pastawski, Horacio M.

2017-03-01

If a magnetic polarization excess is locally injected in a crystal of interacting spins in thermal equilibrium, this ‘excitation’ would spread as consequence of spin-spin interactions. Such an apparently irreversible process is known as spin diffusion and it can lead the system back to ‘equilibrium’. Even so, a unitary quantum dynamics would ensure a precise memory of the non-equilibrium initial condition. Then, if at a certain time, say t/2, an experimental protocol reverses the many-body dynamics by changing the sign of the effective Hamiltonian, it would drive the system back to the initial non-equilibrium state at time t. As a matter of fact, the reversal is always perturbed by small experimental imperfections and/or uncontrolled internal or environmental degrees of freedom. This limits the amount of signal M(t) recovered locally at time t. The degradation of M(t) accounts for these perturbations, which can also be seen as the sources of decoherence. This general idea defines the Loschmidt echo (LE), which embodies the various time-reversal procedures implemented in nuclear magnetic resonance. Here, we present an invitation to the study of the LE following the pathway induced by the experiments. With such a purpose, we provide a historical and conceptual overview that briefly revisits selected phenomena that underlie the LE dynamics including chaos, decoherence, localization and equilibration. This guiding thread ultimately leads us to the discussion of decoherence and irreversibility as an emergent phenomenon. In addition, we introduce the LE formalism by means of spin-spin correlation functions in a manner suitable for presentation in a broad scope physics journal. Last, but not least, we present new results that could trigger new experiments and theoretical ideas. In particular, we propose to transform an initially localized excitation into a more complex initial state, enabling a dynamically prepared LE. This induces a global definition of the LE in terms of the raw overlap between many-body wave functions. Our results show that as the complexity of the prepared state increases, it becomes more fragile towards small perturbations.

Advanced cardiac chemical exchange saturation transfer (cardioCEST) MRI for in vivo cell tracking and metabolic imaging

PubMed Central

Pumphrey, Ashley; Yang, Zhengshi; Ye, Shaojing; Powell, David K.; Thalman, Scott; Watt, David S.; Abdel-Latif, Ahmed; Unrine, Jason; Thompson, Katherine; Fornwalt, Brandon; Ferrauto, Giuseppe; Vandsburger, Moriel

2016-01-01

An improved pre-clinical cardiac chemical exchange saturation transfer (CEST) pulse sequence (cardioCEST) was used to selectively visualize paramagnetic CEST (paraCEST)-labeled cells following intramyocardial implantation. In addition, cardioCEST was used to examine the effect of diet-induced obesity upon myocardial creatine CEST contrast. CEST pulse sequences were designed from standard turbo-spin-echo and gradient-echo sequences, and a cardiorespiratory-gated steady-state cine gradient-echo sequence. In vitro validation studies performed in phantoms composed of 20mM Eu-HPDO3A, 20mM Yb-HPDO3A, or saline demonstrated similar CEST contrast by spin-echo and gradient-echo pulse sequences. Skeletal myoblast cells (C2C12) were labeled with either Eu-HPDO3A or saline using a hypotonic swelling procedure and implanted into the myocardium of C57B6/J mice. Inductively coupled plasma mass spectrometry confirmed cellular levels of Eu of 2.1 × 10−3 ng/cell in Eu-HPDO3A-labeled cells and 2.3 × 10−5 ng/cell in saline-labeled cells. In vivo cardioCEST imaging of labeled cells at ±15ppm was performed 24 h after implantation and revealed significantly elevated asymmetric magnetization transfer ratio values in regions of Eu-HPDO3A-labeled cells when compared with surrounding myocardium or saline-labeled cells. We further utilized the cardioCEST pulse sequence to examine changes in myocardial creatine in response to diet-induced obesity by acquiring pairs of cardioCEST images at ±1.8 ppm. While ventricular geometry and function were unchanged between mice fed either a high-fat diet or a corresponding control low-fat diet for 14 weeks, myocardial creatine CEST contrast was significantly reduced in mice fed the high-fat diet. The selective visualization of paraCEST-labeled cells using cardioCEST imaging can enable investigation of cell fate processes in cardioregenerative medicine, or multiplex imaging of cell survival with imaging of cardiac structure and function and additional imaging of myocardial creatine. PMID:26684053

Three- and four-dimensional reconstruction of intra-cardiac anatomy from two-dimensional magnetic resonance images.

PubMed

Miquel, M E; Hill, D L G; Baker, E J; Qureshi, S A; Simon, R D B; Keevil, S F; Razavi, R S

2003-06-01

The present study was designed to evaluate the feasibility and clinical usefulness of three-dimensional (3D) reconstruction of intra-cardiac anatomy from a series of two-dimensional (2D) MR images using commercially available software. Sixteen patients (eight with structurally normal hearts but due to have catheter radio-frequency ablation of atrial tachyarrhythmias and eight with atrial septal defects (ASD) due for trans-catheter closure) and two volunteers were imaged at 1T. For each patient, a series of ECG-triggered images (5 mm thick slices, 2-3 mm apart) were acquired during breath holding. Depending on image quality, T1- or T2-weighted spin-echo images or gradient-echo cine images were used. The 3D reconstruction was performed off-line: the blood pools within cardiac chambers and great vessels were semi-automatically segmented, their outer surface was extracted using a marching cube algorithm and rendered. Intra- and inter-observer variability, effect of breath-hold position and differences between pulse sequences were assessed by imaging a volunteer. The 3D reconstructions were assessed by three cardiologists and compared with the 2D MR images and with 2D and 3D trans-esophagal and intra-cardiac echocardiography obtained during interventions. In every case, an anatomically detailed 3D volume was obtained. In the two patients where a 3 mm interval between slices was used, the resolution was not as good but it was still possible to visualize all the major anatomical structures. Spin-echo images lead to reconstructions more detailed than those obtained from gradient-echo images. However, gradient-echo images are easier to segment due to their greater contrast. Furthermore, because images were acquired at least at ten points in the cardiac cycles for every slice it was possible to reconstruct a cine loop and, for example, to visualize the evolution of the size and margins of the ASD during the cardiac cycle. 3D reconstruction proved to be an effective way to assess the relationship between the different parts of the cardiac anatomy. The technique was useful in planning interventions in these patients.

Using 3D spatial correlations to improve the noise robustness of multi component analysis of 3D multi echo quantitative T2 relaxometry data.

PubMed

Kumar, Dushyant; Hariharan, Hari; Faizy, Tobias D; Borchert, Patrick; Siemonsen, Susanne; Fiehler, Jens; Reddy, Ravinder; Sedlacik, Jan

2018-05-12

We present a computationally feasible and iterative multi-voxel spatially regularized algorithm for myelin water fraction (MWF) reconstruction. This method utilizes 3D spatial correlations present in anatomical/pathological tissues and underlying B1 + -inhomogeneity or flip angle inhomogeneity to enhance the noise robustness of the reconstruction while intrinsically accounting for stimulated echo contributions using T2-distribution data alone. Simulated data and in vivo data acquired using 3D non-selective multi-echo spin echo (3DNS-MESE) were used to compare the reconstruction quality of the proposed approach against those of the popular algorithm (the method by Prasloski et al.) and our previously proposed 2D multi-slice spatial regularization spatial regularization approach. We also investigated whether the inter-sequence correlations and agreements improved as a result of the proposed approach. MWF-quantifications from two sequences, 3DNS-MESE vs 3DNS-gradient and spin echo (3DNS-GRASE), were compared for both reconstruction approaches to assess correlations and agreements between inter-sequence MWF-value pairs. MWF values from whole-brain data of six volunteers and two multiple sclerosis patients are being reported as well. In comparison with competing approaches such as Prasloski's method or our previously proposed 2D multi-slice spatial regularization method, the proposed method showed better agreements with simulated truths using regression analyses and Bland-Altman analyses. For 3DNS-MESE data, MWF-maps reconstructed using the proposed algorithm provided better depictions of white matter structures in subcortical areas adjoining gray matter which agreed more closely with corresponding contrasts on T2-weighted images than MWF-maps reconstructed with the method by Prasloski et al. We also achieved a higher level of correlations and agreements between inter-sequence (3DNS-MESE vs 3DNS-GRASE) MWF-value pairs. The proposed algorithm provides more noise-robust fits to T2-decay data and improves MWF-quantifications in white matter structures especially in the sub-cortical white matter and major white matter tract regions. Copyright © 2018 Elsevier Inc. All rights reserved.

Suppression of Pauli Spin Blockade in Few Hole Laterally Gated Double Quantum Dots

NASA Astrophysics Data System (ADS)

Gaudreau, Louis; Bogan, Alex; Studenikin, Sergei; Korkusinski, Marek; Aers, Geof; Zawadzki, Piotr; Sachrajda, Andy; Tracy, Lisa; Reno, John; Hargett, Terry; National Research Council Team; Sandia Labs Team

Hole spins have attracted increasing attention as candidates for qubits in quantum information applications. The p-type character of their wavefunction leads to smaller hyperfine interaction with the nuclei resulting in longer coherence times. Additionally, strong spin-orbit interaction allows for enhanced all-electrical manipulation of spin qubit states. Single hole spins have been electrically studied in InSb and Si nanowire quantum dots, however, electrostatically confined hole spins in a 2D hole gas have thus far been limited to the many hole regime. In this talk we will present a full description of the two-hole spin spectrum in a lateral GaAs/AlGaAs double quantum. High-bias magneto-transport spectroscopy reveals all four states of the spectrum (singlet and triplets) in both the (1,1) and (2,0) configurations, essential for spin readout based on Pauli spin blockade. We show that spin-flip tunneling between dots is as strong as spin conserving tunneling, a consequence of the strong spin-orbit interaction. This suppresses the Pauli spin blockade. Our results suggest that alternate techniques for single hole spin qubit readout need to be explored.

Quantitative analysis of the breath-holding half-Fourier acquisition single-shot turbo spin-echo technique in abdominal MRI

NASA Astrophysics Data System (ADS)

Dong, Kyung-Rae; Goo, Eun-Hoe; Lee, Jae-Seung; Chung, Woon-Kwan

2013-01-01

A consecutive series of 50 patients (28 males and 22 females) who underwent hepatic magnetic resonance imaging (MRI) from August to December 2011 were enrolled in this study. The appropriate parameters for abdominal MRI scans were determined by comparing the images (TE = 90 and 128 msec) produced using the half-Fourier acquisition single-shot turbo spin-echo (HASTE) technique at different signal acquisition times. The patients consisted of 15 normal patients, 25 patients with a hepatoma and 10 patients with a hemangioma. The TE in a single patient was set to either 90 msec or 128 msec. This was followed by measurements using the four normal rendering methods of the biliary tract system and the background signal intensity using the maximal signal intensity techniques in the liver, spleen, pancreas, gallbladder, fat, muscles and hemangioma. The signal-to-noise and the contrast-to-noise ratios were obtained. The image quality was assessed subjectively, and the results were compared. The signal-to-noise and the contrast-to-noise ratios were significantly higher at TE = 128 msec than at TE = 90 when diseases of the liver, spleen, pancreas, gallbladder, and fat and muscles, hepatocellular carcinomas and hemangiomas, and rendering the hepatobiliary tract system based on the maximum signal intensity technique were involved (p < 0.05). In addition, the presence of artifacts, the image clarity and the overall image quality were excellent at TE = 128 msec (p < 0.05). In abdominal MRI, the breath-hold half-Fourier acquisition single-shot turbo spin-echo (HASTE) was found to be effective in illustrating the abdominal organs for TE = 128 msec. Overall, the image quality at TE = 128 msec was better than that at TE = 90 msec due to the improved signal-to-noise (SNR) and contrast-to-noise (CNR) ratios. Overall, the HASTE technique for abdominal MRI based on a high-magnetic field (3.0 T) at a TE of 128 msec can provide useful data.

Diffusion-weighted magnetic resonance imaging of uterine cervical cancer.

PubMed

Liu, Ying; Bai, Renju; Sun, Haoran; Liu, Haidong; Wang, Dehua

2009-01-01

To determine the feasibility of diffusion-weighted magnetic resonance (MR) imaging (DWI) of uterine cervical cancer and to investigate whether the apparent diffusion coefficient (ADC) values of cervical cancer differ from those of normal cervix and whether they could indicate the histologic type and the pathologic grade of tumor. Forty-two female patients with histopathologically proven uterine cervical cancer and 15 female patients with uterine leiomyomas underwent preoperative MR examinations using a 1.5-T clinical scanner (GE 1.5T Twin-Speed Infinity with Excite II scanner; GE Healthcare, Waukesha, Wis). Scanning sequences included T2-weighted fast spin-echo imaging, T2-weighted fast spin-echo with fat suppression imaging, T1-weighted spin-echo imaging, and DWI with diffusion factors of 0 and 1000 s/mm2. Parameters evaluated consisted of ADC values of uterine cervical cancer and normal cervix. Histologic specimens were stained with hematoxylin and eosin. The cellular densities of 32 uterine cervical cancers were calculated, which were regarded as the ratio of the total area of tumor cell nuclei divided by the area of sample image. Apparent diffusion coefficient value was statistically different (P = 0.000) between normal and cancerous tissue in the uterine cervix; the former one was (mean [SD], 1.50 [0.16]) x 10(-3) mm2/s, and the latter one was (0.88 [0.15]) x 10(-3) mm2/s. Apparent diffusion coefficient value of squamous carcinoma was statistically lower than that of adenocarcinoma (P = 0.040). The ADC value of uterine cervical cancer correlated negatively with cellular density (r = -0.711, P = 0.000) and the grading of tumor (r = -0.778, P = 0.000). Diffusion-weighted MR imaging has a potential ability to differentiate between normal and cancerous tissue in the uterine cervix, and it can indicate the histologic type of uterine cervical cancer as well. The ADC value of uterine cervical cancer represents tumor cellular density, thus providing a new method for evaluating the pathologic grading of tumor.

Articular cartilage grading of the knee: diagnostic performance of fat-suppressed 3D volume isotropic turbo spin-echo acquisition (VISTA) compared with 3D T1 high-resolution isovolumetric examination (THRIVE).

PubMed

Lee, Young Han; Hahn, Seok; Lim, Daekeon; Suh, Jin-Suck

2017-02-01

Background Conventionally, two-dimensional (2D) fast spin-echo (FSE) sequences have been widely used for clinical cartilage imaging as well as gradient (GRE) sequences. Recently, three-dimensional (3D) volumetric magnetic resonance imaging (MRI) has been introduced with one 3D volumetric scan, and this is replacing slice-by-slice 2D MR scans. Purpose To evaluate the image quality and diagnostic performance of two 3D sequences for abnormalities of knee cartilage: fat-suppressed (FS) FSE-based 3D volume isotropic turbo spin-echo acquisition (VISTA) and GRE-based 3D T1 high-resolution isovolumetric examination (THRIVE). Material and Methods The institutional review board approved the protocol of this retrospective review. This study enrolled 40 patients (41 knees) with arthroscopically confirmed abnormalities of cartilage. All patients underwent isovoxel 3D-VISTA and 3D-THRIVE MR sequences on 3T MRI. We assessed the cartilage grade on the two 3D sequences using arthroscopy as a gold standard. Inter-observer agreement for each technique was evaluated with the intraclass correlation coefficient (ICC). Differences in the area under the curve (AUC) were compared between the 3D-THRIVE and 3D-VISTA. Results Although inter-observer agreement for both sequences was excellent, the inter-observer agreement for 3D-VISTA was higher than for 3D-THRIVE for cartilage grading in all regions of the knee. There was no significant difference in the diagnostic performance ( P > 0.05) between the two sequences for detecting cartilage grade. Conclusion FSE-based 3D-VISTA images had good diagnostic performance that was comparable to GRE-based 3D-THRIVE images in the evaluation of knee cartilage, and can be used in routine knee MR protocols for the evaluation of cartilage.

Assessing the accuracy of using oscillating gradient spin echo sequences with AxCaliber to infer micron-sized axon diameters.

PubMed

Mercredi, Morgan; Vincent, Trevor J; Bidinosti, Christopher P; Martin, Melanie

2017-02-01

Current magnetic resonance imaging (MRI) axon diameter measurements rely on the pulsed gradient spin-echo sequence, which is unable to provide diffusion times short enough to measure small axon diameters. This study combines the AxCaliber axon diameter fitting method with data generated from Monte Carlo simulations of oscillating gradient spin-echo sequences (OGSE) to infer micron-sized axon diameters, in order to determine the feasibility of using MRI to infer smaller axon diameters in brain tissue. Monte Carlo computer simulation data were synthesized from tissue geometries of cylinders of different diameters using a range of gradient frequencies in the cosine OGSE sequence . Data were fitted to the AxCaliber method modified to allow the new pulse sequence. Intra- and extra-axonal water were studied separately and together. The simulations revealed the extra-axonal model to be problematic. Rather than change the model, we found that restricting the range of gradient frequencies such that the measured apparent diffusion coefficient was constant over that range resulted in more accurate fitted diameters. Thus a careful selection of frequency ranges is needed for the AxCaliber method to correctly model extra-axonal water, or adaptations to the method are needed. This restriction helped reduce the necessary gradient strengths for measurements that could be performed with parameters feasible for a Bruker BG6 gradient set. For these experiments, the simulations inferred diameters as small as 0.5 μm on square-packed and randomly packed cylinders. The accuracy of the inferred diameters was found to be dependent on the signal-to-noise ratio (SNR), with smaller diameters more affected by noise, although all diameter distributions were distinguishable from one another for all SNRs tested. The results of this study indicate the feasibility of using MRI with OGSE on preclinical scanners to infer small axon diameters.

Ultrafast MR imaging of the pelvic floor.

PubMed

Unterweger, M; Marincek, B; Gottstein-Aalame, N; Debatin, J F; Seifert, B; Ochsenbein-Imhof, N; Perucchini, D; Kubik-Huch, R A

2001-04-01

The aim of this study was to compare pelvic floor anatomy and laxity at rest and on straining (Valsalva's maneuver) using dynamic ultrafast MR imaging in women who were continent versus those with stress incontinence differing in obstetric history. Thirty continent women were divided into three equal groups (nulliparous, previous cesarean delivery, previous vaginal delivery) and compared with 10 women with stress-incontinence with a history of at least one vaginal delivery. MR imaging of the pelvic floor at rest and on maximal strain was performed, using axial T2-weighted fast spin-echo images followed by sagittal ultrafast T2-weighted single-shot fast spin-echo sequences. Mean population age (age range, 22-45 years; mean +/- SD, 36 +/- 5.4 years), was similar in the four groups, as was parity in the three parous groups. Mean distances between the bladder floor and pubococcygeal line at rest did not differ between the four groups. On straining, bladder floor descent was 1.1 +/- 0.9, 1.0 +/- 1.1, and 1.9 +/- 0.9 cm in continent nulliparous, cesarean delivery, and vaginal delivery women, respectively, versus 3.2 +/- 1.0 cm in incontinent women (p = 0.0005). Cervical descent was greater in incontinent versus nulliparous women (p = 0.0019). Bladder floor descent was greater in the continent vaginal delivery group than in continent cesarean delivery control patients (p = 0.04). In patients with stress incontinence, symptoms did not correlate with amplitude of descent. The right levator muscle was thinner overall than the left, regardless of frequency direction (p = 0.001). Ultrafast MR imaging using the T2-weighted single-shot fast spin-echo sequence allows dynamic evaluation of the pelvic compartments at maximal strain with no need for contrast medium. Pelvic floor laxity and supporting fascia abnormalities were most common in patients with stress incontinence followed by continent women with a history of vaginal delivery. The results are therefore compatible with the hypothesis of vaginal delivery as a contributory factor to stress incontinence in older parous women.

Double-quantum homonuclear correlations of spin I=5/2 nuclei.

PubMed

Iuga, Dinu

2011-02-01

The challenges associated with acquiring double-quantum homonuclear Nuclear Magnetic Resonance correlation spectra of half-integer quadrupolar nuclei are described. In these experiments the radio-frequency irradiation amplitude is necessarily weak in order to selectively excite the central transition. In this limit only one out of the 25 double-quantum coherences possible for two coupled spin I=5/2 nuclei is excited. An investigation of all the 25 two spins double quantum transitions reveals interesting effects such as a compensation of the first-order quadrupolar interaction between the two single quantum transitions involved in the double quantum coherence. In this paper a full numerical study of a hypothetical two spin I=5/2 system is used to show what happens when the RF amplitude during recoupling is increased. In principle this is advantageous, since the required double quantum coherence should build up faster, but in practice it also induces adiabatic passage transfer of population and coherence which impedes any build up. Finally an optimized rotary resonance recoupling (oR(3)) sequence is introduced in order to decrease these transfers. This sequence consists of a spin locking irradiation whose amplitude is reduced four times during one rotor period, and allows higher RF powers to be used during recoupling. The sequence is used to measure (27)Al DQ dipolar correlation spectra of Y(3)Al(5)O(12) (YAG) and gamma alumina (γAl(2)O(3)). The results prove that aluminium vacancies in gamma alumina mainly occur in the tetrahedral sites. Copyright © 2010 Elsevier Inc. All rights reserved.

Delayed entanglement echo for individual control of a large number of nuclear spins

PubMed Central

Wang, Zhen-Yu; Casanova, Jorge; Plenio, Martin B.

2017-01-01

Methods to selectively detect and manipulate nuclear spins by single electrons of solid-state defects play a central role for quantum information processing and nanoscale nuclear magnetic resonance (NMR). However, with standard techniques, no more than eight nuclear spins have been resolved by a single defect centre. Here we develop a method that improves significantly the ability to detect, address and manipulate nuclear spins unambiguously and individually in a broad frequency band by using a nitrogen-vacancy (NV) centre as model system. On the basis of delayed entanglement control, a technique combining microwave and radio frequency fields, our method allows to selectively perform robust high-fidelity entangling gates between hardly resolved nuclear spins and the NV electron. Long-lived qubit memories can be naturally incorporated to our method for improved performance. The application of our ideas will increase the number of useful register qubits accessible to a defect centre and improve the signal of nanoscale NMR. PMID:28256508

Delayed entanglement echo for individual control of a large number of nuclear spins.

PubMed

Wang, Zhen-Yu; Casanova, Jorge; Plenio, Martin B

2017-03-03

Methods to selectively detect and manipulate nuclear spins by single electrons of solid-state defects play a central role for quantum information processing and nanoscale nuclear magnetic resonance (NMR). However, with standard techniques, no more than eight nuclear spins have been resolved by a single defect centre. Here we develop a method that improves significantly the ability to detect, address and manipulate nuclear spins unambiguously and individually in a broad frequency band by using a nitrogen-vacancy (NV) centre as model system. On the basis of delayed entanglement control, a technique combining microwave and radio frequency fields, our method allows to selectively perform robust high-fidelity entangling gates between hardly resolved nuclear spins and the NV electron. Long-lived qubit memories can be naturally incorporated to our method for improved performance. The application of our ideas will increase the number of useful register qubits accessible to a defect centre and improve the signal of nanoscale NMR.

Coherent manipulation of mononuclear lanthanide-based single-molecule magnets

NASA Astrophysics Data System (ADS)

Datta, Saiti; Ghosh, Sanhita; Krzystek, Jurek; Hill, Stephen; Del Barco, Enrique; Cardona-Serra, Salvador; Coronado, Eugenio

2010-03-01

Using electron spin echo (ESE) spectroscopy, we report measurements of the longitudinal (T1) and transverse (T2) relaxation times of diluted single-crystals containing recently discovered mononuclear lanthanide-based single-molecule magnets (SMMs) encapsulated in polyoxometallate cages [AlDamen et al. J. Am. Chem. Soc. 130, 8874 -- 8875 (2008)]. This encapsulation offers the potential for preserving bulk SMM properties outside of a crystal, e.g. in molecular spintronic devices. The magnetic anisotropy in these complexes arises from the spin-orbit splitting of the ground state J multiplet of the lanthanide ion in the presence of a ligand field. At low frequencies only hyperfine-split transitions within the lowest ground state ±mJ doublet are observed. Spin relaxation times were measured for a holmium complex, and the results were compared for different hyperfine transitions and crystal dilutions. Clear Rabi oscillations were also observed, indicating that one can manipulate the spin coherently in these complexes.

Real-time monitoring of Lévy flights in a single quantum system

NASA Astrophysics Data System (ADS)

Issler, M.; Höller, J.; Imamoǧlu, A.

2016-02-01

Lévy flights are random walks where the dynamics is dominated by rare events. Even though they have been studied in vastly different physical systems, their observation in a single quantum system has remained elusive. Here we analyze a periodically driven open central spin system and demonstrate theoretically that the dynamics of the spin environment exhibits Lévy flights. For the particular realization in a single-electron charged quantum dot driven by periodic resonant laser pulses, we use Monte Carlo simulations to confirm that the long waiting times between successive nuclear spin-flip events are governed by a power-law distribution; the corresponding exponent η =-3 /2 can be directly measured in real time by observing the waiting time distribution of successive photon emission events. Remarkably, the dominant intrinsic limitation of the scheme arising from nuclear quadrupole coupling can be minimized by adjusting the magnetic field or by implementing spin echo.

A new detection scheme for ultrafast 2D J-resolved spectroscopy

NASA Astrophysics Data System (ADS)

Giraudeau, Patrick; Akoka, Serge

2007-06-01

Recent ultrafast techniques enable 2D NMR spectra to be obtained in a single scan. A modification of the detection scheme involved in this technique is proposed, permitting the achievement of 2D 1H J-resolved spectra in 500 ms. The detection gradient echoes are substituted by spin echoes to obtain spectra where the coupling constants are encoded along the direct ν2 domain. The use of this new J-resolved detection block after continuous phase-encoding excitation schemes is discussed in terms of resolution and sensitivity. J-resolved spectra obtained on cinnamic acid and 3-ethyl bromopropionate are presented, revealing the expected 2D J-patterns with coupling constants as small as 2 Hz.

7 Tesla compatible in-bore display for functional magnetic resonance imaging.

PubMed

Groebner, Jens; Berger, Moritz Cornelius; Umathum, Reiner; Bock, Michael; Rauschenberg, Jaane

2013-08-01

A liquid crystal display was modified for use inside a 7 T MR magnet. SNR measurements were performed using different imaging sequences with the monitor absent, present, or activated. fMRI with a volunteer was conducted using a visual stimulus. SNR was reduced by 3.7%/7.9% in echo planar/fast-spin echo images when the monitor was on which can be explained by the limited shielding of the coated front window (40 dB). In the fMRI experiments, activated regions in the visual cortex were clearly visible. The monitor provided excellent resolution at minor SNR reduction in EPI images, and is thus suitable for fMRI at ultra-high field.

Spin-orbit signatures in the dynamics of singlet-triplet qubits in double quantum dots

NASA Astrophysics Data System (ADS)

Rolon, Juan E.; Cota, Ernesto; Ulloa, Sergio E.

2017-05-01

We characterize numerically and analytically the signatures of the spin-orbit interaction in a two-electron GaAs double quantum dot in the presence of an external magnetic field. In particular, we obtain the return probability of the singlet state by simulating Landau-Zener voltage detuning sweeps which traverse the singlet-triplet (S -T+ ) resonance. Our results indicate that non-spin-conserving interdot tunneling processes arising from the spin-orbit interaction have well defined signatures. These allow direct access to the spin-orbit interaction scales and are characterized by a frequency shift and Fourier amplitude modulation of the Rabi flopping dynamics of the singlet-triplet qubits S -T0 and S -T+ . By applying the Bloch-Feshbach projection formalism, we demonstrate analytically that the aforementioned effects originate from the interplay between spin-orbit interaction and processes driven by the hyperfine interaction between the electron spins and those of the GaAs nuclei.

Comparison of Diffusion-Weighted Imaging in the Human Brain Using Readout-Segmented EPI and PROPELLER Turbo Spin Echo With Single-Shot EPI at 7 T MRI.

PubMed

Kida, Ikuhiro; Ueguchi, Takashi; Matsuoka, Yuichiro; Zhou, Kun; Stemmer, Alto; Porter, David

2016-07-01

The purpose of the present study was to compare periodically rotated overlapping parallel lines with enhanced reconstruction-type turbo spin echo diffusion-weighted imaging (pTSE-DWI) and readout-segmented echo planar imaging (rsEPI-DWI) with single-shot echo planar imaging (ssEPI-DWI) in a 7 T human MR system. We evaluated the signal-to-noise ratio (SNR), image distortion, and apparent diffusion coefficient values in the human brain. Six healthy volunteers were included in this study. The study protocol was approved by our institutional review board. All measurements were performed at 7 T using pTSE-DWI, rsEPI-DWI, and ssEPI-DWI sequences. The spatial resolution was 1.2 × 1.2 mm in-plane with a 3-mm slice thickness. Signal-to-noise ratio was measured using 2 scans. The ssEPI-DWI sequence showed significant image blurring, whereas pTSE-DWI and rsEPI-DWI sequences demonstrated high image quality with low geometrical distortion compared with reference T2-weighted, turbo spin echo images. Signal loss in ventral regions near the air-filled paranasal sinus/nasal cavity was found in ssEPI-DWI and rsEPI-DWI but not pTSE-DWI. The apparent diffusion coefficient values for ssEPI-DWI were 824 ± 17 × 10 and 749 ± 25 × 10 mm/s in the gray matter and white matter, respectively; the values obtained for pTSE-DWI were 798 ± 21 × 10 and 865 ± 40 × 10 mm/s; and the values obtained for rsEPI-DWI were 730 ± 12 × 10 and 722 ± 25 × 10 mm/s. The pTSE-DWI images showed no additional distortion comparison to the T2-weighted images, but had a lower SNR than ssEPI-DWI and rsEPI-DWI. The rsEPI-DWI sequence provided high-quality images with minor distortion and a similar SNR to ssEPI-DWI. Our results suggest that the benefits of the rsEPI-DWI and pTSE-DWI sequences, in terms of SNR, image quality, and image distortion, appear to outweigh those of ssEPI-DWI. Thus, pTSE-DWI and rsEPI-DWI at 7 T have great potential use for clinical diagnoses. However, it is noteworthy that both sequences are limited by the scan time required. In addition, pTSE-DWI has limitations on the number of slices due to specific absorption rate. Overall, rsEPI-DWI is a favorable imaging sequence, taking into account the SNR and image quality at 7 T.

Isolated Spin Qubits in SiC with a High-Fidelity Infrared Spin-to-Photon Interface

NASA Astrophysics Data System (ADS)

Christle, David J.; Klimov, Paul V.; de las Casas, Charles F.; Szász, Krisztián; Ivády, Viktor; Jokubavicius, Valdas; Ul Hassan, Jawad; Syväjärvi, Mikael; Koehl, William F.; Ohshima, Takeshi; Son, Nguyen T.; Janzén, Erik; Gali, Ádám; Awschalom, David D.

2017-04-01

The divacancies in SiC are a family of paramagnetic defects that show promise for quantum communication technologies due to their long-lived electron spin coherence and their optical addressability at near-telecom wavelengths. Nonetheless, a high-fidelity spin-photon interface, which is a crucial prerequisite for such technologies, has not yet been demonstrated. Here, we demonstrate that such an interface exists in isolated divacancies in epitaxial films of 3C-SiC and 4H-SiC. Our data show that divacancies in 4H-SiC have minimal undesirable spin mixing, and that the optical linewidths in our current sample are already similar to those of recent remote entanglement demonstrations in other systems. Moreover, we find that 3C-SiC divacancies have a millisecond Hahn-echo spin coherence time, which is among the longest measured in a naturally isotopic solid. The presence of defects with these properties in a commercial semiconductor that can be heteroepitaxially grown as a thin film on Si shows promise for future quantum networks based on SiC defects.

MR Fingerprinting Using The Quick Echo Splitting NMR Imaging Technique

PubMed Central

Jiang, Yun; Ma, Dan; Jerecic, Renate; Duerk, Jeffrey; Seiberlich, Nicole; Gulani, Vikas; Griswold, Mark A.

2016-01-01

Purpose The purpose of the study is to develop a quantitative method for the relaxation properties with a reduced radio frequency (RF) power deposition by combining Magnetic Resonance Fingerprinting (MRF) technique with Quick Echo Splitting NMR Imaging Technique (QUEST). Methods A QUEST-based MRF sequence was implemented to acquire high order echoes by increasing the gaps between RF pulses. Bloch simulations were used to calculate a dictionary containing the range of physically plausible signal evolutions using a range of T1 and T2 values based on the pulse sequence. MRF-QUEST was evaluated by comparing to the results of spin-echo methods. The SAR of QUEST-MRF was compared to the clinically available methods. Results MRF-QUEST quantifies the relaxation properties with good accuracy at the estimated head Specific Absorption Rate (SAR) of 0.03 W/kg. T1 and T2 values estimated by MRF-QUEST are in good agreement with the traditional methods. Conclusion The combination of the MRF and the QUEST provides an accurate quantification of T1 and T2 simultaneously with reduced RF power deposition. The resulting lower SAR may provide a new acquisition strategy for MRF when RF energy deposition is problematic. PMID:26924639

Backscattering of sound from targets in an Airy caustic formed by a curved reflecting surface

NASA Astrophysics Data System (ADS)

Dzikowicz, Benjamin Robert

The focusing of a caustic associated with the reflection of a locally curved sea floor or surface affects the scattering of sound by underwater targets. The most elementary caustic formed when sound reflects off a naturally curved surface is an Airy caustic. The case of a spherical target is examined here. With a point source acting also as a receiver, a point target lying in a shadow region returns only one echo directly from the target. When the target is on the Airy caustic, there are two echoes: one path is directly to the target and the other focuses off the curved surface. Echoes may be focused in both directions, the doubly focused case being the largest and the latest echo. With the target in the lit region, these different paths produce multiple echoes. For a finite sized sphere near an Airy caustic, all these echoes are manifest, but they occur at shifted target positions. Echoes of tone bursts reflecting only once overlap and interfere with each other, as do those reflecting twice. Catastrophe theory is used to analyze the echo amplitudes arising from these overlaps. The echo pressure for single reflections is shown to have a dependence on target position described by an Airy function for both a point and a finite target. With double focusing, this dependence is the square of an Airy function for a point target. With a finite sized target, (as in the experiment) this becomes a hyperbolic umbilic catastrophe integral with symmetric arguments. The arguments of each of these functions are derived from only the relative echo times of a transient pulse. Transient echo times are calculated using a numerical ray finding technique. Experiment confirms the predicted merging of transient echoes in the time domain, as well as the Airy and hyperbolic umbilic diffraction integral amplitudes for a tone burst. This method allows targets to be observed at greater distances in the presence of a focusing surface.

Fast Single-Shot Hold Spin Readout in Double Quantum Dots

NASA Astrophysics Data System (ADS)

Bogan, Alexander; Studenikin, Sergei; Korkusinski, Marek; Aers, Geof; Gaudreau, Louis; Zawadzki, Piotr; Sachrajda, Andy; Tracy, Lisa; Reno, John; Hargett, Terry

Solid state spin qubits in quantum dots hold promise as scalable, high-density qubits in quantum information processing architectures. While much of the experimental investigation of these devices and their physics has focused on confined electron spins, hole spins in III-V semiconductors are attractive alternatives to electrons due to the reduced hyperfine coupling between the spin and the incoherent nuclear environment. In this talk, we will discuss a measurement protocol of the hole spin relaxation time T1 in a gated lateral GaAs double quantum dot tuned to the one and two-hole regimes, as well as a new technique for single-shot projective measurement of a single spin in tens of nanoseconds or less. The technique makes use of fast non-spin-conserving inter-dot transitions permitted by strong spin-orbit interactions for holes, as well as the latching of the charge state of the second quantum dot for enhanced sensitivity. This technique allows a direct measurement of the single spin relaxation time on time-scales set by physical device rather than by limitations of the measurement circuit.

Spin foam propagator: A new perspective to include the cosmological constant

NASA Astrophysics Data System (ADS)

Han, Muxin; Huang, Zichang; Zipfel, Antonia

2018-04-01

In recent years, the calculation of the first nonvanishing order of the metric 2-point function or graviton propagator in a semiclassical limit has evolved as a standard test for the credibility of a proposed spin foam model. The existing results of spin foam graviton propagators rely heavily on the so-called double scaling limit where spins j are large and the Barbero-Immirzi parameter γ is small such that the area A ∝j γ is approximately constant. However, it seems that this double scaling limit is bound to break down in models including a cosmological constant. We explore this in detail for the recently proposed model [7 H. M. Haggard, M. Han, W. Kaminski, and A. Riello, Nucl. Phys. B900, 1 (2015), 10.1016/j.nuclphysb.2015.08.023.] by Haggard, Han, Kaminski, and Riello and discuss alternative definitions of a graviton propagator, in which the double scaling limit can be avoided.

Echoes of the Vision: When the Rest of the Organization Talks Total Quality.

ERIC Educational Resources Information Center

Fairhurst, Gail T.

1993-01-01

Describes a case study of an organization that recently began implementing W. E. Deming's Total Quality (TQ). Finds and discusses five framing devices used in routine work conversations between leaders and members to implement the TQ vision: communicated predicaments, possible futures, jargon and vision themes, positive spin, and agenda setting.…

Decoherence and fluctuation dynamics of the quantum dot nuclear spin bath probed by nuclear magnetic resonance

NASA Astrophysics Data System (ADS)

Chekhovich, Evgeny A.

2017-06-01

Dynamics of nuclear spin decoherence and nuclear spin flip-flops in self-assembled InGaAs/GaAs quantum dots are studied experimentally using optically detected nuclear magnetic resonance (NMR). Nuclear spin-echo decay times are found to be in the range 1-4 ms. This is a factor of ~3 longer than in strain-free GaAs/AlGaAs structures and is shown to result from strain-induced quadrupolar effects that suppress nuclear spin flip-flops. The correlation times of the flip-flops are examined using a novel frequency-comb NMR technique and are found to exceed 1 s, a factor of ~1000 longer than in strain-free structures. These findings complement recent studies of electron spin coherence and reveal the paradoxical dual role of the quadrupolar effects in self-assembled quantum dots: large increase of the nuclear spin bath coherence and at the same time significant reduction of the electron spin-qubit coherence. Approaches to increasing electron spin coherence are discussed. In particular the nanohole filled GaAs/AlGaAs quantum dots are an attractive option: while their optical quality matches the self-assembled dots the quadrupolar effects measured in NMR spectra are a factor of 1000 smaller.

Large spin-orbit torques in Pt/Co-Ni/W heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Jiawei; Qiu, Xuepeng; Legrand, William

2016-07-25

The spin orbit torques (SOTs) in perpendicularly magnetized Co-Ni multilayers sandwiched between two heavy metals (HM) have been studied. By exploring various HM materials, we show an efficient enhancement or cancellation of the total SOT, depending on the combination of the two HM materials. The maximum SOT effective field is obtained in Pt/Co-Ni/W heterostructures. We also model our double HM system and show that the effective spin Hall angle has a peak value at certain HM thicknesses. Measuring the SOT in Pt/Co-Ni/W for various W thicknesses confirms an effective spin Hall angle up to 0.45 in our double HM system.

DNA with Parallel Strand Orientation: A Nanometer Distance Study with Spin Labels in the Watson-Crick and the Reverse Watson-Crick Double Helix.

PubMed

Wunnicke, Dorith; Ding, Ping; Yang, Haozhe; Seela, Frank; Steinhoff, Heinz-Jürgen

2015-10-29

Parallel-stranded (ps) DNA characterized by its sugar-phosphate backbones pointing in the same direction represents an alternative pairing system to antiparallel-stranded (aps) DNA with the potential to inhibit transcription and translation. 25-mer oligonucleotides were selected containing only dA·dT base pairs to compare spin-labeled nucleobase distances over a range of 10 or 15 base pairs in ps DNA with those in aps DNA. By means of the copper(I)-catalyzed Huisgen-Meldal-Sharpless alkyne-azide cycloaddition, the spin label 4-azido-2,2,6,6-tetramethylpiperidine-1-oxyl was clicked to 7-ethynyl-7-deaza-2'-deoxyadenosine or 5-ethynyl-2'-deoxyuridine to yield 25-mer oligonucleotides incorporating two spin labels. The interspin distances between spin labeled residues were determined by pulse EPR spectroscopy. The results reveal that in ps DNA these distances are between 5 and 10% longer than in aps DNA when the labeled DNA segment is located near the center of the double helix. The interspin distance in ps DNA becomes shorter compared with aps DNA when one of the spin labels occupies a position near the end of the double helix.

MTR and In-vivo 1H-MRS studies on mouse brain with parkinson's disease

NASA Astrophysics Data System (ADS)

Yoon, Moon-Hyun; Kim, Hyeon-Jin; Chung, Jin-Yeung; Doo, Ah-Reum; Park, Hi-Joon; Kim, Seung-Nam; Choe, Bo-Young

2012-12-01

The aim of this study was to investigate whether the changes in the magnetization transfer ratio (MTR) histogram are related to specific characteristics of Parkinson's disease (PD) and to investigate whether the MTR histogram parameters are associated with neurochemical dysfunction by performing in vivo proton magnetic resonance spectroscopy (1H-MRS). MTR and in vivo 1H-MRS studies were performed on control mice (n = 10) and 1-methyl-1,2,3,6-tetrahydropyridine intoxicated mice (n = 10). All the MTR and in vivo 1H-MRS experiments were performed on a 9.4 T MRI/MRS system (Bruker Biospin, Germany) using a standard head coil. The protondensity fast spin echo (FSE) images and the T2-weighted spin echo (SE) images were acquired with no gap. Outer volume suppression (OVS), combined with the ultra-short echo-time stimulated echo acquisition mode (STEAM), was used for the localized in-vivo 1H-MRS. The quantitative analysis of metabolites was performed from the 1H spectra obtained in vivo on the striatum (ST) by using jMRUI (Lyon, France). The peak height of the MTR histograms in the PD model group was significantly lower than that in the control group (p < 0.05). The midbrain MTR values for volume were lower in the PD group than the control group(p < 0.05). The complex peak (Glx: glutamine+glutamate+ GABA)/creatine (Cr) ratio of the right ST in the PD group was significantly increased as compared to that of the control group. The present study revealed that the peak height of the MTR histogram was significantly decreased in the ST and substantia nigra, and a significant increase in the Gl x /Cr ratio was found in the ST of the PD group, as compared with that of the control group. These findings could reflect the early phase of neuronal dysfunction of neurotransmitters.

Simultaneous Measurement of T2 and Apparent Diffusion Coefficient (T2+ADC) in the Heart With Motion-Compensated Spin Echo Diffusion-Weighted Imaging

PubMed Central

Aliotta, Eric; Moulin, Kévin; Zhang, Zhaohuan; Ennis, Daniel B.

2018-01-01

Purpose To evaluate a technique for simultaneous quantitative T2 and apparent diffusion coefficient (ADC) mapping in the heart (T2+ADC) using spin echo (SE) diffusion-weighted imaging (DWI). Theory and Methods T2 maps from T2+ADC were compared with single-echo SE in phantoms and with T2-prepared (T2-prep) balanced steady-state free precession (bSSFP) in healthy volunteers. ADC maps from T2+ADC were compared with conventional DWI in phantoms and in vivo. T2+ADC was also demonstrated in a patient with acute myocardial infarction (MI). Results Phantom T2 values from T2+ADC were closer to a single-echo SE reference than T2-prep bSSFP (−2.3 ± 6.0% vs 22.2 ± 16.3%; P < 0.01), and ADC values were in excellent agreement with DWI (0.28 ± 0.4%). In volunteers, myocardial T2 values from T2+ADC were significantly shorter than T2-prep bSSFP (35.8 ± 3.1 vs 46.8 ± 3.8 ms; P < 0.01); myocardial ADC was not significantly (N.S.) different between T2+ADC and conventional motion-compensated DWI (1.39 ± 0.18 vs 1.38 ± 0.18 mm2/ms; P = N.S.). In the patient, T2 and ADC were both significantly elevated in the infarct compared with remote myocardium (T2: 40.4 ± 7.6 vs 56.8 ± 22.0; P < 0.01; ADC: 1.47 ± 0.59 vs 1.65 ± 0.65 mm2/ms; P < 0.01). Conclusion T2+ADC generated coregistered, free-breathing T2 and ADC maps in healthy volunteers and a patient with acute MI with no cost in accuracy, precision, or scan time compared with DWI. PMID:28516485

TU-H-CAMPUS-IeP2-01: Quantitative Evaluation of PROPELLER DWI Using QIBA Diffusion Phantom

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yung, J; Ai, H; Liu, H

Purpose: The purpose of this study is to determine the quantitative variability of apparent diffusion coefficient (ADC) values when varying imaging parameters in a diffusion-weighted (DW) fast spin echo (FSE) sequence with Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction (PROPELLER) k-space trajectory. Methods: Using a 3T MRI scanner, a NIST traceable, quantitative magnetic resonance imaging (MRI) diffusion phantom (High Precision Devices, Inc, Boulder, Colorado) consisting of 13 vials filled with various concentrations of polymer polyvinylpyrrolidone (PVP) in aqueous solution was imaged with a standard Quantitative Imaging Biomarkers Alliance (QIBA) DWI spin echo, echo planar imaging (SE EPI) acquisition. Themore » same phantom was then imaged with a DWI PROPELLER sequence at varying echo train lengths (ETL) of 8, 20, and 32, as well as b-values of 400, 900, and 2000. QIBA DWI phantom analysis software was used to generate ADC maps and create region of interests (ROIs) for quantitative measurements of each vial. Mean and standard deviations of the ROIs were compared. Results: The SE EPI sequence generated ADC values that showed very good agreement with the known ADC values of the phantom (r2 = 0.9995, slope = 1.0061). The ADC values measured from the PROPELLER sequences were inflated, but were highly correlated with an r2 range from 0.8754 to 0.9880. The PROPELLER sequence with an ETL=20 and b-value of 0 and 2000 showed the closest agreement (r2 = 0.9034, slope = 0.9880). Conclusion: The DW PROPELLER sequence is promising for quantitative evaluation of ADC values. A drawback of the PROPELLER sequence is the longer acquisition time. The 180° refocusing pulses may also cause the observed increase in ADC values compared to the standard SE EPI DW sequence. However, the FSE sequence offers an advantage with in-plane motion and geometric distortion which will be investigated in future studies.« less

Imaging of pediatric great vessel stents: Computed tomography or magnetic resonance imaging?

PubMed Central

van Hamersvelt, R. W.; Budde, R. P. J.; de Jong, P. A.; Schilham, A. M. R.; Bos, C.; Breur, J. M. P. J.; Leiner, T.

2017-01-01

Background Complications might occur after great vessel stent implantation in children. Therefore follow-up using imaging is warranted. Purpose To determine the optimal imaging modality for the assessment of stents used to treat great vessel obstructions in children. Material and methods Five different large vessel stents were evaluated in an in-vitro setting. All stents were expanded to the maximal vendor recommended diameter (20mm; n = 4 or 10mm; n = 1), placed in an anthropomorphic chest phantom and imaged with a 256-slice CT-scanner. MRI images were acquired at 1.5T using a multi-slice T2-weighted turbo spin echo, an RF-spoiled three-dimensional T1-weighted Fast Field Echo and a balanced turbo field echo 3D sequence. Two blinded observers assessed stent lumen visibility (measured diameter/true diameter *100%) in the center and at the outlets of the stent. Reproducibility of diameter measurements was evaluated using the intraclass correlation coefficient for reliability and 95% limits of agreement for agreement analysis. Results Median stent lumen visibility was 88 (IQR 86–90)% with CT for all stents at both the center and outlets. With MRI, the T2-weighted turbo spin echo sequence was preferred which resulted in 82 (78–84%) stent lumen visibility. Interobserver reliability and agreement was good for both CT (ICC 0.997, mean difference -0.51 [-1.07–0.05] mm) and MRI measurements (ICC 0.951, mean difference -0.05 [-2.52 –-2.41] mm). Conclusion Good in-stent lumen visibility was achievable in this in-vitro study with both CT and MRI in different great vessel stents. Overall reliability was good with clinical acceptable limits of agreement for both CT and MRI. However, common conditions such as in-stent stenosis and associated aneurysms were not tested in this in-vitro study, limiting the value of the in-vitro study. PMID:28141852

Magnetic resonance imaging investigation of the bone conduction implant – a pilot study at 1.5 Tesla

PubMed Central

Jansson, Karl-Johan Fredén; Håkansson, Bo; Reinfeldt, Sabine; Rigato, Cristina; Eeg-Olofsson, Måns

2015-01-01

Purpose The objective of this pilot study was to investigate if an active bone conduction implant (BCI) used in an ongoing clinical study withstands magnetic resonance imaging (MRI) of 1.5 Tesla. In particular, the MRI effects on maximum power output (MPO), total harmonic distortion (THD), and demagnetization were investigated. Implant activation and image artifacts were also evaluated. Methods and materials One implant was placed on the head of a test person at the position corresponding to the normal position of an implanted BCI and applied with a static pressure using a bandage and scanned in a 1.5 Tesla MRI camera. Scanning was performed both with and without the implant, in three orthogonal planes, and for one spin-echo and one gradient-echo pulse sequence. Implant functionality was verified in-between the scans using an audio processor programmed to generate a sequence of tones when attached to the implant. Objective verification was also carried out by measuring MPO and THD on a skull simulator as well as retention force, before and after MRI. Results It was found that the exposure of 1.5 Tesla MRI only had a minor effect on the MPO, ie, it decreased over all frequencies with an average of 1.1±2.1 dB. The THD remained unchanged above 300 Hz and was increased only at lower frequencies. The retention magnet was demagnetized by 5%. The maximum image artifacts reached a distance of 9 and 10 cm from the implant in the coronal plane for the spin-echo and the gradient-echo sequence, respectively. The test person reported no MRI induced sound from the implant. Conclusion This pilot study indicates that the present BCI may withstand 1.5 Tesla MRI with only minor effects on its performance. No MRI induced sound was reported, but the head image was highly distorted near the implant. PMID:26604836

Magnetic resonance imaging investigation of the bone conduction implant - a pilot study at 1.5 Tesla.

PubMed

Jansson, Karl-Johan Fredén; Håkansson, Bo; Reinfeldt, Sabine; Rigato, Cristina; Eeg-Olofsson, Måns

2015-01-01

The objective of this pilot study was to investigate if an active bone conduction implant (BCI) used in an ongoing clinical study withstands magnetic resonance imaging (MRI) of 1.5 Tesla. In particular, the MRI effects on maximum power output (MPO), total harmonic distortion (THD), and demagnetization were investigated. Implant activation and image artifacts were also evaluated. One implant was placed on the head of a test person at the position corresponding to the normal position of an implanted BCI and applied with a static pressure using a bandage and scanned in a 1.5 Tesla MRI camera. Scanning was performed both with and without the implant, in three orthogonal planes, and for one spin-echo and one gradient-echo pulse sequence. Implant functionality was verified in-between the scans using an audio processor programmed to generate a sequence of tones when attached to the implant. Objective verification was also carried out by measuring MPO and THD on a skull simulator as well as retention force, before and after MRI. It was found that the exposure of 1.5 Tesla MRI only had a minor effect on the MPO, ie, it decreased over all frequencies with an average of 1.1±2.1 dB. The THD remained unchanged above 300 Hz and was increased only at lower frequencies. The retention magnet was demagnetized by 5%. The maximum image artifacts reached a distance of 9 and 10 cm from the implant in the coronal plane for the spin-echo and the gradient-echo sequence, respectively. The test person reported no MRI induced sound from the implant. This pilot study indicates that the present BCI may withstand 1.5 Tesla MRI with only minor effects on its performance. No MRI induced sound was reported, but the head image was highly distorted near the implant.

BOLD temporal dynamics of rat superior colliculus and lateral geniculate nucleus following short duration visual stimulation.

PubMed

Lau, Condon; Zhou, Iris Y; Cheung, Matthew M; Chan, Kevin C; Wu, Ed X

2011-04-29

The superior colliculus (SC) and lateral geniculate nucleus (LGN) are important subcortical structures for vision. Much of our understanding of vision was obtained using invasive and small field of view (FOV) techniques. In this study, we use non-invasive, large FOV blood oxygenation level-dependent (BOLD) fMRI to measure the SC and LGN's response temporal dynamics following short duration (1 s) visual stimulation. Experiments are performed at 7 tesla on Sprague Dawley rats stimulated in one eye with flashing light. Gradient-echo and spin-echo sequences are used to provide complementary information. An anatomical image is acquired from one rat after injection of monocrystalline iron oxide nanoparticles (MION), a blood vessel contrast agent. BOLD responses are concentrated in the contralateral SC and LGN. The SC BOLD signal measured with gradient-echo rises to 50% of maximum amplitude (PEAK) 0.2±0.2 s before the LGN signal (p<0.05). The LGN signal returns to 50% of PEAK 1.4±1.2 s before the SC signal (p<0.05). These results indicate the SC signal rises faster than the LGN signal but settles slower. Spin-echo results support these findings. The post-MION image shows the SC and LGN lie beneath large blood vessels. This subcortical vasculature is similar to that in the cortex, which also lies beneath large vessels. The LGN lies closer to the large vessels than much of the SC. The differences in response timing between SC and LGN are very similar to those between deep and shallow cortical layers following electrical stimulation, which are related to depth-dependent blood vessel dilation rates. This combined with the similarities in vasculature between subcortex and cortex suggest the SC and LGN timing differences are also related to depth-dependent dilation rates. This study shows for the first time that BOLD responses in the rat SC and LGN following short duration visual stimulation are temporally different.

Imaging of pediatric great vessel stents: Computed tomography or magnetic resonance imaging?

PubMed

den Harder, A M; Suchá, D; van Hamersvelt, R W; Budde, R P J; de Jong, P A; Schilham, A M R; Bos, C; Breur, J M P J; Leiner, T

2017-01-01

Complications might occur after great vessel stent implantation in children. Therefore follow-up using imaging is warranted. To determine the optimal imaging modality for the assessment of stents used to treat great vessel obstructions in children. Five different large vessel stents were evaluated in an in-vitro setting. All stents were expanded to the maximal vendor recommended diameter (20mm; n = 4 or 10mm; n = 1), placed in an anthropomorphic chest phantom and imaged with a 256-slice CT-scanner. MRI images were acquired at 1.5T using a multi-slice T2-weighted turbo spin echo, an RF-spoiled three-dimensional T1-weighted Fast Field Echo and a balanced turbo field echo 3D sequence. Two blinded observers assessed stent lumen visibility (measured diameter/true diameter *100%) in the center and at the outlets of the stent. Reproducibility of diameter measurements was evaluated using the intraclass correlation coefficient for reliability and 95% limits of agreement for agreement analysis. Median stent lumen visibility was 88 (IQR 86-90)% with CT for all stents at both the center and outlets. With MRI, the T2-weighted turbo spin echo sequence was preferred which resulted in 82 (78-84%) stent lumen visibility. Interobserver reliability and agreement was good for both CT (ICC 0.997, mean difference -0.51 [-1.07-0.05] mm) and MRI measurements (ICC 0.951, mean difference -0.05 [-2.52 --2.41] mm). Good in-stent lumen visibility was achievable in this in-vitro study with both CT and MRI in different great vessel stents. Overall reliability was good with clinical acceptable limits of agreement for both CT and MRI. However, common conditions such as in-stent stenosis and associated aneurysms were not tested in this in-vitro study, limiting the value of the in-vitro study.

Contrast-enhanced 3-dimensional SPACE versus MP-RAGE for the detection of brain metastases: considerations with a 32-channel head coil.

PubMed

Reichert, Miriam; Morelli, John N; Runge, Val M; Tao, Ai; von Ritschl, Ruediger; von Ritschl, Andreas; Padua, Abraham; Dix, James E; Marra, Michael J; Schoenberg, Stefan O; Attenberger, Ulrike I

2013-01-01

The aim of this study was to compare the detection of brain metastases at 3 T using a 32-channel head coil with 2 different 3-dimensional (3D) contrast-enhanced sequences, a T1-weighted fast spin-echo-based (SPACE; sampling perfection with application-optimized contrasts using different flip angle evolutions) sequence and a conventional magnetization-prepared rapid gradient-echo (MP-RAGE) sequence. Seventeen patients with 161 brain metastases were examined prospectively using both SPACE and MP-RAGE sequences on a 3-T magnetic resonance system. Eight healthy volunteers were similarly examined for determination of signal-to-noise ratio (SNR) values. Parameters were adjusted to equalize acquisition times between the sequences (3 minutes and 30 seconds). The order in which sequences were performed was randomized. Two blinded board-certified neuroradiologists evaluated the number of detectable metastatic lesions with each sequence relative to a criterion standard reading conducted at the Gamma Knife facility by a neuroradiologist with access to all clinical and imaging data. In the volunteer assessment with SPACE and MP-RAGE, SNR (10.3 ± 0.8 vs 7.7 ± 0.7) and contrast-to-noise ratio (0.8 ± 0.2 vs 0.5 ± 0.1) were statistically significantly greater with the SPACE sequence (P < 0.05). Overall, lesion detection was markedly improved with the SPACE sequence (99.1% of lesions for reader 1 and 96.3% of lesions for reader 2) compared with the MP-RAGE sequence (73.6% of lesions for reader 1 and 68.5% of lesions for reader 2; P < 0.01). A 3D T1-weighted fast spin echo sequence (SPACE) improves detection of metastatic lesions relative to 3D T1-weighted gradient-echo-based scan (MP-RAGE) imaging when implemented with a 32-channel head coil at identical scan acquisition times (3 minutes and 30 seconds).

The robustness of T2 value as a trabecular structural index at multiple spatial resolutions of 7 Tesla MRI.

PubMed

Lee, D K; Song, Y K; Park, B W; Cho, H P; Yeom, J S; Cho, G; Cho, H

2018-04-15

To evaluate the robustness of MR transverse relaxation times of trabecular bone from spin-echo and gradient-echo acquisitions at multiple spatial resolutions of 7 T. The effects of MRI resolutions to T 2 and T2* of trabecular bone were numerically evaluated by Monte Carlo simulations. T 2 , T2*, and trabecular structural indices from multislice multi-echo and UTE acquisitions were measured in defatted human distal femoral condyles on a 7 T scanner. Reference structural indices were extracted from high-resolution microcomputed tomography images. For bovine knee trabecular samples with intact bone marrow, T 2 and T2* were measured by degrading spatial resolutions on a 7 T system. In the defatted trabecular experiment, both T 2 and T2* values showed strong ( |r| > 0.80) correlations with trabecular spacing and number, at a high spatial resolution of 125 µm 3 . The correlations for MR image-segmentation-derived structural indices were significantly degraded ( |r| < 0.50) at spatial resolutions of 250 and 500 µm 3 . The correlations for T2* rapidly dropped ( |r| < 0.50) at a spatial resolution of 500 µm 3 , whereas those for T 2 remained consistently high ( |r| > 0.85). In the bovine trabecular experiments with intact marrow, low-resolution (approximately 1 mm 3 , 2 minutes) T 2 values did not shorten ( |r| > 0.95 with respect to approximately 0.4 mm 3 , 11 minutes) and maintained consistent correlations ( |r| > 0.70) with respect to trabecular spacing (turbo spin echo, 22.5 minutes). T 2 measurements of trabeculae at 7 T are robust with degrading spatial resolution and may be preferable in assessing trabecular spacing index with reduced scan time, when high-resolution 3D micro-MRI is difficult to obtain. © 2018 International Society for Magnetic Resonance in Medicine.

Diagnosis of hepatic metastasis: comparison of respiration-triggered diffusion-weighted echo-planar MRI and five t2-weighted turbo spin-echo sequences.

PubMed

Bruegel, Melanie; Gaa, Jochen; Waldt, Simone; Woertler, Klaus; Holzapfel, Konstantin; Kiefer, Berthold; Rummeny, Ernst J

2008-11-01

The purpose of this study was to compare the value of respiration-triggered diffusion-weighted (DW) single-shot echo-planar MRI (EPI) and five variants of T2-weighted turbo spin-echo (TSE) sequences in the diagnosis of hepatic metastasis. Fifty-two patients with extrahepatic primary malignant tumors underwent 1.5-T MRI that included DW EPI and the following variants of T2-weighted TSE techniques: breath-hold fat-suppressed HASTE, breath-hold fat-supressed TSE, respiration-triggered fat-suppressed TSE, breath-hold STIR, and respiration-triggered STIR. Images were reviewed independently by two blinded observers who used a 5-point confidence scale to identify lesions. Results were correlated with surgical and histopathologic findings and follow-up imaging findings. The accuracy of each technique was measured with free-response receiver operating characteristic analysis. A total of 118 hepatic metastatic lesions (mean diameter, 12.8 mm; range, 3-84 mm) were evaluated. Accuracy values were higher (p < 0.001) with DW EPI (0.91-0.92) than with the T2-weighted TSE techniques (0.47-0.67). Imaging with the HASTE sequence (0.47-0.52) was less accurate (p < 0.05) than imaging with the breath-hold TSE, breath-hold STIR, respiration-triggered TSE, and respiration-triggered STIR sequences (0.59-0.67). Sensitivity was higher (p < 0.001) with DW EPI (0.88-0.91) than with T2-weighted TSE techniques (0.45-0.62). For small (< or = 10 mm) metastatic lesions only, the differences in sensitivity between DW EPI (0.85) and T2-weighted TSE techniques (0.26-0.44) were even more pronounced. DW EPI was more sensitive and more accurate than imaging with T2-weighted TSE techniques. Because of the black-blood effect on vessels and low susceptibility to motion artifacts, DW EPI was particularly useful for the detection of small (< or = 10 mm) metastatic lesions.

Charge separation in photoredox reactions. Technical progress report, May 1, 1981-May 1, 1984. [N,N,N',N'-tetramethylbenzidine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kevan, L.

1984-05-01

The structural aspects controlling charge separation in molecular photoionization reactions in organized molecular assemblies involving micelles and vesicles are being studied by optical and electron magnetic resonance techniques including the time domain technique of electron spin echo modulation (ESEM). Photoionization of N,N,N',N'-tetramethylbenzidine (TMB) to give the cation radical has been carried out in both liquid and frozen micellar and vesicular solutions. Cation-water interactions have been detected by ESEM analysis and indicate that the cation is localized asymmetrically within these organized molecular assemblies. x-Doxylstearic acid spin probes have been used to determine that the neutral TMB molecule before photoionization is alsomore » localized asymmetrically within such organized molecular assemblies. Electron spin echo detection of laser photogenerated TMB cation in liquid micellar solutions gives a direct measurement of the phase memory magnetic relaxation time which gives additional structural information. The photoionization efficiency has been related to cation-water interactions measured by ESEM. The photoionization efficiency is also dependent on surface charge and is about twofold greater in cationic micelles and vesicles compared to anionic micelles and vesicles. TMB is in a less polar environment in vesicles compared to micelles consistent with ESEM results. The preferential adsorption of metal species at micellar surfaces has been detected by ESEM. Modifications in the micelle surface have been effected by added salts and varying counterions which have been related to cation-water interactions and to the TMB photoionization efficiency. Corresponding changes in the surface and internal micellar structure have been investigated by x-doxylstearic acid spin probes and specifically deuterated surfactants. The decay kinetics of TMB cations in micelles have been interpreted in terms of a time dependent rate constant.« less

Effect of added sodium chloride on the molecular environment and photoionization of N,N,N',N'-tetramethylbenzidine in micellar solutions as studied by electron spin echo and electron spin resonance spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maldonado, R.; Kevan, L.; Szajdzinska-Pietek, E.

1984-11-01

The electron spin echo modulation (ESEM) and electron spin resonance (ESR) spectra of the cation radical of N,N,N',N'-tetramethylbenzidine (TMB) in frozen sodium dodecyl sulfate (SDS)= and dodecyltrimethylammonium chloride (DTAC) micelles were studied as a function of sodium chloride concentration. TMB/sup +center-dot/ was produced by photoionization at 350 nm of the parent compound in the micelles at 77 K. From the ESEM analysis it is found that the cation--water interactions increase with salt addition in both anionic and cationic micelles to a maximum near 0.2 M NaCl and then decrease somewhat. The increase is interpreted in terms of an increase inmore » the water density at the micellar surface due to an increased surface concentration of hydrated counterions. The decrease may be due to TMB moving further from the polar micellar surface with added salt. From ESR spectra the photoionization yields of TMB at 77 K were determined. For DTAC micelles the yields are found to decrease with salt addition as expected from electrostatic considerations. For SDS micelles the photoionization yields increase for salt concentrations up to about 0.15 M and decrease for greater salt concentrations up to 0.5 M. The initial increase in cation yield correlates with electrostatic expectations. The decrease may be due to TMB moving further from the polar micellar surface with added salt. The possible effect of differing TMB protonation equilibria between anionic and cationic micelles on the photoionization yields was found to be unimportant by adjusting the bulk solution pH. An important conclusion is that salt addition can be used to optimize charge separation for photoionized solutes in anionic micelles.« less

Electron spin relaxation governed by Raman processes both for Cu2+ ions and carbonate radicals in KHCO3 crystals: EPR and electron spin echo studies

NASA Astrophysics Data System (ADS)

Hoffmann, Stanislaw K.; Goslar, Janina; Lijewski, Stefan

2012-08-01

EPR studies of Cu2+ and two free radicals formed by γ-radiation were performed for KHCO3 single crystal at room temperature. From the rotational EPR results we concluded that Cu2+ is chelated by two carbonate molecules in a square planar configuration with spin-Hamiltonian parameters g|| = 2.2349 and A|| = 18.2 mT. Free radicals were identified as neutral HOCOrad with unpaired electron localized on the carbon atom and a radical anion CO3·- with unpaired electron localized on two oxygen atoms. The hyperfine splitting of the EPR lines by an interaction with a single hydrogen atom of HOCOrad was observed with isotropic coupling constants ao = 0.31 mT. Two differently oriented radical sites were identified in the crystal unit cell. Electron spin-lattice relaxation measured by electron spin echo methods shows that both Cu2+ and free radicals relax via two-phonon Raman processes with almost the same relaxation rate. The temperature dependence of the relaxation rate 1/T1 is well described with the effective Debye temperature ΘD = 175 K obtained from a fit to the Debye-type phonon spectrum. We calculated a more realistic Debye temperature value from available elastic constant values of the crystal as ΘD = 246 K. This ΘD-value and the Debye phonon spectrum approximation give a much worse fit to the experimental results. Possible contributions from a local mode or an optical mode are considered and it is suggested that the real phonon spectrum should be used for the relaxation data interpretation. It is unusual that free radicals in KHCO3 relax similarly to the well localized Cu2+ ions, which suggests a small destruction of the host crystal lattice by the ionizing irradiation allowing well coupling between radical and lattice dynamics.

Unanticipated spin gap measured in the frustrated quasi-FCC d3 double perovskites La2 LiXO6 (X = Ru, Os)

NASA Astrophysics Data System (ADS)

Maharaj, Dalini D.; Sala, Gabriele; Marjerrison, Casey A.; Greedan, John; Gaulin, Bruce; Stone, Matthew

There is much current interest in the influence of strong spin-orbit (SO) interactions on exotic ground state selection in new 4d and 5d magnets, particularly involving 4d5 Ir. Here we consider double perovskites of the form A2 BB'O6 which are based on heavy 4d or 5d magnetic ions, where the SO interaction is expected to be significant as it increases as ~Z4 . The double perovskite structure can accommodate a variety of magnetic ions on the B' site, providing a playground for systematic studies of the exotic ground states stabilized by strong SO coupling. Here, we report inelastic neutron scattering (INS) measurements conducted on the frustrated monoclinic magnets, La2LiXO6 (X = Ru, Os), wherein the magnetic moments decorate a quasi face-centered-cubic lattice. Our results show the development of a spin gap in the spin excitation spectrum of size ΔOs = 8 meV and ΔRu = 2.5meV concomitant with TN, which is unexpected for orbitally quenched d3 systems. We liken these results to INS results obtained for Ba2YXO6 and La2NaXO6, which were also shown to exhibit spin gaps that correlate with TN. We shall discuss trends observed in these three d3 double perovskite families which correlate strong SO coupling, spin gap and TN.

Double perovskites with strong spin-orbit coupling

NASA Astrophysics Data System (ADS)

Cook, Ashley M.

We first present theoretical analysis of powder inelastic neutron scattering experiments in Ba2FeReO6 performed by our experimental collaborators. Ba2FeReO6, a member of the double perovskite family of materials, exhibits half-metallic behavior and high Curie temperatures Tc, making it of interest for spintronics applications. To interpret the experimental data, we develop a local moment model, which incorporates the interaction of Fe spins with spin-orbital locked magnetic moments on Re, and show that it captures the experimental observations. We then develop a tight-binding model of the double perovskite Ba 2FeReO6, a room temperature ferrimagnet with correlated and spin-orbit coupled Re t2g electrons moving in the background of Fe moments stabilized by Hund's coupling. We show that for such 3d/5d double perovskites, strong correlations on the 5d-element (Re) are essential in driving a half-metallic ground state. Incorporating both strong spin-orbit coupling and the Hubbard repulsion on Re leads to a band structure consistent with ab initio calculations. The uncovered interplay of strong correlations and spin-orbit coupling lends partial support to our previous work, which used a local moment description to capture the spin wave dispersion found in neutron scattering measurements. We then adapt this tight-binding model to study {111}-grown bilayers of half-metallic double perovskites such as Sr2FeMoO6. The combination of spin-orbit coupling, inter-orbital hybridization and symmetry-allowed trigonal distortion leads to a rich phase diagram with tunable ferromagnetic order, topological C= +/-1, +/-2 Chern bands, and a C = +/-2 quantum anomalous Hall insulator regime. We have also performed theoretical analysis of inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites La2ZnIrO 6 and La2MgIrO6. Models with dominant Kitaev exchange seem to most naturally account for the neutron data as well as the measured frustration parameters of these materials, while the uniaxial Ising anisotropy does not. Our findings highlight how even seemingly conventional magnetic orders in oxide materials containing heavy transition metal ions may be driven by highly-directional exchange interactions rooted in strong spin-orbit coupling. Motivated by experiments on the double perovskites La2ZnIrO 6 and La2MgIrO6, we lastly study the magnetism of spin-orbit coupled jeff =1/2 iridium moments on the three-dimensional, geometrically frustrated, facecentered cubic lattice. The symmetry-allowed nearest-neighbor interaction includes Heisenberg, Kitaev, and symmetric off-diagonal exchange. A Luttinger-Tisza analysis shows a rich variety of orders, including collinear AII type antiferromagnetism, stripe order with moments along the {111}-direction, and incommensurate non-coplanar spirals, and we use Monte Carlo simulations to determine their magnetic ordering temperatures.

Spin-polarized currents in a two-terminal double quantum ring driven by magnetic fields and Rashba spin-orbit interaction

NASA Astrophysics Data System (ADS)

Dehghan, E.; Khoshnoud, D. Sanavi; Naeimi, A. S.

2018-06-01

Aim of this study is to investigate spin transportation in double quantum ring (DQR). We developed an array of DQR to measure the transmission coefficient and analyze the spin transportation through this system in the presence of Rashba spin-orbit interaction (RSOI) and magnetic flux estimated using S-matrix method. In this article, we compute the spin transport and spin-current characteristics numerically as functions of electron energy, angles between the leads, coupling constant of the leads, RSOI, and magnetic flux. Our results suggest that, for typical values of the magnetic flux (ϕ /ϕ0) and Rashba constant (αR), such system can demonstrates many spintronic properties. It is possible to design a new geometry of DQR by incoming electrons polarization in a way to optimize the system to work as a spin-filtering and spin-inverting nano-device with very high efficiency. The results prove that the spin current will strongly modulate with an increase in the magnetic flux and Rashba constant. Moreover it is shown that, when the lead coupling is weak, the perfect spin-inverter does not occur.

Reorientation of the diagonal double-stripe spin structure at Fe 1+yTe bulk and thin-film surfaces

DOE PAGES

Hanke, Torben; Singh, Udai Raj; Cornils, Lasse; ...

2017-01-06

Here, establishing the relation between ubiquitous antiferromagnetism in the parent compounds of unconventional superconductors and their superconducting phase is important for understanding the complex physics in these materials. Going from bulk systems to thin films additionally affects their phase diagram. For Fe 1+yTe, the parent compound of Fe 1+ySe 1$-x$Tex superconductors, bulk-sensitive neutron diffraction revealed an in-plane oriented diagonal double-stripe antiferromagnetic spin structure. Here we show by spin-resolved scanning tunnelling microscopy that the spin direction at the surfaces of bulk Fe 1+yTe and thin films grown on the topological insulator Bi 2Te 3 is canted out of the high-symmetry directionsmore » of the surface unit cell resulting in a perpendicular spin component, keeping the diagonal double-stripe order. As the magnetism of the Fe d-orbitals is intertwined with the superconducting pairing in Fe-based materials, our results imply that the superconducting properties at the surface of the related superconducting compounds might be different from the bulk.« less

Reorientation of the diagonal double-stripe spin structure at Fe 1+yTe bulk and thin-film surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanke, Torben; Singh, Udai Raj; Cornils, Lasse

Here, establishing the relation between ubiquitous antiferromagnetism in the parent compounds of unconventional superconductors and their superconducting phase is important for understanding the complex physics in these materials. Going from bulk systems to thin films additionally affects their phase diagram. For Fe 1+yTe, the parent compound of Fe 1+ySe 1$-x$Tex superconductors, bulk-sensitive neutron diffraction revealed an in-plane oriented diagonal double-stripe antiferromagnetic spin structure. Here we show by spin-resolved scanning tunnelling microscopy that the spin direction at the surfaces of bulk Fe 1+yTe and thin films grown on the topological insulator Bi 2Te 3 is canted out of the high-symmetry directionsmore » of the surface unit cell resulting in a perpendicular spin component, keeping the diagonal double-stripe order. As the magnetism of the Fe d-orbitals is intertwined with the superconducting pairing in Fe-based materials, our results imply that the superconducting properties at the surface of the related superconducting compounds might be different from the bulk.« less

Reexamination of Spin Transport Through a DOUBLE-δ Magnetic Barrier with Spin-Orbit Interactions

NASA Astrophysics Data System (ADS)

Bi, Caihua; Zhai, Feng

We revisit the properties of spin transport through a semiconductor 2DEG system subjected to the modulation of both a ferromagnetic metal (FM) stripe on top and the Rashba and Dresselhaus spin-orbit interactions (SOIs). The FM stripe has a magnetization along the transporting direction and generates an inhomogeneous magnetic field in the 2DEG plane which is taken as a double-δ shape. It is found that the spin polarization of this system generated from a spin-unpolarized injection can be remarkable only within a low Fermi energy region and is not more than 30% for the parameters available in current experiments. In this energy region, both the magnitude and the orientation of the spin polarization can be tuned by the Rashba strength, the Dresselhaus strength, and the magnetic field strength. The magnetization reversal of the FM stripe cannot result in a change of the conductance, but can rotate the orientation of the spin polarization. The results are in contrast to those in [ J. Phys.: Condens. Matter 15 (2003) L31] where a pure spin state for incident electrons is artificially assumed.

Improving Limits on Exotic Spin Dependent Long Range Forces using Double Boson Exchange

NASA Astrophysics Data System (ADS)

Aldaihan, Sheakha; Snow, William Michael; Krause, Dennis; Long, Joshua

2016-03-01

The existence of very light weakly interacting particles that mediate new long range forces has been suggested in many extensions of the Standard Model. Such particles span a length scale between a μm and a few meters and include axions, familons, Majorons,and arions. Parameterizations of forces in this range show that they are composite-dependent, have a Yukawa shape, and have both spin-dependent as well as spin independent components. Very stringent limits on spin-independent couplings exist. For long range spin dependent forces, limits are weaker by 20 orders of magnitude compared to their spin independent analogs. The disparity in the limits raises the question of whether interesting limits on spin dependent couplings can be inferred from spin independent searches for long range forces. We show that this is possible using higher order contributions corresponding to double boson exchange and report the limits placed on spin dependent couplings using this method. We gratefully acknowledge the support of Indiana University and the National Science Foundation. The first author also acknowdges King Abdullah scholarship program.

T2 relaxation time is related to liver fibrosis severity

PubMed Central

Siqueira, Luiz; Uppal, Ritika; Alford, Jamu; Fuchs, Bryan C.; Yamada, Suguru; Tanabe, Kenneth; Chung, Raymond T.; Lauwers, Gregory; Chew, Michael L.; Boland, Giles W.; Sahani, Duhyant V.; Vangel, Mark; Hahn, Peter F.; Caravan, Peter

2016-01-01

Background The grading of liver fibrosis relies on liver biopsy. Imaging techniques, including elastography and relaxometric, techniques have had varying success in diagnosing moderate fibrosis. The goal of this study was to determine if there is a relationship between the T2-relaxation time of hepatic parenchyma and the histologic grade of liver fibrosis in patients with hepatitis C undergoing both routine, liver MRI and liver biopsy, and to validate our methodology with phantoms and in a rat model of liver fibrosis. Methods This study is composed of three parts: (I) 123 patients who underwent both routine, clinical liver MRI and biopsy within a 6-month period, between July 1999 and January 2010 were enrolled in a retrospective study. MR imaging was performed at 1.5 T using dual-echo turbo-spin echo equivalent pulse sequence. T2 relaxation time of liver parenchyma in patients was calculated by mono-exponential fit of a region of interest (ROI) within the right lobe correlating to histopathologic grading (Ishak 0–6) and routine serum liver inflammation [aspartate aminotransferase (AST) and alanine aminotransferase (ALT)]. Statistical comparison was performed using ordinary logistic and ordinal logistic regression and ANOVA comparing T2 to Ishak fibrosis without and using AST and ALT as covariates; (II) a phantom was prepared using serial dilutions of dextran coated magnetic iron oxide nanoparticles. T2 weighed imaging was performed by comparing a dual echo fast spin echo sequence to a Carr-Purcell-Meigboom-Gill (CPMG) multi-echo sequence at 1.5 T. Statistical comparison was performed using a paired t-test; (III) male Wistar rats receiving weekly intraperitoneal injections of phosphate buffer solution (PBS) control (n=4 rats); diethylnitrosamine (DEN) for either 5 (n=5 rats) or 8 weeks (n=4 rats) were MR imaged on a Bruker Pharmascan 4.7 T magnet with a home-built bird-cage coil. T2 was quantified by using a mono-exponential fitting algorithm on multi-slice multi echo T2 weighted data. Statistical comparison was performed using ANOVA. Results (I) Histopathologic evaluation of both rat and human livers demonstrated no evidence of steatosis or hemochromatosis There was a monotonic increase in mean T2 value with increasing degree of fibrosis (control 65.4±2.9 ms, n=6 patients); mild (Ishak 1–2) 66.7±1.9 ms (n=30); moderate (Ishak 3–4) 71.6±1.7 ms (n=26); severe (Ishak 5–6) 72.4±1.4 ms (n=61); with relatively low standard error (~2.9 ms). There was a statistically significant difference between degrees of mild (Ishak <4) vs. moderate to severe fibrosis (Ishak >4) (P=0.03) based on logistic regression of T2 and Ishak, which became insignificant (P=0.07) when using inflammatory markers as covariates. Expanding on this model using ordinal logistic regression, there was significance amongst all 4 groups comparing T2 to Ishak (P=0.01), with significance using inflammation as a covariate (P=0.03) and approaching statistical significance amongst all groups by ANOVA (P=0.07); (II) there was a monotonic increase in T2 and statistical significance (ANOVA P<0.0001) between each rat subgroup [phosphate buffer solution (PBS) 25.2±0.8, DEN 5-week (31.1±1.5), and DEN 9-week (49.4±0.4) ms]; (III) the phantoms that had T2 values within the relevant range for the human liver (e.g., 20–100 ms), demonstrated no statistical difference between two point fits on turbo spin echo (TSE) data and multi-echo CPMG data (P=0.9). Conclusions The finding of increased T2 with liver fibrosis may relate to inflammation that may be an alternative or adjunct to other noninvasive MR imaging based approaches for assessing liver fibrosis. PMID:27190762

Modulation of spin transfer torque amplitude in double barrier magnetic tunnel junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clément, P.-Y.; Baraduc, C., E-mail: claire.baraduc@cea.fr; Chshiev, M.

2015-09-07

Magnetization switching induced by spin transfer torque is used to write magnetic memories (Magnetic Random Access Memory, MRAM) but can be detrimental to the reading process. It would be quite convenient therefore to modulate the efficiency of spin transfer torque. A solution is adding an extra degree of freedom by using double barrier magnetic tunnel junctions with two spin-polarizers, with controllable relative magnetic alignment. We demonstrate, for these structures, that the amplitude of in-plane spin transfer torque on the middle free layer can be efficiently tuned via the magnetic configuration of the electrodes. Using the proposed design could thus pavemore » the way towards more reliable read/write schemes for MRAM. Moreover, our results suggest an intriguing effect associated with the out-of-plane (field-like) spin transfer torque, which has to be further investigated.« less

Primary and secondary relaxation process in plastically crystalline cyanocyclohexane studied by 2H nuclear magnetic resonance. I.

PubMed

Micko, B; Lusceac, S A; Zimmermann, H; Rössler, E A

2013-02-21

We study the main (α-) and secondary (β-) relaxation in the plastically crystalline (PC) phase of cyanocyclohexane by various 2H nuclear magnetic resonance (NMR) methods (line-shape, spin-lattice relaxation, stimulated echo, and two-dimensional spectra) above and below the glass transition temperature T(g) = 134 K. Our results regarding the α-process demonstrate that molecular motion is not governed by the symmetry of the lattice. Rather it is similar to the one reported for structural glass formers and can be modeled by a reorientation proceeding via a distribution of small and large angular jumps. A solid-echo line-shape analysis regarding the β-process below T(g) yields again very similar results when compared to those of the structural glass formers ethanol and toluene. Hence we cannot confirm an intramolecular origin for the β-process in cyanocyclohexane. The fast β-process in the PC phase allows for the first time a detailed 2H NMR study of the process also at T > T(g): an additional minimum in the spin-lattice relaxation time reflecting the β-process is found. Furthermore the solid-echo spectra show a distinct deviation from the rigid limit Pake pattern, which allows a direct determination of the temperature dependent spatial restriction of the process. In Part II of this work, a quantitative analysis is carried out, where we demonstrate that within the model of a "wobbling in a cone" the mean cone angle increases above T(g) and the corresponding relaxation strength is compared to dielectric results.

Full analytical solution of the bloch equation when using a hyperbolic-secant driving function.

PubMed

Zhang, Jinjin; Garwood, Michael; Park, Jang-Yeon

2017-04-01

The frequency-swept pulse known as the hyperbolic-secant (HS) pulse is popular in NMR for achieving adiabatic spin inversion. The HS pulse has also shown utility for achieving excitation and refocusing in gradient-echo and spin-echo sequences, including new ultrashort echo-time imaging (e.g., Sweep Imaging with Fourier Transform, SWIFT) and B 1 mapping techniques. To facilitate the analysis of these techniques, the complete theoretical solution of the Bloch equation, as driven by the HS pulse, was derived for an arbitrary state of initial magnetization. The solution of the Bloch-Riccati equation for transverse and longitudinal magnetization for an arbitrary initial state was derived analytically in terms of HS pulse parameters. The analytical solution was compared with the solutions using both the Runge-Kutta method and the small-tip approximation. The analytical solution was demonstrated on different initial states at different frequency offsets with/without a combination of HS pulses. Evolution of the transverse magnetization was influenced significantly by the choice of HS pulse parameters. The deviation of the magnitude of the transverse magnetization, as obtained by comparing the small-tip approximation to the analytical solution, was < 5% for flip angles < 30 °, but > 10% for the flip angles > 40 °. The derived analytical solution provides insights into the influence of HS pulse parameters on the magnetization evolution. Magn Reson Med 77:1630-1638, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Evaluation of chondromalacia of the patella with axial inversion recovery-fast spin-echo imaging.

PubMed

Lee, S H; Suh, J S; Cho, J; Kim, S J; Kim, S J

2001-03-01

The purpose of our study was to assess the accuracy of inversion recovery-fast spin-echo (IR-FSE) imaging for the evaluation of chondromalacia of the patella. Eighty-six patients were included, they underwent magnetic resonance (MR) examination and subsequent knee arthroscopy. Medial and lateral facets of the patella were evaluated separately. Axial images were obtained by using IR-FSE (TR/TE/TI = 3000/25/150 msec; echo train length, 8; 4-mm thickness; 12-cm field of view; 512 x 256 matrix; two, number of excitations) with a 1.5-T MR machine. MR interpretation of chondromalacia was made on the basis of the arthroscopic grading system. Of a total of 172 facets graded, arthroscopy revealed chondromalacia in 14 facets with various grades (G0, 158; G1, 1; G2, 3; G3, 6; G4, 4). Sensitivity, specificity, and accuracy in the chondromalacia grades were 57.1%, 93.0%, and 90.1%, respectively. There was one false-negative case (G4) and 11 false-positive cases (G1, eight; G2, two; G3, one). Sensitivity and specificity corrected by one grade difference were improved to 85.7% and 98.1%, respectively. When cartilage changes were grouped into early (corresponding to grade 1 and 2) and advanced (grade 3 and 4) diseases, sensitivity and specificity of the early and advanced diseases were 75% and 94% and 80% and 99%, respectively. IR-FSE imaging of the knee revealed high specificity but low sensitivity for the evaluation of chondromalacia of the patella.

Lung Parenchymal Signal Intensity in MRI: A Technical Review with Educational Aspirations Regarding Reversible Versus Irreversible Transverse Relaxation Effects in Common Pulse Sequences.

PubMed

Mulkern, Robert; Haker, Steven; Mamata, Hatsuho; Lee, Edward; Mitsouras, Dimitrios; Oshio, Koichi; Balasubramanian, Mukund; Hatabu, Hiroto

2014-03-01

Lung parenchyma is challenging to image with proton MRI. The large air space results in ~l/5th as many signal-generating protons compared to other organs. Air/tissue magnetic susceptibility differences lead to strong magnetic field gradients throughout the lungs and to broad frequency distributions, much broader than within other organs. Such distributions have been the subject of experimental and theoretical analyses which may reveal aspects of lung microarchitecture useful for diagnosis. Their most immediate relevance to current imaging practice is to cause rapid signal decays, commonly discussed in terms of short T 2 * values of 1 ms or lower at typical imaging field strengths. Herein we provide a brief review of previous studies describing and interpreting proton lung spectra. We then link these broad frequency distributions to rapid signal decays, though not necessarily the exponential decays generally used to define T 2 * values. We examine how these decays influence observed signal intensities and spatial mapping features associated with the most prominent torso imaging sequences, including spoiled gradient and spin echo sequences. Effects of imperfect refocusing pulses on the multiple echo signal decays in single shot fast spin echo (SSFSE) sequences and effects of broad frequency distributions on balanced steady state free precession (bSSFP) sequence signal intensities are also provided. The theoretical analyses are based on the concept of explicitly separating the effects of reversible and irreversible transverse relaxation processes, thus providing a somewhat novel and more general framework from which to estimate lung signal intensity behavior in modern imaging practice.

Lung Parenchymal Signal Intensity in MRI: A Technical Review with Educational Aspirations Regarding Reversible Versus Irreversible Transverse Relaxation Effects in Common Pulse Sequences

PubMed Central

MULKERN, ROBERT; HAKER, STEVEN; MAMATA, HATSUHO; LEE, EDWARD; MITSOURAS, DIMITRIOS; OSHIO, KOICHI; BALASUBRAMANIAN, MUKUND; HATABU, HIROTO

2014-01-01

Lung parenchyma is challenging to image with proton MRI. The large air space results in ~l/5th as many signal-generating protons compared to other organs. Air/tissue magnetic susceptibility differences lead to strong magnetic field gradients throughout the lungs and to broad frequency distributions, much broader than within other organs. Such distributions have been the subject of experimental and theoretical analyses which may reveal aspects of lung microarchitecture useful for diagnosis. Their most immediate relevance to current imaging practice is to cause rapid signal decays, commonly discussed in terms of short T2* values of 1 ms or lower at typical imaging field strengths. Herein we provide a brief review of previous studies describing and interpreting proton lung spectra. We then link these broad frequency distributions to rapid signal decays, though not necessarily the exponential decays generally used to define T2* values. We examine how these decays influence observed signal intensities and spatial mapping features associated with the most prominent torso imaging sequences, including spoiled gradient and spin echo sequences. Effects of imperfect refocusing pulses on the multiple echo signal decays in single shot fast spin echo (SSFSE) sequences and effects of broad frequency distributions on balanced steady state free precession (bSSFP) sequence signal intensities are also provided. The theoretical analyses are based on the concept of explicitly separating the effects of reversible and irreversible transverse relaxation processes, thus providing a somewhat novel and more general framework from which to estimate lung signal intensity behavior in modern imaging practice. PMID:25228852

Coagulative interstitial laser-induced thermotherapy of benign prostatic hyperplasia: online imaging with a T2-weighted fast spin-echo MR sequence--experience in six patients.

PubMed

Mueller-Lisse, U G; Thoma, M; Faber, S; Heuck, A F; Muschter, R; Schneede, P; Weninger, E; Hofstetter, A G; Reiser, M F

1999-02-01

To determine if hypointense lesions clearly outline on T2-weighted fast spin-echo (SE) magnetic resonance (MR) images obtained during coagulative interstitial laser-induced thermotherapy (LITT) of a prostate with benign hyperplasia. In six patients with benign prostatic hyperplasia (BPH), 12 LITT treatments were followed online with repetitive axial T2-weighted fast SE imaging (repetition time, 3,700 msec; echo time, 138 msec; acquisition time, 19 seconds). Development, time course, correlation with interstitial tissue temperature, and diameters of hypointense lesions around the laser diffusor tip were investigated. Lesion diameters on T2-weighted images acquired during LITT were compared with diameters of final lesions on T2-weighted images and unperfused lesions on enhanced T1-weighted SE images obtained at the end of therapy. Hypointense lesions developed within 20-40 seconds of LITT. Average correlation coefficients between interstitial temperature development and signal intensity development were 0.92 during LITT and 0.90 after LITT. Regression slopes were significantly steeper during LITT (0.67% signal intensity change per degree Celsius) than after LITT (0.47% per degree Celsius; P = .038). Lesions remained visible after LITT for all procedures. Average maximum diameters of lesions were 1-3 mm larger during LITT than after LITT (P = .0006-.019). Repetitive T2-weighted fast SE MR imaging during interstitial coagulative LITT of BPH demonstrates the development of permanent hypointense prostate lesions. However, posttherapeutic lesion diameters tend to be overestimated during LITT.

Targeted Single-Shot Methods for Diffusion-Weighted Imaging in the Kidneys

PubMed Central

Jin, Ning; Deng, Jie; Zhang, Longjiang; Zhang, Zhuoli; Lu, Guangming; Omary, Reed A.; Larson, Andrew C.

2011-01-01

Purpose To investigate the feasibility of combining the inner-volume-imaging (IVI) technique with single-shot diffusion-weighted (DW) spin-echo echo-planar imaging (SE-EPI) and DW-SPLICE (split acquisition of fast spin-echo) sequences for renal DW imaging. Materials and Methods Renal DW imaging was performed in 10 healthy volunteers using single-shot DW-SE-EPI, DW-SPLICE, targeted-DW-SE-EPI and targeted-DW-SPLICE. We compared the quantitative diffusion measurement accuracy and image quality of these targeted-DW-SE-EPI and targeted DW-SPLICE methods with conventional full FOV DW-SE-EPI and DW-SPLICE measurements in phantoms and normal volunteers. Results Compared with full FOV DW-SE-EPI and DW-SPLICE methods, targeted-DW-SE-EPI and targeted-DW-SPLICE approaches produced images of superior overall quality with fewer artifacts, less distortion and reduced spatial blurring in both phantom and volunteer studies. The ADC values measured with each of the four methods were similar and in agreement with previously published data. There were no statistically significant differences between the ADC values and intra-voxel incoherent motion (IVIM) measurements in the kidney cortex and medulla using single-shot DW-SE-EPI, targeted-DW-EPI and targeted-DW-SPLICE (p > 0.05). Conclusion Compared with full-FOV DW imaging methods, targeted-DW-SE-EPI and targeted-DW-SPLICE techniques reduced image distortion and artifacts observed in the single-shot DW-SE-EPI images, reduced blurring in DW-SPLICE images and produced comparable quantitative DW and IVIM measurements to those produced with conventional full-FOV approaches. PMID:21591023

MR Imaging with Metal-suppression Sequences for Evaluation of Total Joint Arthroplasty.

PubMed

Talbot, Brett S; Weinberg, Eric P

2016-01-01

Metallic artifact at orthopedic magnetic resonance (MR) imaging continues to be an important problem, particularly in the realm of total joint arthroplasty. Complications often follow total joint arthroplasty and can be expected for a small percentage of all implanted devices. Postoperative complications involve not only osseous structures but also adjacent soft tissues-a highly problematic area at MR imaging because of artifacts from metallic prostheses. Without special considerations, susceptibility artifacts from ferromagnetic implants can unacceptably degrade image quality. Common artifacts include in-plane distortions (signal loss and signal pileup), poor or absent fat suppression, geometric distortion, and through-section distortion. Basic methods to reduce metallic artifacts include use of spin-echo or fast spin-echo sequences with long echo train lengths, short inversion time inversion-recovery (STIR) sequences for fat suppression, a high bandwidth, thin section selection, and an increased matrix. With care and attention to the alloy type (eg, titanium, cobalt-chromium, stainless steel), orientation of the implant, and magnetic field strength, as well as use of proprietary and nonproprietary metal-suppression techniques, previously nondiagnostic studies can yield key diagnostic information. Specifically, sequences such as the metal artifact reduction sequence (MARS), WARP (Siemens Healthcare, Munich, Germany), slice encoding for metal artifact correction (SEMAC), and multiacquisition with variable-resonance image combination (MAVRIC) can be optimized to reveal pathologic conditions previously hidden by periprosthetic artifacts. Complications of total joint arthroplasty that can be evaluated by using MR imaging with metal-suppression sequences include pseudotumoral conditions such as metallosis and particle disease, infection, aseptic prosthesis loosening, tendon injury, and muscle injury. ©RSNA, 2015.

Electromagnetic Interactions in a Shielded PET/MRI System for Simultaneous PET/MR Imaging in 9.4 T: Evaluation and Results

NASA Astrophysics Data System (ADS)

Maramraju, Sri Harsha; Smith, S. David; Rescia, Sergio; Stoll, Sean; Budassi, Michael; Vaska, Paul; Woody, Craig; Schlyer, David

2012-10-01

We previously integrated a magnetic resonance-(MR-) compatible small-animal positron emission tomograph (PET) in a Bruker 9.4 T microMRI system to obtain simultaneous PET/MR images of a rat's brain and of a gated mouse-heart. To minimize electromagnetic interactions in our MR-PET system, viz., the effect of radiofrequency (RF) pulses on the PET, we tested our modular front-end PET electronics with various shield configurations, including a solid aluminum shield and one of thin segmented layers of copper. We noted that the gradient-echo RF pulses did not affect PET data when the PET electronics were shielded with either the aluminum- or the segmented copper-shields. However, there were spurious counts in the PET data resulting from high-intensity fast spin-echo RF pulses. Compared to the unshielded condition, they were attenuated effectively by the aluminum shield ( 97%) and the segmented copper shield ( 90%). We noted a decline in the noise rates as a function of increasing PET energy-discriminator threshold. In addition, we observed a notable decrease in the signal-to-noise ratio in spin-echo MR images with the segmented copper shields in place; however, this did not substantially degrade the quality of the MR images we obtained. Our results demonstrate that by surrounding a compact PET scanner with thin layers of segmented copper shields and integrating it inside a 9.4 T MR system, we can mitigate the impact of the RF on PET, while acquiring good-quality MR images.

Image domain propeller fast spin echo☆

PubMed Central

Skare, Stefan; Holdsworth, Samantha J.; Lilja, Anders; Bammer, Roland

2013-01-01

A new pulse sequence for high-resolution T2-weighted (T2-w) imaging is proposed –image domain propeller fast spin echo (iProp-FSE). Similar to the T2-w PROPELLER sequence, iProp-FSE acquires data in a segmented fashion, as blades that are acquired in multiple TRs. However, the iProp-FSE blades are formed in the image domain instead of in the k-space domain. Each iProp-FSE blade resembles a single-shot fast spin echo (SSFSE) sequence with a very narrow phase-encoding field of view (FOV), after which N rotated blade replicas yield the final full circular FOV. Our method of combining the image domain blade data to a full FOV image is detailed, and optimal choices of phase-encoding FOVs and receiver bandwidths were evaluated on phantom and volunteers. The results suggest that a phase FOV of 15–20%, a receiver bandwidth of ±32–63 kHz and a subsequent readout time of about 300 ms provide a good tradeoff between signal-to-noise ratio (SNR) efficiency and T2 blurring. Comparisons between iProp-FSE, Cartesian FSE and PROPELLER were made on single-slice axial brain data, showing similar T2-w tissue contrast and SNR with great anatomical conspicuity at similar scan times –without colored noise or streaks from motion. A new slice interleaving order is also proposed to improve the multislice capabilities of iProp-FSE. PMID:23200683

Evaluation of dose delivery accuracy of gamma knife using MRI polymer gel dosimeter in an inhomogeneous phantom

NASA Astrophysics Data System (ADS)

Pourfallah T, A.; Alam N, Riahi; M, Allahverdi; M, Ay; M, Zahmatkesh

2009-05-01

Polymer gel dosimetry is still the only dosimetry method for directly measuring three-dimensional dose distributions. MRI Polymer gel dosimeters are tissue equivalent and can act as a phantom material. Because of high dose response sensitivity, the MRI was chosen as readout device. In this study dose profiles calculated with treatment-planning software (LGP) and measurements with the MR polymer gel dosimeter for single-shot irradiations were compared. A custom-built 16 cm diameter spherical plexiglas head phantom was used in this study. Inside the phantom, there is a cubic cutout for insertion of gel phantoms and another cutout for inserting the inhomogeneities. The phantoms were scanned with a 1.5T MRI (Siemens syngo MR 2004A 4VA25A) scanner. The multiple spin-echo sequence with 32 echoes was used for the MRI scans. Calibration relations between the spin-spin relaxation rate and the absorbed dose were obtained by using small cylindrical vials, which were filled with the PAGAT polymer gel from the same batch as for the spherical phantom. 1D and 2D data obtained using gel dosimeter for homogeneous and inhomogeneous phantoms were compared with dose obtained using LGP calculation. The distance between relative isodose curves obtained for homogeneous phantom and heterogeneous phantoms exceed the accepted total positioning error (>±2mm). The findings of this study indicate that dose measurement using PAGAT gel dosimeter can be used for verifying dose delivering accuracy in GK unit in presence of inhomogeneities.

Optically controlled locking of the nuclear field via coherent dark-state spectroscopy.

PubMed

Xu, Xiaodong; Yao, Wang; Sun, Bo; Steel, Duncan G; Bracker, Allan S; Gammon, Daniel; Sham, L J

2009-06-25

A single electron or hole spin trapped inside a semiconductor quantum dot forms the foundation for many proposed quantum logic devices. In group III-V materials, the resonance and coherence between two ground states of the single spin are inevitably affected by the lattice nuclear spins through the hyperfine interaction, while the dynamics of the single spin also influence the nuclear environment. Recent efforts have been made to protect the coherence of spins in quantum dots by suppressing the nuclear spin fluctuations. However, coherent control of a single spin in a single dot with simultaneous suppression of the nuclear fluctuations has yet to be achieved. Here we report the suppression of nuclear field fluctuations in a singly charged quantum dot to well below the thermal value, as shown by an enhancement of the single electron spin dephasing time T(2)*, which we measure using coherent dark-state spectroscopy. The suppression of nuclear fluctuations is found to result from a hole-spin assisted dynamic nuclear spin polarization feedback process, where the stable value of the nuclear field is determined only by the laser frequencies at fixed laser powers. This nuclear field locking is further demonstrated in a three-laser measurement, indicating a possible enhancement of the electron spin T(2)* by a factor of several hundred. This is a simple and powerful method of enhancing the electron spin coherence time without use of 'spin echo'-type techniques. We expect that our results will enable the reproducible preparation of the nuclear spin environment for repetitive control and measurement of a single spin with minimal statistical broadening.

Spin-orbit splitted excited states using explicitly-correlated equation-of-motion coupled-cluster singles and doubles eigenvectors

NASA Astrophysics Data System (ADS)

Bokhan, Denis; Trubnikov, Dmitrii N.; Perera, Ajith; Bartlett, Rodney J.

2018-04-01

An explicitly-correlated method of calculation of excited states with spin-orbit couplings, has been formulated and implemented. Developed approach utilizes left and right eigenvectors of equation-of-motion coupled-cluster model, which is based on the linearly approximated explicitly correlated coupled-cluster singles and doubles [CCSD(F12)] method. The spin-orbit interactions are introduced by using the spin-orbit mean field (SOMF) approximation of the Breit-Pauli Hamiltonian. Numerical tests for several atoms and molecules show good agreement between explicitly-correlated results and the corresponding values, calculated in complete basis set limit (CBS); the highly-accurate excitation energies can be obtained already at triple- ζ level.

Spin-dependent dwell times of electron tunneling through double- and triple-barrier structures

NASA Astrophysics Data System (ADS)

Erić, Marko; Radovanović, Jelena; Milanović, Vitomir; Ikonić, Zoran; Indjin, Dragan

2008-04-01

We have analyzed the influence of Dresselhaus and Rashba spin-orbit couplings (caused by the bulk inversion asymmetry and the structural asymmetry, respectively) on electron tunneling through a double- and triple-barrier structures, with and without an externally applied electric field. The results indicate that the degree of structural asymmetry and external electric field can greatly affect the dwell times of electrons with opposite spin orientation. This opens up the possibilities of obtaining efficient spin separation in the time domain. The material system of choice is AlxGa1-xSb, and the presented model takes into account the position dependence of material parameters, as well as the effects of band nonparabolicity.

Evaluation of muscle injury using magnetic resonance imaging

NASA Technical Reports Server (NTRS)

LeBlanc, A. D.; Jaweed, M.; Evans, H.

1993-01-01

The objective of this study was to investigate spin echo T2 relaxation time changes in thigh muscles after intense eccentric exercise in healthy men. Spin echo and calculated T2 relaxation time images of the thighs were obtained on several occasions after exercise of one limb; the contralateral limb served as control. Muscle damage was verified by elevated levels of serum creatine kinase (CK). Thirty percent of the time no exercise effect was discernible on the magnetic resonance (MR) images. In all positive MR images (70%) the semitendinosus muscle was positive, while the biceps femoris, short head, and gracilis muscles were also positive in 50% and 25% of the total cases, respectively. The peak T2 relaxation time and serum CK were correlated (r = 0.94, p<0.01); temporal changes in muscle T2 relaxation time and serum CK were similar, although T2 relaxation time remained positive after serum CK returned to background levels. We conclude that magnetic resonance imaging can serve as a useful tool in the evaluation of eccentric exercise muscle damage by providing a quantitative indicator of damage and its resolution as well as the specific areas and muscles.

Correlated displacement-T2 MRI by means of a Pulsed Field Gradient-Multi Spin Echo Method.

PubMed

Windt, Carel W; Vergeldt, Frank J; Van As, Henk

2007-04-01

A method for correlated displacement-T2 imaging is presented. A Pulsed Field Gradient-Multi Spin Echo (PFG-MSE) sequence is used to record T2 resolved propagators on a voxel-by-voxel basis, making it possible to perform single voxel correlated displacement-T2 analyses. In spatially heterogeneous media the method thus gives access to sub-voxel information about displacement and T2 relaxation. The sequence is demonstrated using a number of flow conducting model systems: a tube with flowing water of variable intrinsic T2's, mixing fluids of different T2's in an "X"-shaped connector, and an intact living plant. PFG-MSE can be applied to yield information about the relation between flow, pore size and exchange behavior, and can aid volume flow quantification by making it possible to correct for T2 relaxation during the displacement labeling period Delta in PFG displacement imaging methods. Correlated displacement-T2 imaging can be of special interest for a number of research subjects, such as the flow of liquids and mixtures of liquids or liquids and solids moving through microscopic conduits of different sizes (e.g., plants, porous media, bioreactors, biomats).

Slow Domain Motions of an Oligomeric Protein from Deep-Sea Hyperthermophile probed by Neutron Spin Echo

NASA Astrophysics Data System (ADS)

Bhowmik, Debsindhu; Shrestha, Utsab; Dhindsa, Gurpreet; Sharp, Melissa; Stingaciu, Laura R.; Chu, Xiang-Qiang; Xiang-Qiang Chu Team

Deep-sea microorganisms have the ability to survive under extreme conditions, such as high pressure and high temperature. In this work, we used the combination of the neutron spin-echo (NSE) and the small angle neutron scattering (SANS) techniques to study the inter-domain motions of the inorganic pyrophosphate (IPPase) enzyme derived from thermostable microorganisms Thermococcus thioreducens. The IPPase has hexameric quaternary structure with molecular mass of approx. 120kDa (each subunit of 20kDa), which is a large oligomeric structure. The understanding of its slow inter-domain motions can be the key to explain how they are able to perform catalytic activity at higher temperature compared to mesophilic enzymes, thus leading to adapt to extreme environment present at the seabed. The NSE can probe these slow motions directly in the time domain up to several tens of nanoseconds at the nanometers length scales, while the corresponding structural change can be explored by the SANS. Our results provide a better picture of the local flexibility and conformational substates unique to these types of proteins, which will help us better understandthe relation between protein dynamics and their biological activities

[MRI of focal liver lesions using a 1.5 turbo-spin-echo technique compared with spin-echo technique].

PubMed

Steiner, S; Vogl, T J; Fischer, P; Steger, W; Neuhaus, P; Keck, H

1995-08-01

The aim of our study was to evaluate a T2-weighted turbo-spinecho sequence in comparison to a T2-weighted spinecho sequence in imaging focal liver lesions. In our study 35 patients with suspected focal liver lesions were examined. Standardised imaging protocol included a conventional T2-weighted SE sequence (TR/TE = 2000/90/45, acquisition time = 10.20) as well as a T2-weighted TSE sequence (TR/TE = 4700/90, acquisition time = 6.33). Calculation of S/N and C/N ratio as a basis of quantitative evaluation was done using standard methods. A diagnostic score was implemented to enable qualitative assessment. In 7% (n = 2) the TSE sequence enabled detection of further liver lesions showing a size of less than 1 cm in diameter. Comparing anatomical details the TSE sequence was superior. S/N and C/N ratio of anatomic and pathologic structures of the TSE sequence were higher compared to results of the SE sequence. Our results indicate that the T2-weighted turbo-spinecho sequence is well appropriate for imaging focal liver lesions, and leads to reduction of imaging time.

Nuclear relaxation and critical fluctuations in membranes containing cholesterol

NASA Astrophysics Data System (ADS)

McConnell, Harden

2009-04-01

Nuclear resonance frequencies in bilayer membranes depend on lipid composition. Our calculations describe the combined effects of composition fluctuations and diffusion on nuclear relaxation near a miscibility critical point. Both tracer and gradient diffusion are included. The calculations involve correlation functions and a correlation length ξ =ξ0T/(T -Tc), where T -Tc is temperature above the critical temperature and ξ0 is a parameter of molecular length. Several correlation functions are examined, each of which is related in some degree to the Ising model correlation function. These correlation functions are used in the calculation of transverse deuterium relaxation rates in magic angle spinning and quadrupole echo experiments. The calculations are compared with experiments that report maxima in deuterium and proton nuclear relaxation rates at the critical temperature [Veatch et al., Proc. Nat. Acad. Sci. U.S.A. 104, 17650 (2007)]. One Ising-model-related correlation function yields a maximum 1/T2 relaxation rate at the critical temperature for both magic angle spinning and quadrupole echo experiments. The calculated rates at the critical temperature are close to the experimental rates. The rate maxima involve relatively rapid tracer diffusion in a static composition gradient over distances of up to 10-100 nm.

Small-Angle Neutron Scattering and Neutron Spin Echo Characterization of Monoclonal Antibody Self-Associations at High Concentrations

NASA Astrophysics Data System (ADS)

Yearley, Eric; Zarraga, Isidro (Dan); Godfrin, Paul (Doug); Perevozchikova, Tatiana; Wagner, Norman; Liu, Yun

2013-03-01

Concentrated therapeutic protein formulations offer numerous delivery and stability challenges. In particular, it has been found that several therapeutic proteins exhibit a large increase in viscosity as a function of concentration that may be dependent on the protein-protein interactions. Small-Angle Neutron Scattering (SANS) and Neutron Spin Echo (NSE) investigations have been performed to probe the protein-protein interactions and diffusive properties of highly concentrated MAbs. The SANS data demonstrate that the inter-particle interactions for a highly viscous MAb at high concentrations (MAb1) are highly attractive, anisotropic and change significantly with concentration while the viscosity and interactions do not differ considerably for MAb2. The NSE results furthermore indicate that MAb1 and MAb2 have strong concentration dependencies of dynamics at high Q that are correlated to the translational motion of the proteins. Finally, it has also been revealed that the individual MAb1 proteins form small clusters at high concentrations in contrast to the MAb2 proteins, which are well-dispersed. It is proposed that the formation of these clusters is the primary cause of the dramatic increase in viscosity of MAb1 in crowded or concentrated environments.

MR imaging of ore for heap bioleaching studies using pure phase encode acquisition methods

NASA Astrophysics Data System (ADS)

Fagan, Marijke A.; Sederman, Andrew J.; Johns, Michael L.

2012-03-01

Various MRI techniques were considered with respect to imaging of aqueous flow fields in low grade copper ore. Spin echo frequency encoded techniques were shown to produce unacceptable image distortions which led to pure phase encoded techniques being considered. Single point imaging multiple point acquisition (SPI-MPA) and spin echo single point imaging (SESPI) techniques were applied. By direct comparison with X-ray tomographic images, both techniques were found to be able to produce distortion-free images of the ore packings at 2 T. The signal to noise ratios (SNRs) of the SESPI images were found to be superior to SPI-MPA for equal total acquisition times; this was explained based on NMR relaxation measurements. SESPI was also found to produce suitable images for a range of particles sizes, whereas SPI-MPA SNR deteriorated markedly as particles size was reduced. Comparisons on a 4.7 T magnet showed significant signal loss from the SPI-MPA images, the effect of which was accentuated in the case of unsaturated flowing systems. Hence it was concluded that SESPI was the most robust imaging method for the study of copper ore heap leaching hydrology.

Single-shot EPI with Nyquist ghost compensation: Interleaved Dual-Echo with Acceleration (IDEA) EPI

PubMed Central

Poser, Benedikt A; Barth, Markus; Goa, Pål-Erik; Deng, Weiran; Stenger, V Andrew

2012-01-01

Echo planar imaging is most commonly used for BOLD fMRI, owing to its sensitivity and acquisition speed. A major problem with EPI is Nyquist (N/2) ghosting, most notably at high field. EPI data are acquired under an oscillating readout gradient and hence vulnerable to gradient imperfections such as eddy current delays and off-resonance effects, as these cause inconsistencies between odd and even k-space lines after time reversal. We propose a straightforward and pragmatic method herein termed Interleaved Dual Echo with Acceleration (IDEA) EPI: Two k-spaces (echoes) are acquired under the positive and negative readout lobes, respectively, by performing phase blips only before alternate readout gradients. From these two k-spaces, two almost entirely ghost free images per shot can be constructed, without need for phase correction. The doubled echo train length can be compensated by parallel imaging and/or partial Fourier acquisition. The two k-spaces can either be complex-averaged during reconstruction, which results in near-perfect cancellation of residual phase errors, or reconstructed into separate images. We demonstrate the efficacy of IDEA EPI and show phantom and in vivo images at both 3 and 7 Tesla. PMID:22411762

The publication echo: effects of retrieving literature in PubMed by year of publication.

PubMed

Spreckelsen, Cord; Deserno, Thomas M; Spitzer, Klaus

2010-04-01

In PubMed search forms, the publication date refers to both the date of electronic and printed publication. This fact is documented in PubMed, but difficult to anticipate by the users and can provoke misinterpretations of search results. The Technical Note aims at systematically investing the effect (referred to as the publication echo), clarifying onset and extent of the publication echo, and comments on its impact. Papers with ambiguous publication dates are systematically retrieved and a trend analysis with seasonal decomposition on monthly publication data is performed. First doubled search results were found for 1999, their number since then rapidly increasing. Up to 17.6% of all articles of a year are found to be published electronically and in print, which can be before or afterwards. Maximum delay between the two dates is three years, except for one singular publication, where it is five years. Publication trends are exponential and linear when considering echoed and echo-cleaned data, respectively. As a conclusion, we suggest using a query formulation that unambiguously retrieves literature from PubMed by the date of publication. (c) 2010 Elsevier Ireland Ltd. All rights reserved.

Structure determination of a peptide model of the repeated helical domain in Samia cynthia ricini silk fibroin before spinning by a combination of advanced solid-state NMR methods.

PubMed

Nakazawa, Yasumoto; Asakura, Tetsuo

2003-06-18

Fibrous proteins unlike globular proteins, contain repetitive amino acid sequences, giving rise to very regular secondary protein structures. Silk fibroin from a wild silkworm, Samia cynthia ricini, consists of about 100 repeats of alternating polyalanine (poly-Ala) regions of 12-13 residues in length and Gly-rich regions. In this paper, the precise structure of the model peptide, GGAGGGYGGDGG(A)(12)GGAGDGYGAG, which is a typical repeated sequence of the silk fibroin, was determined using a combination of three kinds of solid-state NMR studies; a quantitative use of (13)C CP/MAS NMR chemical shift with conformation-dependent (13)C chemical shift contour plots, 2D spin diffusion (13)C solid-state NMR under off magic angle spinning and rotational echo double resonance. The structure of the model peptide corresponding to the silk fibroin structure before spinning was determined. The torsion angles of the central Ala residue, Ala(19), in the poly-Ala region were determined to be (phi, psi) = (-59 degrees, -48 degrees ) which are values typically associated with alpha-helical structures. However, the torsion angles of the Gly(25) residue adjacent to the C-terminal side of the poly-Ala chain were determined to be (phi, psi) = (-66 degrees, -22 degrees ) and those of Gly(12) and Ala(13) residues at the N-terminal of the poly-Ala chain to be (phi, psi) = (-70 degrees, -30 degrees ). In addition, REDOR experiments indicate that the torsion angles of the two C-terminal Ala residues, Ala(23) and Ala(24), are (phi, psi) = (-66 degrees, -22 degrees ) and those of N-terminal two Ala residues, Ala(13) and Ala(14) are (phi, psi) = (-70 degrees, -30 degrees ). Thus, the local structure of N-terminal and C-terminal residues, and also the neighboring residues of alpha-helical poly-Ala chain in the model peptide is a more strongly wound structure than found in typical alpha-helix structures.

3D Double-Quantum/Double-Quantum Exchange Spectroscopy of Protons under 100 kHz Magic Angle Spinning.

PubMed

Zhang, Rongchun; Duong, Nghia Tuan; Nishiyama, Yusuke; Ramamoorthy, Ayyalusamy

2017-06-22

Solid-state 1 H NMR spectroscopy has attracted much attention in the recent years due to the remarkable spectral resolution improvement by ultrafast magic-angle-spinning (MAS) as well as due to the sensitivity enhancement rendered by proton detection. Although these developments have enabled the investigation of a variety of challenging chemical and biological solids, the proton spectral resolution is still poor for many rigid solid systems owing to the presence of conformational heterogeneity and the unsuppressed residual proton-proton dipolar couplings even with the use of the highest currently feasible sample spinning speed of ∼130 kHz. Although a further increase in the spinning speed of the sample could be beneficial to some extent, there is a need for alternate approaches to enhance the spectral resolution. Herein, by fully utilizing the benefits of double-quantum (DQ) coherences, we propose a single radio frequency channel proton-based 3D pulse sequence that correlates double-quantum (DQ), DQ, and single-quantum (SQ) chemical shifts of protons. In addition to the two-spin homonuclear proximity information, the proposed 3D DQ/DQ/SQ experiment also enables the extraction of three-spin and four-spin proximities, which could be beneficial for revealing the dipolar coupled proton network in the solid state. Besides, the 2D DQ/DQ spectrum sliced at different isotropic SQ chemical shift values of the 3D DQ/DQ/SQ spectrum will also facilitate the identification of DQ correlation peaks and improve the spectral resolution, as it only provides the local homonuclear correlation information associated with the specific protons selected by the SQ chemical shift frequency. The 3D pulse sequence and its efficiency are demonstrated experimentally on small molecular compounds in the solid state. We expect that this approach would create avenues for further developments by suitably combining the benefits of partial deuteration of samples, selective excitation/decoupling pulses, heteronuclear spins for spectral editing, and nonuniform sampling.

Proton decoupling and recoupling under double-nutation irradiation in solid-state NMR

NASA Astrophysics Data System (ADS)

Takeda, Kazuyuki; Wakisaka, Asato; Takegoshi, K.

2014-12-01

The effect of 1H decoupling in magic-angle spinning solid-state NMR is studied under radiofrequency irradiation causing simultaneous nutations around a pair of orthogonal axes. Double-nutation with an arbitrary pair of nutation frequencies is implemented through modulation of the amplitude, phase, and frequency of the transmitting pulses. Similarity and difference of double-nutation decoupling and two-pulse phase-modulation decoupling schemes [A. E. Bennett, C. M. Rienstra, M. Auger, K. V. Lakshmi, and R. G. Griffin, J. Chem. Phys. 103, 6951-6958 (1995) and I. Scholz, P. Hodgkinson, B. H. Meier, and M. Ernst, J. Chem. Phys. 130, 114510 (2009)] are discussed. The structure of recoupling bands caused by interference of the 1H spin nutation with sample spinning is studied by both experiments and numerical simulations.

Structural and magnetic properties of the 5d 2 double perovskites Sr 2 BReO 6 ( B = Y, In)

DOE PAGES

Aczel, A. A.; Zhao, Z.; Calder, S.; ...

2016-06-01

With this study, we have performed magnetic susceptibility, heat capacity, neutron powder diffraction, and muon spin relaxation experiments to investigate the magnetic ground states of the 5more » $d^2$ double perovskites Sr$$_2$$YReO$$_6$$ and Sr$$_2$$InReO$$_6$$. We find that Sr$$_2$$YReO$$_6$$ is a spin glass, while Sr$$_2$$InReO$$_6$$ hosts a non-magnetic singlet state. By making detailed comparisons with other 5$d^2$ double perovskites, we argue that a delicate interplay between spin-orbit coupling, non-cubic crystal fields, and exchange interactions plays a key role in the great variation of magnetic ground states observed for this family of materials.« less

High Frequency QPOs due to Black Hole Spin

NASA Technical Reports Server (NTRS)

Kazanas, Demos; Fukumura, K.

2009-01-01

We present detailed computations of photon orbits emitted by flares at the innermost stable circular orbit (ISCO) of accretion disks around rotating black holes. We show that for sufficiently large spin parameter, i.e. a > 0.94 M, flare a sufficient number of photons arrive at an observer after multiple orbits around the black hole, to produce an "photon echo" of constant lag, i.e. independent of the relative phase between the black hole and the observer, of T approximates 14 M. This constant time delay, then, leads to a power spectrum with a QPO at a frequency nu approximates 1/14M, even for a totally random ensemble of such flares. Observation of such a QPO will provide incontrovertible evidence for the high spin of the black hole and a very accurate, independent, measurement of its mass.

Knight shift and spin-echo decay time of YBa{sub 2}Cu{sub 4}O{sub 8} and YBa{sub 2}Cu{sub 3}O{sub 7} in the superconducting state

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pines, D.; Wrobel, P.

1996-03-01

We report on calculations of the Knight shift and spin-echo decay time, {ital T}{sub 2{ital G}}, in the superconducting state which are based on a nearly antiferromagnetic Fermi-liquid description of the spin-fluctuation spectrum, in which a single spin component is responsible for the dynamic spin behavior and the magnetic interaction between the planar quasiparticles brings the system close to antiferromagnetic behavior. The dynamic spin susceptibility is described by a random-phase-approximation-like expression, with a restoring force which is unchanged from the normal state, and an irreducible particle-hole susceptibility which reflects the {ital d}{sub {ital x}{sup 2}{minus}{ital y}{sup 2}} symmetry of themore » gap parameter and a quasiparticle Fermi surface consistent with photoemission experiments. We obtain a quantitative fit to the Knight shift results for YBa{sub 2}Cu{sub 4}O{sub 8} with a {ital d}{sub {ital x}{sup 2}{minus}{ital y}{sup 2}} strong coupling gap of maximum magnitude 2.8{ital k}{sub {ital BT}}{sub {ital c}}, and show that quantitative agreement with the recent measurements of {ital T}{sub 2{ital G}} by Corey {ital et al}. may be obtained with this {ital d}{sub {ital x}{sup 2}-{ital y}{sup 2}} pairing state and a quite substantial antiferromagnetic enhancement ({approximately}140) of the static {open_quote}{open_quote}band structure{close_quote}{close_quote} spin susceptibility at wave vectors in the vicinity of {bold Q}=({pi},{pi}). We demonstrate that the experimental results of Corey {ital et al}. rule out an anisotropic {ital s}-wave state. Analogous calculations for the Knight shift of YBa{sub 2}Cu{sub 3}O{sub 7} suggest that the {ital d}{sub {ital x}{sup 2}-{ital y}{sup 2}} strong coupling gap possesses a maximum magnitude, 2.6{ital k}{sub {ital BT}}{sub {ital c}}, and on this basis, we predict a reduction in {ital T}{sup -1}{sub 2{ital G}} of some 5% for the smaller antiferromagnetic enhancement ({approximately}38) expected for this system.« less

Diffusion weighted imaging: a comprehensive evaluation of a fast spin echo DWI sequence with BLADE (PROPELLER) k-space sampling at 3 T, using a 32-channel head coil in acute brain ischemia.

PubMed

Attenberger, Ulrike I; Runge, Val M; Stemmer, Alto; Williams, Kenneth D; Naul, L Gill; Michaely, Henrik J; Schoenberg, Stefan O; Reiser, Maximilian F; Wintersperger, Bernd J

2009-10-01

To evaluate the signal-to-noise ratio (SNR) and diagnostic quality of diffusion weighted imaging (DWI) using a fast spin echo (FSE) sequence with BLADE k-space trajectory at 3 T in combination with a 32-channel head coil. The scan was compared with a standard spin echo (SE) echo-planar imaging (EPI) DWI and a high resolution SE EPI DWI sequence. Fourteen patients with acute brain ischemia were included in this Institutional Review Board approved study. All patients were evaluated with 3 different image sequences, using a 3 T scanner and a 32-channel head coil: (a) a standard SE EPI DWI (matrix size 192 x 192), (b) a high resolution SE EPI DWI (matrix size of 256 x 256) and (c) a FSE DWI BLADE (matrix size 192 x 192). The SNR of the 3 scans was compared in 10 healthy volunteers by a paired student t test. Image quality was evaluated with 4 dedicated questions in a blinded read: (1) The scans were ranked in terms of bulk susceptibility artifact. (2) The scan preference for diagnosis of any diffusion abnormality that might occur and (3) the preference for visualization of the diffusion abnormality actually present was determined. (4) The influence of bulk susceptibility on image evaluation for the diffusion abnormality present was assessed. For visualization of the diffusion abnormality present, BLADE DWI was the scan sequence preferred most by both readers (reader 1: 41.7%, reader 2: 35.7%). For visualization of any diffusion abnormality present, BLADE DWI was the preferred scan in 13 of 14 cases for reader 1 (93%) and in 11 of 14 cases for reader 2 (78.6%). No high resolution SE EPI DWI scan was rated best by reader 1. Reader 2 rated the high resolution SE EPI DWI scan superior in only 1 of 56 judgments. The standard EPI DWI sequence (21.8 +/- 5.3) had in comparison to the high resolution EPI DWI (11.9 +/- 2.6) and the BLADE DWI scans (11.3 +/- 3.8) significantly higher SNR mean values. Our preliminary data demonstrates the feasibility of a FSE EPI DWI scan with radial-like k-space sampling, using a 32-channel coil at 3 T in acute brain ischemia. The BLADE DWI was the preferred scan for the detection of acute diffusion abnormalities because of the lack of bulk susceptibility artifacts.

Attenuation of the NMR signal in a field gradient due to stochastic dynamics with memory

NASA Astrophysics Data System (ADS)

Lisý, Vladimír; Tóthová, Jana

2017-03-01

The attenuation function S(t) for an ensemble of spins in a magnetic-field gradient is calculated by accumulation of the phase shifts in the rotating frame resulting from the displacements of spin-bearing particles. The found S(t), expressed through the particle mean square displacement, is applicable for any kind of stationary stochastic motion of spins, including their non-markovian dynamics with memory. The known expressions valid for normal and anomalous diffusion are obtained as special cases in the long time approximation. The method is also applicable to the NMR pulse sequences based on the refocusing principle. This is demonstrated by describing the Hahn spin echo experiment. The attenuation of the NMR signal is also evaluated providing that the random motion of particle is modeled by the generalized Langevin equation with the memory kernel exponentially decaying in time. The models considered in our paper assume massive particles driven by much smaller particles.

Dynamic and Inherent B0 Correction for DTI Using Stimulated Echo Spiral Imaging

PubMed Central

Avram, Alexandru V.; Guidon, Arnaud; Truong, Trong-Kha; Liu, Chunlei; Song, Allen W.

2013-01-01

Purpose To present a novel technique for high-resolution stimulated echo (STE) diffusion tensor imaging (DTI) with self-navigated interleaved spirals (SNAILS) readout trajectories that can inherently and dynamically correct for image artifacts due to spatial and temporal variations in the static magnetic field (B0) resulting from eddy currents, tissue susceptibilities, subject/physiological motion, and hardware instabilities. Methods The Hahn spin echo formed by the first two 90° radio-frequency pulses is balanced to consecutively acquire two additional images with different echo times (TE) and generate an inherent field map, while the diffusion-prepared STE signal remains unaffected. For every diffusion-encoding direction, an intrinsically registered field map is estimated dynamically and used to effectively and inherently correct for off-resonance artifacts in the reconstruction of the corresponding diffusion-weighted image (DWI). Results After correction with the dynamically acquired field maps, local blurring artifacts are specifically removed from individual STE DWIs and the estimated diffusion tensors have significantly improved spatial accuracy and larger fractional anisotropy. Conclusion Combined with the SNAILS acquisition scheme, our new method provides an integrated high-resolution short-TE DTI solution with inherent and dynamic correction for both motion-induced phase errors and off-resonance effects. PMID:23630029

Quantification of in vivo short echo-time proton magnetic resonance spectra at 14.1 T using two different approaches of modelling the macromolecule spectrum

NASA Astrophysics Data System (ADS)

Cudalbu, C.; Mlynárik, V.; Xin, L.; Gruetter, Rolf

2009-10-01

Reliable quantification of the macromolecule signals in short echo-time 1H MRS spectra is particularly important at high magnetic fields for an accurate quantification of metabolite concentrations (the neurochemical profile) due to effectively increased spectral resolution of the macromolecule components. The purpose of the present study was to assess two approaches of quantification, which take the contribution of macromolecules into account in the quantification step. 1H spectra were acquired on a 14.1 T/26 cm horizontal scanner on five rats using the ultra-short echo-time SPECIAL (spin echo full intensity acquired localization) spectroscopy sequence. Metabolite concentrations were estimated using LCModel, combined with a simulated basis set of metabolites using published spectral parameters and either the spectrum of macromolecules measured in vivo, using an inversion recovery technique, or baseline simulated by the built-in spline function. The fitted spline function resulted in a smooth approximation of the in vivo macromolecules, but in accordance with previous studies using Subtract-QUEST could not reproduce completely all features of the in vivo spectrum of macromolecules at 14.1 T. As a consequence, the measured macromolecular 'baseline' led to a more accurate and reliable quantification at higher field strengths.

MR fingerprinting using the quick echo splitting NMR imaging technique.

PubMed

Jiang, Yun; Ma, Dan; Jerecic, Renate; Duerk, Jeffrey; Seiberlich, Nicole; Gulani, Vikas; Griswold, Mark A

2017-03-01

The purpose of the study is to develop a quantitative method for the relaxation properties with a reduced radio frequency (RF) power deposition by combining magnetic resonance fingerprinting (MRF) technique with quick echo splitting NMR imaging technique (QUEST). A QUEST-based MRF sequence was implemented to acquire high-order echoes by increasing the gaps between RF pulses. Bloch simulations were used to calculate a dictionary containing the range of physically plausible signal evolutions using a range of T 1 and T 2 values based on the pulse sequence. MRF-QUEST was evaluated by comparing to the results of spin-echo methods. The specific absorption rate (SAR) of MRF-QUEST was compared with the clinically available methods. MRF-QUEST quantifies the relaxation properties with good accuracy at the estimated head SAR of 0.03 W/kg. T 1 and T 2 values estimated by MRF-QUEST are in good agreement with the traditional methods. The combination of the MRF and the QUEST provides an accurate quantification of T 1 and T 2 simultaneously with reduced RF power deposition. The resulting lower SAR may provide a new acquisition strategy for MRF when RF energy deposition is problematic. Magn Reson Med 77:979-988, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Spin-Orbit Dimers and Noncollinear Phases in d1 Cubic Double Perovskites

NASA Astrophysics Data System (ADS)

Romhányi, Judit; Balents, Leon; Jackeli, George

2017-05-01

We formulate and study a spin-orbital model for a family of cubic double perovskites with d1 ions occupying a frustrated fcc sublattice. A variational approach and a complementary analytical analysis reveal a rich variety of phases emerging from the interplay of Hund's rule and spin-orbit coupling. The phase digram includes noncollinear ordered states, with or without a net moment, and, remarkably, a large window of a nonmagnetic disordered spin-orbit dimer phase. The present theory uncovers the physical origin of the unusual amorphous valence bond state experimentally suggested for Ba2B Mo O6 (B =Y , Lu) and predicts possible ordered patterns in Ba2B Os O6 (B =Na , Li) compounds.

Optimization of multiply acquired magnetic flux density B(z) using ICNE-Multiecho train in MREIT.

PubMed

Nam, Hyun Soo; Kwon, Oh In

2010-05-07

The aim of magnetic resonance electrical impedance tomography (MREIT) is to visualize the electrical properties, conductivity or current density of an object by injection of current. Recently, the prolonged data acquisition time when using the injected current nonlinear encoding (ICNE) method has been advantageous for measurement of magnetic flux density data, Bz, for MREIT in the signal-to-noise ratio (SNR). However, the ICNE method results in undesirable side artifacts, such as blurring, chemical shift and phase artifacts, due to the long data acquisition under an inhomogeneous static field. In this paper, we apply the ICNE method to a gradient and spin echo (GRASE) multi-echo train pulse sequence in order to provide the multiple k-space lines during a single RF pulse period. We analyze the SNR of the measured multiple B(z) data using the proposed ICNE-Multiecho MR pulse sequence. By determining a weighting factor for B(z) data in each of the echoes, an optimized inversion formula for the magnetic flux density data is proposed for the ICNE-Multiecho MR sequence. Using the ICNE-Multiecho method, the quality of the measured magnetic flux density is considerably increased by the injection of a long current through the echo train length and by optimization of the voxel-by-voxel noise level of the B(z) value. Agarose-gel phantom experiments have demonstrated fewer artifacts and a better SNR using the ICNE-Multiecho method. Experimenting with the brain of an anesthetized dog, we collected valuable echoes by taking into account the noise level of each of the echoes and determined B(z) data by determining optimized weighting factors for the multiply acquired magnetic flux density data.

Fast detection of diffuse axonal damage in severe traumatic brain injury: comparison of gradient-recalled echo and turbo proton echo-planar spectroscopic imaging MRI sequences.

PubMed

Giugni, Elisabetta; Sabatini, Umberto; Hagberg, Gisela E; Formisano, Rita; Castriota-Scanderbeg, Alessandro

2005-05-01

Diffuse axonal injury (DAI) is a common type of primary neuronal injury in patients with severe traumatic brain injury (TBI), and is frequently accompanied by tissue tear hemorrhage. T2-weighted gradient-recalled echo (GRE) sequences are more sensitive than T2-weighted spin-echo images for detection of hemorrhage. The purpose of this study is to compare turbo Proton Echo Planar Spectroscopic Imaging (t-PEPSI), an extremely fast sequence, with GRE sequence in the detection of DAI. Twenty-one patients (mean age 26.8 years) with severe TBI occurred at least 3 months earlier, underwent a brain MR Imaging study on a 1.5-T scanner. A qualitative evaluation of the t-PEPSI sequences was performed by identifying the optimal echo time and in-plane resolution. The number and size of DAI lesions, as well as the signal intensity contrast ratio (SI CR), were computed for each set of GRE and t-PEPSI images, and divided according to their anatomic location as lobar and/or deep brain. There was no significant difference between GRE and t-PEPSI sequences in the detection of the total number of DAI lesions (291 vs. 230, respectively). GRE sequence delineated a higher number of DAI in the temporal lobe compared to the t-PEPSI sequence (74 vs. 37, P < .004), while no differences were found for the other regions. The SI CR was significantly lower with the t-PEPSI than the GRE sequence (P < .00001). Owing to its very short scan time and high sensitivity to the hemorrhage foci, the t-PEPSI sequence may be used as an alternative to the GRE to assess brain DAI in severe TBI patients, especially if uncooperative and medically unstable.

Magnetic resonance imaging changes of sacroiliac joints in patients with recent-onset inflammatory back pain: inter-reader reliability and prevalence of abnormalities.

PubMed

Heuft-Dorenbosch, Liesbeth; Weijers, René; Landewé, Robert; van der Linden, Sjef; van der Heijde, Désirée

2006-01-01

To study the inter-reader reliability of detecting abnormalities of sacroiliac (SI) joints in patients with recent-onset inflammatory back pain by magnetic resonance imaging (MRI), and to study the prevalence of inflammation and structural changes at various sites of the SI joints. Sixty-eight patients with inflammatory back pain (at least four of the five following criteria: symptom onset before age 40, insidious onset, morning stiffness, duration >3 months, improvement with exercise--or three out of five of these plus night pain) were included (38% male; mean age, 34.9 years [standard deviation 10.3]; 46% HLA-B27-positive; mean symptom duration, 18 months), with symptom duration <2 years. A MRI scan of the SI joints was made in the coronal plane with the following sequences: T1-weighted spin echo, short-tau inversion recovery, T2-weighted fast-spin echo with fat saturation, and T1-spin echo with fat saturation after the administration of gadolinium. Both SI joints were scored for inflammation (separately for subchondral bone and bone marrow, joint space, joint capsule, ligaments) as well as for structural changes (erosions, sclerosis, ankylosis), by two observers independently. Agreement between the two readers was analysed by concordance and discordance rates and by kappa statistics. Inflammation was present in 32 SI joints of 22 patients, most frequently located in bone marrow and/or subchondral bone (29 joints in 21 patients). Readers agreed on the presence of inflammation in 85% of the cases in the right SI joint and in 78% of the cases in the left SI joint. Structural changes on MRI were present in 11 patients. Ten of these 11 patients also showed signs of inflammation. Agreement on the presence or absence of inflammation and structural changes of SI joints by MRI was acceptable, and was sufficiently high to be useful in ascertaining inflammatory and structural changes due to sacroiliitis. About one-third of patients with recent-onset inflammatory back pain show inflammation, and about one-sixth show structural changes in at least one SI joint.

Phase transitions and magnetization of the mixed-spin Ising–Heisenberg double sawtooth frustrated ladder

NASA Astrophysics Data System (ADS)

Arian Zad, Hamid; Ananikian, Nerses

2018-04-01

The mixed spin-(1,1/2) Ising–Heisenberg double sawtooth ladder containing a mixture of both spin-1 and spin-1/2 nodal atoms, and the spin-1/2 interstitial dimers are approximately solved by the transfer-matrix method. Here, we study in detail the ground-state phase diagrams, also influences of the bilinear exchange coupling on the rungs and cyclic four-spin exchange interaction in square plaquette of each block on the magnetization and magnetic susceptibility of the suggested ladder at low temperature. Such a double sawtooth ladder may be found in a Shastry-Sutherland lattice-type. In spite of the spin ordering of odd and even blocks being different from each other, due to the commutation relation between all different block Hamiltonians, phase diagrams, magnetization behavior and thermodynamic properties of the model are the same for odd and even blocks. We show that at low temperature, both exchange couplings can change the quality and quantity of the magnetization plateaus versus the magnetic field changes. Specially, we find a new magnetization plateau M/Ms= 5/6 for this model. Besides, we examine the magnetic susceptibility and specific heat of the model in detail. It is proven that behaviors of the magnetization and the magnetic susceptibility coincide at low temperature. The specific heat displays diverse temperature dependencies, which include a Schottky-type peak at a special temperature interval. We observe that with increase of the bilinear exchange coupling on the rungs, second peak temperature dependence grows.

Study on the spin-states of cobalt-based double-layer perovskite Sr2Y0.5Ca0.5Co2O7

NASA Astrophysics Data System (ADS)

He, H.; Zhang, W. Y.

2008-02-01

The spin-states of cobalt based perovskite compounds depend sensitively on the valence state and local crystal environment of Co ions and the rich physical properties arise from strong coupling among charge, spin, and orbital degrees of freedom. While extensive studies have been carried out in the past, most of them concentrated on the isotropic compound LaCoO3. In this paper, using the unrestricted Hartree-Fock approximation and the real-space recursion method, we have investigated the competition of various magnetically ordered spin-states of anisotropic double-layered perovskite Sr2Y0.5Ca0.5Co2O7. The energy comparison among these states shows that the nearest-neighbor high-spin-intermediate-spin ferromagnetically ordered state is the relevant magnetic ground state of the compound. The magnetic structure and sizes of magnetic moments are consistent with the recent experimental observation.

SU(4) Kondo effect in double quantum dots with ferromagnetic leads

NASA Astrophysics Data System (ADS)

Weymann, Ireneusz; Chirla, Razvan; Trocha, Piotr; Moca, Cǎtǎlin Paşcu

2018-02-01

We investigate the spin-resolved transport properties, such as the linear conductance and the tunnel magnetoresistance, of a double quantum dot device attached to ferromagnetic leads and look for signatures of the SU (4 ) symmetry in the Kondo regime. We show that the transport behavior greatly depends on the magnetic configuration of the device, and the spin-SU(2) as well as the orbital and spin-SU(4) Kondo effects become generally suppressed when the magnetic configuration of the leads varies from the antiparallel to the parallel one. Furthermore, a finite spin polarization of the leads lifts the spin degeneracy and drives the system from the SU(4) to an orbital-SU(2) Kondo state. We analyze in detail the crossover and show that the Kondo temperature between the two fixed points has a nonmonotonic dependence on the degree of spin polarization of the leads. In terms of methods used, we characterize transport by using a combination of analytical and numerical renormalization group approaches.

Proton decoupling and recoupling under double-nutation irradiation in solid-state NMR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takeda, Kazuyuki, E-mail: takezo@kuchem.kyoto-u.ac.jp; Wakisaka, Asato; Takegoshi, K.

The effect of {sup 1}H decoupling in magic-angle spinning solid-state NMR is studied under radiofrequency irradiation causing simultaneous nutations around a pair of orthogonal axes. Double-nutation with an arbitrary pair of nutation frequencies is implemented through modulation of the amplitude, phase, and frequency of the transmitting pulses. Similarity and difference of double-nutation decoupling and two-pulse phase-modulation decoupling schemes [A. E. Bennett, C. M. Rienstra, M. Auger, K. V. Lakshmi, and R. G. Griffin, J. Chem. Phys. 103, 6951–6958 (1995) and I. Scholz, P. Hodgkinson, B. H. Meier, and M. Ernst, J. Chem. Phys. 130, 114510 (2009)] are discussed. The structuremore » of recoupling bands caused by interference of the {sup 1}H spin nutation with sample spinning is studied by both experiments and numerical simulations.« less

Spatial-mode storage in a gradient-echo memory

NASA Astrophysics Data System (ADS)

Higginbottom, D. B.; Sparkes, B. M.; Rancic, M.; Pinel, O.; Hosseini, M.; Lam, P. K.; Buchler, B. C.

2012-08-01

Three-level atomic gradient echo memory (Λ-GEM) is a proposed candidate for efficient quantum storage and for linear optical quantum computation with time-bin multiplexing [Hosseini , Nature (London)NATUAS0028-083610.1038/nature08325 461, 241 (2009)]. In this paper we investigate the spatial multimode properties of a Λ-GEM system. Using a high-speed triggered CCD, we demonstrate the storage of complex spatial modes and images. We also present an in-principle demonstration of spatial multiplexing by showing selective recall of spatial elements of a stored spin wave. Using our measurements, we consider the effect of diffusion within the atomic vapor and investigate its role in spatial decoherence. Our measurements allow us to quantify the spatial distortion due to both diffusion and inhomogeneous control field scattering and compare these to theoretical models.

Longitudinal double-spin asymmetry A1p and spin-dependent structure function g1p of the proton at small values of x and Q2

NASA Astrophysics Data System (ADS)

Aghasyan, M.; Alexeev, M. G.; Alexeev, G. D.; Amoroso, A.; Andrieux, V.; Anfimov, N. V.; Anosov, V.; Antoshkin, A.; Augsten, K.; Augustyniak, W.; Austregesilo, A.; Azevedo, C. D. R.; Badełek, B.; Balestra, F.; Ball, M.; Barth, J.; Beck, R.; Bedfer, Y.; Bernhard, J.; Bicker, K.; Bielert, E. R.; Birsa, R.; Bodlak, M.; Bordalo, P.; Bradamante, F.; Bressan, A.; Büchele, M.; Burtsev, V. E.; Capozza, L.; Chang, W.-C.; Chatterjee, C.; Chiosso, M.; Choi, I.; Chumakov, A. G.; Chung, S.-U.; Cicuttin, A.; Crespo, M. L.; Dalla Torre, S.; Dasgupta, S. S.; Dasgupta, S.; Denisov, O. Yu.; Dhara, L.; Donskov, S. V.; Doshita, N.; Dreisbach, Ch.; Dünnweber, W.; Dusaev, R. R.; Dziewiecki, M.; Efremov, A.; Eversheim, P. D.; Faessler, M.; Ferrero, A.; Finger, M.; Finger, M.; Fischer, H.; Franco, C.; Du Fresne von Hohenesche, N.; Friedrich, J. M.; Frolov, V.; Fuchey, E.; Gautheron, F.; Gavrichtchouk, O. P.; Gerassimov, S.; Giarra, J.; Giordano, F.; Gnesi, I.; Gorzellik, M.; Grasso, A.; Gridin, A.; Grosse Perdekamp, M.; Grube, B.; Grussenmeyer, T.; Guskov, A.; Hahne, D.; Hamar, G.; von Harrach, D.; Heinsius, F. H.; Heitz, R.; Herrmann, F.; Horikawa, N.; D'Hose, N.; Hsieh, C.-Y.; Huber, S.; Ishimoto, S.; Ivanov, A.; Iwata, T.; Jary, V.; Joosten, R.; Jörg, P.; Kabuß, E.; Kerbizi, A.; Ketzer, B.; Khaustov, G. V.; Khokhlov, Yu. A.; Kisselev, Yu.; Klein, F.; Koivuniemi, J. H.; Kolosov, V. N.; Kondo, K.; Königsmann, K.; Konorov, I.; Konstantinov, V. F.; Kotzinian, A. M.; Kouznetsov, O. M.; Kral, Z.; Krämer, M.; Kremser, P.; Krinner, F.; Kroumchtein, Z. V.; Kulinich, Y.; Kunne, F.; Kurek, K.; Kurjata, R. P.; Kuznetsov, I. I.; Kveton, A.; Lednev, A. A.; Levchenko, E. A.; Levillain, M.; Levorato, S.; Lian, Y.-S.; Lichtenstadt, J.; Longo, R.; Lyubovitskij, V. E.; Maggiora, A.; Magnon, A.; Makins, N.; Makke, N.; Mallot, G. K.; Mamon, S. A.; Marianski, B.; Martin, A.; Marzec, J.; Matoušek, J.; Matsuda, H.; Matsuda, T.; Meshcheryakov, G. V.; Meyer, M.; Meyer, W.; Mikhailov, Yu. V.; Mikhasenko, M.; Mitrofanov, E.; Mitrofanov, N.; Miyachi, Y.; Moretti, A.; Nagaytsev, A.; Nerling, F.; Neyret, D.; Nový, J.; Nowak, W.-D.; Nukazuka, G.; Nunes, A. S.; Olshevsky, A. G.; Orlov, I.; Ostrick, M.; Panzieri, D.; Parsamyan, B.; Paul, S.; Peng, J.-C.; Pereira, F.; Pešek, M.; Pešková, M.; Peshekhonov, D. V.; Pierre, N.; Platchkov, S.; Pochodzalla, J.; Polyakov, V. A.; Pretz, J.; Quaresma, M.; Quintans, C.; Ramos, S.; Regali, C.; Reicherz, G.; Riedl, C.; Rogacheva, N. S.; Ryabchikov, D. I.; Rybnikov, A.; Rychter, A.; Salac, R.; Samoylenko, V. D.; Sandacz, A.; Santos, C.; Sarkar, S.; Savin, I. A.; Sawada, T.; Sbrizzai, G.; Schiavon, P.; Schmidt, K.; Schmieden, H.; Schönning, K.; Seder, E.; Selyunin, A.; Silva, L.; Sinha, L.; Sirtl, S.; Slunecka, M.; Smolik, J.; Srnka, A.; Steffen, D.; Stolarski, M.; Subrt, O.; Sulc, M.; Suzuki, H.; Szabelski, A.; Szameitat, T.; Sznajder, P.; Tasevsky, M.; Tessaro, S.; Tessarotto, F.; Thiel, A.; Tomsa, J.; Tosello, F.; Tskhay, V.; Uhl, S.; Vasilishin, B. I.; Vauth, A.; Veloso, J.; Vidon, A.; Virius, M.; Wallner, S.; Weisrock, T.; Wilfert, M.; Windmolders, R.; Ter Wolbeek, J.; Zaremba, K.; Zavada, P.; Zavertyaev, M.; Zemlyanichkina, E.; Ziembicki, M.; Compass Collaboration

2018-06-01

We present a precise measurement of the proton longitudinal double-spin asymmetry A1p and the proton spin-dependent structure function g1p at photon virtualities 0.006(GeV / c) 2

Measurement of Single and Double Spin Asymmetries in p(e, e' pi(+/-,0))X Semi-Inclusive Deep-Inelastic Scattering

NASA Astrophysics Data System (ADS)

Jawalkar, Sucheta Shrikant

Measurements in the late 1980s at CERN revealed that quark spins account for a small fraction of the proton's spin. This so-called spin crisis spurred a number of new experiments to identify the proton's silent spin contributors, namely, the spin of the gluons, which hold the quarks together, and the orbital angular momentum of both quarks and gluons. One such experiment was eg1-dvcs at the Thomas Jefferson National Accelerator Facility in Newport News, Va., which ran in 2009 and collected approximately 19 billion electron triggers for hydrogen. I will present new measurements of the single and double-spin asymmetries ALU, AUL and ALL for pi+, pi - and pi0, measured as a function of Bjorken xB, squared momentum transfer Q2, hadron energy fraction z, and hadron transverse momentum Ph ⊥. These asymmetries, which are convolutions of transverse-momentum-dependent parton distributions and fragmentation functions, correlate with the transverse momentum, and therefore with the orbital motion, of the struck quark.

Bone marrow edema pattern in advanced hip osteoarthritis: quantitative assessment with magnetic resonance imaging and correlation with clinical examination, radiographic findings, and histopathology.

PubMed

Taljanovic, Mihra S; Graham, Anna R; Benjamin, James B; Gmitro, Arthur F; Krupinski, Elizabeth A; Schwartz, Stephanie A; Hunter, Tim B; Resnick, Donald L

2008-05-01

To correlate the amount of bone marrow edema (BME) calculated by magnetic resonance imaging(MRI) with clinical findings, histopathology, and radiographic findings, in patients with advanced hip osteoarthritis(OA). The study was approved by The Institutional Human Subject Protection Committee. Coronal MRI of hips was acquired in 19 patients who underwent hip replacement. A spin echo (SE) sequence with four echoes and separate fast spin echo (FSE) proton density (PD)-weighted SE sequences of fat (F) and water (W) were acquired with water and fat suppression, respectively. T2 and water:fat ratio calculations were made for the outlined regions of interest. The calculated MRI values were correlated with the clinical, radiographic, and histopathologic findings. Analyses of variance were done on the MRI data for W/(W + F) and for T2 values (total and focal values) for the symptomatic and contralateral hips. The values were significantly higher in the study group. Statistically significant correlations were found between pain and total W/(W + F), pain and focal T2 values, and the number of microfractures and calculated BME for the focal W/(W + F) in the proximal femora. Statistically significant correlations were found between the radiographic findings and MRI values for total W/(W + F), focal W/(W + F) and focal T2 and among the radiographic findings, pain, and hip movement. On histopathology, only a small amount of BME was seen in eight proximal femora. The amount of BME in the OA hip, as measured by MRI, correlates with the severity of pain, radiographic findings, and number of microfractures.

Accelerated whole brain intracranial vessel wall imaging using black blood fast spin echo with compressed sensing (CS-SPACE).

PubMed

Zhu, Chengcheng; Tian, Bing; Chen, Luguang; Eisenmenger, Laura; Raithel, Esther; Forman, Christoph; Ahn, Sinyeob; Laub, Gerhard; Liu, Qi; Lu, Jianping; Liu, Jing; Hess, Christopher; Saloner, David

2018-06-01

Develop and optimize an accelerated, high-resolution (0.5 mm isotropic) 3D black blood MRI technique to reduce scan time for whole-brain intracranial vessel wall imaging. A 3D accelerated T 1 -weighted fast-spin-echo prototype sequence using compressed sensing (CS-SPACE) was developed at 3T. Both the acquisition [echo train length (ETL), under-sampling factor] and reconstruction parameters (regularization parameter, number of iterations) were first optimized in 5 healthy volunteers. Ten patients with a variety of intracranial vascular disease presentations (aneurysm, atherosclerosis, dissection, vasculitis) were imaged with SPACE and optimized CS-SPACE, pre and post Gd contrast. Lumen/wall area, wall-to-lumen contrast ratio (CR), enhancement ratio (ER), sharpness, and qualitative scores (1-4) by two radiologists were recorded. The optimized CS-SPACE protocol has ETL 60, 20% k-space under-sampling, 0.002 regularization factor with 20 iterations. In patient studies, CS-SPACE and conventional SPACE had comparable image scores both pre- (3.35 ± 0.85 vs. 3.54 ± 0.65, p = 0.13) and post-contrast (3.72 ± 0.58 vs. 3.53 ± 0.57, p = 0.15), but the CS-SPACE acquisition was 37% faster (6:48 vs. 10:50). CS-SPACE agreed with SPACE for lumen/wall area, ER measurements and sharpness, but marginally reduced the CR. In the evaluation of intracranial vascular disease, CS-SPACE provides a substantial reduction in scan time compared to conventional T 1 -weighted SPACE while maintaining good image quality.

Diffusion-weighted imaging of the spine with a non-carr-purcell-meiboom-gill single-shot fast spin-echo sequence: initial experience.

PubMed

Oner, A Y; Tali, T; Celikyay, F; Celik, A; Le Roux, P

2007-03-01

To prospectively evaluate the signal-to-noise ratio (SNR) improvement in diffusion-weighted imaging (DWI) of the spine with the use of a newly developed non-Carr-Purcell-Meiboom-Gill (non-CPMG) single-shot fast spin-echo (SS-FSE) sequence and its effect on apparent diffusion coefficient (ADC) measurements. Twenty-four patients were enrolled after written informed consent. DWI of the spine was obtained with an echo-planar imaging (EPI)-based sequence followed by a non-CPMG SS-FSE technique. SNR and ADC values were measured over a lesion-free vertebral corpus. A quality score was assigned for each set of images to assess the image quality. When a spinal lesion was present, contrast-to-noise ratio (CNR) and ADC were also measured. Student t tests were used for statistical analysis. Mean SNR values were 5.83 +/- 2.2 and 11.68 +/- 2.87 for EPI and non-CPMG SS-FSE DWI, respectively. SNR values measured in DWI using parallel imaging were found to be significantly higher (P < .01). Mean ADCs of the spine were 0.53 +/- 0.15 and 0.35 +/- 0.15 x 10(-3) mm(2)/s for EPI and non-CPMG SS-FSE DWI, respectively. Quality scores were found to be higher for the non-CPMG SS-FSE DWI technique (P < .05). Overall lesion CNR was found to be higher in DWI with non-CPMG SS-FSE. The non-CPMG SS-FSE technique provides a significant improvement to current EPI-based DWI of the spine. A study including a larger number of patients is required to determine the use of this DWI sequence as a supplementary tool to conventional MR imaging for increasing diagnostic confidence in spinal pathologic conditions.

Effects of salt and nanoparticles on the segmental motion of poly(ethylene oxide) in its crystalline and amorphous phases: 2H and 7Li NMR studies.

PubMed

Vogel, M; Herbers, C; Koch, B

2008-09-11

We use (2)H NMR to investigate the segmental motion of poly(ethylene oxide) (PEO) in neat and nanocomposite materials that do and do not contain salt. Specifically, in addition to a neat low-molecular-weight PEO, we study mixtures of this polymer with TiO 2 nanoparticles and LiClO 4. To characterize the polymer dynamics over a wide range of time scales, we combine (2)H NMR spin-lattice relaxation, line-shape, and stimulated-echo analyses. The results consistently show that the presence of nanoparticles hardly affects the behavior of the polymer, while addition of salt leads to substantial changes; e.g., it reduces the crystallinity. For neat PEO and a PEO-TiO 2 mixture, stimulated-echo spectroscopy enables measurement of rotational correlation functions for the crystalline phase. Analysis of the decays allows us to determine correlation times, to demonstrate the existence of a nonexponential relaxation, which implies a high complexity of the polymer dynamics in the crystal, and to show that the reorientation can be described as a large-angle jump. For a PEO-TiO 2-LiClO 4 mixture, we use (2)H and (7)Li NMR to study the polymer and the lithium dynamics, respectively. Analysis of the (7)Li spin-lattice relaxation reveals a high lithium ionic mobility in this nanocomposite polymer electrolyte. The (7)Li stimulated-echo decay is well described by a stretched exponential extending over about 6 orders of magnitude, indicating that a broad and continuous distribution of correlation times characterizes the fluctuations of the local lithium ionic environments.

Distortion-free diffusion tensor imaging for evaluation of lumbar nerve roots: Utility of direct coronal single-shot turbo spin-echo diffusion sequence.

PubMed

Sakai, Takayuki; Doi, Kunio; Yoneyama, Masami; Watanabe, Atsuya; Miyati, Tosiaki; Yanagawa, Noriyuki

2018-06-01

Diffusion tensor imaging (DTI) based on a single-shot echo planer imaging (EPI-DTI) is an established method that has been used for evaluation of lumbar nerve disorders in previous studies, but EPI-DTI has problems such as a long acquisition time, due to a lot of axial slices, and geometric distortion. To solve these problems, we attempted to apply DTI based on a single-shot turbo spin echo (TSE-DTI) with direct coronal acquisition. Our purpose in this study was to investigate whether TSE-DTI may be more useful for evaluation of lumbar nerve disorders than EPI-DTI. First, lumbar nerve roots of five healthy volunteers were evaluated for optimization of imaging parameters with TSE-DTI including b-values and the number of motion proving gradient (MPG) directions. Subsequently, optimized TSE-DTI was quantitatively compared with conventional EPI-DTI by using fractional anisotropy (FA) values and visual scores in subjective visual evaluation of tractography. Lumbar nerve roots of six patients, who had unilateral neurologic symptoms in one leg, were evaluated by the optimized TSE-DTI. TSE-DTI with b-value of 400 s/mm 2 and 32 diffusion-directions could reduce the image distortion compared with EPI-DTI, and showed that the average FA values on the symptomatic side for six patients were significantly lower than those on the non-symptomatic side (P < 0.05). Tractography with TSE-DTI might show damaged areas of lumbar nerve roots without severe image distortion. TSE-DTI might improve the reproducibility in measurements of FA values for quantification of a nerve disorder, and would become a useful tool for diagnosis of low back pain. Copyright © 2018 Elsevier Inc. All rights reserved.

[Carotid plaque assessment using inversion recovery T1 weighted-3 dimensions variable refocus flip angle turbo spin echo sampling perfection with application optimized contrast using different angle evolutions black blood imaging].

PubMed

Inoue, Yuji; Yoneyama, Masami; Nakamura, Masanobu; Ozaki, Satoshi; Ito, Kenjiro; Hiura, Mikio

2012-01-01

Vulnerable plaque can be attributed to induction of ischemic symptoms and magnetic resonance imaging of carotid artery is valuable to detect the plaque. Magnetization prepared rapid acquisition with gradient echo (MPRAGE) method could detect hemorrhagic vulnerable plaque as high intensity signal; however, blood flow is not sufficiently masked by this method. The contrast for plaque in T1 weighted image (T1WI) could not be obtained sufficiently with black blood image (BBI) by sampling perfection with application optimized contrast using different angle evolutions (SPACE) method as turbo spin echo (TSE). In addition, an appearance of artifact by slow flow is a problem. Considering these controversial situations in plaque imaging, we examined the modified BBI inversion recovery (IR)-SPACE in which IR was added for SPACE method so that the contrast for plaque in T1WI was optimized. We investigated the application of this method in plaque imaging. As a result of phantom imaging, the contrast for plaque in T1WI was definitely obtained by choosing an appropriate inversion time (TI) for the corresponding repetition time. In clinical cases, blood flow was sufficiently masked by IR-SPACE method and the plaque imaging was clearly obtained in clinical cases to the same extent as MPRAGE method. Since BBI with IR-SPACE method was derived from both IR pulse and flow void effect, this method could obtain the blood flow masking effect definitely. The present study suggested that SPACE method might be applicable to estimate properties of carotid artery plaque.

[Non-contrast time-resolved magnetic resonance angiography combining high resolution multiple phase echo planar imaging based signal targeting and alternating radiofrequency contrast inherent inflow enhanced multi phase angiography combining spatial resolution echo planar imaging based signal targeting and alternating radiofrequency in intracranial arteries].

PubMed

Nakamura, Masanobu; Yoneyama, Masami; Tabuchi, Takashi; Takemura, Atsushi; Obara, Makoto; Sawano, Seishi

2012-01-01

Detailed information on anatomy and hemodynamics in cerebrovascular disorders such as AVM and Moyamoya disease is mandatory for defined diagnosis and treatment planning. Arterial spin labeling technique has come to be applied to magnetic resonance angiography (MRA) and perfusion imaging in recent years. However, those non-contrast techniques are mostly limited to single frame images. Recently we have proposed a non-contrast time-resolved MRA technique termed contrast inherent inflow enhanced multi phase angiography combining spatial resolution echo planar imaging based signal targeting and alternating radiofrequency (CINEMA-STAR). CINEMA-STAR can extract the blood flow in the major intracranial arteries at an interval of 70 ms and thus permits us to observe vascular construction in full by preparing MIP images of axial acquisitions with high spatial resolution. This preliminary study demonstrates the usefulness of the CINEMA-STAR technique in evaluating the cerebral vasculature.

Spinning particles, axion radiation, and the classical double copy

NASA Astrophysics Data System (ADS)

Goldberger, Walter D.; Li, Jingping; Prabhu, Siddharth G.

2018-05-01

We extend the perturbative double copy between radiating classical sources in gauge theory and gravity to the case of spinning particles. We construct, to linear order in spins, perturbative radiating solutions to the classical Yang-Mills equations sourced by a set of interacting color charges with chromomagnetic dipole spin couplings. Using a color-to-kinematics replacement rule proposed earlier by one of the authors, these solutions map onto radiation in a theory of interacting particles coupled to massless fields that include the graviton, a scalar (dilaton) ϕ and the Kalb-Ramond axion field Bμ ν. Consistency of the double copy imposes constraints on the parameters of the theory on both the gauge and gravity sides of the correspondence. In particular, the color charges carry a chromomagnetic interaction which, in d =4 , corresponds to a gyromagnetic ratio equal to Dirac's value g =2 . The color-to-kinematics map implies that on the gravity side, the bulk theory of the fields (ϕ ,gμ ν,Bμ ν) has interactions which match those of d -dimensional "string gravity," as is the case both in the BCJ double copy of pure gauge theory scattering amplitudes and the KLT relations between the tree-level S -matrix elements of open and closed string theory.

Efficacy and safety of rilpivirine (TMC278) versus efavirenz at 48 weeks in treatment-naive HIV-1-infected patients: pooled results from the phase 3 double-blind randomized ECHO and THRIVE Trials.

PubMed

Cohen, Calvin J; Molina, Jean-Michel; Cahn, Pedro; Clotet, Bonaventura; Fourie, Jan; Grinsztejn, Beatriz; Wu, Hao; Johnson, Margaret A; Saag, Michael; Supparatpinyo, Khuanchai; Crauwels, Herta; Lefebvre, Eric; Rimsky, Laurence T; Vanveggel, Simon; Williams, Peter; Boven, Katia

2012-05-01

Pooled analysis of phase 3, double-blind, double-dummy ECHO and THRIVE trials comparing rilpivirine (TMC278) and efavirenz. Treatment-naive HIV-1-infected adults were randomized 1:1 to rilpivirine 25 mg once daily or efavirenz 600 mg once daily, with background tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) (ECHO) or TDF/FTC, zidovudine/lamivudine, or abacavir/lamivudine (THRIVE). The primary endpoint was confirmed response [viral load <50 copies per milliliter; intent-to-treat time-to-loss-of-virologic-response (ITT-TLOVR) algorithm] at week 48. The pooled data set enabled analyses of subgroups and predictors of response/virologic failure. Confirmed responses were 84% (rilpivirine) and 82% (efavirenz). The difference in response rates (95% confidence interval) was 2.0% (-2.0% to 6.0%). The incidence of virologic failure was 9% (rilpivirine) versus 5% (efavirenz). Responses in ITT-TLOVR and ITT-snapshot analyses were consistent. Responses were similar for rilpivirine and efavirenz by background regimen, gender, race and clade. Suboptimal adherence and higher baseline viral load resulted in lower responses, higher virologic failure, and development of resistance in both groups; the effects on virologic failure were more apparent with rilpivirine. CD4 cell count increased over time in both groups. Rilpivirine compared with efavirenz gave smaller incidences of adverse events leading to discontinuation (3% vs. 8%, respectively), treatment-related grade 2-4 adverse events (16% vs. 31%), rash (3% vs. 14%), dizziness (8% vs. 26%), abnormal dreams/nightmares (8% vs. 13%), and grade 2-4 lipid abnormalities. At week 48, rilpivirine 25 mg once daily and efavirenz 600 mg once daily had comparable response rates. Rilpivirine had more virologic failures and improved tolerability versus efavirenz.

Intracardiac echo-guided radiofrequency catheter ablation of atrial fibrillation in patients with atrial septal defect or patent foramen ovale repair: a feasibility, safety, and efficacy study.

PubMed

Lakkireddy, Dhanunjaya; Rangisetty, Umamahesh; Prasad, Subramanya; Verma, Atul; Biria, Mazda; Berenbom, Loren; Pimentel, Rhea; Emert, Martin; Rosamond, Thomas; Fahmy, Tamer; Patel, Dimpi; Di Biase, Luigi; Schweikert, Robert; Burkhardt, David; Natale, Andrea

2008-11-01

Intracardiac Echo-Guided Radiofrequency Catheter. Patients with atrial septal defect (ASD) are at higher risk for atrial fibrillation (AF) even after repair. Transseptal access in these patients is perceived to be difficult. We describe the feasibility, safety, and efficacy of pulmonary vein antral isolation (PVAI) in these patients. We prospectively compared post-ASD/patent foramen ovale (PFO) repair patients (group I, n = 45) with age-gender-AF type matched controls (group II, n = 45). All the patients underwent PVAI through a double transseptal puncture with a roving circular mapping catheter technique guided by intracardiac echocardiography (ICE). The short-term (3 months) and long-term (12 month) failure rates were assessed. In group I, 23 (51%) had percutaneous closure devices and 22 (49%) had a surgical closure. There was no significant difference between group I and II in the baseline characteristics. Intracardiac echo-guided double transseptal access was obtained in 98% of patients in group I and in 100% of patients in group II. PVAI was performed in all patients, with right atrial flutter ablation in 7 patients in group I and in 4 patients in group II. Over a mean follow-up of 15 +/- 4 months, group I had higher short-term (18% vs 13%, P = 0.77) and long-term recurrence (24% vs 18%, P = 0.6) than group II. There was no significant difference in the perioperative complications between the two groups. Echocardiography at 3 months showed interatrial communication in 2 patients in group I and 1 patient in group II, which resolved at 12 months. Percutaneous AF ablation using double transseptal access is feasible, safe, and efficacious in patients with ASD and PFO repairs.

Accurate measurement of heteronuclear dipolar couplings by phase-alternating R-symmetry (PARS) sequences in magic angle spinning NMR spectroscopy

NASA Astrophysics Data System (ADS)

Hou, Guangjin; Lu, Xingyu; Vega, Alexander J.; Polenova, Tatyana

2014-09-01

We report a Phase-Alternating R-Symmetry (PARS) dipolar recoupling scheme for accurate measurement of heteronuclear 1H-X (X = 13C, 15N, 31P, etc.) dipolar couplings in MAS NMR experiments. It is an improvement of conventional C- and R-symmetry type DIPSHIFT experiments where, in addition to the dipolar interaction, the 1H CSA interaction persists and thereby introduces considerable errors in the dipolar measurements. In PARS, phase-shifted RN symmetry pulse blocks applied on the 1H spins combined with π pulses applied on the X spins at the end of each RN block efficiently suppress the effect from 1H chemical shift anisotropy, while keeping the 1H-X dipolar couplings intact. Another advantage over conventional DIPSHIFT experiments, which require the signal to be detected in the form of a reduced-intensity Hahn echo, is that the series of π pulses refocuses the X chemical shift and avoids the necessity of echo formation. PARS permits determination of accurate dipolar couplings in a single experiment; it is suitable for a wide range of MAS conditions including both slow and fast MAS frequencies; and it assures dipolar truncation from the remote protons. The performance of PARS is tested on two model systems, [15N]-N-acetyl-valine and [U-13C,15N]-N-formyl-Met-Leu-Phe tripeptide. The application of PARS for site-resolved measurement of accurate 1H-15N dipolar couplings in the context of 3D experiments is presented on U-13C,15N-enriched dynein light chain protein LC8.

Intrinsic errors in transporting a single-spin qubit through a double quantum dot

NASA Astrophysics Data System (ADS)

Li, Xiao; Barnes, Edwin; Kestner, J. P.; Das Sarma, S.

2017-07-01

Coherent spatial transport or shuttling of a single electron spin through semiconductor nanostructures is an important ingredient in many spintronic and quantum computing applications. In this work we analyze the possible errors in solid-state quantum computation due to leakage in transporting a single-spin qubit through a semiconductor double quantum dot. In particular, we consider three possible sources of leakage errors associated with such transport: finite ramping times, spin-dependent tunneling rates between quantum dots induced by finite spin-orbit couplings, and the presence of multiple valley states. In each case we present quantitative estimates of the leakage errors, and discuss how they can be minimized. The emphasis of this work is on how to deal with the errors intrinsic to the ideal semiconductor structure, such as leakage due to spin-orbit couplings, rather than on errors due to defects or noise sources. In particular, we show that in order to minimize leakage errors induced by spin-dependent tunnelings, it is necessary to apply pulses to perform certain carefully designed spin rotations. We further develop a formalism that allows one to systematically derive constraints on the pulse shapes and present a few examples to highlight the advantage of such an approach.

Communication: Evaluating non-empirical double hybrid functionals for spin-state energetics in transition-metal complexes

NASA Astrophysics Data System (ADS)

Wilbraham, Liam; Adamo, Carlo; Ciofini, Ilaria

2018-01-01

The computationally assisted, accelerated design of inorganic functional materials often relies on the ability of a given electronic structure method to return the correct electronic ground state of the material in question. Outlining difficulties with current density functionals and wave function-based approaches, we highlight why double hybrid density functionals represent promising candidates for this purpose. In turn, we show that PBE0-DH (and PBE-QIDH) offers a significant improvement over its hybrid parent functional PBE0 [as well as B3LYP* and coupled cluster singles and doubles with perturbative triples (CCSD(T))] when computing spin-state splitting energies, using high-level diffusion Monte Carlo calculations as a reference. We refer to the opposing influence of Hartree-Fock (HF) exchange and MP2, which permits higher levels of HF exchange and a concomitant reduction in electronic density error, as the reason for the improved performance of double-hybrid functionals relative to hybrid functionals. Additionally, using 16 transition metal (Fe and Co) complexes, we show that low-spin states are stabilised by increasing contributions from MP2 within the double hybrid formulation. Furthermore, this stabilisation effect is more prominent for high field strength ligands than low field strength ligands.

Project Echo: 960-Megacycle, 10-Kilowatt Transmitter

NASA Technical Reports Server (NTRS)

Schafer, J. P.; Brandt, R. H.

1961-01-01

A 10-kw transmitter operating at 960 to 961 Mc was used at the eastern terminus of the Project Echo communications experiment. This transmitter is located on Crawford's Hill near Holmdel, New Jersey. The 10-kw output feeds into a waveguide line leading to a 60-foot dish antenna. Exciter-driver units are available to drive the power amplifier with various modulations, such as wide-deviation FM, low-index phase modulation, single-sideband or double-sideband modulation with or without carrier, 960.05 or 961.05 Mc constant-frequency CW, and radar on-off pulses at 961.05 Mc. The main output amplifier consists primarily of a four-stage, externally-tuned-cavity, water-cooled klystron, operating at a beam voltage of 16 to 18 kv. The transmitter has been operated during many Moonbounce, tropospheric scatter, and Echo I tests with very satisfactory results. This paper describes its use before March 1, 1961.

One-electron versus electron-electron interaction contributions to the spin-spin coupling mechanism in nuclear magnetic resonance spectroscopy: Analysis of basic electronic effects

NASA Astrophysics Data System (ADS)

Gräfenstein, Jürgen; Cremer, Dieter

2004-12-01

For the first time, the nuclear magnetic resonance (NMR) spin-spin coupling mechanism is decomposed into one-electron and electron-electron interaction contributions to demonstrate that spin-information transport between different orbitals is not exclusively an electron-exchange phenomenon. This is done using coupled perturbed density-functional theory in conjunction with the recently developed J-OC-PSP [=J-OC-OC-PSP: Decomposition of J into orbital contributions using orbital currents and partial spin polarization)] method. One-orbital contributions comprise Ramsey response and self-exchange effects and the two-orbital contributions describe first-order delocalization and steric exchange. The two-orbital effects can be characterized as external orbital, echo, and spin transport contributions. A relationship of these electronic effects to zeroth-order orbital theory is demonstrated and their sign and magnitude predicted using simple models and graphical representations of first order orbitals. In the case of methane the two NMR spin-spin coupling constants result from totally different Fermi contact coupling mechanisms. 1J(C,H) is the result of the Ramsey response and the self-exchange of the bond orbital diminished by external first-order delocalization external one-orbital effects whereas 2J(H,H) spin-spin coupling is almost exclusively mitigated by a two-orbital steric exchange effect. From this analysis, a series of prediction can be made how geometrical deformations, electron lone pairs, and substituent effects lead to a change in the values of 1J(C,H) and 2J(H,H), respectively, for hydrocarbons.

Carbon-deuterium rotational-echo double-resonance NMR spectroscopy of lyophilized aspartame formulations.

PubMed

Luthra, Suman A; Utz, Marcel; Gorman, Eric M; Pikal, Michael J; Munson, Eric J; Lubach, Joseph W

2012-01-01

In this study, changes in the local conformation of aspartame were observed in annealed lyophilized glasses by monitoring changes in the distance between two labeled sites using C-(2)H rotational-echo double-resonance (REDOR) nuclear magnetic resonance (NMR) spectroscopy. Confirmation that the REDOR experiments were producing accurate distance measurement was ensured by measuring the (13)C-(15)N distance in glycine. The experiment was further verified by measuring the REDOR dephasing curve on (13)C-(2)H methionine. (13)C-(2)H REDOR dephasing curves were then measured on lyophilized aspartame-disaccharide formulations. In aspartame-sucrose formulation, the internuclear distances increased upon annealing, which correlated with decreased chemical reactivity. By contrast, annealing had only a minimal effect on the dephasing curve in aspartame-trehalose formulation. The results show that stability is a function of both mobility and local structure (conformation), even in a small molecule system such as lyophilized aspartame-sucrose. Copyright © 2011 Wiley-Liss, Inc.

Theoretical explanation of spin-Hamiltonian parameters and local structure for the orthorhombic MnO2 -4 clusters in K2CrO4 : Mn6 + crystal

NASA Astrophysics Data System (ADS)

Wang, Ning; Xie, Linhua

2017-12-01

In this paper, the spin-Hamiltonian parameters (g factors gx, gy, gz and hyperfine structure constants A Ax, Ay, Az) and the absorption spectrum of K2CrO4 : Mn6 + crystal are theoretically explained by using the high-order perturbation theory, the double-spin-orbit-coupling model theory and the double-mechanism theory (the crystal field mechanism and the charge-transfer (CT) mechanism). The calculation results show that the contribution of the CT mechanism cannot be neglected for Mn6 + ions in orthorhombic clusters with the ground state ?.

[Comparison of susceptibility artifacts generated by microchips with different geometry at 1.5 Tesla magnet resonance imaging. A phantom pilot study referring to the ASTM standard test method F2119-07].

PubMed

Dengg, S; Kneissl, S

2013-01-01

Ferromagnetic material in microchips, used for animal identification, causes local signal increase, signal void or distortion (susceptibility artifact) on MR images. To measure the impact of microchip geometry on the artifact's size, an MRI phantom study was performed. Microchips of the labels Datamars®, Euro-I.D.® and Planet-ID® (n  =  15) were placed consecutively in a phantom and examined with respect to the ASTM Standard Test Method F2119-07 using spin echo (TR 500 ms, TE 20 ms), gradient echo (TR 300 ms, TE 15 ms, flip angel 30°) and otherwise constant imaging parameters (slice thickness 3 mm, field of view 250 x 250 mm, acquisition matrix 256 x 256 pixel, bandwidth 32 kHz) at 1.5 Tesla. Image acquisition was undertaken with a microchip positioned in the x- and z-direction and in each case with a phase-encoding direction in the y- and z-direction. The artifact size was determined with a) a measurement according to the test method F2119-07 using a homogeneous point operation, b) signal intensity measurement according to Matsuura et al. and c) pixel counts in the artifact according to Port and Pomper. There was a significant difference in artifact size between the three microchips tested (Wilcoxon p = 0.032). A two- to three-fold increase in microchip volume generated an up to 76% larger artifact, depending on the sequence type, phase-encoding direction and chip position to B0. The smaller the microchip geometry, the less is the susceptibility artifact. Spin echoes (SE) generated smaller artifacts than gradient echoes (GE). In relation to the spatial measurement of the artifact, the switch in phase-encoding direction had less influence on the artifact size in GE- than in SE-sequences. However, the artifact shape and direction of SE-sequences can be changed by altering the phase. The artifact size, caused by the microchip, plays a major clinical role in the evaluation of MRI from the head, shoulder and neck regions.

Assessment of magnetic field interactions and radiofrequency-radiation-induced heating of metallic spinal implants in 7 T field.

PubMed

Tsukimura, Itsuko; Murakami, Hideki; Sasaki, Makoto; Endo, Hirooki; Yamabe, Daisuke; Oikawa, Ryosuke; Doita, Minoru

2017-08-01

The safety of metallic spinal implants in magnetic resonance imaging (MRI) performed using ultrahigh fields has not been established. Hence, we examined whether the displacement forces caused by a static magnetic field and the heating induced by radiofrequency radiation are substantial for spinal implants in a 7 T field. We investigated spinal rods of various lengths and materials, a screw, and a cross-linking bridge in accordance with the American Society for Testing and Materials guidelines. The displacement forces of the metallic implants in static 7 T and 3 T static magnetic fields were measured and compared. The temperature changes of the implants during 15-min-long fast spin-echo and balanced gradient-echo image acquisition sequences were measured in the 7 T field. The deflection angles of the metallic spinal materials in the 7 T field were 5.0-21.0° [median: 6.7°], significantly larger than those in the 3 T field (1.0-6.3° [2.2°]). Among the metallic rods, the cobalt-chrome rods had significantly larger deflection angles (17.8-21.0° [19.8°]) than the pure titanium and titanium alloy rods (5.0-7.7° [6.2°]). The temperature changes of the implants, including the cross-linked rods, were 0.7-1.0°C [0.8°C] and 0.6-1.0°C [0.7°C] during the fast spin-echo and balanced gradient-echo sequences, respectively; these changes were slightly larger than those of the controls (0.4-1.1°C [0.5°C] and 0.3-0.9°C [0.6°C], respectively). All of the metallic spinal implants exhibited small displacement forces and minimal heating, indicating that MRI examinations using 7 T fields may be performed safely on patients with these implants. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:1831-1837, 2017. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society.

[Signal loss in magnetic resonance imaging caused by intraoral anchored dental magnetic materials].

PubMed

Blankenstein, F H; Truong, B; Thomas, A; Schröder, R J; Naumann, M

2006-08-01

To measure the maximum extent of the signal loss areas in the center of the susceptibility artifacts generated by ferromagnetic dental magnet attachments using three different sequences in the 1.5 and 3.0 Tesla MRI. Five different pieces of standard dental magnet attachments with volumes of 6.5 to 31.4 mm(3) were used: a NdFeB magnet with an open magnetic field, a NdFeB magnet with a closed magnetic field, a SmCo magnet with an open magnetic field, a stainless steel keeper (AUM-20) and a PdCo piece. The attachments were placed between two cylindrical phantoms and examined in 1.5 and 3.0 Tesla MRI using gradient echo and T1- and T2-weighted spin echoes. We measured the maximum extent of the generated signal loss areas parallel and perpendicular to the direction of B (O). In gradient echoes the artifacts were substantially larger and symmetrically adjusted around the object. The areas with total signal loss were mushroom-like with a maximum extent of 7.4 to 9.7 cm parallel to the direction of B (O) and 6.7 to 7.4 cm perpendicular to B (O). In spin echoes the signal loss areas were obviously smaller, but not centered. The maximum values ranged between 4.9 and 7.2 cm (parallel B (O)) and 3.6 and 7.0 cm (perpendicular B (O)). The different ferromagnetic attachments had no clinically relevant influence on the signal loss neither in 1.5 T nor 3.0 T MRI. Ferromagnetic materials used in dentistry are not intraorally standardized. To ensure, that the area of interest is not affected by the described artifacts, the maximum extent of the signal loss area should be assumed: a radius of up to 7 cm in 1.5 and 3.0 T MRI by T1 and T2 sequences, and a radius of up to 10 cm in T2* sequences. To decide whether magnet attachments have to be removed before MR imaging, physicians should consider both the intact retention of the keepers and the safety distance between the ferromagnetic objects and the area of interest.

Correcting for the echo-time effect after measuring the cerebral blood flow by arterial spin labeling.

PubMed

Foucher, Jack R; Roquet, Daniel; Marrer, Corinne; Pham, Bich-Thuy; Gounot, Daniel

2011-10-01

To take into account the echo time (TE) influence on arterial spin labeling (ASL) signal when converting it in regional cerebral blood flow (rCBF). Gray matter ASL signal decrease with increasing TE as a consequence of the difference in the apparent transverse relaxation rates between labeled water in capillaries and nonlabeled water in the tissue (δR 2*). We aimed to measure ASL/rCBF changes in different parts of the brain and correct them. Fifteen participants underwent ASL measurements at TEs of 9.7-30 ms. Decreases in ASL values were localized by statistical parametric mapping. The corrections assessed were a subject-per-subject adjustment, an average δR 2* value adjustment, and a two-compartment model adjustment. rCBF decreases associated with increasing TEs were found for gray matter and were corrected using an average δR 2* value of 20 s(-1) . Conversely, for white matter, rCBF values increased with increasing TEs (δR 2* = -23 s(-1)). Our correction was as good as using a two-compartment model. However, it must be done separately for the gray and white matter rCBF values because the capillary R 2* values are, respectively, larger and smaller than those of surrounding tissues. Copyright © 2011 Wiley-Liss, Inc.

Elucidation of spin echo small angle neutron scattering correlation functions through model studies.

PubMed

Shew, Chwen-Yang; Chen, Wei-Ren

2012-02-14

Several single-modal Debye correlation functions to approximate part of the overall Debey correlation function of liquids are closely examined for elucidating their behavior in the corresponding spin echo small angle neutron scattering (SESANS) correlation functions. We find that the maximum length scale of a Debye correlation function is identical to that of its SESANS correlation function. For discrete Debye correlation functions, the peak of SESANS correlation function emerges at their first discrete point, whereas for continuous Debye correlation functions with greater width, the peak position shifts to a greater value. In both cases, the intensity and shape of the peak of the SESANS correlation function are determined by the width of the Debye correlation functions. Furthermore, we mimic the intramolecular and intermolecular Debye correlation functions of liquids composed of interacting particles based on a simple model to elucidate their competition in the SESANS correlation function. Our calculations show that the first local minimum of a SESANS correlation function can be negative and positive. By adjusting the spatial distribution of the intermolecular Debye function in the model, the calculated SESANS spectra exhibit the profile consistent with that of hard-sphere and sticky-hard-sphere liquids predicted by more sophisticated liquid state theory and computer simulation. © 2012 American Institute of Physics

Measurement of the ferric diffusion coefficient in agarose and gelatine gels by utilization of the evolution of a radiation induced edge as reflected in relaxation rate images.

PubMed

Pedersen, T V; Olsen, D R; Skretting, A

1997-08-01

A method has been developed to determine the diffusion coefficients of ferric ions in ferrous sulphate doped gels. A radiation induced edge was created in the gel, and two spin-echo sequences were used to acquire a pair of images of the gel at different points of time. For each of these image pairs, a longitudinal relaxation rate image was derived. From profiles through these images, the standard deviations of the Gaussian functions that characterize diffusion were determined. These data provided the basis for the determination of the ferric diffusion coefficients by two different methods. Simulations indicate that the use of single spin-echo images in this procedure may in some cases lead to a significant underestimation of the diffusion coefficient. The technique was applied to different agarose and gelatine gels that were prepared, irradiated and imaged simultaneously. The results indicate that the diffusion coefficient is lower in a gelatine gel than in an agarose gel. Addition of xylenol orange to a gelatine gel lowers the diffusion coefficient from 1.45 to 0.81 mm2 h-1, at the cost of significantly lower Rl sensitivity. The addition of benzoic acid to the latter gel did not increase the Rl sensitivity.

Biophysical and physiological origins of blood oxygenation level-dependent fMRI signals.

PubMed

Kim, Seong-Gi; Ogawa, Seiji

2012-07-01

After its discovery in 1990, blood oxygenation level-dependent (BOLD) contrast in functional magnetic resonance imaging (fMRI) has been widely used to map brain activation in humans and animals. Since fMRI relies on signal changes induced by neural activity, its signal source can be complex and is also dependent on imaging parameters and techniques. In this review, we identify and describe the origins of BOLD fMRI signals, including the topics of (1) effects of spin density, volume fraction, inflow, perfusion, and susceptibility as potential contributors to BOLD fMRI, (2) intravascular and extravascular contributions to conventional gradient-echo and spin-echo BOLD fMRI, (3) spatial specificity of hemodynamic-based fMRI related to vascular architecture and intrinsic hemodynamic responses, (4) BOLD signal contributions from functional changes in cerebral blood flow (CBF), cerebral blood volume (CBV), and cerebral metabolic rate of O(2) utilization (CMRO(2)), (5) dynamic responses of BOLD, CBF, CMRO(2), and arterial and venous CBV, (6) potential sources of initial BOLD dips, poststimulus BOLD undershoots, and prolonged negative BOLD fMRI signals, (7) dependence of stimulus-evoked BOLD signals on baseline physiology, and (8) basis of resting-state BOLD fluctuations. These discussions are highly relevant to interpreting BOLD fMRI signals as physiological means.

Free-breathing black-blood CINE fast-spin echo imaging for measuring abdominal aortic wall distensibility: a feasibility study

NASA Astrophysics Data System (ADS)

Lin, Jyh-Miin; Patterson, Andrew J.; Chao, Tzu-Cheng; Zhu, Chengcheng; Chang, Hing-Chiu; Mendes, Jason; Chung, Hsiao-Wen; Gillard, Jonathan H.; Graves, Martin J.

2017-05-01

The paper reports a free-breathing black-blood CINE fast-spin echo (FSE) technique for measuring abdominal aortic wall motion. The free-breathing CINE FSE includes the following MR techniques: (1) variable-density sampling with fast iterative reconstruction; (2) inner-volume imaging; and (3) a blood-suppression preparation pulse. The proposed technique was evaluated in eight healthy subjects. The inner-volume imaging significantly reduced the intraluminal artifacts of respiratory motion (p  =  0.015). The quantitative measurements were a diameter of 16.3  ±  2.8 mm and wall distensibility of 2.0  ±  0.4 mm (12.5  ±  3.4%) and 0.7  ±  0.3 mm (4.1  ±  1.0%) for the anterior and posterior walls, respectively. The cyclic cross-sectional distensibility was 35  ±  15% greater in the systolic phase than in the diastolic phase. In conclusion, we developed a feasible CINE FSE method to measure the motion of the abdominal aortic wall, which will enable clinical scientists to study the elasticity of the abdominal aorta.

Spoiled gradient recalled acquisition in the steady state technique is superior to conventional postcontrast spin echo technique for magnetic resonance imaging detection of adrenocorticotropin-secreting pituitary tumors.

PubMed

Patronas, Nicholas; Bulakbasi, Nail; Stratakis, Constantine A; Lafferty, Antony; Oldfield, Edward H; Doppman, John; Nieman, Lynnette K

2003-04-01

Recent studies show that the standard T1-weighted spin echo (SE) technique for magnetic resonance imaging (MRI) fails to identify 40% of corticotrope adenomas. We hypothesized that the superior soft tissue contrast and thinner sections obtained with spoiled gradient recalled acquisition in the steady state (SPGR) would improve tumor detection. We compared the performance of SE and SPGR MRI in 50 patients (age, 7-67 yr) with surgically confirmed corticotrope adenoma. Coronal SE and SPGR MR images were obtained before and after administration of gadolinium contrast, using a 1.5 T scanner. SE scans were obtained over 5.1 min (12-cm field of view; interleaved sections, 3 mm). SPGR scans were obtained over 3.45 min (12- or 18-cm field of view, contiguous 1- or 2-mm slices). The MRI interpretations of two radiologists were compared with findings at surgical resection. Compared with SE for detection of tumor, SPGR had superior sensitivity (80%; confidence interval, 68-91; vs. 49%; confidence interval, 34-63%), but a higher false positive rate (2% vs. 4%). We recommend the addition of SPGR to SE sequences using pituitary-specific technical parameters to improve the MRI detection of ACTH-secreting pituitary tumors.

From the quantum transfer matrix to the quench action: the Loschmidt echo in XXZ Heisenberg spin chains

NASA Astrophysics Data System (ADS)

Piroli, Lorenzo; Pozsgay, Balázs; Vernier, Eric

2017-02-01

We consider the computation of the Loschmidt echo after quantum quenches in the interacting XXZ Heisenberg spin chain both for real and imaginary times. We study two-site product initial states, focusing in particular on the Néel and tilted Néel states. We apply the quantum transfer matrix (QTM) approach to derive generalized TBA equations, which follow from the fusion hierarchy of the appropriate QTM’s. Our formulas are valid for arbitrary imaginary time and for real times at least up to a time t 0, after which the integral equations have to be modified. In some regimes, t 0 is seen to be either very large or infinite, allowing to explore in detail the post-quench dynamics of the system. As an important part of our work, we show that for the Néel state our imaginary time results can be recovered by means of the quench action approach, unveiling a direct connection with the quantum transfer matrix formalism. In particular, we show that in the zero-time limit, the study of our TBA equations allows for a simple alternative derivation of the recently obtained Bethe ansatz distribution functions for the Néel, tilted Néel and tilted ferromagnet states.

Magnetic resonance cholangiopancreatography: value of using the half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence.

PubMed

Ho, J T; Yap, C K

1999-05-01

The purpose of this study was to evaluate the accuracy of magnetic resonance cholangiopancreatography (MRCP) for visualisation and diagnosis of pancreatico-biliary diseases. Our results of 35 case studies, correlating with results from endoscopic, percutaneous cholangiopancreatography or laparotomy, showed that MRCP performed using the half-Fourier acquisition single-shot turbo spin echo (HASTE) sequences was fast and accurate for depiction of the biliary and pancreatic system, with a diagnostic value comparable to that of direct cholangiography. The presence of biliary obstruction was accurately diagnosed in all but one patient. In hilar strictures, MR cholangiogram was able to depict the intrahepatic biliary tree proximal to the level of obstruction which was not readily displayed by endoscopic retrograde cholangiopancreatography (ERCP) (Figs. 1 & 2). This overview of the entire biliary system was found to be advantageous for preprocedural planning. However, the accuracy for stone detection was limited by the presence of aerobilia from previous sphincterotomy or biliary-enteric anastomosis. Ductal stones less than 3 mm in size within a non-dilated system may be missed due to inadequate spatial resolution. This occurred in a patient with pancreatic duct stones. It is hoped that the accuracy of HASTE magnetic resonance cholangiopancreatography in evaluation of pancreatico-biliary disease would obviate the need for diagnostic invasive cholangiography in selected patients.

Probing the Oxygen Environment in UO22+ by Solid-State O-17 Nuclear Magnetic Resonance Spectroscopy and Relativistic Density Functional Calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, Herman M.; De Jong, Wibe A.; Soderquist, Chuck Z.

A combined theoretical and solid-state O-17 NMR study of the electronic structure of the uranyl ion UO22+ in (NH4)4UO2(CO3)3 and rutherfordine UO2CO3 is presented, the former representing a system with a hydrogen-bonding environment around the uranyl oxygens, and the latter exemplifying a uranyl environment without hydrogens. A fully relativistic ab initio treatment reveals unique features of the U-O covalent bond, including the finding of O-17 chemical shift anisotropies that are among the largest ever reported (>1200 ppm). Computational results for the oxygen electric field gradient tensor are found to be consistently larger in magnitude than experimental solid-state O-17 NMR measurementsmore » in a 7.05 T magnetic field indicate. A modified version of the Solomon theory of the two-spin echo amplitude for a spin-5/2 nucleus is developed and applied to the analysis of the O-17 echo signal of UO22+. The William R. Wiley environmental Molecular Sciences Laboratory is a US Department of Energy national scientific user facility located at Pacific Northwest National Laboratory (PNNL) in Richland, Washington. PNNL is operated by Battelle for the US Department of Energy.« less

Biophysical and physiological origins of blood oxygenation level-dependent fMRI signals

PubMed Central

Kim, Seong-Gi; Ogawa, Seiji

2012-01-01

After its discovery in 1990, blood oxygenation level-dependent (BOLD) contrast in functional magnetic resonance imaging (fMRI) has been widely used to map brain activation in humans and animals. Since fMRI relies on signal changes induced by neural activity, its signal source can be complex and is also dependent on imaging parameters and techniques. In this review, we identify and describe the origins of BOLD fMRI signals, including the topics of (1) effects of spin density, volume fraction, inflow, perfusion, and susceptibility as potential contributors to BOLD fMRI, (2) intravascular and extravascular contributions to conventional gradient-echo and spin-echo BOLD fMRI, (3) spatial specificity of hemodynamic-based fMRI related to vascular architecture and intrinsic hemodynamic responses, (4) BOLD signal contributions from functional changes in cerebral blood flow (CBF), cerebral blood volume (CBV), and cerebral metabolic rate of O2 utilization (CMRO2), (5) dynamic responses of BOLD, CBF, CMRO2, and arterial and venous CBV, (6) potential sources of initial BOLD dips, poststimulus BOLD undershoots, and prolonged negative BOLD fMRI signals, (7) dependence of stimulus-evoked BOLD signals on baseline physiology, and (8) basis of resting-state BOLD fluctuations. These discussions are highly relevant to interpreting BOLD fMRI signals as physiological means. PMID:22395207

Bending moduli of microemulsions; comparison of results from small angle neutron scattering and neutron spin-echo spectroscopy

NASA Astrophysics Data System (ADS)

Monkenbusch, M.; Holderer, O.; Frielinghaus, H.; Byelov, D.; Allgaier, J.; Richter, D.

2005-08-01

The properties of bicontinuous microemulsions, consisting of water, oil and a surfactant, depend to a large extent on the bending moduli of the surfactant containing oil-water interface. In systems with CiEj as surfactant these moduli can be modified by the addition of diblock copolymers (boosting effect) and homopolymers (inverse boosting effect) or a combination of both. The influence of the addition of homopolymers (PEPX and PEOX, X = 5 or 10 kg/mol molecular weight) on the structure, bending modulus and dynamics of the surfactant layer is studied with small angle neutron scattering (SANS) and neutron spin-echo spectroscopy (NSE). Besides providing information on the microemulsion structure, neutron scattering is a microscopic probe that can be used to measure the local bending modulus κ. The polymer addition gives access to a homologous series of microemulsions with changing κ values. We relate the results obtained by analysis of SANS to those from NSE experiments. Comparison of the bending moduli obtained sheds light on the different renormalization length scales for NSE and SANS. Comparison of SANS and NSE derived κ values yields a consistent picture if renormalization properties are observed. Finally a ready to use method for converting NSE data into reliable values for κ is presented.

Intracranial cerebrospinal fluid spaces imaging using a pulse-triggered three-dimensional turbo spin echo MR sequence with variable flip-angle distribution.

PubMed

Hodel, Jérôme; Silvera, Jonathan; Bekaert, Olivier; Rahmouni, Alain; Bastuji-Garin, Sylvie; Vignaud, Alexandre; Petit, Eric; Durning, Bruno; Decq, Philippe

2011-02-01

To assess the three-dimensional turbo spin echo with variable flip-angle distribution magnetic resonance sequence (SPACE: Sampling Perfection with Application optimised Contrast using different flip-angle Evolution) for the imaging of intracranial cerebrospinal fluid (CSF) spaces. We prospectively investigated 18 healthy volunteers and 25 patients, 20 with communicating hydrocephalus (CH), five with non-communicating hydrocephalus (NCH), using the SPACE sequence at 1.5T. Volume rendering views of both intracranial and ventricular CSF were obtained for all patients and volunteers. The subarachnoid CSF distribution was qualitatively evaluated on volume rendering views using a four-point scale. The CSF volumes within total, ventricular and subarachnoid spaces were calculated as well as the ratio between ventricular and subarachnoid CSF volumes. Three different patterns of subarachnoid CSF distribution were observed. In healthy volunteers we found narrowed CSF spaces within the occipital aera. A diffuse narrowing of the subarachnoid CSF spaces was observed in patients with NCH whereas patients with CH exhibited narrowed CSF spaces within the high midline convexity. The ratios between ventricular and subarachnoid CSF volumes were significantly different among the volunteers, patients with CH and patients with NCH. The assessment of CSF spaces volume and distribution may help to characterise hydrocephalus.

Dental MRI using a dedicated RF-coil at 3 Tesla.

PubMed

Prager, Marcel; Heiland, Sabine; Gareis, Daniel; Hilgenfeld, Tim; Bendszus, Martin; Gaudino, Chiara

2015-12-01

To assess the benefit of a dedicated surface coil to visualize dental structures in comparison to standard head/neck coil. Measurements were performed using the standard head/neck coil and a dedicated array coil for dental MRI at 3 T. As MRI methods, we used a T1-weighted spin-echo sequence with and without spectral fat saturation, a T2-weighted turbo-spin-echo sequence and a 3-dimensional T2-weighted SPACE sequence. Measurements were performed in a phantom to examine sensitivity profiles. Then the signal gain in dental structures was examined in volunteers and in a patient. As expected for a surface coil, the signal gain of the dental coil was highest at the surface of the phantom and decreased with increasing distance to the coil; it was >120% even at a depth of 30 mm, measured from the centre of the coil. The signal gain within the pulp of the volunteers ranged between 236 and 413%. The dedicated array coil offers a significantly higher signal within the region of interest for dental MR imaging thus allowing for better depiction of pathologies within the periodontium and for delineation and tracking of the branches of the maxillary and mandibular nerves. Copyright © 2015 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.

Reduction of Diffusion-Weighted Imaging Contrast of Acute Ischemic Stroke at Short Diffusion Times.

PubMed

Baron, Corey Allan; Kate, Mahesh; Gioia, Laura; Butcher, Kenneth; Emery, Derek; Budde, Matthew; Beaulieu, Christian

2015-08-01

Diffusion-weighted imaging (DWI) of tissue water is a sensitive and specific indicator of acute brain ischemia, where reductions of the diffusion of tissue water are observed acutely in the stroke lesion core. Although these diffusion changes have been long attributed to cell swelling, the precise nature of the biophysical mechanisms remains uncertain. The potential cause of diffusion reductions after stroke was investigated using an advanced DWI technique, oscillating gradient spin-echo DWI, that enables much shorter diffusion times and can improve specificity for alterations of structure at the micron level. Diffusion measurements in the white matter lesions of patients with acute ischemic stroke were reduced by only 8% using oscillating gradient spin-echo DWI, in contrast to a 37% decrease using standard DWI. Neurite beading has recently been proposed as a mechanism for the diffusion changes after ischemic stroke with some ex vivo evidence. To explore whether beading could cause such differential results, simulations of beaded cylinders and axonal swelling were performed, yielding good agreement with experiment. Short diffusion times result in dramatically reduced diffusion contrast of human stroke. Simulations implicate a combination of neuronal beading and axonal swelling as the key structural changes leading to the reduced apparent diffusion coefficient after stroke. © 2015 American Heart Association, Inc.

Improving spectral resolution in spatial encoding dimension of single-scan nuclear magnetic resonance 2D spin echo correlated spectroscopy

NASA Astrophysics Data System (ADS)

Lin, Liangjie; Wei, Zhiliang; Yang, Jian; Lin, Yanqin; Chen, Zhong

2014-11-01

The spatial encoding technique can be used to accelerate the acquisition of multi-dimensional nuclear magnetic resonance spectra. However, with this technique, we have to make trade-offs between the spectral width and the resolution in the spatial encoding dimension (F1 dimension), resulting in the difficulty of covering large spectral widths while preserving acceptable resolutions for spatial encoding spectra. In this study, a selective shifting method is proposed to overcome the aforementioned drawback. This method is capable of narrowing spectral widths and improving spectral resolutions in spatial encoding dimensions by selectively shifting certain peaks in spectra of the ultrafast version of spin echo correlated spectroscopy (UFSECSY). This method can also serve as a powerful tool to obtain high-resolution correlated spectra in inhomogeneous magnetic fields for its resistance to any inhomogeneity in the F1 dimension inherited from UFSECSY. Theoretical derivations and experiments have been carried out to demonstrate performances of the proposed method. Results show that the spectral width in spatial encoding dimension can be reduced by shortening distances between cross peaks and axial peaks with the proposed method and the expected resolution improvement can be achieved. Finally, the shifting-absent spectrum can be recovered readily by post-processing.

Metric of two balancing Kerr particles in physical parametrization

NASA Astrophysics Data System (ADS)

Manko, V. S.; Ruiz, E.

2015-11-01

The present paper aims at elaborating a completely physical representation for the general 4-parameter family of the extended double-Kerr spacetimes describing two spinning sources in gravitational equilibrium. This involved problem is solved in a concise analytical form by using the individual Komar masses and angular momenta as arbitrary parameters, and the simplest equatorially symmetric specialization of the general expressions obtained by us yields the physical representation for the well-known Dietz-Hoenselaers superextreme case of two balancing identical Kerr constituents. The existence of the physically meaningful "black-hole-superextreme-object" equilibrium configurations permitted by the general solution may be considered as a clear indication that the spin-spin repulsion force might actually be by far stronger than expected earlier, when only the balance between two superextreme Kerr sources was thought possible. We also present the explicit analytical formulas relating the equilibrium states in the double-Kerr and double-Reissner-Nordström configurations.

A peripheral component interconnect express-based scalable and highly integrated pulsed spectrometer for solution state dynamic nuclear polarization.

PubMed

He, Yugui; Feng, Jiwen; Zhang, Zhi; Wang, Chao; Wang, Dong; Chen, Fang; Liu, Maili; Liu, Chaoyang

2015-08-01

High sensitivity, high data rates, fast pulses, and accurate synchronization all represent challenges for modern nuclear magnetic resonance spectrometers, which make any expansion or adaptation of these devices to new techniques and experiments difficult. Here, we present a Peripheral Component Interconnect Express (PCIe)-based highly integrated distributed digital architecture pulsed spectrometer that is implemented with electron and nucleus double resonances and is scalable specifically for broad dynamic nuclear polarization (DNP) enhancement applications, including DNP-magnetic resonance spectroscopy/imaging (DNP-MRS/MRI). The distributed modularized architecture can implement more transceiver channels flexibly to meet a variety of MRS/MRI instrumentation needs. The proposed PCIe bus with high data rates can significantly improve data transmission efficiency and communication reliability and allow precise control of pulse sequences. An external high speed double data rate memory chip is used to store acquired data and pulse sequence elements, which greatly accelerates the execution of the pulse sequence, reduces the TR (time of repetition) interval, and improves the accuracy of TR in imaging sequences. Using clock phase-shift technology, we can produce digital pulses accurately with high timing resolution of 1 ns and narrow widths of 4 ns to control the microwave pulses required by pulsed DNP and ensure overall system synchronization. The proposed spectrometer is proved to be both feasible and reliable by observation of a maximum signal enhancement factor of approximately -170 for (1)H, and a high quality water image was successfully obtained by DNP-enhanced spin-echo (1)H MRI at 0.35 T.

Driving mechanisms of ionic polymer actuators having electric double layer capacitor structures.

PubMed

Imaizumi, Satoru; Kato, Yuichi; Kokubo, Hisashi; Watanabe, Masayoshi

2012-04-26

Two solid polymer electrolytes, composed of a polyether-segmented polyurethaneurea (PEUU) and either a lithium salt (lithium bis(trifluoromethanesulfonyl)amide: Li[NTf2]) or a nonvolatile ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide: [C2mim][NTf2]), were prepared in order to utilize them as ionic polymer actuators. These salts were preferentially dissolved in the polyether phases. The ionic transport mechanism of the polyethers was discussed in terms of the diffusion coefficients and ionic transference numbers of the incorporated ions, which were estimated by means of pulsed-field gradient spin-echo (PGSE) NMR. There was a distinct difference in the ionic transport properties of each polymer electrolyte owing to the difference in the magnitude of interactions between the cations and the polyether. The anionic diffusion coefficient was much faster than that of the cation in the polyether/Li[NTf2] electrolyte, whereas the cation diffused faster than the anion in the polyether/[C2mim][NTf2] electrolyte. Ionic polymer actuators, which have a solid-state electric-double-layer-capacitor (EDLC) structure, were prepared using these polymer electrolyte membranes and ubiquitous carbon materials such as activated carbon and acetylene black. On the basis of the difference in the motional direction of each actuator against applied voltages, a simple model of the actuation mechanisms was proposed by taking the difference in ionic transport properties into consideration. This model discriminated the behavior of the actuators in terms of the products of transference numbers and ionic volumes. The experimentally observed behavior of the actuators was successfully explained by this model.

A peripheral component interconnect express-based scalable and highly integrated pulsed spectrometer for solution state dynamic nuclear polarization

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Yugui; Liu, Chaoyang, E-mail: chyliu@wipm.ac.cn; State Key Laboratory of Magnet Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071

2015-08-15

High sensitivity, high data rates, fast pulses, and accurate synchronization all represent challenges for modern nuclear magnetic resonance spectrometers, which make any expansion or adaptation of these devices to new techniques and experiments difficult. Here, we present a Peripheral Component Interconnect Express (PCIe)-based highly integrated distributed digital architecture pulsed spectrometer that is implemented with electron and nucleus double resonances and is scalable specifically for broad dynamic nuclear polarization (DNP) enhancement applications, including DNP-magnetic resonance spectroscopy/imaging (DNP-MRS/MRI). The distributed modularized architecture can implement more transceiver channels flexibly to meet a variety of MRS/MRI instrumentation needs. The proposed PCIe bus with highmore » data rates can significantly improve data transmission efficiency and communication reliability and allow precise control of pulse sequences. An external high speed double data rate memory chip is used to store acquired data and pulse sequence elements, which greatly accelerates the execution of the pulse sequence, reduces the TR (time of repetition) interval, and improves the accuracy of TR in imaging sequences. Using clock phase-shift technology, we can produce digital pulses accurately with high timing resolution of 1 ns and narrow widths of 4 ns to control the microwave pulses required by pulsed DNP and ensure overall system synchronization. The proposed spectrometer is proved to be both feasible and reliable by observation of a maximum signal enhancement factor of approximately −170 for {sup 1}H, and a high quality water image was successfully obtained by DNP-enhanced spin-echo {sup 1}H MRI at 0.35 T.« less

Modified echo peak correction for radial acquisition regime (RADAR).

PubMed

Takizawa, Masahiro; Ito, Taeko; Itagaki, Hiroyuki; Takahashi, Tetsuhiko; Shimizu, Kanichirou; Harada, Junta

2009-01-01

Because radial sampling imposes many limitations on magnetic resonance (MR) imaging hardware, such as on the accuracy of the gradient magnetic field or the homogeneity of B(0), some correction of the echo signal is usually needed before image reconstruction. In our previous study, we developed an echo-peak-shift correction (EPSC) algorithm not easily affected by hardware performance. However, some artifacts remained in lung imaging, where tissue is almost absent, or in cardiac imaging, which is affected by blood flow. In this study, we modified the EPSC algorithm to improve the image quality of the radial aquisition regime (RADAR) and expand its application sequences. We assumed the artifacts were mainly caused by errors in the phase map for EPSC and used a phantom on a 1.5-tesla (T) MR scanner to investigate whether to modify the EPSC algorithm. To evaluate the effectiveness of EPSC, we compared results from T(1)- and T(2)-weighted images of a volunteer's lung region using the current and modified EPSC. We then applied the modified EPSC to RADAR spin echo (SE) and RADAR balanced steady-state acquisition with rewound gradient echo (BASG) sequence. The modified EPSC reduced phase discontinuity in the reference data used for EPSC and improved visualization of blood vessels in the lungs. Motion and blood flow caused no visible artifacts in the resulting images in either RADAR SE or RADAR BASG sequence. Use of the modified EPSC eliminated artifacts caused by signal loss in the reference data for EPSC. In addition, the modified EPSC was applied to RADAR SE and RADAR BASG sequences.

BLIPPED (BLIpped Pure Phase EncoDing) high resolution MRI with low amplitude gradients

NASA Astrophysics Data System (ADS)

Xiao, Dan; Balcom, Bruce J.

2017-12-01

MRI image resolution is proportional to the maximum k-space value, i.e. the temporal integral of the magnetic field gradient. High resolution imaging usually requires high gradient amplitudes and/or long spatial encoding times. Special gradient hardware is often required for high amplitudes and fast switching. We propose a high resolution imaging sequence that employs low amplitude gradients. This method was inspired by the previously proposed PEPI (π Echo Planar Imaging) sequence, which replaced EPI gradient reversals with multiple RF refocusing pulses. It has been shown that when the refocusing RF pulse is of high quality, i.e. sufficiently close to 180°, the magnetization phase introduced by the spatial encoding magnetic field gradient can be preserved and transferred to the following echo signal without phase rewinding. This phase encoding scheme requires blipped gradients that are identical for each echo, with low and constant amplitude, providing opportunities for high resolution imaging. We now extend the sequence to 3D pure phase encoding with low amplitude gradients. The method is compared with the Hybrid-SESPI (Spin Echo Single Point Imaging) technique to demonstrate the advantages in terms of low gradient duty cycle, compensation of concomitant magnetic field effects and minimal echo spacing, which lead to superior image quality and high resolution. The 3D imaging method was then applied with a parallel plate resonator RF probe, achieving a nominal spatial resolution of 17 μm in one dimension in the 3D image, requiring a maximum gradient amplitude of only 5.8 Gauss/cm.

Optical resonance imaging: An optical analog to MRI with sub-diffraction-limited capabilities.

PubMed

Allodi, Marco A; Dahlberg, Peter D; Mazuski, Richard J; Davis, Hunter C; Otto, John P; Engel, Gregory S

2016-12-21

We propose here optical resonance imaging (ORI), a direct optical analog to magnetic resonance imaging (MRI). The proposed pulse sequence for ORI maps space to time and recovers an image from a heterodyne-detected third-order nonlinear photon echo measurement. As opposed to traditional photon echo measurements, the third pulse in the ORI pulse sequence has significant pulse-front tilt that acts as a temporal gradient. This gradient couples space to time by stimulating the emission of a photon echo signal from different lateral spatial locations of a sample at different times, providing a widefield ultrafast microscopy. We circumvent the diffraction limit of the optics by mapping the lateral spatial coordinate of the sample with the emission time of the signal, which can be measured to high precision using interferometric heterodyne detection. This technique is thus an optical analog of MRI, where magnetic-field gradients are used to localize the spin-echo emission to a point below the diffraction limit of the radio-frequency wave used. We calculate the expected ORI signal using 15 fs pulses and 87° of pulse-front tilt, collected using f /2 optics and find a two-point resolution 275 nm using 800 nm light that satisfies the Rayleigh criterion. We also derive a general equation for resolution in optical resonance imaging that indicates that there is a possibility of superresolution imaging using this technique. The photon echo sequence also enables spectroscopic determination of the input and output energy. The technique thus correlates the input energy with the final position and energy of the exciton.

Measurement of short transverse relaxation times by pseudo-echo nutation experiments

NASA Astrophysics Data System (ADS)

Ferrari, Maude; Moyne, Christian; Canet, Daniel

2018-07-01

Very short NMR transverse relaxation times may be difficult to measure by conventional methods. Nutation experiments constitute an alternative approach. Nutation is, in the rotating frame, the equivalent of precession in the laboratory frame. It consists in monitoring the rotation of magnetization around the radio-frequency (rf) field when on-resonance conditions are fulfilled. Depending on the amplitude of the rf field, nutation may be sensitive to the two relaxation rates R1 and R2. A full theoretical development has been worked out for demonstrating how these two relaxation rates could be deduced from a simple nutation experiment, noticing however that inhomogeneity of the rf field may lead to erroneous results. This has led us to devise new experiments which are the equivalent of echo techniques in the rotating frame (pseudo spin-echo nutation experiment and pseudo gradient-echo experiment). Full equations of motion have been derived. Although complicated, they indicate that the sum of the two relaxation rates can be obtained very accurately and not altered by rf field inhomogeneity. This implies however an appropriate data processing accounting for the oscillations which are superposed to the echo decays and, anyway, theoretically predicted. A series of experiments has been carried out for different values of the rf field amplitude on samples of water doped with a paramagnetic compound at different concentrations. Pragmatically, as R1 can be easily measured by conventional methods, its value is entered in the data processing algorithm which then returns exclusively the value of the transverse relaxation time. Very consistent results are obtained that way.

Measurement of short transverse relaxation times by pseudo-echo nutation experiments.

PubMed

Ferrari, Maude; Moyne, Christian; Canet, Daniel

2018-05-03

Very short NMR transverse relaxation times may be difficult to measure by conventional methods. Nutation experiments constitute an alternative approach. Nutation is, in the rotating frame, the equivalent of precession in the laboratory frame. It consists in monitoring the rotation of magnetization around the radio-frequency (rf) field when on-resonance conditions are fulfilled. Depending on the amplitude of the rf field, nutation may be sensitive to the two relaxation rates R 1 and R 2 . A full theoretical development has been worked out for demonstrating how these two relaxation rates could be deduced from a simple nutation experiment, noticing however that inhomogeneity of the rf field may lead to erroneous results. This has led us to devise new experiments which are the equivalent of echo techniques in the rotating frame (pseudo spin-echo nutation experiment and pseudo gradient-echo experiment). Full equations of motion have been derived. Although complicated, they indicate that the sum of the two relaxation rates can be obtained very accurately and not altered by rf field inhomogeneity. This implies however an appropriate data processing accounting for the oscillations which are superposed to the echo decays and, anyway, theoretically predicted. A series of experiments has been carried out for different values of the rf field amplitude on samples of water doped with a paramagnetic compound at different concentrations. Pragmatically, as R 1 can be easily measured by conventional methods, its value is entered in the data processing algorithm which then returns exclusively the value of the transverse relaxation time. Very consistent results are obtained that way. Copyright © 2018 Elsevier Inc. All rights reserved.