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Sample records for acquisition gradient echo

  1. Improved Sensitivity of Spin Echo and Parallel Acquisitions Using SENSE Compared to Gradient Echo Sequences in fMRI

    NASA Astrophysics Data System (ADS)

    El Mrini, Sanaa; Hamri, Mohammed

    2012-03-01

    This work aims to validate the performance of spin echo and parallel acquisition using "SENSitivity Encoding (SENSE)" by comparing it to different imaging techniques, including gradient echo-planar imaging using parallel acquisition and SENSE usually used and gradient echo sequences and that of the echo of echo-planar spin. It compares the performance of sequences and their sensitivity to motor activity reflected by activation within the motor part of the brain. Image analysis of volunteers were processed individually. Image analysis techniques, such as normalization and smoothing, were used. Analyses were carried out using `Statistical Parametric Mapping' operating under Matlab.

  2. Multi-echo acquisition

    PubMed Central

    Posse, Stefan

    2011-01-01

    The rapid development of fMRI was paralleled early on by the adaptation of MR spectroscopic imaging (MRSI) methods to quantify water relaxation changes during brain activation. This review describes the evolution of multi-echo acquisition from high-speed MRSI to multi-echo EPI and beyond. It highlights milestones in the development of multi-echo acquisition methods, such as the discovery of considerable gains in fMRI sensitivity when combining echo images, advances in quantification of the BOLD effect using analytical biophysical modeling and interleaved multi-region shimming. The review conveys the insight gained from combining fMRI and MRSI methods and concludes with recent trends in ultra-fast fMRI, which will significantly increase temporal resolution of multi-echo acquisition. PMID:22056458

  3. Gradient echo MRI

    PubMed Central

    Copenhaver, B R.; Shin, J; Warach, S; Butman, J A.; Saver, J L.; Kidwell, C S.

    2009-01-01

    Background: Recent studies have demonstrated that gradient echo (GRE) MRI sequences are as accurate as CT for the detection of intracerebral hemorrhage (ICH) in the context of acute stroke. However, many physicians who currently read acute stroke imaging studies may be unfamiliar with interpretation of GRE images. Methods: An NIH Web-based training program was developed including a pretest, tutorial, and posttest. Physicians involved in the care of acute stroke patients were encouraged to participate. The tutorial covered acute, chronic, and mimic hemorrhages as they appear on CT, diffusion-weighted imaging, and GRE sequences. Ability of users to identify ICH presence, type, and age on GRE was compared from the pretest to posttest timepoint. Results: A total of 104 users completed the tutorial. Specialties represented included general radiology (42%), general neurology (16%), neuroradiology (15%), stroke neurology (14%), emergency medicine (1%), and other (12%). Median overall score improved pretest to posttest from 66.7% to 83.3%, p < 0.001. Improvement by category was as follows: acute ICH, 66.7%–100%, p < 0.001; chronic ICH, 33.3%–66.7%, p < 0.001; ICH negatives/mimics, 100%–100%, p = 0.787. Sensitivity for identification of acute hemorrhage improved from 68.2% to 96.4%. Conclusions: Physicians involved in acute stroke care achieved significant improvement in gradient echo (GRE) hemorrhage interpretation after completing the NIH GRE MRI tutorial. This indicates that a Web-based tutorial may be a viable option for the widespread education of physicians to achieve an acceptable level of diagnostic accuracy at reading GRE MRI, thus enabling confident acute stroke treatment decisions. GLOSSARY AHA/ASA = American Heart Association/American Stroke Association; CME = continuing medical education; DWI = diffusion-weighted imaging; GRE = gradient echo; ICH = intracerebral hemorrhage; tPA = tissue plasminogen activator. PMID:19414724

  4. Diffusion weighted vertical gradient and spin echo.

    PubMed

    Engström, Mathias; Bammer, Roland; Skare, Stefan

    2012-12-01

    In this work, diffusion weighting and parallel imaging is combined with a vertical gradient and spin echo data readout. This sequence was implemented and evaluated on healthy volunteers using a 1.5 and a 3 T whole-body MR system. As the vertical gradient and spin echo trajectory enables a higher k-space velocity in the phase-encoding direction than single-shot echo planar imaging, the geometrical distortions are reduced. When combined with parallel imaging such as generalized autocalibrating partially parallel acquisition, the geometric distortions are reduced even further, while also keeping the minimum echo time reasonably low. However, this combination of a diffusion preparation and multiple refocusing pulses during the vertical gradient and spin echo readout, generally violates the Carr-Purcell-Meiboom-Gill condition, which leads to interferences between echo pathways. To suppress the stimulated echo pathway, refocusing pulses with a sharper slice profiles and an odd/even crusher variation scheme were implemented and evaluated. Being a single-shot acquisition technique, the reconstructed images are robust to rigid-body head motion and spatially varying brain motion, both of which are common sources of artifacts in diffusion MRI.

  5. 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

  6. 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

  7. 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

  8. Gradient moment nulling in fast spin echo.

    PubMed

    Hinks, R S; Constable, R T

    1994-12-01

    The fast spin echo sequence combines data from many echo signals in a Carr-Purcell-Meiboom-Gill echo train to form a single image. Much of the signal in the second and later echoes results from the coherent addition of stimulated echo signal components back to the spin echo signal. Because stimulated echoes experience no dephasing effects during the time that they are stored as Mz magnetization, they experience a different gradient first moment than does the spin echo. This leads to flow-related phase differences between different echo components and results in flow voids and ghosting, even when the first moment is nulled for the spin echo signal. A method of gradient moment nulling that correctly compensates both spin echo and stimulated echo components has been developed. The simplest solution involves nulling the first gradient moment at least at the RF pulses and preferably at both the RF pulses and the echoes. Phantom and volunteer studies demonstrate good suppression of flow-related artifacts.

  9. Simultaneous acquisition of perfusion and permeability from corrected relaxation rates with dynamic susceptibility contrast dual gradient echo.

    PubMed

    Kim, Eun-Ju; Kim, Dae-Hong; Lee, Sang Hoon; Huh, Yong-Min; Song, Ho-Taek; Suh, Jin-Suck

    2004-04-01

    This study compared two methods, corrected (separation of T(1) and T(2)* effects) and uncorrected, in order to determine the suitability of the perfusion and permeability measures through Delta R(2)* and Delta R(1) analyses. A dynamic susceptibility contrast dual gradient echo (DSC-DGE) was used to image the fixed phantoms and flow phantoms (Sephadex perfusion phantoms and dialyzer phantom for the permeability measurements). The results confirmed that the corrected relaxation rate was linearly proportional to gadolinium-diethyltriamine pentaacetic acid (Gd-DTPA) concentration, whereas the uncorrected relaxation rate did not in the fixed phantom and simulation experiments. For the perfusion measurements, it was found that the correction process was necessary not only for the Delta R(1) time curve but also for the Delta R(2)* time curve analyses. Perfusion could not be measured without correcting the Delta R(2)* time curve. The water volume, which was expressed as the perfusion amount, was found to be closer to the theoretical value when using the corrected Delta R(1) curve in the calculations. However, this may occur in the low concentration of Gd-DTPA in tissue used in this study. For the permeability measurements based on the two-compartment model, the permeability factor (k(ev); e = extravascular, v = vascular) from the outside to the inside of the hollow fibers was greater in the corrected Delta R(1) method than in the uncorrected Delta R(1) method. The differences between the corrected and the uncorrected Delta R(1) values were confirmed by the simulation experiments. In conclusion, this study proposes that the correction for the relaxation rates, Delta R(2)* and Delta R(1), is indispensable in making accurate perfusion and permeability measurements, and that DSC-DGE is a useful method for obtaining information on perfusion and permeability, simultaneously. PMID:15062926

  10. Multi-Echo Acquisition of O-Space Data

    PubMed Central

    Galiana, Gigi; Peters, Dana; Tam, Leo; Constable, R. Todd

    2014-01-01

    Purpose Nonlinear gradient encoding methods, such as O-Space imaging, have been shown to provide good images from very few echoes. Acquiring data in a train of spin or gradient echoes is a very flexible way to further speed acquisition time. However, combining these strategies presents significant challenges, both in terms of the contrast and artifacts. We present strategies in both pulse sequence design and image processing to mitigate these effects. Theory and Methods The three strategies include a new echo ordering that takes into account the unique way that O-Space samples the k-space of the image; a new post-processing filter that allows tuning of T2-weighting by emphasizing the contribution of low frequency spatial information at selectable points in space and time; and an offset between linear and nonlinear gradients that makes the central point of each echo unique. Results Simulations indicate that these strategies mitigate artifacts introduced by T2 (or T2*) decay and produce contrast that reflects relaxation at a given TE. Conclusion Turbo spin echo O-Space is theoretically feasible, and the greater undersampling should make it possible to use shorter echo trains for a given scan time. PMID:24459076

  11. A simple method for MR elastography: a gradient-echo type multi-echo sequence.

    PubMed

    Numano, Tomokazu; Mizuhara, Kazuyuki; Hata, Junichi; Washio, Toshikatsu; Homma, Kazuhiro

    2015-01-01

    To demonstrate the feasibility of a novel MR elastography (MRE) technique based on a conventional gradient-echo type multi-echo MR sequence which does not need additional bipolar magnetic field gradients (motion encoding gradient: MEG), yet is sensitive to vibration. In a gradient-echo type multi-echo MR sequence, several images are produced from each echo of the train with different echo times (TEs). If these echoes are synchronized with the vibration, each readout's gradient lobes achieve a MEG-like effect, and the later generated echo causes a greater MEG-like effect. The sequence was tested for the tissue-mimicking agarose gel phantoms and the psoas major muscles of healthy volunteers. It was confirmed that the readout gradient lobes caused an MEG-like effect and the later TE images had higher sensitivity to vibrations. The magnitude image of later generated echo suffered the T2 decay and the susceptibility artifacts, but the wave image and elastogram of later generated echo were unaffected by these effects. In in vivo experiments, this method was able to measure the mean shear modulus of the psoas major muscle. From the results of phantom experiments and volunteer studies, it was shown that this method has clinical application potential.

  12. Improved time efficiency and accuracy in diffusion tensor microimaging with multiple-echo acquisition

    NASA Astrophysics Data System (ADS)

    Gulani, Vikas; Weber, Thomas; Neuberger, Thomas; Webb, Andrew G.

    2005-12-01

    In high-field NMR microscopy rapid single-shot imaging methods, for example, echo planar imaging, cannot be used for determination of the apparent diffusion tensor (ADT) due to large magnetic susceptibility effects. We propose a pulse sequence in which a diffusion-weighted spin-echo is followed by multiple gradient-echoes with additional diffusion weighting. These additional echoes can be used to calculate the ADT and T2∗ maps. We show here that this results in modest but consistent improvements in the accuracy of ADT determination within a given total data acquisition time. The method is tested on excised, chemically fixed rat spinal cords.

  13. An Improved Susceptibility Weighted Imaging Method using Multi-Echo Acquisition

    PubMed Central

    Oh, Sung Suk; Oh, Se-Hong; Nam, Yoonho; Han, Dongyeob; Stafford, Randall B.; Hwang, Jinyoung; Kim, Dong-Hyun; Park, HyunWook; Lee, Jongho

    2013-01-01

    Purpose To introduce novel acquisition and post-processing approaches for susceptibility weighted imaging (SWI) to remove background field inhomogeneity artifacts in both magnitude and phase data. Method The proposed method acquires three echoes in a 3D gradient echo (GRE) sequence, with a field compensation gradient (z-shim gradient) applied to the third echo. The artifacts in the magnitude data are compensated by signal estimation from all three echoes. The artifacts in phase signals are removed by modeling the background phase distortions using Gaussians. The method was applied in vivo and compared with conventional SWI. Results The method successfully compensates for background field inhomogeneity artifacts in magnitude and phase images, and demonstrated improved SWI images. In particular, vessels in frontal lobe, which were not observed in conventional SWI, were identified in the proposed method. Conclusion The new method improves image quality in SWI by restoring signal in the frontal and temporal regions. PMID:24105838

  14. Ultrafast 3D spin-echo acquisition improves Gadolinium-enhanced MRI signal contrast enhancement

    PubMed Central

    Han, S. H.; Cho, F. H.; Song, Y. K.; Paulsen, J.; Song, Y. Q.; Kim, Y. R.; Kim, J. K.; Cho, G.; Cho, H.

    2014-01-01

    Long scan times of 3D volumetric MR acquisitions usually necessitate ultrafast in vivo gradient-echo acquisitions, which are intrinsically susceptible to magnetic field inhomogeneities. This is especially problematic for contrast-enhanced (CE)-MRI applications, where non-negligible T2* effect of contrast agent deteriorates the positive signal contrast and limits the available range of MR acquisition parameters and injection doses. To overcome these shortcomings without degrading temporal resolution, ultrafast spin-echo acquisitions were implemented. Specifically, a multiplicative acceleration factor from multiple spin echoes (×32) and compressed sensing (CS) sampling (×8) allowed highly-accelerated 3D Multiple-Modulation-Multiple-Echo (MMME) acquisition. At the same time, the CE-MRI of kidney with Gd-DOTA showed significantly improved signal enhancement for CS-MMME acquisitions (×7) over that of corresponding FLASH acquisitions (×2). Increased positive contrast enhancement and highly accelerated acquisition of extended volume with reduced RF irradiations will be beneficial for oncological and nephrological applications, in which the accurate in vivo 3D quantification of contrast agent concentration is necessary with high temporal resolution. PMID:24863102

  15. A new technique for MR elastography of the supraspinatus muscle: A gradient-echo type multi-echo sequence.

    PubMed

    Ito, Daiki; Numano, Tomokazu; Mizuhara, Kazuyuki; Takamoto, Koichi; Onishi, Takaaki; Nishijo, Hisao

    2016-10-01

    Magnetic resonance elastography (MRE) can measure tissue stiffness quantitatively and noninvasively. Supraspinatus muscle injury is a significant problem among throwing athletes. The purpose of this study was to develop an MRE technique for application to the supraspinatus muscle by using a conventional magnetic resonance imaging (MRI). MRE acquisitions were performed with a gradient-echo type multi-echo MR sequence at 100Hz pneumatic vibration. A custom-designed vibration pad was used as a pneumatic transducer in order to adapt to individual shoulder shapes. In a gradient-echo type multi-echo MR sequence, without motion encoding gradient (MEG) that synchronizes with vibrations, bipolar readout gradient lobes achieved a similar function to MEG (MEG-like effect). In other words, a dedicated MRE sequence (built-in MEG) is not always necessary for MRE. In this study, 7 healthy volunteers underwent MRE. We investigated the effects of direction of the MEG-like effect and selected imaging planes on the patterns of wave propagation (wave image). The results indicated that wave images showed clear wave propagation on a condition that the direction of the MEG-like effect was nearly perpendicular to the long axis of the supraspinatus muscle, and that the imaging plane was superior to the proximal supraspinatus muscle. This limited condition might be ascribed to specific features of fibers in the supraspinatus muscle and wave reflection from the boundaries of the supraspinous fossa. The mean stiffness of the supraspinatus muscle was 10.6±3.17kPa. Our results demonstrated that using MRE, our method can be applied to the supraspinatus muscle by using conventional MRI. PMID:27374984

  16. A new technique for MR elastography of the supraspinatus muscle: A gradient-echo type multi-echo sequence.

    PubMed

    Ito, Daiki; Numano, Tomokazu; Mizuhara, Kazuyuki; Takamoto, Koichi; Onishi, Takaaki; Nishijo, Hisao

    2016-10-01

    Magnetic resonance elastography (MRE) can measure tissue stiffness quantitatively and noninvasively. Supraspinatus muscle injury is a significant problem among throwing athletes. The purpose of this study was to develop an MRE technique for application to the supraspinatus muscle by using a conventional magnetic resonance imaging (MRI). MRE acquisitions were performed with a gradient-echo type multi-echo MR sequence at 100Hz pneumatic vibration. A custom-designed vibration pad was used as a pneumatic transducer in order to adapt to individual shoulder shapes. In a gradient-echo type multi-echo MR sequence, without motion encoding gradient (MEG) that synchronizes with vibrations, bipolar readout gradient lobes achieved a similar function to MEG (MEG-like effect). In other words, a dedicated MRE sequence (built-in MEG) is not always necessary for MRE. In this study, 7 healthy volunteers underwent MRE. We investigated the effects of direction of the MEG-like effect and selected imaging planes on the patterns of wave propagation (wave image). The results indicated that wave images showed clear wave propagation on a condition that the direction of the MEG-like effect was nearly perpendicular to the long axis of the supraspinatus muscle, and that the imaging plane was superior to the proximal supraspinatus muscle. This limited condition might be ascribed to specific features of fibers in the supraspinatus muscle and wave reflection from the boundaries of the supraspinous fossa. The mean stiffness of the supraspinatus muscle was 10.6±3.17kPa. Our results demonstrated that using MRE, our method can be applied to the supraspinatus muscle by using conventional MRI.

  17. Ultrashort echo time (UTE) imaging using gradient pre-equalization and compressed sensing

    NASA Astrophysics Data System (ADS)

    Fabich, Hilary T.; Benning, Martin; Sederman, Andrew J.; Holland, Daniel J.

    2014-08-01

    Ultrashort echo time (UTE) imaging is a well-known technique used in medical MRI, however, the implementation of the sequence remains non-trivial. This paper introduces UTE for non-medical applications and outlines a method for the implementation of UTE to enable accurate slice selection and short acquisition times. Slice selection in UTE requires fast, accurate switching of the gradient and r.f. pulses. Here a gradient “pre-equalization” technique is used to optimize the gradient switching and achieve an effective echo time of 10 μs. In order to minimize the echo time, k-space is sampled radially. A compressed sensing approach is used to minimize the total acquisition time. Using the corrections for slice selection and acquisition along with novel image reconstruction techniques, UTE is shown to be a viable method to study samples of cork and rubber with a shorter signal lifetime than can typically be measured. Further, the compressed sensing image reconstruction algorithm is shown to provide accurate images of the samples with as little as 12.5% of the full k-space data set, potentially permitting real time imaging of short T2* materials.

  18. Actively Shielded Gradient Coils and Echo-Planar MRI

    NASA Astrophysics Data System (ADS)

    Elekes, Almos A.

    Echo-planar imaging (EPI), which produces images in 25-100 msec, is the fastest magnetic resonance imaging (MRI) technique. Its implementation is hampered by the demands it places on the scanner components. It requires strong magnetic gradient fields, produced by rapidly switched gradient coils; therefore the coils must have low inductance. They also have to be accommodated without inducing eddy currents in the magnet's metallic structure, otherwise the images would be degraded. All the major technical problems of echo-planar imaging are solved. Two transverse, actively shielded gradient coils were designed, built and tested. The coils were designed by the combined application of the minimum inductance and target field methods. The gradient strengths are 10 and 13 G/cm, unusually high for EPI, but well suited for microimaging, MR spectroscopy and petrochemical core analysis. The gradient time constants are short, so high resolution images are possible under 50 ms. The research was carried out at on a 4.5T/30cm superconducting, superferric shielded magnet located at the Texas Accelerator Center. The results of EPI and microimaging are presented.

  19. Communication: Phase incremented echo train acquisition in NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Baltisberger, Jay H.; Walder, Brennan J.; Keeler, Eric G.; Kaseman, Derrick C.; Sanders, Kevin J.; Grandinetti, Philip J.

    2012-06-01

    We present an improved and general approach for implementing echo train acquisition (ETA) in magnetic resonance spectroscopy, particularly where the conventional approach of Carr-Purcell-Meiboom-Gill (CPMG) acquisition would produce numerous artifacts. Generally, adding ETA to any N-dimensional experiment creates an N + 1 dimensional experiment, with an additional dimension associated with the echo count, n, or an evolution time that is an integer multiple of the spacing between echo maxima. Here we present a modified approach, called phase incremented echo train acquisition (PIETA), where the phase of the mixing pulse and every other refocusing pulse, ϕP, is incremented as a single variable, creating an additional phase dimension in what becomes an N + 2 dimensional experiment. A Fourier transform with respect to the PIETA phase, ϕP, converts the ϕP dimension into a Δp dimension where desired signals can be easily separated from undesired coherence transfer pathway signals, thereby avoiding cumbersome or intractable phase cycling schemes where the receiver phase must follow a master equation. This simple modification eliminates numerous artifacts present in NMR experiments employing CPMG acquisition and allows "single-scan" measurements of transverse relaxation and J-couplings. Additionally, unlike CPMG, we show how PIETA can be appended to experiments with phase modulated signals after the mixing pulse.

  20. Improved convection compensating pulsed field gradient spin-echo and stimulated-echo methods.

    PubMed

    Sørland, G H; Seland, J G; Krane, J; Anthonsen, H W

    2000-02-01

    The need for convection compensating methods in NMR has been manifested through an increasing number of publications related to the subject over the past few years (J. Magn. Reson. 125, 372 (1997); 132, 13 (1998); 131, 126 (1998); 118, 50 (1996); 133, 379 (1998)). When performing measurements at elevated temperature, small convection currents may give rise to erroneous values of the diffusion coefficient. In work with high resolution NMR spectroscopy, the application of magnetic field gradients also introduces an eddy-current magnetic field which may result in errors in phase and baseline in the FFT-spectra. The eddy current field has been greatly suppressed by the application of bipolar magnetic field gradients. However, when introducing bipolar magnetic field gradients, the pulse sequence is lengthened significantly. This has recently been pointed out as a major drawback because of the loss of coherence and of NMR-signal due to transverse relaxation processes. Here we present modified convection compensating pulsed field gradient double spin echo and double stimulated echo sequences which suppress the eddy-current magnetic field without increasing the duration of the pulse sequences.

  1. Assessment of a combined spin- and gradient-echo (SAGE) DSC-MRI method for preclinical neuroimaging.

    PubMed

    Stokes, Ashley M; Skinner, Jack T; Quarles, C Chad

    2014-12-01

    The goal of this study was to optimize and validate a combined spin- and gradient-echo (SAGE) sequence for dynamic susceptibility-contrast magnetic resonance imaging to obtain hemodynamic parameters in a preclinical setting. The SAGE EPI sequence was applied in phantoms and in vivo rat brain (normal, tumor, and stroke tissue). Partial and full Fourier encoding schemes were implemented and characterized. Maps of cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), vessel size index (VSI), volume transfer constant (K(trans)), and volume fraction of the extravascular extracellular space (ve) were obtained. Partial Fourier encoding provided shortened echo times with acceptable signal-to-noise ratio and temporal stability, thus enabling reliable characterization of T2, T2(*) and T1 in both phantoms and rat brain. The hemodynamic parameters CBV, CBF, and MTT for gradient-echo and spin-echo contrast were determined in tumor and stroke; VSI, K(trans), and ve were also computed in tumor tissue. The SAGE EPI sequence allows the acquisition of multiple gradient- and spin-echoes, from which measures of perfusion, permeability, and vessel size can be obtained in a preclinical setting. Partial Fourier encoding can be used to minimize SAGE echo times and reliably quantify dynamic T2 and T2(*) changes. This acquisition provides a more comprehensive assessment of hemodynamic status in brain tissue with vascular and perfusion abnormalities.

  2. Gradient Echo Quantum Memory in Warm Atomic Vapor

    PubMed Central

    Pinel, Olivier; Hosseini, Mahdi; Sparkes, Ben M.; Everett, Jesse L.; Higginbottom, Daniel; Campbell, Geoff T.; Lam, Ping Koy; Buchler, Ben C.

    2013-01-01

    Gradient echo memory (GEM) is a protocol for storing optical quantum states of light in atomic ensembles. The primary motivation for such a technology is that quantum key distribution (QKD), which uses Heisenberg uncertainty to guarantee security of cryptographic keys, is limited in transmission distance. The development of a quantum repeater is a possible path to extend QKD range, but a repeater will need a quantum memory. In our experiments we use a gas of rubidium 87 vapor that is contained in a warm gas cell. This makes the scheme particularly simple. It is also a highly versatile scheme that enables in-memory refinement of the stored state, such as frequency shifting and bandwidth manipulation. The basis of the GEM protocol is to absorb the light into an ensemble of atoms that has been prepared in a magnetic field gradient. The reversal of this gradient leads to rephasing of the atomic polarization and thus recall of the stored optical state. We will outline how we prepare the atoms and this gradient and also describe some of the pitfalls that need to be avoided, in particular four-wave mixing, which can give rise to optical gain. PMID:24300586

  3. Gradient echo quantum memory in warm atomic vapor.

    PubMed

    Pinel, Olivier; Hosseini, Mahdi; Sparkes, Ben M; Everett, Jesse L; Higginbottom, Daniel; Campbell, Geoff T; Lam, Ping Koy; Buchler, Ben C

    2013-11-11

    Gradient echo memory (GEM) is a protocol for storing optical quantum states of light in atomic ensembles. The primary motivation for such a technology is that quantum key distribution (QKD), which uses Heisenberg uncertainty to guarantee security of cryptographic keys, is limited in transmission distance. The development of a quantum repeater is a possible path to extend QKD range, but a repeater will need a quantum memory. In our experiments we use a gas of rubidium 87 vapor that is contained in a warm gas cell. This makes the scheme particularly simple. It is also a highly versatile scheme that enables in-memory refinement of the stored state, such as frequency shifting and bandwidth manipulation. The basis of the GEM protocol is to absorb the light into an ensemble of atoms that has been prepared in a magnetic field gradient. The reversal of this gradient leads to rephasing of the atomic polarization and thus recall of the stored optical state. We will outline how we prepare the atoms and this gradient and also describe some of the pitfalls that need to be avoided, in particular four-wave mixing, which can give rise to optical gain.

  4. Spectroscopic Localization by Simultaneous Acquisition of the Double-Spin and Stimulated Echoes

    PubMed Central

    Tal, Assaf; Gonen, Oded

    2014-01-01

    Purpose To design a proton MR spectroscopy (1H-MRS) localization sequence that combines the signal-to-noise-ratio (SNR) benefits of Point Resolved Spectroscopy (PRESS) with the high pulse bandwidths, low chemical shift displacements (CSD), low specific absorption rates (SAR), short echo times (TE) and superior radio-frequency transmit field (B1+) immunity of Stimulated Echo Acquisition Mode (STEAM), by simultaneously refocusing and acquiring both the double-spin and stimulated echo coherence pathways from the volume of interest. Methods We propose a family of 1H-MRS sequences comprising three orthogonal spatially-selective pulses with flip angles 90°<α, β, γ<128°. The stimulated and double-spin echo are refocused in-phase simultaneously by altering the pulses’ phases, flip angles and timing, as well as the inter-pulse gradient spoiling moments. The ≈90° nutations of α, β, γ provide STEAM-like advantages (lower SAR, in-plane CSD and TE; greater B1+ immunity), but with SNRs comparable with PRESS. Results Phantom and in vivo brain experiments show that 83–100% of the PRESS SNR (metabolite-dependent) is achieved at under 75% of the SAR and 66% lower in-plane CSD. Conclusion The advantages of STEAM can be augmented with the higher SNR of PRESS by combining the spin and stimulated echoes. Quantification, especially of J-coupled resonances and intermediate and long TEs, must be carefully considered. PMID:24664399

  5. Magnetization transfer prepared gradient echo MRI for CEST imaging.

    PubMed

    Dai, Zhuozhi; Ji, Jim; Xiao, Gang; Yan, Gen; Li, Shengkai; Zhang, Guishan; Lin, Yan; Shen, Zhiwei; Wu, Renhua

    2014-01-01

    Chemical exchange saturation transfer (CEST) is an emerging MRI contrast mechanism that is capable of noninvasively imaging dilute CEST agents and local properties such as pH and temperature, augmenting the routine MRI methods. However, the routine CEST MRI includes a long RF saturation pulse followed by fast image readout, which is associated with high specific absorption rate and limited spatial resolution. In addition, echo planar imaging (EPI)-based fast image readout is prone to image distortion, particularly severe at high field. To address these limitations, we evaluated magnetization transfer (MT) prepared gradient echo (GRE) MRI for CEST imaging. We proved the feasibility using numerical simulations and experiments in vitro and in vivo. Then we optimized the sequence by serially evaluating the effects of the number of saturation steps, MT saturation power (B1), GRE readout flip angle (FA), and repetition time (TR) upon the CEST MRI, and further demonstrated the endogenous amide proton CEST imaging in rats brains (n = 5) that underwent permanent middle cerebral artery occlusion. The CEST images can identify ischemic lesions in the first 3 hours after occlusion. In summary, our study demonstrated that the readily available MT-prepared GRE MRI, if optimized, is CEST-sensitive and remains promising for translational CEST imaging. PMID:25384020

  6. [Reduction of vascular artifact on T1-weighted images of the brain by using three-dimensional double IR fast spoiled gradient echo recalled acquisition in the steady state (FSPGR) at 3.0 Tesla].

    PubMed

    Fujiwara, Yasuhiro; Matsuda, Tsuyoshi; Ishimori, Yoshiyuki; Yamaguchi, Isao; Hayashi, Hiroyuki; Ookoshi, Yusuke; Ootani, Yuriko; Miyati, Tosiaki; Kimura, Hirohiko

    2007-11-20

    The purpose of this study was to decrease vascular artifacts caused by the in-flow effect in three-dimensional inversion recovery prepared fast spoiled gradient recalled acquisition in the steady state (3D IR FSPGR) at 3.0 Tesla. We developed 3D double IR FSPGR and investigated the signal characteristics of the new sequence. The 3D double IR FSPGR sequence uses two inversion pulses, the first for obtaining tissue contrast and the second for nulling vascular signal, which is applied at the time of the first IR period at the neck region. We have optimized scan parameters based on both phantom and in-vivo study. As a result, optimized parameters (1st TI=700 ms, 2nd TI=400 ms) successfully have produced much less vessel signal at reduction than conventional 3D IR FSPGR over a wide imaging range, while preserving the signal-to-noise ratio (SNR) and gray/white matter contrast. Moreover, the decreased artifact was also confirmed by visual inspection of the images obtained in vivo using those parameters. Thus, 3D double IR FSPGR was a useful sequence for the acquisition of T1-weighted images at 3.0 Tesla.

  7. A comparison of dual gradient-echo and spin-echo fMRI of the inferior temporal lobe.

    PubMed

    Halai, Ajay D; Welbourne, Stephen R; Embleton, Karl; Parkes, Laura M

    2014-08-01

    Magnetic susceptibility differences at tissue interfaces lead to signal loss in conventional gradient-echo (GE) EPI. This poses a problem for fMRI in language and memory paradigms, which activate the most affected regions. Two methods proposed to overcome this are spin-echo EPI and dual GE EPI, where two EPI read-outs are serially collected at a short and longer echo time. The spin-echo method applies a refocusing pulse to recover dephased MR signal due to static field inhomogeneities, but is known to have a relatively low blood oxygenation level dependant (BOLD) sensitivity. In comparison, GE has superior BOLD sensitivity, and by employing an additional shorter echo, in a dual GE sequence, it can reduce signal loss due to spin dephasing. We directly compared dual GE and spin-echo fMRI during a semantic categorization task, which has been shown to activate the inferior temporal region-a region known to be affected by magnetic susceptibility. A whole brain analysis showed that the dual GE resulted in significantly higher activation within the left inferior temporal fusiform (ITF) cortex, compared to spin-echo. The inferior frontal gyrus (IFG) was activated for dual GE, but not spin-echo. Regions of interest analysis was carried out on the anterior and posterior ITF, left and right IFG, and part of the cerebellum. Dual GE outperformed spin-echo in the anterior and posterior ITF and bilateral IFG regions, whilst being equal in the cerebellum. Hence, dual GE should be the method of choice for fMRI studies of inferior temporal regions. PMID:24677506

  8. Size Distribution Imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE) MRI.

    PubMed

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

    2015-01-01

    Objects making up complex porous systems in Nature usually span a range of sizes. These size distributions play fundamental roles in defining the physicochemical, biophysical and physiological properties of a wide variety of systems - ranging from advanced catalytic materials to Central Nervous System diseases. Accurate and noninvasive measurements of size distributions in opaque, three-dimensional objects, have thus remained long-standing and important challenges. Herein we describe how a recently introduced diffusion-based magnetic resonance methodology, Non-Uniform-Oscillating-Gradient-Spin-Echo (NOGSE), can determine such distributions noninvasively. The method relies on its ability to probe confining lengths with a (length)6 parametric sensitivity, in a constant-time, constant-number-of-gradients fashion; combined, these attributes provide sufficient sensitivity for characterizing the underlying distributions in μm-scaled cellular systems. Theoretical derivations and simulations are presented to verify NOGSE's ability to faithfully reconstruct size distributions through suitable modeling of their distribution parameters. Experiments in yeast cell suspensions - where the ground truth can be determined from ancillary microscopy - corroborate these trends experimentally. Finally, by appending to the NOGSE protocol an imaging acquisition, novel MRI maps of cellular size distributions were collected from a mouse brain. The ensuing micro-architectural contrasts successfully delineated distinctive hallmark anatomical sub-structures, in both white matter and gray matter tissues, in a non-invasive manner. Such findings highlight NOGSE's potential for characterizing aberrations in cellular size distributions upon disease, or during normal processes such as development. PMID:26197220

  9. Size Distribution Imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE) MRI

    PubMed Central

    Shemesh, Noam; Álvarez, Gonzalo A.; Frydman, Lucio

    2015-01-01

    Objects making up complex porous systems in Nature usually span a range of sizes. These size distributions play fundamental roles in defining the physicochemical, biophysical and physiological properties of a wide variety of systems – ranging from advanced catalytic materials to Central Nervous System diseases. Accurate and noninvasive measurements of size distributions in opaque, three-dimensional objects, have thus remained long-standing and important challenges. Herein we describe how a recently introduced diffusion-based magnetic resonance methodology, Non-Uniform-Oscillating-Gradient-Spin-Echo (NOGSE), can determine such distributions noninvasively. The method relies on its ability to probe confining lengths with a (length)6 parametric sensitivity, in a constant-time, constant-number-of-gradients fashion; combined, these attributes provide sufficient sensitivity for characterizing the underlying distributions in μm-scaled cellular systems. Theoretical derivations and simulations are presented to verify NOGSE’s ability to faithfully reconstruct size distributions through suitable modeling of their distribution parameters. Experiments in yeast cell suspensions – where the ground truth can be determined from ancillary microscopy – corroborate these trends experimentally. Finally, by appending to the NOGSE protocol an imaging acquisition, novel MRI maps of cellular size distributions were collected from a mouse brain. The ensuing micro-architectural contrasts successfully delineated distinctive hallmark anatomical sub-structures, in both white matter and gray matter tissues, in a non-invasive manner. Such findings highlight NOGSE’s potential for characterizing aberrations in cellular size distributions upon disease, or during normal processes such as development. PMID:26197220

  10. Accounting for signal loss due to dephasing in the correction of distortions in gradient-echo EPI via nonrigid registration.

    PubMed

    Li, Yong; Xu, Ning; Fitzpatrick, J Michael; Morgan, Victoria L; Pickens, David R; Dawant, Benoit M

    2007-12-01

    Gradient-echo (GE) echo planar imaging (EPI) is susceptible to both geometric distortions and signal loss. This paper presents a retrospective correction approach based on nonrigid image registration. A new physics-based intensity correction factor derived to compensate for intravoxel dephasing in GE EPI images is incorporated into a previously reported nonrigid registration algorithm. Intravoxel dephasing causes signal loss and thus intensity attenuation in the images. The new rephasing factor we introduce, which changes the intensity of a voxel in images during the registration, is used to improve the accuracy of the intensity-based nonrigid registration method and mitigate the intensity attenuation effect. Simulation-based experiments are first used to evaluate the method. A magnetic resonance (MR) simulator and a real field map are used to generate a realistic GE EPI image. The geometric distortion computed from the field map is used as the ground truth to which the estimated nonrigid deformation is compared. We then apply the algorithm to a set of real human brain images. The results show that, after registration, alignment between EPI and multi-shot, spin-echo images, which have relatively long acquisition times but negligible distortion, is improved and that signal loss caused by dephasing can be recovered. PMID:18092739

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

    NASA Astrophysics Data System (ADS)

    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 50-3000 Hz using a 6 T/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.

  12. 3D hyperpolarized He-3 MRI of ventilation using a multi-echo projection acquisition

    PubMed Central

    Holmes, James H.; O’Halloran, Rafael L.; Brodsky, Ethan K.; Jung, Youngkyoo; Block, Walter F.; Fain, Sean B.

    2010-01-01

    A method is presented for high resolution 3D imaging of the whole lung using inhaled hyperpolarized (HP) He-3 MR with multiple half-echo radial trajectories that can accelerate imaging through undersampling. A multiple half-echo radial trajectory can be used to reduce the level of artifact for undersampled 3D projection reconstruction (PR) imaging by increasing the amount of data acquired per unit time for HP He-3 lung imaging. The point spread functions (PSFs) for breath-held He-3 MRI using multiple half-echo trajectories were evaluated using simulations to predict the effects of T2* and gas diffusion on image quality. Results from PSF simulations were consistent with imaging results in volunteer studies showing improved image quality with increasing number of echoes using up to 8 half-echoes. The 8 half-echo acquisition is shown to accommodate lost breath-holds as short as 6 s using a retrospective reconstruction at reduced resolution as well as to allow reduced breath-hold time compared to an equivalent Cartesian trajectory. Furthermore, preliminary results from a 3D dynamic inhalation-exhalation maneuver are demonstrated using the 8 half-echo trajectory. Results demonstrate the first high resolution 3D PR imaging of ventilation and respiratory dynamics in humans using HP He-3 MR. PMID:18429034

  13. Uncertainty and bias in contrast concentration measurements using spoiled gradient echo pulse sequences.

    PubMed

    Schabel, Matthias C; Parker, Dennis L

    2008-05-01

    Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a widely used technique for assessing tissue physiology. Spoiled gradient echo (SPGR) pulse sequences are one of the most common methods for acquisition of DCE-MRI data, providing high temporal and spatial resolution with strong T(1)-weighting. Conversion of SPGR signal to concentration is briefly reviewed, and a new closed-form expression for concentration measurement uncertainty for finite signal-to-noise ratio (SNR) and baseline scan time is derived. This result is applicable to arbitrary concentration-dependent relaxation rate and is valid over the same domain as the theoretical SPGR signal equation. Expressions for the lower and upper bounds on measurable concentration are also derived. The existence of a concentration- and tissue-dependent optimal flip angle that minimizes concentration uncertainty is demonstrated and it is shown that, for clinically relevant pulse sequence parameters, this optimal flip angle is significantly larger than the corresponding Ernst angle. Analysis of three pulse sequences from the DCE-MRI literature shows that optimization of flip angle using the methods discussed here leads to potential improvements of 10-1166% in effective SNR over the 0.5-5.0 mM concentration range with minimal or no loss of measurement accuracy down to 0.1 mM. In vivo data from three study patients provide further support for our theoretical expression for concentration measurement uncertainty, with predicted and experimental estimates agreeing to within +/- 30%. Equations for concentration bias resulting from biases in flip angle and from pre-contrast relaxation time and contrast relaxivity (both longitudinal and transverse) are also derived in closed-form. The resulting equations show the potential for significant contributions to bias in concentration measurement arising from even relatively small mis-specification of flip angle and/or pre-contrast longitudinal relaxation time, particularly

  14. Localization of the cortical motor area by functional magnetic resonance imaging with gradient echo and echo-planar methods, using clinical 1.5 Tesla MR imaging systems.

    PubMed

    Nakayama, K

    1997-06-01

    Functional magnetic resonance imaging (MRI) with gradient echo and echo-planar sequences was applied to healthy volunteers and neurological patients to evaluate the feasibility of detecting and localizing the motor cortex. Time course of the change in signal intensity by an alternate repetition of motor task (squeezing hand) and rest periods was also examined. The motor cortex was localized as the area of signal increase in 88.9% of 45 healthy volunteers by gradient echo method, which mainly reflected the cortical vein, and 83.3% of 30 healthy volunteers by echo-planar method, which mainly reflected the cerebral gyrus. Among 21 volunteers who participated in the both studies, success rate in the localization for the motor cortex was 90.5% (21 volunteers) by gradient echo method and 81% (17 volunteers) by echo-planar method. It was also shown from the time course of the change in signal intensity that signal increase in the most significantly activated area generally corresponded with the periods of the motor task, and the latency between the onset of signal increase and the onset of motor task was usually about 4 seconds. In four of 6 patients with brain tumor, the motor cortex was localized, although activated areas were displaced or distorted. The results indicate that fMRI, either with gradient echo or echo-planar sequence, is a useful method for localizing the primary motor area activated during the motor task and clinically available for noninvasive evaluation of the anatomical relation between brain tumors and the motor area before surgical therapy.

  15. Gradient-echo 3D imaging of Rb polarization in fiber-coupled atomic magnetometer.

    PubMed

    Savukov, I

    2015-07-01

    The analogy between atomic and nuclear spins is exploited to implement 3D imaging of polarization inside the cell of an atomic magnetometer. The resolution of 0.8mm×1.2mm×1.4mm has been demonstrated with the gradient-echo imaging method. The imaging can be used in many applications. One such an application is the evaluation of active volume of an atomic magnetometer for sensitivity analysis and optimization. It has been found that imaging resolution is limited due to de-phasing from spin-exchange collisions and diffusion in the presence of gradients, and for a given magnetometer operational parameters, the imaging sequence has been optimized. Diffusion decay of the signal in the presence of gradients has been modeled numerically and analytically, and the analytical results, which agreed with numerical simulations, have been used to fit the spin-echo gradient measurements to extract the diffusion coefficient. The diffusion coefficient was found in agreement with previous measurements.

  16. Minimizing TE in moment-nulled or flow-encoded two- and three-dimensional gradient-echo imaging.

    PubMed

    Bernstein, M A; Shimakawa, A; Pelc, N J

    1992-01-01

    A method for minimizing field-echo delay in moment-nulled gradient-echo imaging is presented. Even though ramps are accounted for, the analysis yields simple closed-form solutions. The method is then generalized to the section-select waveform for three-dimensional volume imaging and to flow encoding for phase-contrast imaging. Three strategies for first-moment selection in phase-contrast imaging are discussed, including a new strategy that always yields the minimum echo delay. Trapezoidal and triangular gradient lobe shapes are analyzed.

  17. Variable flip angle imaging and fat suppression in combined gradient and spin-echo (GREASE) techniques

    SciTech Connect

    Vinitski, S.; Mitchell, D.G.; Szumowski, J.; Burk, D.L. Jr.; Rifkin, M.D. )

    1990-01-01

    Conventional proton density and T2-weighted spin-echo images are susceptible to motion induced artifact, which is exacerbated by lipid signals. Gradient moment nulling can reduce motion artifact but lengthens the minimum TE, degrading the proton density contrast. We designed a pulse sequence capable of optimizing proton density and T2-weighted contrast while suppressing lipid signals and motion induced artifacts. Proton density weighting was obtained by rapid readout gradient reversal immediately after the excitation RF pulse, within a conventional spin-echo sequence. By analyzing the behavior of the macroscopic magnetization and optimizing excitation flip angle, we suppressed T1 contribution to the image, thereby enhancing proton density and T2-weighted contrast with a two- to four-fold reduction of repetition time. This permitted an increased number of averages to be used, reducing motion induced artifacts. Fat suppression in the presence of motion was investigated in two groups of 8 volunteers each by (i) modified Dixon technique, (ii) selective excitation, and (iii) hybrid of both. Elimination of fat signal by the first technique was relatively uniform across the field of view, but it did not fully suppress the ghosts originating from fat motion. Selective excitation, while sensitive to the main field inhomogeneity, largely eliminated the ghosts (0.21 +/- 0.05 vs. 0.29 +/- 0.06, p less than 0.01). The hybrid of both techniques combined with bandwidth optimization, however, showed the best results (0.17 +/- 0.04, p less than 0.001). Variable flip-angle imaging allows optimization of image contrast which, along with averaging and effective fat suppression, significantly improves gradient- and spin-echo imaging, particularly in the presence of motion.

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

    PubMed

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

    2009-03-01

    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 (< or equal 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) > or =5 for echo train lengths (ETLs) > or =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 > or =4 echoes and for T2*(<1.0%) with > or =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 < or =16 echoes for one- and two-peak systems. Preliminary ex vivo

  19. 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

  20. Characterization and correction of system delays and eddy currents for MR imaging with ultrashort echo-time and time-varying gradients.

    PubMed

    Atkinson, Ian C; Lu, Aiming; Thulborn, Keith R

    2009-08-01

    Reconstruction of high-quality MR images requires precise knowledge of the dynamic gradient magnetic fields used to perform spatial encoding. System delays and eddy currents can perturb the gradient fields in both time and space and significantly degrade the image quality for acquisitions with an ultrashort echo time or with rapidly varying readout gradient waveforms. A technique for simultaneously characterizing and correcting the system delay and linear- and zero-order eddy currents of an MR system is proposed. A single set of calibration scans were used to compute a set of system constants that describe the effects of system delays and eddy currents to enable accurate reconstruction of data collected before uncorrected eddy currents have decayed. The ability of the proposed technique to reproducibly characterize small fixed delays (<50 micros) and short-time constant (<1 ms) eddy currents is demonstrated.

  1. Gradient preemphasis calibration in diffusion-weighted echo-planar imaging.

    PubMed

    Papadakis, N G; Martin, K M; Pickard, J D; Hall, L D; Carpenter, T A; Huang, C L

    2000-10-01

    This article describes a method which enables fast and objective pulse-sequence-specific preemphasis calibration, using standard pulse sequences and system hardware. The method is based on a k-space measurement technique, and has been applied to single-shot, diffusion-weighted, spin-echo, echo-planar imaging (DW-SE-EPI), which is particularly sensitive to eddy-current-induced image distortions. The efficiency of the technique was demonstrated not only by the reduction of eddy-current fields to a negligible level using full preemphasis compensation, but also by the fact that adjustment of the slow time-base alone sufficed for the practical elimination of image distortions in the DW-SE-EPI images and the subsequent diffusion tensor maps (in a phantom and a human brain). By seeking to eliminate directly the effect of eddy-current-induced phase shifts during the EPI data collection, the method is free of the complications and restrictions associated with other eddy-current correction techniques for DW-SE-EPI (such as acquisition of additional calibration scans, intense postprocessing, extensive pulse-sequence modifications), making their use redundant.

  2. Quantitative analysis of polymer mixtures in solution by pulsed field-gradient spin echo NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Van Lokeren, Luk; Ben Sassi, Hanen; Van Assche, Guy; Ribot, François

    2013-06-01

    Pulsed Field-Gradient Spin Echo (PGSE) NMR, which associates to a spectral dimension the measure of diffusion coefficients, is a convenient technique for mixture analysis. Unfortunately, because of relaxation, the quantification of mixtures by PGSE NMR is far from straightforward for mixtures with strong spectral overlap. Antalek (J. Am. Chem. Soc. 128 (2006) 8402-8403) proposed a quantification strategy based on DECRA analysis and extrapolation to zero of the diffusion delay. More recently, Barrère et al. (J. Magn. Reson. 216 (2012) 201-208) presented a new strategy based also on DECRA and on the renormalization of the intensities using estimates of the T1 and T2 relaxation times. Here we report an alternative quantification approach in which the fractions are obtained by analyzing the PGSE attenuation profile with a general Stejskal-Tanner equation that explicitly includes the relaxation effects. The required values of T1 and T2 relaxation times are either independently measured with conventional sequences or determined, along with the fractions and the diffusion coefficients, from the simultaneous analysis of up to 6 PGSE data sets recorded with different diffusion delays. This method yields errors lower than 3% for the fractions, even for complete spectral overlap, as demonstrated on model binary and ternary mixtures of polystyrene in the case of a convection compensating double stimulated echo (DSTE) sequence.

  3. Quantitative analysis of polymer mixtures in solution by pulsed field-gradient spin echo NMR spectroscopy.

    PubMed

    Van Lokeren, Luk; Ben Sassi, Hanen; Van Assche, Guy; Ribot, François

    2013-06-01

    Pulsed Field-Gradient Spin Echo (PGSE) NMR, which associates to a spectral dimension the measure of diffusion coefficients, is a convenient technique for mixture analysis. Unfortunately, because of relaxation, the quantification of mixtures by PGSE NMR is far from straightforward for mixtures with strong spectral overlap. Antalek (J. Am. Chem. Soc. 128 (2006) 8402-8403) proposed a quantification strategy based on DECRA analysis and extrapolation to zero of the diffusion delay. More recently, Barrère et al. (J. Magn. Reson. 216 (2012) 201-208) presented a new strategy based also on DECRA and on the renormalization of the intensities using estimates of the T1 and T2 relaxation times. Here we report an alternative quantification approach in which the fractions are obtained by analyzing the PGSE attenuation profile with a general Stejskal-Tanner equation that explicitly includes the relaxation effects. The required values of T1 and T2 relaxation times are either independently measured with conventional sequences or determined, along with the fractions and the diffusion coefficients, from the simultaneous analysis of up to 6 PGSE data sets recorded with different diffusion delays. This method yields errors lower than 3% for the fractions, even for complete spectral overlap, as demonstrated on model binary and ternary mixtures of polystyrene in the case of a convection compensating double stimulated echo (DSTE) sequence.

  4. Assessment of cerebral venous sinus thrombosis using T2*-weighted gradient echo magnetic resonance imaging sequences

    PubMed Central

    Bidar, Fatemeh; Faeghi, Fariborz; Ghorbani, Askar

    2016-01-01

    Background: The purpose of this study is to demonstrate the advantages of gradient echo (GRE) sequences in the detection and characterization of cerebral venous sinus thrombosis compared to conventional magnetic resonance sequences. Methods: A total of 17 patients with cerebral venous thrombosis (CVT) were evaluated using different magnetic resonance imaging (MRI) sequences. The MRI sequences included T1-weighted spin echo (SE) imaging, T*2-weighted turbo SE (TSE), fluid attenuated inversion recovery (FLAIR), T*2-weighted conventional GRE, and diffusion weighted imaging (DWI). MR venography (MRV) images were obtained as the golden standard. Results: Venous sinus thrombosis was best detectable in T*2-weighted conventional GRE sequences in all patients except in one case. Venous thrombosis was undetectable in DWI. T*2-weighted GRE sequences were superior to T*2-weighted TSE, T1-weighted SE, and FLAIR. Enhanced MRV was successful in displaying the location of thrombosis. Conclusion: T*2-weighted conventional GRE sequences are probably the best method for the assessment of cerebral venous sinus thrombosis. The mentioned method is non-invasive; therefore, it can be employed in the clinical evaluation of cerebral venous sinus thrombosis. PMID:27326365

  5. MRI of lung parenchyma in rats and mice using a gradient-echo sequence.

    PubMed

    Beckmann, N; Tigani, B; Mazzoni, L; Fozard, J R

    2001-08-01

    Signal of lung parenchymal tissue from the living rat and mouse lung was detected at 4.7 T with a good signal-to-noise ratio and motion-suppressed artifacts using a short TE gradient-echo sequence. Neither cardiac nor respiratory gating were applied, and animals respired freely during data collection. Mean T(2)* relaxation times of parenchyma in the anterior, middle and posterior regions of both lungs ranged between 403 and 657 micros and 397 and 751 micros, respectively for the rat and mouse. For the rat in the prone position, there was a gradient in T(2)* values, from the posterior to the anterior regions of both lungs. In the supine position, however, T(2)* values were larger in the posterior and in the anterior portions. For the mouse in both prone and supine positions, there was a tendential gradient in T(2)* from the anterior to the posterior portions. The robustness of the approach renders it well suited for routine applications, e.g. in pharmacological studies concerning asthma models in small rodents. The method was applied to lung inflammation models involving challenge with ovalbumin or lipopolysaccharide.

  6. 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. PMID:21159532

  7. 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.

  8. 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.

  9. Detection of microscopic anisotropy in gray matter and in a novel tissue phantom using double Pulsed Gradient Spin Echo MR.

    PubMed

    Komlosh, M E; Horkay, F; Freidlin, R Z; Nevo, U; Assaf, Y; Basser, P J

    2007-11-01

    A double Pulsed Gradient Spin Echo (d-PGSE) MR experiment was used to measure and assess the degree of local diffusion anisotropy in brain gray matter, and in a novel "gray matter" phantom that consists of randomly oriented tubes filled with water. In both samples, isotropic diffusion was observed at a macroscopic scale while anisotropic diffusion was observed at a microscopic scale, however, the nature of the resulting echo attenuation profiles were qualitatively different. Gray matter, which contains multiple cell types and fibers, exhibits a more complicated echo attenuation profile than the phantom. Since microscopic anisotropy was observed in both samples in the low q regime comparable to that achievable in clinical scanner, it may offer a new potential contrast mechanism for characterizing gray matter microstructure in medical and biological applications. PMID:17869147

  10. Physiological noise in murine solid tumours using T2*-weighted gradient-echo imaging: a marker of tumour acute hypoxia?

    NASA Astrophysics Data System (ADS)

    Baudelet, Christine; Ansiaux, Réginald; Jordan, Bénédicte F.; Havaux, Xavier; Macq, Benoit; Gallez, Bernard

    2004-08-01

    T2*-weighted gradient-echo magnetic resonance imaging (T2*-weighted GRE MRI) was used to investigate spontaneous fluctuations in tumour vasculature non-invasively. FSa fibrosarcomas, implanted intramuscularly (i.m.) in the legs of mice, were imaged at 4.7 T, over a 30 min or 1 h sampling period. On a voxel-by-voxel basis, time courses of signal intensity were analysed using a power spectrum density (PSD) analysis to isolate voxels for which signal changes did not originate from Gaussian white noise or linear drift. Under baseline conditions, the tumours exhibited spontaneous signal fluctuations showing spatial and temporal heterogeneity over the tumour. Statistically significant fluctuations occurred at frequencies ranging from 1 cycle/3 min to 1 cycle/h. The fluctuations were independent of the scanner instabilities. Two categories of signal fluctuations were reported: (i) true fluctuations (TFV), i.e., sequential signal increase and decrease, and (ii) profound drop in signal intensity with no apparent signal recovery (SDV). No temporal correlation between tumour and contralateral muscle fluctuations was observed. Furthermore, treatments aimed at decreasing perfusion-limited hypoxia, such as carbogen combined with nicotinamide and flunarizine, decreased the incidence of tumour T2*-weighted GRE fluctuations. We also tracked dynamic changes in T2* using multiple GRE imaging. Fluctuations of T2* were observed; however, fluctuation maps using PSD analysis could not be generated reliably. An echo-time dependency of the signal fluctuations was observed, which is typical to physiological noise. Finally, at the end of T2*-weighted GRE MRI acquisition, a dynamic contrast-enhanced MRI was performed to characterize the microenvironment in which tumour signal fluctuations occurred in terms of vessel functionality, vascularity and microvascular permeability. Our data showed that TFV were predominantly located in regions with functional vessels, whereas SDV occurred in regions

  11. Optimization of White-Matter-Nulled Magnetization Prepared Rapid Gradient Echo (MP-RAGE) Imaging

    PubMed Central

    Saranathan, Manojkumar; Tourdias, Thomas; Bayram, Ersin; Ghanouni, Pejman; Rutt, Brian K.

    2014-01-01

    Purpose To optimize the white-matter-nulled (WMn) Magnetization Prepared Rapid Gradient Echo (MP-RAGE) sequence at 7T, with comparisons to 3T. Methods Optimal parameters for maximising SNR efficiency were derived. The effect of flip angle and TR on image blurring was modeled using simulations and validated in vivo. A novel 2D-centric radial fan beam (RFB) k-space segmentation scheme was used to shorten scan times and improve parallel imaging. Healthy subjects as well as patients with multiple sclerosis and tremor were scanned using the optimized protocols. Results Inversion repetition times (TS) of 4.5s and 6s were found to yield the highest SNR efficiency for WMn MP-RAGE at 3T and 7T, respectively. Blurring was more sensitive to flip in WMn than in CSFn MP-RAGE and relatively insensitive to TR for both regimes. The 2D RFB scheme had 19% and 47% higher thalamic SNR and SNR efficiency than the 1D centric scheme for WMn MP-RAGE. Compared to 3T, SNR and SNR efficiency were higher for the 7T WMn regime by 56% and 41% respectively. MS lesions in the cortex and thalamus as well as thalamic subnuclei in tremor patients were clearly delineated using WMn MP-RAGE. Conclusion Optimization and new view ordering enabled MP-RAGE imaging with 0.8–1 mm3 isotropic spatial resolution in scan times of 5 minutes with whole brain coverage. PMID:24889754

  12. Optimizing the Magnetization-Prepared Rapid Gradient-Echo (MP-RAGE) Sequence

    PubMed Central

    Wang, Jinghua; He, Lili; Zheng, Hairong; Lu, Zhong-Lin

    2014-01-01

    The three-dimension (3D) magnetization-prepared rapid gradient-echo (MP-RAGE) sequence is one of the most popular sequences for structural brain imaging in clinical and research settings. The sequence captures high tissue contrast and provides high spatial resolution with whole brain coverage in a short scan time. In this paper, we first computed the optimal k-space sampling by optimizing the contrast of simulated images acquired with the MP-RAGE sequence at 3.0 Tesla using computer simulations. Because the software of our scanner has only limited settings for k-space sampling, we then determined the optimal k-space sampling for settings that can be realized on our scanner. Subsequently we optimized several major imaging parameters to maximize normal brain tissue contrasts under the optimal k-space sampling. The optimal parameters are flip angle of 12°, effective inversion time within 900 to 1100 ms, and delay time of 0 ms. In vivo experiments showed that the quality of images acquired with our optimal protocol was significantly higher than that of images obtained using recommended protocols in prior publications. The optimization of k-spacing sampling and imaging parameters significantly improved the quality and detection sensitivity of brain images acquired with MP-RAGE. PMID:24879508

  13. Intensity correction with a pair of spoiled gradient recalled echo images

    NASA Astrophysics Data System (ADS)

    Noterdaeme, Olivier; Anderson, Mark; Gleeson, Fergus; Brady, Michael, Sir

    2009-06-01

    Intensity inhomogeneities in magnetic resonance images (MRI) are a frequently occurring artefact, and result in the same tissue class to have vastly different intensities within an image. These inhomogeneities can be modelled by a slowly varying field, which is also called the bias field. Previous phantom-, image- or sequence based approaches suffer from long scan times, post-processing times or do not sufficiently remove the intensity variations. These intensity variations cause problems for quantitative image analysis algorithms (segmentation, registration) as well as clinicians (e.g. by complicating the visual assessment). This paper presents a novel technique (COIN, correction of intensity inhomogeneities) that uses two calibration images (fast spoiled gradient echo) to map a parameter containing the bias field, which is specific to the patient during a particular exam. This parametric map can then be used to correct any other images acquired during the same exam, regardless of the sequence employed. By using a short repetition time (less than 5 ms) for the calibration scans, the additional scan time is reduced to 60 s (max). The subsequent post-processing time is approximately 60 s per 20 slices. We successfully validate our approach on simulated brain MRI as well as real liver and spinal images. These images were acquired with a number of different coils, sequences and weightings. A comparison of our method with an existing, commercially available algorithm by radiologists shows that COIN is superior.

  14. Quantitative assessment of microvasculopathy in arcAβ mice with USPIO-enhanced gradient echo MRI

    PubMed Central

    Deistung, Andreas; Ielacqua, Giovanna D; Seuwen, Aline; Kindler, Diana; Schweser, Ferdinand; Vaas, Markus; Kipar, Anja; Reichenbach, Jürgen R; Rudin, Markus

    2015-01-01

    Magnetic resonance imaging employing administration of iron oxide-based contrast agents is widely used to visualize cellular and molecular processes in vivo. In this study, we investigated the ability of R2* and quantitative susceptibility mapping to quantitatively assess the accumulation of ultrasmall superparamagnetic iron oxide (USPIO) particles in the arcAβ mouse model of cerebral amyloidosis. Gradient-echo data of mouse brains were acquired at 9.4 T after injection of USPIO. Focal areas with increased magnetic susceptibility and R2* values were discernible across several brain regions in 12-month-old arcAβ compared to 6-month-old arcAβ mice and to non-transgenic littermates, indicating accumulation of particles after USPIO injection. This was concomitant with higher R2* and increased magnetic susceptibility differences relative to cerebrospinal fluid measured in USPIO-injected compared to non-USPIO-injected 12-month-old arcAβ mice. No differences in R2* and magnetic susceptibility were detected in USPIO-injected compared to non-injected 12-month-old non-transgenic littermates. Histological analysis confirmed focal uptake of USPIO particles in perivascular macrophages adjacent to small caliber cerebral vessels with radii of 2–8 µm that showed no cerebral amyloid angiopathy. USPIO-enhanced R2* and quantitative susceptibility mapping constitute quantitative tools to monitor such functional microvasculopathies. PMID:26661253

  15. In vivo quantitative NMR imaging of fruit tissues during growth using Spoiled Gradient Echo sequence.

    PubMed

    Kenouche, S; Perrier, M; Bertin, N; Larionova, J; Ayadi, A; Zanca, M; Long, J; Bezzi, N; Stein, P C; Guari, Y; Cieslak, M; Godin, C; Goze-Bac, C

    2014-12-01

    Nondestructive studies of physiological processes in agronomic products require increasingly higher spatial and temporal resolutions. Nuclear Magnetic Resonance (NMR) imaging is a non-invasive technique providing physiological and morphological information on biological tissues. The aim of this study was to design a robust and accurate quantitative measurement method based on NMR imaging combined with contrast agent (CA) for mapping and quantifying water transport in growing cherry tomato fruits. A multiple flip-angle Spoiled Gradient Echo (SGE) imaging sequence was used to evaluate the intrinsic parameters maps M0 and T1 of the fruit tissues. Water transport and paths flow were monitored using Gd(3+)/[Fe(CN)6](3-)/D-mannitol nanoparticles as a tracer. This dynamic study was carried out using a compartmental modeling. The CA was preferentially accumulated in the surrounding tissues of columella and in the seed envelopes. The total quantities and the average volume flow of water estimated are: 198 mg, 1.76 mm(3)/h for the columella and 326 mg, 2.91 mm(3)/h for the seed envelopes. We demonstrate in this paper that the NMR imaging technique coupled with efficient and biocompatible CA in physiological medium has the potential to become a major tool in plant physiology research. PMID:25131625

  16. Quantitative assessment of microvasculopathy in arcAβ mice with USPIO-enhanced gradient echo MRI.

    PubMed

    Klohs, Jan; Deistung, Andreas; Ielacqua, Giovanna D; Seuwen, Aline; Kindler, Diana; Schweser, Ferdinand; Vaas, Markus; Kipar, Anja; Reichenbach, Jürgen R; Rudin, Markus

    2016-09-01

    Magnetic resonance imaging employing administration of iron oxide-based contrast agents is widely used to visualize cellular and molecular processes in vivo. In this study, we investigated the ability of [Formula: see text] and quantitative susceptibility mapping to quantitatively assess the accumulation of ultrasmall superparamagnetic iron oxide (USPIO) particles in the arcAβ mouse model of cerebral amyloidosis. Gradient-echo data of mouse brains were acquired at 9.4 T after injection of USPIO. Focal areas with increased magnetic susceptibility and [Formula: see text] values were discernible across several brain regions in 12-month-old arcAβ compared to 6-month-old arcAβ mice and to non-transgenic littermates, indicating accumulation of particles after USPIO injection. This was concomitant with higher [Formula: see text] and increased magnetic susceptibility differences relative to cerebrospinal fluid measured in USPIO-injected compared to non-USPIO-injected 12-month-old arcAβ mice. No differences in [Formula: see text] and magnetic susceptibility were detected in USPIO-injected compared to non-injected 12-month-old non-transgenic littermates. Histological analysis confirmed focal uptake of USPIO particles in perivascular macrophages adjacent to small caliber cerebral vessels with radii of 2-8 µm that showed no cerebral amyloid angiopathy. USPIO-enhanced [Formula: see text] and quantitative susceptibility mapping constitute quantitative tools to monitor such functional microvasculopathies. PMID:26661253

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

    NASA Astrophysics Data System (ADS)

    Shemesh, Noam; Álvarez, 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.

  18. Optimization of magnetic flux density for fast MREIT conductivity imaging using multi-echo interleaved partial fourier acquisitions

    PubMed Central

    2013-01-01

    Background Magnetic resonance electrical impedance tomography (MREIT) has been introduced as a non-invasive method for visualizing the internal conductivity and/or current density of an electrically conductive object by externally injected currents. The injected current through a pair of surface electrodes induces a magnetic flux density distribution inside the imaging object, which results in additional magnetic flux density. To measure the magnetic flux density signal in MREIT, the phase difference approach in an interleaved encoding scheme cancels out the systematic artifacts accumulated in phase signals and also reduces the random noise effect by doubling the measured magnetic flux density signal. For practical applications of in vivo MREIT, it is essential to reduce the scan duration maintaining spatial-resolution and sufficient contrast. In this paper, we optimize the magnetic flux density by using a fast gradient multi-echo MR pulse sequence. To recover the one component of magnetic flux density Bz, we use a coupled partial Fourier acquisitions in the interleaved sense. Methods To prove the proposed algorithm, we performed numerical simulations using a two-dimensional finite-element model. For a real experiment, we designed a phantom filled with a calibrated saline solution and located a rubber balloon inside the phantom. The rubber balloon was inflated by injecting the same saline solution during the MREIT imaging. We used the multi-echo fast low angle shot (FLASH) MR pulse sequence for MRI scan, which allows the reduction of measuring time without a substantial loss in image quality. Results Under the assumption of a priori phase artifact map from a reference scan, we rigorously investigated the convergence ratio of the proposed method, which was closely related with the number of measured phase encode set and the frequency range of the background field inhomogeneity. In the phantom experiment with a partial Fourier acquisition, the total scan time was

  19. Acute pancreatitis with gradient echo T2*-weighted magnetic resonance imaging

    PubMed Central

    Tang, Meng Yue; Chen, Tian Wu; Huang, Xiao Hua; Li, Xing Hui; Wang, Si Yue; Liu, Nian

    2016-01-01

    Background To study gradient recalled echo (GRE) T2*-weighted imaging (T2*WI) for normal pancreas and acute pancreatitis (AP). Methods Fifty-one patients without any pancreatic disorders (control group) and 117 patients with AP were recruited. T2* values derived from T2*WI of the pancreas were measured for the two groups. The severity of AP was graded by the magnetic resonance severity index (MRSI) and the Acute Physiology and Chronic Healthy Evaluation II (APACHE II) scoring system. Logistic regression was used to analyze the relationship between the T2* values and AP severity. The usefulness of the T2* value for diagnosing AP and the relationship between the T2* values and the severity of AP were analyzed. Results On GRE-T2*WI, the normal pancreas showed a well-marinated and consistently homogeneous isointensity. Edematous AP, as well as the non-necrotic area in necrotizing AP, showed ill-defined but homogeneous signal intensity. AP with pancreatic hemorrhage showed a decreased T2* value and a signal loss on the signal decay curve. The T2* value of pancreas in the AP group was higher than that of the control group (t=−8.20, P<0.05). The T2* value tended to increase along with the increase in MRSI scores but not with the APACHE II scores (P>0.05). AP was associated with a one standard deviation increment in the T2* value (OR =1.37; 95% CI: 1.216–1.532). Conclusions T2*WI demonstrates a few characteristics of the normal pancreas and AP, which could potentially be helpful for detecting hemorrhage, and contributes to diagnosing AP and its severity. PMID:27190768

  20. Reference-free unwarping of single-shot spatiotemporally encoded MRI using asymmetric self-refocused echoes acquisition

    NASA Astrophysics Data System (ADS)

    Chen, Ying; Chen, Song; Zhong, Jianhui; Chen, Zhong

    2015-05-01

    This paper presents a phase evolution rewinding algorithm for correcting the geometric and intensity distortions in single-shot spatiotemporally encoded (SPEN) MRI with acquisition of asymmetric self-refocused echo trains. Using the field map calculated from the phase distribution of the source image, the off-resonance induced phase errors are successfully rewound through deconvolution. The alias-free partial Fourier transform reconstruction helps improve the signal-to-noise ratio of the field maps and the output images. The effectiveness of the proposed algorithm was validated through 7 T MRI experiments on a lemon, a water phantom, and in vivo rat head. SPEN imaging was evaluated using rapid acquisition by sequential excitation and refocusing (RASER) which produces uniform T2 weighting. The results indicate that the new technique can more robustly deal with the cases in which the images obtained with conventional single-shot spin-echo EPI are difficult to be restored due to serious field variations.

  1. 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).

  2. Single Echo MRI

    PubMed Central

    Galiana, Gigi; Constable, R. Todd

    2014-01-01

    Purpose Previous nonlinear gradient research has focused on trajectories that reconstruct images with a minimum number of echoes. Here we describe sequences where the nonlinear gradients vary in time to acquire the image in a single readout. The readout is designed to be very smooth so that it can be compressed to minimal time without violating peripheral nerve stimulation limits, yielding an image from a single 4 ms echo. Theory and Methods This sequence was inspired by considering the code of each voxel, i.e. the phase accumulation that a voxel follows through the readout, an approach connected to traditional encoding theory. We present simulations for the initial sequence, a low slew rate analog, and higher resolution reconstructions. Results Extremely fast acquisitions are achievable, though as one would expect, SNR is reduced relative to the slower Cartesian sampling schemes because of the high gradient strengths. Conclusions The prospect that nonlinear gradients can acquire images in a single <10 ms echo makes this a novel and interesting approach to image encoding. PMID:24465837

  3. Dynamic diffusion tensor measurements in muscle tissue using Single Line Multiple Echo Diffusion Tensor Acquisition Technique at 3T

    PubMed Central

    Baete, Steven H.; Cho, Gene; Sigmund, Eric E.

    2015-01-01

    When diffusion biomarkers display transient changes, i.e. in muscle following exercise, traditional diffusion tensor imaging (DTI) methods lack temporal resolution to resolve the dynamics. This paper presents an MRI method for dynamic diffusion tensor acquisitions on a clinical 3T scanner. This method, SL-MEDITATE (Single Line Multiple Echo Diffusion Tensor Acquisition Technique) achieves a high temporal resolution (4s) (1) by rapid diffusion encoding through the acquisition of multiple echoes with unique diffusion sensitization and (2) by limiting the readout to a single line volume. The method is demonstrated in a rotating anisotropic phantom, in a flow phantom with adjustable flow speed, and in in vivo skeletal calf muscle of healthy volunteers following a plantar flexion exercise. The rotating and flow-varying phantom experiments show that SL-MEDITATE correctly identifies the rotation of the first diffusion eigenvector and the changes in diffusion tensor parameter magnitudes, respectively. Immediately following exercise, the in vivo mean diffusivity (MD) time-courses show, before the well-known increase, an initial decrease which is not typically observed in traditional DTI. In conclusion, SL-MEDITATE can be used to capture transient changes in tissue anisotropy in a single line. Future progress might allow for dynamic DTI when combined with appropriate k-space trajectories and compressed sensing reconstruction. PMID:25900166

  4. Ultrashort-TE stimulated echo acquisition mode (STEAM) improves the quantification of lipids and fatty acid chain unsaturation in the human liver at 7 T.

    PubMed

    Gajdošík, Martin; Chadzynski, Grzegorz L; Hangel, Gilbert; Mlynárik, Vladimír; Chmelík, Marek; Valkovič, Ladislav; Bogner, Wolfgang; Pohmann, Rolf; Scheffler, Klaus; Trattnig, Siegfried; Krššák, Martin

    2015-10-01

    Ultrahigh-field, whole-body MR systems increase the signal-to-noise ratio (SNR) and improve the spectral resolution. Sequences with a short TE allow fast signal acquisition with low signal loss as a result of spin-spin relaxation. This is of particular importance in the liver for the precise quantification of the hepatocellular content of lipids (HCL). In this study, we introduce a spoiler Gradient-switching Ultrashort STimulated Echo AcqUisition (GUSTEAU) sequence, which is a modified version of a stimulated echo acquisition mode (STEAM) sequence, with a minimum TE of 6 ms. With the high spectral resolution at 7 T, the efficient elimination of water sidebands and the post-processing suppression of the water signal, we estimated the composition of fatty acids (FAs) via the detection of the olefinic lipid resonance and calculated the unsaturation index (UI) of hepatic FAs. The performance of the GUSTEAU sequence for the assessment of UI was validated against oil samples and provided excellent results in agreement with the data reported in the literature. When measuring HCL with GUSTEAU in 10 healthy volunteers, there was a high correlation between the results obtained at 7 and 3 T (R(2) = 0.961). The test-retest measurements yielded low coefficients of variation for HCL (4 ± 3%) and UI (11 ± 8%) when measured with the GUSTEAU sequence at 7 T. A negative correlation was found between UI and HCL (n = 10; p < 0.033). The ultrashort TE MRS sequence (GUSTEAU; TE = 6 ms) provided high repeatability for the assessment of HCL. The improved spectral resolution at 7 T with the elimination of water sidebands and the offline water subtraction also enabled an assessment of the unsaturation of FAs. This all highlights the potential use of this MRS acquisition scheme for studies of hepatic lipid composition in vivo.

  5. Comparison of Multi-Echo Dixon Methods with Volume Interpolated Breath-Hold Gradient Echo Magnetic Resonance Imaging in Fat-Signal Fraction Quantification of Paravertebral Muscle

    PubMed Central

    Yoo, Yeon Hwa; Kim, Hak-Sun; Lee, Young Han; Yoon, Choon-Sik; Paek, Mun Young; Yoo, Hanna; Kannengiesser, Stephan; Chung, Tae-Sub; Song, Ho-Taek; Suh, Jin-Suck

    2015-01-01

    Objective To assess whether multi-echo Dixon magnetic resonance (MR) imaging with simultaneous T2* estimation and correction yields more accurate fat-signal fraction (FF) measurement of the lumbar paravertebral muscles, in comparison with non-T2*-corrected two-echo Dixon or T2*-corrected three-echo Dixon, using the FF measurements from single-voxel MR spectroscopy as the reference standard. Materials and Methods Sixty patients with low back pain underwent MR imaging with a 1.5T scanner. FF mapping images automatically obtained using T2*-corrected Dixon technique with two (non-T2*-corrected), three, and six echoes, were compared with images from single-voxel MR spectroscopy at the paravertebral muscles on levels L4 through L5. FFs were measured directly by two radiologists, who independently drew the region of interest on the mapping images from the three sequences. Results A total of 117 spectroscopic measurements were performed either bilaterally (57 of 60 subjects) or unilaterally (3 of 60 subjects). The mean spectroscopic FF was 14.3 ± 11.7% (range, 1.9-63.7%). Interobserver agreement was excellent between the two radiologists. Lin's concordance correlation between the spectroscopic findings and all the imaging-based FFs were statistically significant (p < 0.001). FFs obtained from the T2*-corrected six-echo Dixon sequences showed a significantly better concordance with the spectroscopic data, with its concordance correlation coefficient being 0.99 and 0.98 (p < 0.001), as compared with two- or three-echo methods. Conclusion T2*-corrected six-echo Dixon sequence would be a better option than two- or three-echo methods for noninvasive quantification of lumbar muscle fat quantification. PMID:26357503

  6. An analysis of the uncertainty and bias in DCE-MRI measurements using the spoiled gradient-recalled echo pulse sequence

    SciTech Connect

    Subashi, Ergys; Choudhury, Kingshuk R.; Johnson, G. Allan

    2014-03-15

    Purpose: The pharmacokinetic parameters derived from dynamic contrast-enhanced (DCE) MRI have been used in more than 100 phase I trials and investigator led studies. A comparison of the absolute values of these quantities requires an estimation of their respective probability distribution function (PDF). The statistical variation of the DCE-MRI measurement is analyzed by considering the fundamental sources of error in the MR signal intensity acquired with the spoiled gradient-echo (SPGR) pulse sequence. Methods: The variance in the SPGR signal intensity arises from quadrature detection and excitation flip angle inconsistency. The noise power was measured in 11 phantoms of contrast agent concentration in the range [0–1] mM (in steps of 0.1 mM) and in onein vivo acquisition of a tumor-bearing mouse. The distribution of the flip angle was determined in a uniform 10 mM CuSO{sub 4} phantom using the spin echo double angle method. The PDF of a wide range of T1 values measured with the varying flip angle (VFA) technique was estimated through numerical simulations of the SPGR equation. The resultant uncertainty in contrast agent concentration was incorporated in the most common model of tracer exchange kinetics and the PDF of the derived pharmacokinetic parameters was studied numerically. Results: The VFA method is an unbiased technique for measuringT1 only in the absence of bias in excitation flip angle. The time-dependent concentration of the contrast agent measured in vivo is within the theoretically predicted uncertainty. The uncertainty in measuring K{sup trans} with SPGR pulse sequences is of the same order, but always higher than, the uncertainty in measuring the pre-injection longitudinal relaxation time (T1{sub 0}). The lowest achievable bias/uncertainty in estimating this parameter is approximately 20%–70% higher than the bias/uncertainty in the measurement of the pre-injection T1 map. The fractional volume parameters derived from the extended Tofts model

  7. Doppler echo evaluation of pulmonary venous-left atrial pressure gradients: human and numerical model studies

    NASA Technical Reports Server (NTRS)

    Firstenberg, M. S.; Greenberg, N. L.; Smedira, N. G.; Prior, D. L.; Scalia, G. M.; Thomas, J. D.; Garcia, M. J.

    2000-01-01

    The simplified Bernoulli equation relates fluid convective energy derived from flow velocities to a pressure gradient and is commonly used in clinical echocardiography to determine pressure differences across stenotic orifices. Its application to pulmonary venous flow has not been described in humans. Twelve patients undergoing cardiac surgery had simultaneous high-fidelity pulmonary venous and left atrial pressure measurements and pulmonary venous pulsed Doppler echocardiography performed. Convective gradients for the systolic (S), diastolic (D), and atrial reversal (AR) phases of pulmonary venous flow were determined using the simplified Bernoulli equation and correlated with measured actual pressure differences. A linear relationship was observed between the convective (y) and actual (x) pressure differences for the S (y = 0.23x + 0.0074, r = 0.82) and D (y = 0.22x + 0.092, r = 0.81) waves, but not for the AR wave (y = 0. 030x + 0.13, r = 0.10). Numerical modeling resulted in similar slopes for the S (y = 0.200x - 0.127, r = 0.97), D (y = 0.247x - 0. 354, r = 0.99), and AR (y = 0.087x - 0.083, r = 0.96) waves. Consistent with numerical modeling, the convective term strongly correlates with but significantly underestimates actual gradient because of large inertial forces.

  8. Design of laser echo data acquisition system based on USB2.0

    NASA Astrophysics Data System (ADS)

    Shang, Fuzhou; Song, Yong; Hao, Qun; Zhang, Kai; Li, Meinan; Zhang, Wenlong

    2012-11-01

    In this paper, a high-speed data acquisition system based on the technology of USB2.0 (Universal Serial Bus) is designed, in which USB master logic is implemented in an FPGA (Field Programmable Gate Array). Firstly, the hardware of data acquisition system is discussed, which includes chip selection, data acquisition and transmission circuit and power conversion circuit. Secondly, the corresponding software including USB firmware program, USB device driver and application program as well as its modifications have been described. The designed hardware and software will help to achieve a data acquisition system with the characterstics of high speed and high accuracy, etc.

  9. Gradient Echo MRI Characterization of Development of Atherosclerosis in the Abdominal Aorta in Watanabe Heritable Hyperlipidemic Rabbits

    SciTech Connect

    Wang, Yi-Xiang J. Kuribayashi, Hideto; Wagberg, Maria; Holmes, Andrew P.; Tessier, Jean J.; Waterton, John C.

    2006-08-15

    Purpose. The Watanabe Heritable Hyperlipidemic (WHHL) rabbit provides an important model of spontaneous atherosclerosis. With a strain of WHHL rabbits which do not develop abdominal aorta lumen stenosis even with advanced atherosclerosis, we studied the MRI-histology correlation, and the natural progression of atherosclerosis in the abdominal aorta. In addition, intra-reader segmentation repeatability and scan-rescan reproducibility were assessed. Methods. Two batches of female WHHL rabbits were used. The first batch of 6 rabbits was scanned at 20 weeks old. A second batch of 17 rabbits was scanned at 50 weeks old and then randomly divided into two subgroups: 8 were killed for histologic investigation; 9 were kept alive for follow-up, with repeat scanning a week later to assess scan-rescan reproducibility, and again at 73 weeks old to assess disease progression. MR images were acquired at 4.7 T using a chemical shift selective fat suppression gradient echo with a saturation band suppressing blood signal within the aortic lumen. Five slices per animal were acquired, centered around the renal artery region of the abdominal aorta, with in-plane resolution of 0.195 mm and slice thickness of 3 mm. Results. The coefficient of variation for intra-reader reproducibility for aortic wall thickness measurements was 2.5% for repeat segmentations of the same scans on the same day, but segmentations of these same scans made 8 months later showed a systematic change, suggesting that intra-reader bias as well as increased variability could compromise assessments made over time. Comparative analyses were therefore performed in one postprocessing session. The coefficient of variation for scan-rescan reproducibility for aortic wall thickness was 5.5% for nine pairs of scans acquired a week apart and segmented on the same day. Good MRI-histology correlation was obtained. The MRI-measured mean aortic wall thickness of animals at 20 weeks of age was 76% that of animals at 50 weeks of

  10. Stimulated Anti-Echo Selection in Spatially Localized NMR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhu, Jian-Ming; Smith, Ian C. P.

    1999-01-01

    Spectral localization using the stimulated-echo acquisition mode (STEAM) is one of the most popular methods in volume-localizedin vivoNMR spectroscopy. The localized volume signal is generated via stimulated echoes from spins excited by three 90° RF pulses, and the conventional STEAM sequence detects the stimulated-echo signal. From an analysis of the STEAM pulse sequence using the coherence transfer pathway formalism, stimulated anti-echoes are also formed by the same pulse sequence, which constitute the other half of the localized signal in the STEAM experiment. A new scheme of pulsed field gradients for the selection of stimulated anti-echoes was proposed, and localized spectroscopy in the stimulated anti-echo selection mode was achieved on a phantom and fromin vivorat brain.

  11. An exploration of task based fMRI in neonates using echo-shifting to allow acquisition at longer TE without loss of temporal efficiency.

    PubMed

    Ferrazzi, Giulio; Nunes, Rita G; Arichi, Tomoki; Gaspar, Andreia S; Barone, Giovanni; Allievi, Alessandro; Vasylechko, Serge; Abaei, Maryam; Hughes, Emer; Rueckert, Daniel; Price, Anthony N; Hajnal, Joseph V

    2016-02-15

    Optimal contrast to noise ratio of the BOLD signal in neonatal and foetal fMRI has been hard to achieve because of the much longer T2(⁎) values in developing brain tissue in comparison to those in the mature adult brain. The conventional approach of optimizing fMRI sequences would suggest matching the echo time (TE) and the T2(⁎) of the neonatal and foetal brain. However, the use of a long echo time would typically increase the minimum repetition time (TR) resulting in inefficient sampling. Here we apply the concept of echo shifting to task based neonatal fMRI in order to achieve an improved contrast to noise ratio and efficient data sampling at the same time. Echo shifted EPI (es-EPI) is a modification of a standard 2D-EPI sequence which enables echo times longer than the time between consecutive excitations (TE>TS=TRNS, where NS is the number of acquired slices and TS the inter-slice repetition time). The proposed method was tested on neonatal subjects using a passive sensori-motor task paradigm. Dual echo EPI datasets with an identical readout structure to es-EPI were also acquired and used as control data to assess BOLD activation. From the results of the latter analysis, an average increase of 78±41% in contrast to noise ratio was observable when comparing late to short echoes. Furthermore, es-EPI allowed the acquisition of data with an identical contrast to the late echo, but more efficiently since a higher number of slices could be acquired in the same amount of time. PMID:26708014

  12. Breath-hold black blood quantitative T1rho imaging of liver using single shot fast spin echo acquisition

    PubMed Central

    Chan, Queenie; Wáng, Yì-Xiáng J.

    2016-01-01

    Background Liver fibrosis is a key feature in most chronic liver diseases. T1rho magnetic resonance imaging is a potentially important technique for noninvasive diagnosis, severity grading, and therapy monitoring of liver fibrosis. However, it remains challenging to perform robust T1rho quantification of liver on human subjects. One major reason is that the presence of rich blood signal in liver can cause artificially high T1rho measurement and makes T1rho quantification susceptible to motion. Methods A pulse sequence based on single shot fast/turbo spin echo (SSFSE/SSTSE) acquisition, with theoretical analysis and simulation based on the extended phase graph (EPG) algorithm, was presented for breath-hold single slice quantitative T1rho imaging of liver with suppression of blood signal. The pulse sequence was evaluated in human subjects at 3.0 T with 500 Hz spinlock frequency and time-of-spinlock (TSL) 0, 10, 30 and 50 ms. Results Human scan demonstrated that the entire T1rho data sets with four spinlock time can be acquired within a single breath-hold of 10 seconds with black blood effect. T1rho quantification with suppression of blood signal results in significantly reduced T1rho value of liver compared to the results without blood suppression. Conclusions A signal-to-noise ratio (SNR) efficient pulse sequence was reported for T1rho quantification of liver. The black blood effect, together with a short breath-hold, mitigates the risk of quantification errors as would occur in the conventional methods. PMID:27190769

  13. Characterization of Nyquist ghost in EPI-fMRI acquisition sequences implemented on two clinical 1.5 T MR scanner systems: effect of readout bandwidth and echo spacing.

    PubMed

    Giannelli, Marco; Diciotti, Stefano; Tessa, Carlo; Mascalchi, Mario

    2010-07-12

    In EPI-fMRI acquisitions, various readout bandwidth (BW) values are used as a function of gradients' characteristics of the MR scanner system. Echo spacing (ES) is another fundamental parameter of EPI-fMRI sequences, but the employed ES value is not usually reported in fMRI studies. Nyquist ghost is a typical EPI artifact that can degrade the overall quality of fMRI time series. In this work, the authors assessed the basic effect of BW and ES for two clinical 1.5 T MR scanner systems (scanner-A, scanner-B) on Nyquist ghost of gradient-echo EPI-fMRI sequences. BW range was: scanner-A, 1953-3906 Hz/pixel; scanner-B, 1220-2894 Hz/pixel. ES range was: scanner-A, scanner-B: 0.75-1.33 ms. The ghost-to-signal ratio of time series acquisition (GSRts) and drift of ghost-to-signal ratio (DRGSR) were measured in a water phantom. For both scanner-A (93% of variation) and scanner-B (102% of variation) the mean GSRts significantly increased with increasing BW. GSRts values of scanner-A did not significantly depended on ES. On the other hand, GSRts values of scanner-B significantly varied with ES, showing a downward trend (81% of variation) with increasing ES. In addition, a GSRts spike point at ES = 1.05 ms indicating a potential resonant effect was revealed. For both scanners, no significant effect of ES on DRGSR was revealed. DRGSR values of scanner-B did not significantly vary with BW, whereas DRGSR values of scanner-A significantly depended on BW showing an upward trend from negative to positive values with increasing BW. GSRts and DRGSR can significantly vary with BW and ES, and the specific pattern of variation may depend on gradients performances, EPI sequence calibrations and functional design of radiofrequency coil. Thus, each MR scanner system should be separately characterized. In general, the employment of low BW values seems to reduce the intensity and temporal variation of Nyquist ghost in EPI-fMRI time series. On the other hand, the use of minimum ES value might

  14. Multi-echo imaging in highly inhomogeneous magnetic fields.

    PubMed

    Casanova, F; Perlo, J; Blümich, B; Kremer, K

    2004-01-01

    A new pulsed field gradient multi-echo imaging technique to encode position in the phase of every echo generated by a CPMG sequence in the presence of a strongly inhomogeneous static magnetic field is presented. It was applied to improve the sensitivity in an imaging experiment by adding the echo train acquired during the CPMG sequence and to spatially resolve relaxation times of inhomogeneous specimens using single-sided probes. The sequence was implemented in a new bar-magnet MOUSE equipped with a gradient coil system to apply a pulsed magnetic field with a constant gradient along one spatial coordinate. An important reduction by a factor larger than two orders of magnitude in the acquisition time was obtained compared to the previously published single-point imaging technique. PMID:14675822

  15. Quantitative comparison of functional contrast from BOLD-weighted spin-echo and gradient-echo echoplanar imaging at 1.5 Tesla and H2 15O PET in the whole brain.

    PubMed

    Lowe, M J; Lurito, J T; Mathews, V P; Phillips, M D; Hutchins, G D

    2000-09-01

    Spin-echo and gradient-echo echoplanar functional magnetic resonance imaging (fMRI) studies at 1.5 Tesla (T) were used to obtain blood oxygenation level-dependent (BOLD) contrast images of the whole brain in seven strongly right-handed women during execution of a complex motor task. Five subjects underwent subsequent H215O positron emission tomography (PET) studies while performing the same task. Group-averaged results for changes in the MRI relaxation rates R2* and R2 at 1.5T in response to neuronal activation in nine cortical, subcortical, and cerebellar motor regions are reported. Results for each method are grouped according to tissue type-cerebral cortex (precentral gyrus and supplementary motor area), subcortical regions (thalamus and putamen), and cerebellar cortex (superior lobule). The observed changes in R2* from activation-induced oxygenation changes were more variable across brain regions with different tissue characteristics than observed changes in R2. The ratio of deltaR2* to deltaR2 was 3.3 +/- 0.9 for cerebral cortex and 2.0 +/- 0.6 for subcortical tissue. deltaR2*, deltaR2, and relative blood flow changes were deltaR2* = -0.201 +/- 0.040 (s-1), deltaR2 = -0.064 +/- 0.011 s(-1), and deltaf/f = 16.7 +/- 0.8% in the cerebral cortex; deltaR2* = -0.100 +/- 0.026 s(-1), deltaR2 = -0.049 +/- 0.009 s(-1), and deltaf/f = 9.4 +/- 0.7% in the subcortical regions; and deltaR2* = -0.215 +/- 0.093 s(-1), deltaR2 = -0.069 +/- 0.012 s(-1), and deltaf/f = 16.2 +/- 1.2% in the cerebellar cortex.

  16. Characterization of gradient echo signal decays in healthy and cancerous prostate at 3T improves with a Gaussian augmentation of the mono-exponential (GAME) model.

    PubMed

    Ciris, Pelin Aksit; Balasubramanian, Mukund; Seethamraju, Ravi T; Tokuda, Junichi; Scalera, Jonathan; Penzkofer, Tobias; Fennessy, Fiona M; Tempany-Afdhal, Clare M; Tuncali, Kemal; Mulkern, Robert V

    2016-07-01

    A biomarker of cancer aggressiveness, such as hypoxia, could substantially impact treatment decisions in the prostate, especially radiation therapy, by balancing treatment morbidity (urinary incontinence, erectile dysfunction, etc.) against mortality. R2 (*) mapping with Mono-Exponential (ME) decay modeling has shown potential for identifying areas of prostate cancer hypoxia at 1.5T. However, Gaussian deviations from ME decay have been observed in other tissues at 3T. The purpose of this study is to assess whether gradient-echo signal decays are better characterized by a standard ME decay model, or a Gaussian Augmentation of the Mono-Exponential (GAME) decay model, in the prostate at 3T. Multi-gradient-echo signals were acquired on 20 consecutive patients with a clinical suspicion of prostate cancer undergoing MR-guided prostate biopsies. Data were fitted with both ME and GAME models. The information contents of these models were compared using Akaike's information criterion (second order, AICC ), in skeletal muscle, the prostate central gland (CG), and peripheral zone (PZ) regions of interest (ROIs). The GAME model had higher information content in 30% of the prostate on average (across all patients and ROIs), covering up to 67% of cancerous PZ ROIs, and up to 100% of cancerous CG ROIs (in individual patients). The higher information content of GAME became more prominent in regions that would be assumed hypoxic using ME alone, reaching 50% of the PZ and 70% of the CG as ME R2 (*) approached 40 s(-1) . R2 (*) mapping may have important applications in MRI; however, information lost due to modeling could mask differences in parameters due to underlying tissue anatomy or physiology. The GAME model improves characterization of signal behavior in the prostate at 3T, and may increase the potential for determining correlates of fit parameters with biomarkers, for example of oxygenation status.

  17. Suppression of artifacts in multiple-echo magnetic resonance

    NASA Astrophysics Data System (ADS)

    Barker, Gareth J.; Mareci, Thomas H.

    Many techniques in both magnetic resonance imaging and magnetic resonance spectroscopy use two or more RF pulses to excite the spin system and detect the echo signals which form between or after the pulses. In general many different echoes form during each acquisition interval, only one of which carries the information required. The others lead to distortion of peak heights and lineshapes in MRS, and to ghost images and similar artifacts in MRI. The "coherence transfer pathway" formalism of Bodenhausen et al. allows the evolution of each echo to be studied and suggests methods of removing the unwanted signals. The general phase-cycling methods described by Bodenhausen et al. require a degree of flexibility in the control of RF pulses which is not available on all spectrometers, however, so simpler schemes requiring only 180° phase shifts have been investigated. With certain restrictions, these schemes give cancellation of the unwanted echoes during any particular acquisition interval, and in certain cases can be extended to cancel the unwanted echoes in all acquisition intervals of a multiple-echo sequence. All such schemes, however, require a large number of transients to be collected, so a second method has been investigated whereby the systematic application of magnetic field gradients can produce similar results within a single transient. Both of these approaches have been reported previously, but we introduce a novel formalism which allows the required pulse phases and gradient magnitudes to be systematically calculated, rather than empirically determined, for any pulse sequence. Examples of the application of each method to the spin-echo and TART imaging sequences are given, although both methods are equally applicable to many pulse sequences used in spectroscopy.

  18. Liver Lobe Based Multi-Echo Gradient Recalled Echo T2*-Weighted Imaging in Chronic Hepatitis B-Related Cirrhosis: Association with the Presence and Child-Pugh Class of Cirrhosis

    PubMed Central

    Wang, Dan; Chen, Tian-wu; Zhang, Xiao-ming; Li, Jie; Zeng, Nan-lin; Li, Li; Tang, Yu-lian; Huang, Yu-cheng; Li, Rui; Chen, Fan; Chen, Yan-li

    2016-01-01

    Purpose To investigate whether liver lobe based T2* values measured on gradient recalled echo T2*-weighted imaging are associated with the presence and Child-Pugh class of hepatitis B-related cirrhosis. Methods Fifty-six patients with hepatitis B-related cirrhosis and 23 healthy control individuals were enrolled in this study and underwent upper abdominal T2*-weighted magnetic resonance imaging. T2* values of the left lateral lobe (LLL), left medial lobe (LML), right lobe (RL) and caudate lobe (CL) were measured on T2*-weighted imaging. Statistical analyses were performed to determine the association between liver lobe based T2* values and the presence and Child-Pugh class of cirrhosis. Results The T2* values of the LLL, LML and RL decreased with the progression of cirrhosis from Child-Pugh class A to C (r = -0.231, -0.223, and -0.395, respectively; all P < 0.05), except that of the CL (r = -0.181, P > 0.05). To a certain extent, Mann-Whitney U tests with Bonferroni correction for multigroup comparisons showed that the T2* values of the LLL, LML and RL could distinguish cirrhotic liver from healthy liver (all P < 0.05), whereas the T2* values of the CL could not (P > 0.05). Receiver operating characteristic analysis demonstrated that the T2* value of the RL could best distinguish cirrhosis from healthy liver, with an area under the receiver operating characteristic curve (AUC) of 0.713 among T2* values of the liver lobes, and that only the T2* value of the RL could distinguish Child-Pugh class C from A-B, with an AUC of 0.697 (all P < 0.05). Conclusion The T2* value of the RL can be associated with the presence and Child-Pugh class of hepatitis B-related cirrhosis. PMID:27171422

  19. Multi-gradient echo MR thermometry for monitoring of the near-field area during MR-guided high intensity focused ultrasound heating.

    PubMed

    Lam, Mie K; de Greef, Martijn; Bouwman, Job G; Moonen, Chrit T W; Viergever, Max A; Bartels, Lambertus W

    2015-10-01

    The multi-gradient echo MR thermometry (MGE MRT) method is proposed to use at the interface of the muscle and fat layers found in the abdominal wall, to monitor MR-HIFU heating. As MGE MRT uses fat as a reference, it is field-drift corrected. Relative temperature maps were reconstructed by subtracting absolute temperature maps. Because the absolute temperature maps are reconstructed of individual scans, MGE MRT provides the flexibility of interleaved mapping of temperature changes between two arbitrary time points. The method's performance was assessed in an ex vivo water bath experiment. An ex vivo HIFU experiment was performed to show the method's ability to monitor heating of consecutive HIFU sonications and to estimate cooling time constants, in the presence of field drift. The interleaved use between scans of a clinical protocol was demonstrated in vivo in a patient during a clinical uterine fibroid treatment. The relative temperature measurements were accurate (mean absolute error 0.3 °C) and provided excellent visualization of the heating of consecutive HIFU sonications. Maps were reconstructed of estimated cooling time constants and mean ROI values could be well explained by the applied heating pattern. Heating upon HIFU sonication and subsequent cooling could be observed in the in vivo demonstration.

  20. Multi-gradient echo MR thermometry for monitoring of the near-field area during MR-guided high intensity focused ultrasound heating

    NASA Astrophysics Data System (ADS)

    Lam, Mie K.; de Greef, Martijn; Bouwman, Job G.; Moonen, Chrit T. W.; Viergever, Max A.; Bartels, Lambertus W.

    2015-10-01

    The multi-gradient echo MR thermometry (MGE MRT) method is proposed to use at the interface of the muscle and fat layers found in the abdominal wall, to monitor MR-HIFU heating. As MGE MRT uses fat as a reference, it is field-drift corrected. Relative temperature maps were reconstructed by subtracting absolute temperature maps. Because the absolute temperature maps are reconstructed of individual scans, MGE MRT provides the flexibility of interleaved mapping of temperature changes between two arbitrary time points. The method’s performance was assessed in an ex vivo water bath experiment. An ex vivo HIFU experiment was performed to show the method’s ability to monitor heating of consecutive HIFU sonications and to estimate cooling time constants, in the presence of field drift. The interleaved use between scans of a clinical protocol was demonstrated in vivo in a patient during a clinical uterine fibroid treatment. The relative temperature measurements were accurate (mean absolute error 0.3 °C) and provided excellent visualization of the heating of consecutive HIFU sonications. Maps were reconstructed of estimated cooling time constants and mean ROI values could be well explained by the applied heating pattern. Heating upon HIFU sonication and subsequent cooling could be observed in the in vivo demonstration.

  1. Pore-to-pore hopping model for the interpretation of the pulsed gradient spin echo attenuation of water diffusion in cell suspension systems.

    PubMed Central

    Jiang, P C; Yu, T Y; Perng, W C; Hwang, L P

    2001-01-01

    A simplified pore-to-pore hopping model for the two-phase diffusion problem is developed for the analysis of the pulsed gradient spin echo (PGSE) attenuation of water diffusion in the condensed cell suspension systems. In this model, the two phases inside and outside the cells are treated as two different kinds of pores, and the spin-bearing molecules perform hopping diffusion between them. The size and the orientations of those two respective pores are considered, and then the diffraction pattern of the PGSE attenuation may be well simulated. Nevertheless, the intensity of the characteristic peak decreases with increasing membrane permeability, from which the exchange time may be estimated. We then analyze the experimental 1H PGSE results of the erythrocytes suspension system. The water-residence lifetime in the erythrocyte is obtained to be 10 ms, which is the same as that estimated from the two-region approximation. Furthermore, the PGSE attenuation curve of addition of p-Chloromercuribenzenesulfonate (p-CMBS) is also discussed. It predicts that the alignment of erythrocytes will become normal to the magnetic field direction after the addition of p-CMBS, and inspection using a light microscope confirms that result. PMID:11371428

  2. 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.

  3. Single-shot T1 mapping using simultaneous acquisitions of spin- and stimulated-echo-planar imaging (2D ss-SESTEPI).

    PubMed

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

    2010-09-01

    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. Two-dimensional single-shot spin- and stimulated-echo-planar imaging (ss-SESTEPI) is an echo-planar-imaging-based single-shot imaging technique that simultaneously acquires a spin-echo-planar image and a stimulated-echo-planar image after a single radiofrequency excitation. The magnitudes of the spin-echo-planar image and stimulated-echo-planar image differ by T(1) decay and diffusion weighting for perfect 90 degrees radiofrequency and thus can be used to rapidly measure T(1). However, the spatial variation of amplitude of radiofrequency field induces uneven splitting of the transverse magnetization for the spin-echo-planar image and stimulated-echo-planar image within the imaging field of view. Correction for amplitude of radiofrequency field inhomogeneity is therefore critical for two-dimensional ss-SESTEPI to be used for T(1) measurement. We developed a method for amplitude of radiofrequency field inhomogeneity correction by acquiring an additional stimulated-echo-planar image with minimal mixing time, calculating the difference between the spin echo and the stimulated echo and multiplying the stimulated-echo-planar image by the inverse functional map. Diffusion-induced decay is corrected by measuring the average diffusivity during the prescanning. Rapid single-shot T(1) mapping may be useful for various applications, such as dynamic T(1) mapping for real-time estimation of the concentration of contrast agent in dynamic contrast enhancement MRI.

  4. Long-term follow-up results of linear accelerator-based radiosurgery for vestibular schwannoma using serial three-dimensional spoiled gradient-echo MRI.

    PubMed

    Matsuo, Takayuki; Okunaga, Tomohiro; Kamada, Kensaku; Izumo, Tsuyoshi; Hayashi, Nobuyuki; Nagata, Izumi

    2015-02-01

    We examined the characteristic changes in vestibular schwannoma (VS) volume after treatment with linear accelerator-based radiosurgery (LBRS) and the long-term therapeutic effects, by performing three-dimensional (3D) MRI evaluations of tumor volumes. We included 44 patients in whom tumor volume changes could be observed using 3D-spoiled gradient-echo MRI for at least 5 years. Examinations were performed every 3-4 months for the first 2 years after treatment and every 6-12 months thereafter. Enlargement or shrinkage was determined as a change of at least 20% from the volume at the time of treatment. The median observation period was 13.8 years (range, 5.5-19.5 years). The tumor control rates at 5 and 10 years after treatment and at the final MRI were 90.9%, 90.0%, and 88.6%, respectively. Tumor volume changes were categorized into the following four patterns: enlargement, five patients (11.4%); stable, three patients (6.8%); transient enlargement, 24 patients (54.5%); and direct shrinkage, 12 patients (27.3%). Bimodal peaks were observed in three of the 24 patients with transient enlargement. Tumor volume changes from 5 and 10 years post-LBRS to the final observation point were observed in 27 (64.2%) and 10 patients (33.3%), respectively. The long-term tumor volume changes observed after LBRS suggest that radiation exerts long-term effects on tumors. Furthermore, while transient enlargements in tumor volume were characteristic, true tumor enlargements should be characterized by increased volumes of more than two-fold and continued growth for at least 2 years. PMID:25443082

  5. Development and Validation of a Simple Conversion Model for Comparison of Intracerebral Hemorrhage Volumes Measured on CT and Gradient Recalled Echo MRI

    PubMed Central

    Burgess, Richard E.; Warach, Steven; Schaewe, Timothy J.; Copenhaver, Brittany R.; Alger, Jeffry R.; Vespa, Paul; Martin, Neil; Saver, Jeffrey L.; Kidwell, Chelsea S.

    2009-01-01

    Background and Purpose Gradient recalled echo MRI (GRE) has been shown to be as accurate as CT for the detection of acute intracerebral hemorrhage (ICH). However, because of the differences in the signal parameter being detected, apparent hemorrhage size is expected to vary by imaging modality, with GRE providing larger volumes attributable to susceptibility effects. Methods Image data from patients participating in 3 ICH studies were retrospectively reviewed. Patients with acute ICH were included if (1) concurrent MRI and CT were performed within 72 hours of symptom onset, and (2) each modality was performed within 240 minutes of each other. ICH volumes were calculated using a semiautomated image analysis program. The least squares method was used to develop a conversion equation based on a linear regression of GRE volume on CT volume. Results Thirty-six patients met inclusion criteria. MRI was performed first in 18, CT first in 18. Mean hemorrhage volume was 25.2cc (range 0.1 to 83.9cc) on CT and 32.7cc (range 0.1 to 98.7cc) measured on GRE. A linear relationship defined by CT Volume=GRE Volume*0.8 (Spearman’s correlation coefficient=0.992, P<0.001) was derived. Conclusions Acute ICH volumes as measured on GRE pulse sequences are consistently larger than CT volumes. A simple mathematical conversion model has been developed: CT volume=0.8*GRE volume. This formula can be used in studies using both imaging modalities, across different studies, or to track ICH growth over time independent of imaging modality in an individual patient. PMID:18483414

  6. Long-term follow-up results of linear accelerator-based radiosurgery for vestibular schwannoma using serial three-dimensional spoiled gradient-echo MRI.

    PubMed

    Matsuo, Takayuki; Okunaga, Tomohiro; Kamada, Kensaku; Izumo, Tsuyoshi; Hayashi, Nobuyuki; Nagata, Izumi

    2015-02-01

    We examined the characteristic changes in vestibular schwannoma (VS) volume after treatment with linear accelerator-based radiosurgery (LBRS) and the long-term therapeutic effects, by performing three-dimensional (3D) MRI evaluations of tumor volumes. We included 44 patients in whom tumor volume changes could be observed using 3D-spoiled gradient-echo MRI for at least 5 years. Examinations were performed every 3-4 months for the first 2 years after treatment and every 6-12 months thereafter. Enlargement or shrinkage was determined as a change of at least 20% from the volume at the time of treatment. The median observation period was 13.8 years (range, 5.5-19.5 years). The tumor control rates at 5 and 10 years after treatment and at the final MRI were 90.9%, 90.0%, and 88.6%, respectively. Tumor volume changes were categorized into the following four patterns: enlargement, five patients (11.4%); stable, three patients (6.8%); transient enlargement, 24 patients (54.5%); and direct shrinkage, 12 patients (27.3%). Bimodal peaks were observed in three of the 24 patients with transient enlargement. Tumor volume changes from 5 and 10 years post-LBRS to the final observation point were observed in 27 (64.2%) and 10 patients (33.3%), respectively. The long-term tumor volume changes observed after LBRS suggest that radiation exerts long-term effects on tumors. Furthermore, while transient enlargements in tumor volume were characteristic, true tumor enlargements should be characterized by increased volumes of more than two-fold and continued growth for at least 2 years.

  7. Exploring the acquisition and production of grammatical constructions through human-robot interaction with echo state networks

    PubMed Central

    Hinaut, Xavier; Petit, Maxime; Pointeau, Gregoire; Dominey, Peter Ford

    2014-01-01

    One of the principal functions of human language is to allow people to coordinate joint action. This includes the description of events, requests for action, and their organization in time. A crucial component of language acquisition is learning the grammatical structures that allow the expression of such complex meaning related to physical events. The current research investigates the learning of grammatical constructions and their temporal organization in the context of human-robot physical interaction with the embodied sensorimotor humanoid platform, the iCub. We demonstrate three noteworthy phenomena. First, a recurrent network model is used in conjunction with this robotic platform to learn the mappings between grammatical forms and predicate-argument representations of meanings related to events, and the robot's execution of these events in time. Second, this learning mechanism functions in the inverse sense, i.e., in a language production mode, where rather than executing commanded actions, the robot will describe the results of human generated actions. Finally, we collect data from naïve subjects who interact with the robot via spoken language, and demonstrate significant learning and generalization results. This allows us to conclude that such a neural language learning system not only helps to characterize and understand some aspects of human language acquisition, but also that it can be useful in adaptive human-robot interaction. PMID:24834050

  8. Exploring the acquisition and production of grammatical constructions through human-robot interaction with echo state networks.

    PubMed

    Hinaut, Xavier; Petit, Maxime; Pointeau, Gregoire; Dominey, Peter Ford

    2014-01-01

    One of the principal functions of human language is to allow people to coordinate joint action. This includes the description of events, requests for action, and their organization in time. A crucial component of language acquisition is learning the grammatical structures that allow the expression of such complex meaning related to physical events. The current research investigates the learning of grammatical constructions and their temporal organization in the context of human-robot physical interaction with the embodied sensorimotor humanoid platform, the iCub. We demonstrate three noteworthy phenomena. First, a recurrent network model is used in conjunction with this robotic platform to learn the mappings between grammatical forms and predicate-argument representations of meanings related to events, and the robot's execution of these events in time. Second, this learning mechanism functions in the inverse sense, i.e., in a language production mode, where rather than executing commanded actions, the robot will describe the results of human generated actions. Finally, we collect data from naïve subjects who interact with the robot via spoken language, and demonstrate significant learning and generalization results. This allows us to conclude that such a neural language learning system not only helps to characterize and understand some aspects of human language acquisition, but also that it can be useful in adaptive human-robot interaction.

  9. Comparison of Twice Refocused Spin Echo versus Stimulated Echo Diffusion Tensor Imaging for Tracking Muscle Fibers

    PubMed Central

    Noehren, Brian; Andersen, Anders; Feiweier, Thorsten; Damon, Bruce; Hardy, Peter

    2014-01-01

    Purpose To compare the precision of measuring the pennation angle and fiber length in the Vastus Lateralis (VL) using two distinctly different diffusion tensor imaging sequences. Materials and Methods We imaged the thigh of ten normal subjects on a 3T MR imager with twice refocused spin echo (TRSE) and stimulated echo (STEAM) DTI-MRI techniques. Both techniques took the same total acquisition time, employed the same diffusion weighting and gradient directions. Using the diffusion tensor images produced by each sequence muscle fiber bundles were tracked from the aponeurosis by following the first eigenvector of the diffusion tensor. From these tracks we calculated the pennation angle and fiber length. Results The STEAM acquisition resulted in significantly higher SNR, lower ADC, higher FA values and longer fibers than the TRSE. Although no difference in the pennation angle between the two acquisitions was found, the TRSE sequence had a significantly greater within subject dispersion in the pennation angle of tracked fibers which may indicate a reduction in the coherence of fiber bundles. Conclusion Diffusion tensor imaging of muscle using a STEAM acquisition resulted in significant improvements in the SNR and FA, resulting in tracking a larger number of muscle fiber bundles over longer distances and with less within subject dispersion. PMID:24554376

  10. Gradient-based correction of chromatic aberration in the joint acquisition of color and near-infrared images

    NASA Astrophysics Data System (ADS)

    Sadeghipoor, Zahra; Lu, Yue M.; Süsstrunk, Sabine

    2015-02-01

    Chromatic aberration distortions such as wavelength-dependent blur are caused by imperfections in photographic lenses. These distortions are much more severe in the case of color and near-infrared joint acquisition, as a wider band of wavelengths is captured. In this paper, we consider a scenario where the color image is in focus, and the NIR image captured with the same lens and same focus settings is out-of-focus and blurred. To reduce chromatic aberration distortions, we propose an algorithm that estimates the blur kernel and deblurs the NIR image using the sharp color image as a guide in both steps. In the deblurring step, we retrieve the lost details of the NIR image by exploiting the sharp edges of the color image, as the gradients of color and NIR images are often correlated. However, differences of scene reflections and light in visible and NIR bands cause the gradients of color and NIR images to be different in some regions of the image. To handle this issue, our algorithm measures the similarities and differences between the gradients of the NIR and color channels. The similarity measures guide the deblurring algorithm to efficiently exploit the gradients of the color image in reconstructing high-frequency details of NIR, without discarding the inherent differences between these images. Simulation results verify the effectiveness of our algorithm, both in estimating the blur kernel and deblurring the NIR image, without producing ringing artifacts inherent to the results of most deblurring methods.

  11. Validation of Perfusion Quantification with 3D Gradient Echo Dynamic Contrast-Enhanced Magnetic Resonance Imaging Using a Blood Pool Contrast Agent in Skeletal Swine Muscle

    PubMed Central

    Hindel, Stefan; Sauerbrey, Anika; Maaß, Marc; Maderwald, Stefan; Schlamann, Marc; Lüdemann, Lutz

    2015-01-01

    The purpose of our study was to validate perfusion quantification in a low-perfused tissue by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with shared k-space sampling using a blood pool contrast agent. Perfusion measurements were performed in a total of seven female pigs. An ultrasonic Doppler probe was attached to the right femoral artery to determine total flow in the hind leg musculature. The femoral artery was catheterized for continuous local administration of adenosine to increase blood flow up to four times the baseline level. Three different stable perfusion levels were induced. The MR protocol included a 3D gradient-echo sequence with a temporal resolution of approximately 1.5 seconds. Before each dynamic sequence, static MR images were acquired with flip angles of 5°, 10°, 20°, and 30°. Both static and dynamic images were used to generate relaxation rate and baseline magnetization maps with a flip angle method. 0.1 mL/kg body weight of blood pool contrast medium was injected via a central venous catheter at a flow rate of 5 mL/s. The right hind leg was segmented in 3D into medial, cranial, lateral, and pelvic thigh muscles, lower leg, bones, skin, and fat. The arterial input function (AIF) was measured in the aorta. Perfusion of the different anatomic regions was calculated using a one- and a two-compartment model with delay- and dispersion-corrected AIFs. The F-test for model comparison was used to decide whether to use the results of the one- or two-compartment model fit. Total flow was calculated by integrating volume-weighted perfusion values over the whole measured region. The resulting values of delay, dispersion, blood volume, mean transit time, and flow were all in physiologically and physically reasonable ranges. In 107 of 160 ROIs, the blood signal was separated, using a two-compartment model, into a capillary and an arteriolar signal contribution, decided by the F-test. Overall flow in hind leg muscles, as measured by the

  12. Validation of Perfusion Quantification with 3D Gradient Echo Dynamic Contrast-Enhanced Magnetic Resonance Imaging Using a Blood Pool Contrast Agent in Skeletal Swine Muscle.

    PubMed

    Hindel, Stefan; Sauerbrey, Anika; Maaß, Marc; Maderwald, Stefan; Schlamann, Marc; Lüdemann, Lutz

    2015-01-01

    The purpose of our study was to validate perfusion quantification in a low-perfused tissue by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with shared k-space sampling using a blood pool contrast agent. Perfusion measurements were performed in a total of seven female pigs. An ultrasonic Doppler probe was attached to the right femoral artery to determine total flow in the hind leg musculature. The femoral artery was catheterized for continuous local administration of adenosine to increase blood flow up to four times the baseline level. Three different stable perfusion levels were induced. The MR protocol included a 3D gradient-echo sequence with a temporal resolution of approximately 1.5 seconds. Before each dynamic sequence, static MR images were acquired with flip angles of 5°, 10°, 20°, and 30°. Both static and dynamic images were used to generate relaxation rate and baseline magnetization maps with a flip angle method. 0.1 mL/kg body weight of blood pool contrast medium was injected via a central venous catheter at a flow rate of 5 mL/s. The right hind leg was segmented in 3D into medial, cranial, lateral, and pelvic thigh muscles, lower leg, bones, skin, and fat. The arterial input function (AIF) was measured in the aorta. Perfusion of the different anatomic regions was calculated using a one- and a two-compartment model with delay- and dispersion-corrected AIFs. The F-test for model comparison was used to decide whether to use the results of the one- or two-compartment model fit. Total flow was calculated by integrating volume-weighted perfusion values over the whole measured region. The resulting values of delay, dispersion, blood volume, mean transit time, and flow were all in physiologically and physically reasonable ranges. In 107 of 160 ROIs, the blood signal was separated, using a two-compartment model, into a capillary and an arteriolar signal contribution, decided by the F-test. Overall flow in hind leg muscles, as measured by the

  13. Validation of Perfusion Quantification with 3D Gradient Echo Dynamic Contrast-Enhanced Magnetic Resonance Imaging Using a Blood Pool Contrast Agent in Skeletal Swine Muscle.

    PubMed

    Hindel, Stefan; Sauerbrey, Anika; Maaß, Marc; Maderwald, Stefan; Schlamann, Marc; Lüdemann, Lutz

    2015-01-01

    The purpose of our study was to validate perfusion quantification in a low-perfused tissue by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with shared k-space sampling using a blood pool contrast agent. Perfusion measurements were performed in a total of seven female pigs. An ultrasonic Doppler probe was attached to the right femoral artery to determine total flow in the hind leg musculature. The femoral artery was catheterized for continuous local administration of adenosine to increase blood flow up to four times the baseline level. Three different stable perfusion levels were induced. The MR protocol included a 3D gradient-echo sequence with a temporal resolution of approximately 1.5 seconds. Before each dynamic sequence, static MR images were acquired with flip angles of 5°, 10°, 20°, and 30°. Both static and dynamic images were used to generate relaxation rate and baseline magnetization maps with a flip angle method. 0.1 mL/kg body weight of blood pool contrast medium was injected via a central venous catheter at a flow rate of 5 mL/s. The right hind leg was segmented in 3D into medial, cranial, lateral, and pelvic thigh muscles, lower leg, bones, skin, and fat. The arterial input function (AIF) was measured in the aorta. Perfusion of the different anatomic regions was calculated using a one- and a two-compartment model with delay- and dispersion-corrected AIFs. The F-test for model comparison was used to decide whether to use the results of the one- or two-compartment model fit. Total flow was calculated by integrating volume-weighted perfusion values over the whole measured region. The resulting values of delay, dispersion, blood volume, mean transit time, and flow were all in physiologically and physically reasonable ranges. In 107 of 160 ROIs, the blood signal was separated, using a two-compartment model, into a capillary and an arteriolar signal contribution, decided by the F-test. Overall flow in hind leg muscles, as measured by the

  14. Echo's Legacy

    NASA Technical Reports Server (NTRS)

    1980-01-01

    The Echo 1 Satellite is simply a very large balloon, the diameter of a 10 story building. Metallized Products, Inc. developed a special material for NASA used for the balloons's skin. For "bouncing signals," material had to be reflective, lightweight, and thin enough to be folded into a beach ball size canister for delivery into orbit, where it would automatically inflate. Material selected was mylar polyester, with a reflective layer of tiny aluminum particles so fine that Echo's skin had a thickness half that of cellophane on a cigarette package.

  15. Tracking of an interventional catheter with a ferromagnetic tip using dual-echo projections.

    PubMed

    Zhang, Ke; Maier, Florian; Krafft, Axel Joachim; Umathum, Reiner; Semmler, Wolfhard; Bock, Michael

    2013-09-01

    Interventional devices with ferromagnetic components can be manipulated remotely using forces induced by the MRI gradients. To deflect the tip of an endovascular catheter, large ferromagnetic spheres of 2 mm diameter are required to exert sufficiently high magnetic forces; however, tracking of these devices is difficult due to the large image artifacts. In this study, a new dual-echo technique is proposed to improve the stability of localizing and tracking medical devices with ferromagnetic components. MR tracking methods with selective off-resonant excitation and phase compensation with a rephasing gradient can detect ferromagnetic spheres up to a diameter of 1 mm only. In this work, a dual-echo technique is used with two rephasing gradients to stabilize the off-set localization. With rephasing being applied in orthogonal directions, an SNR of 5 was achieved in the signal projections. Compared to a single-echo acquisition the dual-echo method reduces the position error in a phantom from 8 mm to 1.6 mm. In an in vivo study a tracking precision of 4 mm was measured without steering gradients at an image update rate of 2 images per second. Steering experiments were successfully performed with a prototype catheter with ferromagnetic sphere in an aorta phantom and in the vena cava of a pig. PMID:23892103

  16. Tracking of an interventional catheter with a ferromagnetic tip using dual-echo projections

    NASA Astrophysics Data System (ADS)

    Zhang, Ke; Maier, Florian; Krafft, Axel Joachim; Umathum, Reiner; Semmler, Wolfhard; Bock, Michael

    2013-09-01

    Interventional devices with ferromagnetic components can be manipulated remotely using forces induced by the MRI gradients. To deflect the tip of an endovascular catheter, large ferromagnetic spheres of 2 mm diameter are required to exert sufficiently high magnetic forces; however, tracking of these devices is difficult due to the large image artifacts. In this study, a new dual-echo technique is proposed to improve the stability of localizing and tracking medical devices with ferromagnetic components. MR tracking methods with selective off-resonant excitation and phase compensation with a rephasing gradient can detect ferromagnetic spheres up to a diameter of 1 mm only. In this work, a dual-echo technique is used with two rephasing gradients to stabilize the off-set localization. With rephasing being applied in orthogonal directions, an SNR of 5 was achieved in the signal projections. Compared to a single-echo acquisition the dual-echo method reduces the position error in a phantom from 8 mm to 1.6 mm. In an in vivo study a tracking precision of 4 mm was measured without steering gradients at an image update rate of 2 images per second. Steering experiments were successfully performed with a prototype catheter with ferromagnetic sphere in an aorta phantom and in the vena cava of a pig.

  17. Fast and Tissue-Optimized Mapping of Magnetic Susceptibility and T2* with Multi-Echo and Multi-Shot Spirals

    PubMed Central

    Wu, Bing; Li, Wei; Avram, Alexandru Vlad; Gho, Sung-Min; Liu, Chunlei

    2011-01-01

    Gradient-echo MRI of resonance-frequency shift and T2* values exhibits unique tissue contrast and offers relevant physiological information. However, acquiring 3D-phase images and T2* maps [A1] with the standard spoiled gradient echo (SPGR) sequence is lengthy for routine imaging at high-spatial resolution and whole-brain coverage. In addition, with the standard SPGR sequence, optimal signal-to-noise ratio (SNR) cannot be achieved for every tissue type given their distributed resonance frequency and T2* value. To address these two issues, a SNR optimized multi-echo sequence with a stack-of-spiral acquisition is proposed and implemented for achieving fast and simultaneous acquisition of image phase and T2* maps. The analytical behavior of the phase SNR is derived as a function of resonance frequency, T2* and echo time. This relationship is utilized to achieve tissue optimized SNR by combining phase images with different echo times. Simulations and in vivo experiments were designed to verify the theoretical predictions. Using the multi-echo spiral acquisition, whole-brain coverage with 1 mm isotropic resolution can be achieved within 2.5 minutes, shortening the scan time by a factor of 8. The resulting multi-echo phase map shows similar SNR to that of the standard SPGR. The acquisition can be further accelerated with non-Cartesian parallel imaging. The technique can be readily extended to other multi-shot readout trajectories besides spiral. It may provide a practical acquisition strategy for high resolution and simultaneous 3D mapping of magnetic susceptibility and T2*. PMID:21784162

  18. Quantitative comparison between a multiecho sequence and a single-echo sequence for susceptibility-weighted phase imaging.

    PubMed

    Gilbert, Guillaume; Savard, Geneviève; Bard, Céline; Beaudoin, Gilles

    2012-06-01

    The aim of this study was to investigate the benefits arising from the use of a multiecho sequence for susceptibility-weighted phase imaging using a quantitative comparison with a standard single-echo acquisition. Four healthy adult volunteers were imaged on a clinical 3-T system using a protocol comprising two different three-dimensional susceptibility-weighted gradient-echo sequences: a standard single-echo sequence and a multiecho sequence. Both sequences were repeated twice in order to evaluate the local noise contribution by a subtraction of the two acquisitions. For the multiecho sequence, the phase information from each echo was independently unwrapped, and the background field contribution was removed using either homodyne filtering or the projection onto dipole fields method. The phase information from all echoes was then combined using a weighted linear regression. R2 maps were also calculated from the multiecho acquisitions. The noise standard deviation in the reconstructed phase images was evaluated for six manually segmented regions of interest (frontal white matter, posterior white matter, globus pallidus, putamen, caudate nucleus and lateral ventricle). The use of the multiecho sequence for susceptibility-weighted phase imaging led to a reduction of the noise standard deviation for all subjects and all regions of interest investigated in comparison to the reference single-echo acquisition. On average, the noise reduction ranged from 18.4% for the globus pallidus to 47.9% for the lateral ventricle. In addition, the amount of noise reduction was found to be strongly inversely correlated to the estimated R2 value (R=-0.92). In conclusion, the use of a multiecho sequence is an effective way to decrease the noise contribution in susceptibility-weighted phase images, while preserving both contrast and acquisition time. The proposed approach additionally permits the calculation of R2 maps.

  19. π Echo-Planar Imaging with concomitant field compensation for porous media MRI.

    PubMed

    Xiao, Dan; Balcom, Bruce J

    2015-11-01

    The π Echo Planar Imaging (PEPI) method was modified to compensate for concomitant magnetic fields by waveform symmetrization. Samples with very short T2(∗) (a few hundred microseconds) and short T2 (tens of milliseconds to hundreds of milliseconds) were investigated. Echo spacings as short as 1.2 ms were achieved with the gradient pre-equalization method, enabling rapid 3D imaging of short relaxation time species with sub-millimeter resolution. The PEPI method yields superior quality images, compared to the Fast Spin Echo (FSE) method, with significantly reduced gradient duty cycle. Accelerated PEPI measurements with a variable number of centric interleaves are presented. Restricted k-space sampling was demonstrated for specific sample geometries, notably a Locharbriggs sandstone core plug, with the acquisition time further reduced. These methods generate proton density weighted images considering the echo time to sample T2 ratio. These methods are principally designed for 3D studies of fluid saturation in rock core plugs, evolving in time due to some manner of external perturbation, such as water flooding. PMID:26398928

  20. π Echo-Planar Imaging with concomitant field compensation for porous media MRI.

    PubMed

    Xiao, Dan; Balcom, Bruce J

    2015-11-01

    The π Echo Planar Imaging (PEPI) method was modified to compensate for concomitant magnetic fields by waveform symmetrization. Samples with very short T2(∗) (a few hundred microseconds) and short T2 (tens of milliseconds to hundreds of milliseconds) were investigated. Echo spacings as short as 1.2 ms were achieved with the gradient pre-equalization method, enabling rapid 3D imaging of short relaxation time species with sub-millimeter resolution. The PEPI method yields superior quality images, compared to the Fast Spin Echo (FSE) method, with significantly reduced gradient duty cycle. Accelerated PEPI measurements with a variable number of centric interleaves are presented. Restricted k-space sampling was demonstrated for specific sample geometries, notably a Locharbriggs sandstone core plug, with the acquisition time further reduced. These methods generate proton density weighted images considering the echo time to sample T2 ratio. These methods are principally designed for 3D studies of fluid saturation in rock core plugs, evolving in time due to some manner of external perturbation, such as water flooding.

  1. Superficial siderosis of the central nervous system induced by a single-episode of traumatic subarachnoid hemorrhage: a study using MRI-enhanced gradient echo T2 star-weighted angiography.

    PubMed

    Zhao, Hongwei; Wang, Jin; Lu, Zhonglie; Wu, Qingjie; Lv, Haijuan; Liu, Hu; Gong, Xiangyang

    2015-01-01

    The purpose of this study was to examine whether a single episode of traumatic subarachnoid hemorrhage (tSAH) could cause superficial siderosis of the central nervous system (SS-CNS).This study was approved by the local ethics committee. Thirty-two patients with a history of a single episode of tSAH were enrolled in the study. An episode of tSAH was confirmed in patients based on a CT scan or a lumbar puncture, and a follow-up examination was conducted at least six weeks after the brain trauma. A follow-up MRI examination was performed, using enhanced gradient echo T2 star-weighted angiography (ESWAN) to detect hemosiderin deposition on the cortical surface. The extent to which hemosiderin deposition was associated with several clinical factors was investigated. Various degrees of hemosiderin deposition were detected in 31 of 32 (96.9%) single-episode tSAH patients. Analysis of contingency tables revealed an association between the regions of subarachnoid bleeding based on CT images and the regions of hemosiderin deposition based on ESWAN images (χ2 = 17.73, P<0.05). SS-CNS was determined to be a common consequence after a single episode of tSAH. The extent of hemosiderin deposition is closely correlated with the initial bleeding sites and bleeding volume.

  2. Two-dimensional spectroscopic imaging with combined free induction decay and long-TE acquisition (FID echo spectroscopic imaging, FIDESI) for the detection of intramyocellular lipids in calf muscle at 7 T.

    PubMed

    Just Kukurova, Ivica; Valkovič, Ladislav; Bogner, Wolfgang; Gajdošík, Martin; Krššák, Martin; Gruber, Stephan; Trattnig, Siegfried; Chmelík, Marek

    2014-08-01

    The aim of this study was to introduce a two-dimensional chemical shift imaging (2D CSI) sequence, with simultaneous acquisition of free induction decay (FID) and long TEs, for the detection and quantification of intramyocellular lipids (IMCLs) in the calf at 7 T. The feasibility of the new 2D CSI sequence, which acquires FID (acquisition delay, 1.3 ms) and an echo (long TE) in one measurement, was evaluated in phantoms and volunteers (n = 5): TR/TE*/TE = 800/1.3/156 ms; 48 × 48 matrix; field of view, 200 × 200 × 20 mm(3) ; Hamming filter; no water suppression; measurement time, 22 min 2 s. The IMCL concentration and subcutaneous lipid contamination were assessed. Spectra in the tibialis anterior (TA), gastrocnemius (GM) and soleus (SOL) muscles were analyzed. The water signal from the FID acquisition was used as an internal concentration reference. In the spectra from subcutaneous adipose tissue (SUB) and bone marrow (BM), an unsaturation index (UI) of the vinyl-H (5.3 ppm) to methyl-CH3 ratio, and a polyunsaturation index (pUI) of the diallylic-H (2.77 ppm) to -CH3 ratio, were calculated. Long-TE spectra from muscles showed a simplified spectral pattern with well-separated IMCL for several muscle groups in the same scan. The IMCL to water ratio was largest in SOL (0.66% ± 0.23%), and lower in GM (0.37% ± 0.14%) and TA (0.36% ± 0.12%). UI and pUI for SUB were 0.65 ± 0.06 and 0.18 ± 0.04, respectively, and for BM were 0.60 ± 0.16 and 0.18 ± 0.08, respectively. The new sequence, with the proposed name 'free induction decay echo spectroscopic imaging' (FIDESI), provides information on both specific lipid resonances and water signal from different tissues in the calf, with high spectral and spatial resolution, as well as minimal voxel bleeding and subcutaneous lipid contamination, in clinically acceptable measurement times. PMID:24912448

  3. Magnetization-prepared rapid acquisition with gradient echo magnetic resonance imaging signal and texture features for the prediction of mild cognitive impairment to Alzheimer's disease progression.

    PubMed

    Martinez-Torteya, Antonio; Rodriguez-Rojas, Juan; Celaya-Padilla, José M; Galván-Tejada, Jorge I; Treviño, Victor; Tamez-Peña, Jose

    2014-10-01

    Early diagnoses of Alzheimer's disease (AD) would confer many benefits. Several biomarkers have been proposed to achieve such a task, where features extracted from magnetic resonance imaging (MRI) have played an important role. However, studies have focused exclusively on morphological characteristics. This study aims to determine whether features relating to the signal and texture of the image could predict mild cognitive impairment (MCI) to AD progression. Clinical, biological, and positron emission tomography information and MRI images of 62 subjects from the AD neuroimaging initiative were used in this study, extracting 4150 features from each MRI. Within this multimodal database, a feature selection algorithm was used to obtain an accurate and small logistic regression model, generated by a methodology that yielded a mean blind test accuracy of 0.79. This model included six features, five of them obtained from the MRI images, and one obtained from genotyping. A risk analysis divided the subjects into low-risk and high-risk groups according to a prognostic index. The groups were statistically different ([Formula: see text]). These results demonstrated that MRI features related to both signal and texture add MCI to AD predictive power, and supported the ongoing notion that multimodal biomarkers outperform single-modality ones.

  4. 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

  5. Sensitivity-encoded (SENSE) proton echo-planar spectroscopic imaging (PEPSI) in the human brain.

    PubMed

    Lin, Fa-Hsuan; Tsai, Shang-Yueh; Otazo, Ricardo; Caprihan, Arvind; Wald, Lawrence L; Belliveau, John W; Posse, Stefan

    2007-02-01

    Magnetic resonance spectroscopic imaging (MRSI) provides spatially resolved metabolite information that is invaluable for both neuroscience studies and clinical applications. However, lengthy data acquisition times, which are a result of time-consuming phase encoding, represent a major challenge for MRSI. Fast MRSI pulse sequences that use echo-planar readout gradients, such as proton echo-planar spectroscopic imaging (PEPSI), are capable of fast spectral-spatial encoding and thus enable acceleration of image acquisition times. Combining PEPSI with recent advances in parallel MRI utilizing RF coil arrays can further accelerate MRSI data acquisition. Here we investigate the feasibility of ultrafast spectroscopic imaging at high field (3T and 4T) by combining PEPSI with sensitivity-encoded (SENSE) MRI using eight-channel head coil arrays. We show that the acquisition of single-average SENSE-PEPSI data at a short TE (15 ms) can be accelerated to 32 s or less, depending on the field strength, to obtain metabolic images of choline (Cho), creatine (Cre), N-acetyl-aspartate (NAA), and J-coupled metabolites (e.g., glutamate (Glu) and inositol (Ino)) with acceptable spectral quality and localization. The experimentally measured reductions in signal-to-noise ratio (SNR) and Cramer-Rao lower bounds (CRLBs) of metabolite resonances were well explained by both the g-factor and reduced measurement times. Thus, this technology is a promising means of reducing the scan times of 3D acquisitions and time-resolved 2D measurements.

  6. Sensitivity-encoded (SENSE) proton echo-planar spectroscopic imaging (PEPSI) in the human brain.

    PubMed

    Lin, Fa-Hsuan; Tsai, Shang-Yueh; Otazo, Ricardo; Caprihan, Arvind; Wald, Lawrence L; Belliveau, John W; Posse, Stefan

    2007-02-01

    Magnetic resonance spectroscopic imaging (MRSI) provides spatially resolved metabolite information that is invaluable for both neuroscience studies and clinical applications. However, lengthy data acquisition times, which are a result of time-consuming phase encoding, represent a major challenge for MRSI. Fast MRSI pulse sequences that use echo-planar readout gradients, such as proton echo-planar spectroscopic imaging (PEPSI), are capable of fast spectral-spatial encoding and thus enable acceleration of image acquisition times. Combining PEPSI with recent advances in parallel MRI utilizing RF coil arrays can further accelerate MRSI data acquisition. Here we investigate the feasibility of ultrafast spectroscopic imaging at high field (3T and 4T) by combining PEPSI with sensitivity-encoded (SENSE) MRI using eight-channel head coil arrays. We show that the acquisition of single-average SENSE-PEPSI data at a short TE (15 ms) can be accelerated to 32 s or less, depending on the field strength, to obtain metabolic images of choline (Cho), creatine (Cre), N-acetyl-aspartate (NAA), and J-coupled metabolites (e.g., glutamate (Glu) and inositol (Ino)) with acceptable spectral quality and localization. The experimentally measured reductions in signal-to-noise ratio (SNR) and Cramer-Rao lower bounds (CRLBs) of metabolite resonances were well explained by both the g-factor and reduced measurement times. Thus, this technology is a promising means of reducing the scan times of 3D acquisitions and time-resolved 2D measurements. PMID:17260356

  7. Gradient-Modulated PETRA MRI

    PubMed Central

    Kobayashi, Naoharu; Goerke, Ute; Wang, Luning; Ellermann, Jutta; Metzger, Gregory J.; Garwood, Michael

    2015-01-01

    Image blurring due to off-resonance and fast T2* signal decay is a common issue in radial ultrashort echo time MRI sequences. One solution is to use a higher readout bandwidth, but this may be impractical for some techniques like pointwise encoding time reduction with radial acquisition (PETRA), which is a hybrid method of zero echo time and single point imaging techniques. Specifically, PETRA has severe specific absorption rate (SAR) and radiofrequency (RF) pulse peak power limitations when using higher bandwidths in human measurements. In this study, we introduce gradient modulation (GM) to PETRA to reduce image blurring artifacts while keeping SAR and RF peak power low. Tolerance of GM-PETRA to image blurring was evaluated in simulations and experiments by comparing with the conventional PETRA technique. We performed inner ear imaging of a healthy subject at 7T. GM-PETRA showed significantly less image blurring due to off-resonance and fast T2* signal decay compared to PETRA. In in vivo imaging, GM-PETRA nicely captured complex structures of the inner ear such as the cochlea and semicircular canals. Gradient modulation can improve the PETRA image quality and mitigate SAR and RF peak power limitations without special hardware modification in clinical scanners. PMID:26771005

  8. Modified Jeener Solid-Echo Pulse Sequences for the Measurement of the Proton Dipolar Spin-Lattice Relaxation-Time ( T1D) of Tissue Solid-like Macromolecular Components

    NASA Astrophysics Data System (ADS)

    Yang, H.; Schleich, T.

    Modified Jeener solid-echo pulse sequences are proposed for the measurement of the proton dipolar spin-lattice relaxation time, T1D, of motionally restricted (solid-like) components in the presence of mobile molecular species, such as encountered in biological tissue. A phase-cycled composite-pulse sequence was used for detection of the dipolar signal and cancellation of the Zeeman signal. A homospoil gradient pulse was added to the Jeener echo pulse sequence to enhance dephasing of the transverse magnetization components of mobile species, thereby aiding in elimination of the Zeeman signal during dipolar signal acquisition. A modified Jeener echo sequence incorporating water suppression is also proposed as a means to further depress the Zeeman signal arising from mobile components. The modified Jeener echo sequences were successfully used for the measurement of proton T1D values of solid 2,6-dimethylphenol and Sephadex gels of differing degrees of cross linking and hydration.

  9. 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

  10. Comparison of spoiled gradient echo and steady-state free-precession imaging for native myocardial T1 mapping using the slice-interleaved T1 mapping (STONE) sequence.

    PubMed

    Jang, Jihye; Bellm, Steven; Roujol, Sébastien; Basha, Tamer A; Nezafat, Maryam; Kato, Shingo; Weingärtner, Sebastian; Nezafat, Reza

    2016-10-01

    Cardiac T1 mapping allows non-invasive imaging of interstitial diffuse fibrosis. Myocardial T1 is commonly calculated by voxel-wise fitting of the images acquired using balanced steady-state free precession (SSFP) after an inversion pulse. However, SSFP imaging is sensitive to B1 and B0 imperfection, which may result in additional artifacts. A gradient echo (GRE) imaging sequence has been used for myocardial T1 mapping; however, its use has been limited to higher magnetic field to compensate for the lower signal-to-noise ratio (SNR) of GRE versus SSFP imaging. A slice-interleaved T1 mapping (STONE) sequence with SSFP readout (STONE-SSFP) has been recently proposed for native myocardial T1 mapping, which allows longer recovery of magnetization (>8 R-R) after each inversion pulse. In this study, we hypothesize that a longer recovery allows higher SNR and enables native myocardial T1 mapping using STONE with GRE imaging readout (STONE-GRE) at 1.5T. Numerical simulations and phantom and in vivo imaging were performed to compare the performance of STONE-GRE and STONE-SSFP for native myocardial T1 mapping at 1.5T. In numerical simulations, STONE-SSFP shows sensitivity to both T2 and off resonance. Despite the insensitivity of GRE imaging to T2 , STONE-GRE remains sensitive to T2 due to the dependence of the inversion pulse performance on T2 . In the phantom study, STONE-GRE had inferior accuracy and precision and similar repeatability as compared with STONE-SSFP. In in vivo studies, STONE-GRE and STONE-SSFP had similar myocardial native T1 times, precisions, repeatabilities and subjective T1 map qualities. Despite the lower SNR of the GRE imaging readout compared with SSFP, STONE-GRE provides similar native myocardial T1 measurements, precision, repeatability, and subjective image quality when compared with STONE-SSFP at 1.5T. PMID:27658506

  11. Motion and distortion correction of skeletal muscle echo planar images.

    PubMed

    Davis, Andrew D; Noseworthy, Michael D

    2016-07-01

    This paper examines two artifacts facing researchers who use gradient echo (GRE) echo planar imaging (EPI) for time series studies of skeletal muscles in limbs. The first is through-plane blood flow during the acquisition, causing a vessel motion artifact that inhibits proper motion correction of the data. The second is distortion of EPI images caused by B0 field inhomogeneities. Though software tools are available for correcting these artifacts in brain EPI images, the tools do not perform well on muscle images. The severity of the two artifacts was described using image similarity measures, and the data was processed with both a conventional motion correction program and custom written tools. The conventional program did not perform well on the limb images, in fact significantly degrading image quality in some trials. Data is presented which proves that arterial pulsatile signal caused the impairment in motion correction. The new tools were shown to perform much better, achieving substantial motion correction and distortion correction of the muscle EPI images. PMID:26972774

  12. Meteoric Head Echoes

    NASA Astrophysics Data System (ADS)

    Hajduk, A.; Galád, A.

    1995-01-01

    Results of the analysis of 3261 radar meteor head echoes observed during the Orionid and Lyrid periods by the high-power radar of the Springhill Meteor Observatory are given. Dependence of the occurence of head echoes on the geometrical factors and physical properties of the meteoroids has been studied. Increas of the head echo rates with the elevation of the shower radiant and with the velocity of meteoroids has been observed.

  13. How can dolphins recognize fish according to their echoes? A statistical analysis of fish echoes.

    PubMed

    Yovel, Yossi; Au, Whitlow W L

    2010-01-01

    Echo-based object classification is a fundamental task of animals that use a biosonar system. Dolphins and porpoises should be able to rely on echoes to discriminate a predator from a prey or to select a desired prey from an undesired object. Many studies have shown that dolphins and porpoises can discriminate between objects according to their echoes. All of these studies however, used unnatural objects that can be easily characterized in human terminologies (e.g., metallic spheres, disks, cylinders). In this work, we collected real fish echoes from many angles of acquisition using a sonar system that mimics the emission properties of dolphins and porpoises. We then tested two alternative statistical approaches in classifying these echoes. Our results suggest that fish species can be classified according to echoes returning from porpoise- and dolphin-like signals. These results suggest how dolphins and porpoises can classify fish based on their echoes and provide some insight as to which features might enable the classification.

  14. Project Echo Task Group

    NASA Technical Reports Server (NTRS)

    1964-01-01

    'A technician assigned to the Project Echo Task Group separates the two hemispheres of the Echo 1 container for inspection. The charge that freed the balloon was placed inside of a ring encircling the canister at its equator.' Published in James R. Hansen, Spaceflight Revolution: NASA Langley Research Center From Sputnik to Apollo, NASA SP-4308, p. 181.

  15. Imaging efficiency and contrast enhancement in the fast gradient refocusing technique

    SciTech Connect

    Vinitski, S.; Fuka, M.Z.; Griffey, R.H.; Matwiyoff, N.A.; Rifkin, M.D.

    1987-08-01

    The gradient recalled (refocused) echo technique produces images in very short scanning time. The signal to noise/unit time of the image is slightly better at small flip angles, provided Tl is estimated carefully. A short TR without dead space at low flip angles allows acquisition of high resolution 3D contiguous volume data within a few minutes. The gradient refocusing technique, however, can produce image artifacts due to uncompensated gradient induced phase shifts. The use of phase encoding gradient reversal removes the artifact, but also introduces signal dependence on transverse magnetization, which results in reduced tissue contrast. In this work the authors demonstrate that by inserting a strong gradient at the end of the pulse sequence in the slice encoding direction, tissue contrast is restored to the original level with the absence of phase artifact.

  16. Light echoes - Novae

    NASA Technical Reports Server (NTRS)

    Schaefer, Bradley E.

    1988-01-01

    The sudden brilliance of a nova eruption will be reflected on surrounding dust grains to create a phantom nebula. Previous searches for these light echoes have used relatively short exposures with photograhic detectors. This paper reports on a search around eight recent novae with long exposures using a CCD camera. Despite an increase of sensitivity by over an order of magnitude, no light echoes were detected. It is found that the average grain density must be less than about 10 to the -9th per cu cm for distances from 0.1 pc to 1000 pc from the novae. The light echo around Nova Persei 1901 was caused by reflection off clouds with grain densities of several times 10 to the -9th per cu cm which are at distances between 0.1 pc and 10 pc. Echoes from dust in a circumstellar shell or ejected during a previous eruption will be effectively unobservable.

  17. Billiard-ball echo model

    NASA Astrophysics Data System (ADS)

    Beach, R.; Hartmann, S. R.; Friedberg, R.

    1982-05-01

    Photon echoes in gaseous media are explained with the use of a simple heuristic model in which the atoms behave like composite billiard balls. The laser providing the excitation pulses becomes an atom smasher which "splits" the atoms and then by judicious programming puts them back together again. The most general photon-echo reordering process is explained without recourse to formal analysis so that an intuitive feeling is obtained which works equally well for the ordinary two-pulse photon echo, the Raman echo, the trilevel echo, the grating echo, etc. A formal analysis of the billiard-ball echo model is presented in its support.

  18. Ultrasound Echoes as Biometric Navigators

    PubMed Central

    Schwartz, Benjamin M.; McDannold, Nathan J.

    2014-01-01

    We demonstrate a new method of using ultrasound data to achieve prospective motion compensation in MRI, especially for respiratory motion during interventional MRI procedures in moving organs such as the liver. The method relies on fingerprint-like biometrically distinct ultra-sound echo patterns produced by different locations in tissue, which are collated with geometrical information from MRI during a training stage to form a mapping table that relates ultrasound measurements to positions. During prospective correction, the system makes frequent ultrasound measurements and uses the map to determine the corresponding position. Results in motorized linear motion phantoms and freely breathing animals indicate that the system performs well. Apparent motion is reduced by up to 97.8%, and motion artifacts are reduced or eliminated in 2D Spoiled Gradient-Echo images. The motion compensation is sufficient to permit MRI thermometry of focused ultrasound heating during respiratory-like motion, with results similar to those obtained in the absence of motion. This new technique may have applications for MRI thermometry and other dynamic imaging in the abdomen during free breathing. PMID:22648783

  19. Reducing Inhomogeneity Artifacts in Functional MRI of Human Brain Activation—Thin Sections vs Gradient Compensation

    NASA Astrophysics Data System (ADS)

    Merboldt, Klaus-Dietmar; Finsterbusch, Jürgen; Frahm, Jens

    2000-08-01

    We evaluated two methods for correcting inhomogeneity-induced signal losses in magnetic resonance gradient-echo imaging that either use gradient compensation or simply acquire thin sections. The strategies were tested in the human brain in terms of achievable quality of T2*-weighted images at the level of the hippocampus and of functional activation maps of the visual cortex. Experiments were performed at 2.0 T and based on single-shot echo-planar imaging at 2.0 × 2.0 mm2 resolution, 4 mm section thickness, and 2.0 s temporal resolution. Gradient compensation involved a sequential 16-step variation of the refocusing lobe of the slice-selection gradient (TR/TE = 125/53 ms, flip angle 15°), whereas thin sections divided the 4-mm target plane into either four 1-mm or eight 0.5-mm interleaved multislice acquisitions (TR/TE = 2000/54 ms, flip angle 70°). Both approaches were capable of alleviating the inhomogeneity problem for structures in the base of the brain. When compared to standard 4-mm EPI, functional mapping in the visual cortex was partially compromised because of a lower signal-to-noise ratio of inhomogeneity-corrected images by either method. Relative to each other, consistently better results were obtained with the use of contiguous thin sections, in particular for a thickness of 1 mm. Multislice acquisitions of thin sections require minimal technical adjustments.

  20. ECHO Status for International Partners

    NASA Technical Reports Server (NTRS)

    Weinstein, Beth; Lubelczyk, Jeff

    2006-01-01

    The EOS Clearinghouse (ECHO) is a clearinghouse of spatial and temporal metadata, inclusive of NASA's Distributed Active Archive Center (DAAC) data holdings, that enables the science community to more easily exchange NASA data and information. Currently, ECHO has metadata descriptors for over 55 million individual data granules and 13 million browse images. The majority of ECHO's holdings come directly from data held in the NASA DAACs. The science disciplines and domains represented in ECHO are diverse and include metadata for all of NASA's Science Focus Area data. As middleware for a service-oriented enterprise, ECHO offers access to its capabilities through a set of publicly available Application Program Interfaces (APIs). More information about ECHO is available at http://eos.nasa.gov.echo. The presentation will discuss the status of the ECHO Partners, holdings, and activities, including the transition from the EOS Data Gateway to the Warehouse Inventory Search Tool (WIST)

  1. Retrospective correction of B0-field-induced geometric distortions in multislice echo planar images: a 3D solution

    NASA Astrophysics Data System (ADS)

    McColl, Roderick W.; Coburn, Edward A.

    2000-04-01

    A method has been developed to utilize a 3D B0 fieldmap, with a multi-volume-of-interest segmentation map, to quantify and correct geometric distortions in echo-planar images. The purpose is to provide accurate co-registration of anatomical MRI to functional MRI time course sequences. A data structure capable of extracting and reporting the necessary information forms a central part of the solution. Images were obtained from a 1.5 Tesla scanner with an experimental y-gradient insert coil. Two 3D-gradient echo sequences supply the data needed to calculate the B0 map across the volume. Segmentation of the volume into brain/background produces the data needed for the phase unwrapping and volume(s) of interest generation, from which the global B0 variation map is obtained. Subsequent EPI acquisition yields the fMRI time- course information. Tests were carried out on a phantom and a human volunteer engaged in a motor task (finger-tapping). Strong distortions were measured, and subsequently corrected, particularly near the petrous bone/mastoid air cells and in the frontal and maxillary sinuses. Additionally, a strong eddy current resulting from the unshielded y-gradient was detected. The method facilitates geometric distortion correction through an imaging volume, containing multiple regions of interest within a slice, starting from a single starting point.

  2. Echo Boom Impact

    ERIC Educational Resources Information Center

    Dordai, Phillipe; Rizzo, Joseph

    2006-01-01

    Like their baby-boomer parents, the echo-boom generation is reshaping the college and university landscape. At 80 million strong, this group of children and young adults born between 1980 and 1995 now is flooding the college and university system, spurring a college building boom. According to Campus Space Crunch, a Hillier Architecture survey of…

  3. Experimental observation of fractional echoes

    NASA Astrophysics Data System (ADS)

    Karras, G.; Hertz, E.; Billard, F.; Lavorel, B.; Siour, G.; Hartmann, J.-M.; Faucher, O.; Gershnabel, Erez; Prior, Yehiam; Averbukh, Ilya Sh.

    2016-09-01

    We report the observation of fractional echoes in a double-pulse excited nonlinear system. Unlike standard echoes, which appear periodically at delays which are integer multiples of the delay between the two exciting pulses, the fractional echoes appear at rational fractions of this delay. We discuss the mechanism leading to this phenomenon, and provide experimental demonstration of fractional echoes by measuring third harmonic generation in a thermal gas of CO2 molecules excited by a pair of femtosecond laser pulses.

  4. Variabilities of low latitude mesospheric and E region echoes: linked to common sources?

    NASA Astrophysics Data System (ADS)

    Dharmalingam, Selvaraj; Patra, Amit; Sathishkumar, Sundararaman; Narayana Rao, D.

    2016-07-01

    Variability in dynamics of the mesospheric and E region echoes have been studied in isolation. Both echoing phenomena are directly or indirectly coupled with each other through neutral dynamics. This is especially so for the low-latitudes outside the equatorial electrojet belt, where E region plasma irregularities causing radar echoes are governed by neutral dynamics, such as tides and gravity waves. Although these regions are close to each other, no effort has been made yet to understand the dynamical coupling processes manifesting the observed variabilities in the two echoing phenomena. To investigate linkage between the two phenomena, if any, we conducted systematic observations of low latitude mesospheric and E region echoes during 2011-2012 using the Gadanki MST radar and used these in conjunction with SABER temperature, MF radar wind, and sporadic E observations. Both echoes are found to occur in the height regions where temperature observations show negative gradients. Mesospheric echoes are collocated with temperature gradient associated with mesospheric temperature inversion while the E region echoes are collocated with negative temperature gradient close to the mesopause. Observations have revealed a common signature of semi-annual variations in the occurrence of both mesospheric and ionospheric E-region - occurrences peak in the equinoxes. The E region echoes have an additional peak occurring in the summer and this occurrence is well correlated with the enhancement in the diurnal tidal amplitude. We surmise that the enhancement in the diurnal tidal amplitude is linked with non-migrating tide of tropospheric weather phenomena in summer. Intriguingly, mesospheric echoing layers display descending pattern quite similar to the E region echoes and sporadic E layer, which have been used to invoke tidal dynamics in manifesting similar morphology in both mesospheric and E region echoes. These results will be presented and the role of tidal dynamics on the

  5. Complex echo classification by echo-locating bats: a review.

    PubMed

    Yovel, Yossi; Franz, Matthias O; Stilz, Peter; Schnitzler, Hans-Ulrich

    2011-05-01

    Echo-locating bats constantly emit ultrasonic pulses and analyze the returning echoes to detect, localize, and classify objects in their surroundings. Echo classification is essential for bats' everyday life; for instance, it enables bats to use acoustical landmarks for navigation and to recognize food sources from other objects. Most of the research of echo based object classification in echo-locating bats was done in the context of simple artificial objects. These objects might represent prey, flower, or fruit and are characterized by simple echoes with a single up to several reflectors. Bats, however, must also be able to use echoes that return from complex structures such as plants or other types of background. Such echoes are characterized by superpositions of many reflections that can only be described using a stochastic statistical approach. Scientists have only lately started to address the issue of complex echo classification by echo-locating bats. Some behavioral evidence showing that bats can classify complex echoes has been accumulated and several hypotheses have been suggested as to how they do so. Here, we present a first review of this data. We raise some hypotheses regarding possible interpretations of the data and point out necessary future directions that should be pursued. PMID:20848111

  6. Correction for Eddy Current-Induced Echo-Shifting Effect in Partial-Fourier Diffusion Tensor Imaging.

    PubMed

    Truong, Trong-Kha; Song, Allen W; Chen, Nan-Kuei

    2015-01-01

    In most diffusion tensor imaging (DTI) studies, images are acquired with either a partial-Fourier or a parallel partial-Fourier echo-planar imaging (EPI) sequence, in order to shorten the echo time and increase the signal-to-noise ratio (SNR). However, eddy currents induced by the diffusion-sensitizing gradients can often lead to a shift of the echo in k-space, resulting in three distinct types of artifacts in partial-Fourier DTI. Here, we present an improved DTI acquisition and reconstruction scheme, capable of generating high-quality and high-SNR DTI data without eddy current-induced artifacts. This new scheme consists of three components, respectively, addressing the three distinct types of artifacts. First, a k-space energy-anchored DTI sequence is designed to recover eddy current-induced signal loss (i.e., Type 1 artifact). Second, a multischeme partial-Fourier reconstruction is used to eliminate artificial signal elevation (i.e., Type 2 artifact) associated with the conventional partial-Fourier reconstruction. Third, a signal intensity correction is applied to remove artificial signal modulations due to eddy current-induced erroneous T2(∗) -weighting (i.e., Type 3 artifact). These systematic improvements will greatly increase the consistency and accuracy of DTI measurements, expanding the utility of DTI in translational applications where quantitative robustness is much needed.

  7. Correction for Eddy Current-Induced Echo-Shifting Effect in Partial-Fourier Diffusion Tensor Imaging.

    PubMed

    Truong, Trong-Kha; Song, Allen W; Chen, Nan-Kuei

    2015-01-01

    In most diffusion tensor imaging (DTI) studies, images are acquired with either a partial-Fourier or a parallel partial-Fourier echo-planar imaging (EPI) sequence, in order to shorten the echo time and increase the signal-to-noise ratio (SNR). However, eddy currents induced by the diffusion-sensitizing gradients can often lead to a shift of the echo in k-space, resulting in three distinct types of artifacts in partial-Fourier DTI. Here, we present an improved DTI acquisition and reconstruction scheme, capable of generating high-quality and high-SNR DTI data without eddy current-induced artifacts. This new scheme consists of three components, respectively, addressing the three distinct types of artifacts. First, a k-space energy-anchored DTI sequence is designed to recover eddy current-induced signal loss (i.e., Type 1 artifact). Second, a multischeme partial-Fourier reconstruction is used to eliminate artificial signal elevation (i.e., Type 2 artifact) associated with the conventional partial-Fourier reconstruction. Third, a signal intensity correction is applied to remove artificial signal modulations due to eddy current-induced erroneous T2(∗) -weighting (i.e., Type 3 artifact). These systematic improvements will greatly increase the consistency and accuracy of DTI measurements, expanding the utility of DTI in translational applications where quantitative robustness is much needed. PMID:26413505

  8. Spin Echo in Synchrotrons

    SciTech Connect

    Chao, Alexander W.; Courant, Ernest D.; /Brookhaven

    2006-12-01

    As a polarized beam is accelerated through a depolarization resonance, its polarization is reduced by a well-defined calculable reduction factor. When the beam subsequently crosses a second resonance, the final beam polarization is considered to be reduced by the product of the two reduction factors corresponding to the two crossings, each calculated independently of the other. This is a good approximation when the spread of spin precession frequency {Delta}{nu}{sub spin} of the beam (particularly due to its energy spread) is sufficiently large that the spin precession phases of individual particles smear out completely during the time {tau} between the two crossings. This approximate picture, however, ignores two spin dynamics effects: an interference effect and a spin echo effect. This paper is to address these two effects. The interference effect occurs when {Delta}{nu}{sub spin} is too small, or when {tau} is too short, to complete the smearing process. In this case, the two resonance crossings interfere with each other, and the final polarization exhibits constructive or destructive patterns depending on the exact value of {tau}. Typically, the beam's energy spread is large and this interference effect does not occur. To study this effect, therefore, it is necessary to reduce the beam energy spread and to consider two resonance crossings very close to each other. The other mechanism, also due to the interplay between two resonance crossings, is spin echo. It turns out that even when the precession phases appear to be completely smeared between the two crossings, there will still be a sudden and short-lived echo signal of beam polarization at a time {tau} after the second crossing; the magnitude of which can be as large as 57%. This echo signal exists even when the beam has a sizable energy spread and when {tau} is very large, and could be a sensitive (albeit challenging) way to experimentally test the intricate spin dynamics in a synchrotron. After giving an

  9. The design and implementation of a multi-waveform radar echo simulator.

    PubMed

    Quan, Yinghui; Gao, Xiaoxiao; Li, Yachao; Xing, Mengdao

    2015-10-01

    Radar simulator is an effective tool for performance assessment of radar systems by accurately reproducing echo signals from complicated environment. This paper presents a design of fast multi-waveform radar echo generation based on deconvolution method. First, scene information is retrieved from outfield data based on improved conjugate gradient algorithm. Then, the new radar echoes are generated through convolution of new transmitted signal and restored scene information. A fast and area-efficient field programmable gate array realization is provided to meet the real-time requirement of radar echo simulation. Finally, a series of experiments are performed to evaluate the effectiveness of proposed radar simulation instrument.

  10. The design and implementation of a multi-waveform radar echo simulator

    NASA Astrophysics Data System (ADS)

    Quan, Yinghui; Gao, Xiaoxiao; Li, Yachao; Xing, Mengdao

    2015-10-01

    Radar simulator is an effective tool for performance assessment of radar systems by accurately reproducing echo signals from complicated environment. This paper presents a design of fast multi-waveform radar echo generation based on deconvolution method. First, scene information is retrieved from outfield data based on improved conjugate gradient algorithm. Then, the new radar echoes are generated through convolution of new transmitted signal and restored scene information. A fast and area-efficient field programmable gate array realization is provided to meet the real-time requirement of radar echo simulation. Finally, a series of experiments are performed to evaluate the effectiveness of proposed radar simulation instrument.

  11. Modeling of Field-Aligned Guided Echoes in the Plasmasphere

    NASA Technical Reports Server (NTRS)

    Fung, Shing F.; Green, James L.

    2004-01-01

    The conditions under which high frequency (f>>f(sub uh)) long-range extraordinary-mode discrete field-aligned echoes observed by the Radio Plasma Imager (RPI) on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite in the plasmasphere are investigated by ray tracing modeling. Field-aligned discrete echoes are most commonly observed by RPI in the plasmasphere although they are also observed over the polar cap region. The plasmasphere field-aligned echoes appearing as multiple echo traces at different virtual ranges are attributed to signals reflected successively between conjugate hemispheres that propagate along or nearly along closed geomagnetic field lines. The ray tracing simulations show that field-aligned ducts with as little as 1% density perturbations (depletions) and less than 10 wavelengths wide can guide nearly field-aligned propagating high frequency X mode waves. Effective guidance of wave at a given frequency and wave normal angle (Psi) depends on the cross-field density scale of the duct, such that ducts with stronger density depletions need to be wider in order to maintain the same gradient of refractive index across the magnetic field. While signal guidance by field aligned density gradient without ducting is possible only over the polar region, conjugate field-aligned echoes that have traversed through the equatorial region are most likely guided by ducting.

  12. Transverse Echo Measurements in RHIC

    SciTech Connect

    Fischer, Wolfram

    2006-03-20

    Diffusion counteracts cooling and the knowledge of diffusion rates is important for the calculation of cooling times and equilibrium beam sizes. Echo measurements are a potentially sensitive method to determine diffusion rates, and longitudinal measurements were done in a number of machines. We report on transverse echo measurements in RHIC and the observed dependence of echo amplitudes on a number of parameters for beams of gold and copper ions, and protons. In particular we examine the echo amplitudes of gold and copper ion bunches of varying intensity, which exhibit different diffusion rates from intrabeam scattering.

  13. TRANSVERSE ECHO MEASUREMENTS IN RHIC.

    SciTech Connect

    FISCHER, W.

    2005-09-18

    Diffusion counteracts cooling and the knowledge of diffusion rates is important for the calculation of cooling times and equilibrium beam sizes. Echo measurements are a potentially sensitive method to determine diffusion rates, and longitudinal measurements were done in a number of machines. We report on transverse echo measurements in RHIC and the observed dependence of echo amplitudes on a number of parameters for beams of gold and copper ions, and protons. In particular they examine the echo amplitudes of gold and copper ion bunches of varying intensity, which exhibit different diffusion rates from intrabeam scattering.

  14. Echo 1 container

    NASA Technical Reports Server (NTRS)

    1964-01-01

    Echo 1 container: The design of this container was one of the most difficult technical tasks. Hansen writes: 'After several weeks of examining potential solutions to this problem, the Langley engineers narrowed the field of ideas to five. They then built working models of these five container designs, and 12-foot-diameter models of the satellite for simulation studies. With help from Langley's Engineering Service and Mechanical Service divisions, the Echo group built a special 41-foot-diameter spherical vacuum chamber equipped with pressure-proof windows. There the dynamics of opening the container and inflating the satelloon could be studies as the satelloon fell to the bottom of the tank.' 'The container-opening mechanism that eventually resulted from these vacuum tests was surely one of the oddest explosive devices ever contrived. The container was a sphere that opened at its equator into top and bottom hemispheres. the top half fit on the bottom half much like a lid fits snugly atop a kitchen pot. The joint between the two hemispheres, therefore, formed a sliding valve. The halves had to move apart an inch or two before the canister was actually open. It was in this joint between the hemispheres that the charge was placed.' The whole whole system was laced together with fishing line which resulted in many disdainful comments from visiting scientists and engineers but the system worked. Published in James R. Hansen, Spaceflight Revolution: NASA Langley Research Center From Sputnik to Apollo, (Washington: NASA, 1995), p. 180.

  15. Dissecting a Light Echo

    NASA Technical Reports Server (NTRS)

    2008-01-01

    [figure removed for brevity, see original site] Click on image for audio animation

    This animation illustrates how a light echo works, and how an optical illusion of material moving outward is created.

    A light echo occurs when a star explodes, acting like a cosmic flashbulb. The light from this explosion zips through nearby dust clumps, illuminating and heating them up slightly. This brief period of warming causes them to glow in infrared, like a chain of Christmas bulbs lighting up one by one.

    The animation starts by showing the explosion of a star, which results in a flash of light that moves outward in all directions. The direction of our line of sight from Earth is indicated by the blue arrow.

    When the light flash reaches surrounding dust, shown here as three dark clouds, the dust is heated up, creating infrared light that begins to travel toward Earth (indicated by the red arrows). Dust closest to the explosion lights up first, while the explosion's shock wave takes longer to reach more distant material. This results in light from different parts of the cloud reaching Earth at different times, creating the illusion of motion over time.

    As the animation shows, the inclination of the cloud toward our line of sight can result in the material seeming to move both away from and toward the central star.

  16. High-resolution 2D NMR spectra in inhomogeneous fields via 3D acquisition

    NASA Astrophysics Data System (ADS)

    Lin, Yanqin; Wei, Zhiliang; Zhang, Liandi; Lin, Liangjie; Chen, Zhong

    2014-04-01

    High-resolution nuclear magnetic resonance (NMR) spectroscopy plays an important role in chemical studies. Here, a pulse sequence, based on coherence transfer module of tracking differences of precession frequencies of two spins and spin echo module, is proposed to obtain two dimension (2D) high-resolution NMR spectra via 3D acquisition under large field inhomogeneity. The proposed scheme composes of simple hard pulses and rectangle gradients. Resulting 2D spectra exhibit chemical shift differences and J coupling splittings in two orthogonal dimensions. The method developed here may offer a promising way for in situ high-resolution NMR studies on combinatorial chemistry.

  17. MR angiography with two-dimensional acquisition and three-dimensional display. Work in progress.

    PubMed

    Keller, P J; Drayer, B P; Fram, E K; Williams, K D; Dumoulin, C L; Souza, S P

    1989-11-01

    Magnetic resonance arteriograms of healthy volunteers and selected patients were produced with a new spoiled gradient-echo pulse sequence based on time-of-flight phenomena. The procedure involves sequential acquisition of many contiguous, thin (1.5-mm) axial two-dimensional sections. These volume data are then submitted to a raytracing projection program, which retrospectively yields multiple arbitrary projection angles rotating through any plane. Venous structures are suppressed with a presaturation slab superior to the current section. The slab location is advanced in concert with advancement of each new section location. The acquisition time varies from 6 to 13 minutes, depending on the number of sections acquired for three-dimensional display. This method obviates the subtraction of image data sets to suppress signals from stationary spins, is more sensitive to slow blood flow than three-dimensional methods of acquisition, and shows special promise for the study of extracranial vascular disease. PMID:2798885

  18. Properties of echo spectra observed by MST radars

    NASA Technical Reports Server (NTRS)

    Wakasugi, K.

    1983-01-01

    Turbulent scatter and Fresnel reflection are the fundamental echoing mechanisms to interpret the signals observed by Mesosphere-stratosphere-troposphere (MST) radars. Turbulent scattered echoes provide information about the turbulence structure and mean flow of the atmosphere. Observational results with VHF MST radars, however, show the importance of Fresnel reflection due to the infinite gradient of reflectivity at the edges of a scattering layer. This condition is excluded for the weak fluctuation models but it is still possible to include the observed aspect sensitivity by assuming an anisotropic structure of fluctuations. Another explanation of the aspect sensitivity observed by MST radars is advanced. Spectral estimates by the widely used periodogram were related to a four-dimensional spectrum of atmospheric fluctuations with anisotropic structure. Effects of the radar system such as antenna beam width, beam direction and Fast Fourier Transformations (FFT) data length were discussed for the anisotropic turbulent atmosphere. Echo parameters were also estimated.

  19. Fast T(2) relaxometry with an accelerated multi-echo spin-echo sequence.

    PubMed

    Sénégas, Julien; Liu, Wei; Dahnke, Hannes; Song, Hotaek; Jordan, E Kay; Frank, Joseph A

    2010-10-01

    A new method has been developed to reduce the number of phase-encoding steps in a multi-echo spin-echo imaging sequence allowing fast T(2) mapping without loss of spatial resolution. In the proposed approach, the k-space data at each echo time were undersampled and a reconstruction algorithm that exploited the temporal correlation of the MR signal in k-space was used to reconstruct alias-free images. A specific application of this algorithm with multiple-receiver acquisition, offering an alternative to existing parallel imaging methods, has also been introduced. The fast T(2) mapping method has been validated in human brain T(2) measurements in a group of nine volunteers with acceleration factors up to 3.4. The results demonstrated that the proposed method exhibited excellent linear correlation with the regular T(2) mapping with full sampling and achieved better image reconstruction and T(2) mapping with respect to SNR and reconstruction artifacts than the selected reference acceleration techniques. The new method has also been applied for quantitative tracking of injected magnetically labeled breast cancer cells in the rat brain with acceleration factors of 1.8 and 3.0. The proposed technique can provide an effective approach for accelerated T(2) quantification, especially for experiments with single-channel coil when parallel imaging is not applicable. PMID:20878973

  20. Q-ball imaging with PROPELLER EPI acquisition.

    PubMed

    Chou, Ming-Chung; Huang, Teng-Yi; Chung, Hsiao-Wen; Hsieh, Tsyh-Jyi; Chang, Hing-Chiu; Chen, Cheng-Yu

    2013-12-01

    Q-ball imaging (QBI) is an imaging technique that is capable of resolving intravoxel fiber crossings; however, the signal readout based on echo-planar imaging (EPI) introduces geometric distortions in the presence of susceptibility gradients. This study proposes an imaging technique that reduces susceptibility distortions in QBI by short-axis PROPELLER EPI acquisition. Conventional QBI and PROPELLER QBI data were acquired from two 3T MR scans of the brains of five healthy subjects. Prior to the PROPELLER reconstruction, residual distortions in single-blade low-resolution b0 and diffusion-weighted images (DWIs) were minimized by linear affine and nonlinear diffeomorphic demon registrations. Subsequently, the PROPELLER keyhole reconstruction was applied to the corrected DWIs to obtain high-resolution PROPELLER DWIs. The generalized fractional anisotropy and orientation distribution function maps contained fewer distortions in PROPELLER QBI than in conventional QBI, and the fiber tracts more closely matched the brain anatomy depicted by turbo spin-echo (TSE) T2-weighted imaging (T2WI). Furthermore, for fixed T(E), PROPELLER QBI enabled a shorter scan time than conventional QBI. We conclude that PROPELLER QBI can reduce susceptibility distortions without lengthening the acquisition time and is suitable for tracing neuronal fiber tracts in the human brain.

  1. Vibrational Echo Correlation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Asbury, John B.; Steinel, Tobias; Fayer, M. D.

    Multidimensional vibrational echo correlation spectroscopy with full phase resolution is used to measure hydrogen bond dynamics in water and methanol. The OD hydroxyl stretches of methanol-OD oligomers in CCl4 and HOD inH2O are studied using the shortest mid-IR pulses (< 45 fs, < 4 cycles of light) produced to date. The pulses have sufficient spectral bandwidth to span the very broad (> 400 cm-1) spectrum of the 0-1 and 1-2 vibrational transitions. Hydrogen bond population dynamics are extricated with exceptional detail in MeOD oligomers because the different hydrogen-bonded species are spectrally distinct. The experimental results along with detailed calculations indicate the strongest hydrogen bonds are selectively broken through a non-equilibrium relaxation pathway following vibrational relaxation of the hydroxyl stretch. Following hydrogen bond breaking, the broken MeOD oligomers retain a detailed structural memory of the prior intact hydrogen bond network. The correlation spectra are also a sensitive probe of the structural fluctuations in water and provide a stringent test of water models that are widely used in simulations of aqueous systems. The analysis of the 2D band shapes demonstrates that different hydrogen-bonded species are subject to distinct (wavelength-dependent) ultrafast (˜ 100 fs) local fluctuations and essentially identical slower (0.4 ps and ˜ 2 ps) structural rearrangements. Observation of wavelength-dependent dynamics demonstrates that standard theoretical approaches assuming Gaussian fluctuations cannot adequately describe water dynamics.

  2. X-ray Echo Spectroscopy.

    PubMed

    Shvyd'ko, Yuri

    2016-02-26

    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 >10^{8}) with broadband ≃5-13  meV dispersing systems are introduced featuring more than 10^{3} signal enhancement. The technique is general, applicable in different photon frequency domains. PMID:26967404

  3. ENVISAT Radar Altimeter Individual Echoes

    NASA Astrophysics Data System (ADS)

    Zanifé, O. Z.; Roca, M.; Rémy, F.; Legrèsy, B.; Chapron, B.; Laxon, S.; Pilar Milagro, M.; Benveniste, J.

    2006-07-01

    A unique feature of the ENVISAT RA-2 is to provide bursts of individual, unav eraged Ku band echo s ample data in phase (I) and quadrature (Q), at the full rate 1800 Hz. This data offers a unique possibility to assess the full capabilities of altimeter measurements. Both technically and scientifically, much can be expected fro m these bursts o f individual echoes, e.g., speckle characteristics over different altimeter scen es, o cean , ice, land, but also, potential blurring effects associat ed with range windo w changes during the 100 echoes on-board av eraging. Moreover, for the first time in altimetry fro m space, investigations can be carried on the direct use of phase information from backscatter signals. ENVISAT RA-2 also features a second frequency in S band. The co mbination bet ween absolutely calibrated Ku and S b and d ata can yield interesting improvement for wind speed, wav e period, g as exchang e estimates , etc. ESA has launched a study on this topic to seed the use of individual echoes by s cientists. This study is reaching completion and reconstructed echoes will be made available for the first time to the scientific community. Results fro m the technical and s cientific application of individual echoes will be pres ented.

  4. X-ray Echo Spectroscopy.

    PubMed

    Shvyd'ko, Yuri

    2016-02-26

    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 >10^{8}) with broadband ≃5-13  meV dispersing systems are introduced featuring more than 10^{3} signal enhancement. The technique is general, applicable in different photon frequency domains.

  5. Diffusion weighted inner volume imaging of lumbar disks based on turbo-STEAM acquisition.

    PubMed

    Hiepe, Patrick; Herrmann, Karl-Heinz; Ros, Christian; Reichenbach, Jürgen R

    2011-09-01

    A magnetic resonance imaging (MRI) technique for diffusion weighted imaging (DWI) is described which, in contrast to echo planar imaging (EPI), is insensitive to off-resonance effects caused by tissue susceptibility differences, magnetic field inhomogeneities, or chemical shifts. The sequence combines a diffusion weighted (DW) spin-echo preparation and a stimulated echo acquisition mode (STEAM) module. Inner volume imaging (IVI) allows reduced rectangular field-of-view (FoV) in the phase encode direction, while suppressing aliasing artifacts that are usually the consequence of reduced FoVs. Sagittal turbo-STEAM images of the lumbar spine were acquired at 3.0T with 2.0 × 2.0 mm² in-plane resolution and 7 mm slice thickness with acquisition times of 407 ms per image. To calculate the apparent diffusion coefficient (ADC) in lumbar intervertebral disks (IVDs), the DW gradients were applied in three orthogonal gradient directions with b-values of 0 and 300 s/mm². For initial assessment of the ADC of normal and abnormal IVDs a pilot study with 8 subjects was performed. Mean ADC values of all normal IVDs were (2.27±0.40)×10⁻³ mm²/s and (1.89±0.34)×10⁻³ mm²/s for turbo-STEAM IVI and SE-EPI acquisition, respectively. Corresponding mean ADC values, averaged over all abnormal disks, were (1.93±0.39)×10⁻³ mm²/s and (1.51±0.46)×10⁻³ mm²/s, respectively, indicating a substantial ADC decrease (p<0.001).

  6. Echo particle image velocimetry.

    PubMed

    DeMarchi, Nicholas; White, Christopher

    2012-12-27

    The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.(1) Consequently, a prerequisite for understanding, predicting, and controlling fluid flows is the capability to measure the velocity field with adequate spatial and temporal resolution.(2) For velocity measurements in optically opaque fluids or through optically opaque geometries, echo particle image velocimetry (EPIV) is an attractive diagnostic technique to generate "instantaneous" two-dimensional fields of velocity.(3,4,5,6) In this paper, the operating protocol for an EPIV system built by integrating a commercial medical ultrasound machine(7) with a PC running commercial particle image velocimetry (PIV) software(8) is described, and validation measurements in Hagen-Poiseuille (i.e., laminar pipe) flow are reported. For the EPIV measurements, a phased array probe connected to the medical ultrasound machine is used to generate a two-dimensional ultrasound image by pulsing the piezoelectric probe elements at different times. Each probe element transmits an ultrasound pulse into the fluid, and tracer particles in the fluid (either naturally occurring or seeded) reflect ultrasound echoes back to the probe where they are recorded. The amplitude of the reflected ultrasound waves and their time delay relative to transmission are used to create what is known as B-mode (brightness mode) two-dimensional ultrasound images. Specifically, the time delay is used to determine the position of the scatterer in the fluid and the amplitude is used to assign intensity to the scatterer. The time required to obtain a single B-mode image, t, is determined by the time it take to pulse all the elements of the phased array probe. For acquiring multiple B-mode images, the frame rate of the system in frames per second (fps) = 1/δt. (See 9 for a review of ultrasound imaging.) For a typical EPIV experiment, the frame rate is between 20-60 fps

  7. Range gate dependence of specular echoes

    NASA Technical Reports Server (NTRS)

    Green, J. L.

    1983-01-01

    Some controversy has surrounded the interpretation of the enhancement of VHF radar echoes at vertical incidence (also known as partial reflections, specular reflections and Fresnel scattering) since they were reported by the Sunset and the SOUSY radars. There is little doubt as to the observational fact of this enhancement since it was observed by experimenters using at least eleven MST or ST radars. In addition to the Sunset and SOUSY radars, this result was obtained in the lower atmosphere at the Platteville, Poker Flat, Jicamarca Arecibo radars as well as the three radars of the ALPEX experiments. In the upper atmosphere, specular or partial reflections were observed. These vertical enhancements were associated with increases in the static stability of the atmosphere, with a temperature gradient in the stratosphere, were used to monitor the height of the tropopause, and were associated with the passage of fronts.

  8. Enhancement of BOLD-contrast sensitivity by single-shot multi-echo functional MR imaging.

    PubMed

    Posse, S; Wiese, S; Gembris, D; Mathiak, K; Kessler, C; Grosse-Ruyken, M L; Elghahwagi, B; Richards, T; Dager, S R; Kiselev, V G

    1999-07-01

    Improved data acquisition and processing strategies for blood oxygenation level-dependent (BOLD)-contrast functional magnetic resonance imaging (fMRI), which enhance the functional contrast-to-noise ratio (CNR) by sampling multiple echo times in a single shot, are described. The dependence of the CNR on T2*, the image encoding time, and the number of sampled echo times are investigated for exponential fitting, echo summation, weighted echo summation, and averaging of correlation maps obtained at different echo times. The method is validated in vivo using visual stimulation and turbo proton echoplanar spectroscopic imaging (turbo-PEPSI), a new single-shot multi-slice MR spectroscopic imaging technique, which acquires up to 12 consecutive echoplanar images with echo times ranging from 12 to 213 msec. Quantitative T2*-mapping significantly increases the measured extent of activation and the mean correlation coefficient compared with conventional echoplanar imaging. The sensitivity gain with echo summation, which is computationally efficient provides similar sensitivity as fitting. For all data processing methods sensitivity is optimum when echo times up to 3.2 T2* are sampled. This methodology has implications for comparing functional sensitivity at different magnetic field strengths and between brain regions with different magnetic field inhomogeneities.

  9. Enhancement of BOLD-contrast sensitivity by single-shot multi-echo functional MR imaging.

    PubMed

    Posse, S; Wiese, S; Gembris, D; Mathiak, K; Kessler, C; Grosse-Ruyken, M L; Elghahwagi, B; Richards, T; Dager, S R; Kiselev, V G

    1999-07-01

    Improved data acquisition and processing strategies for blood oxygenation level-dependent (BOLD)-contrast functional magnetic resonance imaging (fMRI), which enhance the functional contrast-to-noise ratio (CNR) by sampling multiple echo times in a single shot, are described. The dependence of the CNR on T2*, the image encoding time, and the number of sampled echo times are investigated for exponential fitting, echo summation, weighted echo summation, and averaging of correlation maps obtained at different echo times. The method is validated in vivo using visual stimulation and turbo proton echoplanar spectroscopic imaging (turbo-PEPSI), a new single-shot multi-slice MR spectroscopic imaging technique, which acquires up to 12 consecutive echoplanar images with echo times ranging from 12 to 213 msec. Quantitative T2*-mapping significantly increases the measured extent of activation and the mean correlation coefficient compared with conventional echoplanar imaging. The sensitivity gain with echo summation, which is computationally efficient provides similar sensitivity as fitting. For all data processing methods sensitivity is optimum when echo times up to 3.2 T2* are sampled. This methodology has implications for comparing functional sensitivity at different magnetic field strengths and between brain regions with different magnetic field inhomogeneities. PMID:10398954

  10. Commissioning the Echo-Seeding Experiment Echo-7 at SLAC

    SciTech Connect

    Weathersby, S.a E.Colby; Dunning, M.; Gilevich, S.; Hast, C.; Jobe, K.; McCormick, D.; Nelson, J.; Raubenheimer, T.O.; Soong, K.; Stupakov, G.; Szalata, Z.; Walz, D.; Woodley, M.; Xiang, D.; Pernet, P-L.; /Ecole Polytechnique, Lausanne

    2011-06-02

    ECHO-7 is a proof-of-principle echo-enabled harmonic generation (EEHG) FEL experiment in the Next Linear Collider Test Accelerator (NLCTA) at SLAC. The experiment is intended to test the EEHG principle at low electron beam energy, 120 MeV, and determine the sensitivities and limitations to understand the expected performance at the higher energy scales and harmonic numbers required for x-ray FELs. In this paper we present the experimental results from the commissioning run of the completed experimental setup which started in April 2010.

  11. Quantitative characterizations of ultrashort echo (UTE) images for supporting air-bone separation in the head.

    PubMed

    Hsu, Shu-Hui; Cao, Yue; Lawrence, Theodore S; Tsien, Christina; Feng, Mary; Grodzki, David M; Balter, James M

    2015-04-01

    Accurate separation of air and bone is critical for creating synthetic CT from MRI to support Radiation Oncology workflow. This study compares two different ultrashort echo-time sequences in the separation of air from bone, and evaluates post-processing methods that correct intensity nonuniformity of images and account for intensity gradients at tissue boundaries to improve this discriminatory power. CT and MRI scans were acquired on 12 patients under an institution review board-approved prospective protocol. The two MRI sequences tested were ultra-short TE imaging using 3D radial acquisition (UTE), and using pointwise encoding time reduction with radial acquisition (PETRA). Gradient nonlinearity correction was applied to both MR image volumes after acquisition. MRI intensity nonuniformity was corrected by vendor-provided normalization methods, and then further corrected using the N4itk algorithm. To overcome the intensity-gradient at air-tissue boundaries, spatial dilations, from 0 to 4 mm, were applied to threshold-defined air regions from MR images. Receiver operating characteristic (ROC) analyses, by comparing predicted (defined by MR images) versus 'true' regions of air and bone (defined by CT images), were performed with and without residual bias field correction and local spatial expansion. The post-processing corrections increased the areas under the ROC curves (AUC) from 0.944 ± 0.012 to 0.976 ± 0.003 for UTE images, and from 0.850 ± 0.022 to 0.887 ± 0.012 for PETRA images, compared to without corrections. When expanding the threshold-defined air volumes, as expected, sensitivity of air identification decreased with an increase in specificity of bone discrimination, but in a non-linear fashion. A 1 mm air mask expansion yielded AUC increases of 1 and 4% for UTE and PETRA images, respectively. UTE images had significantly greater discriminatory power in separating air from bone than PETRA images. Post-processing strategies improved the

  12. Quantitative characterizations of ultrashort echo (UTE) images for supporting air-bone separation in the head

    NASA Astrophysics Data System (ADS)

    Hsu, Shu-Hui; Cao, Yue; Lawrence, Theodore S.; Tsien, Christina; Feng, Mary; Grodzki, David M.; Balter, James M.

    2015-04-01

    Accurate separation of air and bone is critical for creating synthetic CT from MRI to support Radiation Oncology workflow. This study compares two different ultrashort echo-time sequences in the separation of air from bone, and evaluates post-processing methods that correct intensity nonuniformity of images and account for intensity gradients at tissue boundaries to improve this discriminatory power. CT and MRI scans were acquired on 12 patients under an institution review board-approved prospective protocol. The two MRI sequences tested were ultra-short TE imaging using 3D radial acquisition (UTE), and using pointwise encoding time reduction with radial acquisition (PETRA). Gradient nonlinearity correction was applied to both MR image volumes after acquisition. MRI intensity nonuniformity was corrected by vendor-provided normalization methods, and then further corrected using the N4itk algorithm. To overcome the intensity-gradient at air-tissue boundaries, spatial dilations, from 0 to 4 mm, were applied to threshold-defined air regions from MR images. Receiver operating characteristic (ROC) analyses, by comparing predicted (defined by MR images) versus ‘true’ regions of air and bone (defined by CT images), were performed with and without residual bias field correction and local spatial expansion. The post-processing corrections increased the areas under the ROC curves (AUC) from 0.944 ± 0.012 to 0.976 ± 0.003 for UTE images, and from 0.850 ± 0.022 to 0.887 ± 0.012 for PETRA images, compared to without corrections. When expanding the threshold-defined air volumes, as expected, sensitivity of air identification decreased with an increase in specificity of bone discrimination, but in a non-linear fashion. A 1 mm air mask expansion yielded AUC increases of 1 and 4% for UTE and PETRA images, respectively. UTE images had significantly greater discriminatory power in separating air from bone than PETRA images. Post-processing strategies improved the

  13. Proton echo-planar spectroscopic imaging with highly effective outer volume suppression using combined presaturation and spatially selective echo dephasing.

    PubMed

    Chu, Archie; Alger, Jeffry R; Moore, Gregory J; Posse, Stefan

    2003-05-01

    A highly effective outer volume suppression (OVS) technique, termed spatially selective echo dephasing (SSED), which employs gradient dephasing of spatially selective spin echoes, is introduced. SSED, which is relatively insensitive to T(1) dispersion among lipid signals and B(1) inhomogeneity, was integrated with very high spatial resolution 2D proton echo-planar spectroscopic imaging (PEPSI) to assess residual lipid bleeding into cortical regions in the human brain. The method was optimized to minimize signal refocusing of secondary spin-echoes in areas of overlapping suppression slices. A comparison of spatial presaturation with single or double SSED, and with combined presaturation and SSED shows that the latter method has superior performance with spatially uniform lipid suppression factors in excess of 70. Metabolite mapping (choline, creatine, and NAA) with a 64 x 64 spatial matrix and 0.3 cm(3) voxels in close proximity to peripheral lipid regions was demonstrated at 1.5 T with a scan time of 32 min using the standard head coil.

  14. Proton echo-planar spectroscopic imaging with highly effective outer volume suppression using combined presaturation and spatially selective echo dephasing.

    PubMed

    Chu, Archie; Alger, Jeffry R; Moore, Gregory J; Posse, Stefan

    2003-05-01

    A highly effective outer volume suppression (OVS) technique, termed spatially selective echo dephasing (SSED), which employs gradient dephasing of spatially selective spin echoes, is introduced. SSED, which is relatively insensitive to T(1) dispersion among lipid signals and B(1) inhomogeneity, was integrated with very high spatial resolution 2D proton echo-planar spectroscopic imaging (PEPSI) to assess residual lipid bleeding into cortical regions in the human brain. The method was optimized to minimize signal refocusing of secondary spin-echoes in areas of overlapping suppression slices. A comparison of spatial presaturation with single or double SSED, and with combined presaturation and SSED shows that the latter method has superior performance with spatially uniform lipid suppression factors in excess of 70. Metabolite mapping (choline, creatine, and NAA) with a 64 x 64 spatial matrix and 0.3 cm(3) voxels in close proximity to peripheral lipid regions was demonstrated at 1.5 T with a scan time of 32 min using the standard head coil. PMID:12704763

  15. A real-time data acquisition and control of gradient coil noise for fMRI identification of hearing disorder in children with history of ear infection

    PubMed Central

    Lee, Jaeseung; Holte, James

    2013-01-01

    Early ear infection and trauma, from birth to age 12 are known to have a significant effect on sensory and cognitive development. This effect can be demonstrated through the fMRI study of children who have a history of ear infection compared to a control group. A second research question is the extent to which brain plasticity at an early age can reduce the impact of infection on hearing and cognitive development. Functional Magnetic Resonance Imaging (fMRI) provides a mapping of brain activity in cognitive and sensory regions by recording the oxygenation state of the local cerebral blood flow. The gradient coils of fMRI scanners generate intense acoustic noise (GCN) - to which the subject is in close proximity - in the range of 90 to 140 db SPL during the imaging process. Clearly this noise will impress its signature on low level brain response patterns. An Active Noise Canceller (ANC) system can suppress the effect of GCN on the subject’s perception of a phonetic stimulus at the phoneme, word or phrase level. Due to a superimposition of the frequency and time domain components of the test signal and GCN for MR test, the ANC filtering system performs its function in real time - we must capture the brain’s response to the test signal AFTER the noise has been removed. This goal is achieved through the application of field programmable gate array (FPGA) technology of NI LabVIEW. The presentation (in the noisy fMRI environment) of test words and phrases to hearing impaired children can identify sources of distortion to their perceptual processes associated with GCN. Once this distortion has been identified, learning strategies may be introduced to replace the hearing function distorted by early infection as well as the short term effect of GCN. The study of speech cognition without the confounding effect of GCN and with the varying level of GCN for a repeated test signal at later age can be allowed to a measure of recovery through brain plasticity. PMID:23482910

  16. Exponential excitation pulses for improved water content mapping in the presence of background gradients.

    PubMed

    Preibisch, Christine; Volz, Steffen; Anti, Sandra; Deichmann, Ralf

    2008-10-01

    Several water content mapping techniques are based on the acquisition of multiple gradient echoes (GE) with different echo times (TE). However, in the presence of linear magnetic field gradients G(susc) the signal decay is no longer exponential but in the case of a rectangular slice profile weighted by a sinc function, giving rise to erroneous initial amplitudes S(0) in monoexponential fitting. Generally, it can be shown that the signal decay is weighted by the time profile of the excitation pulse. Thus, for an excitation pulse with an exponential time profile, i.e., a Lorentzian slice profile, the signal decay remains exponential and exponential fitting still yields the correct amplitude S(0). Multiecho GE images of a gel phantom and five human volunteers were acquired at 3 T using a sinc-shaped and an exponential excitation pulse. In addition, simulations were performed to investigate the influence of saturation effects due to distortion of the ideal Lorentzian slice profile. A considerable overestimation of S(0) when using a sinc-shaped excitation pulse was observed. Errors were greatly reduced with an exponential excitation pulse. We thus propose the use of excitation pulses with exponential time profile to obtain accurate estimates for S(0) from exponential fitting. PMID:18816811

  17. A Method for Unwrapping Highly Wrapped Multi-echo Phase Images at Very High Field: UMPIRE

    PubMed Central

    Robinson, Simon; Schödl, Horst; Trattnig, Siegfried

    2014-01-01

    Purpose To develop a method of unwrapping phase images from multi-echo scans that works even where there are several wraps between echoes, and which generates unwrapped phase images in addition to phase difference (PD) images. Theory The difference between the echo spacings in an acquisition with three unevenly spaced echoes (an imposed delay) can be selected such that the phase evolution in that time is in the range −π to +π in all voxels of interest. Under this condition, an image of the difference between the phase evolutions in the two inter-echo periods, an estimate of ΔB0, is free of wraps. This ΔB0 estimate can be used to identify and remove receiver phase offsets and wraps in phase images. Methods The approach was tested on simulated data and high-resolution in vivo brain data acquired from six subjects at 7 Tesla. Results The method generated wrap-free phase images. It was able to remove more wraps than is possible with PD imaging and was faster and more reliable than spatial unwrapping. Conclusion Unwrapping Multi-echo Phase Images with iRregular Echo spacings (UMPIRE) is conceptually simple, fast, reliable, and requires no fitting, thresholds, or operator intervention. PMID:23901001

  18. Temporal phase correction of multiple echo T2 magnetic resonance images

    NASA Astrophysics Data System (ADS)

    Bjarnason, Thorarin A.; Laule, Cornelia; Bluman, Joel; Kozlowski, Piotr

    2013-06-01

    Typically, magnetic resonance imaging (MRI) analysis is performed on magnitude data, and multiple echo T2 data consist of numerous images of the same slice taken with different echo spacing, giving voxel-wise temporal sampling of the noise as the signals decay according to T2 relaxation. Magnitude T2 decay data has Rician distributed noise which is characterized by a change in the noise distribution from Gaussian, through a transitional region, to Rayleigh as the signal to noise ratio decreases with increasing echo time. Non-Gaussian noise distributions may produce errors in the commonly applied non-negative least squares (NNLS) algorithm that is used to assess multiple echo decays for compartmentalized water environments through the creation of T2 distributions. Typically, Gaussian noise is sought by performing spatial-based phase correction on the MRI data however, these methods cannot capitalize on the temporal information available from multiple echo T2 acquisitions. Here we describe a temporal phase correction (TPC) algorithm that utilizes the temporal noise information available in multiple echo T2 acquisitions to put the relevant decay information in the Real portion of the decay data and leave only noise in the Imaginary portion. We apply this TPC algorithm to create real-valued multiple echo T2 data from human subjects measured at 1.5 T. We show that applying TPC causes changes in the T2 distribution estimates; notably the possible resolution of separate extracellular and intracellular water environments, and the disappearance of the commonly labeled cerebrospinal fluid peak, which might be an artefact observed in many previously published multiple echo T2 analyses.

  19. On the origin of 150-km echoes: Recent observational results and current understanding

    NASA Astrophysics Data System (ADS)

    Patra, Amit

    2012-07-01

    Discovered nearly 45 years ago, the so-called 150-km echoing phenomenon continues to be a puzzle. These are the coherent radar echoes coming from the height region of 140-180 km during daytime and are of special interest to the ionospheric scientists since they are very useful means for estimating the daytime electric fields, a crucial parameter for studying daytime electrodynamics and plasma physics, and can be observed by radar with moderate sensitivity. Although the 150-km echoes are being regularly used for studying low latitude electrodynamics, it is a bit awkward using them in the scientific work without knowing their origin. This paper is meant to present and discuss new results obtained from Gadanki (13.5o N, 79.2o E, mag. lat. 6.5o N), India to elucidate the underlying physical processes, not considered before. Two new findings, one obtained during the passage of a solar eclipse and another linked with the intermediate layer type descending properties of 150-km echoes, clearly indicate the role of electron density gradient in generating the irregularities responsible for the 150-km radar echoes, not envisioned before. Given the fact that Gadanki is located at magnetically low latitude, it is proposed that the descending echoing layers are produced by interchange instability on the gradient of daytime descending ion layer formed by meridional wind shear associated with tidal/gravity waves quite similar to that observed during nighttime. Comparative anatomy of daytime 150-km echoes and nighttime intermediate layer echoes will also be presented and discussed in an effort to have a deeper understanding on the underlying instability processes.

  20. Echo-Enabled Harmonic Generation

    SciTech Connect

    Stupakov, Gennady; /SLAC

    2012-06-28

    A recently proposed concept of the Echo-Enabled Harmonic Generation (EEHG) FEL uses two laser modulators in combination with two dispersion sections to generate a high-harmonic density modulation in a relativistic beam. This seeding technique holds promise of a one-stage soft x-ray FEL that radiates not only transversely but also longitudinally coherent pulses. Currently, an experimental verification of the concept is being conducted at the SLAC National Accelerator Laboratory aimed at the demonstration of the EEHG.

  1. Echo-Enabled Harmonic Generation

    SciTech Connect

    Stupakov, Gennady

    2010-08-25

    A recently proposed concept of the Echo-Enabled Harmonic Generation (EEHG) FEL uses two laser modulators in combination with two dispersion sections to generate a high-harmonic density modulation in a relativistic beam. This seeding technique holds promise of a one-stage soft x-ray FEL that radiates not only transversely but also longitudinally coherent pulses. Currently, an experimental verification of the concept is being conducted at the SLAC National Accelerator Laboratory aimed at the demonstration of the EEHG.

  2. Dance of the Light Echoes

    NASA Technical Reports Server (NTRS)

    2008-01-01

    [figure removed for brevity, see original site] Click on image for larger poster version

    This composite image from NASA's Spitzer Space Telescope shows the remnant of a star that exploded, called Cassiopeia A (center) and its surrounding 'light echoes' -- dances of light through dusty clouds, created when stars blast apart. The light echoes are colored and the surrounding clouds of dust are gray.

    In figure 1, dramatic changes are highlighted in phenomena referred to as light echoes (colored areas) around the Cassiopeia A supernova remnant (center). Cassiopeia A is the remnant of a once massive star that died in a violent supernova explosion. It consists of a dead star, called a neutron star, and a surrounding shell of material that was blasted off as the star died.

    A light echo occurs when a star explodes, acting like a cosmic flashbulb. The light from this explosion zips through nearby dust clumps, illuminating and heating them up slightly. This brief period of warming causes them to glow in infrared, like a chain of Christmas bulbs lighting up one by one. The result is an optical illusion, in which the dust appears to be flying outward at the speed of light. In figure 1, this apparent motion can be seen here by the shift in colored dust clumps

    Cassiopeia A is the remnant of a once massive star that died in a violent supernova explosion. It consists of a dead star, called a neutron star, and a surrounding shell of material that was blasted off as the star died. This remnant is located 11,000 light-years away in the northern constellation Cassiopeia.

    This composite consists of six processed images taken over a time span of three years. Dust features that have not changed over time appear gray, while those that have changed are colored blue or orange. Bluer colors represent an earlier time and redder ones, a later time. The progression of the light echo through the dust can be seen here by the shift in colored dust clumps.

    This

  3. Echo characteristics of two salmon species

    NASA Astrophysics Data System (ADS)

    Nealson, Patrick A.; Horne, John K.; Burwen, Debby L.

    2005-04-01

    The Alaska Department of Fish and Game relies on split-beam hydroacoustic techniques to estimate Chinook salmon (Oncorhynchus tshawytscha) returns to the Kenai River. Chinook counts are periodically confounded by large numbers of smaller sockeye salmon (O. nerka). Echo target-strength has been used to distinguish fish length classes, but was too variable to separate Kenai River chinook and sockeye distributions. To evaluate the efficacy of alternate echo metrics, controlled acoustic measurements of tethered chinook and sockeye salmon were collected at 200 kHz. Echo returns were digitally sampled at 48 kHz. A suite of descriptive metrics were collected from a series of 1,000 echoes per fish. Measurements of echo width were least variable at the -3 dB power point. Initial results show echo elongation and ping-to-ping variability in echo envelope width were significantly greater for chinook than for sockeye salmon. Chinook were also observed to return multiple discrete peaks from a single broadcast echo. These characteristics were attributed to the physical width of chinook exceeding half of the broadcast echo pulse width at certain orientations. Echo phase variability, correlation coefficient and fractal dimension distributions did not demonstrate significant discriminatory power between the two species. [Work supported by ADF&G, ONR.

  4. A Comparison Study of Single-Echo Susceptibility Weighted Imaging and Combined Multi-Echo Susceptibility Weighted Imaging in Visualizing Asymmetric Medullary Veins in Stroke Patients

    PubMed Central

    Wang, Chao; Qiu, Tiantian; Song, Ruirui; Jiaerken, Yerfan; Yang, Linglin; Wang, Shaoze

    2016-01-01

    Background Asymmetric medullary veins (AMV) are frequently observed in stroke patients and single-echo susceptibility weighted imaging (SWIs) is the main technique in detecting AMV. Our study aimed to investigate which echo time (TE) on single-echo susceptibility is the optimal echo for visualizing AMV and to compare the ability in detecting AMV in stroke patients between SWIs and multi-echo susceptibility weighted imaging (SWIc). Materials and Methods Twenty patients with middle cerebral artery stroke were included. SWI was acquired by using a multi-echo gradient-echo sequence with six echoes ranging from 5 ms to 35.240 ms. Three different echoes of SWIs including SWIs1 (TE = 23.144 ms), SWIs2 (TE = 29.192 ms) and SWIs3 (TE = 35.240 ms) were reconstructed. SWIc was averaged using the three echoes of SWIs. Image quality and venous contrast of medullary veins were compared between SWIs and SWIc using peak signal-to-noise ratio (PSNR), mean opinion score (MOS), contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR). The presence of AMV was evaluated in each SWIs (1–3) and SWIc. Results SWIs2 had the highest PSNR, MOS and CNR and SWIs1 had the highest SNR among three different echoes of SWIs. No significant difference was found in SNR between SWIs1 and SWIs2. PSNR, MOS and CNR in SWIc were significantly increased by 27.9%, 28.2% and 17.2% compared with SWIs2 and SNR in SWIc was significantly increased by 32.4% compared with SWIs1. 55% of patients with AMV were detected in SWIs2, SWIs3 and SWIc, while 50% AMV were found in SWIs1. Conclusions SWIs using TE around 29ms was optimal in visualizing AMV. SWIc could improve image quality and venous contrast, but was equal to SWIs using a relative long TE in evaluating AMV. These results provide the technique basis for further research of AMV in stroke. PMID:27494171

  5. RARE/Turbo Spin Echo Imaging with Simultaneous MultiSlice Wave-CAIPI

    PubMed Central

    Eichner, Cornelius; Bhat, Himanshu; Grant, P. Ellen; Wald, Lawrence L.; Setsompop, Kawin

    2014-01-01

    Purpose To enable highly accelerated RARE/Turbo Spin Echo (TSE) imaging using Simultaneous MultiSlice (SMS) Wave-CAIPI acquisition with reduced g-factor penalty. Methods SMS Wave-CAIPI incurs slice shifts across simultaneously excited slices while playing sinusoidal gradient waveforms during the readout of each encoding line. This results in an efficient k-space coverage that spreads aliasing in all three dimensions to fully harness the encoding power of coil sensitivities. The novel MultiPINS radiofrequency (RF) pulses dramatically reduce the power deposition of multiband (MB) refocusing pulse, thus allowing high MB factors within the Specific Absorption Rate (SAR) limit. Results Wave-CAIPI acquisition with MultiPINS permits whole brain coverage with 1 mm isotropic resolution in 70 seconds at effective MB factor 13, with maximum and average g-factor penalties of gmax=1.34 and gavg=1.12, and without √R penalty. With blipped-CAIPI, the g-factor performance was degraded to gmax=3.24 and gavg=1.42; a 2.4-fold increase in gmax relative to Wave-CAIPI. At this MB factor, the SAR of the MultiBand and PINS pulses are 4.2 and 1.9 times that of the MultiPINS pulse, while the peak RF power are 19.4 and 3.9 times higher. Conclusion Combination of the two technologies, Wave-CAIPI and MultiPINS pulse, enables highly accelerated RARE/TSE imaging with low SNR penalty at reduced SAR. PMID:25640187

  6. Quaternion-valued echo state networks.

    PubMed

    Xia, Yili; Jahanchahi, Cyrus; Mandic, Danilo P

    2015-04-01

    Quaternion-valued echo state networks (QESNs) are introduced to cater for 3-D and 4-D processes, such as those observed in the context of renewable energy (3-D wind modeling) and human centered computing (3-D inertial body sensors). The introduction of QESNs is made possible by the recent emergence of quaternion nonlinear activation functions with local analytic properties, required by nonlinear gradient descent training algorithms. To make QENSs second-order optimal for the generality of quaternion signals (both circular and noncircular), we employ augmented quaternion statistics to introduce widely linear QESNs. To that end, the standard widely linear model is modified so as to suit the properties of dynamical reservoir, typically realized by recurrent neural networks. This allows for a full exploitation of second-order information in the data, contained both in the covariance and pseudocovariances, and a rigorous account of second-order noncircularity (improperness), and the corresponding power mismatch and coupling between the data components. Simulations in the prediction setting on both benchmark circular and noncircular signals and on noncircular real-world 3-D body motion data support the analysis.

  7. Quaternion-valued echo state networks.

    PubMed

    Xia, Yili; Jahanchahi, Cyrus; Mandic, Danilo P

    2015-04-01

    Quaternion-valued echo state networks (QESNs) are introduced to cater for 3-D and 4-D processes, such as those observed in the context of renewable energy (3-D wind modeling) and human centered computing (3-D inertial body sensors). The introduction of QESNs is made possible by the recent emergence of quaternion nonlinear activation functions with local analytic properties, required by nonlinear gradient descent training algorithms. To make QENSs second-order optimal for the generality of quaternion signals (both circular and noncircular), we employ augmented quaternion statistics to introduce widely linear QESNs. To that end, the standard widely linear model is modified so as to suit the properties of dynamical reservoir, typically realized by recurrent neural networks. This allows for a full exploitation of second-order information in the data, contained both in the covariance and pseudocovariances, and a rigorous account of second-order noncircularity (improperness), and the corresponding power mismatch and coupling between the data components. Simulations in the prediction setting on both benchmark circular and noncircular signals and on noncircular real-world 3-D body motion data support the analysis. PMID:25794374

  8. Optimized 3D Ultrashort Echo Time Pulmonary MRI

    PubMed Central

    Johnson, Kevin M.; Fain, Sean B.; Schiebler, Mark L.; Nagle, Scott

    2012-01-01

    Purpose To optimize 3D radial ultrashort echo time MRI for high resolution whole-lung imaging. Methods 3D radial ultrashort echo time was implemented on a 3T scanner to investigate the effects of: (1) limited field-of-view excitation, (2) variable density readouts, and (3) radial oversampling. Improvements in noise performance and spatial resolution were assessed through simulation and phantom studies. Their effects on lung and airway visualization in five healthy male human subjects (mean age 32 years) were compared qualitatively through blinded ordinal scoring by two cardiothoracic radiologists using a nonparametric Friedman test (P < 0.05). Relative signal difference between endobronchial air and adjacent lung tissue, normalized to nearby vessel, was used as a surrogate for lung tissue signal. Quantitative measures were compared using the paired Student's t-test (P < 0.05). Finally, clinical feasibility was investigated in a patient with interstitial fibrosis. Results Simulation and phantom studies showed up to 67% improvement in SNR and reduced blurring for short T2* species using all three optimizations. In vivo images showed decreased artifacts and improved lung tissue and airway visualization both qualitatively and quantitatively. Conclusion The use of limited field-of-view excitation, variable readout gradients, and radial oversampling significantly improve the technical quality of 3D radial ultrashort echo time lung images. PMID:23213020

  9. Impact of gradient timing error on the tissue sodium concentration bioscale measured using flexible twisted projection imaging

    NASA Astrophysics Data System (ADS)

    Lu, Aiming; Atkinson, Ian C.; Vaughn, J. Thomas; Thulborn, Keith R.

    2011-12-01

    The rapid biexponential transverse relaxation of the sodium MR signal from brain tissue requires efficient k-space sampling for quantitative imaging in a time that is acceptable for human subjects. The flexible twisted projection imaging (flexTPI) sequence has been shown to be suitable for quantitative sodium imaging with an ultra-short echo time to minimize signal loss. The fidelity of the k-space center location is affected by the readout gradient timing errors on the three physical axes, which is known to cause image distortion for projection-based acquisitions. This study investigated the impact of these timing errors on the voxel-wise accuracy of the tissue sodium concentration (TSC) bioscale measured with the flexTPI sequence. Our simulations show greater than 20% spatially varying quantification errors when the gradient timing errors are larger than 10 μs on all three axes. The quantification is more tolerant of gradient timing errors on the Z-axis. An existing method was used to measure the gradient timing errors with <1 μs error. The gradient timing error measurement is shown to be RF coil dependent, and timing error differences of up to ˜16 μs have been observed between different RF coils used on the same scanner. The measured timing errors can be corrected prospectively or retrospectively to obtain accurate TSC values.

  10. The Echoes of Earth Science

    NASA Technical Reports Server (NTRS)

    2006-01-01

    NASA s Earth Observing System Data and Information System (EOSDIS) acquires, archives, and manages data from all of NASA s Earth science satellites, for the benefit of the Space Agency and for the benefit of others, including local governments, first responders, the commercial remote sensing industry, teachers, museums, and the general public. EOSDIS is currently handling an extraordinary amount of NASA scientific data. To give an idea of the volume of information it receives, NASA s Terra Earth-observing satellite, just one of many NASA satellites sending down data, sends it hundreds of gigabytes a day, almost as much data as the Hubble Space Telescope acquires in an entire year, or about equal to the amount of information that could be found in hundreds of pickup trucks filled with books. To make EOSDIS data completely accessible to the Earth science community, NASA teamed up with private industry in 2000 to develop an Earth science "marketplace" registry that lets public users quickly drill down to the exact information they need. It also enables them to publish their research and resources alongside of NASA s research and resources. This registry is known as the Earth Observing System ClearingHOuse, or ECHO. The charter for this project focused on having an infrastructure completely independent from EOSDIS that would allow for more contributors and open up additional data access options. Accordingly, it is only fitting that the term ECHO is more than just an acronym; it represents the functionality of the system in that it can echo out and create interoperability among other systems, all while maturing with time as industry technologies and standards change and improve.

  11. The impact of gradient strength on in vivo diffusion MRI estimates of axon diameter.

    PubMed

    Huang, Susie Y; Nummenmaa, Aapo; Witzel, Thomas; Duval, Tanguy; Cohen-Adad, Julien; Wald, Lawrence L; McNab, Jennifer A

    2015-02-01

    Diffusion magnetic resonance imaging (MRI) methods for axon diameter mapping benefit from higher maximum gradient strengths than are currently available on commercial human scanners. Using a dedicated high-gradient 3T human MRI scanner with a maximum gradient strength of 300 mT/m, we systematically studied the effect of gradient strength on in vivo axon diameter and density estimates in the human corpus callosum. Pulsed gradient spin echo experiments were performed in a single scan session lasting approximately 2h on each of three human subjects. The data were then divided into subsets with maximum gradient strengths of 77, 145, 212, and 293 mT/m and diffusion times encompassing short (16 and 25 ms) and long (60 and 94 ms) diffusion time regimes. A three-compartment model of intra-axonal diffusion, extra-axonal diffusion, and free diffusion in cerebrospinal fluid was fitted to the data using a Markov chain Monte Carlo approach. For the acquisition parameters, model, and fitting routine used in our study, it was found that higher maximum gradient strengths decreased the mean axon diameter estimates by two to three fold and decreased the uncertainty in axon diameter estimates by more than half across the corpus callosum. The exclusive use of longer diffusion times resulted in axon diameter estimates that were up to two times larger than those obtained with shorter diffusion times. Axon diameter and density maps appeared less noisy and showed improved contrast between different regions of the corpus callosum with higher maximum gradient strength. Known differences in axon diameter and density between the genu, body, and splenium of the corpus callosum were preserved and became more reproducible at higher maximum gradient strengths. Our results suggest that an optimal q-space sampling scheme for estimating in vivo axon diameters should incorporate the highest possible gradient strength. The improvement in axon diameter and density estimates that we demonstrate from

  12. Loschmidt echo for quantum metrology

    NASA Astrophysics Data System (ADS)

    Macrı, Tommaso; Smerzi, Augusto; Pezzè, Luca

    2016-07-01

    We propose a versatile Loschmidt echo protocol to detect and quantify multiparticle entanglement. It allows us to extract the quantum Fisher information for arbitrary pure states, and finds direct application in quantum metrology. In particular, the protocol applies to states that are generally difficult to characterize, as non-Gaussian states, and states that are not symmetric under particle exchange. We focus on atomic systems, including trapped ions, polar molecules, and Rydberg atoms, where entanglement is generated dynamically via long-range interaction, and show that the protocol is stable against experimental detection errors.

  13. Acquisition strategy to obtain quantitative diffusion NMR data

    NASA Astrophysics Data System (ADS)

    Barrère, Caroline; Thureau, Pierre; Thévand, André; Viel, Stéphane

    2012-03-01

    Pulsed Gradient Spin Echo (PGSE) diffusion NMR experiments constitute a powerful tool for analyzing complex mixtures because they can in principle separate the NMR spectra of each mixture component. However, because these experiments intrinsically rely on spin echoes, they are traditionally regarded as non-quantitative, due to the signal attenuation caused by longitudinal (T1) and transverse (T2) nuclear magnetic relaxation during the rather long delays of the pulse sequence. Alternatively to the quantitative Direct Exponential Curve Resolution Algorithm (qDECRA) approach proposed by Antalek (J. Am. Chem. Soc. 128 (2006) 8402-8403), this work presents an acquisition strategy that renormalizes this relaxation attenuation using estimates of the T1 and T2 relaxation times for all the nuclei in the mixture, as obtained directly with the pulse sequence used to record the PGSE experiment. More specifically, it is shown that only three distinct PGSE experiments need to be recorded, each with a specific set of acquisition parameters. For small- and medium-sized molecules, only T1 is required for obtaining accurate quantification. For larger molecular weight species, which typically exhibit short T2 values, estimates of T2 must also be included but only a rough estimation is required. This appears fortunate because these data are especially hard to obtain with good accuracy when analyzing homonuclear scalar-coupled systems. Overall, the proposed methodology is shown to yield a quantification accuracy of ±5%, both in the absence and in the presence of spectral overlap, giving rise - at least, in our hands - to results that superseded those achieved by qDECRA, while requiring substantially less experimental time.

  14. Bunched beam echos in the AGS

    SciTech Connect

    Kewisch, J.; Brennan, J.M.

    1998-08-01

    Beam echos have been measured at FNAL and CERN in coasting beams. A coherent oscillation introduced by a short RF burst decoheres quickly, but a coherent echo of this oscillation can be observed if the decohered oscillation is bounced off a second RF burst. In this report the authors describe first longitudinal echo measurements of bunched beam in the AGS accelerator. They applied a method proposed by Stupakov for transverse beam echos, where the initial oscillation is produced by a dipole kick and is bounced off a quadrupole kick. In the longitudinal case the dipole and quadrupole kicks are produced by cavities operating at a 90 and 0{degree} phase shift, respectively.

  15. Spin echo versus stimulated echo diffusion tensor imaging of the in vivo human heart

    PubMed Central

    von Deuster, Constantin; Stoeck, Christian T.; Genet, Martin; Atkinson, David

    2015-01-01

    Purpose To compare signal‐to‐noise ratio (SNR) efficiency and diffusion tensor metrics of cardiac diffusion tensor mapping using acceleration‐compensated spin‐echo (SE) and stimulated echo acquisition mode (STEAM) imaging. Methods Diffusion weighted SE and STEAM sequences were implemented on a clinical 1.5 Tesla MR system. The SNR efficiency of SE and STEAM was measured (b = 50–450 s/mm2) in isotropic agar, anisotropic diffusion phantoms and the in vivo human heart. Diffusion tensor analysis was performed on mean diffusivity, fractional anisotropy, helix and transverse angles. Results In the isotropic phantom, the ratio of SNR efficiency for SE versus STEAM, SNRt(SE/STEAM), was 2.84 ± 0.08 for all tested b‐values. In the anisotropic diffusion phantom the ratio decreased from 2.75 ± 0.05 to 2.20 ± 0.13 with increasing b‐value, similar to the in vivo decrease from 2.91 ± 0.43 to 2.30 ± 0.30. Diffusion tensor analysis revealed reduced deviation of helix angles from a linear transmural model and reduced transverse angle standard deviation for SE compared with STEAM. Mean diffusivity and fractional anisotropy were measured to be statistically different (P < 0.001) between SE and STEAM. Conclusion Cardiac DTI using motion‐compensated SE yields a 2.3–2.9× increase in SNR efficiency relative to STEAM and improved accuracy of tensor metrics. The SE method hence presents an attractive alternative to STEAM based approaches. Magn Reson Med 76:862–872, 2016. © 2015 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:26445426

  16. Light echoes - Type II supernovae

    NASA Technical Reports Server (NTRS)

    Schaefer, Bradley E.

    1987-01-01

    Type II supernovae (SNs) light curves show a remarkable range of shapes. Data have been collected for the 12 Type II SNs that have light curve information for more than four months past maximum. Contrary to previous reports, it is found that (1) the decay rate after 100 days past maximum varies by almost an order of magnitude and (2) the light curve shapes are not bimodally distributed, but actually form a continuum. In addition, it is found that the extinctions to the SNs are related to the light curve shapes. This implies that the absorbing dust is local to the SNs. The dust is likely to be part of a circumstellar shell emitted by the SN progenitor that Dwek (1983) has used to explain infrared echoes. The optical depth of the shell can get quite large. In such cases, it is found that the photons scattered and delayed by reflection off dust grains will dominate the light curve several months after peak brightness. This 'light echo' offers a straightforward explanation of the diversity of Type II SN light curves.

  17. Minimum complexity echo state network.

    PubMed

    Rodan, Ali; Tino, Peter

    2011-01-01

    Reservoir computing (RC) refers to a new class of state-space models with a fixed state transition structure (the reservoir) and an adaptable readout form the state space. The reservoir is supposed to be sufficiently complex so as to capture a large number of features of the input stream that can be exploited by the reservoir-to-output readout mapping. The field of RC has been growing rapidly with many successful applications. However, RC has been criticized for not being principled enough. Reservoir construction is largely driven by a series of randomized model-building stages, with both researchers and practitioners having to rely on a series of trials and errors. To initialize a systematic study of the field, we concentrate on one of the most popular classes of RC methods, namely echo state network, and ask: What is the minimal complexity of reservoir construction for obtaining competitive models and what is the memory capacity (MC) of such simplified reservoirs? On a number of widely used time series benchmarks of different origin and characteristics, as well as by conducting a theoretical analysis we show that a simple deterministically constructed cycle reservoir is comparable to the standard echo state network methodology. The (short-term) MC of linear cyclic reservoirs can be made arbitrarily close to the proved optimal value.

  18. Iterative method for predistortion of MRI gradient waveforms.

    PubMed

    Harkins, Kevin D; Does, Mark D; Grissom, William A

    2014-08-01

    The purpose of this work is to correct for transient gradient waveform errors in magnetic resonance imaging (MRI), whether from eddy currents, group delay, or gradient amplifier nonlinearities, which are known to affect image quality. An iterative method is proposed to minimize error between desired and measured gradient waveforms, whose success does not depend on accurate knowledge of the gradient system impulse response. The method was applied to half-pulse excitation for 2-D ultra-short echo time (UTE) imaging on a small animal MRI system and to spiral 2-D excitation on a human 7T MRI system. Predistorted gradient waveforms reduced temporal signal variation caused by excitation gradient trajectory errors in 2-D UTE, and improved the quality of excitation patterns produced by spiral excitation pulses. Iterative gradient predistortion is useful for minimizing transient gradient errors without requiring accurate characterization of the gradient system impulse response. PMID:24801945

  19. Functional cerebral blood volume mapping with simultaneous multi-slice acquisition.

    PubMed

    Huber, Laurentius; Ivanov, Dimo; Guidi, Maria; Turner, Robert; Uludağ, Kâmil; Möller, Harald E; Poser, Benedikt A

    2016-01-15

    The aim of this study is to overcome the current limits of brain coverage available with multi-slice echo planar imaging (EPI) for vascular space occupancy (VASO) mapping. By incorporating simultaneous multi-slice (SMS) EPI image acquisition into slice-saturation slab-inversion VASO (SS-SI VASO), many more slices can be acquired for non-invasive functional measurements of blood volume responses. Blood-volume-weighted VASO and gradient echo blood oxygenation level-dependent (GE-BOLD) data were acquired in humans at 7T with a 32-channel head coil. SMS-VASO was applied in three scenarios: A) high-resolution acquisition of spatially distant brain areas in the visuo-motor network (V1/V5/M1/S1); B) high-resolution acquisition of an imaging slab covering the entire M1/S1 hand regions; and C) low-resolution acquisition with near whole-brain coverage. The results show that the SMS-VASO sequence provided images enabling robust detection of blood volume changes in up to 20 slices with signal readout durations shorter than 150ms. High-resolution application of SMS-VASO revealed improved specificity of VASO to GM tissue without contamination from large draining veins compared to GE-BOLD in the visual cortex and in the sensory-motor cortex. It is concluded that VASO fMRI with SMS-EPI allows obtaining a reasonable three-dimensional coverage not achievable with standard VASO during the short time period when blood magnetization is approximately nulled. Due to the increased brain coverage and better spatial specificity to GM tissue of VASO compared to GE-BOLD signal, the proposed method may play an important role in high-resolution human fMRI at 7T. PMID:26522423

  20. Solar Sail Model Validation from Echo Trajectories

    NASA Technical Reports Server (NTRS)

    Heaton, Andrew F.; Brickerhoff, Adam T.

    2007-01-01

    The NASA In-Space Propulsion program has been engaged in a project to increase the technology readiness of solar sails. Recently, these efforts came to fruition in the form of several software tools to model solar sail guidance, navigation and control. Furthermore, solar sails are one of five technologies competing for the New Millennium Program Space Technology 9 flight demonstration mission. The historic Echo 1 and Echo 2 balloons were comprised of aluminized Mylar, which is the near-term material of choice for solar sails. Both spacecraft, but particularly Echo 2, were in low Earth orbits with characteristics similar to the proposed Space Technology 9 orbit. Therefore, the Echo balloons are excellent test cases for solar sail model validation. We present the results of studies of Echo trajectories that validate solar sail models of optics, solar radiation pressure, shape and low-thrust orbital dynamics.

  1. Electron Echo 6 - a Study by Particle Detectors of Electrons Artificially Injected Into the Magnetosphere.

    NASA Astrophysics Data System (ADS)

    Malcolm, Perry Robert

    The ECHO-6 sounding rocket was launched from the Poker Flat Research Range, Alaska on 30 March 1983. A Terrier-Black Brant launch vehicle carried the payload on a northward trajectory over an auroral arc and to an apogee of 216 kilometers. The primary objective of the ECHO-6 experiment was to evaluate electric fields, magnetic fields, and plasma processes in the distant magnetosphere by injecting electron beams in the ionosphere and observing conjugate echoes. The experiment succeeded in injecting 10-36 KeV beams during the existence of a moderate growth phase aurora, an easterly electrojet system, and a pre -midnight inflation condition of the magnetosphere. The ECHO-6 payload system consisted of an accelerator MAIN payload, a free-flying Plasma Diagnostics Package (PDP), and four rocket propelled Throw Away Detectors (TADs). The PDP was ejected from the MAIN payload to analyze electric fields, plasma particles, energetic electrons, and photometric effects produced by beam injections. The TADs were ejected from the MAIN payload in a pattern to detect echoes in the conjugate echo region south of the beam emitting MAIN payload. The TADs reached distances exceeding 3 kilometers from the MAIN payload and made measurements of the ambient electrons by means of solid state detectors and electrostatic analyzers. In spite of the perfect operation of the TAD system and a rigorous analysis of the particle data, no conjugate echoes have been identified. Through the use of a new dynamic magnetic field model (Olson and Pfitzer, 1982) and satellite magnetometer measurements, it has been determined that the echoing electrons returned out of range of the TADs as a result of their bounce times and curvature-gradient drifts being increased beyond the expected limits for an inflated magnetic field. This dynamic model was then applied to the study of echoes seen during the ECHO-4 flight resulting in a significant increase in the calculated energy of the echo electrons and better

  2. Gradient networks

    NASA Astrophysics Data System (ADS)

    Toroczkai, Zoltán; Kozma, Balázs; Bassler, Kevin E.; Hengartner, N. W.; Korniss, G.

    2008-04-01

    Gradient networks are defined (Toroczkai and Bassler 2004 Nature 428 716) as directed graphs formed by local gradients of a scalar field distributed on the nodes of a substrate network G. We present the derivation for some of the general properties of gradient graphs and give an exact expression for the in-degree distribution R(l) of the gradient network when the substrate is a binomial (Erd{\\;\\kern -0.10em \\raise -0.35ex \\{{^{^{\\prime\\prime}}}}\\kern -0.57em \\o} s-Rényi) random graph, G_{N,p} , and the scalars are independent identically distributed (i.i.d.) random variables. We show that in the limit N \\to \\infty, p \\to 0, z = pN = \\mbox{const} \\gg 1, R(l)\\propto l^{-1} for l < l_c = z , i.e., gradient networks become scale-free graphs up to a cut-off degree. This paper presents the detailed derivation of the results announced in Toroczkai and Bassler (2004 Nature 428 716).

  3. Theory of Quantum Loschmidt Echoes

    NASA Astrophysics Data System (ADS)

    Prosen, T.; Seligman, T. H.; Žnidarič, M.

    In this paper we review our recent work on the theoretical approach to quantum Loschmidt echoes, i.e., various properties of the so-called echo dynamics -- the composition of forward and backward time evolutions generated by two slightly different Hamiltonians, such as the state autocorrelation function (fidelity) and the purity of a reduced density matrix traced over a subsystem (purity fidelity). Our main theoretical result is a linear response formalism, expressing the fidelity and purity fidelity in terms of integrated time autocorrelation function of the generator of the perturbation. Surprisingly, this relation predicts that the decay of fidelity is the slower the faster the decay of correlations. In particular for a static (time-independent) perturbation, and for non-ergodic and non-mixing dynamics where asymptotic decay of correlations is absent, a qualitatively different and faster decay of fidelity is predicted on a time scale ∝ 1/δ as opposed to mixing dynamics where the fidelity is found to decay exponentially on a time-scale ∝ 1/δ2, where δ is a strength of perturbation. A detailed discussion of a semi-classical regime of small effective values of Planck constant hbar is given where classical correlation functions can be used to predict quantum fidelity decay. Note that the correct and intuitively expected classical stability behavior is recovered in the classical limit hbarto 0, as the two limits δto 0 and hbarto 0 do not commute. The theoretical results are demonstrated numerically for two models, the quantized kicked top and the multi-level Jaynes Cummings model. Our method can for example be applied to the stability analysis of quantum computation and quantum information processing.

  4. Fixed and pulsed gradient diffusion methods in low-field core analysis.

    PubMed

    Leu, Gabriela; Fordham, Edmund J; Hürlimann, Martin D; Frulla, Phil

    2005-02-01

    We review diffusion-weighted relaxation protocols for two-dimensional diffusion/relaxation time (D, T(2)) distributions and their application to fluid-saturated sedimentary rocks at low fields typical of oil-well logging tools (< or = 2 MHz for 1H). Fixed field gradient (FFG) protocols may be implemented in logging tools and in the laboratory; there, pulsed field gradient (PFG) protocols are also available. In either category, direct or stimulated echoes may be used for the diffusion evolution periods. We compare the results of several variant FFG and PFG protocols obtained on liquids and two contrasting sedimentary rocks. For liquids and rocks of negligible internal gradients (g(int)), results are comparable, as expected, for all the studied protocols. For rocks of strong g(int), protocol-dependent artifacts are seen in the joint (D, T2) distributions, consistent with the effects of the internal fields. For laboratory petrophysics, the PFG methods offer several advantages: (a) significantly improved signal-to-noise ratio and acquisition times for repetitions over many samples; (b) freedom from heteronuclear contamination when fluorinated liquids are used in core holders; and (c) a palette of variants--one comparable with the FFG--for the study of rocks of significant g(int). Given suitable hardware, both PFG and FFG methods can be implemented in the same bench-top apparatus, providing a versatile test bed for application in a petrophysical laboratory. PMID:15833632

  5. Fixed and pulsed gradient diffusion methods in low-field core analysis.

    PubMed

    Leu, Gabriela; Fordham, Edmund J; Hürlimann, Martin D; Frulla, Phil

    2005-02-01

    We review diffusion-weighted relaxation protocols for two-dimensional diffusion/relaxation time (D, T(2)) distributions and their application to fluid-saturated sedimentary rocks at low fields typical of oil-well logging tools (< or = 2 MHz for 1H). Fixed field gradient (FFG) protocols may be implemented in logging tools and in the laboratory; there, pulsed field gradient (PFG) protocols are also available. In either category, direct or stimulated echoes may be used for the diffusion evolution periods. We compare the results of several variant FFG and PFG protocols obtained on liquids and two contrasting sedimentary rocks. For liquids and rocks of negligible internal gradients (g(int)), results are comparable, as expected, for all the studied protocols. For rocks of strong g(int), protocol-dependent artifacts are seen in the joint (D, T2) distributions, consistent with the effects of the internal fields. For laboratory petrophysics, the PFG methods offer several advantages: (a) significantly improved signal-to-noise ratio and acquisition times for repetitions over many samples; (b) freedom from heteronuclear contamination when fluorinated liquids are used in core holders; and (c) a palette of variants--one comparable with the FFG--for the study of rocks of significant g(int). Given suitable hardware, both PFG and FFG methods can be implemented in the same bench-top apparatus, providing a versatile test bed for application in a petrophysical laboratory.

  6. Quantitative comparison of cortical surface reconstructions from MP2RAGE and multi-echo MPRAGE data at 3 and 7 T.

    PubMed

    Fujimoto, Kyoko; Polimeni, Jonathan R; van der Kouwe, André J W; Reuter, Martin; Kober, Tobias; Benner, Thomas; Fischl, Bruce; Wald, Lawrence L

    2014-04-15

    The Magnetization-Prepared 2 Rapid Acquisition Gradient Echo (MP2RAGE) method achieves spatially uniform contrast across the entire brain between gray matter and surrounding white matter tissue and cerebrospinal fluid by rapidly acquiring data at two points during an inversion recovery, and then combining the two volumes so as to cancel out sources of intensity and contrast bias, making it useful for neuroimaging studies at ultrahigh field strengths (≥7T). To quantify the effectiveness of the MP2RAGE method for quantitative morphometric neuroimaging, we performed tissue segmentation and cerebral cortical surface reconstruction of the MP2RAGE data and compared the results with those generated from conventional multi-echo MPRAGE (MEMPRAGE) data across a group of healthy subjects. To do so, we developed a preprocessing scheme for the MP2RAGE image data to allow for automatic cortical segmentation and surface reconstruction using FreeSurfer and analysis methods to compare the positioning of the surface meshes. Using image volumes with 1mm isotropic voxels we found a scan-rescan reproducibility of cortical thickness estimates to be 0.15 mm (or 6%) for the MEMPRAGE data and a slightly lower reproducibility of 0.19 mm (or 8%) for the MP2RAGE data. We also found that the thickness estimates were systematically smaller in the MP2RAGE data, and that both the interior and exterior cortical boundaries estimated from the MP2RAGE data were consistently positioned within the corresponding boundaries estimated from the MEMPRAGE data. Therefore several measureable differences exist in the appearance of cortical gray matter and its effect on automatic segmentation methods that must be considered when choosing an acquisition or segmentation method for studies requiring cortical surface reconstructions. We propose potential extensions to the MP2RAGE method that may help to reduce or eliminate these discrepancies.

  7. Quantitative comparison of cortical surface reconstructions from MP2RAGE and Multi-Echo MPRAGE data at 3 and 7 Tesla

    PubMed Central

    Fujimoto, Kyoko; Polimeni, Jonathan R.; van der Kouwe, Andre J. W.; Reuter, Martin; Kober, Tobias; Benner, Thomas; Fischl, Bruce; Wald, Lawrence L.

    2014-01-01

    The Magnetization-Prepared 2 Rapid Acquisition Gradient Echo (MP2RAGE) method achieves spatially uniform contrast across the entire brain between gray matter and surrounding white matter tissue and cerebrospinal fluid by rapidly acquiring data at two points during an inversion recovery, and then combining the two volumes so as to cancel out sources of intensity and contrast bias, making it useful for neuroimaging studies at ultrahigh field strengths (≥ 7 T). To quantify the effectiveness of the MP2RAGE method for quantitative morphometric neuroimaging, we performed tissue segmentation and cerebral cortical surface reconstruction of the MP2RAGE data and compared the results with those generated from conventional Multi-Echo MPRAGE (MEMPRAGE) data across a group of healthy subjects. To do so, we developed a preprocessing scheme for the MP2RAGE image data to allow for automatic cortical segmentation and surface reconstruction using FreeSurfer and analysis methods to compare positioning of the surface meshes. Using image volumes with 1 mm isotropic voxels we found a scan-rescan reproducibility of cortical thickness estimates to be 0.15 mm (or 6%) for the MEMPRAGE data and a slightly lower reproducibility of 0.19 mm (or 8%) for the MP2RAGE data. We also found that the thickness estimates were systematically smaller in the MP2RAGE data, and that both the interior and exterior cortical boundaries estimated from the MP2RAGE data were consistently positioned within the corresponding boundaries estimated from the MEMPRAGE data. Therefore several measureable differences exist in the appearance of cortical gray matter and its effect on automatic segmentation methods that must be considered when choosing an acquisition or segmentation method for studies requiring cortical surface reconstructions. We propose potential extensions to the MP2RAGE method that may help to reduce or eliminate these discrepancies. PMID:24345388

  8. Echo planar diffusion-weighted imaging: possibilities and considerations with 12- and 32-channel head coils.

    PubMed

    Morelli, John N; Saettele, Megan R; Rangaswamy, Rajesh A; Vu, Lan; Gerdes, Clint M; Zhang, Wei; Ai, Fei

    2012-01-01

    Interest in clinical brain magnetic resonance imaging using 32-channel head coils for signal reception continues to increase. The present investigation assesses possibilities for improving diffusion-weighted image quality using a 32-channel in comparison to a conventional 12-channel coil. The utility of single-shot (ss) and an approach to readout-segmented (rs) echo planar imaging (EPI) are examined using both head coils. Substantial image quality improvements are found with rs-EPI. Imaging with a 32-channel head coil allows for implementation of greater parallel imaging acceleration factors or acquisition of scans at a higher resolution. Specifically, higher resolution imaging with rs-EPI can be achieved by increasing the number of readout segments without increasing echo-spacing or echo time to the degree necessary with ss-EPI - a factor resulting in increased susceptibility artifact and reduced signal-to-noise with the latter.

  9. Generating Super Stimulated-Echoes in MRI and their Application to Hyperpolarized C-13 Diffusion Metabolic Imaging

    PubMed Central

    Larson, Peder E. Z.; Kerr, Adam B.; Reed, Galen D.; Hurd, Ralph E.; Kurhanewicz, John; Pauly, John M.; Vigneron, Daniel B.

    2011-01-01

    Stimulated-echoes in MR can be used to provide high sensitivity to motion and flow, creating diffusion and perfusion weighting as well as T1 contrast, but conventional approaches inherently suffer from a 50% signal loss. The super stimulated-echo, which uses a specialized radiofrequency (RF) pulse train, has been proposed in order to improve the signal while preserving motion and T1 sensitivity. This paper presents a novel and straightforward method for designing the super stimulated-echo pulse train using inversion pulse design techniques. This method can also create adiabatic designs with an improved response to RF transmit field variations. The scheme was validated in phantom experiments and shown in vivo to improve SNR. We have applied a super stimulated-echo to metabolic MRI with hyperpolarized 13C-labeled molecules. For spectroscopic imaging of hyperpolarized agents, several repetition times are required but only a single stimulated-echo encoding is feasible, which can lead to unwanted motion blurring. To address this, a super stimulated-echo preparation scheme was used in which the diffusion weighting is terminated prior to the acquisition, and we observed a SNR increases of 60% in phantoms and 49% in vivo over a conventional stimulated-echo. Experiments following injection of hyperpolarized [1-13C]-pyruvate in murine transgenic cancer models have shown improved delineation for tumors since signals from metabolites within tumor tissues are retained while those from the vasculature are suppressed by the diffusion preparation scheme. PMID:22027366

  10. 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

  11. Stabilization of echo amplitudes in FSE sequences.

    PubMed

    Le Roux, P; Hinks, R S

    1993-08-01

    The classical CPMG sequence and its extension as an imaging sequence, fast spin echo (FSE, based on RARE), suffer from signal magnitude variations in the early echoes when the refocusing pulses are not set exactly to 180 degrees. It has been suggested that by varying the value of the nutation angle of each refocusing pulse the signal magnitude could be made constant. This article describes an algorithm permitting the generation of sequences of nutation angles yielding series of echoes with constant signal magnitudes. This result is then used to design selective pulses for the FSE imaging technique.

  12. Coronal plasma-frequency radio echoes

    SciTech Connect

    Eremin, A.B.

    1986-06-01

    If the mechanism that Zaitsev and the author propose for generating the fundamental mode of type III solar radio bursts is correct, then coronal echo events can occur at the plasma frequency. Certain events recorded during the type IIIb-III storm of July 1974 are identifiable as echoes. Radio-wave reflection from moving solar-wind irregularities consistently shifts the echoes to shorter wavelengths than the primary burst, yielding an estimate of about 10 to the 7th cm/sec for the mean wind velocity 1-2 solar radii from the photosphere. 8 references.

  13. [Optimization of Three-dimensional Ultrashort Echo Time Magnetic Resonance Imaging at a Low Field].

    PubMed

    Huang, Yuli; Du, Yiping

    2015-12-01

    Conventional magnetic resonance (MR) pulse sequences typically have an echo time (TE) of 1 ms or longer, providing an excellent contrast between different soft tissues. However, some short T2 tissues appear dark in conventional MR images because the signal from these tissues has decayed to nearly zero before the center of k-space is acquired. Because of the ability of directly imaging short T2 tissues, ultrashort echo time technique has been widely studied in recent years. An overwhelming majority of the studies were carried out at high fields, while many low- field scanner systems are still used in developing countries. To investigate the effects of the delay between analog-to-digital converter sampling and the readout gradient, the TE of the second echo used to calculate the R2 * map, and the undersampling ratio on the results of three-dimensional (3D) ultrashort echo time imaging at a low field, we implemented a 3D ultrashort echo time sequence on a 0. 35T scanner. Different parameters were used and the reconstructed images and R2 * maps were compared. Images reconstructed with slightly varying delays appeared quite different. Different contrast between short and long T2 tissues were found in R2 * maps calculated with different echoes. The result of undersampling study indicated that excessive undersampling could cause unwanted blurring, making it difficult to better visualize the short T2 tissues in the R2 * map. The results suggested that cautions should be taken in the choice of these parameters in 3D ultrashort echo time imaging. Short T2 tissues can be visualized with appropriate imaging parameters at this low field. PMID:27079094

  14. Imaging tooth enamel using zero echo time (ZTE) magnetic resonance imaging

    NASA Astrophysics Data System (ADS)

    Rychert, Kevin M.; Zhu, Gang; Kmiec, Maciej M.; Nemani, Venkata K.; Williams, Benjamin B.; Flood, Ann B.; Swartz, Harold M.; Gimi, Barjor

    2015-03-01

    In an event where many thousands of people may have been exposed to levels of radiation that are sufficient to cause the acute radiation syndrome, we need technology that can estimate the absorbed dose on an individual basis for triage and meaningful medical decision making. Such dose estimates may be achieved using in vivo electron paramagnetic resonance (EPR) tooth biodosimetry, which measures the number of persistent free radicals that are generated in tooth enamel following irradiation. However, the accuracy of dose estimates may be impacted by individual variations in teeth, especially the amount and distribution of enamel in the inhomogeneous sensitive volume of the resonator used to detect the radicals. In order to study the relationship between interpersonal variations in enamel and EPR-based dose estimates, it is desirable to estimate these parameters nondestructively and without adding radiation to the teeth. Magnetic Resonance Imaging (MRI) is capable of acquiring structural and biochemical information without imparting additional radiation, which may be beneficial for many EPR dosimetry studies. However, the extremely short T2 relaxation time in tooth structures precludes tooth imaging using conventional MRI methods. Therefore, we used zero echo time (ZTE) MRI to image teeth ex vivo to assess enamel volumes and spatial distributions. Using these data in combination with the data on the distribution of the transverse radio frequency magnetic field from electromagnetic simulations, we then can identify possible sources of variations in radiation-induced signals detectable by EPR. Unlike conventional MRI, ZTE applies spatial encoding gradients during the RF excitation pulse, thereby facilitating signal acquisition almost immediately after excitation, minimizing signal loss from short T2 relaxation times. ZTE successfully provided volumetric measures of tooth enamel that may be related to variations that impact EPR dosimetry and facilitate the development

  15. Imaging tooth enamel using zero echo time (ZTE) magnetic resonance imaging

    PubMed Central

    Rychert, Kevin M.; Zhu, Gang; Kmiec, Maciej M.; Nemani, Venkata K.; Williams, Benjamin B.; Flood, Ann Barry; Swartz, Harold M.; Gimi, Barjor

    2015-01-01

    In an event where many thousands of people may have been exposed to levels of radiation that are sufficient to cause the acute radiation syndrome, we need technology that can estimate the absorbed dose on an individual basis for triage and meaningful medical decision making. Such dose estimates may be achieved using in vivo electron paramagnetic resonance (EPR) tooth biodosimetry, which measures the number of persistent free radicals that are generated in tooth enamel following irradiation. However, the accuracy of dose estimates may be impacted by individual variations in teeth, especially the amount and distribution of enamel in the inhomogeneous sensitive volume of the resonator used to detect the radicals. In order to study the relationship between interpersonal variations in enamel and EPR-based dose estimates, it is desirable to estimate these parameters nondestructively and without adding radiation to the teeth. Magnetic Resonance Imaging (MRI) is capable of acquiring structural and biochemical information without imparting additional radiation, which may be beneficial for many EPR dosimetry studies. However, the extremely short T2 relaxation time in tooth structures precludes tooth imaging using conventional MRI methods. Therefore, we used zero echo time (ZTE) MRI to image teeth ex vivo to assess enamel volumes and spatial distributions. Using these data in combination with the data on the distribution of the transverse radio frequency magnetic field from electromagnetic simulations, we then can identify possible sources of variations in radiation-induced signals detectable by EPR. Unlike conventional MRI, ZTE applies spatial encoding gradients during the RF excitation pulse, thereby facilitating signal acquisition almost immediately after excitation, minimizing signal loss from short T2 relaxation times. ZTE successfully provided volumetric measures of tooth enamel that may be related to variations that impact EPR dosimetry and facilitate the development

  16. MEASUREMENT OF TRANSVERSE ECHOES IN RHIC.

    SciTech Connect

    FISCHER, W.; SATOGATA, T.; TOMAS. R.

    2005-05-16

    Beam echoes are a very sensitive method to measure diffusion, and longitudinal echo measurements were performed in a number of machines. In RHIC, for the first time, a transverse beam echo was observed after applying a dipole kick followed by a quadrupole .kick. After application of the dipole kick, the dipole moment decohered completely due to lattice nonlinearities. When a quadrupole kick is applied at time {tau} after the dipole kick, the beam re-cohered at time 2{tau} thus showing an echo response. We describe the experimental setup and measurement results. In the measurements the dipole and quadrupole kick amplitudes, amplitude dependent tune shift, and the time between dipole and quadrupole kick were varied. In addition, measurements were taken with gold bunches of different intensities. These should exhibit different transverse diffusion rates due to intra-beam scattering.

  17. Geometric spin echo under zero field

    NASA Astrophysics Data System (ADS)

    Sekiguchi, Yuhei; Komura, Yusuke; Mishima, Shota; Tanaka, Touta; Niikura, Naeko; Kosaka, Hideo

    2016-05-01

    Spin echo is a fundamental tool for quantum registers and biomedical imaging. It is believed that a strong magnetic field is needed for the spin echo to provide long memory and high resolution, since a degenerate spin cannot be controlled or addressed under a zero magnetic field. While a degenerate spin is never subject to dynamic control, it is still subject to geometric control. Here we show the spin echo of a degenerate spin subsystem, which is geometrically controlled via a mediating state split by the crystal field, in a nitrogen vacancy centre in diamond. The demonstration reveals that the degenerate spin is protected by inherent symmetry breaking called zero-field splitting. The geometric spin echo under zero field provides an ideal way to maintain the coherence without any dynamics, thus opening the way to pseudo-static quantum random access memory and non-invasive biosensors.

  18. Data processing of records of meteoric echoes

    NASA Astrophysics Data System (ADS)

    Dolinský, P.

    2016-01-01

    The data obtained in the period from 4 November 2014 to 31 July 2014 by our receiving and recording system was statistically processed. The system records meteoric echoes from the TV transmitter Lviv 49.739583 MHz (N49.8480° E24.0369°, Ukraine) using a 4-element Yagi antenna with horizontal polarization (elevation of 0° and azimuth of 60°), receiver ICOM R-75 in the CW mode, and a computer with a recording using HROFFT v1.0.0f. The main goal was to identify weak showers in these data. Mayor or strong showers are visible without processing (referred at IMC2015, Mistelbach). To find or to identify weaker showers is more difficult. Not all echoes are meteoric echoes, but also ionospheric echoes or lightning disturbances are present.

  19. Geometric spin echo under zero field

    PubMed Central

    Sekiguchi, Yuhei; Komura, Yusuke; Mishima, Shota; Tanaka, Touta; Niikura, Naeko; Kosaka, Hideo

    2016-01-01

    Spin echo is a fundamental tool for quantum registers and biomedical imaging. It is believed that a strong magnetic field is needed for the spin echo to provide long memory and high resolution, since a degenerate spin cannot be controlled or addressed under a zero magnetic field. While a degenerate spin is never subject to dynamic control, it is still subject to geometric control. Here we show the spin echo of a degenerate spin subsystem, which is geometrically controlled via a mediating state split by the crystal field, in a nitrogen vacancy centre in diamond. The demonstration reveals that the degenerate spin is protected by inherent symmetry breaking called zero-field splitting. The geometric spin echo under zero field provides an ideal way to maintain the coherence without any dynamics, thus opening the way to pseudo-static quantum random access memory and non-invasive biosensors. PMID:27193936

  20. On the nature of radar echoes below 95 km during counter streaming in the equatorial electrojet

    NASA Astrophysics Data System (ADS)

    Tsunoda, Roland T.; Ecklund, Warner L.

    Using data obtained with a 49.92-MHz radar on the island of Pohnpei (Federated States of Micronesia), we show that a weak, westward current exists at the base of the normal eastward electrojet. We suggest that this counter stream is driven by a downward-directed electric field associated with positive-charge accumulation near the base of the eastward electrojet. To explain the existence of radar echoes from this counter-streaming region, where conditions are not conducive to irregularity generation by the gradient-drift instability (GDI), we suggest that “seed” plasma structure may be produced by neutral turbulence. If so, the GDI could act on appropriately directed gradients in plasma density that are associated with the seed structure to generate the secondary type-2 irregularities responsible for the radar echoes.

  1. Estimation of Characteristics of Echo Envelope Using RF Echo Signal from the Liver

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Tadashi; Hachiya, Hiroyuki; Kamiyama, Naohisa; Ikeda, Kazuki; Moriyasu, Norifumi

    2001-05-01

    To realize quantitative diagnosis of liver cirrhosis, we have been analyzing the probability density function (PDF) of echo amplitude using B-mode images. However, the B-mode image is affected by the various signal and image processing techniques used in the diagnosis equipment, so a detailed and quantitative analysis is very difficult. In this paper, we analyze the PDF of echo amplitude using RF echo signal and B-mode images of normal and cirrhotic livers, and compare both results to examine the validity of the RF echo signal.

  2. Pore geometry information via pulsed field gradient NMR.

    PubMed

    Lucas, A J; Gibbs, S J; Peyron, M; Pierens, G K; Hall, L D; Stewart, R C; Phelps, D W

    1994-01-01

    Studies of echo attenuation at long diffusion times in pulsed field gradient NMR experiments on a variety of rock core samples are interpreted in the light of recent theoretical analysis of the effect of pore geometry and surface relaxation. This study is motivated by the need to test the applicability of that theory to real rock systems.

  3. Relaxation of AB Spin Systems in Stimulated-Echo Spectroscopy

    NASA Astrophysics Data System (ADS)

    Straubinger, Klaus; Schick, Fritz; Lutz, Otto

    1995-12-01

    The behavior of the strongly coupled AB spin system during the STEAM (stimulated echo acquisition mode) sequence was calculated analytically. Relaxation during the TM interval, in which longitudinal magnetization and zero-quantum coherences (ZQCs) occur, was accounted for by following the course of the different density-matrix terms. The result allows one to determine sequence timings to provide high signal intensities or signals resulting from certain coherences. Theoretically calculated spectra can be generated, using an analytical function. Series of proton spectra were recorded from a 0.1maqueous solution of citrate on a 1.5 T whole-body imager at 22°C. Spectra series with constant echo time TE were used to evaluate the longitudinal relaxation timeT1as well as the zero-quantum relaxation timeTZQby fitting the theoretically predicted curve to the experimental data. The evaluated proton relaxation timesT1andTZQin citrate differ strongly:T1= 770 ms,TZQ= 1300 ms.

  4. DENSE: Displacement Encoding with Stimulated Echoes in Cardiac Functional MRI

    NASA Astrophysics Data System (ADS)

    Aletras, Anthony H.; Ding, Shujun; Balaban, Robert S.; Wen, Han

    1999-03-01

    Displacement encoding with stimulated echoes (DENSE) was developed for high-resolution myocardial displacement mapping. Pixel phase is modulated by myocardial displacement and data spatial resolution is limited only by pixel size. 2D displacement vector maps were generated for the systolic action in canines with 0.94 × 1.9 mm nominal in-plane resolution and 2.3 mm/π displacement encoding. A radial strain of 0.208 was measured across the free left ventricular wall over 105 ms during systole. DENSE displacement maps require small first-order gradient moments for encoding. DENSE magnitude images exhibit black-blood contrast which allows for better myocardial definition and reduced motion-related artifacts.

  5. Improving the accuracy of pulsed field gradient NMR diffusion experiments: Correction for gradient non-uniformity

    NASA Astrophysics Data System (ADS)

    Connell, Mark A.; Bowyer, Paul J.; Adam Bone, P.; Davis, Adrian L.; Swanson, Alistair G.; Nilsson, Mathias; Morris, Gareth A.

    2009-05-01

    Pulsed field gradient NMR is a well-established technique for the determination of self-diffusion coefficients. However, a significant source of systematic error exists in the spatial variation of the applied pulsed field gradient. Non-uniform pulsed field gradients cause the decay of peak amplitudes to deviate from the expected exponential dependence on gradient squared. This has two undesirable effects: the apparent diffusion coefficient will deviate from the true value to an extent determined by the choice of experimental parameters, and the error estimated by the nonlinear least squares fitting will contain a significant systematic contribution. In particular, the apparent diffusion coefficient determined by exponential fitting of the diffusional attenuation of NMR signals will depend both on the exact pulse widths used and on the range of gradient amplitudes chosen. These problems can be partially compensated for if experimental attenuation data are fitted to a function corrected for the measured spatial dependence of the gradient and signal strength. This study describes a general alternative to existing methods for the calibration of NMR diffusion measurements. The dominant longitudinal variation of the pulsed field gradient amplitude and the signal strength are mapped by measuring pulsed field gradient echoes in the presence of a weak read gradient. These data are then used to construct a predicted signal decay function for the whole sample, which is parameterised as the exponential of a power series. Results are presented which compare diffusion coefficients obtained using the new calibration method with previous literature values.

  6. Characteristics of Meteor Echoes and Preliminary Winds Collected With a Narrow-Beam Radar at Piura, Peru

    NASA Astrophysics Data System (ADS)

    Lau, E. M.; Avery, S. K.; Avery, J. P.

    2002-12-01

    During the mid 1990's a MEDAC system was attached to the VHF wind profiler located in Piura, Peru to detect and collect meteor echoes and provide measurements of winds in the mesosphere-lower thermosphere. The collected data were different from those of similar systems operating at mid-latitudes and other equatorial sites. In particular, the echo rate was relatively low, the echoes were highly aspect sensitive, many of the meteor echoes were relatively weak suggesting the possibility that they were seen through a sidelobe instead of the main lobe of the antenna, and a great deal of activity was observed at nighttime when E-region echoes were also observed. A series of experiments have been designed to better understand the system and the resulting wind measurements. The first experiment was designed to increase the sensitivity of the radar and was conducted during one week in July 2002. Two transmitters were used instead of the single transmitter that normally feeds the transmit antenna on the wind profiler. Data was collected using three different systems: the wind profiler's own acquisition system, the MEDAC system, and a mode in which all data was collected and saved to the hard drive. This poster presents the results of the aforementioned experiment, compares the results provided by each data collection system, outlines the main features of the meteor echoes seen at Piura, and discusses the preliminary wind measurements.

  7. Fast magnetospheric echoes of energetic electron beams

    NASA Technical Reports Server (NTRS)

    Wilhelm, K.; Bernstein, W.; Kellogg, P. J.; Whalen, B. A.

    1985-01-01

    Electron beam experiments using rocketborne instrumentation have confirmed earlier observations of fast magnetospheric echoes of artificially injected energetic electrons. A total of 234 echoes have been observed in a pitch angle range from 9 to 110 deg at energies of 1.87 and 3.90 keV. Out of this number, 95 echoes could unambiguously be identified with known accelerator operations at 2-, 4-, or 8-keV energy and highest current levels resulting in the determination of transit times of typically 300 to 400 ms. In most cases, when echoes were present in both energy channels, the higher-energy electrons led the lower-energy ones by 50 to 70 ms. Adiabatic theory applied to these observations yields a reflection height of 3000 to 4000 km. An alternative interpretation is briefly examined, and its relative merit in describing the observations is evaluated. The injection process is discussed in some detail as the strong beam-plasma interaction that occurred near the electron accelerator appears to be instrumental in generating the source of heated electrons required for successful echo detection for both processes.

  8. Light Echoes of Galactic Explosions and Eruptions

    NASA Astrophysics Data System (ADS)

    Rest, Armin; Bianco, Federica; Chornock, Ryan; Foley, Ryan; Matheson, Thomas; Olsen, Knut; Prieto, Jose Luis; Sinnott, Brendan; Smith, Chris; Smith, Nathan; Welch, Doug

    2013-02-01

    We propose to continue our search for the first light echoes (LEs) associated with historical Galactic supernovae and LBV outbursts: SN 1006, Kepler's SN, RCW 86, Crab Nebula, and P Cygni. In previously granted NOAO time, we have discovered light echoes of three ancient SNe in the LMC as well as from the historic SN events of Cas A and Tycho [2, 3], which allowed their spectroscopic classification [6, 7, 10] and 3D spectroscopy [8, 9]. Most recently, we discovered light echoes of the mid-19th-century Great Eruption of eta Carinae using CTIO 4m Mosaic images [11]. Subsequent spectroscopic follow-up of Eta Carinae revealed that its outburst spectral type was most similar to those of G-type supergiants, rather than reported LBV outburst spectral types of F-type (or earlier) [11]. We propose to continue our search for light echoes of the remaining historical events. With DECam, we have a 10-15 fold improvement in efficiency over the retired Mosaic camera, which allows us to cover the bigger search areas of most of the remaining targets. The study of scattered-light echoes from these Galactic supernovae and eruptions will give us the opportunity to directly compare the original outburst and its current remnant, and in favorable cases (like Eta Carinae), it provides a three-dimensional view of the event and/or a spectral time series.

  9. Transient Loschmidt echo in quenched Ising chains

    NASA Astrophysics Data System (ADS)

    Lupo, Carla; Schiró, Marco

    2016-07-01

    We study the response to sudden local perturbations of highly excited quantum Ising spin chains. The key quantity encoding this response is the overlap between time-dependent wave functions, which we write as a transient Loschmidt Echo. Its asymptotics at long time differences contain crucial information about the structure of the highly excited nonequilibrium environment induced by the quench. We compute the echo perturbatively for a weak local quench but for arbitrarily large global quench, using a cumulant expansion. Our perturbative results suggest that the echo decays exponentially, rather than power law as in the low-energy orthogonality catastrophe, a further example of quench-induced decoherence already found in the case of quenched Luttinger liquids. The emerging decoherence scale is set by the strength of the local potential and the bulk excitation energy.

  10. Coronal plasma-frequency radio echoes?

    NASA Astrophysics Data System (ADS)

    Eremin, A. B.

    1986-06-01

    In the frame of the mechanism of generation of the fundamental mode of type III solar radio bursts suggested by Eremin and Zajtsev (1985) the formation of an echo event in the corona at plasma frequency is shown to be possible. Examples of events are given which were observed during the type IIIb-III radio storm in July, 1974 and may be identified as radio echos. A regular "violet" (in comparison with the primary burst) frequency shift of the echo burst has been detected that results from the radiation reflection from moving inhomogeneities of the solar wind. An estimate of the mean velocity of the solar wind of VSW ≅ 107cm/s at the distance R_sun; from the photosphere is obtained.

  11. Echo Mapping of Active Galactic Nuclei

    NASA Technical Reports Server (NTRS)

    Peterson, B. M.; Horne, K.

    2004-01-01

    Echo mapping makes use of the intrinsic variability of the continuum source in active galactic nuclei to map out the distribution and kinematics of line-emitting gas from its light travel time-delayed response to continuum changes. Echo mapping experiments have yielded sizes for the broad line-emitting region in about three dozen AGNs. The dynamics of the line-emitting gas seem to be dominated by the gravity of the central black hole, enabling measurement of the black-hole masses in AGNs. We discuss requirements for future echo-mapping experiments that will yield the high quality velocity-delay maps of the broad-line region that are needed to determine its physical nature.

  12. Research of laser echo signal simulator

    NASA Astrophysics Data System (ADS)

    Xu, Rui; Shi, Rui; Wang, Xin; Li, Zhou

    2015-11-01

    Laser echo signal simulator is one of the most significant components of hardware-in-the-loop (HWIL) simulation systems for LADAR. System model and time series model of laser echo signal simulator are established. Some influential factors which could induce fixed error and random error on the simulated return signals are analyzed, and then these system insertion errors are analyzed quantitatively. Using this theoretical model, the simulation system is investigated experimentally. The results corrected by subtracting fixed error indicate that the range error of the simulated laser return signal is less than 0.25m, and the distance range that the system can simulate is from 50m to 20km.

  13. Evolution of entanglement under echo dynamics

    NASA Astrophysics Data System (ADS)

    Prosen, Tomaž; Seligman, Thomas H.; Žnidarič, Marko

    2003-04-01

    Echo dynamics and fidelity are often used to discuss stability in quantum-information processing and quantum chaos. Yet fidelity yields no information about entanglement, the characteristic property of quantum mechanics. We study the evolution of entanglement in echo dynamics. We find qualitatively different behavior between integrable and chaotic systems on one hand and between random and coherent initial states for integrable systems on the other. For the latter the evolution of entanglement is given by a classical time scale. Analytic results are illustrated numerically in a Jaynes-Cummings model.

  14. Measurement of excited-state lifetime using two-pulse photon echoes in rubidium vapor

    SciTech Connect

    Rotberg, E. A.; Barrett, B.; Beattie, S.; Chudasama, S.; Weel, M.; Chan, I.; Kumarakrishnan, A.

    2007-03-15

    We report a measurement of the 5P{sub 3/2} excited-state lifetime using two-pulse photon echoes in Rb vapor. The measurement is precise to {approx}1% and agrees with the best measurement of atomic lifetime in Rb. The results suggest that a measurement precise to {approx}0.25% is possible through additional data acquisition and study of systematic effects. The experiment relies on short optical pulses generated from a cw laser using acousto-optic modulators. The excitation pulses are on resonance with the F=3{yields}F{sup '}=4 transition in {sup 85}Rb or the F=2{yields}F{sup '}=3 transition in {sup 87}Rb. The resulting photon echo signal is detected using a heterodyne detection technique. The excited-state lifetime is determined by measuring the exponential decay of the echo intensity as a function of the time between the excitation pulses. We also present a study of the echo intensity as a function of excitation pulse area and compare the results to simulations based on optical Bloch equations. The simulations include the effects of spontaneous emission as well as spatial and temporal variations of the intensities of excitation pulses.

  15. Multi-Echo Segmented k-space Imaging: An Optimized Hybrid Sequence for Ultrafast Cardiac Imaging

    PubMed Central

    Reeder, Scott B.; Atalar, Ergin; Faranesh, Anthony Z.; McVeigh, Elliot R.

    2007-01-01

    Cardiac magnetic resonance imaging requires high temporal resolution to resolve motion and contrast uptake with low total scan times to avoid breathing artifacts. While spoiled gradient echo (SPGR) imaging is robust and reproducible, it is relatively inefficient and requires long breath-holds to acquire high time resolution movies of the heart. Echo planar imaging (EPI) is highly efficient with excellent signal-to-noise ratio (SNR) behavior; however, it is particularly difficult to use in the heart because of its sensitivity to chemical shift, susceptibility, and motion. EPI may also require reference scans, which are used to measure hardware delays and phase offsets that cause ghosting artifacts; these reference scans are more difficult and less reliable in the heart. Consequently, a hybrid EPI/SPGR sequence is proposed for application to rapid cardiac imaging. A detailed optimization of SNR and echo train length for multi-echo sequences is presented. It is shown that significant reductions in total scan time are possible while maintaining good image quality. This will allow complete motion sampling of the entire heart in one to three breath-holds, necessary for MR cardiac dobutamine stress testing. Improved speed performance also permits sampling of three to six slices every heartbeat for bolus injection perfusion studies. PMID:10080287

  16. Empirical results of using back-propagation neural networks to separate single echoes from multiple echoes.

    PubMed

    Chang, W; Bosworth, B; Carter, G C

    1993-01-01

    Empirical results illustrate the pitfalls of applying an artificial neural network (ANN) to classification of underwater active sonar returns. During training, a back-propagation ANN classifier learns to recognize two classes of reflected active sonar waveforms: waveforms having two major sonar echoes or peaks and those having one major echo or peak. It is shown how the classifier learns to distinguish between the two classes. Testing the ANN classifier with different waveforms of each type generated unexpected results: the number of echo peaks was nor the feature used to separate classes.

  17. The first in-situ observations of echoing HF radar backscatter targets

    NASA Astrophysics Data System (ADS)

    Moen, J. I.; Oksavik, K.; Abe, T.; Lester, M.; Saito, Y.; Bekkeng, J. K.; Jacobsen, K. S.; Bekkeng, T. A.

    2010-12-01

    The first direct measurements of HF-backscatter echoing electron density structures were conduced by the ICI-2 sounding rocket launched into the cusp ionosphere over Svalbard 5 December 2008. The echoing targets for coherent HF radars are 10-m scale electron density structures, half the operating radar wave length. Descending from ~300-200 km altitude, ICI-2 traversed volumes of HF backscatter detected by the CUTLASS radar, near the poleward boundary of the active cusp. ICI-2 carried a novel 4-Needle Langmuir Probe system capable to measure absolute electron density at 5.7 kHz sampling rate which means sub-meter resolution along the trajectory. The payload was also equipped with a high resolution electron spectrometer to resolve fine scale structures in the cusp auroral precipitation, and it carried an electric field experiment to measure the plasma drift surrounding the space craft. The 10-m plasma irregularities were observed near the trailing edge of km scale gradients in the electron density, which is in favour of the gradient drift instability. The electron density gradients on which the gradient drift instability could operate were apparently modulated by the electron precipitation. Furthermore, plasma structuring also occurred near the centre of the inverted V electron beam, indicating that a current driven instability process is also to be considered.

  18. Solid-State NMR Imaging by Tetrahedral-Magic-Echo Time-Suspension Sequences

    NASA Astrophysics Data System (ADS)

    Matsui, S.; Uraoka, A.; Inouye, T.

    A new approach to solid-state imaging using tetrahedral magic echoes (TME) is proposed and compared with the previously reported modified-magic-echo (MME) approaches. The comparison has shown that for common organic solids, where the homonuclear 1H- 1H dipolar interaction is dominant, the degree of TME line narrowing is nearly the same as that of time-suspended MME line narrowing; however, the TME narrowing is substantially superior to the MME narrowing for solids where the heteronuclear dipolar interaction between 1H and a second spin species is comparable in magnitude to the homonuclear 1H- 1H dipolar interaction. This superiority stems from the fact that the homonuclear and hereronuclear interactions do not commute with each other. The TME approach further possesses certain practical advantages over the MME approaches. For example, the optional application of gradient pulses during the RF irradiation periods in the TME sequences increases the scaling factor of the gradient amplitude from {1}/{4} to {1}/{2}, making the gradient switching easier. No apparent deterioration of the TME line-narrowing by the optional gradient application was noted.

  19. On the reliability of hook echoes as tornado indicators

    NASA Technical Reports Server (NTRS)

    Forbes, G. S.

    1981-01-01

    A study of radar echoes associated with the tornadoes of the 3 April 1974 outbreak was performed to evaluate the usefulness of echo shape as an indicator of tornadic thunderstorms. The hook shape was usually successful in characterizing an echo as tornadic, with a false alarm rate of 16%. Because hook echoes were relatively rare, however, a less restrictive shape called distinctive was more successful at detecting tornadic thunderstorms, identifying 65% of the tornadic echoes. An echo had a distinctive shape if it possessed a marked appendage on its right rear flank or was in the shape of a spiral, comma or line echo wave pattern (LEWP). Characteristics of the distinctive echo are given.

  20. Relationship between tornadoes and hook echoes on April 3, 1974

    NASA Technical Reports Server (NTRS)

    Forbes, G. S.

    1975-01-01

    Radar observations of tornado families occurring on April 3, 1974 are discussed. Of the 93 tornadoes included in the sample, 81% were associated with hook-like echoes with appendages at least 40 deg to the south of the echo movement. At least one tornado was associated with 62% of the hook-like echoes observed. All of the tornadoes with intensities of F 4 and F 5 were produced by hook-like echoes; the mean intensity of all tornadoes associated with this type of echo was F 3, while the mean intensity of the remaining tornadoes was F1. The tornadic hook-like echoes moved to the right of the non-tornadic echoes forming a tornado line in advance of the squall line. Some tornadoes were associated with 'spiral' echoes.

  1. Time-efficient fast spin echo imaging at 4.7 T with low refocusing angles.

    PubMed

    Lebel, R Marc; Wilman, Alan H

    2009-07-01

    An implementation of fast spin echo at 4.7 T designed for versatile and time-efficient T(2)-weighted imaging of the human brain is presented. Reduced refocusing angles (alpha < 180 degrees) were employed to overcome specific absorption rate (SAR) constraints and their effects on image quality assessed. Image intensity and tissue contrast variations from heterogeneous RF transmit fields and incidental magnetization transfer effects were investigated at reduced refocusing angles. We found that intraslice signal variations are minimized with refocusing angles near 180 degrees, but apparent gray/white matter contrast is independent of refocusing angle. Incidental magnetization transfer effects from multislice acquisitions were shown to attenuate white matter intensity by 25% and gray matter intensity by 15% at 180 degrees; less than 5% attenuation was seen in all tissues at flip angles below 60 degrees. We present multislice images acquired without excess delay time for SAR mitigation using a variety of protocols. Subsecond half Fourier acquisition single-shot turbo spin echo (HASTE) images were obtained with a novel variable refocusing angle echo train (20 degrees < alpha < 58 degrees) and high-resolution scans with a voxel volume of 0.18 mm(3) were acquired in 6.5 min with refocusing angles of 100 degrees.

  2. Asymmetric radar echo patterns from insects

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Radar echoes from insects, birds, and bats in the atmosphere exhibit both symmetry and asymmetry in polarimetric patterns. Symmetry refers to similar magnitudes of polarimetric variables at opposite azimuths, and asymmetry relegates to differences in these magnitudes. Asymmetry can be due to diffe...

  3. Light Echoes of Galactic Explosions and Eruptions

    NASA Astrophysics Data System (ADS)

    Rest, Armin; Bianco, Federica; Chornock, Ryan; Foley, Ryan; Matheson, Thomas; Narayan, Gautham; Olsen, Knut; Prieto, Jose Luis; Smith, Chris; Smith, Nathan; Suntzeff, Nick; Welch, Doug; Zenteno, Alfredo

    2014-02-01

    We propose to continue our search for the first light echoes (LEs) associated with historical Galactic supernovae and LBV outbursts: SN 1006, Kepler's SN, RCW 86, Crab Nebula, and P Cygni. In previously granted NOAO time, we have discovered LEs of three ancient SNe in the LMC as well as from the historic SN events of Cas A and Tycho [2, 3], which allowed their spectroscopic classification [6, 7, 10] and 3D spectroscopy [8, 9]. Most recently, we discovered light echoes of the mid-19th-century Great Eruption of η Carinae using CTIO 4m Mosaic images [11]. Subsequent spectroscopic follow-up of Eta Carinae revealed that its outburst spectral type was most similar to those of G-type supergiants, rather than reported LBV outburst spectral types of F-type (or earlier) [11]. We propose to continue our search for light echoes of the remaining historical events. With DECam, we have a 10-15 fold improvement in efficiency over the retired CTIO-Mosaic camera, which allows us to cover the bigger search areas of most of the remaining targets. With the KPNO 4-m, we will observe fields too far north for CTIO/DECam. The study of scattered-light echoes from these Galactic supernovae and eruptions will give us the opportunity to directly compare the original outburst and its current remnant, and in favorable cases (like Eta Carinae), it provides a three-dimensional view of the event and/or a spectral time series.

  4. AN ECHO OF SUPERNOVA 2008bk

    SciTech Connect

    Van Dyk, Schuyler D.

    2013-08-01

    I have discovered a prominent light echo around the low-luminosity Type II-plateau supernova (SN) 2008bk in NGC 7793, seen in archival images obtained with the Wide Field Channel of the Advanced Camera for Surveys on board the Hubble Space Telescope (HST). The echo is a partial ring, brighter to the north and east than to the south and west. The analysis of the echo I present suggests that it is due to the SN light pulse scattered by a sheet, or sheets, of dust located Almost-Equal-To 15 pc from the SN. The composition of the dust is assumed to be of standard Galactic diffuse interstellar grains. The visual extinction of the dust responsible for the echo is A{sub V} Almost-Equal-To 0.05 mag in addition to the extinction due to the Galactic foreground toward the host galaxy. That the SN experienced much less overall extinction implies that it is seen through a less dense portion of the interstellar medium in its environment. The late-time HST photometry of SN 2008bk also clearly demonstrates that the progenitor star has vanished.

  5. Preliminary Results of the Echo-Seeding Experiment ECHO-7 at SLAC

    SciTech Connect

    Xiang, D.; Colby, E.; Ding, Y.; Dunning, M.; Frederico, J.; Gilevich, S.; Hast, C.; Jobe, K.; McCormick, D.; Nelson, J.; Raubenheimer, T.O.; Soong, K.; Stupakov, G.; Szalata, Z.; Walz, D.; Weathersby, S.; Woodley, M.; Corlett, J.; Qiang, J.; Penn, G.; Prestemon, S.; /LBL, Berkeley /LPHE, Lausanne

    2010-06-15

    ECHO-7 is a proof-of-principle echo-enabled harmonic generation FEL experiment in the Next Linear Collider Test Accelerator (NLCTA) at SLAC. The experiment aims to generate coherent radiation at 318 nm and 227 nm, which are the 5th and 7th harmonic of the infrared seed laser. In this paper we present the preliminary results from the commissioning run of the completed experimental setup which started in April 2010.

  6. 21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1560 Ultrasonic pulsed echo imaging system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended to project a... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Ultrasonic pulsed echo imaging system....

  7. 21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1560 Ultrasonic pulsed echo imaging system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended to project a... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Ultrasonic pulsed echo imaging system....

  8. 21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Ultrasonic pulsed echo imaging system. 892.1560... (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1560 Ultrasonic pulsed echo imaging system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended to project...

  9. The Exoplanet Characterisation Observatory (EChO) payload electronics

    NASA Astrophysics Data System (ADS)

    Focardi, M.; Pancrazzi, M.; Di Giorgio, A. M.; Pezzuto, S.; Micela, G.; Pace, E.

    2012-09-01

    The EChO Payload is an integrated spectrometer designed to cover the 0.55-16 μm (11 to 16 μm as a goal) wavelength band, subdivided into 5 channels from visible to thermal IR with a common set of optics spectrally dividing the field of view by means of dichroics and a unique electronics interface to the spacecraft, the Data Control Unit (DCU). DCU is mainly a digital unit with processing capabilities based on a rad-hard space qualified processor running the main Application SW (the scientific SW) and some programmable logics. DCU will host the detector’s warm front-end electronics (FEEs) and its main tasks are to implement the payload instruments commanding, the science and housekeeping (HK) data acquisition, conversion and packetisation, the onboard spectra pre-processing, and, finally, to provide finely regulated voltage levels to FEEs. Detector’s proximity cold electronics send analog data and HKs to DCU for digital conversion by sharing a redundant ADC aboard DCU. Analog HKs are previously multiplexed, elaborated and converted to digital format before sending them to the satellite platform, via the SpaceWire (SpW) links. DCU controls the FEEs syncronization (interpreting and routing sync signals and time stamps sent by OBC by means of SpW Time Codes) and runs the main logics to perform all the required tasks and memory management. The EChO DCU electronics basically focuses on the data and command flows, the clock/synchronization and power distribution network and on an overall architecture for a trade-off solution removing or reducing any electronics single-point failure.

  10. Manifestation of the geometric phase in neutron spin-echo experiments

    NASA Astrophysics Data System (ADS)

    Kraan, W. H.; Grigoriev, S. V.; Rekveldt, M. T.

    2010-07-01

    We show how the geometric (Berry’s) phase becomes manifest on adiabatic rotation of the polarization vector in the magnetic field configuration in the arms in a neutron spin echo (NSE) experiment. When the neutron beam used is monochromatic, a geometric phase collected in one spin-echo arm can be exactly compensated in the other arm either by an opposite geometrical rotation or by adding/subtracting a dynamic (Larmor) phase. This is not possible in a white beam, because, contrary to the dynamic phase, the geometric phase is independent of wavelength. Therefore, the NSE pattern can be disturbed. We demonstrate that adiabatic resonant spin flippers inherently produce a geometric phase which can influence the performance of NSE setups based on such flippers. This effect can be avoided by a proper mutual symmetry of the gradient fields in these flippers.

  11. 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.

  12. Preliminary study of the EChO data sampling and processing

    NASA Astrophysics Data System (ADS)

    Farina, M.; Di Giorgio, A. M.; Focardi, M.; Pace, E.; Micela, G.; Galli, E.; Giusi, G.; Liu, S. J.; Pezzuto, S.

    2014-08-01

    The EChO Payload is an integrated spectrometer with six different channels covering the spectral range from the visible up to the thermal infrared. A common Instrument Control Unit (ICU) implements all the instrument control and health monitoring functionalities as well as all the onboard science data processing. To implement an efficient design of the ICU on board software, separate analysis of the unit requirements are needed for the commanding and housekeeping collection as well as for the data acquisition, sampling and compression. In this work we present the results of the analysis carried out to optimize the EChO data acquisition and processing chain. The HgCdTe detectors used for EChO mission allow for non-destructive readout modes, such that the charge may be read without removing it after reading out. These modes can reduce the equivalent readout noise and the gain in signal to noise ratio can be computed using well known relations based on fundamental principles. In particular, we considered a multiaccumulation approach based on non-destructive reading of detector samples taken at equal time intervals. All detectors are periodically reset after a certain number of samples have been acquired and the length of the reset interval, as well as the number of samples and the sampling rate can be adapted to the brightness of the considered source. The estimation of the best set of parameters for the signal to noise ratio optimization and of the best sampling technique has been done by taking into account also the needs of mitigating the expected radiation effects on the acquired data. Cosmic rays can indeed be one of the major sources of data loss for a space observatory, and the studies made for the JWST mission allowed us to evaluate the actual need of the implementation of a dedicated deglitching procedure on board EChO.

  13. Intensity-Corrected Dual-Echo Echo-Planar Imaging (DE-EPI) for Improved Pediatric Brain Diffusion Imaging

    PubMed Central

    Straka, Matus; Iv, Michael; Moseley, Michael E.; Barnes, Patrick D.; Skare, Stefan

    2015-01-01

    Here we investigate the utility of a dual-echo Echo-Planar Imaging (DE-EPI) Diffusion Weighted Imaging (DWI) approach to improve lesion conspicuity in pediatric imaging. This method delivers two ‘echo images’ for one diffusion-preparation period. We also demonstrate how the echoes can be utilized to remove transmit/receive coil-induced and static magnetic field intensity modulations on both echo images, which often mimic pathology and thereby pose diagnostic challenges. DE-EPI DWI data were acquired in 18 pediatric patients with abnormal diffusion lesions, and 46 pediatric patient controls at 3T. Echo1 [TE = 45ms] and Echo2 [TE = 86ms] were corrected for signal intensity variation across the images by exploiting the images equivalent coil-sensitivity and susceptibility-induced modulations. Two neuroradiologists independently reviewed Echo1 and Echo2 and their intensity-corrected variants (cEcho1 and cEcho2) on a 7-point Likert scale, with grading on lesion conspicuity diagnostic confidence. The apparent diffusion coefficient (ADC) map from Echo1 was used to validate presence of true pathology. Echo2 was unanimously favored over Echo1 for its sensitivity for detecting acute brain injury, with a mean respective lesion conspicuity of 5.7/4.4 (p < 0.005) and diagnostic confidence of 5.1/4.3 (p = 0.025). cEcho2 was rated higher than cEcho1, with a mean respective lesion conspicuity of 5.5/4.3 (p < 0.005) and diagnostic confidence of 5.4/4.4 (p < 0.005). cEcho2 was favored over all echoes for its diagnostic reliability, particularly in regions close to the head coil. This work concludes that DE-EPI DWI is a useful alternative to conventional single-echo EPI DWI, whereby Echo2 and cEcho2 allows for improved lesion detection and overall higher diagnostic confidence. PMID:26069959

  14. Artifact reduction in moving-table acquisitions using parallel imaging and multiple averages.

    PubMed

    Fautz, H P; Honal, M; Saueressig, U; Schäfer, O; Kannengiesser, S A R

    2007-01-01

    Two-dimensional (2D) axial continuously-moving-table imaging has to deal with artifacts due to gradient nonlinearity and breathing motion, and has to provide the highest scan efficiency. Parallel imaging techniques (e.g., generalized autocalibrating partially parallel acquisition GRAPPA)) are used to reduce such artifacts and avoid ghosting artifacts. The latter occur in T(2)-weighted multi-spin-echo (SE) acquisitions that omit an additional excitation prior to imaging scans for presaturation purposes. Multiple images are reconstructed from subdivisions of a fully sampled k-space data set, each of which is acquired in a single SE train. These images are then averaged. GRAPPA coil weights are estimated without additional measurements. Compared to conventional image reconstruction, inconsistencies between different subsets of k-space induce less artifacts when each k-space part is reconstructed separately and the multiple images are averaged afterwards. These inconsistencies may lead to inaccurate GRAPPA coil weights using the proposed intrinsic GRAPPA calibration. It is shown that aliasing artifacts in single images are canceled out after averaging. Phantom and in vivo studies demonstrate the benefit of the proposed reconstruction scheme for free-breathing axial continuously-moving-table imaging using fast multi-SE sequences.

  15. Single Acquisition Electrical Property Mapping Based on Relative Coil Sensitivities: A Proof-of-Concept Demonstration

    PubMed Central

    Marques, José P.; Sodickson, Daniel K.; Ipek, Ozlem; Collins, Christopher M.; Gruetter, Rolf

    2015-01-01

    Purpose All methods presented to date to map both conductivity and permittivity rely on multiple acquisitions to compute quantitatively the magnitude of radiofrequency transmit fields, B1+. In this work, we propose a method to compute both conductivity and permittivity based solely on relative receive coil sensitivities (B1−) that can be obtained in one single measurement without the need to neither explicitly perform transmit/receive phase separation nor make assumptions regarding those phases. Theory and Methods To demonstrate the validity and the noise sensitivity of our method we used electromagnetic finite differences simulations of a 16-channel transceiver array. To experimentally validate our methodology at 7 Tesla, multi compartment phantom data was acquired using a standard 32-channel receive coil system and two-dimensional (2D) and 3D gradient echo acquisition. The reconstructed electric properties were correlated to those measured using dielectric probes. Results The method was demonstrated both in simulations and in phantom data with correlations to both the modeled and bench measurements being close to identity. The noise properties were modeled and understood. Conclusion The proposed methodology allows to quantitatively determine the electrical properties of a sample using any MR contrast, with the only constraint being the need to have 4 or more receive coils and high SNR. PMID:25099920

  16. Artifact reduction in moving-table acquisitions using parallel imaging and multiple averages.

    PubMed

    Fautz, H P; Honal, M; Saueressig, U; Schäfer, O; Kannengiesser, S A R

    2007-01-01

    Two-dimensional (2D) axial continuously-moving-table imaging has to deal with artifacts due to gradient nonlinearity and breathing motion, and has to provide the highest scan efficiency. Parallel imaging techniques (e.g., generalized autocalibrating partially parallel acquisition GRAPPA)) are used to reduce such artifacts and avoid ghosting artifacts. The latter occur in T(2)-weighted multi-spin-echo (SE) acquisitions that omit an additional excitation prior to imaging scans for presaturation purposes. Multiple images are reconstructed from subdivisions of a fully sampled k-space data set, each of which is acquired in a single SE train. These images are then averaged. GRAPPA coil weights are estimated without additional measurements. Compared to conventional image reconstruction, inconsistencies between different subsets of k-space induce less artifacts when each k-space part is reconstructed separately and the multiple images are averaged afterwards. These inconsistencies may lead to inaccurate GRAPPA coil weights using the proposed intrinsic GRAPPA calibration. It is shown that aliasing artifacts in single images are canceled out after averaging. Phantom and in vivo studies demonstrate the benefit of the proposed reconstruction scheme for free-breathing axial continuously-moving-table imaging using fast multi-SE sequences. PMID:17191244

  17. On gradient field theories: gradient magnetostatics and gradient elasticity

    NASA Astrophysics Data System (ADS)

    Lazar, Markus

    2014-09-01

    In this work, the fundamentals of gradient field theories are presented and reviewed. In particular, the theories of gradient magnetostatics and gradient elasticity are investigated and compared. For gradient magnetostatics, non-singular expressions for the magnetic vector gauge potential, the Biot-Savart law, the Lorentz force and the mutual interaction energy of two electric current loops are derived and discussed. For gradient elasticity, non-singular forms of all dislocation key formulas (Burgers equation, Mura equation, Peach-Koehler stress equation, Peach-Koehler force equation, and mutual interaction energy of two dislocation loops) are presented. In addition, similarities between an electric current loop and a dislocation loop are pointed out. The obtained fields for both gradient theories are non-singular due to a straightforward and self-consistent regularization.

  18. Spatial release from simultaneous echo masking in bat sonar.

    PubMed

    Warnecke, Michaela; Bates, Mary E; Flores, Victoria; Simmons, James A

    2014-05-01

    Big brown bats (Eptesicus fuscus) use biosonar to navigate and locate objects in their surroundings. During natural foraging, they often encounter echoes returned by a target of interest located to the front while other, often stronger, clutter echoes are returned from objects, such as vegetation, located to the sides or above. Nevertheless, bats behave as if they do not suffer interference from this clutter. Using a two-choice delay discrimination procedure, bats were tested for the masking effectiveness of clutter echoes on target echoes when the target echoes were delivered from the bat's front while clutter echoes were delivered from 90° overhead, a direction of lowpass filtering by the external ears. When clutter echoes are presented from the front at the same delay as target echoes, detection performance declines and clutter masking occurs. When the clutter echoes are presented at the same delay but from overhead, discrimination performance is unaffected and no masking occurs. Thus there is masking release for simultaneous off-axis lowpass clutter compared to masking by simultaneous clutter from the front. The bat's performance for simultaneous target and clutter echoes indicates a new role for the mechanism that separates overlapping echoes by decomposing the bat's auditory time-frequency representation.

  19. The relationship between fireballs and HRO Long Echos

    NASA Astrophysics Data System (ADS)

    Yanagida, E.; Amikura, S.

    Ham-band Radio Observation (HRO) is one of the major methods used to observe meteor activity in Japan. We receive certain types of meteor echoes. One of the types is the long-lasting echo called a ``Long Echo''. We have the impression that Long Echoes correspond to fireballs. The present research found this relation and tried to identify fireball data from visual observations with Long Echo data of the 2002 Leonids, Geminids, and Quadrantids. From these data, we found that the identification percentage tended to be higher for fainter magnitudes, but that the percentage is small, the percentages of each meteor stream being less than 30 %. From these results, this research found that we could not simply say that brighter meteors were received as Long Echoes. It depends on the geocentric velocity of the meteor stream, with a possibility that Long Echoes correspond to darker as well as brighter fireballs.

  20. Stark echo modulation for quantum memories

    NASA Astrophysics Data System (ADS)

    Arcangeli, A.; Ferrier, A.; Goldner, Ph.

    2016-06-01

    Quantum memories for optical and microwave photons provide key functionalities in quantum processing and communications. Here we propose a protocol well adapted to solid-state ensemble-based memories coupled to cavities. It is called Stark echo modulation memory (SEMM) and allows large storage bandwidths and low noise. This is achieved in an echo-like sequence combined with phase shifts induced by small electric fields through the linear Stark effect. We investigated the protocol for rare-earth nuclear spins and found a high suppression of unwanted collective emissions that is compatible with single-photon-level operation. Broadband storage together with high fidelity for the Stark retrieval process is also demonstrated. SEMM could be used to store optical or microwave photons in ions and/or spins. This includes nitrogen-vacancy centers in diamond and rare-earth-doped crystals, which are among the most promising solid-state quantum memories.

  1. Light-echo spectroscopy of historic Supernovae

    NASA Astrophysics Data System (ADS)

    Krause, Oliver

    Young Galactic supernova remnants are unique laboratories for supernova physics. Due to their proximity they provide us with the most detailed view of the outcome of a supernova. However, the exact spectroscopic types of their original explosions have been undetermined so far -hindering to link the wealth of multi-wavelength knowledge about their remnants with the diverse population of supernovae. Light echoes, reflektions of the brilliant supernova burst of light by interstellar dust, provide a unique opportunity to reobserve today -with powerful scientific instruments of the 21st century -historic supernova exlosions even after hundreds of years and to conclude on their nature. We report on optical light-echo spectroscopy of two famous Galactic supernovae: Tycho Brahe's SN 1572 and the supernova that created the Cassiopeia A remnant around the year 1680. These observations finally recovered the missing spectroscopic classifications and provide new constraints on explosion models for future studies.

  2. Statistical properties of bistatic clutter echoes

    NASA Astrophysics Data System (ADS)

    Stevens, William G.; Rangaswamy, Muralidhar

    1994-03-01

    In this report we present statistical results of bistatic terrain reflectivity measurements. A new technique for estimating statistical properties from limited data sets was used to examine underlying temporal probability density functions (PDFs) and correlation properties of echoes from several clutter range resolution bins. The case of locally vertically incident-vertically received signal polarization is reported for a single bistatic geometry. The terrain in the experiment consisted primarily of early-development deciduous trees. 10-15 feet high and brush approximately 8 feet high. The measurement system was a high resolution instrumentation radar operating at 3.2 GHz. Results from the estimation algorithm showed that there were small groups of contiguous clutter cells where the members within the group could be described by the same family of PDFs. while other PDF families would best describe neighboring clutter cell groups. Algorithm results for all tested clutter cells showed that the high-resolution, bistatic echoes were non-Rayleigh distributed.

  3. Light Echo From Star V838 Monocerotis

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This photo, captured by the NASA Hubble Space Telescope's (HST) Advanced Camera for Surveys, is Hubble's latest view of an expanding halo of light around the distant star V838 Monocerotis, or V Mon, caused by an unusual stellar outburst that occurred back in January 2002. A burst of light from the bizarre star is spreading into space and reflecting off of surrounding circumstellar dust. As different parts are sequentially illuminated, the appearance of the dust changes. This effect is referred to as a 'light echo'. Located about 20,000 light-years away in the winter constellation Monoceros (the Unicorn), the star brightened to more than 600,000 times our Sun's luminosity. The light echo gives the illusion of contracting, until it finally disappears by the end of the decade.

  4. Ultrasonic unipolar pulse/echo instrument

    DOEpatents

    Hughes, Michael S.; Hsu, David K.; Thompson, Donald O.; Wormley, Samuel J.

    1993-01-01

    An ultrasonic unipolar pulse/echo instrument uses active switches and a timing and drive circuitry to control electrical energy to a transducer, the discharging of the transducer, and the opening of an electrical pathway to the receiving circuitry for the returning echoes. The active switches utilize MOSFET devices along with decoupling circuitry to insure the preservation of the unipolar nature of the pulses, insure fast transition times, and maintain broad band width and time resolution. A housing contains the various circuitry and switches and allows connection to a power supply and a movable ultrasonic transducer. The circuitry maintains low impedance input to the transducer during transmitting cycles, and high impedance between the transducer and the receiving circuit during receive cycles to maintain the unipolar pulse shape. A unipolar pulse is valuable for nondestructive evaluation, a prime use for the present instrument.

  5. Ultrasonic unipolar pulse/echo instrument

    DOEpatents

    Hughes, M.J.; Hsu, D.K.; Thompson, D.O.; Wormley, S.J.

    1993-04-06

    An ultrasonic unipolar pulse/echo instrument uses active switches and a timing and drive circuitry to control electrical energy to a transducer, the discharging of the transducer, and the opening of an electrical pathway to the receiving circuitry for the returning echoes. The active switches utilize MOSFET devices along with decoupling circuitry to insure the preservation of the unipolar nature of the pulses, insure fast transition times, and maintain broad band width and time resolution. A housing contains the various circuitry and switches and allows connection to a power supply and a movable ultrasonic transducer. The circuitry maintains low impedance input to the transducer during transmitting cycles, and high impedance between the transducer and the receiving circuit during receive cycles to maintain the unipolar pulse shape. A unipolar pulse is valuable for nondestructive evaluation, a prime use for the present instrument.

  6. The electron Echo 6 mechanical deployment systems

    NASA Technical Reports Server (NTRS)

    Meyers, S. C.; Steffen, J. E.; Malcolm, P. R.; Winckler, J. R.

    1984-01-01

    The Echo 6 sounding rocket payload was flown on a Terrier boosted Black Brant vehicle on March 30, 1983. The experiment requirements resulted in the new design of a rocket propelled Throw Away Detector System (TADS) with onboard Doppler radar, a free-flyer forward experiment designated the Plasma Diagnostic Package (PDP), and numerous other basic systems. The design, developmental testing, and flight preparations of the payload and the mechanical deployment systems are described.

  7. The Light Echoes around V838 Monocerotis

    NASA Astrophysics Data System (ADS)

    Bond, Howard

    2009-07-01

    V838 Monocerotis, which burst upon the astronomical scene in early 2002, is a completely unanticipated new object. It underwent a large-amplitude and very luminous outburst, during which its spectrum remained that of an extremely cool supergiant. A rapidly evolving set of light echoes around V838 Mon was discovered soon after the outburst, and quickly became the most spectacular display of the phenomenon yet seen. These light echoes provide the means to accomplish three unique types of measurements based on continued HST imaging during the event: {1} Study effects of MHD turbulence at high resolution and in 3 dimensions; {2} Construct the first unambiguous and fully 3-D map of a circumstellar dust envelope in the Milky Way; {3} Study dust physics in a unique setting where the spectrum and light curve of the illumination, and the scattering angle, are unambiguously known. We have also used our HST data to determine the distance to V838 Mon through a novel direct geometric technique. Because of the extreme rarity of light echoes, this is almost certainly the only opportunity to achieve such results during the lifetime of HST. We propose two visits during Cycle 17, using the repaired ACS {or WFC3} in order to continue the mapping of the circumstellar dust and to accomplish the other goals listed above.

  8. The Light Echoes around V838 Monocerotis

    NASA Astrophysics Data System (ADS)

    Bond, Howard

    2007-07-01

    V838 Monocerotis, which burst upon the astronomical scene in early 2002, is a completely unanticipated new object. It underwent a large-amplitude and very luminous outburst, during which its spectrum remained that of an extremely cool supergiant. A rapidly evolving set of light echoes around V838 Mon was discovered soon after the outburst, and quickly became the most spectacular display of the phenomenon ever seen. These light echoes provide the means to accomplish three unique types of measurements based on continued HST imaging during the event: {1} Study effects of MHD turbulence at high resolution and in 3 dimensions; {2} Construct the first unambiguous and fully 3-D map of a circumstellar dust envelope in the Milky Way; {3} Study dust physics in a unique setting where the spectrum and light curve of the illumination, and the scattering angle, are unambiguously known. We have also used our HST data to determine the distance to V838 Mon through direct geometric techniques. Because of the extreme rarity of light echoes, this is almost certainly the only opportunity to achieve such results during the lifetime of HST. We propose two visits during Cycle 16, in order to continue the mapping of the circumstellar dust and to accomplish the other goals listed above.

  9. The Light Echoes around V838 Monocerotis

    NASA Astrophysics Data System (ADS)

    Bond, Howard

    2010-09-01

    V838 Monocerotis, which burst upon the astronomical scene in early 2002, is a completely unanticipated new object. It underwent a large-amplitude and very luminous outburst, during which its spectrum remained that of an extremely cool supergiant. A rapidly evolving set of light echoes around V838 Mon was discovered soon after the outburst, and quickly became the most spectacular display of the phenomenon yet seen. These light echoes provide the means to accomplish three unique types of measurements based on continued HST imaging during the event: {1} Study effects of MHD turbulence at high resolution and in 3 dimensions; {2} Construct the first unambiguous and fully 3-D map of a circumstellar dust envelope in the Milky Way; {3} Study dust physics in a unique setting where the spectrum and light curve of the illumination, and the scattering angle, are unambiguously known. We have also used our HST data to determine the distance to V838 Mon through a novel direct geometric technique. Because of the extreme rarity of light echoes, this is almost certainly the only opportunity to achieve such results during the lifetime of HST. We propose one visit during Cycle 18, using ACS, in order to continue the mapping of the circumstellar dust and to accomplish the other goals listed above.

  10. Light Echoes of Galactic Explosions and Eruptions

    NASA Astrophysics Data System (ADS)

    Rest, Armin; Bianco, Federica; Chornock, Ryan; Foley, Ryan; Kunder, Andrea; Matheson, Thomas; Olsen, Knut; Prieto, Jose Luis; Sinnott, Brendan; Smith, Chris; Smith, Nathan; Welch, Doug

    2013-08-01

    We propose to search for light echoes (LEs) from the historical brightening of the Luminous Blue Variable (LBV) P Cygni using the KPNO 4m Mosaic 1.1 imager. We also propose to conclude our search - so far unsuccessful - for LEs from the the Crab supernova SN 1054 by surveying one remaining region of the LE ellipsoid behind the plane of the supernova remnant on the sky. In addition, we continue to monitor the LEs from the Cas A and Tycho supernovae in order to identify suitable LE candidates for 3D-spectroscopy and spectral time series. In previously granted NOAO time, we have discovered light echoes of three ancient SNe in the LMC as well as from the historic SN events of Cas A and Tycho [2, 3], which allowed their spectroscopic classification [6, 7, 10] and 3D spectroscopy [8, 9]. Most recently, we discovered light echoes of the mid-19th-century Great Eruption of η Carinae using CTIO 4m Mosaic images [11]. Subsequent spectroscopic follow-up of Eta Carinae revealed that its outburst spectral type was most similar to those of G-type supergiants, rather than reported LBV outburst spectral types of F-type (or earlier) [11]. Our extension of LE techniques to LBV outbursts promises to extend our ability to record outburst activity hundreds of years into the past - a timescale which is likely a significant fraction of the brief final phases of these probable core- collapse supernova precursors.

  11. Light Echoes of Galactic Explosions and Eruptions

    NASA Astrophysics Data System (ADS)

    Rest, Armin; Bianco, Federica; Chornock, Ryan; Clocchiatti, Alejandro; Foley, Ryan; James, David; Matheson, Thomas; Narayan, Gautham; Olsen, Knut; Points, Sean; Prieto, Jose Luis; Smith, Chris; Smith, Nathan; Suntzeff, Nick; Welch, Doug; Zenteno, Alfredo

    2014-08-01

    We propose to search for light echoes (LEs) from the historical brightening of the Luminous Blue Variable (LBV) P Cygni using the KPNO 4m Mosaic 1.1 imager. We also propose to us DECam to continue our search for LEs from the the Crab supernova SN 1054. In addition, we continue to monitor the LEs from the Cas A and Tycho supernovae in order to identify suitable LE candidates for 3D-spectroscopy and spectral time series. In previously granted NOAO time, we have discovered light echoes of three ancient SNe in the LMC as well as from the historic SN events of Cas A and Tycho [2, 3], which allowed their spectroscopic classification [6, 7, 10] and 3D spectroscopy [8, 9]. Most recently, we discovered light echoes of the mid-19th-century Great Eruption of η Carinae using CTIO 4m Mosaic images [11]. Subsequent spectroscopic follow-up of Eta Carinae revealed that its outburst spectral type was most similar to those of G-type supergiants, rather than reported LBV outburst spectral types of F-type (or earlier) [11]. Our extension of LE techniques to LBV outbursts promises to extend our ability to record outburst activity hundreds of years into the past - a timescale which is likely a significant fraction of the brief final phases of these probable core- collapse supernova precursors.

  12. Dependence of the time of the appearance of a Stark echo response on irreversible relaxation of a system

    NASA Astrophysics Data System (ADS)

    Akhmedshina, E. N.; Nefed'ev, L. A.; Garnaeva, G. I.

    2016-09-01

    The dependence of the time of the appearance of a Stark (gradient) echo response on the irreversible transverse relaxation time of a system in the nanosecond range and on the width of the excitation region of an inhomogeneously broadened line has been investigated. It has been shown that the use of nonresonant laser pulses with an artificially created spatial inhomogeneity makes it possible to determine the relaxation time in the nanosecond range from the time of the appearance of a Stark (gradient) echo response, which is a more accurate method than the method of determining the relaxation time from the decay of the intensity by varying time intervals of the exposure to inhomogeneous electromagnetic fields.

  13. Echo amplitude sensitivity of bat auditory neurons improves with decreasing pulse-echo gap.

    PubMed

    Jen, Philip H-S; Wu, Chung Hsin

    2015-01-01

    During hunting, insectivorous bats systematically vary the parameters of emitted pulses and analyze the returning echoes to extract prey features. As such, the duration of the pulse (P) and echo (E), the P-E gap, and the P-E amplitude difference progressively decrease throughout the prey-approach sequence. Our previous studies have shown that most inferior collicular neurons of bats discharge maximally to a best duration, and they have the sharpest echo frequency and amplitude sensitivity when stimulated with P-E pairs with duration the same as the best duration. Furthermore, their echo duration and frequency sensitivity improves with decreasing P-E duration and P-E gap. The present study shows that this is also true in the amplitude domain. Thus, all these data indicate that bats can better extract multiple parameters of expected rather than unexpected echo after pulse emission. They also support the hypothesis that a bat's inferior collicular neurons improve the response sensitivity in multiple parametric domains as the prey is approached to increase the success of hunting. PMID:25426829

  14. Perception of echo delay is disrupted by small temporal misalignment of echo harmonics in bat sonar.

    PubMed

    Bates, Mary E; Simmons, James A

    2011-02-01

    Echolocating big brown bats emit ultrasonic frequency-modulated (FM) biosonar sounds containing two prominent downward-sweeping harmonics (FM1 and FM2) and perceive target distance from echo delay. In naturally occurring echoes, FM1 and FM2 are delayed by the same amount. Even though echoes from targets located off-axis or far away are lowpass filtered, which weakens FM2 relative to FM1, their delays remain the same. We show here that misalignment of FM2 with FM1 by only 2.6 μs is sufficient to significantly disrupt acuity, which then persists for larger misalignments up to 300 μs. However, when FM2 is eliminated entirely rather than just misaligned, acuity is effectively restored. For naturally occurring, lowpass-filtered echoes, neuronal responses to weakened FM2 are retarded relative to FM1 because of amplitude-latency trading, which misaligns the harmonics in the bat's internal auditory representations. Electronically delaying FM2 relative to FM1 mimics the retarded neuronal responses for FM2 relative to FM1 caused by amplitude-latency trading. Echoes with either electronically or physiologically misaligned harmonics are not perceived as having a clearly defined delay. This virtual collapse of delay acuity may suppress interference from off-axis or distant clutter through degradation of delay images for clutter in contrast to sharp images for nearer, frontal targets.

  15. Acquisition strategies

    SciTech Connect

    Zimmer, M.J.; Lynch, P.W. )

    1993-11-01

    Acquiring projects takes careful planning, research and consideration. Picking the right opportunities and avoiding the pitfalls will lead to a more valuable portfolio. This article describes the steps to take in evaluating an acquisition and what items need to be considered in an evaluation.

  16. meta-DENSE complex acquisition for reduced intravoxel dephasing

    NASA Astrophysics Data System (ADS)

    Aletras, Anthony H.; Arai, Andrew E.

    2004-08-01

    Displacement encoding with stimulated echoes (DENSE) with a meta-DENSE readout and RF phase cycling to suppress the STEAM anti-echo is described for reducing intravoxel dephasing signal loss. This RF phase cycling scheme, when combined with existing meta-DENSE suppression of the T1 recovering signal, yields higher quality DENSE myocardial strain maps. Phantom and human images are provided to demonstrate the technique, which is capable of acquiring phase contrast displacement encoded images at low encoding gradient strengths providing better spatial resolution and less signal loss due to intravoxel dephasing than prior methods.

  17. The EChO science case

    NASA Astrophysics Data System (ADS)

    Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul; Hartogh, Paul; Isaak, Kate; Linder, Martin; Lovis, Christophe; Micela, Giusi; Ollivier, Marc; Puig, Ludovic; Ribas, Ignasi; Snellen, Ignas; Swinyard, Bruce; Allard, France; Barstow, Joanna; Cho, James; Coustenis, Athena; Cockell, Charles; Correia, Alexandre; Decin, Leen; de Kok, Remco; Deroo, Pieter; Encrenaz, Therese; Forget, Francois; Glasse, Alistair; Griffith, Caitlin; Guillot, Tristan; Koskinen, Tommi; Lammer, Helmut; Leconte, Jeremy; Maxted, Pierre; Mueller-Wodarg, Ingo; Nelson, Richard; North, Chris; Pallé, Enric; Pagano, Isabella; Piccioni, Guseppe; Pinfield, David; Selsis, Franck; Sozzetti, Alessandro; Stixrude, Lars; Tennyson, Jonathan; Turrini, Diego; Zapatero-Osorio, Mariarosa; Beaulieu, Jean-Philippe; Grodent, Denis; Guedel, Manuel; Luz, David; Nørgaard-Nielsen, Hans Ulrik; Ray, Tom; Rickman, Hans; Selig, Avri; Swain, Mark; Banaszkiewicz, Marek; Barlow, Mike; Bowles, Neil; Branduardi-Raymont, Graziella; du Foresto, Vincent Coudé; Gerard, Jean-Claude; Gizon, Laurent; Hornstrup, Allan; Jarchow, Christopher; Kerschbaum, Franz; Kovacs, Géza; Lagage, Pierre-Olivier; Lim, Tanya; Lopez-Morales, Mercedes; Malaguti, Giuseppe; Pace, Emanuele; Pascale, Enzo; Vandenbussche, Bart; Wright, Gillian; Ramos Zapata, Gonzalo; Adriani, Alberto; Azzollini, Ruymán; Balado, Ana; Bryson, Ian; Burston, Raymond; Colomé, Josep; Crook, Martin; Di Giorgio, Anna; Griffin, Matt; Hoogeveen, Ruud; Ottensamer, Roland; Irshad, Ranah; Middleton, Kevin; Morgante, Gianluca; Pinsard, Frederic; Rataj, Mirek; Reess, Jean-Michel; Savini, Giorgio; Schrader, Jan-Rutger; Stamper, Richard; Winter, Berend; Abe, L.; Abreu, M.; Achilleos, N.; Ade, P.; Adybekian, V.; Affer, L.; Agnor, C.; Agundez, M.; Alard, C.; Alcala, J.; Allende Prieto, C.; Alonso Floriano, F. J.; Altieri, F.; Alvarez Iglesias, C. A.; Amado, P.; Andersen, A.; Aylward, A.; Baffa, C.; Bakos, G.; Ballerini, P.; Banaszkiewicz, M.; Barber, R. J.; Barrado, D.; Barton, E. J.; Batista, V.; Bellucci, G.; Belmonte Avilés, J. A.; Berry, D.; Bézard, B.; Biondi, D.; Błęcka, M.; Boisse, I.; Bonfond, B.; Bordé, P.; Börner, P.; Bouy, H.; Brown, L.; Buchhave, L.; Budaj, J.; Bulgarelli, A.; Burleigh, M.; Cabral, A.; Capria, M. T.; Cassan, A.; Cavarroc, C.; Cecchi-Pestellini, C.; Cerulli, R.; Chadney, J.; Chamberlain, S.; Charnoz, S.; Christian Jessen, N.; Ciaravella, A.; Claret, A.; Claudi, R.; Coates, A.; Cole, R.; Collura, A.; Cordier, D.; Covino, E.; Danielski, C.; Damasso, M.; Deeg, H. J.; Delgado-Mena, E.; Del Vecchio, C.; Demangeon, O.; De Sio, A.; De Wit, J.; Dobrijévic, M.; Doel, P.; Dominic, C.; Dorfi, E.; Eales, S.; Eiroa, C.; Espinoza Contreras, M.; Esposito, M.; Eymet, V.; Fabrizio, N.; Fernández, M.; Femenía Castella, B.; Figueira, P.; Filacchione, G.; Fletcher, L.; Focardi, M.; Fossey, S.; Fouqué, P.; Frith, J.; Galand, M.; Gambicorti, L.; Gaulme, P.; García López, R. J.; Garcia-Piquer, A.; Gear, W.; Gerard, J.-C.; Gesa, L.; Giani, E.; Gianotti, F.; Gillon, M.; Giro, E.; Giuranna, M.; Gomez, H.; Gomez-Leal, I.; Gonzalez Hernandez, J.; González Merino, B.; Graczyk, R.; Grassi, D.; Guardia, J.; Guio, P.; Gustin, J.; Hargrave, P.; Haigh, J.; Hébrard, E.; Heiter, U.; Heredero, R. L.; Herrero, E.; Hersant, F.; Heyrovsky, D.; Hollis, M.; Hubert, B.; Hueso, R.; Israelian, G.; Iro, N.; Irwin, P.; Jacquemoud, S.; Jones, G.; Jones, H.; Justtanont, K.; Kehoe, T.; Kerschbaum, F.; Kerins, E.; Kervella, P.; Kipping, D.; Koskinen, T.; Krupp, N.; Lahav, O.; Laken, B.; Lanza, N.; Lellouch, E.; Leto, G.; Licandro Goldaracena, J.; Lithgow-Bertelloni, C.; Liu, S. J.; Lo Cicero, U.; Lodieu, N.; Lognonné, P.; Lopez-Puertas, M.; Lopez-Valverde, M. A.; Lundgaard Rasmussen, I.; Luntzer, A.; Machado, P.; MacTavish, C.; Maggio, A.; Maillard, J.-P.; Magnes, W.; Maldonado, J.; Mall, U.; Marquette, J.-B.; Mauskopf, P.; Massi, F.; Maurin, A.-S.; Medvedev, A.; Michaut, C.; Miles-Paez, P.; Montalto, M.; Montañés Rodríguez, P.; Monteiro, M.; Montes, D.; Morais, H.; Morales, J. C.; Morales-Calderón, M.; Morello, G.; Moro Martín, A.; Moses, J.; Moya Bedon, A.; Murgas Alcaino, F.; Oliva, E.; Orton, G.; Palla, F.; Pancrazzi, M.; Pantin, E.; Parmentier, V.; Parviainen, H.; Peña Ramírez, K. Y.; Peralta, J.; Perez-Hoyos, S.; Petrov, R.; Pezzuto, S.; Pietrzak, R.; Pilat-Lohinger, E.; Piskunov, N.; Prinja, R.; Prisinzano, L.; Polichtchouk, I.; Poretti, E.; Radioti, A.; Ramos, A. A.; Rank-Lüftinger, T.; Read, P.; Readorn, K.; Rebolo López, R.; Rebordão, J.; Rengel, M.; Rezac, L.; Rocchetto, M.; Rodler, F.; Sánchez Béjar, V. J.; Sanchez Lavega, A.; Sanromá, E.; Santos, N.; Sanz Forcada, J.; Scandariato, G.; Schmider, F.-X.; Scholz, A.; Scuderi, S.; Sethenadh, J.; Shore, S.; Showman, A.; Sicardy, B.; Sitek, P.; Smith, A.; Soret, L.; Sousa, S.; Stiepen, A.; Stolarski, M.; Strazzulla, G.; Tabernero, H. M.; Tanga, P.; Tecsa, M.; Temple, J.; Terenzi, L.; Tessenyi, M.; Testi, L.; Thompson, S.; Thrastarson, H.; Tingley, B. W.; Trifoglio, M.; Martín Torres, J.; Tozzi, A.; Turrini, D.; Varley, R.; Vakili, F.; de Val-Borro, M.; Valdivieso, M. L.; Venot, O.; Villaver, E.; Vinatier, S.; Viti, S.; Waldmann, I.; Waltham, D.; Ward-Thompson, D.; Waters, R.; Watkins, C.; Watson, D.; Wawer, P.; Wawrzaszk, A.; White, G.; Widemann, T.; Winek, W.; Wiśniowski, T.; Yelle, R.; Yung, Y.; Yurchenko, S. N.

    2015-12-01

    The discovery of almost two thousand exoplanets has revealed an unexpectedly diverse planet population. We see gas giants in few-day orbits, whole multi-planet systems within the orbit of Mercury, and new populations of planets with masses between that of the Earth and Neptune—all unknown in the Solar System. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? How do planetary systems work and what causes the exceptional diversity observed as compared to the Solar System? The EChO (Exoplanet Characterisation Observatory) space mission was conceived to take up the challenge to explain this diversity in terms of formation, evolution, internal structure and planet and atmospheric composition. This requires in-depth spectroscopic knowledge of the atmospheres of a large and well-defined planet sample for which precise physical, chemical and dynamical information can be obtained. In order to fulfil this ambitious scientific program, EChO was designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large, diverse and well-defined planet sample within its 4-year mission lifetime. The transit and eclipse spectroscopy method, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allows us to measure atmospheric signals from the planet at levels of at least 10-4 relative to the star. This can only be achieved in conjunction with a carefully designed stable payload and satellite platform. It is also necessary to provide broad instantaneous wavelength coverage to detect as many molecular species as possible, to probe the thermal structure of the planetary atmospheres and to correct for the contaminating effects of the stellar photosphere. This requires wavelength

  18. High-Resolution Fast Spin Echo Imaging of the Human Brain at 4.7 T: Implementation and Sequence Characteristics

    PubMed Central

    Thomas, David L.; Vita, Enrico De; Roberts, Steven; Turner, Robert; Yousry, Tarek A.; Ordidge, Roger J.

    2007-01-01

    In this work, a number of important issues associated with fast spin echo (FSE) imaging of the human brain at 4.7 T are addressed. It is shown that FSE enables the acquisition of images with high resolution and good tissue contrast throughout the brain at high field strength. By employing an echo spacing (ES) of 22 ms, one can use large flip angle refocusing pulses (162°) and a low acquisition bandwidth (50 kHz) to maximize the signal-to-noise ratio (SNR). A new method of phase encode (PE) ordering (called “feathering”) designed to reduce image artifacts is described, and the contributions of RF (B1) inhomogeneity, different echo coherence pathways, and magnetization transfer (MT) to FSE signal intensity and contrast are investigated. B1 inhomogeneity is measured and its effect is shown to be relatively minor for high-field FSE, due to the self-compensating characteristics of the sequence. Thirty-four slice data sets (slice thickness = 2 mm; in-plane resolution = 0.469 mm; acquisition time = 11 min 20 s) from normal volunteers are presented, which allow visualization of brain anatomy in fine detail. This study demonstrates that high-field FSE produces images of the human brain with high spatial resolution, SNR, and tissue contrast, within currently prescribed power deposition guidelines. Magn Reson Med 51:1254-1264, 2004. PMID:15170847

  19. Effective Gradients in Porous Media Due to Susceptibility Differences

    PubMed

    Hürlimann

    1998-04-01

    In porous media, magnetic susceptibility differences between the solid phase and the fluid filling the pore space lead to field inhomogeneities inside the pore space. In many cases, diffusion of the spins in the fluid phase through these internal inhomogeneities controls the transverse decay rate of the NMR signal. In disordered porous media such as sedimentary rocks, a detailed evaluation of this process is in practice not possible because the field inhomogeneities depend not only on the susceptibility difference but also on the details of the pore geometry. In this report, the major features of diffusion in internal gradients are analyzed with the concept of effective gradients. Effective gradients are related to the field inhomogeneities over the dephasing length, the typical length over which the spins diffuse before they dephase. For the CPMG sequence, the dependence of relaxation rate on echo spacing can be described to first order by a distribution of effective gradients. It is argued that for a given susceptibility difference, there is a maximum value for these effective gradients, gmax, that depends on only the diffusion coefficient, the Larmor frequency, and the susceptibility difference. This analysis is applied to the case of water-saturated sedimentary rocks. From a set of NMR measurements and a compilation of a large number of susceptibility measurements, we conclude that the effective gradients in carbonates are typically smaller than gradients of current NMR well logging tools, whereas in many sandstones, internal gradients can be comparable to or larger than tool gradients. Copyright 1998 Academic Press.

  20. Fine elasticity imaging utilizing the iterative RF-echo phase matching method.

    PubMed

    Sumi, C

    1999-01-01

    To non-invasively quantify elasticity of soft tissue, we previously developed the iterative two-dimensional (2-D) rf-echo phase matching method for accurately measuring a 2-D displacement vector field generated in vivo in soft tissue during acquisition of two successive rf-echo data frames. We also developed a stable method for uniquely reconstructing a shear modulus distribution using strains derived from the measurement data. However, as in our measurement method a displacement is determined by using the phase characteristics of the finite local echo data as the index to iteratively search for the corresponding local data, change of the local phase characteristics due to tissue deformation deteriorates the accuracy of the determination. Thus, we improve the previous method such that, in principle, the displacement can be determined using an infinitesimal phase characteristics. That is, we incorporate an effective mechanism into the previous iterative phase matching scheme: the local size is made suitably smaller during the iterative phase matching. The demonstrated ability of measurement and reconstruction in simulation, and experiments on in vitro in pork rib and in vivo in breast tissue, shows this refinement allows not only better spatial resolution of the shear modulus image but also improved accuracy, and indicates that the improved method has a high potential to be applied for various soft tissues. PMID:18238410

  1. 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

  2. Tailoring the flow sensitivity of fast spin-echo sequences for noncontrast peripheral MR angiography

    PubMed Central

    Storey, Pippa; Atanasova, Iliyana P.; Lim, Ruth P.; Xu, Jian; Kim, Daniel; Chen, Qun; Lee, Vivian S.

    2011-01-01

    There has recently been renewed interest in non-contrast techniques for peripheral MR angiography following the discovery of an association between gadolinium-based contrast agents and nephrogenic systemic fibrosis (NSF) in patients with renal insufficiency. The ‘fresh blood imaging’ technique proposed by Miyazaki et al. involves the subtraction of two 3D fast spin-echo image sets, one acquired in systole, when the arteries appear dark due to flow-related dephasing, and the other obtained in diastole, when the arteries are brighter. Our goal was to investigate how parameters of the fast spin-echo sequence influence its flow sensitivity, and how that in turn impacts the depiction of large and small arteries. Results from phantom experiments and human studies in the calf suggest that the flow sensitivity is governed largely by the flip angle of the radiofrequency refocusing pulses. The area of the spoiler gradients has a lesser effect, and at low flip angles the echo time plays a role. These parameters can be optimized to obtain good depiction of the calf arteries in healthy subjects. It remains to be seen whether they provide sufficient control over flow sensitivity to achieve diagnostic-quality images in other vascular beds and in the presence of pathology. PMID:20725934

  3. Dephasing of Hahn echo in rocks by diffusion in susceptibility-induced field inhomogeneities.

    PubMed

    Hürlimann, M D; Helmer, K G; Sotak, C H

    1998-01-01

    The decay of the Hahn spin echo of water in the pore space of many porous media is dominated by the dephasing of spins in internal-field inhomogeneities, produced by susceptibility contrasts, rather than surface or bulk relaxation. This is particularly the case for measurements at moderate and high fields in samples such as fluid-saturated sedimentary rocks and some biological materials. Here, we study the behavior of the Hahn-echo decay in rocks with grains much larger and smaller than the average dephasing length, which is typically of the order of a few microns. It is shown that the decay in these two cases is qualitatively different. For coarse-grained rocks, the decay can be modeled to first order by a distribution of local, effective field gradients. This is in contrast to the case of fine-grained rocks, where motional narrowing of the field inhomogeneities occurs. These interpretations are supported by measurements of the temperature dependence of the Hahn echo decay and the diffusion time dependence of the diffusion coefficient.

  4. Echo tracker/range finder for radars and sonars

    NASA Technical Reports Server (NTRS)

    Constantinides, N. J. (Inventor)

    1982-01-01

    An echo tracker/range finder or altimeter is described. The pulse repetition frequency (PFR) of a predetermined plurality of transmitted pulses is adjusted so that echo pulses received from a reflecting object are positioned between transmitted pulses and divided their interpulse time interval into two time intervals having a predetermined ratio with respect to each other. The invention described provides a means whereby the arrival time of a plurality of echo pulses is defined as the time at which a composite echo pulse formed of a sum of the individual echo pulses has the highest amplitude. The invention is applicable to radar systems, sonar systems, or any other kind of system in which pulses are transmitted and echoes received therefrom.

  5. The Light Echoes around V838 Monocerotis

    NASA Astrophysics Data System (ADS)

    Bond, Howard

    2011-10-01

    V838 Monocerotis, which burst upon the astronomical scene in early 2002, is a completely unanticipated new object. It underwent a large-amplitude and very luminous outburst, during which its spectrum remained that of an extremely cool supergiant. A rapidly evolving set of light echoes around V838 Mon was discovered soon after the outburst, and quickly became the most spectacular display of the phenomenon yet seen. These light echoes provide the means to accomplish three unique types of measurements based on continued HST imaging during the event: {1} Study effects of MHD turbulence at high resolution and in 3 dimensions; {2} Construct the first unambiguous and fully 3-D map of a circumstellar dust envelope in the Milky Way; {3} Study dust physics in a unique setting where the spectrum and light curve of the illumination, and the scattering angle, are unambiguously known. We have also used our HST data to determine the distance to V838 Mon through a novel direct geometric technique, and the results showed that V838 Mon had a maximum luminosity brighter than a classical nova.Because of the extreme rarity of light echoes, this is almost certainly the only opportunity to achieve such results during the lifetime of HST. Similar intermediate-luminosity red transients are now being discovered in nearby galaxies, and it has become important to understand the physics of their outbursts and the nature of their progenitors. We propose one visit during Cycle 19, using ACS, in order to continue the mapping of the circumstellar dust and to accomplish the other goals listed above.

  6. Prospective motion correction of 3D echo-planar imaging data for functional MRI using optical tracking.

    PubMed

    Todd, Nick; Josephs, Oliver; Callaghan, Martina F; Lutti, Antoine; Weiskopf, Nikolaus

    2015-06-01

    We evaluated the performance of an optical camera based prospective motion correction (PMC) system in improving the quality of 3D echo-planar imaging functional MRI data. An optical camera and external marker were used to dynamically track the head movement of subjects during fMRI scanning. PMC was performed by using the motion information to dynamically update the sequence's RF excitation and gradient waveforms such that the field-of-view was realigned to match the subject's head movement. Task-free fMRI experiments on five healthy volunteers followed a 2 × 2 × 3 factorial design with the following factors: PMC on or off; 3.0mm or 1.5mm isotropic resolution; and no, slow, or fast head movements. Visual and motor fMRI experiments were additionally performed on one of the volunteers at 1.5mm resolution comparing PMC on vs PMC off for no and slow head movements. Metrics were developed to quantify the amount of motion as it occurred relative to k-space data acquisition. The motion quantification metric collapsed the very rich camera tracking data into one scalar value for each image volume that was strongly predictive of motion-induced artifacts. The PMC system did not introduce extraneous artifacts for the no motion conditions and improved the time series temporal signal-to-noise by 30% to 40% for all combinations of low/high resolution and slow/fast head movement relative to the standard acquisition with no prospective correction. The numbers of activated voxels (p<0.001, uncorrected) in both task-based experiments were comparable for the no motion cases and increased by 78% and 330%, respectively, for PMC on versus PMC off in the slow motion cases. The PMC system is a robust solution to decrease the motion sensitivity of multi-shot 3D EPI sequences and thereby overcome one of the main roadblocks to their widespread use in fMRI studies.

  7. Prospective motion correction of 3D echo-planar imaging data for functional MRI using optical tracking

    PubMed Central

    Todd, Nick; Josephs, Oliver; Callaghan, Martina F.; Lutti, Antoine; Weiskopf, Nikolaus

    2015-01-01

    We evaluated the performance of an optical camera based prospective motion correction (PMC) system in improving the quality of 3D echo-planar imaging functional MRI data. An optical camera and external marker were used to dynamically track the head movement of subjects during fMRI scanning. PMC was performed by using the motion information to dynamically update the sequence's RF excitation and gradient waveforms such that the field-of-view was realigned to match the subject's head movement. Task-free fMRI experiments on five healthy volunteers followed a 2 × 2 × 3 factorial design with the following factors: PMC on or off; 3.0 mm or 1.5 mm isotropic resolution; and no, slow, or fast head movements. Visual and motor fMRI experiments were additionally performed on one of the volunteers at 1.5 mm resolution comparing PMC on vs PMC off for no and slow head movements. Metrics were developed to quantify the amount of motion as it occurred relative to k-space data acquisition. The motion quantification metric collapsed the very rich camera tracking data into one scalar value for each image volume that was strongly predictive of motion-induced artifacts. The PMC system did not introduce extraneous artifacts for the no motion conditions and improved the time series temporal signal-to-noise by 30% to 40% for all combinations of low/high resolution and slow/fast head movement relative to the standard acquisition with no prospective correction. The numbers of activated voxels (p < 0.001, uncorrected) in both task-based experiments were comparable for the no motion cases and increased by 78% and 330%, respectively, for PMC on versus PMC off in the slow motion cases. The PMC system is a robust solution to decrease the motion sensitivity of multi-shot 3D EPI sequences and thereby overcome one of the main roadblocks to their widespread use in fMRI studies. PMID:25783205

  8. Project Echo: FM Demodulators with Negative Feedback

    NASA Technical Reports Server (NTRS)

    Ruthroff, Clyde L.

    1961-01-01

    The primary experimental objective of Project Echo was the transmission of radio communications between points on the earth by reflection from the balloon satellite. Owing to the large path losses from transmitter to receiver via the satellite, a wide-band frequency modulation technique was used in which bandwidth was traded for signal-to-noise ratio. This paper describes the FM receiving demodulators employed. Negative feedback applied to the local oscillator reduces the FM modulation index in the receiver IF amplifiers, resulting in threshold performance superior to that of conventional FM receivers.

  9. Temporal signal processing of dolphin biosonar echoes from salmon prey.

    PubMed

    Au, Whitlow W L; Ou, Hui Helen

    2014-08-01

    Killer whales project short broadband biosonar clicks. The broadband nature of the clicks provides good temporal resolution of echo highlights and allows for the discriminations of salmon prey. The echoes contain many highlights as the signals reflect off different surfaces and parts of the fish body and swim bladder. The temporal characteristics of echoes from salmon are highly aspect dependent and six temporal parameters were used in a support vector machine to discriminate between species. Results suggest that killer whales can classify salmon based on their echoes and provide some insight as to which features might enable the classification. PMID:25096148

  10. Temporal signal processing of dolphin biosonar echoes from salmon prey.

    PubMed

    Au, Whitlow W L; Ou, Hui Helen

    2014-08-01

    Killer whales project short broadband biosonar clicks. The broadband nature of the clicks provides good temporal resolution of echo highlights and allows for the discriminations of salmon prey. The echoes contain many highlights as the signals reflect off different surfaces and parts of the fish body and swim bladder. The temporal characteristics of echoes from salmon are highly aspect dependent and six temporal parameters were used in a support vector machine to discriminate between species. Results suggest that killer whales can classify salmon based on their echoes and provide some insight as to which features might enable the classification.

  11. Extra echo spaces: ultrasonography and computerised tomography correlations.

    PubMed Central

    Wada, T; Honda, M; Matsuyama, S

    1982-01-01

    Among the echocardiograms of 844 patients of the International Goodwill Hospital from January 1980 to April 1981, 700 showed clinically inexplicable extra echo spaces. Fifty of the 700 had computerised tomography of their hearts which showed the extra echo spaces to be caused either by anterior or posterior subepicardial fat. Six of the 50 cases had both fat and pericardial effusions, which are difficult to differentiate echocardiographically unless follow-up clinical observations are performed. Subepicardial fat deposits are reasonable explanations for the extra echo spaces frequently observed by echocardiography: they correlate well with clinical findings. Subepicardial fat should be recognised as the cause of such extra echo spaces. Images PMID:7073903

  12. Neutron spin echo scattering angle measurement (SESAME)

    SciTech Connect

    Pynn, R.; Fitzsimmons, M.R.; Fritzsche, H.; Gierlings, M.; Major, J.; Jason, A.

    2005-05-15

    We describe experiments in which the neutron spin echo technique is used to measure neutron scattering angles. We have implemented the technique, dubbed spin echo scattering angle measurement (SESAME), using thin films of Permalloy electrodeposited on silicon wafers as sources of the magnetic fields within which neutron spins precess. With 30-{mu}m-thick films we resolve neutron scattering angles to about 0.02 deg. with neutrons of 4.66 A wavelength. This allows us to probe correlation lengths up to 200 nm in an application to small angle neutron scattering. We also demonstrate that SESAME can be used to separate specular and diffuse neutron reflection from surfaces at grazing incidence. In both of these cases, SESAME can make measurements at higher neutron intensity than is available with conventional methods because the angular resolution achieved is independent of the divergence of the neutron beam. Finally, we discuss the conditions under which SESAME might be used to probe in-plane structure in thin films and show that the method has advantages for incident neutron angles close to the critical angle because multiple scattering is automatically accounted for.

  13. Light Echoes of Transients and Variables

    NASA Astrophysics Data System (ADS)

    Rest, Armin

    2012-04-01

    abstract-type="normal">SummaryTycho Brahe's observations of a supernova in 1572 challenged the contemporaneous European view of the cosmos that the celestial realm was unchanging. 439 years later we have once again seen the light that Tycho saw, as some of the light from the 1572 supernova is reflected off dust and is only now reaching Earth. These light echoes, as well as ones detected from other transients and variables, give us a very rare opportunity in astronomy: direct observation of the cause (the supernova explosion) and the effect (the supernova remnant) of the same astronomical event. Furthermore, in some cases we can compare light echoes at different angles around a supernova remnant, and thus investigate possible asymmetry in the supernova explosion. In addition, in cases where the scattering dust is favorably positioned, the geometric distance to the SN remnant can be determined using polarization measurements. These techniques have been successfully applied to various transients in the last decade, and the talk gave an overview of the scientific results and techniques, with a particular focus on the challenges we will face in the current and upcoming wide-field time-domain surveys.

  14. Light Echo From Star V838 Monocerotis

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This series of photos, captured by the NASA Hubble Space Telescope's (HST) Advanced Camera for Surveys from May to December 2002, dramatically demonstrates the reverberation of light through space caused by an unusual stellar outburst in January 2002. A burst of light from the bizarre star is spreading into space and reflecting off of surrounding circumstellar dust. As different parts are sequentially illuminated, the appearance of the dust changes. This effect is referred to as a 'light echo'. The red star at the center of the eyeball like feature is the unusual erupting super giant called V838 Monocerotis, or V Mon, located about 20,000 light-years away in the winter constellation Monoceros (the Unicorn). During its outburst, the star brightened to more than 600,000 times our Sun's luminosity. The circular feature has now expanded to slightly larger than the angular size of Jupiter on the sky, and will continue to expand for several more years until the light from the back side of the nebula begins to arrive. The light echo will then give the illusion of contracting, until it finally disappears by the end of the decade.

  15. Implementation and assessment of diffusion-weighted partial Fourier readout-segmented echo-planar imaging.

    PubMed

    Frost, Robert; Porter, David A; Miller, Karla L; Jezzard, Peter

    2012-08-01

    Single-shot echo-planar imaging has been used widely in diffusion magnetic resonance imaging due to the difficulties in correcting motion-induced phase corruption in multishot data. Readout-segmented EPI has addressed the multishot problem by introducing a two-dimensional nonlinear navigator correction with online reacquisition of uncorrectable data to enable acquisition of high-resolution diffusion data with reduced susceptibility artifact and T*(2) blurring. The primary shortcoming of readout-segmented EPI in its current form is its long acquisition time (longer than similar resolution single-shot echo-planar imaging protocols by approximately the number of readout segments), which limits the number of diffusion directions. By omitting readout segments at one side of k-space and using partial Fourier reconstruction, readout-segmented EPI imaging times could be reduced. In this study, the effects of homodyne and projection onto convex sets reconstructions on estimates of the fractional anisotropy, mean diffusivity, and diffusion orientation in fiber tracts and raw T(2)- and trace-weighted signal are compared, along with signal-to-noise ratio results. It is found that projections onto convex sets reconstruction with 3/5 segments in a 2 mm isotropic diffusion tensor image acquisition and 9/13 segments in a 0.9 × 0.9 × 4.0 mm(3) diffusion-weighted image acquisition provide good fidelity relative to the full k-space parameters. This allows application of readout-segmented EPI to tractography studies, and clinical stroke and oncology protocols.

  16. The Future of ECHO: Evaluating Open Source Possibilities

    NASA Astrophysics Data System (ADS)

    Pilone, D.; Gilman, J.; Baynes, K.; Mitchell, A. E.

    2012-12-01

    NASA's Earth Observing System ClearingHOuse (ECHO) is a format agnostic metadata repository supporting over 3000 collections and 100M science granules. ECHO exposes FTP and RESTful Data Ingest APIs in addition to both SOAP and RESTful search and order capabilities. Built on top of ECHO is a human facing search and order web application named Reverb. ECHO processes hundreds of orders, tens of thousands of searches, and 1-2M ingest actions each week. As ECHO's holdings, metadata format support, and visibility have increased, the ECHO team has received requests by non-NASA entities for copies of ECHO that can be run locally against their data holdings. ESDIS and the ECHO Team have begun investigations into various deployment and Open Sourcing models that can balance the real constraints faced by the ECHO project with the benefits of providing ECHO capabilities to a broader set of users and providers. This talk will discuss several release and Open Source models being investigated by the ECHO team along with the impacts those models are expected to have on the project. We discuss: - Addressing complex deployment or setup issues for potential users - Models of vetting code contributions - Balancing external (public) user requests versus our primary partners - Preparing project code for public release, including navigating licensing issues related to leveraged libraries - Dealing with non-free project dependencies such as commercial databases - Dealing with sensitive aspects of project code such as database passwords, authentication approaches, security through obscurity, etc. - Ongoing support for the released code including increased testing demands, bug fixes, security fixes, and new features.

  17. [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.

  18. The EChO science case

    NASA Astrophysics Data System (ADS)

    Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul; Hartogh, Paul; Isaak, Kate; Linder, Martin; Lovis, Christophe; Micela, Giusi; Ollivier, Marc; Puig, Ludovic; Ribas, Ignasi; Snellen, Ignas; Swinyard, Bruce; Allard, France; Barstow, Joanna; Cho, James; Coustenis, Athena; Cockell, Charles; Correia, Alexandre; Decin, Leen; de Kok, Remco; Deroo, Pieter; Encrenaz, Therese; Forget, Francois; Glasse, Alistair; Griffith, Caitlin; Guillot, Tristan; Koskinen, Tommi; Lammer, Helmut; Leconte, Jeremy; Maxted, Pierre; Mueller-Wodarg, Ingo; Nelson, Richard; North, Chris; Pallé, Enric; Pagano, Isabella; Piccioni, Guseppe; Pinfield, David; Selsis, Franck; Sozzetti, Alessandro; Stixrude, Lars; Tennyson, Jonathan; Turrini, Diego; Zapatero-Osorio, Mariarosa; Beaulieu, Jean-Philippe; Grodent, Denis; Guedel, Manuel; Luz, David; Nørgaard-Nielsen, Hans Ulrik; Ray, Tom; Rickman, Hans; Selig, Avri; Swain, Mark; Banaszkiewicz, Marek; Barlow, Mike; Bowles, Neil; Branduardi-Raymont, Graziella; du Foresto, Vincent Coudé; Gerard, Jean-Claude; Gizon, Laurent; Hornstrup, Allan; Jarchow, Christopher; Kerschbaum, Franz; Kovacs, Géza; Lagage, Pierre-Olivier; Lim, Tanya; Lopez-Morales, Mercedes; Malaguti, Giuseppe; Pace, Emanuele; Pascale, Enzo; Vandenbussche, Bart; Wright, Gillian; Ramos Zapata, Gonzalo; Adriani, Alberto; Azzollini, Ruymán; Balado, Ana; Bryson, Ian; Burston, Raymond; Colomé, Josep; Crook, Martin; Di Giorgio, Anna; Griffin, Matt; Hoogeveen, Ruud; Ottensamer, Roland; Irshad, Ranah; Middleton, Kevin; Morgante, Gianluca; Pinsard, Frederic; Rataj, Mirek; Reess, Jean-Michel; Savini, Giorgio; Schrader, Jan-Rutger; Stamper, Richard; Winter, Berend; Abe, L.; Abreu, M.; Achilleos, N.; Ade, P.; Adybekian, V.; Affer, L.; Agnor, C.; Agundez, M.; Alard, C.; Alcala, J.; Allende Prieto, C.; Alonso Floriano, F. J.; Altieri, F.; Alvarez Iglesias, C. A.; Amado, P.; Andersen, A.; Aylward, A.; Baffa, C.; Bakos, G.; Ballerini, P.; Banaszkiewicz, M.; Barber, R. J.; Barrado, D.; Barton, E. J.; Batista, V.; Bellucci, G.; Belmonte Avilés, J. A.; Berry, D.; Bézard, B.; Biondi, D.; Błęcka, M.; Boisse, I.; Bonfond, B.; Bordé, P.; Börner, P.; Bouy, H.; Brown, L.; Buchhave, L.; Budaj, J.; Bulgarelli, A.; Burleigh, M.; Cabral, A.; Capria, M. T.; Cassan, A.; Cavarroc, C.; Cecchi-Pestellini, C.; Cerulli, R.; Chadney, J.; Chamberlain, S.; Charnoz, S.; Christian Jessen, N.; Ciaravella, A.; Claret, A.; Claudi, R.; Coates, A.; Cole, R.; Collura, A.; Cordier, D.; Covino, E.; Danielski, C.; Damasso, M.; Deeg, H. J.; Delgado-Mena, E.; Del Vecchio, C.; Demangeon, O.; De Sio, A.; De Wit, J.; Dobrijévic, M.; Doel, P.; Dominic, C.; Dorfi, E.; Eales, S.; Eiroa, C.; Espinoza Contreras, M.; Esposito, M.; Eymet, V.; Fabrizio, N.; Fernández, M.; Femenía Castella, B.; Figueira, P.; Filacchione, G.; Fletcher, L.; Focardi, M.; Fossey, S.; Fouqué, P.; Frith, J.; Galand, M.; Gambicorti, L.; Gaulme, P.; García López, R. J.; Garcia-Piquer, A.; Gear, W.; Gerard, J.-C.; Gesa, L.; Giani, E.; Gianotti, F.; Gillon, M.; Giro, E.; Giuranna, M.; Gomez, H.; Gomez-Leal, I.; Gonzalez Hernandez, J.; González Merino, B.; Graczyk, R.; Grassi, D.; Guardia, J.; Guio, P.; Gustin, J.; Hargrave, P.; Haigh, J.; Hébrard, E.; Heiter, U.; Heredero, R. L.; Herrero, E.; Hersant, F.; Heyrovsky, D.; Hollis, M.; Hubert, B.; Hueso, R.; Israelian, G.; Iro, N.; Irwin, P.; Jacquemoud, S.; Jones, G.; Jones, H.; Justtanont, K.; Kehoe, T.; Kerschbaum, F.; Kerins, E.; Kervella, P.; Kipping, D.; Koskinen, T.; Krupp, N.; Lahav, O.; Laken, B.; Lanza, N.; Lellouch, E.; Leto, G.; Licandro Goldaracena, J.; Lithgow-Bertelloni, C.; Liu, S. J.; Lo Cicero, U.; Lodieu, N.; Lognonné, P.; Lopez-Puertas, M.; Lopez-Valverde, M. A.; Lundgaard Rasmussen, I.; Luntzer, A.; Machado, P.; MacTavish, C.; Maggio, A.; Maillard, J.-P.; Magnes, W.; Maldonado, J.; Mall, U.; Marquette, J.-B.; Mauskopf, P.; Massi, F.; Maurin, A.-S.; Medvedev, A.; Michaut, C.; Miles-Paez, P.; Montalto, M.; Montañés Rodríguez, P.; Monteiro, M.; Montes, D.; Morais, H.; Morales, J. C.; Morales-Calderón, M.; Morello, G.; Moro Martín, A.; Moses, J.; Moya Bedon, A.; Murgas Alcaino, F.; Oliva, E.; Orton, G.; Palla, F.; Pancrazzi, M.; Pantin, E.; Parmentier, V.; Parviainen, H.; Peña Ramírez, K. Y.; Peralta, J.; Perez-Hoyos, S.; Petrov, R.; Pezzuto, S.; Pietrzak, R.; Pilat-Lohinger, E.; Piskunov, N.; Prinja, R.; Prisinzano, L.; Polichtchouk, I.; Poretti, E.; Radioti, A.; Ramos, A. A.; Rank-Lüftinger, T.; Read, P.; Readorn, K.; Rebolo López, R.; Rebordão, J.; Rengel, M.; Rezac, L.; Rocchetto, M.; Rodler, F.; Sánchez Béjar, V. J.; Sanchez Lavega, A.; Sanromá, E.; Santos, N.; Sanz Forcada, J.; Scandariato, G.; Schmider, F.-X.; Scholz, A.; Scuderi, S.

    2015-12-01

    The discovery of almost two thousand exoplanets has revealed an unexpectedly diverse planet population. We see gas giants in few-day orbits, whole multi-planet systems within the orbit of Mercury, and new populations of planets with masses between that of the Earth and Neptune—all unknown in the Solar System. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? How do planetary systems work and what causes the exceptional diversity observed as compared to the Solar System? The EChO (Exoplanet Characterisation Observatory) space mission was conceived to take up the challenge to explain this diversity in terms of formation, evolution, internal structure and planet and atmospheric composition. This requires in-depth spectroscopic knowledge of the atmospheres of a large and well-defined planet sample for which precise physical, chemical and dynamical information can be obtained. In order to fulfil this ambitious scientific program, EChO was designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large, diverse and well-defined planet sample within its 4-year mission lifetime. The transit and eclipse spectroscopy method, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allows us to measure atmospheric signals from the planet at levels of at least 10-4 relative to the star. This can only be achieved in conjunction with a carefully designed stable payload and satellite platform. It is also necessary to provide broad instantaneous wavelength coverage to detect as many molecular species as possible, to probe the thermal structure of the planetary atmospheres and to correct for the contaminating effects of the stellar photosphere. This requires wavelength

  19. In vivo thermal ablation monitoring using ultrasound echo decorrelation imaging.

    PubMed

    Subramanian, Swetha; Rudich, Steven M; Alqadah, Amel; Karunakaran, Chandra Priya; Rao, Marepalli B; Mast, T Douglas

    2014-01-01

    Previous work indicated that ultrasound echo decorrelation imaging can track and quantify changes in echo signals to predict thermal damage during in vitro radiofrequency ablation (RFA). In the in vivo studies reported here, the feasibility of using echo decorrelation imaging as a treatment monitoring tool was assessed. RFA was performed on normal swine liver (N = 5), and ultrasound ablation using image-ablate arrays was performed on rabbit liver implanted with VX2 tumors (N = 2). Echo decorrelation and integrated backscatter were computed from Hilbert transformed pulse-echo data acquired during RFA and ultrasound ablation treatments. Receiver operating characteristic (ROC) curves were employed to assess the ability of echo decorrelation imaging and integrated backscatter to predict ablation. Area under the ROC curves (AUROC) was determined for RFA and ultrasound ablation using echo decorrelation imaging. Ablation was predicted more accurately using echo decorrelation imaging (AUROC = 0.832 and 0.776 for RFA and ultrasound ablation, respectively) than using integrated backscatter (AUROC = 0.734 and 0.494). PMID:24239361

  20. Psychoacoustic influences of the echoing environments of prehistoric art

    NASA Astrophysics Data System (ADS)

    Waller, Steven J.

    2002-11-01

    Cave paintings and ancient petroglyphs around the world are typically found in echo rich locations such as caves, canyons, and rocky cliff faces. Analysis of field data shows that echo decibel levels at a large number of prehistoric art sites are higher than those at nondecorated locations. The selection of these echoing environments by the artists appears not to be a mere coincidence. This paper considers the perception of an echoed sound as a psychoacoustic event that would have been inexplicable to ancient humans. A variety of ancient legends from cultures on several continents attribute the phenomenon of echoes to supernatural beings. These legends, together with the quantitative data, strongly implicate echoing as relevant to the artists of the past. The notion that the echoes were caused by spirits within the rock would explain not only the unusual locations of prehistoric art, but also the perplexing subject matter. For example, the common theme of hoofed animal imagery could have been inspired by echoes of percussion noises perceived as hoof beats. Further systematic acoustical studies of prehistoric art sites is warranted. Conservation of the natural acoustic properties of rock art environments--a previously unrecognized need--is urged.

  1. ECHOS: Early Childhood Hands-On Science Efficacy Study

    ERIC Educational Resources Information Center

    Brown, Judy A.; Greenfield, Daryl B.; Bell, Elizabeth; Juárez, Cheryl Lani; Myers, Ted; Nayfeld, Irena

    2013-01-01

    "ECHOS: Early Childhood Hands-On Science" was developed at the Miami Science Museum as a comprehensive set of science lessons sequenced to lead children toward a deeper understanding of science content and the use of science process skills. The purpose of the research is to determine whether use of the "ECHOS" model will…

  2. A Detection-Theoretic Model of Echo Inhibition

    ERIC Educational Resources Information Center

    Saberi, Kourosh; Petrosyan, Agavni

    2004-01-01

    A detection-theoretic analysis of the auditory localization of dual-impulse stimuli is described, and a model for the processing of spatial cues in the echo pulse is developed. Although for over 50 years "echo suppression" has been the topic of intense theoretical and empirical study within the hearing sciences, only a rudimentary understanding of…

  3. Target structure and echo spectral discrimination by echolocating bats.

    PubMed

    Simmons, J A; Lavender, W A; Lavender, B A; Doroshow, C A; Kiefer, S W; Livingston, R; Scallet, A C; Crowley, D E

    1974-12-20

    Echolocating bats can use sonar to discriminate among targets which reflect echoes differing in spectral distribution of energy but not in overall intensity. They can detect differences smaller than 1 millimeter in fine target structure. Bats may be capable of classifying targets from echo spectral signatures and might thus be able to distinguish among flying insect prey by sonar.

  4. Neural coding of echo-envelope disparities in echolocating bats.

    PubMed

    Borina, Frank; Firzlaff, Uwe; Wiegrebe, Lutz

    2011-05-01

    The effective use of echolocation requires not only measuring the delay between the emitted call and returning echo to estimate the distance of an ensonified object. To locate an object in azimuth and elevation, the bat's auditory system must analyze the returning echoes in terms of their binaural properties, i.e., the echoes' interaural intensity and time differences (IIDs and ITDs). The effectiveness of IIDs for echolocation is undisputed, but when bats ensonify complex objects, the temporal structure of echoes may facilitate the analysis of the echo envelope in terms of envelope ITDs. Using extracellular recordings from the auditory midbrain of the bat, Phyllostomus discolor, we found a population of neurons that are sensitive to envelope ITDs of echoes of their sonar calls. Moreover, the envelope-ITD sensitivity improved with increasing temporal fluctuations in the echo envelopes, a sonar parameter related to the spatial statistics of complex natural reflectors like vegetation. The data show that in bats envelope ITDs may be used not only to locate external, prey-generated rustling sounds but also in the context of echolocation. Specifically, the temporal fluctuations in the echo envelope, which are created when the sonar emission is reflected from a complex natural target, support ITD-mediated echolocation.

  5. 21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Ultrasonic pulsed echo imaging system. 892.1560 Section 892.1560 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended to project...

  6. 21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Ultrasonic pulsed echo imaging system. 892.1560 Section 892.1560 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES... system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended to project...

  7. Diurnal variation of overdense meteor echo duration and ozone

    NASA Technical Reports Server (NTRS)

    Simek, Milos

    1992-01-01

    The diurnal variation of the median duration of overdense sporadic radar meteor echoes is examined. The meteors recorded in August, December, and January by the Ondrejov meteor radar during the period 1958-1990 were used for the analysis. A maximum median echo duration 1-3 hours after the time of local sunrise in the meteor region confirms the already known sunrise effect. Minimum echo duration occurring at the time of sunset seems to be the most important point of diurnal variation of the echo duration, when ozone is no longer dissociated by solar UV radiation. The effect of diurnal changes of the echo duration should be considered when the mass distribution of meteor showers is analyzed.

  8. Echoes from anharmonic normal modes in model glasses.

    PubMed

    Burton, Justin C; Nagel, Sidney R

    2016-03-01

    Glasses display a wide array of nonlinear acoustic phenomena at temperatures T ≲ 1 K. This behavior has traditionally been explained by an ensemble of weakly coupled, two-level tunneling states, a theory that is also used to describe the thermodynamic properties of glasses at low temperatures. One of the most striking acoustic signatures in this regime is the existence of phonon echoes, a feature that has been associated with two-level systems with the same formalism as spin echoes in NMR. Here we report the existence of a distinctly different type of acoustic echo in classical models of glassy materials. Our simulations consist of finite-ranged, repulsive spheres and also particles with attractive forces using Lennard-Jones interactions. We show that these echoes are due to anharmonic, weakly coupled vibrational modes and perhaps provide an alternative explanation for the phonon echoes observed in glasses at low temperatures. PMID:27078434

  9. Echoes from anharmonic normal modes in model glasses.

    PubMed

    Burton, Justin C; Nagel, Sidney R

    2016-03-01

    Glasses display a wide array of nonlinear acoustic phenomena at temperatures T ≲ 1 K. This behavior has traditionally been explained by an ensemble of weakly coupled, two-level tunneling states, a theory that is also used to describe the thermodynamic properties of glasses at low temperatures. One of the most striking acoustic signatures in this regime is the existence of phonon echoes, a feature that has been associated with two-level systems with the same formalism as spin echoes in NMR. Here we report the existence of a distinctly different type of acoustic echo in classical models of glassy materials. Our simulations consist of finite-ranged, repulsive spheres and also particles with attractive forces using Lennard-Jones interactions. We show that these echoes are due to anharmonic, weakly coupled vibrational modes and perhaps provide an alternative explanation for the phonon echoes observed in glasses at low temperatures.

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

    PubMed

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

    2015-03-01

    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 diffusion-tensor imaging (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 (three and two volunteers, respectively). Evaluation of the new approach was conducted by comparing the results with reconstructions performed with gridding, combined parallel imaging and compressed sensing and a recently proposed model-based approach. The experiments demonstrated improvements 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.

  11. 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

  12. Parallel electric fields detected via conjugate electron echoes during the Echo 7 sounding rocket flight

    NASA Technical Reports Server (NTRS)

    Nemzek, R. J.; Winckler, J. R.

    1991-01-01

    Electron detectors on the Echo 7 active sounding rocket experiment measured 'conjugate echoes' resulting from artificial electron beam injections. Analysis of the drift motion of the electrons after a complete bounce leads to measurements of the magnetospheric convection electric field mapped to ionospheric altitudes. The magnetospheric field was highly variable, changing by tens of mV/m on time scales of as little as hundreds of millisec. While the smallest-scale magnetospheric field irregularities were mapped out by ionospheric conductivity, larger-scale features were enhanced by up to 50 mV/m in the ionosphere. The mismatch between magnetospheric and ionspheric convection fields indicates a violation of the equipotential field line condition. The parallel fields occurred in regions roughly 10 km across and probably supported a total potential drop of 10-100 V.

  13. Recent Results for the ECHo Experiment

    NASA Astrophysics Data System (ADS)

    Hassel, C.; Blaum, K.; Goodacre, T. Day; Dorrer, H.; Düllmann, Ch. E.; Eberhardt, K.; Eliseev, S.; Enss, C.; Filianin, P.; Fäßler, A.; Fleischmann, A.; Gastaldo, L.; Goncharov, M.; Hengstler, D.; Jochum, J.; Johnston, K.; Keller, M.; Kempf, S.; Kieck, T.; Köster, U.; Krantz, M.; Marsh, B.; Mokry, C.; Novikov, Yu. N.; Ranitzsch, P. C. O.; Rothe, S.; Rischka, A.; Runke, J.; Saenz, A.; Schneider, F.; Scholl, S.; Schüssler, R. X.; Simkovic, F.; Stora, T.; Thörle-Pospiech, P.; Türler, A.; Veinhard, M.; Wegner, M.; Wendt, K.; Zuber, K.

    2016-08-01

    The Electron Capture in ^{163}Ho experiment, ECHo, is designed to investigate the electron neutrino mass in the sub-eV range by means of the analysis of the calorimetrically measured spectrum following the electron capture (EC) in ^{163}Ho. Arrays of low-temperature metallic magnetic calorimeters (MMCs), read-out by microwave SQUID multiplexing, will be used in this experiment. With a first MMC prototype having the ^{163}Ho source ion-implanted into the absorber, we performed the first high energy resolution measurement of the EC spectrum, which demonstrated the feasibility of such an experiment. In addition to the technological challenges for the development of MMC arrays, which preserve the single pixel performance in terms of energy resolution and bandwidth, the success of the experiment relies on the availability of large ultra-pure ^{163}Ho samples, on the precise description of the expected spectrum, and on the identification and reduction of background. We present preliminary results obtained with standard MMCs developed for soft X-ray spectroscopy, maXs-20, where the ^{163}Ho ion-implantation was performed using a high-purity ^{163}Ho source produced by advanced chemical and mass separation. With these measurements, we aim at determining an upper limit for the background level due to source contamination and provide a refined description of the calorimetrically measured spectrum. We discuss the plan for a medium scale experiment, ECHo-1k, in which about 1000 mathrm {Bq} of high-purity ^{163}Ho will be ion-implanted into detector arrays. With one year of measuring time, we will be able to achieve a sensitivity on the electron neutrino mass below 20 eV/c^2 (90 % C.L.), improving the present limit by more than one order of magnitude. This experiment will guide the necessary developments to reach the sub-eV sensitivity.

  14. A magnetic gradient induced force in NMR restricted diffusion experiments.

    PubMed

    Ghadirian, Bahman; Stait-Gardner, Tim; Castillo, Reynaldo; Price, William S

    2014-03-28

    We predict that the phase cancellation of a precessing magnetisation field carried by a diffusing species in a bounded geometry under certain nuclear magnetic resonance pulsed magnetic field gradient sequences results in a small force over typically micrometre length scales. Our calculations reveal that the total magnetisation energy in a pore under the influence of a pulsed gradient will be distance-dependent thus resulting in a force acting on the boundary. It is shown that this effect of the magnetisation of diffusing particles will appear as either an attractive or repulsive force depending on the geometry of the pore and magnetic properties of the material. A detailed analysis is performed for the case of a pulsed gradient spin-echo experiment on parallel planes. It is shown that the force decays exponentially in terms of the spin-spin relaxation. The proof is based on classical electrodynamics. An application of this effect to soft matter is suggested.

  15. A magnetic gradient induced force in NMR restricted diffusion experiments

    SciTech Connect

    Ghadirian, Bahman; Stait-Gardner, Tim; Castillo, Reynaldo; Price, William S.

    2014-03-28

    We predict that the phase cancellation of a precessing magnetisation field carried by a diffusing species in a bounded geometry under certain nuclear magnetic resonance pulsed magnetic field gradient sequences results in a small force over typically micrometre length scales. Our calculations reveal that the total magnetisation energy in a pore under the influence of a pulsed gradient will be distance-dependent thus resulting in a force acting on the boundary. It is shown that this effect of the magnetisation of diffusing particles will appear as either an attractive or repulsive force depending on the geometry of the pore and magnetic properties of the material. A detailed analysis is performed for the case of a pulsed gradient spin-echo experiment on parallel planes. It is shown that the force decays exponentially in terms of the spin-spin relaxation. The proof is based on classical electrodynamics. An application of this effect to soft matter is suggested.

  16. Ultrasound Echo is Related to Stress, Strain in Tendon

    PubMed Central

    Duenwald, Sarah; Kobayashi, Hirohito; Frisch, Kayt; Lakes, Roderic; Vanderby, Ray

    2010-01-01

    The mechanical behavior of tendons has been well studied in vitro. A noninvasive method to acquire mechanical data would be highly beneficial. Elastography has been a promising method of gathering in vivo tissue mechanical behavior, but it has inherent limitations. This study presents acoustoelasticity as an alternative ultrasound-based method of measuring tendon stress and strain by reporting a relationship between ultrasonic echo intensity (B mode ultrasound image brightness) and mechanical behavior of tendon in vitro. Porcine digital flexor tendons were cyclically loaded in a mechanical testing system while ultrasonic echo response was recorded. We report that echo intensity closely follows the applied cyclic strain pattern in time with higher strain protocols resulting in larger echo intensity changes. We also report that echo intensity is related nonlinearly to stress and nearly linearly to strain. This indicates that ultrasonic echo intensity is related to the mechanical behavior in a loaded tissue by an acoustoelastic response, as previously described in homogeneous, nearly incompressible materials. Acoustoelasticity is therefore able to relate strain-dependent stiffness and stress to the reflected echo, even in the processed B-mode signals reflected from viscoelastic, inhomogeneous material such as tendon, and is a promising metric to acquire in vivo mechanical data noninvasively. PMID:21030024

  17. Ultrasound echo is related to stress and strain in tendon.

    PubMed

    Duenwald, Sarah; Kobayashi, Hirohito; Frisch, Kayt; Lakes, Roderic; Vanderby, Ray

    2011-02-01

    The mechanical behavior of tendons has been well studied in vitro. A noninvasive method to acquire mechanical data would be highly beneficial. Elastography has been a promising method of gathering in vivo tissue mechanical behavior, but it has inherent limitations. This study presents acoustoelasticity as an alternative ultrasound-based method of measuring tendon stress and strain by reporting a relationship between ultrasonic echo intensity (B-mode ultrasound image brightness) and mechanical behavior of tendon in vitro. Porcine digital flexor tendons were cyclically loaded in a mechanical testing system while an ultrasonic echo response was recorded. We report that echo intensity closely follows the applied cyclic strain pattern in time with higher strain protocols resulting in larger echo intensity changes. We also report that echo intensity is related nonlinearly to stress and nearly linearly to strain. This indicates that ultrasonic echo intensity is related to the mechanical behavior in a loaded tissue by an acoustoelastic response, as previously described in homogeneous, nearly incompressible materials. Acoustoelasticity is therefore able to relate strain-dependent stiffness and stress to the reflected echo, even in the processed B-mode signals reflected from viscoelastic and inhomogeneous material such as tendon, and is a promising metric to acquire in vivo mechanical data noninvasively.

  18. Kinematics of illumination patterns and light echoes from flashes.

    PubMed

    Zhong, Qi

    2016-09-01

    Flash-induced light echoes-the observation of light reflected from a burst-have been observed in astronomical settings for more than a century and have been observed in the laboratory recently. Because of the flight time of light, perceived light echoes are different from real light illumination patterns on a scattering plane, neglecting interreflections and non-opaque scattering effects. The shape and motion of real illumination patterns are studied from a spherical flash. Then, ellipsoids of constant time delay for a specifically chosen coordinate system are applied. Generally, perceived light echoes are elliptical annular rings and the center of a light echo will not start at the flash, which leads to light echoes moving angularly toward the flash instead of away from it, a phenomenon actually recorded by other groups. The brightness of perceived light echoes was studied, and maximum brightness occurred close to the flash's projective point on the scattering plane. Two specific examples are given and a magnification effect between perceived echoes and real illumination patterns is proposed. PMID:27607505

  19. Oblique echoes at unusually high frequencies in MARSIS-AIS measurements of the topside ionosphere of Mars

    NASA Astrophysics Data System (ADS)

    Fallows, Kathryn J.; Withers, Paul; Morgan, David

    2016-10-01

    The topside plasma density measurements from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on the Mars Express orbiter have been invaluable for studying the influence of the crustal magnetic fields on the distribution of plasma in the Mars ionosphere. A common feature, especially in the southern crustal field region, is an "oblique echo," or an off-nadir reflection consistent with the spacecraft passing by, or directly above, a localized region with a sharp gradient in electron density. These are often interpreted as regions where the ionosphere is heated by the solar wind fields and plasma which penetrate the ionosphere along vertical field lines.We present a subset of these oblique echoes which are characterized by reflections at frequencies much higher than those from the nadir ionosphere. If these are interpreted in the same way as typical return signals, where the frequency of the reflected signal is assumed to be the plasma frequency at the point of reflection, then these may be the highest plasma densities reported to date at Mars. In two cases, reflections are detected at the maximum sounding frequency of the instrument, 5.5 MHz, which corresponds to electron densities of 3.75x105 cm-3.These features are associated with strong, vertical magnetic fields, as expected for typical oblique echoes. However, they are only observed in regions where there is also an above-average likelihood of the field lines being open to the solar wind. This is consistent with the interpretation that these cusp-like regions can allow for interaction with the solar wind, but it is not yet clear whether these are an extreme case of "typical" oblique echoes, or whether these high-frequency echoes are caused by a unique physical process or observation geometry.

  20. High-resolution MRI encoding using radiofrequency phase gradients.

    PubMed

    Sharp, Jonathan C; King, Scott B; Deng, Qunli; Volotovskyy, Vyacheslav; Tomanek, Boguslaw

    2013-11-01

    Although MRI offers highly diagnostic medical imagery, patient access to this modality worldwide is very limited when compared with X-ray or ultrasound. One reason for this is the expense and complexity of the equipment used to generate the switched magnetic fields necessary for MRI encoding. These field gradients are also responsible for intense acoustic noise and have the potential to induce nerve stimulation. We present results with a new MRI encoding principle which operates entirely without the use of conventional B0 field gradients. This new approach--'Transmit Array Spatial Encoding' (TRASE)--uses only the resonant radiofrequency (RF) field to produce Fourier spatial encoding equivalent to conventional MRI. k-space traversal (image encoding) is achieved by spin refocusing with phase gradient transmit fields in spin echo trains. A transmit coil array, driven by just a single transmitter channel, was constructed to produce four phase gradient fields, which allows the encoding of two orthogonal spatial axes. High-resolution two-dimensional-encoded in vivo MR images of hand and wrist were obtained at 0.2 T. TRASE exploits RF field phase gradients, and offers the possibility of very low-cost diagnostics and novel experiments exploiting unique capabilities, such as imaging without disturbance of the main B0 magnetic field. Lower field imaging (<1 T) and micro-imaging are favorable application domains as, in both cases, it is technically easier to achieve the short RF pulses desirable for long echo trains, and also to limit RF power deposition. As TRASE is simply an alternative mechanism (and technology) of moving through k space, there are many close analogies between it and conventional B0 -encoded techniques. TRASE is compatible with both B0 gradient encoding and parallel imaging, and so hybrid sequences containing all three spatial encoding approaches are possible.

  1. Temperature echoes revisited to probe the vibrational behavior of dendrimers.

    PubMed

    Paulo, Pedro M R

    2010-03-21

    Temperature quench echoes were induced in molecular dynamics simulations of dendrimers. This phenomenon was used to probe the vibrational behavior of these molecules by comparing simulation results with harmonic model predictions. The echo depth for short time intervals between temperature quenches is well described by the harmonic approximation and the fluctuations observed are related to the vibrational density of states. The echo depth for long time intervals decays progressively revealing dephasing due to anharmonic interactions. The density of states was calculated from the temperature fluctuations after the first quench and high-frequency modes were assigned by comparison with vibrational spectra of similar dendrimers.

  2. Fast T2 Mapping With Improved Accuracy Using Undersampled Spin-Echo MRI and Model-Based Reconstructions With a Generating Function

    PubMed Central

    Petrovic, Andreas; Uecker, Martin; Knoll, Florian; Frahm, Jens

    2015-01-01

    A model-based reconstruction technique for accelerated T2 mapping with improved accuracy is proposed using under-sampled Cartesian spin-echo magnetic resonance imaging (MRI) data. The technique employs an advanced signal model for T2 relaxation that accounts for contributions from indirect echoes in a train of multiple spin echoes. An iterative solution of the nonlinear inverse reconstruction problem directly estimates spin-density and T2 maps from undersampled raw data. The algorithm is validated for simulated data as well as phantom and human brain MRI at 3T. The performance of the advanced model is compared to conventional pixel-based fitting of echo-time images from fully sampled data. The proposed method yields more accurate T2 values than the mono-exponential model and allows for retrospective under-sampling factors of at least 6. Although limitations are observed for very long T2 relaxation times, respective reconstruction problems may be overcome by a gradient dampening approach. The analytical gradient of the utilized cost function is included as Appendix. The source code is made available to the community. PMID:24988592

  3. First radar echoes from cumulus clouds

    NASA Technical Reports Server (NTRS)

    Knight, Charles A.; Miller, L. J.

    1993-01-01

    In attempting to use centimeter-wavelength radars to investigate the early stage of precipitation formation in clouds, 'mantle echoes' are rediscovered and shown to come mostly from scattering by small-scale variations in refractive index, a Bragg kind of scattering mechanism. This limits the usefulness of single-wavelength radar for studies of hydrometeor growth, according to data on summer cumulus clouds in North Dakota, Hawaii, and Florida, to values of reflectivity factor above about 10 dBZe with 10-cm radar, 0 dBZe with 5-cm radar, and -10 dBZe with 3-cm radar. These are limits at or above which the backscattered radar signal from the kinds of clouds observed can be assumed to be almost entirely from hydrometeors or (rarely) other particulate material such as insects. Dual-wavelength radar data can provide the desired information about hydrometeors at very low reflectivity levels if assumptions can be made about the inhomogeneities responsible for the Bragg scattering. The Bragg scattering signal itself probably will be a useful way to probe inhomogeneities one-half the radar wavelength in scale for studying cloud entrainment and mixing processes. However, this use is possible only before scattering from hydrometeors dominates the radar return.

  4. Light Echoes of Galactic Explosions and Eruptions

    NASA Astrophysics Data System (ADS)

    Rest, Armin; Bianco, Federica; Chornock, Ryan; Foley, Ryan; Huber, Mark E.; Matheson, Thomas; McDonald, Brittany; Olsen, Knut; Prieto, Jose Luis; Sinnott, Brendan; Smith, Nathan; Welch, Doug

    2012-08-01

    We propose to search for light echoes (LEs) from the historical brightening of the Luminous Blue Variable (LBV) P Cygni using the KPNO 4m Mosaic 1.1 imager. We also propose to conclude our search - so far unsuccessful - for LEs from the the Crab supernova SN 1054 by surveying one remaining region of the LE ellipsoid behind the plane of the supernova remnant on the sky. In addition, we continue to monitor the LEs from the Cas A and Tycho supernovae in order to identify suitable LE candidates for 3D-spectroscopy and spectral time series. Recently, we discovered LEs of the mid-19th-century Great Eruption of η Carinae using CTIO 4m Mosaic images. Subsequent spectroscopic follow-up revealed that its outburst spectral type was most similar to those of G-type supergiants, rather than the reported LBV outburst spectral types (F-type or earlier) teRest12_eta. The application of the LE studies to LBVs promises to extend our ability to record outburst activity hundreds of years into the past - a timescale which is likely a significant fraction of the brief final phases of these probable core-collapse supernova precursors.

  5. Decoupled echo state networks with lateral inhibition.

    PubMed

    Xue, Yanbo; Yang, Le; Haykin, Simon

    2007-04-01

    Building on some prior work, in this paper we describe a novel structure termed the decoupled echo state network (DESN) involving the use of lateral inhibition. Two low-complexity implementation schemes, namely, the DESN with reservoir prediction (DESN + RP) and DESN with maximum available information (DESN + MaxInfo), are developed: (1) In the multiple superimposed oscillator (MSO) problem, DESN + MaxInfo exhibits three important attributes: lower generalization mean-square error (MSE), better robustness with respect to the random generation of reservoir weight matrix and feedback connections, and robustness to variations in the sparseness of reservoir weight matrix, compared to DESN + RP. (2) For a noiseless nonlinear prediction task, DESN + RP outperforms the DESN + MaxInfo and single reservoir-based ESN approach in terms of lower prediction MSE and better robustness to a change in the number of inputs and sparsity of the reservoir weight matrix. Finally, in a real-life prediction task using noisy sea clutter data, both schemes exhibit higher prediction accuracy and successful design ratio than a conventional ESN with a single reservoir.

  6. Beam Echo Effect for Generation of Short-Wavelength Radiation

    SciTech Connect

    Stupakov, G.; /SLAC

    2009-12-09

    The Echo-Enabled Harmonic Generation (EEHG) FEL uses two modulators in combination with two dispersion sections to generate a high-harmonic density modulation starting with a relatively small initial energy modulation of the beam. After presenting the concept of the EEHG, we address several practically important issues, such as the effect of coherent and incoherent synchrotron radiation in the dispersion sections. Using a representative realistic set of beam parameters, we show how the EEHG scheme enhances the FEL performance and allows one to generate a fully (both longitudinally and transversely) coherent radiation. We then discuss application of the echo modulation for generation of attosecond pulses of radiation, and also using echo for generation of terahertz radiation. We present main parameters of a proof-of-principle experiment currently being planned at SLAC for demonstration of the echo modulation mechanism.

  7. Free-electron lasers: Echoes of photons past

    NASA Astrophysics Data System (ADS)

    Campbell, Lawrence T.; McNeil, Brian W. J.

    2016-08-01

    High-harmonic generation is an established method to significantly upshift laser photon energies. Now, researchers at the SLAC National Accelerator Laboratory have used echo concepts to generate coherent high-harmonic output from an electron-beam light source.

  8. Asynchronous and timing jitter insensitive data echo cancellation

    NASA Astrophysics Data System (ADS)

    Messerschmitt, David G.

    1986-12-01

    An approach to the implementation of asynchronous and timing jitter insensitive data echo cancellation is described. This approach introduces a small amount of jitter in the transmitted data signal, or alternatively in the received signal sampling, and uses a simple digital phase-locked loop together with the storage of two sets of echo canceller coefficients. The effect of derived timing jitter on the echo cancellation accuracy is completely eliminated for a loop timed transceiver (as in a digital subscriber loop network termination transceiver), and is easily reduced to negligible levels for a nonloop timed transceiver (as in a digital subscriber loop line card transceiver or a voiceband data modem). In the case of a voiceband data modem, this approach is one method to achieve asynchronous echo cancellation without the need to recover and resample a continuous-time far-end data signal.

  9. Loschmidt echo and time reversal in complex systems.

    PubMed

    Goussev, Arseni; Jalabert, Rodolfo A; Pastawski, Horacio M; Wisniacki, Diego A

    2016-06-13

    Echoes are ubiquitous phenomena in several branches of physics, ranging from acoustics, optics, condensed matter and cold atoms to geophysics. They are at the base of a number of very useful experimental techniques, such as nuclear magnetic resonance, photon echo and time-reversal mirrors. Particularly interesting physical effects are obtained when the echo studies are performed on complex systems, either classically chaotic, disordered or many-body. Consequently, the term Loschmidt echo has been coined to designate and quantify the revival occurring when an imperfect time-reversal procedure is applied to a complex quantum system, or equivalently to characterize the stability of quantum evolution in the presence of perturbations. Here, we present the articles which discuss the work that has shaped the field in the past few years. PMID:27140977

  10. Loschmidt echo and time reversal in complex systems.

    PubMed

    Goussev, Arseni; Jalabert, Rodolfo A; Pastawski, Horacio M; Wisniacki, Diego A

    2016-06-13

    Echoes are ubiquitous phenomena in several branches of physics, ranging from acoustics, optics, condensed matter and cold atoms to geophysics. They are at the base of a number of very useful experimental techniques, such as nuclear magnetic resonance, photon echo and time-reversal mirrors. Particularly interesting physical effects are obtained when the echo studies are performed on complex systems, either classically chaotic, disordered or many-body. Consequently, the term Loschmidt echo has been coined to designate and quantify the revival occurring when an imperfect time-reversal procedure is applied to a complex quantum system, or equivalently to characterize the stability of quantum evolution in the presence of perturbations. Here, we present the articles which discuss the work that has shaped the field in the past few years.

  11. Light echoes and transient luminescence near SN 1987A

    NASA Technical Reports Server (NTRS)

    Crotts, Arlin P. S.; Kunkel, William E.; Mccarthy, Patrick J.

    1989-01-01

    The discovery of two new light echoes from sheets of material behind supernova 1987A and present images of the progenitor's circumstellar shell are reported, indicating diffuse echoes from the star's red giant wind. The echo sheets' geometry explains well the behavior of SN 1987's 10-micron flux, but the circumstellar shell appears to be 70 percent larger than the prediction from the analysis of narrow UV emission lines. The sheets' recombination time show them relatively thin and dense. The data also constrain the existence of any fourth star in the Sanduleak -69 deg 202 system and show that the feature reported 8 arcsecs from the supernova is probably not an echo from a thin sheet in SN 1987A's foreground.

  12. Loschmidt echo and time reversal in complex systems

    PubMed Central

    Goussev, Arseni; Jalabert, Rodolfo A.; Pastawski, Horacio M.; Wisniacki, Diego A.

    2016-01-01

    Echoes are ubiquitous phenomena in several branches of physics, ranging from acoustics, optics, condensed matter and cold atoms to geophysics. They are at the base of a number of very useful experimental techniques, such as nuclear magnetic resonance, photon echo and time-reversal mirrors. Particularly interesting physical effects are obtained when the echo studies are performed on complex systems, either classically chaotic, disordered or many-body. Consequently, the term Loschmidt echo has been coined to designate and quantify the revival occurring when an imperfect time-reversal procedure is applied to a complex quantum system, or equivalently to characterize the stability of quantum evolution in the presence of perturbations. Here, we present the articles which discuss the work that has shaped the field in the past few years. PMID:27140977

  13. A model for depolarized radar echoes from Mars

    NASA Technical Reports Server (NTRS)

    Thompson, T. W.; Moore, H. J.

    1989-01-01

    The depolarized radar echoes from Mars are modeled using a combination of remote-sensing observations. The model reproduces the variations of the total radar cross-sections with longitude observed by Goldstone (1986) along 7 S, yields larger magnitudes of total radar cross-sections along 22 N than those along 7 S, and produces depolarized echo spectra that broadly match those observed by the Arecibo radar in 1980 and 1982. The model indicates that volcanoes and lava plains of the Tharsis-Alba Patera, Elysium, and Amazonia regions have the strongest depolarized echoes from the entire planet. Rock populations for the moon and Mars are estimated assuming depolarized radar echoes result from rocks with radii between 1.3 and three times the wavelength.

  14. T2-weighted fast spin-echo magnetic resonance imaging of extraocular muscles

    PubMed Central

    Demer, Joseph L.; Dushyanth, Anita

    2011-01-01

    Purpose Magnetic resonance imaging (MRI) can provide unique information about extraocular muscle (EOM) structure and function. Prior high-resolution motility imaging studies employed T1 weighting, which provides intrinsic contrast of dark-appearing EOMs against bright orbital fat and is suitable for intravenous contrast. However, time-consuming T1 sequences are subject to motion artifacts. We evaluated an alternative T2-weighted fast spin-echo pulse sequence that emphasizes tissue-free fluid. Methods We prospectively used high resolution, surface coil technique for orbital MRI at 1.5T in 21 normal and 113 living strabismic subjects and 2 monkey cadavers using T2 fast spin-echo (T2FSE) weighting (long repetition time, short echo time). T2FSE was compared with T1 in 17 subjects, and with T1 in 506 different living subjects, and 12 cadavers. Results For 2 mm thick coronal MRIs of 312 μm resolution spanning the entire orbit, T1 acquisition required 218 seconds, whereas T2FSE required 150 seconds (31% faster). T2-defined the globe border better, and provided intrinsic contrast between EOMs and their pulleys. While both T1 and T2 demonstrated motor nerves to EOMs in living subjects, only T1 was satisfactory with injected contrast and in cadavers. Conclusions For motility imaging, T2FSE is faster than T1 MRI and demonstrates superior tissue details of EOMs and other orbital tissues. T2FSE of the orbits can be performed using widely available standard equipment. We suggest that T2FSE be the preferred method for clinical imaging of EOM structure, function, and innervation, although T1 may be more appropriate when intravenous contrast must be employed. PMID:21397801

  15. Fast mapping of the T2 relaxation time of cerebral metabolites using proton echo-planar spectroscopic imaging (PEPSI).

    PubMed

    Tsai, Shang-Yueh; Posse, Stefan; Lin, Yi-Ru; Ko, Cheng-Wen; Otazo, Ricardo; Chung, Hsiao-Wen; Lin, Fa-Hsuan

    2007-05-01

    Metabolite T2 is necessary for accurate quantification of the absolute concentration of metabolites using long-echo-time (TE) acquisition schemes. However, lengthy data acquisition times pose a major challenge to mapping metabolite T2. In this study we used proton echo-planar spectroscopic imaging (PEPSI) at 3T to obtain fast T2 maps of three major cerebral metabolites: N-acetyl-aspartate (NAA), creatine (Cre), and choline (Cho). We showed that PEPSI spectra matched T2 values obtained using single-voxel spectroscopy (SVS). Data acquisition for 2D metabolite maps with a voxel volume of 0.95 ml (32 x 32 image matrix) can be completed in 25 min using five TEs and eight averages. A sufficient spectral signal-to-noise ratio (SNR) for T2 estimation was validated by high Pearson's correlation coefficients between logarithmic MR signals and TEs (R2 = 0.98, 0.97, and 0.95 for NAA, Cre, and Cho, respectively). In agreement with previous studies, we found that the T2 values of NAA, but not Cre and Cho, were significantly different between gray matter (GM) and white matter (WM; P < 0.001). The difference between the T2 estimates of the PEPSI and SVS scans was less than 9%. Consistent spatial distributions of T2 were found in six healthy subjects, and disagreement among subjects was less than 10%. In summary, the PEPSI technique is a robust method to obtain fast mapping of metabolite T2.

  16. Fast mapping of the T2 relaxation time of cerebral metabolites using proton echo-planar spectroscopic imaging (PEPSI).

    PubMed

    Tsai, Shang-Yueh; Posse, Stefan; Lin, Yi-Ru; Ko, Cheng-Wen; Otazo, Ricardo; Chung, Hsiao-Wen; Lin, Fa-Hsuan

    2007-05-01

    Metabolite T2 is necessary for accurate quantification of the absolute concentration of metabolites using long-echo-time (TE) acquisition schemes. However, lengthy data acquisition times pose a major challenge to mapping metabolite T2. In this study we used proton echo-planar spectroscopic imaging (PEPSI) at 3T to obtain fast T2 maps of three major cerebral metabolites: N-acetyl-aspartate (NAA), creatine (Cre), and choline (Cho). We showed that PEPSI spectra matched T2 values obtained using single-voxel spectroscopy (SVS). Data acquisition for 2D metabolite maps with a voxel volume of 0.95 ml (32 x 32 image matrix) can be completed in 25 min using five TEs and eight averages. A sufficient spectral signal-to-noise ratio (SNR) for T2 estimation was validated by high Pearson's correlation coefficients between logarithmic MR signals and TEs (R2 = 0.98, 0.97, and 0.95 for NAA, Cre, and Cho, respectively). In agreement with previous studies, we found that the T2 values of NAA, but not Cre and Cho, were significantly different between gray matter (GM) and white matter (WM; P < 0.001). The difference between the T2 estimates of the PEPSI and SVS scans was less than 9%. Consistent spatial distributions of T2 were found in six healthy subjects, and disagreement among subjects was less than 10%. In summary, the PEPSI technique is a robust method to obtain fast mapping of metabolite T2. PMID:17457864

  17. Syntax acquisition.

    PubMed

    Crain, Stephen; Thornton, Rosalind

    2012-03-01

    Every normal child acquires a language in just a few years. By 3- or 4-years-old, children have effectively become adults in their abilities to produce and understand endlessly many sentences in a variety of conversational contexts. There are two alternative accounts of the course of children's language development. These different perspectives can be traced back to the nature versus nurture debate about how knowledge is acquired in any cognitive domain. One perspective dates back to Plato's dialog 'The Meno'. In this dialog, the protagonist, Socrates, demonstrates to Meno, an aristocrat in Ancient Greece, that a young slave knows more about geometry than he could have learned from experience. By extension, Plato's Problem refers to any gap between experience and knowledge. How children fill in the gap in the case of language continues to be the subject of much controversy in cognitive science. Any model of language acquisition must address three factors, inter alia: 1. The knowledge children accrue; 2. The input children receive (often called the primary linguistic data); 3. The nonlinguistic capacities of children to form and test generalizations based on the input. According to the famous linguist Noam Chomsky, the main task of linguistics is to explain how children bridge the gap-Chomsky calls it a 'chasm'-between what they come to know about language, and what they could have learned from experience, even given optimistic assumptions about their cognitive abilities. Proponents of the alternative 'nurture' approach accuse nativists like Chomsky of overestimating the complexity of what children learn, underestimating the data children have to work with, and manifesting undue pessimism about children's abilities to extract information based on the input. The modern 'nurture' approach is often referred to as the usage-based account. We discuss the usage-based account first, and then the nativist account. After that, we report and discuss the findings of several

  18. Syntax acquisition.

    PubMed

    Crain, Stephen; Thornton, Rosalind

    2012-03-01

    Every normal child acquires a language in just a few years. By 3- or 4-years-old, children have effectively become adults in their abilities to produce and understand endlessly many sentences in a variety of conversational contexts. There are two alternative accounts of the course of children's language development. These different perspectives can be traced back to the nature versus nurture debate about how knowledge is acquired in any cognitive domain. One perspective dates back to Plato's dialog 'The Meno'. In this dialog, the protagonist, Socrates, demonstrates to Meno, an aristocrat in Ancient Greece, that a young slave knows more about geometry than he could have learned from experience. By extension, Plato's Problem refers to any gap between experience and knowledge. How children fill in the gap in the case of language continues to be the subject of much controversy in cognitive science. Any model of language acquisition must address three factors, inter alia: 1. The knowledge children accrue; 2. The input children receive (often called the primary linguistic data); 3. The nonlinguistic capacities of children to form and test generalizations based on the input. According to the famous linguist Noam Chomsky, the main task of linguistics is to explain how children bridge the gap-Chomsky calls it a 'chasm'-between what they come to know about language, and what they could have learned from experience, even given optimistic assumptions about their cognitive abilities. Proponents of the alternative 'nurture' approach accuse nativists like Chomsky of overestimating the complexity of what children learn, underestimating the data children have to work with, and manifesting undue pessimism about children's abilities to extract information based on the input. The modern 'nurture' approach is often referred to as the usage-based account. We discuss the usage-based account first, and then the nativist account. After that, we report and discuss the findings of several

  19. Spin Echo in Spinor Dipolar Bose-Einstein Condensates

    SciTech Connect

    Yasunaga, Masashi; Tsubota, Makoto

    2008-11-28

    We theoretically propose and numerically realize spin echo in a spinor Bose-Einstein condensate (BEC). We investigate the influence on the spin echo of phase separation of the condensate. The equation of motion of the spin density exhibits two relaxation times. We use two methods to separate the relaxation times and hence demonstrate a technique to reveal magnetic dipole-dipole interactions in spinor BECs.

  20. The architecture of dynamic reservoir in the echo state network

    NASA Astrophysics Data System (ADS)

    Cui, Hongyan; Liu, Xiang; Li, Lixiang

    2012-09-01

    Echo state network (ESN) has recently attracted increasing interests because of its superior capability in modeling nonlinear dynamic systems. In the conventional echo state network model, its dynamic reservoir (DR) has a random and sparse topology, which is far from the real biological neural networks from both structural and functional perspectives. We hereby propose three novel types of echo state networks with new dynamic reservoir topologies based on complex network theory, i.e., with a small-world topology, a scale-free topology, and a mixture of small-world and scale-free topologies, respectively. We then analyze the relationship between the dynamic reservoir structure and its prediction capability. We utilize two commonly used time series to evaluate the prediction performance of the three proposed echo state networks and compare them to the conventional model. We also use independent and identically distributed time series to analyze the short-term memory and prediction precision of these echo state networks. Furthermore, we study the ratio of scale-free topology and the small-world topology in the mixed-topology network, and examine its influence on the performance of the echo state networks. Our simulation results show that the proposed echo state network models have better prediction capabilities, a wider spectral radius, but retain almost the same short-term memory capacity as compared to the conventional echo state network model. We also find that the smaller the ratio of the scale-free topology over the small-world topology, the better the memory capacities.

  1. A local Echo State Property through the largest Lyapunov exponent.

    PubMed

    Wainrib, Gilles; Galtier, Mathieu N

    2016-04-01

    Echo State Networks are efficient time-series predictors, which highly depend on the value of the spectral radius of the reservoir connectivity matrix. Based on recent results on the mean field theory of driven random recurrent neural networks, enabling the computation of the largest Lyapunov exponent of an ESN, we develop a cheap algorithm to establish a local and operational version of the Echo State Property.

  2. The architecture of dynamic reservoir in the echo state network.

    PubMed

    Cui, Hongyan; Liu, Xiang; Li, Lixiang

    2012-09-01

    Echo state network (ESN) has recently attracted increasing interests because of its superior capability in modeling nonlinear dynamic systems. In the conventional echo state network model, its dynamic reservoir (DR) has a random and sparse topology, which is far from the real biological neural networks from both structural and functional perspectives. We hereby propose three novel types of echo state networks with new dynamic reservoir topologies based on complex network theory, i.e., with a small-world topology, a scale-free topology, and a mixture of small-world and scale-free topologies, respectively. We then analyze the relationship between the dynamic reservoir structure and its prediction capability. We utilize two commonly used time series to evaluate the prediction performance of the three proposed echo state networks and compare them to the conventional model. We also use independent and identically distributed time series to analyze the short-term memory and prediction precision of these echo state networks. Furthermore, we study the ratio of scale-free topology and the small-world topology in the mixed-topology network, and examine its influence on the performance of the echo state networks. Our simulation results show that the proposed echo state network models have better prediction capabilities, a wider spectral radius, but retain almost the same short-term memory capacity as compared to the conventional echo state network model. We also find that the smaller the ratio of the scale-free topology over the small-world topology, the better the memory capacities.

  3. The architecture of dynamic reservoir in the echo state network.

    PubMed

    Cui, Hongyan; Liu, Xiang; Li, Lixiang

    2012-09-01

    Echo state network (ESN) has recently attracted increasing interests because of its superior capability in modeling nonlinear dynamic systems. In the conventional echo state network model, its dynamic reservoir (DR) has a random and sparse topology, which is far from the real biological neural networks from both structural and functional perspectives. We hereby propose three novel types of echo state networks with new dynamic reservoir topologies based on complex network theory, i.e., with a small-world topology, a scale-free topology, and a mixture of small-world and scale-free topologies, respectively. We then analyze the relationship between the dynamic reservoir structure and its prediction capability. We utilize two commonly used time series to evaluate the prediction performance of the three proposed echo state networks and compare them to the conventional model. We also use independent and identically distributed time series to analyze the short-term memory and prediction precision of these echo state networks. Furthermore, we study the ratio of scale-free topology and the small-world topology in the mixed-topology network, and examine its influence on the performance of the echo state networks. Our simulation results show that the proposed echo state network models have better prediction capabilities, a wider spectral radius, but retain almost the same short-term memory capacity as compared to the conventional echo state network model. We also find that the smaller the ratio of the scale-free topology over the small-world topology, the better the memory capacities. PMID:23020466

  4. Transforming echoes into pseudo-action potentials for classifying plants.

    PubMed

    Kuc, R

    2001-10-01

    Animals perceive their environment by converting sensory stimuli into action potentials, or temporal point processes, that are interpreted by the brain. This paper investigates the information content of point processes extracted from echoes from in situ plants in an effort to understand how bats recognize landmarks in the field. A mobile sonar converts echoes into biologically similar temporal point processes. termed pseudo-action potentials (PAPs), whose inter-PAP interval relates to echo amplitude. The sonar forms a sector scan of an object to produce a spatial-temporal PAP field. Classifier neurons apply delays and coincidence detection to the PAP field to identify three distinct echo types, glints, blobs, and fuzz, which characterize plant features. Glints are large amplitude echoes exhibiting coherence over successive echoes in the sector scan, typically produced by favorably oriented isolated specular reflectors. Blobs are large echoes lacking coherence, typically bordering glints or formed by collections of interfering reflectors. Fuzz represents weak echoes, typically produced by collection of weak scatterers or by reflectors on the beam periphery. A small mirror reflector models a flat leaf surface and motivates the glint criteria. Classifiers are applied to experimental data from two types of tree trunks, a glint-producing sycamore (Platanus occidenatalis) and a glint-absent Norway maple (Acer platanoides) and two plants, a glint-producing rhododendron (Rhododendron maximus) and a glint-absent yew (Taxus media). We speculate that our narrow-band sonar models the activity of a single frequency bin in the frequency-modulated (FM) sweep emitted by bats, and that one function of the frequency bins in the FM sweep is to form a sector scan of the environment.

  5. Preliminary results of the echo-seeding experiment at SLAC

    SciTech Connect

    Xiang, D.; Colby, E.; Ding, Y.; Dunning, M.; Frederico, J.; Gilevich, S.; Hast, C.; Jobe, K.; McCormick, D.; Nelson, J.; Raubenheimer, T.O.; Soong, K.; Stupakov, G.; Szalata, Z.; Walz, D.; Weathersby, S.; Woodley, M.; Corlett, J.; Qiang, J.; Penn, G.; Prestemon, S.; Schlueter, R.; Venturini, M.; Wan, W.; Pernet, P-L.

    2010-05-23

    ECHO-7 is a proof-of-principle echo-enabled harmonic generation FEL experiment in the Next Linear Collider Test Accelerator (NLCTA) at SLAC. The experiment aims to generate coherent radiation at 318 nm and 227 nm, which are the 5th and 7th harmonic of the infrared seed laser. In this paper we present the preliminary results from the commissioning run of the completed experimental setup which started in April 2010.

  6. Empirical compensation function for eddy current effects in pulsed field gradient nuclear magnetic resonance experiments.

    PubMed

    Zhu, X X; Macdonald, P M

    1995-05-01

    An empirical compensation function for the correction of eddy current effects in the Stejskal-Tanner pulsed-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR) experiments has been established. Eddy currents may arise as a result of the application of sharp and strong gradient pulses and may cause severe distortion of the NMR signals. In this method, the length of one gradient pulse is altered to compensate for the eddy current effects. The compensation is considered to be ideal when the position and the phase of the spin-echo maximum obtained from an aqueous solution of poly(ethylene glycol) (PEG) is the same in the presence and absence of a gradient pulse in the PGSE pulse sequence. We first characterized the functional dependence of the length of the required compensation on the three principal variables in the PGSE experiment: the gradient strength, the duration of the gradient pulse, and the interval between the two gradient pulses. Subsequently, we derived a model which successfully describes the general relationship between these variables and the size of the induced eddy current. The parameters extracted from fitting the model to the experimental compensation data may be used to predict the correct compensation for any combination of the three principal variables.

  7. EChO: What are exoplanets made of?

    NASA Astrophysics Data System (ADS)

    Tinetti, G.; Drossart, P.; Isaak, K.; Krause, O.; Lovis, C.; Micela, G.; Ollivier, M.; Ribas, I.; Snellen, I.; Swinyard, AB(B.

    2012-09-01

    The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of exoplanetary atmospheres. EChO will expand the playground of planetary science beyond our solar system, by providing a representative sample of exoplanet spectra under a wide range of physical and chemical conditions. The observed chemical composition largely depends on the planet's thermal structure, which in turn depends on the planet's orbital distance and metallicity, and the host star's luminosity and stellar type. The planetary mass determines the planet's ability to retain an atmosphere. The range of planets and stellar environments explored by EChO extends from the very hot to the temperate zone and includes gas-giants, Neptunes and super-Earths. EChO has been selected in 2011 as one of the four ESA M3 mission candidates, and it is currently in assessment phase. Here we will focus on the science of EChO and present the results obtained by the EChO Science Study Team.

  8. 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. PMID:26550870

  9. 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.

  10. Segmented k-space fast cardiac imaging using an echo-train readout.

    PubMed

    Epstein, F H; Wolff, S D; Arai, A E

    1999-03-01

    A segmented k-space fast gradient-echo pulse sequence with an echo-train readout (FGRE-ET) was developed for high-quality cine imaging of the heart in reduced scan times. Using segmented FGRE-ET, cine images of the heart can be acquired in as few as 1-5 heart beats and do not display the geometric distortion and flow-related artifacts typically associated with cardiac echoplanar imaging (EPI). Segmented FGRE-ET was compared with conventional segmented FGRE and with conventional multi-phase EPI in normal volunteers. Segmented FGRE-ET was found to have reduced temporal blurring compared with segmented FGRE for cine imaging in 4 heart beats (P<0.05). Also, segmented FGRE-ET did not display geometric distortion characteristic of conventional EPI (P<0.05). Segmented FGRE-ET may be particularly applicable to functional cardiac stress testing because it allows versatile cine imaging in very short breath-holds.

  11. Control and Detection of the Larmor Precession of F = 2 87Rb Bose-Einstein Condensates by Ramsey Interferometry and Spin-Echo

    NASA Astrophysics Data System (ADS)

    Eto, Yujiro; Sekine, Sawako; Hasegawa, Sho; Sadgrove, Mark; Saito, Hiroki; Hirano, Takuya

    2013-05-01

    Radio-frequency pulses are applied to probe and control the Larmor precession of a spin-2 Bose-Einstein condensate subject to a magnetic field gradient. Using the techniques of Ramsey interferometry and Stern-Gerlach absorption imaging, a helical spin pattern was clearly observed as spatial variations in the atomic density distribution. We experimentally show that the spin echo technique reduces the effects of spatially inhomogeneous and temporally fluctuating spin evolution, and improves the repeatability of the interferometry.

  12. LRS data processing methods for detection of lunar subsurface echoes

    NASA Astrophysics Data System (ADS)

    Oshigami, Shoko; Mochizuki, Kengo; Watanabe, Shiho; Watanabe, Toshiki; Yamaguchi, Yasushi; Yamaji, Atsushi; Ono, Takayuki; Kumamoto, Atsushi; Nakagawa, Hiromu; Kobayashi, Takao; Kasahara, Yoshiya

    Lunar Radar Sounder (LRS) is an instrument for one of fifteen science missions of SE- LENE (KAGUYA). LRS is a ground-penetrating FM-CW radar system of HF-band. LRS detects echoes reflected from subsurface discontinuities where dielectric constants of the rocks change. The range resolution of LRS is 75 m in free space, whereas the sampling interval in the flight direction is about 75 m when the spacecraft altitude is 100 km. The primary objective of LRS is to investigate lunar subsurface structures. We plan to perform global soundings by LRS to contribute to studying the evolution of the Moon. In this presentation, we introduce the techniques to process LRS data to produce data products and to detect subsurface echoes. We have two standard data products of LRS under consideration. The time series data of ‘A-scope' which is a plot of signal power spectrum as a function of range derived from of the waveform data are called ‘B-scan'. Because LRS instruments change timing of data recording (measurement delay time) according to the predicted distance between KAGUYA spacecraft and lunar surface, observation range with respect to the spacecraft varies from pulse to pulse. In addition, flight altitude of KAGUYA changes in the range of several tens of kilometers. Therefore a trace of surface nadir echoes in unprocessed B-scan images does not correspond to actual lunar topography. We corrected variations of the measurement delay time and flight altitude of KAGUYA to produce a B-scan data product with the original spatial resolution (BScan high) and a reduced spatial resolution product (BScan low) both in the PDS format. The echo signals in A-scope data might be classified in the following categories; (1) a surface nadir echo, (2) surface off-nadir backscattering echoes, and (3) subsurface echoes. The most intense signal usually comes from the nadir point, when KAGUYA is flying over a level surface. The A-scope data also include various noises resulted from, for example

  13. Frequency-time correlation of inhomogeneous broadening in a three-level system and the stimulated photon echo locking effect

    NASA Astrophysics Data System (ADS)

    Nefed'ev, L. A.; Nizamova, E. I.; Garnaeva, G. I.

    2016-07-01

    The frequency-time correlation of inhomogeneous broadening on different transitions in a threelevel resonant medium in the presence of external spatially nonuniform electric fields is considered. It is shown that, under a certain relationship between the magnitudes of gradients of external nonuniform electric fields acting at different moments of time, it is possible to control the magnitude of the frequency-time correlation on different frequency transitions. An increase in the frequency-time correlation coefficient with certain strengths of external spatially nonuniform electric fields leads to the recovery of the phase memory of the system and an increase in the stimulated photon echo intensity.

  14. Echo detection and target-ranging neurons in the auditory system of the bat Eptesicus fuscus.

    PubMed

    Feng, A S; Simmons, J A; Kick, S A

    1978-11-10

    Some of the neurons in the nucleus intercollicularis and auditory cortex of the echolocating bat Eptesicus fuscus respond selectively to sonar echoes occurring with specific echo delays or pulse-echo intervals. They do not respond for a wide range of other types of sounds or for sonar echoes at longer or shorter pulse-echo intervals; they may, therefore, be specialized for detection and ranging of sonar targets.

  15. A Field Method for Backscatter Calibration Applied to NOAA's Reson 7125 Multibeam Echo-Sounders

    NASA Astrophysics Data System (ADS)

    Welton, Briana

    Acoustic seafloor backscatter measurements made by multiple Reson multibeam echo-sounders (MBES) used for hydrographic survey are observed to be inconsistent, affecting the quality of data products and impeding large-scale processing efforts. A method to conduct a relative inter and intea sonar calibration in the field using dual frequency Reson 7125 MBES has been developed, tested, and evaluated to improve the consistency of backscatter measurements made from multiple MBES systems. The approach is unique in that it determines a set of corrections for power, gain, pulse length, and an angle dependent calibration term relative to a single Reson 7125 MBES calibrated in an acoustic test tank. These corrections for each MBES can then be applied during processing for any acquisition setting combination. This approach seeks to reduce the need for subjective and inefficient manual data or data product manipulation during post processing, providing a foundation for improved automated seafloor characterization using data from more than one MBES system.

  16. Exoplanetary Characterisation Observatory (EChO)

    NASA Astrophysics Data System (ADS)

    Waldmann, Ingo; Tinetti, Giovanna

    2013-04-01

    The science of extrasolar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 800-plus planets being detected, and over 2000 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are? The Exoplanet Characterisation Observatory (EChO) is a space mission dedicated to undertaking spectroscopy of transiting exoplanets over the widest range possible and is currently being studied by ESA in the context of a medium class mission within the Cosmic Vision programme for launch post 2020. The mission is based around a highly stable space platform with a 1.2 m class telescope at L2, hosting a suit of spectrographs providing continuous spectral coverage from 0.5 to 16 microns. Such a broad and simultaneous wavelength coverage allows the unique insight into the atmospheric make up of these foreign worlds and allows us to study their planetary and atmospheric compositions and evolutions.

  17. Investigating Second Language Acquisition.

    ERIC Educational Resources Information Center

    Jordens, Peter, Ed.; Lalleman, Josine, Ed.

    Essays in second language acquisition include: "The State of the Art in Second Language Acquisition Research" (Josine Lalleman); "Crosslinguistic Influence with Special Reference to the Acquisition of Grammar" (Michael Sharwood Smith); "Second Language Acquisition by Adult Immigrants: A Multiple Case Study of Turkish and Moroccan Learners of…

  18. Dynamics of caged microemulsion droplets: a neutron spin echo and dynamic light scattering study

    NASA Astrophysics Data System (ADS)

    Geyer, Arnaud de; Molle, Boris; Lartigue, Colette; Guillermo, Armel; Farago, Bela

    2004-07-01

    We report a neutron spin echo (NSE) and dynamic light scattering (DLS) study of droplet dynamics in a microemulsion at high droplet packing fraction ( Φdroplet∼62%). NSE measurements in range qr≫1 allow to investigate the short-range Brownian motion of droplets trapped within the cages formed by their nearest neighbors. For a particular scattering contrast, NSE also reveals, for q values around qr∼ π, the shape fluctuations of the caged droplets. In range qr≪1, DLS correlation functions reveal two independent diffusive modes with well separated decay times. Comparing DLS results with NSE and pulsed-field gradient NMR measurements allows to associate both DLS modes with collective dynamics of ‘transient-trapped’ droplets, revealing strong similarity to the long-time and short-time diffusion modes observed by light scattering in concentrated colloidal suspensions below the glass transition.

  19. Noncontrast-enhanced three-dimensional (3D) intracranial MR angiography using pseudocontinuous arterial spin labeling and accelerated 3D radial acquisition.

    PubMed

    Wu, Huimin; Block, Walter F; Turski, Patrick A; Mistretta, Charles A; Johnson, Kevin M

    2013-03-01

    Pseudocontinuous arterial spin labeling (PCASL) can be used to generate noncontrast magnetic resonance angiograms of the cerebrovascular structures. Previously described PCASL-based angiography techniques were limited to two-dimensional projection images or relatively low-resolution three-dimensional (3D) imaging due to long acquisition time. This work proposes a new PCASL-based 3D magnetic resonance angiography method that uses an accelerated 3D radial acquisition technique (VIPR, spoiled gradient echo) as the readout. Benefiting from the sparsity provided by PCASL and noise-like artifacts of VIPR, this new method is able to obtain submillimeter 3D isotropic resolution and whole head coverage with a 8-min scan. Intracranial angiography feasibility studies in healthy (N = 5) and diseased (N = 5) subjects show reduced saturation artifacts in PCASL-VIPR compared with a standard time-of-flight protocol. These initial results show great promise for PCASL-VIPR for static, dynamic, and vessel selective 3D intracranial angiography. PMID:22532423

  20. Cortical neurons of bats respond best to echoes from nearest targets when listening to natural biosonar multi-echo streams

    PubMed Central

    Beetz, M. Jerome; Hechavarría, Julio C.; Kössl, Manfred

    2016-01-01

    Bats orientate in darkness by listening to echoes from their biosonar calls, a behaviour known as echolocation. Recent studies showed that cortical neurons respond in a highly selective manner when stimulated with natural echolocation sequences that contain echoes from single targets. However, it remains unknown how cortical neurons process echolocation sequences containing echo information from multiple objects. In the present study, we used echolocation sequences containing echoes from three, two or one object separated in the space depth as stimuli to study neuronal activity in the bat auditory cortex. Neuronal activity was recorded with multi-electrode arrays placed in the dorsal auditory cortex, where neurons tuned to target-distance are found. Our results show that target-distance encoding neurons are mostly selective to echoes coming from the closest object, and that the representation of echo information from distant objects is selectively suppressed. This suppression extends over a large part of the dorsal auditory cortex and may override possible parallel processing of multiple objects. The presented data suggest that global cortical suppression might establish a cortical “default mode” that allows selectively focusing on close obstacle even without active attention from the animals. PMID:27786252

  1. Centerband-only analysis of rotor-unsynchronized spin echo for measurement of lipid (31) P chemical shift anisotropy.

    PubMed

    Umegawa, Yuichi; Yamaguchi, Toshiyuki; Murata, Michio; Matsuoka, Shigeru

    2015-07-01

    Structural diversity and molecular flexibility of phospholipids are essential for biological membranes to play key roles in numerous cellular processes. Uncovering the behavior of individual lipids in membrane dynamics is crucial for understanding the molecular mechanisms underlying biological functions of cell membranes. In this paper, we introduce a simple method to investigate dynamics of lipid molecules in multi-component systems by measuring the (31) P chemical shift anisotropy (CSA) under magic angle spinning (MAS) conditions. For achieving both signal separation and CSA determination, we utilized a centerband-only analysis of rotor-unsynchronized spin echo (COARSE). This analysis is based on the curve fitting of periodic modulation of centerband intensity along the interpulse delay time in rotor-unsynchronized spin-echo experiments. The utility of COARSE was examined by using phospholipid vesicles, a three-component lipid raft model system, and archaeal purple membranes. We found that the apparent advantages of this method are high resolution and high sensitivity given by the moderate MAS speed and the one-dimensional acquisition with short spin-echo delays. COARSE provides an alternative method for CSA measurement that is effective in the investigation of lipid polymorphologies.

  2. Diffusion-weighted line-scan echo-planar spectroscopic imaging technique to reduce motion artifacts in metabolite diffusion imaging.

    PubMed

    Bito, Yoshitaka; Hirata, Koji; Ebisu, Toshihiko; Kawai, Yuko; Otake, Yosuke; Hirata, Satoshi; Shirai, Toru; Soutome, Yoshihisa; Ochi, Hisaaki; Yamamoto, Etsuji; Umeda, Masahiro; Higuchi, Toshihiro; Tanaka, Chuzo

    2015-01-01

    Metabolite diffusion is expected to provide more specific microstructural and functional information than water diffusion. However, highly accurate measurement techniques have still not been developed, especially for reducing motion artifacts caused by cardiac pulsation and respiration. We developed a diffusion-weighted line-scan echo-planar spectroscopic imaging (DW-LSEPSI) technique to reduce such motion artifacts in measuring diffusion-weighted images (DWI) of metabolites. Our technique uses line-scan and echo-planar techniques to reduce phase errors induced by such motion during diffusion time. The phase errors are corrected using residual water signals in water suppression for each acquisition and at each spatial pixel specified by combining the line-scan and echo-planar techniques. We apply this technique to a moving phantom and a rat brain in vivo to demonstrate the reduction of motion artifacts in DWI and apparent diffusion coefficient (ADC) maps of metabolites. DW-LSEPSI will be useful for investigating a cellular diffusion environment using metabolites as probes.

  3. Separated two-phase flow regime parameter measurement by a high speed ultrasonic pulse-echo system.

    PubMed

    Masala, Tatiana; Harvel, Glenn; Chang, Jen-Shih

    2007-11-01

    In this work, a high speed ultrasonic multitransducer pulse-echo system using a four transducer method was used for the dynamic characterization of gas-liquid two-phase separated flow regimes. The ultrasonic system consists of an ultrasonic pulse signal generator, multiplexer, 10 MHz (0.64 cm) ultrasonic transducers, and a data acquisition system. Four transducers are mounted on a horizontal 2.1 cm inner diameter circular pipe. The system uses a pulse-echo method sampled every 0.5 ms for a 1 s duration. A peak detection algorithm (the C-scan mode) is developed to extract the location of the gas-liquid interface after signal processing. Using the measured instantaneous location of the gas/liquid interface, two-phase flow interfacial parameters in separated flow regimes are determined such as liquid level and void fraction for stratified wavy and annular flow. The shape of the gas-liquid interface and, hence, the instantaneous and cross-sectional averaged void fraction is also determined. The results show that the high speed ultrasonic pulse-echo system provides accurate results for the determination of the liquid level within +/-1.5%, and the time averaged liquid level measurements performed in the present work agree within +/-10% with the theoretical models. The results also show that the time averaged void fraction measurements for a stratified smooth flow, stratified wavy flow, and annular flow qualitatively agree with the theoretical predictions.

  4. LEGUS Discovery of a Light Echo Around Supernova 2012aw

    NASA Astrophysics Data System (ADS)

    Van Dyk, Schuyler D.; Lee, Janice C.; Anderson, Jay; Andrews, Jennifer E.; Calzetti, Daniela; Bright, Stacey N.; Ubeda, Leonardo; Smith, Linda J.; Sabbi, Elena; Grebel, Eva K.; Herrero, Artemio; de Mink, Selma E.

    2015-06-01

    We have discovered a luminous light echo around the normal Type II-Plateau Supernova (SN) 2012aw in Messier 95 (M95; NGC 3351), detected in images obtained approximately two years after explosion with the Wide Field Channel 3 on board the Hubble Space Telescope by the Legacy ExtraGalactic Ultraviolet Survey. The multi-band observations span from the near-ultraviolet through the optical (F275W, F336W, F438W, F555W, and F814W). The apparent brightness of the echo at the time was ˜21-22 mag in all of these bands. The echo appears circular, although less obviously as a ring, with an inhomogeneous surface brightness, in particular, a prominent enhanced brightness to the southeast. The SN itself was still detectable, particularly in the redder bands. We are able to model the light echo as the time-integrated SN light scattered off of diffuse interstellar dust in the SN environment. We have assumed that this dust is analogous to that in the Milky Way with {R}V=3.1. The SN light curves that we consider also include models of the unobserved early burst of light from the SN shock breakout. Our analysis of the echo suggests that the distance from the SN to the scattering dust elements along the echo is ≈ 45 pc. The implied visual extinction for the echo-producing dust is consistent with estimates made previously from the SN itself. Finally, our estimate of the SN brightness in F814W is fainter than that measured for the red supergiant star at the precise SN location in pre-SN images, possibly indicating that the star has vanished and confirming it as the likely SN progenitor.

  5. Research on key technologies of LADAR echo signal simulator

    NASA Astrophysics Data System (ADS)

    Xu, Rui; Shi, Rui; Ye, Jiansen; Wang, Xin; Li, Zhuo

    2015-10-01

    LADAR echo signal simulator is one of the most significant components of hardware-in-the-loop (HWIL) simulation systems for LADAR, which is designed to simulate the LADAR return signal in laboratory conditions. The device can provide the laser echo signal of target and background for imaging LADAR systems to test whether it is of good performance. Some key technologies are investigated in this paper. Firstly, the 3D model of typical target is built, and transformed to the data of the target echo signal based on ranging equation and targets reflection characteristics. Then, system model and time series model of LADAR echo signal simulator are established. Some influential factors which could induce fixed delay error and random delay error on the simulated return signals are analyzed. In the simulation system, the signal propagating delay of circuits and the response time of pulsed lasers are belong to fixed delay error. The counting error of digital delay generator, the jitter of system clock and the desynchronized between trigger signal and clock signal are a part of random delay error. Furthermore, these system insertion delays are analyzed quantitatively, and the noisy data are obtained. The target echo signals are got by superimposing of the noisy data and the pure target echo signal. In order to overcome these disadvantageous factors, a method of adjusting the timing diagram of the simulation system is proposed. Finally, the simulated echo signals are processed by using a detection algorithm to complete the 3D model reconstruction of object. The simulation results reveal that the range resolution can be better than 8 cm.

  6. REDUCTION OF ECHO DECORRELATION VIA COMPLEX PRINCIPAL COMPONENT FILTERING

    PubMed Central

    Mauldin, F. William; Viola, Francesco; Walker, William F.

    2009-01-01

    Ultrasound motion estimation is a fundamental component of clinical and research techniques that include color flow Doppler, spectral Doppler, radiation force imaging and ultrasound-based elasticity estimation. In each of these applications, motion estimates are corrupted by signal decorrelation that originates from nonuniform target motion across the acoustic beam. In this article, complex principal component filtering (PCF) is demonstrated as a filtering technique for dramatically reducing echo decorrelation in blood flow estimation and radiation force imaging. We present simulation results from a wide range of imaging conditions that illustrate a dramatic improvement over simple bandpass filtering in terms of overall echo decorrelation (≤99.9% reduction), root mean square error (≤97.3% reduction) and the standard deviation of displacement estimates (≤97.4% reduction). A radiation force imaging technique, termed sonorheometry, was applied to fresh whole blood during coagulation, and complex PCF operated on the returning echoes. Sonorheometry was specifically chosen as an example radiation force imaging technique in which echo decorrelation corrupts motion estimation. At 2 min after initiation of blood coagulation, the average echo correlation for sonorheometry improved from 0.996 to 0.9999, which corresponded to a 41.0% reduction in motion estimation variance as predicted by the Cramer-Rao lower bound under reasonable imaging conditions. We also applied complex PCF to improve blood velocity estimates from the left carotid artery of a healthy 23-year-old male. At the location of peak blood velocity, complex PCF improved the correlation of consecutive echo signals from an average correlation of 0.94 to 0.998. The improved echo correlation for both sonorheometry and blood flow estimation yielded motion estimates that exhibited more consistent responses with less noise. Complex PCF reduces speckle decorrelation and improves the performance of ultrasonic motion

  7. Laser textured surface gradients

    NASA Astrophysics Data System (ADS)

    Ta, Van Duong; Dunn, Andrew; Wasley, Thomas J.; Li, Ji; Kay, Robert W.; Stringer, Jonathan; Smith, Patrick J.; Esenturk, Emre; Connaughton, Colm; Shephard, Jonathan D.

    2016-05-01

    This work demonstrates a novel technique for fabricating surfaces with roughness and wettability gradients and their subsequent applications for chemical sensors. Surface roughness gradients on brass sheets are obtained directly by nanosecond laser texturing. When these structured surfaces are exposed to air, their wettability decreases with time (up to 20 days) achieving both spatial and temporal wettability gradients. The surfaces are responsive to organic solvents. Contact angles of a series of dilute isopropanol solutions decay exponentially with concentration. In particular, a fall of 132° in contact angle is observed on a surface gradient, one order of magnitude higher than the 14° observed for the unprocessed surface, when the isopropanol concentration increased from 0 to 15.6 wt%. As the wettability changes gradually over the surface, contact angle also changes correspondingly. This effect offers multi-sensitivity at different zones on the surface and is useful for accurate measurement of chemical concentration.

  8. Integrated Image Reconstruction and Gradient Nonlinearity Correction

    PubMed Central

    Tao, Shengzhen; Trzasko, Joshua D.; Shu, Yunhong; Huston, John; Bernstein, Matt A.

    2014-01-01

    Purpose To describe a model-based reconstruction strategy for routine magnetic resonance imaging (MRI) that accounts for gradient nonlinearity (GNL) during rather than after transformation to the image domain, and demonstrate that this approach reduces the spatial resolution loss that occurs during strictly image-domain GNL-correction. Methods After reviewing conventional GNL-correction methods, we propose a generic signal model for GNL-affected MRI acquisitions, discuss how it incorporates into contemporary image reconstruction platforms, and describe efficient non-uniform fast Fourier transform (NUFFT)-based computational routines for these. The impact of GNL-correction on spatial resolution by the conventional and proposed approaches is investigated on phantom data acquired at varying offsets from gradient isocenter, as well as on fully-sampled and (retrospectively) undersampled in vivo acquisitions. Results Phantom results demonstrate that resolution loss that occurs during GNL-correction is significantly less for the proposed strategy than for the standard approach at distances >10 cm from isocenter with a 35 cm FOV gradient coil. The in vivo results suggest that the proposed strategy better preserves fine anatomical detail than retrospective GNL-correction while offering comparable geometric correction. Conclusion Accounting for GNL during image reconstruction allows geometric distortion to be corrected with less spatial resolution loss than is typically observed with the conventional image domain correction strategy. PMID:25298258

  9. A high success rate full-waveform lidar echo decomposition method

    NASA Astrophysics Data System (ADS)

    Xu, Lijun; Li, Duan; Li, Xiaolu

    2016-01-01

    A full-waveform Light detection and ranging (LiDAR) echo decomposition method is proposed in this paper. In this method, the peak points are used to detect the separated echo components, while the inflection points are combined with corresponding peak points to detect the overlapping echo components. The detected echo components are then sorted according to their energies in a descending order. The sorted echo components are one by one added into the decomposition model according to their orders. For each addition, the parameters of all echo components already added into the decomposition model are iteratively renewed. After renewing, the amplitudes and full width at half maximums of the echo components are compared with pre-set thresholds to determine and remove the false echo components. Both simulation and experiment were carried out to evaluate the proposed method. In simulation, 4000 full-waveform echoes with different numbers and parameters of echo components were generated and decomposed using the proposed and three other commonly used methods. Results show that the proposed method is of the highest success rate, 91.43%. In experiment, 9549 Geoscience Laser Altimeter System (GLAS) echoes for Shennongjia forest district in south China were employed as test echoes. The test echoes were first decomposed using the four methods and the decomposition results were also compared with those provided by the National Snow and Ice Data Center. Comparison results show that the determination coefficient ({{R}2} ) of the proposed method is of the largest mean, 0.6838, and the smallest standard deviation, 0.3588, and the distribution of the number of the echo components decomposed from the GLAS echoes is the most satisfied with the situation of full-waveform echoes from the forest area, implying that the superposition of the echo components decomposed from a full-waveform echo by using the proposed method can best approximate the full-waveform echo.

  10. X-ray shout echoing through space

    NASA Astrophysics Data System (ADS)

    2004-01-01

    a flash of X-rays hi-res Size hi-res: 3991 Kb Credits: ESA, S. Vaughan (University of Leicester) EPIC camera shows the expanding rings caused by a flash of X-rays XMM-Newton's X-ray EPIC camera shows the expanding rings caused by a flash of X-rays scattered by dust in our Galaxy. The X-rays were produced by a powerful gamma-ray burst that took place on 3 December 2003. The slowly fading afterglow of the gamma-ray burst is at the centre of the expanding rings. Other, unrelated, X-ray sources can also be seen. The time since the gamma-ray explosion is shown in each panel in hours. At their largest size, the rings would appear in the sky about five times smaller than the full moon. a flash of X-rays hi-res Size hi-res: 2153 Kb Credits: ESA, S. Vaughan (University of Leicester) EPIC camera shows the expanding rings caused by a flash of X-rays (Please choose "hi-res" version for animation) XMM-Newton's X-ray EPIC camera shows the expanding rings caused by a flash of X-rays scattered by dust in our Galaxy. The X-rays were produced by a powerful gamma-ray burst that took place on 3 December 2003. The slowly fading afterglow of the gamma-ray burst is at the centre of the expanding rings. Other, unrelated, X-ray sources can also be seen. The time since the gamma-ray explosion is shown in each panel in seconds. At their largest size, the rings would appear in the sky about five times smaller than the full moon. This echo forms when the powerful radiation of a gamma-ray burst, coming from far away, crosses a slab of dust in our Galaxy and is scattered by it, like the beam of a lighthouse in clouds. Using the expanding rings to precisely pin-point the location of this dust, astronomers can identify places where new stars and planets are likely to form. On 3 December 2003 ESA's observatory, Integral, detected a burst of gamma rays, lasting about 30 seconds, from the direction of a distant galaxy. Within minutes of the detection, thanks to a sophisticated alert network, many

  11. Kemp Echo Lattices Incorporating Hair Cell Nonlinearities

    NASA Astrophysics Data System (ADS)

    Sellami, Louiza

    In this thesis we develop a two-part model of the inner ear that can be used to simulate Kemp echoes, in their impulse response, and from which a characterization of the cochlea can be made. To accomplish this task, in the first part, we propose a linear digital scattering model of the cochlea, based on the well known unidimensional transmission line model into which we incorporate nonuniform and loss properties. The lattice structure of the digital scattering model is obtained by rephrasing the model equations in terms of incident and reflected waves. A spectral estimation method, which treats the system as an ARMA filter with a minimum phase transfer function of unknown degree, is used to estimate the transfer function of the cochlea. This method utilizes the theory of positive real and bounded real functions and Richard's theorem on the concept of degree reduction to determine both the degree and the predictor coefficients of the filter. The scattering model is then realized, using a new synthesis technique, from the overall transfer function and the zeros of transmission, as a cascade of real lossless lattice filters of degree two, closed on a load section. To change the nature of the sections from lossless to lossy, a new method, based on the properties of the proposed lattice structure and the damping parameter of the cochlea, was developed to distribute the load factor among the sections. Each lattice filter is described by a transfer scattering matrix whose entries are functions of the mechanical and geometrical parameters of the cochlea. The proposed synthesis method leads to a systematic estimation of the parameters of the cochlea. In the second part, we introduce a nonlinear bidirectional mechano-electrical model of a hair cell, estimate its components from experimental data, analyze its behavior, simulate it, and compare the results with experimental findings. We than propose a schematic procedure to realize a nonlinear model of the cochlea by

  12. A new gradient shimming method based on undistorted field map of B0 inhomogeneity

    NASA Astrophysics Data System (ADS)

    Bao, Qingjia; Chen, Fang; Chen, Li; Song, Kan; Liu, Zao; Liu, Chaoyang

    2016-04-01

    Most existing gradient shimming methods for NMR spectrometers estimate field maps that resolve B0 inhomogeneity spatially from dual gradient-echo (GRE) images acquired at different echo times. However, the distortions induced by B0 inhomogeneity that always exists in the GRE images can result in estimated field maps that are distorted in both geometry and intensity, leading to inaccurate shimming. This work proposes a new gradient shimming method based on undistorted field map of B0 inhomogeneity obtained by a more accurate field map estimation technique. Compared to the traditional field map estimation method, this new method exploits both the positive and negative polarities of the frequency encoded gradients to eliminate the distortions caused by B0 inhomogeneity in the field map. Next, the corresponding automatic post-data procedure is introduced to obtain undistorted B0 field map based on knowledge of the invariant characteristics of the B0 inhomogeneity and the variant polarity of the encoded gradient. The experimental results on both simulated and real gradient shimming tests demonstrate the high performance of this new method.

  13. Self-motion facilitates echo-acoustic orientation in humans.

    PubMed

    Wallmeier, Ludwig; Wiegrebe, Lutz

    2014-11-01

    The ability of blind humans to navigate complex environments through echolocation has received rapidly increasing scientific interest. However, technical limitations have precluded a formal quantification of the interplay between echolocation and self-motion. Here, we use a novel virtual echo-acoustic space technique to formally quantify the influence of self-motion on echo-acoustic orientation. We show that both the vestibular and proprioceptive components of self-motion contribute significantly to successful echo-acoustic orientation in humans: specifically, our results show that vestibular input induced by whole-body self-motion resolves orientation-dependent biases in echo-acoustic cues. Fast head motions, relative to the body, provide additional proprioceptive cues which allow subjects to effectively assess echo-acoustic space referenced against the body orientation. These psychophysical findings clearly demonstrate that human echolocation is well suited to drive precise locomotor adjustments. Our data shed new light on the sensory-motor interactions, and on possible optimization strategies underlying echolocation in humans. PMID:26064556

  14. Faraday rotation echo spectroscopy and detection of quantum fluctuations.

    PubMed

    Chen, Shao-Wen; Liu, Ren-Bao

    2014-04-15

    Central spin decoherence is useful for detecting many-body physics in environments and moreover, the spin echo control can remove the effects of static thermal fluctuations so that the quantum fluctuations are revealed. The central spin decoherence approach, however, is feasible only in some special configurations and often requires uniform coupling between the central spin and individual spins in the baths, which are very challenging in experiments. Here, by making analogue between central spin decoherence and depolarization of photons, we propose a scheme of Faraday rotation echo spectroscopy (FRES) for studying quantum fluctuations in interacting spin systems. The echo control of the photon polarization is realized by flipping the polarization with a birefringence crystal. The FRES, similar to spin echo in magnetic resonance spectroscopy, can suppress the effects of the static magnetic fluctuations and therefore reveal dynamical magnetic fluctuations. We apply the scheme to a rare-earth compound LiHoF4 and calculate the echo signal, which is related to the quantum fluctuations of the system. We observe enhanced signals at the phase boundary. The FRES should be useful for studying quantum fluctuations in a broad range of spin systems, including cold atoms, quantum dots, solid-state impurities, and transparent magnetic materials.

  15. Faraday rotation echo spectroscopy and detection of quantum fluctuations.

    PubMed

    Chen, Shao-Wen; Liu, Ren-Bao

    2014-01-01

    Central spin decoherence is useful for detecting many-body physics in environments and moreover, the spin echo control can remove the effects of static thermal fluctuations so that the quantum fluctuations are revealed. The central spin decoherence approach, however, is feasible only in some special configurations and often requires uniform coupling between the central spin and individual spins in the baths, which are very challenging in experiments. Here, by making analogue between central spin decoherence and depolarization of photons, we propose a scheme of Faraday rotation echo spectroscopy (FRES) for studying quantum fluctuations in interacting spin systems. The echo control of the photon polarization is realized by flipping the polarization with a birefringence crystal. The FRES, similar to spin echo in magnetic resonance spectroscopy, can suppress the effects of the static magnetic fluctuations and therefore reveal dynamical magnetic fluctuations. We apply the scheme to a rare-earth compound LiHoF4 and calculate the echo signal, which is related to the quantum fluctuations of the system. We observe enhanced signals at the phase boundary. The FRES should be useful for studying quantum fluctuations in a broad range of spin systems, including cold atoms, quantum dots, solid-state impurities, and transparent magnetic materials. PMID:24733086

  16. Echo Meadows Project Winter Artificial Recharge.

    SciTech Connect

    Ziari, Fred

    2002-12-19

    This report discusses the findings of the Echo Meadows Project (BPA Project 2001-015-00). The main purpose of this project is to artificially recharge an alluvial aquifer, WITH water from Umatilla River during the winter high flow period. In turn, this recharged aquifer will discharge an increased flow of cool groundwater back to the river, thereby improving Umatilla River water quality and temperature. A considerable side benefit is that the Umatilla River should improve as a habitat for migration, spanning, and rearing of anadromous and resident fish. The scope of this project is to provide critical baseline information about the Echo Meadows and the associated reach of the Umatilla River. Key elements of information that has been gathered include: (1) Annual and seasonal groundwater levels in the aquifer with an emphasis on the irrigation season, (2) Groundwater hydraulic properties, particularly hydraulic conductivity and specific yield, and (3) Groundwater and Umatilla River water quality including temperature, nutrients and other indicator parameters. One of the major purposes of this data gathering was to develop input to a groundwater model of the area. The purpose of the model is to estimate our ability to recharge this aquifer using water that is only available outside of the irrigation season (December through the end of February) and to estimate the timing of groundwater return flow back to the river. We have found through the data collection and modeling efforts that this reach of the river had historically returned as much as 45 cubic feet per second (cfs) of water to the Umatilla River during the summer and early fall. However, this return flow was reduced to as low as 10 cfs primarily due to reduced quantities of irrigation application, gain in irrigation efficiencies and increased groundwater pumping. Our modeling indicated that it is possible to restore these critical return flows using applied water outside of the irrigation season. We further

  17. Physiological effects of fast oscillating magnetic field gradients.

    PubMed

    Budinger, T F; Fischer, H; Hentschel, D; Reinfelder, H E; Schmitt, F

    1991-01-01

    To evaluate the physiological thresholds of neuromuscular stimulation relevant to very fast NMR imaging studies that use gradient switching at frequencies of 1-2 kHz and a maximum magnetic field of up to 10 mT, a series of studies were done with human volunteers using an experimental echo planar gradient coil set. The threshold for induction of localized and momentary sensations in the human back and abdomen for 10 subjects is 60 T/s for sinusoidally oscillating magnetic fields at 1.27 kHz. The threshold relates to an E field of 6 V/m and is shown to vary with number of oscillations and frequency in accord with theory. Using a simple model of E field induction, the threshold for stimulation of cardiac electrical events should be greater than 4 times this value.

  18. Language Acquisition without an Acquisition Device

    ERIC Educational Resources Information Center

    O'Grady, William

    2012-01-01

    Most explanatory work on first and second language learning assumes the primacy of the acquisition phenomenon itself, and a good deal of work has been devoted to the search for an "acquisition device" that is specific to humans, and perhaps even to language. I will consider the possibility that this strategy is misguided and that language…

  19. Echo-acoustic flow affects flight in bats.

    PubMed

    Kugler, Kathrin; Greiter, Wolfgang; Luksch, Harald; Firzlaff, Uwe; Wiegrebe, Lutz

    2016-06-15

    Flying animals need to react fast to rapid changes in their environment. Visually guided animals use optic flow, generated by their movement through structured environments. Nocturnal bats cannot make use of optic flow, but rely mostly on echolocation. Here, we show that bats exploit echo-acoustic flow to negotiate flight through narrow passages. Specifically, bats' flight between lateral structures is significantly affected by the echo-acoustic salience of those structures, independent of their physical distance. This is true even though echolocation, unlike vision, provides explicit distance cues. Moreover, the bats reduced the echolocation sound levels in stronger flow, probably to compensate for the increased summary target strength of the lateral reflectors. However, bats did not reduce flight velocity under stronger echo-acoustic flow. Our results demonstrate that sensory flow is a ubiquitous principle for flight guidance, independent of the fundamentally different peripheral representation of flow across the senses of vision and echolocation.

  20. Loschmidt echo in one-dimensional interacting Bose gases

    SciTech Connect

    Lelas, K.; Seva, T.; Buljan, H.

    2011-12-15

    We explore Loschmidt echo in two regimes of one-dimensional interacting Bose gases: the strongly interacting Tonks-Girardeau (TG) regime, and the weakly interacting mean-field regime. We find that the Loschmidt echo of a TG gas decays as a Gaussian when small (random and time independent) perturbations are added to the Hamiltonian. The exponent is proportional to the number of particles and the magnitude of a small perturbation squared. In the mean-field regime the Loschmidt echo shows richer behavior: it decays faster for larger nonlinearity, and the decay becomes more abrupt as the nonlinearity increases; it can be very sensitive to the particular realization of the noise potential, especially for relatively small nonlinearities.

  1. Echo-acoustic flow affects flight in bats.

    PubMed

    Kugler, Kathrin; Greiter, Wolfgang; Luksch, Harald; Firzlaff, Uwe; Wiegrebe, Lutz

    2016-06-15

    Flying animals need to react fast to rapid changes in their environment. Visually guided animals use optic flow, generated by their movement through structured environments. Nocturnal bats cannot make use of optic flow, but rely mostly on echolocation. Here, we show that bats exploit echo-acoustic flow to negotiate flight through narrow passages. Specifically, bats' flight between lateral structures is significantly affected by the echo-acoustic salience of those structures, independent of their physical distance. This is true even though echolocation, unlike vision, provides explicit distance cues. Moreover, the bats reduced the echolocation sound levels in stronger flow, probably to compensate for the increased summary target strength of the lateral reflectors. However, bats did not reduce flight velocity under stronger echo-acoustic flow. Our results demonstrate that sensory flow is a ubiquitous principle for flight guidance, independent of the fundamentally different peripheral representation of flow across the senses of vision and echolocation. PMID:27045094

  2. Light echoes - supernovae 1987A and 1986G

    SciTech Connect

    Schaefer, B.E.

    1987-12-01

    The sudden brilliance of a supernova (SN) eruption will be reflected on surrounding dust grains to create a phantom nebula. The paper presents a series of calculations in which the apparent brightness of this light echo is predicted for a variety of situations where the dust is part of the interstellar medium (ISM). It is found that the supernova 1987 A will have a very bright echo off the ISM that may perhaps be visible with binoculars for many years. At a time of 400 days past maximum, the SN 1986G is found to be 2.7 mag brighter than would be predicted by an extrapolation of its light curve. This unique property has an easy explanation as a light echo off the dust in the dust lane of Cen A. 24 references.

  3. Echo-seeding options for LCLS-II

    SciTech Connect

    Xiang, D.; Stupakov, G.; /SLAC

    2010-09-14

    The success of LCLS has opened up a new era of x-ray sciences. An upgrade to LCLS is currently being planned to enhance its capabilities. In this paper we study the feasibility of using the echo-enabled harmonic generation (EEHG) technique to generate narrow bandwidth soft x-ray radiation in the proposed LCLS-II soft x-ray beam line. We focus on the conceptual design, the technical implementation and the expected performances of the echo-seeding scheme. We will also show how the echo-seeding scheme allows one to generate two color x-ray pulses with the higher energy photons leading the lower energy ones as is favored in the x-ray pump-probe experiments.

  4. Ultrafast Optical Spin Echo for Electron Spins in Semiconductors

    SciTech Connect

    Clark, Susan M.; Fu, Kai-Mei C.; Zhang Qiang; Ladd, Thaddeus D.; Yamamoto, Yoshihisa; Stanley, Colin

    2009-06-19

    Spin-based quantum computing and magnetic resonance techniques rely on the ability to measure the coherence time T{sub 2} of a spin system. We report on the experimental implementation of all-optical spin echo to determine the T{sub 2} time of a semiconductor electron-spin system. We use three ultrafast optical pulses to rotate spins an arbitrary angle and measure an echo signal as the time between pulses is lengthened. Unlike previous spin-echo techniques using microwaves, ultrafast optical pulses allow clean T{sub 2} measurements of systems with dephasing times (T{sub 2}*) fast in comparison to the time scale for microwave control. This demonstration provides a step toward ultrafast optical dynamic decoupling of spin-based qubits.

  5. Auditory-tactile echo-reverberating stuttering speech corrector

    NASA Astrophysics Data System (ADS)

    Kuniszyk-Jozkowiak, Wieslawa; Adamczyk, Bogdan

    1997-02-01

    The work presents the construction of a device, which transforms speech sounds into acoustical and tactile signals of echo and reverberation. Research has been done on the influence of the echo and reverberation, which are transmitted as acoustic and tactile stimuli, on speech fluency. Introducing the echo or reverberation into the auditory feedback circuit results in a reduction of stuttering. A bit less, but still significant corrective effects are observed while using the tactile channel for transmitting the signals. The use of joined auditory and tactile channels increases the effects of their corrective influence on the stutterers' speech. The results of the experiment justify the use of the tactile channel in the stutterers' therapy.

  6. Perception of echo phase information in bat sonar.

    PubMed

    Simmons, J A

    1979-06-22

    Echolocating bats (Eptesicus fuscus) can detect changes as small as 500 nanoseconds in the arrival time of sonar echoes when these changes appear as jitter or alternations in arrival time from one echo to the next. The psychophysical function relating the bat's performance to the magnitude of the jitter corresponds to the half-wave rectified cross-correlation function between the emitted sonar signals and the echoes. The bat perceives the phase or period structure of the sounds, which cover the 25- to 100-kilohertz frequency range, as these are represented in the auditory system after peripheral transformation. The acoustic image of a sonar target is apparently derived from time-domain or periodicity information processing by the nervous system.

  7. Magnetic Field Gradient Waveform Monitoring for Magnetic Resonance

    NASA Astrophysics Data System (ADS)

    Han, Hui

    Linear magnetic field gradients have played a central role in Magnetic Resonance Imaging (MRI) since Fourier Transform MRI was proposed three decades ago. Their primary function is to encode spatial information into MR signals. Magnetic field gradients are also used to sensitize the image contrast to coherent and/or incoherent motion, to selectively enhance an MR signal, and to minimize image artifacts. Modern MR imaging techniques increasingly rely on the implementation of complex gradient waveforms for the manipulation of spin dynamics. However, gradient system infidelities caused by eddy currents, gradient amplifier imperfections and group delays, often result in image artifacts and other errors (e.g., phase and intensity errors). This remains a critical problem for a wide range of MRI techniques on modern commercial systems, but is of particular concern for advanced MRI pulse sequences. Measuring the real magnetic field gradients, i.e., characterizing eddy currents, is critical to addressing and remedying this problem. Gradient measurement and eddy current calibration are therefore a general topic of importance to the science of MRI. The Magnetic Field Gradient Monitor (MFGM) idea was proposed and developed specifically to meet these challenges. The MFGM method is the heart of this thesis. MFGM methods permit a variety of magnetic field gradient problems to be investigated and systematically remedied. Eddy current effects associated with MR compatible metallic pressure vessels were analyzed, simulated, measured and corrected. The appropriate correction of eddy currents may enable most MR/MRI applications with metallic pressure vessels. Quantitative imaging (1D/2D) with model pressure vessels was successfully achieved by combining image reconstruction with MFGM determined gradient waveform behaviour. Other categories of MR applications with metallic vessels, including diffusion measurement and spin echo SPI T2 mapping, cannot be realized solely by MFGM guided

  8. Study of simulating dynamic polarization laser echo signal

    NASA Astrophysics Data System (ADS)

    Yang, Di; Liu, Qing; Zhan, Yong-hong; Zeng, Chang-e.

    2014-12-01

    In the test for the laser seeker in the hardware-in-loop simulation, acquiring the effect of polarization laser echo wave to optical stress polarization of the seeker and to the polarization guidance performance was not considered. A new method to generating the dynamic polarization laser echo signal was provided based on the scene model; furthermore, the method to adding the polarization characters to the energy scene was introduced. At last, the insufficient of the method to generating and simulating the dynamic polarization signal was analyzed.

  9. Piston cylinder cell for high pressure ultrasonic pulse echo measurements.

    PubMed

    Kepa, M W; Ridley, C J; Kamenev, K V; Huxley, A D

    2016-08-01

    Ultrasonic techniques such as pulse echo, vibrating reed, or resonant ultrasound spectroscopy are powerful probes not only for studying elasticity but also for investigating electronic and magnetic properties. Here, we report on the design of a high pressure ultrasonic pulse echo apparatus, based on a piston cylinder cell, with a simplified electronic setup that operates with a single coaxial cable and requires sample lengths of mm only. The design allows simultaneous measurements of ultrasonic velocities and attenuation coefficients up to a pressure of 1.5 GPa. We illustrate the performance of the cell by probing the phase diagram of a single crystal of the ferromagnetic superconductor UGe2. PMID:27587156

  10. Piston cylinder cell for high pressure ultrasonic pulse echo measurements

    NASA Astrophysics Data System (ADS)

    Kepa, M. W.; Ridley, C. J.; Kamenev, K. V.; Huxley, A. D.

    2016-08-01

    Ultrasonic techniques such as pulse echo, vibrating reed, or resonant ultrasound spectroscopy are powerful probes not only for studying elasticity but also for investigating electronic and magnetic properties. Here, we report on the design of a high pressure ultrasonic pulse echo apparatus, based on a piston cylinder cell, with a simplified electronic setup that operates with a single coaxial cable and requires sample lengths of mm only. The design allows simultaneous measurements of ultrasonic velocities and attenuation coefficients up to a pressure of 1.5 GPa. We illustrate the performance of the cell by probing the phase diagram of a single crystal of the ferromagnetic superconductor UGe2.

  11. Code division in optical memory devices based on photon echo

    NASA Astrophysics Data System (ADS)

    Kalachev, Alexey A.; Vlasova, Daria D.

    2006-03-01

    The theory of multi-channel optical memory based on photon echo is developed. It is shown that under long-lived photon echo regime the writing and reading of information with code division is possible using phase modulation of reference and reading pulses. A simple method for construction of a system of noise-like signals, which is based on the segmentation of Frank sequence is proposed. It is shown that in comparison to the system of random biphase signals this system leads to the efficient decreasing of mutual influence of channels and increasing of random/noise ratio under reading of information.

  12. HIGH GRADIENT INDUCTION ACCELERATOR

    SciTech Connect

    Caporaso, G J; Sampayan, S; Chen, Y; Blackfield, D; Harris, J; Hawkins, S; Holmes, C; Krogh, M; Nelson, S; Nunnally, W; Paul, A; Poole, B; Rhodes, M; Sanders, D; Selenes, K; Sullivan, J; Wang, L; Watson, J

    2007-06-21

    A new type of compact induction accelerator is under development at the Lawrence Livermore National Laboratory that promises to increase the average accelerating gradient by at least an order of magnitude over that of existing induction machines. The machine is based on the use of high gradient vacuum insulators, advanced dielectric materials and switches and is stimulated by the desire for compact flash x-ray radiography sources. Research describing an extreme variant of this technology aimed at proton therapy for cancer will be described. Progress in applying this technology to several applications will be reviewed.

  13. 1H stray-field long spin-echo trains and MRI: novel studies on the photopolymerization of a commercial dental resin

    NASA Astrophysics Data System (ADS)

    Nunes, Teresa G.; Guillot, Geneviève; Pereira, Sónia G.; Pires, Ricardo

    2002-06-01

    Photopolymerization of a commercial dental resin has been investigated by 1H stray-field (STRAFI) magnetic resonance. The resin is a visible light-cured system, included in a new generation adhesive, which is used to bond the restorative material to enamel or dentin. Different methods were used to follow the curing reaction, which involve long and short spin-echo train acquisitions to obtain one-slice and one-dimensional data, respectively. The echo attenuation, in the limit of very short time delays, could be described as the sum of two exponentials. While the intensity of the early echoes in the train appeared mainly governed by spin-spin relaxation, the decay of the last echoes seemed to depend also on spin-lattice relaxation in the rotating frame. The relative amplitude of the long-time component was found to decrease from 84% to 10% with the photopolymerization progress, and a STRAFI degree of conversion of 74% could thus be suggested. The influence of the curing protocol was observed in STRAFI profiles.

  14. On the VHF radar echoes in the region of midnight aurora: Signs of ground echoes modulated by the ionosphere

    NASA Astrophysics Data System (ADS)

    Kozlovsky, Alexander; Lester, Mark

    2015-03-01

    We present all-sky interferometric meteor radar (MR), VHF (36.9 MHz), observations from Sodankylä Geophysical Observatory and report on the unusual echoes, which were detected at low elevation on the northern horizon, typically during substorms. These echoes have a near-zero Doppler shift, relatively low power, but with a sharp rise to the power peak, short lifetime (less than 2 s), and nonexponential decay (NED). We suggest that such auroral NED echoes are in fact ground backscatter of the MR waves which have been refracted in the ionosphere, passing through the ionosphere in the substorm region, where pulsating aurora (at a frequency higher than 1.7 Hz) occurs and causes quasiperiodic modulation of the wave propagation conditions, which leads to corresponding modulation of the amplitude of return. The MR treats such oscillating signal as meteor trails.

  15. Gradient Refractive Index Lenses.

    ERIC Educational Resources Information Center

    Morton, N.

    1984-01-01

    Describes the nature of gradient refractive index (GRIN) lenses, focusing on refraction in these materials, focal length of a thin Wood lens, and on manufacturing of such lenses. Indicates that GRIN lenses of small cross section are in limited production with applications suggested for optical communication and photocopying fields. (JN)

  16. HASTE sequence with parallel acquisition and T2 decay compensation: application to carotid artery imaging.

    PubMed

    Zhang, Ling; Kholmovski, Eugene G; Guo, Junyu; Choi, Seong-Eun Kim; Morrell, Glen R; Parker, Dennis L

    2009-01-01

    T2-weighted carotid artery images acquired using the turbo spin-echo (TSE) sequence frequently suffer from motion artifacts due to respiration and blood pulsation. The possibility of using HASTE sequence to achieve motion-free carotid images was investigated. The HASTE sequence suffers from severe blurring artifacts due to signal loss in later echoes due to T2 decay. Combining HASTE with parallel acquisition (PHASTE) decreases the number of echoes acquired and thus effectively reduces the blurring artifact caused by T2 relaxation. Further improvement in image sharpness can be achieved by performing T2 decay compensation before reconstructing the PHASTE data. Preliminary results have shown successful suppression of motion artifacts with PHASTE imaging. The image quality was enhanced relative to the original HASTE image, but was still less sharp than a non-motion-corrupted TSE image.

  17. 1. GENERAL VIEW LOOKING NORTH SHOWING 130FOOT SPAN OF ECHO ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. GENERAL VIEW LOOKING NORTH SHOWING 130-FOOT SPAN OF ECHO BRIDGE OVER THE CHARLES RIVER. - Sudbury River Aqueduct, Echo Bridge, Spanning Charles River at Upper Newton Falls, Newton, Middlesex County, MA

  18. 32 CFR 199.5 - TRICARE Extended Care Health Option (ECHO).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Disabilities Education Act and defined at 34 CFR 300.26 and that is specifically designed to accommodate the... order for the ECHO beneficiary to receive authorized ECHO benefits. (ii) Equipment adaptation....

  19. Multi-site study of diffusion metric variability: effects of site, vendor, field strength, and echo time on regions-of-interest and histogram-bin analyses

    NASA Astrophysics Data System (ADS)

    Helmer, K. G.; Chou, M.-C.; Preciado, R. I.; Gimi, B.; Rollins, N. K.; Song, A.; Turner, J.; Mori, S.

    2016-03-01

    It is now common for magnetic-resonance-imaging (MRI) based multi-site trials to include diffusion-weighted imaging (DWI) as part of the protocol. It is also common for these sites to possess MR scanners of different manufacturers, different software and hardware, and different software licenses. These differences mean that scanners may not be able to acquire data with the same number of gradient amplitude values and number of available gradient directions. Variability can also occur in achievable b-values and minimum echo times. The challenge of a multi-site study then, is to create a common protocol by understanding and then minimizing the effects of scanner variability and identifying reliable and accurate diffusion metrics. This study describes the effect of site, scanner vendor, field strength, and TE on two diffusion metrics: the first moment of the diffusion tensor field (mean diffusivity, MD), and the fractional anisotropy (FA) using two common analyses (region-of-interest and mean-bin value of whole brain histograms). The goal of the study was to identify sources of variability in diffusion-sensitized imaging and their influence on commonly reported metrics. The results demonstrate that the site, vendor, field strength, and echo time all contribute to variability in FA and MD, though to different extent. We conclude that characterization of the variability of DTI metrics due to site, vendor, field strength, and echo time is a worthwhile step in the construction of multi-center trials.

  20. Arterial Stiffness Gradient

    PubMed Central

    Fortier, Catherine; Agharazii, Mohsen

    2016-01-01

    Background Aortic stiffness is a strong predictor of cardiovascular mortality in various clinical conditions. The aim of this review is to focus on the arterial stiffness gradient, to discuss the integrated role of medium-sized muscular conduit arteries in the regulation of pulsatile pressure and organ perfusion and to provide a rationale for integrating their mechanical properties into risk prediction. Summary The physiological arterial stiffness gradient results from a higher degree of vascular stiffness as the distance from the heart increases, creating multiple reflective sites and attenuating the pulsatile nature of the forward pressure wave along the arterial tree down to the microcirculation. The stiffness gradient hypothesis simultaneously explains its physiological beneficial effects from both cardiac and peripheral microcirculatory points of view. The loss or reversal of stiffness gradient leads to the transmission of a highly pulsatile pressure wave into the microcirculation. This suggests that a higher degree of stiffness of medium-sized conduit arteries may play a role in protecting the microcirculation from a highly pulsatile forward pressure wave. Using the ratio of carotid-femoral pulse wave velocity (PWV) to carotid-radial PWV, referred to as PWV ratio, a recent study in a dialysis cohort has shown that the PWV ratio is a better predictor of mortality than the classical carotid-femoral PWV. Key Messages Theoretically, the use of the PWV ratio seems more logical for risk determination than aortic stiffness as it provides a better estimation of the loss of stiffness gradient, which is the unifying hypothesis that explains the impact of aortic stiffness both on the myocardium and on peripheral organs. PMID:27195235

  1. Echo frequency selectivity of duration-tuned inferior collicular neurons of the big brown bat, Eptesicus fuscus, determined with pulse-echo pairs.

    PubMed

    Wu, C H; Jen, P H-S

    2008-10-28

    During hunting, insectivorous bats such as Eptesicus fuscus progressively vary the repetition rate, duration, frequency and amplitude of emitted pulses such that analysis of an echo parameter by bats would be inevitably affected by other co-varying echo parameters. The present study is to determine the variation of echo frequency selectivity of duration-tuned inferior collicular neurons during different phases of hunting using pulse-echo (P-E) pairs as stimuli. All collicular neurons discharge maximally to a tone at a particular frequency which is defined as the best frequency (BF). Most collicular neurons also discharge maximally to a BF pulse at a particular duration which is defined as the best duration (BD). A family of echo iso-level frequency tuning curves (iso-level FTC) of these duration-tuned collicular neurons is measured with the number of impulses in response to the echo pulse at selected frequencies when the P-E pairs are presented at varied P-E duration and gap. Our data show that these duration-tuned collicular neurons have narrower echo iso-level FTC when measured with BD than with non-BD echo pulses. Also, IC neurons with low BF and short BD have narrower echo iso-level FTC than IC neurons with high BF and long BD have. The bandwidth of echo iso-level FTC significantly decreases with shortening of P-E duration and P-E gap. These data suggest that duration-tuned collicular neurons not only can facilitate bat's echo recognition but also can enhance echo frequency selectivity for prey feature analysis throughout a target approaching sequence during hunting. These data also support previous behavior studies showing that bats prepare their auditory system to analyze expected returning echoes within a time window to extract target features after pulse emission.

  2. 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.

  3. The first satellite laser echoes recorded on the streak camera

    NASA Technical Reports Server (NTRS)

    Hamal, Karel; Prochazka, Ivan; Kirchner, Georg; Koidl, F.

    1993-01-01

    The application of the streak camera with the circular sweep for the satellite laser ranging is described. The Modular Streak Camera system employing the circular sweep option was integrated into the conventional Satellite Laser System. The experimental satellite tracking and ranging has been performed. The first satellite laser echo streak camera records are presented.

  4. Project Echo: Horn-Reflector Antenna for Space Communication

    NASA Technical Reports Server (NTRS)

    Crawford, A. B.; Hogg, D. C.; Hunt, L. E.

    1961-01-01

    This paper describes the mechanical features of the horn- reflector antenna used for receiving signals reflected from the Project Echo balloon satellite, and presents in some detail the electrical characteristics (radiation patterns and gain) measured at a frequency of 2390 Mc. Theoretically derived characteristics which agree very well with the measurements are also presented; details of the calculations are given in the appendices.

  5. Participatory Culture at the Echo Park Film Center

    ERIC Educational Resources Information Center

    Rosales, Jennifer Ann

    2013-01-01

    The Echo Park Film Center, a Los Angeles nonprofit media education organization, teaches underprivileged youth how to comprehend and make media in order to empower them to speak and be heard. Due to the organization's nonmainstream media courses and its connection to its community, the Center is able to create a participatory and socially…

  6. Pulse-echo probe of rock permeability near oil wells

    NASA Technical Reports Server (NTRS)

    Narasimhan, K. Y.; Parthasarathy, S. P.

    1978-01-01

    Processing method involves sequential insonifications of borehole wall at number of different frequencies. Return signals are normalized in amplitude, and root-mean-square (rms) value of each signal is determined. Values can be processed to yield information on size and number density of microfractures at various depths in rock matrix by using averaging methods developed for pulse-echo technique.

  7. Scheduling the EChO survey with known exoplanets

    NASA Astrophysics Data System (ADS)

    Morales, J. C.; Beaulieu, J.-P.; Coudé du Foresto, V.; Ollivier, M.; Castello, I. Ortega; Clédassou, R.; Jaubert, J.; Van-Troostenberghe, P.; Varley, R.; Waldmann, I. P.; Pascale, E.; Tessenyi, M.

    2015-12-01

    The Exoplanet Characterization Observatory ( EChO) is a concept of a dedicated space telescope optimized for low-resolution transit and occultation spectroscopy to study the exoplanet diversity through the composition of their atmospheres. The scope of this paper is to answer the following question: Can we schedule a nominal EChO mission, with targets known today (in mid 2013), given the science requirements, realistic performances and operational constraints? We examine this issue from the point of view of duration of the mission and the scheduling restrictions with a sample of exoplanet systems known nowadays. We choose different scheduling algorithms taking into account the science and operational constraints and we verified that it is fairly straightforward to schedule a mission scenario over the lifetime of EChO compliant with the science requirements. We identified agility as a critical constraint that reduces significantly the efficiency of the survey. We conclude that even with known targets today the EChO science objectives can be reached in the 4.5 years duration of the mission. We also show that it is possible to use gaps between exoplanet observations, to fit the required calibration observations, data downlinks and station keeping operations or even to observe more exoplanet targets to be discovered in the coming years.

  8. Tomographic reconstruction of the pulse-echo spatiotemporal impulse response

    NASA Astrophysics Data System (ADS)

    Nguyen, Nghia Q.; Abbey, Craig K.; Yapp, Rebecca D.; Insana, Michael F.

    2010-03-01

    Virtually every area of ultrasonic imaging research requires accurate estimation of the spatiotemporal impulse response of the instrument, and yet accurate measurements are difficult to achieve. The impulse response can also be difficult to predict numerically for a specific device because small unknown perturbations in array properties can generate significant changes in predicted pulse-echo field patterns. A typical measurement for a 1-D array transducer employs a line scatterer oriented perpendicular to the scan plane. Echoes from line scatterers located throughout the field of view constitute estimates of shift-varying line response functions. We propose an inverse-problem approach to the reconstruction of point-spread functions from line-spread functions. A collection of echoes recorded for a range of line-scatterer rotation angles are treated as projections of sound pressure onto the transducer array surface. Although the reconstruction is mathematically equivalent to filtered backprojection, it provides significant advantages with respect to interpolation that confound straightforward implementations. Field II predictions used to model measurements made on commercial systems suggest the reconstruction accuracy is with 0.32% for noiseless echo data. Application of the method to data acquired from a commercial system are evaluated from the perspective of deconvolution.

  9. Larry Echo Hawk: A Rising Star from Idaho.

    ERIC Educational Resources Information Center

    Wisecarver, Charmaine

    1993-01-01

    Larry Echo Hawk, Idaho attorney general and former state legislator, discusses success factors in college and law school; early experiences as an Indian lawyer; first election campaign; and his views on tribal sovereignty, state-tribal relationship, gambling, and his dual responsibility to the general public and Native American issues. (SV)

  10. Echolocation in bats: signal processing of echoes for target range.

    PubMed

    Simmons, J A

    1971-03-01

    Echolocating bats Eptesicus fuscus and Phyllostomus hastatus can discriminate between the nearer and farther of two targets. Their errors in discrimination are predicted accurately by the autocorrelation functions of their sonar cries. These bats behave as though they have an ideal sonar system which cross correlates the transmitted cry with the returning echo to extract targetrange information.

  11. Echo thresholds for reflections from acoustically diffusive architectural surfaces.

    PubMed

    Robinson, Philip W; Walther, Andreas; Faller, Christof; Braasch, Jonas

    2013-10-01

    When sound reflects from an irregular architectural surface, it spreads spatially and temporally. Extensive research has been devoted to prediction and measurement of diffusion, but less has focused on its perceptual effects. This paper examines the effect of temporal diffusion on echo threshold. There are several notable differences between the waveform of a reflection identical to the direct sound and one from an architectural surface. The onset and offset are damped and the energy is spread in time; hence, the reflection response has a lower peak amplitude, and is decorrelated from the direct sound. The perceptual consequences of these differences are previously undocumented. Echo threshold tests are conducted with speech and music signals, using direct sound and a simulated reflection that is either identical to the direct sound or has various degrees of diffusion. Results indicate that for a speech signal, diffuse reflections are less easily detectable as a separate auditory event than specular reflections of the same total energy. For a music signal, no differences are observed between the echo thresholds for reflections with and without temporal diffusion. Additionally, echo thresholds are found to be shorter for speech than for music, and shorter for spatialized than for diotic presentation of signals.

  12. In situ pulsed-field gradient NMR determination of the size of oil bodies in vegetable seeds. Analysis of the effect of the gradient pulse length.

    PubMed

    Guillermo, Armel; Bardet, Michel

    2007-09-01

    We report a pulsed-field gradient NMR study of the size of the oil bodies in lettuce seeds. The pulsed-field gradient spin-echo method (PFGSE) was applied to measure the self-diffusion coefficient of triacylglycerol molecules (TAG) inside the oil bodies. The confined nature of TAG diffusion is used to determine the size dispersion of the oil bodies. At long diffusion time, we measure a spin-echo attenuation that is related to the form factor of the confining volumes in the reciprocal q space, where q is proportional to the product of the gradient intensity and the length of the pulse gradient. Specific care was taken in analyzing the influence of the gradient pulse length delta on the shape of the PFGSE decay in order to construct the function corresponding to the short gradient pulse approximation (SGP). The SGP model gives an analytical framework for the PFGSE signal that enables the size distribution of the oil bodies to be determined. The SGP function was unambiguously obtained by varying the gradient pulse length delta in order to linearly extrapolate at delta = 0 the SGP limit. In this work, we also consider the Gaussian phase distribution (GPD) assumption that is often used to analyze confined diffusion experiments. Although the GPD assumption is known to be inaccurate in predicting the fine structure of the PFGSE function in q space, we point out that in the present case it can be used to take into account the finite value of delta. A log-normal distribution of the radius values was assumed in simulating the PFGNMR experiments since this type of distribution is observed in vegetable seeds by transmission electronic microscopy. From a practical and experimental standpoint, the NMR measurements reported here require no specific treatment of the seeds and the size of oil bodies is determined "in situ" on seeds poured into the NMR tube.

  13. Shaping and timing gradient pulses to reduce MRI acoustic noise.

    PubMed

    Segbers, Marcel; Rizzo Sierra, Carlos V; Duifhuis, Hendrikus; Hoogduin, Johannes M

    2010-08-01

    A method to reduce the acoustic noise generated by gradient systems in MRI has been recently proposed; such a method is based on the linear response theory. Since the physical cause of MRI acoustic noise is the time derivative of the gradient current, a common trapezoid current shape produces an acoustic gradient coil response mainly during the rising and falling edge. In the falling edge, the coil acoustic response presents a 180 degrees phase difference compared to the rising edge. Therefore, by varying the width of the trapezoid and keeping the ramps constant, it is possible to suppress one selected frequency and its higher harmonics. This value is matched to one of the prominent resonance frequencies of the gradient coil system. The idea of cancelling a single frequency is extended to a second frequency, using two successive trapezoid-shaped pulses presented at a selected interval. Overall sound pressure level reduction of 6 and 10 dB is found for the two trapezoid shapes and a single pulse shape, respectively. The acoustically optimized pulse shape proposed is additionally tested in a simulated echo planar imaging readout train, obtaining a sound pressure level reduction of 12 dB for the best case.

  14. The Light Echoes around V838 Monocerotis: Cycle 16 DD

    NASA Astrophysics Data System (ADS)

    Bond, Howard

    2007-07-01

    This is a DD program in which we propose to obtain WFPC2 imaging of the light echo around V838 Mon in late 2008 or early 2009. We were awarded Cycle 17 time to image the echo with ACS at 2 epochs {3+4 orbits}. To obtain data of similar quality with WFPC2 requires 7 orbits at 2 different pointings. Because of the SM4 delay, we are therefore requesting a 14-orbit DD program for Cycle 16, leaving the Cycle 17 allocation unchanged for continued monitoring of the event in late 2009 and 2010.V838 Monocerotis, which burst upon the astronomical scene in early 2002, is a completely unanticipated new object. It underwent a large-amplitude and very luminous outburst, during which its spectrum remained that of an extremely cool supergiant. A rapidly evolving set of light echoes around V838 Mon was discovered soon after the outburst, quickly becoming the most spectacular display of the phenomenon yet seen. These light echoes provide the means to accomplish three unique types of measurements based on continued HST imaging: {1} study MHD turbulence at high resolution and in 3 dimensions; {2} construct the first unambiguous and fully 3-D map of a circumstellar dust envelope; {3} study dust physics in a unique setting where the spectrum and light curve of the illumination, and the scattering angle, are unambiguously known. We have also used our HST data to determine the distance to V838 Mon through a novel geometric technique. Because of the extreme rarity of light echoes, this program of regular monitoring provides the only opportunity to achieve such results during the HST lifetime. We propose WFPC2 imaging in late 2008/early 2009, in order to continue the mapping of the circumstellar dust and to accomplish the other goals listed above.

  15. A Year in the Life of an Infrared Echo

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Figure 1: Supernova Remnant Cassiopeia A One Year Apart

    These Spitzer Space Telescope images, taken one year apart, show the supernova remnant Cassiopeia A (yellow ball) and surrounding clouds of dust (reddish orange). The pictures illustrate that a blast of light from Cassiopeia A is waltzing outward through the dusty skies. This dance, called an 'infrared echo,' began when the remnant erupted about 50 years ago.

    Cassiopeia A is the remnant of a once massive star that died in a violent supernova explosion 325 years ago. It consists of a dead star, called a neutron star, and a surrounding shell of material that was blasted off as the star died. This remnant is located 10,000 light-years away in the northern constellation Cassiopeia.

    Infrared echoes are created when a star explodes or erupts, flashing light into surrounding clumps of dust. As the light zips through the dust clumps, it heats them up, causing them to glow successively in infrared, like a chain of Christmas bulbs lighting up one by one. The result is an optical illusion, in which the dust appears to be flying outward at the speed of light. Echoes are distinct from supernova shockwaves, which are made up material that is swept up and hurled outward by exploding stars.

    This infrared echo is the largest ever seen, stretching more than 50 light-years away from Cassiopeia A. If viewed from Earth, the entire movie frame would take up the same amount of space as two full moons.

    Hints of an older infrared echo from Cassiopeia A's supernova explosion hundreds of years ago can also be seen.

    The top Spitzer image was taken on November 30, 2003, and the bottom, on December 2, 2004.

  16. Finland HF and Esrange MST radar observations of polar mesosphere summer echoes

    NASA Astrophysics Data System (ADS)

    Ogawa, T.; Arnold, N. F.; Kirkwood, S.; Nishitani, N.; Lester, M.

    2003-04-01

    Peculiar near range echoes observed in summer with the SuperDARN HF radar in Finland are presented. The echoes were detected at four frequencies of 9, 11, 13 and 15 MHz at slant ranges of 105 250 km for about 100 min. Interferometer measurements indicate that the echoes are returned from 80 100 km altitudes with elevation angles of 20° 60

  17. Clutter interference and the integration time of echoes in the echolocating bat, Eptesicus fuscus.

    PubMed

    Simmons, J A; Freedman, E G; Stevenson, S B; Chen, L; Wohlgenant, T J

    1989-10-01

    The ability of the echolocating bat, Eptesicus fuscus, to detect a sonar target is affected by the presence of other targets along the same axis at slightly different ranges. If echoes from one target arrive at about the same delay as echoes from another target, clutter interference occurs and one set of echoes masks the other. Although the bat's sonar emissions and the echoes themselves are 2 to 5 ms long, echoes (of approximately equal sensation levels--around 15 dB SL) only interfere with each other if they arrive within 200 to 400 microseconds of the same arrival time. This figure is an estimate of the integration time of the bat's sonar receiver for echoes. The fine structure of the clutter-interference data reflects the reinforcement and cancellation of echoes according to their time separation. When clutter interference first occurs, the waveforms of test and cluttering echoes already overlap for much of their duration. The masking effect underlying clutter interference appears specifically due to overlap, not between raw echo waveforms, but between the patterns of mechanical excitation created when echoes pass through bandpass filters equivalent to auditory-nerve tuning curves. While the time scale of clutter interference is substantially shorter than the duration of echo waveforms, it still is much longer than the eventual width of a target's range-axis image expressed in terms of echo delay.

  18. Detection of a Light Echo from the Otherwise Normal SN 2007af

    NASA Astrophysics Data System (ADS)

    Drozdov, D.; Leising, M. D.; Milne, P. A.; Pearcy, J.; Riess, A. G.; Macri, L. M.; Bryngelson, G. L.; Garnavich, P. M.

    2015-05-01

    We present the discovery of a light echo from SN 2007af, a normal Type Ia supernova (SN Ia) in NGC 5584. Hubble Space Telescope images taken three years post explosion reveal two separate echoes: an outer echo and an extended central region, which we propose to be an inner echo for which details are unresolved. Multiple images were obtained in the F160W, F350LP, F555W, and F814W using the Wide Field Camera 3. If the outer echo is produced by an interstellar dust sheet perpendicular to the line of sight, it is located ∼800 pc in front of the SN. The dust for the inner echo is 0.45 pc \\lt d\\lt 90 pc away from the SN. The inner echo color is consistent with typical interstellar dust wavelength-dependent scattering cross-sections, while the outer echo is redder than predicted. Both dust sheets, if in the foreground, are optically thin for scattering, and the outer echo sheet thickness is consistent with the inferred extinction from peak brightness. Whether the inner echo is from interstellar or circumstellar dust is ambiguous. Overall, the echo characteristics are quite similar to previously observed SN Ia echoes.

  19. Effects of balloon angioplasty and stent implantation on intrarenal echo-Doppler velocimetric indices.

    PubMed

    Marana, I; Airoldi, F; Burdick, L; Alberti, C; Lovaria, A; Saccheri, S; Gazzano, G; Palatresi, S; Nador, B; Turolo, L; Morganti, A

    1998-06-01

    This study was aimed at examining whether four intrarenal echo-Doppler velocimetric indices (pulsatility and resistive indices, acceleration and acceleration time) can be useful for assessing the effects of renal artery dilation obtained with either angioplasty or stent implantation. Echo-Doppler studies were performed in 63 hypertensive patients with 68 renal artery stenoses (39 atherosclerotic and 29 fibromuscular) prior to and within five days after the dilation procedures (55 angioplasties, 13 stent implantations), which resulted in an average reduction of arterial narrowing from 79% to 20%. In 24 patients, the velocimetric indices were also examined in relationship to the venoarterial differences of plasma renin activity and of angiotensin II across the stenotic kidneys. We found that after dilation the values of the four indices had returned within the normal range in all but three arteries (one false negative for resistive index and two for acceleration time). However, decrements in acceleration time was the only factor to be significantly correlated with the reduction of arterial narrowing. Moreover, postdilation values of this index were, on average, slightly but significantly higher in arteries that at follow-up developed restenosis rather than in those that remained patent. For similar reductions in arterial narrowing the absolute changes of all indices were similar in atherosclerotic and fibromuscular stenotic arteries and, in a subset of the atheromatous arteries, were also similar after angioplasty and stent implantation. No relationship was found with the changes in the venoarterial differences of plasma renin activity and angiotensin II. It appears that these intrarenal velocimetric indices and, in particular, acceleration time reliably reflect the technical success of renal artery dilation. The acceleration time index may also be valuable for predicting the restenosis of the dilated vessel. None of the indices, however, mirrors the functional

  20. A Volterra series-based method for extracting target echoes in the seafloor mining environment.

    PubMed

    Zhao, Haiming; Ji, Yaqian; Hong, Yujiu; Hao, Qi; Ma, Liyong

    2016-09-01

    The purpose of this research was to evaluate the applicability of the Volterra adaptive method to predict the target echo of an ultrasonic signal in an underwater seafloor mining environment. There is growing interest in mining of seafloor minerals because they offer an alternative source of rare metals. Mining the minerals cause the seafloor sediments to be stirred up and suspended in sea water. In such an environment, the target signals used for seafloor mapping are unable to be detected because of the unavoidable presence of volume reverberation induced by the suspended sediments. The detection of target signals in reverberation is currently performed using a stochastic model (for example, the autoregressive (AR) model) based on the statistical characterisation of reverberation. However, we examined a new method of signal detection in volume reverberation based on the Volterra series by confirming that the reverberation is a chaotic signal and generated by a deterministic process. The advantage of this method over the stochastic model is that attributions of the specific physical process are considered in the signal detection problem. To test the Volterra series based method and its applicability to target signal detection in the volume reverberation environment derived from the seafloor mining process, we simulated the real-life conditions of seafloor mining in a water filled tank of dimensions of 5×3×1.8m. The bottom of the tank was covered with 10cm of an irregular sand layer under which 5cm of an irregular cobalt-rich crusts layer was placed. The bottom was interrogated by an acoustic wave generated as 16μs pulses of 500kHz frequency. This frequency is demonstrated to ensure a resolution on the order of one centimetre, which is adequate in exploration practice. Echo signals were collected with a data acquisition card (PCI 1714 UL, 12-bit). Detection of the target echo in these signals was performed by both the Volterra series based model and the AR model

  1. A Volterra series-based method for extracting target echoes in the seafloor mining environment.

    PubMed

    Zhao, Haiming; Ji, Yaqian; Hong, Yujiu; Hao, Qi; Ma, Liyong

    2016-09-01

    The purpose of this research was to evaluate the applicability of the Volterra adaptive method to predict the target echo of an ultrasonic signal in an underwater seafloor mining environment. There is growing interest in mining of seafloor minerals because they offer an alternative source of rare metals. Mining the minerals cause the seafloor sediments to be stirred up and suspended in sea water. In such an environment, the target signals used for seafloor mapping are unable to be detected because of the unavoidable presence of volume reverberation induced by the suspended sediments. The detection of target signals in reverberation is currently performed using a stochastic model (for example, the autoregressive (AR) model) based on the statistical characterisation of reverberation. However, we examined a new method of signal detection in volume reverberation based on the Volterra series by confirming that the reverberation is a chaotic signal and generated by a deterministic process. The advantage of this method over the stochastic model is that attributions of the specific physical process are considered in the signal detection problem. To test the Volterra series based method and its applicability to target signal detection in the volume reverberation environment derived from the seafloor mining process, we simulated the real-life conditions of seafloor mining in a water filled tank of dimensions of 5×3×1.8m. The bottom of the tank was covered with 10cm of an irregular sand layer under which 5cm of an irregular cobalt-rich crusts layer was placed. The bottom was interrogated by an acoustic wave generated as 16μs pulses of 500kHz frequency. This frequency is demonstrated to ensure a resolution on the order of one centimetre, which is adequate in exploration practice. Echo signals were collected with a data acquisition card (PCI 1714 UL, 12-bit). Detection of the target echo in these signals was performed by both the Volterra series based model and the AR model

  2. Gradient elution capillary electrochromatography and hyphenation with nuclear magnetic resonance.

    PubMed

    Gfrörer, P; Schewitz, J; Pusecker, K; Tseng, L H; Albert, K; Bayer, E

    1999-01-01

    Coupling of gradient capillary electrochromatography (gradient CEC) and capillary zone electrophoresis (CZE) with nuclear magnetic resonance spectroscopy (NMR) was performed using a recently developed capillary NMR interface. This technique was applied for the analysis of pharmaceuticals and food. An analgesic was investigated using isocratic and gradient continuous-flow CEC-NMR. Comparison of the results demonstrated the superiority of gradient CEC over isocratic CEC. Aspartame and caffeine, both ingredients of soft beverages, were separated and analyzed by continuous flow CZE-NMR. The order of elution could be reversed by altering the pH. This reversal led to an increased sample concentration in the NMR detection cell, thus allowing the acquisition of a totally correlated spectroscopy (TOCSY) two-dimensional (2-D) spectrum of the synthetic peptide aspartame. PMID:10065951

  3. Gradient elution capillary electrochromatography and hyphenation with nuclear magnetic resonance.

    PubMed

    Gfrörer, P; Schewitz, J; Pusecker, K; Tseng, L H; Albert, K; Bayer, E

    1999-01-01

    Coupling of gradient capillary electrochromatography (gradient CEC) and capillary zone electrophoresis (CZE) with nuclear magnetic resonance spectroscopy (NMR) was performed using a recently developed capillary NMR interface. This technique was applied for the analysis of pharmaceuticals and food. An analgesic was investigated using isocratic and gradient continuous-flow CEC-NMR. Comparison of the results demonstrated the superiority of gradient CEC over isocratic CEC. Aspartame and caffeine, both ingredients of soft beverages, were separated and analyzed by continuous flow CZE-NMR. The order of elution could be reversed by altering the pH. This reversal led to an increased sample concentration in the NMR detection cell, thus allowing the acquisition of a totally correlated spectroscopy (TOCSY) two-dimensional (2-D) spectrum of the synthetic peptide aspartame.

  4. Image correction during large and rapid B(0) variations in an open MRI system with permanent magnets using navigator echoes and phase compensation.

    PubMed

    Li, Jianqi; Wang, Yi; Jiang, Yu; Xie, Haibin; Li, Gengying

    2009-09-01

    An open permanent magnet system with vertical B(0) field and without self-shielding can be quite susceptible to perturbations from external magnetic sources. B(0) variation in such a system located close to a subway station was measured to be greater than 0.7 microT by both MRI and a fluxgate magnetometer. This B(0) variation caused image artifacts. A navigator echo approach that monitored and compensated the view-to-view variation in magnetic resonance signal phase was developed to correct for image artifacts. Human brain imaging experiments using a multislice gradient-echo sequence demonstrated that the ghosting and blurring artifacts associated with B(0) variations were effectively removed using the navigator method. PMID:19369023

  5. Stress-gradient plasticity

    PubMed Central

    Chakravarthy, Srinath S.; Curtin, W. A.

    2011-01-01

    A new model, stress-gradient plasticity, is presented that provides unique mechanistic insight into size-dependent phenomena in plasticity. This dislocation-based model predicts strengthening of materials when a gradient in stress acts over dislocation source–obstacle configurations. The model has a physical length scale, the spacing of dislocation obstacles, and is validated by several levels of discrete-dislocation simulations. When incorporated into a continuum viscoplastic model, predictions for bending and torsion in polycrystalline metals show excellent agreement with experiments in the initial strengthening and subsequent hardening as a function of both sample-size dependence and grain size, when the operative obstacle spacing is proportional to the grain size. PMID:21911403

  6. A Novel Detection Scheme for High-Resolution Two-Dimensional Spin-Echo Correlated Spectra in Inhomogeneous Fields

    PubMed Central

    Huang, Yuqing; Zhang, Zhiyong; Cai, Shuhui; Chen, Zhong

    2014-01-01

    Background Two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy is a powerful and non-invasive tool for the analysis of molecular structures, conformations, and dynamics. However, the inhomogeneity of magnetic fields experienced by samples will destroy spectral information and hinder spectral analysis. In this study, a new pulse sequence is proposed based on the modulation of distant dipolar field to recover high-resolution 2D spin-echo correlated spectroscopy (SECSY) from inhomogeneous fields. Method and Material By using the new sequence, the correlation information between coupled spins and the J coupled information with straightforward multiplet patterns can be obtained free from inhomogeneous line broadening. In addition, the new sequence is also suitable for non-J coupled spin systems. Although three-dimensional acquisition is needed, the evolution of indirect detection dimensions is carefully designed and the ultrafast acquisition scheme is utilized to improve the acquisition efficiency. A chemical solution of butyl methacrylate (C8H14O2) in DMSO (C2H6SO) in a deshimmed magnetic field was tested to demonstrate the implementation details of the new sequence. The performance of the new sequence relative to the conventional SECSY sequence was shown by using an aqueous solution of main brain metabolites in a deshimmed magnetic field. Conclusion The results reveal that the new sequence provides an attractive way to eliminate the inhomogeneous spectral line broadening for the spin-echo correlated spectrum and is a promising tool for the study of metabolites in metabonomics, even for the applications on in vivo and in situ high-resolution 2D NMR spectroscopy. PMID:24392105

  7. FTMP data acquisition environment

    NASA Technical Reports Server (NTRS)

    Padilla, Peter A.

    1988-01-01

    The Fault-Tolerant Multi-Processing (FTMP) test-bed data acquisition environment is described. The performance of two data acquisition devices available in the test environment are estimated and compared. These estimated data rates are used as measures of the devices' capabilities. A new data acquisition device was developed and added to the FTMP environment. This path increases the data rate available by approximately a factor of 8, to 379 KW/S, while simplifying the experiment development process.

  8. Analysis and interpretation of Cassini Titan radar altimeter echoes

    NASA Astrophysics Data System (ADS)

    Zebker, Howard A.; Gim, Yonggyu; Callahan, Philip; Hensley, Scott; Lorenz, Ralph; Cassini Radar Team

    2009-03-01

    The Cassini spacecraft has acquired 25 radar altimeter elevation profiles along Titan's surface as of April 2008, and we have analyzed 18 of these for which there are currently reconstructed ephemeris data. Altimeter measurements were collected at spatial footprint sizes from 6-60 km along ground tracks of length 400-3600 km. The elevation profiles yield topographic information at this resolution with a statistical height accuracy of 35-50 m and kilometer-scale errors several times greater. The data exhibit significant variations in terrain, from flat regions with little topographic expression to very rugged Titanscapes. The bandwidth of the transmitted waveform admits vertical resolution of the terrain height to 35 m at each observed location on the surface. Variations in antenna pointing and changes in surface statistics cause the range-compressed radar echoes to exhibit strong systematic and time-variable biases of hundreds of meters in delay. It is necessary to correct the received echoes for these changes, and we have derived correction algorithms such that the derived echo profiles are accurate at the 100 m level for off-nadir pointing errors of 0.3° and 0.6°, for leading edge and echo centroid estimators, respectively. The leading edge of the echo yields the elevation of the highest points on the surface, which we take to be the peaks of any terrain variation. The mean value of the echo delay is more representative of the mean elevation, so that the difference of these values gives an estimate of any local mountain heights. Finding locations where these values diverge indicates higher-relief terrain. Elevation features are readily seen in the height profiles. Several of the passes show mountains of several hundred m altitude, spread over 10's or even 100's of km in spatial extent, so that slopes are very small. Large expanses of sub-100 m topography are commonplace on Titan, so it is rather smooth in many locations. Other areas exhibit more relief

  9. Streamlined acquisition handbook

    NASA Technical Reports Server (NTRS)

    1990-01-01

    NASA has always placed great emphasis on the acquisition process, recognizing it as among its most important activities. This handbook is intended to facilitate the application of streamlined acquisition procedures. The development of these procedures reflects the efforts of an action group composed of NASA Headquarters and center acquisition professionals. It is the intent to accomplish the real change in the acquisition process as a result of this effort. An important part of streamlining the acquisition process is a commitment by the people involved in the process to accomplishing acquisition activities quickly and with high quality. Too often we continue to accomplish work in 'the same old way' without considering available alternatives which would require no changes to regulations, approvals from Headquarters, or waivers of required practice. Similarly, we must be sensitive to schedule opportunities throughout the acquisition cycle, not just once the purchase request arrives at the procurement office. Techniques that have been identified as ways of reducing acquisition lead time while maintaining high quality in our acquisition process are presented.

  10. Discrimination of amplitude-modulated synthetic echo trains by an echolocating bottlenose dolphin.

    PubMed

    Dankiewicz, Lois A; Helweg, David A; Moore, Patrick W; Zafran, Justine M

    2002-10-01

    Bottlenose dolphins (Tursiops truncatus) have an acute ability to use target echoes to judge attributes such as size, shape, and material composition. Most target recognition studies have focused on features associated with individual echoes as opposed to information conveyed across echo sequences (feature envelope of the multi-echo train). One feature of aspect-dependent targets is an amplitude modulation (AM) across the return echoes in the echo train created by relative movement of the target and dolphin. The current study examined whether dolphins could discriminate targets with different AM envelopes. "Electronic echoes" triggered by a dolphin's outgoing echolocation clicks were manipulated to create sinusoidal envelopes with varying AM rate and depth. Echo trains were equated for energy, requiring the dolphin to extract and retain information from multiple echoes in order to detect and report the presence of AM. The dolphin discriminated amplitude-modulated echo trains from those that were not modulated. AM depth thresholds were approximately 0.8 dB, similar to other published amplitude limens. Decreasing the rate of modulation from approximately 16 to 2 cycles per second did not affect the dolphin's AM depth sensitivity. The results support multiple-echo processing in bottlenose dolphin echolocation. This capability provides additional theoretical justification for exploring synthetic aperture sonar concepts in models of animal echolocation that potentially support theories postulating formation of images as an ultimate means for target identification.

  11. Bats use echo harmonic structure to distinguish their targets from background clutter.

    PubMed

    Bates, Mary E; Simmons, James A; Zorikov, Tengiz V

    2011-07-29

    When echolocating big brown bats fly in complex surroundings, echoes arriving from irrelevant objects (clutter) located to the sides of their sonar beam can mask perception of relevant objects located to the front (targets), causing "blind spots." Because the second harmonic is beamed more weakly to the sides than the first harmonic, these clutter echoes have a weaker second harmonic. In psychophysical experiments, we found that electronically misaligning first and second harmonics in echoes (to mimic the misalignment of corresponding neural responses to harmonics in clutter echoes) disrupts the bat's echo-delay perception but also prevents clutter masking. Electronically offsetting harmonics to realign their neural responses restores delay perception but also clutter interference. Thus, bats exploit harmonics to distinguish clutter echoes from target echoes, sacrificing delay acuity to suppress masking.

  12. Time reversal and charge echo in an electron gas.

    PubMed

    Creswick, Richard J

    2004-09-01

    Apart from subtle violations of CP symmetry by the weak interactions, the basic laws of physics are time-reversal invariant. Nevertheless, in the macroscopic world, time has a very definite direction, or arrow. Given that the dynamics of a closed system are time-reversal invariant, the arrow of time is introduced through boundary or initial conditions. In this Letter it is argued that if the Hamiltonian for a system, H, has the property THT(-1)=-H for a unitary transformation T, then the system can, in principle, be made to evolve backward in time. The prototype of this sort of behavior is the spin echo. Calculations for a single-band tight-binding model suggest that it may be possible to observe the electronic counterpart, or charge echo.

  13. Doppler radar echoes of lightning and precipitation at vertical incidence

    NASA Technical Reports Server (NTRS)

    Zrnic, D. S.; Rust, W. D.; Taylor, W. L.

    1982-01-01

    Digital time series data at 16 heights within two storms were collected at vertical incidence with a 10-cm Doppler radar. On several occasions during data collection, lightning echoes were observed as increased reflectivity on an oscilloscope display. Simultaneously, lightning signals from nearby electric field change antennas were recorded on an analog recorder together with the radar echoes. Reflectivity, mean velocity, and Doppler spectra were examined by means of time series analysis for times during and after lightning discharges. Spectra from locations where lightning occurred show peaks, due to the motion of the lightning channel at the air speed. These peaks are considerably narrower than the ones due to precipitation. Besides indicating the vertical air velocity that can then be used to estimate hydrometeor-size distribution, the lightning spectra provide a convenient means to estimate the radar cross section of the channel. Subsequent to one discharge, we deduce that a rapid change in the orientation of hydrometeors occurred within the resolution volume.

  14. Benefits of the Multiple Echo Technique for Ultrasonic Thickness Testing

    SciTech Connect

    Elder, J.; Vandekamp, R.

    2011-02-10

    Much effort has been put into determining methods to make accurate thickness measurements, especially at elevated temperatures. An accuracy of +/- 0.001 inches is typically noted for commercial ultrasonic thickness gauges and ultrasonic thickness techniques. Codes and standards put limitations on many inspection factors including equipment, calibration tolerance and temperature variations. These factors are important and should be controlled, but unfortunately do not guarantee accurate and repeatable measurements in the field. Most technicians long for a single technique that is best for every situation, unfortunately, there are no 'silver bullets' when it comes to nondestructive testing. This paper will describe and discuss some of the major contributors to measurement error as well as some advantages and limitations of multiple echo techniques and why multiple echo techniques should be more widely utilized for ultrasonic thickness measurements.

  15. Revision of Spin Echoes in Pure Nuclear Quadrupole Resonance

    NASA Astrophysics Data System (ADS)

    Meriles, C. A.

    2001-04-01

    Goldman's spin-1/2 formalism has been used for describing the response of an I=3/2 spin system to a two-pulse sequence in a pure nuclear quadrupole resonance experiment. A detailed analysis of the polarization evolution and quadrupolar echo generation is carried out through the use of explicit expressions for secular homo- and heteronuclear dipolar interactions. In striking contrast with previous studies, it is predicted that Van Vleck's second moments governing a classical solid-echo or Hahn sequence differ from those obtained by equivalent means in magnetic resonance. In fact, it is shown that, although measured moments still complement each other, the combined use of standard sequences does not allow the separate determination of homo- and heteronuclear dipolar contributions to the linewidth, not even in an indirect manner. In this context, the importance and potential usefulness of a crossed coil probe are also briefly discussed.

  16. Infrared Echoes and the Structure of the ISM

    NASA Astrophysics Data System (ADS)

    Rieke, George; Kim, Yeunjin; Krause, Oliver

    2007-05-01

    We propose to continue a program to map the interstellar medium in three dimensions. Our technique uses infrared echoes from the supernova Cas A, which we discovered during In-Orbit Checkout. We have observed the echoes every six months since, observing the changes in the patterns of heated dust as the light pulse from the supernova propagates through the surrounding ISM. We have developed methods to invert this series of snapshots of planes in the ISM into three dimensional images. By the end of the Spitzer mission, our 3D images will have a depth of 1.5pc at a resolution of about 0.1 pc. This detailed information about the structure of the ISM will have important applications in understanding extinction in dense regions, the radiative transfer and heating of such regions, and in how the ISM fragments, for example to form stars.

  17. Modelling simultaneous echo waveform reconstruction and localization in bats.

    PubMed

    De Mey, F; Schillebeeckx, F; Vanderelst, D; Boen, A; Peremans, H

    2010-05-01

    Echolocating bats perceive the world through sound signals reflecting from the objects around them. In these signals, information is contained about reflector location and reflector identity. Bats are able to extract and separate the cues for location from those that carry identification information. We propose a model based on Wiener deconvolution that also performs this separation for a virtual system mimicking the echolocation system of the lesser spearnosed bat, Phyllostomus discolor. In particular, the model simultaneously reconstructs the reflected echo signal and localizes the reflector from which the echo originates. The proposed technique is based on a model that performs a similar task based on information from the frog's lateral line system. We show that direct application of the frog model to the bat sonar system is not feasible. However, we suggest a technique that does apply to the bat biosonar and indicate its performance in the presence of noise.

  18. Analysis on the characteristics of pulsed laser proximity fuze's echo

    NASA Astrophysics Data System (ADS)

    Wang, Kun; Chen, Huimin

    2011-06-01

    With the rapid development of semiconductor technology and laser technology, a kind of proximity fuze named pulsed laser proximity fuze has been applied. Compared with other fuzes, pulsed laser proximity fuze has high ranging precision and strong resistance to artificial active interference. It is an important development tendency of proximity fuze. The paper analyze the characteristic of target echo of laser signal, and then make theoretical analysis and calculation on the laser signal transmission in the smog. Firstly, use the pulse width of 10ns semiconductor laser fuze to do typical targets experiment, to get the echo information of target distance is 5m; then to do smog interference experiment, by comparing the pulse width amplitude and backscattering signal amplitude of laser fuze in simulation and experiment, analyzing the effect of anti-clutter, providing the evidence for the subsequent of circuit of signal amplification and processing.

  19. Stochastic Maximum Likelihood (SML) parametric estimation of overlapped Doppler echoes

    NASA Astrophysics Data System (ADS)

    Boyer, E.; Petitdidier, M.; Larzabal, P.

    2004-11-01

    This paper investigates the area of overlapped echo data processing. In such cases, classical methods, such as Fourier-like techniques or pulse pair methods, fail to estimate the first three spectral moments of the echoes because of their lack of resolution. A promising method, based on a modelization of the covariance matrix of the time series and on a Stochastic Maximum Likelihood (SML) estimation of the parameters of interest, has been recently introduced in literature. This method has been tested on simulations and on few spectra from actual data but no exhaustive investigation of the SML algorithm has been conducted on actual data: this paper fills this gap. The radar data came from the thunderstorm campaign that took place at the National Astronomy and Ionospheric Center (NAIC) in Arecibo, Puerto Rico, in 1998.

  20. Demonstration of photon-echo rephasing of spontaneous emission.

    PubMed

    Beavan, Sarah E; Hedges, Morgan P; Sellars, Matthew J

    2012-08-31

    In this paper we report the first demonstration of "rephased amplified spontaneous emission" (RASE) with photon-counting detection. This protocol provides an all-in-one photon-pair source and quantum-memory that has applications as a quantum repeater node. The RASE protocol is temporally multimode, and in this demonstration the photon echo was generated in a way that is spatially multimode and includes intermediate storage between two potentially long-lived spin states. A correlation between spontaneous emission and its photon echo was observed, using an ensemble of Pr(3+) ions doped into a Y2SiO5 crystal. Alterations that would allow for the measurement of nonclassical correlations are identified. These should generally apply for future experiments in rare-earth ion crystals, which are promising systems for implementing highly-multiplexed quantum repeater operations.

  1. Gradient equivalent crystal theory.

    PubMed

    Zypman, F R; Ferrante, J

    2006-07-01

    This paper presents an extension of the formalism of equivalent crystal theory (ECT) by introducing an electron density gradient term so that the total model density becomes a more accurate representation of the real local density. Specifically, we allow for the electron density around a lattice site to have directionality, in addition to an average value, as assumed in ECT. We propose that an atom senses its neighbouring density as a weighted sum-the weights given by the its own electronic probability. As a benchmark, the method is used to compute vacancy migration energy curves of iron. These energies are in good agreement with previously published results. PMID:21690822

  2. RESPECT: Neutron resonance spin-echo spectrometer for extreme studies

    NASA Astrophysics Data System (ADS)

    Georgii, R.; Kindervater, J.; Pfleiderer, C.; Böni, P.

    2016-11-01

    We propose the design of a REsonance SPin-echo spECtrometer for exTreme studies, RESPECT, that is ideally suited for the exploration of non-dispersive processes such as diffusion, crystallization, slow dynamics, tunneling processes, crystal electric field excitations, and spin fluctuations. It is a variant of the conventional neutron spin-echo technique (NSE) by (i) replacing the long precession coils by pairs of longitudinal neutron spin-echo coils combined with RF-spin flippers and (ii) by stabilizing the neutron polarization with small longitudinal guide fields that can in addition be used as field subtraction coils thus allowing to adjust the field integrals over a range of 8 orders of magnitude. Therefore, the dynamic range of RESPECT can in principle be varied over 8 orders of magnitude in time, if neutrons with the required energy are made available. Similarly as for existing NSE-spectrometers, spin echo times of up to approximately 1 μs can be reached if the divergence and the correction elements are properly adjusted. Thanks to the optional use of neutron guides and the fact that the currents for the correction coils are much smaller than in standard NSE, intensity gains of at least one order of magnitude are expected, making the concept of RESPECT also competitive for operation at medium flux neutron sources. RESPECT can also be operated in a MIEZE configuration allowing the investigation of relaxation processes in depolarizing environments as they occur when magnetic fields are applied at the sample position, i.e. for the investigation of the dynamics of flux lines in superconductors, magnetic fluctuations in ferromagnetic materials, and samples containing hydrogen.

  3. Breast tissue characterization using FARMA modeling of ultrasonic RF echo.

    PubMed

    Alacam, Burak; Yazici, Birsen; Bilgutay, Nihat; Forsberg, Flemming; Piccoli, Catherine

    2004-10-01

    A number of empirical and analytical studies demonstrated that the ultrasound RF echo reflected from tissue exhibits 1/f characteristics. In this paper, we propose to model 1/f characteristics of the ultrasonic RF echo by a novel parsimonious model, namely the fractional differencing auto regressive moving average (FARMA) process, and evaluated diagnostic value of model parameters for breast cancer malignancy differentiation. FARMA model captures the fractal and long term correlated nature of the backscattered speckle texture and facilitates robust efficient estimation of fractal parameters. In our study, in addition to the computer generated FARMA model parameters, we included patient age and radiologist's prebiopsy level of suspicion (LOS) as potential indicators of malignant and benign masses. We evaluated the performance of the proposed set of features using various classifiers and training methods using 120 in vivo breast images. Our study shows that the area under the receiver operating characteristics (ROC) curve of FARMA model parameters alone is superior to the area under the ROC curve of the radiologist's prebiopsy LOS. The area under the ROC curve of the three sets of features yields a value of 0.87, with a confidence interval of [0.85, 0.89], at a significance level of 0.05. Our results suggest that the proposed method of ultrasound RF echo model leads to parameters that can differentiate breast tumors with a relatively high precision. This set of RF echo features can be incorporated into a comprehensive computer-aided diagnostic system to aid physicians in breast cancer diagnosis.

  4. MISTY ECHO proof test of the GRMPY system

    SciTech Connect

    Deupree, R.G.; Flicker, S.L.; Turner, W.J.; Watson, C.A. ); Khalsa, N.; Macy, D. )

    1990-01-01

    The GRMPY system that was fielded on the MISTY ECHO event demonstrated that a small cadre of people could perform all fielding tasks. This report describes each task in detail and outlines the components of the GRMPY system. Suggestions are made for system improvement. The data are presented that were obtained on eight of the nine GRMPY stations fielded. 2 refs., 22 figs., 3 tabs.

  5. Loschmidt Echo in a System of Interacting Electrons

    SciTech Connect

    Manfredi, G.; Hervieux, P.-A.

    2006-11-10

    We study the Loschmidt echo for a system of electrons interacting through mean-field Coulomb forces. The electron gas is modeled by a self-consistent set of hydrodynamic equations. It is observed that the quantum fidelity drops abruptly after a time that is proportional to the logarithm of the perturbation amplitude. The fidelity drop is related to the breakdown of the symmetry properties of the wave function.

  6. Dual-echo fMRI can detect activations in inferior temporal lobe during intelligible speech comprehension

    PubMed Central

    Halai, Ajay D.; Parkes, Laura M.; Welbourne, Stephen R.

    2015-01-01

    The neural basis of speech comprehension has been investigated intensively during the past few decades. Incoming auditory signals are analysed for speech-like patterns and meaningful information can be extracted by mapping these sounds onto stored semantic representations. Investigation into the neural basis of speech comprehension has largely focused on the temporal lobe, in particular the superior and posterior regions. The ventral anterior temporal lobe (vATL), which includes the inferior temporal gyrus (ITG) and temporal fusiform gyrus (TFG) is consistently omitted in fMRI studies. In contrast, PET studies have shown the involvement of these ventral temporal regions. One crucial factor is the signal loss experienced using conventional echo planar imaging (EPI) for fMRI, at tissue interfaces such as the vATL. One method to overcome this signal loss is to employ a dual-echo EPI technique. The aim of this study was to use intelligible and unintelligible (spectrally rotated) sentences to determine if the vATL could be detected during a passive speech comprehension task using a dual-echo acquisition. A whole brain analysis for an intelligibility contrast showed bilateral superior temporal lobe activations and a cluster of activation within the left vATL. Converging evidence implicates the same ventral temporal regions during semantic processing tasks, which include language processing. The specific role of the ventral temporal region during intelligible speech processing cannot be determined from this data alone, but the converging evidence from PET, MEG, TMS and neuropsychology strongly suggest that it contains the stored semantic representations, which are activated by the speech decoding process. PMID:26037055

  7. Characteristics of lightning echoes observed with VHF ST radar

    NASA Astrophysics Data System (ADS)

    RöTtger, J.; Liu, C. H.; Pan, C. J.; Su, S. Y.

    1995-07-01

    The development of tropospheric convection was observed with the Chung-Li VHF stratosphere-troposphere (ST) radar in Taiwan, Republic of China. Deep convection evolved into thunderstorms during which radar echoes from lightning were recorded with a particular high time resolution program. These lightning echoes usually exist for only several tens to a few hundred milliseconds. To investigate the fine structure in the amplitude and phase of the lightning returns, the necessary time resolution has to be in the order of a few milliseconds. Such time resolutions are for the first time applied with VHF ST radar and the initial results are presented in this paper. Rapid jumps in the phase path were occurring together with sudden amplitude changes. This indicates that the scattering regions change their position, which could be on different branches of the lightning stroke. Large radial velocities of the lightning scattering regions up to several tens of meters per second were observed. Also, strong velocity shears were noticed in these lightning echo regions. Power peaks in Doppler spectra corresponding to velocities of about 300 m s-1 were occasionally detected. It is contemplated that these are caused by Bragg scattering from sound waves resulting from the lightning shock wave. Also a periodic velocity and amplitude modulation of a thin sheet of radar reflectivity was observed which one could attribute to infra-sound with a frequency of about 6-7 Hz. Preliminary conclusions are drawn finally to confirm that our observations are generally consistent with backscatter from lightning.

  8. 15 K pulse tube design for ECHO mission

    NASA Astrophysics Data System (ADS)

    Duval, J. M.; Charles, I.; Chassaing, C.; Butterworth, J.; Aigouy, G.; Mullié, J.

    2014-01-01

    The Exoplanet Characterisation Observatory (EChO) is a proposed space telescope designed to characterize the atmospheres of nearby transiting exoplanets. Its detectors will operate in the 0.4 to 11 micromillimeter range. Two kinds of detectors are currently able to provide the desired sensitivity in this range. Depending on the technology used, cooling to either 6 K or about 30 K will be required. For the former solution, a JT cooler coupled to a pulse tube cooler could be used whereas for the latter, a pulse tube cooler would provide the cooling power. Pulse tube coolers are particularly well adapted for the cryogenics for such mission because of the low level of vibration required and of the temperature range. We developed multistage pulse tube coolers able to cool down to temperature as low as 6 K, with efficient operation from 10 K to 40 K. A design based on our tested prototypes is proposed to fulfill the need for the ECHO missions. This paper describes the experimental results measured with demonstrator models. In particular measured performances of efficient cooling power at 10 K are presented. Several possible configurations for the ECHO cooler will be discussed as well.

  9. Nonlinear system modeling with random matrices: echo state networks revisited.

    PubMed

    Zhang, Bai; Miller, David J; Wang, Yue

    2012-01-01

    Echo state networks (ESNs) are a novel form of recurrent neural networks (RNNs) that provide an efficient and powerful computational model approximating nonlinear dynamical systems. A unique feature of an ESN is that a large number of neurons (the "reservoir") are used, whose synaptic connections are generated randomly, with only the connections from the reservoir to the output modified by learning. Why a large randomly generated fixed RNN gives such excellent performance in approximating nonlinear systems is still not well understood. In this brief, we apply random matrix theory to examine the properties of random reservoirs in ESNs under different topologies (sparse or fully connected) and connection weights (Bernoulli or Gaussian). We quantify the asymptotic gap between the scaling factor bounds for the necessary and sufficient conditions previously proposed for the echo state property. We then show that the state transition mapping is contractive with high probability when only the necessary condition is satisfied, which corroborates and thus analytically explains the observation that in practice one obtains echo states when the spectral radius of the reservoir weight matrix is smaller than 1.

  10. Acquisition of teleological descriptions

    NASA Astrophysics Data System (ADS)

    Franke, David W.

    1992-03-01

    Teleology descriptions capture the purpose of an entity, mechanism, or activity with which they are associated. These descriptions can be used in explanation, diagnosis, and design reuse. We describe a technique for acquiring teleological descriptions expressed in the teleology language TeD. Acquisition occurs during design by observing design modifications and design verification. We demonstrate the acquisition technique in an electronic circuit design.

  11. Quick Ride: Acquisition Overview

    NASA Technical Reports Server (NTRS)

    Adams, W. James

    1999-01-01

    Quick Ride is an outgrowth of rapid spacecraft acquisition. It provides a variety of low-cost, short lead time satellite rides for science instruments. Task order contracts with commercial firms will permit placing a order within 30 days. Secondary objectives include a demonstration of a FAR Part 12 commercial acquisition and the exploration of the use of on-ramps.

  12. Energy in density gradient

    SciTech Connect

    Vranjes, J.; Kono, M.

    2015-01-15

    Inhomogeneous plasmas and fluids contain energy stored in inhomogeneity and they naturally tend to relax into lower energy states by developing instabilities or by diffusion. But the actual amount of energy in such inhomogeneities has remained unknown. In the present work, the amount of energy stored in a density gradient is calculated for several specific density profiles in a cylindrical configuration. This is of practical importance for drift wave instability in various plasmas, and, in particular, in its application in models dealing with the heating of solar corona because the instability is accompanied with stochastic heating, so the energy contained in inhomogeneity is effectively transformed into heat. It is shown that even for a rather moderate increase of the density at the axis in magnetic structures in the corona by a factor 1.5 or 3, the amount of excess energy per unit volume stored in such a density gradient becomes several orders of magnitude greater than the amount of total energy losses per unit volume (per second) in quiet regions in the corona. Consequently, within the life-time of a magnetic structure such energy losses can easily be compensated by the stochastic drift wave heating.

  13. Blood flow structure and dynamics, and ejection mechanism in the left ventricle: analysis using echo-dynamography.

    PubMed

    Tanaka, Motonao; Sakamoto, Tsuguya; Sugawara, Shigeo; Nakajima, Hiroyuki; Katahira, Yoshiaki; Ohtsuki, Shigeo; Kanai, Hiroshi

    2008-10-01

    Using our "echo-dynamography", blood flow structure and flow dynamics during ventricular systole were investigated in 10 normal volunteers. The velocity vector distribution demonstrated blood flow during ejection was laminar along the ventricular septum. The characteristic flow structure was observed in each cardiac phases, early, mid- and late systole and was generated depending on the wall dynamic events such as peristaltic squeezing, hinge-like movement of the mitral ring plane, bellows action of the ventricle and dimensional changes in the funnel shape of the basal part of the ventricle, which were disclosed macroscopically by using the new technology of high speed scanning echo-tomography and microscopically by the strain rate distribution measured by phase tracking method. The pump function was reflected on the changes in the flow structure represented by the flow axis line distribution and the acceleration along the flow axis line. The acceleration of the ejection had three modes, "A", "B" and "C", and generated by the wall dynamic events. "A" appeared from the apical to the outflow area along the main flow axis line, "B" along the anterior mitral leaflet and the branched flow axis line, and "C" generated by the high speed vortex behind the mitral valve. The magnitude of the acceleration was estimated quantitatively from the velocity gradient along the flow axis line. Macroscopic and microscopic asynchrony in the myocardial contraction and extension appeared systematically in the local part of the ventricular wall, which was helpful for making the flow structure and for performing the smooth pump function.

  14. Generation of attenuation map for MR-based attenuation correction of PET data in the head area employing 3D short echo time MR imaging

    NASA Astrophysics Data System (ADS)

    Khateri, Parisa; Salighe Rad, Hamidreza; Fathi, Anahita; Ay, Mohammad Reza

    2013-02-01

    Attenuation correction is a crucial step to get accurate quantification of Positron Emission Tomography (PET) data. An attenuation map to provide attenuation coefficients at 511 keV can be generated using Magnetic Resonance Images (MRI). One of the main steps involved in MR-based attenuation correction (MRAC) of PET data is to separate bone from air. Low signal intensity of bone in conventional MRI makes it difficult to separate bone from air in the head area, while their attenuation coefficients are very different. In literature, several groups proposed ultrashort echo-time (UTE) sequences to differentiate bone from air [4,5,7], because these sequences are capable of imaging tissues with short T2* relaxation time, such as cortical bone; however, they are difficult to use, expensive and time-consuming. Employing short echo-time (STE) MRI in combination with long echo-time (LTE) MRI, and along with high performance image processing algorithms is a good substitute for UTE-based PET attenuation correction; they are widely available, easy to use, inexpensive and much faster than UTE pulse sequences. In this work, we propose the use of STE sequences along with LTE ones, as well as a dedicated image processing method to differentiate bone from air cavities in the head area by creating contrast between the tissues. Attenuation coefficients at 511 kev, relying on literature [5], will then be assigned to the voxels. Acquisition was performed on a clinical 3T Tim Trio scanner (Siemens Medical Solution, Erlangen, Germany), employing a dual echo sequence. To achieve an optimized protocol with the best result for discrimination of bone and air, two types of acquisitions were performed, with and without fat suppression; the acquisition parameters were as follows: TE=1.21/5 ms, TR=5/17, FA=30, and TE=1.12/3.16 ms, TR=5/5, FA=12 for non-fat-suppressed and fat-suppressed protocol, respectively. Contrast enhancement and tissue segmentation were applied as processing steps, to

  15. What a plant sounds like: the statistics of vegetation echoes as received by echolocating bats.

    PubMed

    Yovel, Yossi; Stilz, Peter; Franz, Matthias O; Boonman, Arjan; Schnitzler, Hans-Ulrich

    2009-07-01

    A critical step on the way to understanding a sensory system is the analysis of the input it receives. In this work we examine the statistics of natural complex echoes, focusing on vegetation echoes. Vegetation echoes constitute a major part of the sensory world of more than 800 species of echolocating bats and play an important role in several of their daily tasks. Our statistical analysis is based on a large collection of plant echoes acquired by a biomimetic sonar system. We explore the relation between the physical world (the structure of the plant) and the characteristics of its echo. Finally, we complete the story by analyzing the effect of the sensory processing of both the echolocation and the auditory systems on the echoes and interpret them in the light of information maximization. The echoes of all different plant species we examined share a surprisingly robust pattern that was also reproduced by a simple Poisson model of the spatial reflector arrangement. The fine differences observed between the echoes of different plant species can be explained by the spatial characteristics of the plants. The bat's emitted signal enhances the most informative spatial frequency range where the species-specific information is large. The auditory system filtering affects the echoes in a similar way, thus enhancing the most informative spatial frequency range even more. These findings suggest how the bat's sensory system could have evolved to deal with complex natural echoes.

  16. Apparatus and method for measuring relative phase of signals in a multiple-echo system

    NASA Technical Reports Server (NTRS)

    Froggatt, Mark E. (Inventor)

    1998-01-01

    An apparatus and method for measuring the relative phase of echo signals in a multiple-echo system. A signal generator generates an exciting tone burst and subsequent tone bursts delayed in phase from the exciting tone burst. The exciting tone burst is gated into a transducer coupled to the multiple-echo system. Each subsequent tone burst is converted into a series of pulses. Each pulse triggers a sample/hold circuit to sample each echo signal. The samples of the echo signal are averaged and then compared to a reference value. The signal generator is controlled to vary the subsequent tone burst phase delay to determine for each echo signal a subsequent tone burst phase delay that causes the average of the samples of the echo signal to be substantially equal to the reference value wherein the determined subsequent tone burst phase delay is the phase delay of the echo signal with respect to the exciting tone burst. The control circuit then determines the difference in phase delay between echo signals to determine the relative phase delay of the echo signals.

  17. The matrix formalism for generalised gradients with time-varying orientation in diffusion NMR

    NASA Astrophysics Data System (ADS)

    Drobnjak, Ivana; Zhang, Hui; Hall, Matt G.; Alexander, Daniel C.

    2011-05-01

    The matrix formalism is a general framework for evaluating the diffusion NMR signal from restricted spins under generalised gradient waveforms. The original publications demonstrate the method for waveforms that vary only in magnitude and have fixed orientation. In this work, we extend the method to allow for variations in the direction of the gradient. This extension is necessary, for example to incorporate the effects of crusher gradients or imaging gradients in diffusion MRI, to characterise signal anisotropy in double pulsed field gradient (dPFG) experiments, or to optimise the gradient waveform for microstructure sensitivity. In particular, we show for primitive geometries (planes, cylinders and spheres), how to express the matrix operators at each time point of the gradient waveform as a linear combination of one or two fundamental matrices. Thus we obtain an efficient implementation with both the storage and CPU demands similar to the fixed-orientation case. Comparison with Monte Carlo simulations validates the implementation on three different sequences: dPFG, helical waveforms and the stimulated echo (STEAM) sequence.

  18. On a summer maximum in the occurrence frequency of 150 km (F1) radar echoes over Pohnpei

    NASA Astrophysics Data System (ADS)

    Tsunoda, Roland T.; Ecklund, Warner L.

    2004-03-01

    Using three and a half years of 50 MHz radar data collected from Pohnpei, Federated States of Micronesia (6.96°N, 158.19°E geographic, 0.3° magnetic dip latitude), we show for the first time that the occurrence frequency of 150 km (or F1) echoes has a broad but conspicuous maximum during northern summer in this longitude sector with minimal activity in other months. Given a seasonal similarity to sporadic E (Es), we suggest that an Es-layer instability [Cosgrove and Tsunoda, 2002] generates a polarization electric field ($\\vec E$), which maps along geomagnetic field lines to the F1 region. There, $\\vec E$ forms thin plasma sheets that provide gradients to excite 3-m-scale plasma waves via an interchange process.

  19. Modelling the horizontal structure of mid-latitude E(s) from its refraction effects on F-region echoes

    NASA Astrophysics Data System (ADS)

    Barnes, R. I.

    1991-02-01

    The observation of the refraction of F-region echoes presently reported implies that significant horizontal structure exists within some E(s) clouds. A modeling of the data collected with the Bribie Island HF radar indicates that wind shear variations can account for examples in which irregularities either pass through, or pass with, existing layers of E(s) which create the cloudy, nonblanketing variety of E(s). The blanketing variety of E(s) seems to have little or no horizontal structure, and most likely drifts with the same velocity as the irregularities which produce nonblanketing E(s). Irregularities with strong horizontal gradients act as diverging lenses, leading to an overestimation of cloud size via simple occulting geometry.

  20. Feasibility and Reproducibility of Echo Planar Spectroscopic Imaging on the Quantification of Hepatic Fat

    PubMed Central

    Lin, Yi-Ru; Chiu, Jian-Jia; Tsai, Shang-Yueh

    2014-01-01

    Objectives 1H-MRS is widely regarded as the most accurate noninvasive method to quantify hepatic fat content (HFC). When practical period of breath holding, and acquisition of HFC over multiple liver areas is considered, a fast MR spectroscopic imaging technique is desired. The aim of this study is to examine the feasibility and reproducibility of echo planar spectroscopic imaging (EPSI) on the quantification of HFC in subject with various HFCs. Methods Twenty two volunteers were examined in a 3T MR system. The acquisition time of proposed EPSI protocol was 18 seconds. The EPSI scans were repeated 8 times for each subject to test reproducibility. The peak of water and individual peaks of fat including methyl, methylene, and allylic peaks at 0.9, 1.3, and 2.0 ppm were fitted. Calculated amount of water and fat content were corrected for T2 relaxation. The total HFC was defined as the combination of individual peaks. Standard deviation (SD), coefficient of variance (COV) and fitting reliability of HFC quantified by LCModel were calculated. Results Our results show that the SDs of total HFC for all subjects are less than 2.5%. Fitting reliability is mostly under 10% and positively correlates with COV. Subjects separated into three subgroups according to quantified total HFC show that improved fitting reliability and reproducibility can be achieved on subjects with higher total HFC. Conclusions We have demonstrated feasibility of the proposed EPSI protocols on the quantification of HFC over a whole slice of liver with scan time in a single breath hold. PMID:25514348

  1. Classification of brain tumours using short echo time 1H MR spectra

    NASA Astrophysics Data System (ADS)

    Devos, A.; Lukas, L.; Suykens, J. A. K.; Vanhamme, L.; Tate, A. R.; Howe, F. A.; Majós, C.; Moreno-Torres, A.; van der Graaf, M.; Arús, C.; Van Huffel, S.

    2004-09-01

    The purpose was to objectively compare the application of several techniques and the use of several input features for brain tumour classification using Magnetic Resonance Spectroscopy (MRS). Short echo time 1H MRS signals from patients with glioblastomas ( n = 87), meningiomas ( n = 57), metastases ( n = 39), and astrocytomas grade II ( n = 22) were provided by six centres in the European Union funded INTERPRET project. Linear discriminant analysis, least squares support vector machines (LS-SVM) with a linear kernel and LS-SVM with radial basis function kernel were applied and evaluated over 100 stratified random splittings of the dataset into training and test sets. The area under the receiver operating characteristic curve (AUC) was used to measure the performance of binary classifiers, while the percentage of correct classifications was used to evaluate the multiclass classifiers. The influence of several factors on the classification performance has been tested: L2- vs. water normalization, magnitude vs. real spectra and baseline correction. The effect of input feature reduction was also investigated by using only the selected frequency regions containing the most discriminatory information, and peak integrated values. Using L2-normalized complete spectra the automated binary classifiers reached a mean test AUC of more than 0.95, except for glioblastomas vs. metastases. Similar results were obtained for all classification techniques and input features except for water normalized spectra, where classification performance was lower. This indicates that data acquisition and processing can be simplified for classification purposes, excluding the need for separate water signal acquisition, baseline correction or phasing.

  2. Non Linear Conjugate Gradient

    2006-11-17

    Software that simulates and inverts electromagnetic field data for subsurface electrical properties (electrical conductivity) of geological media. The software treats data produced by a time harmonic source field excitation arising from the following antenna geometery: loops and grounded bipoles, as well as point electric and magnetic dioples. The inversion process is carried out using a non-linear conjugate gradient optimization scheme, which minimizes the misfit between field data and model data using a least squares criteria.more » The software is an upgrade from the code NLCGCS_MP ver 1.0. The upgrade includes the following components: Incorporation of new 1 D field sourcing routines to more accurately simulate the 3D electromagnetic field for arbitrary geologic& media, treatment for generalized finite length transmitting antenna geometry (antennas with vertical and horizontal component directions). In addition, the software has been upgraded to treat transverse anisotropy in electrical conductivity.« less

  3. Light Echoes and Late-Time Emissions of Type Ia Supernovae

    NASA Astrophysics Data System (ADS)

    Drozdov, Dina

    2016-05-01

    Type Ia supernovae have many applications in astronomy, yet with fundamental properties still not fully understood, new methods for investigating the environment of a supernova need to be developed. A light echo is produced from the scattering of light from a bright source and can be used to analyze the dust in the vicinity of the supernova and learn invaluable information about the source. These techniques can put constraints on explosion and progenitor models. Although light echo detections from Type Ia supernovae are rare, with only seven total extragalactic detections, this could be due to the lack of thorough late-epoch monitoring. Since key information is determined from even a single light echo detection, light echo searches should be undertaken in the future to supplement our understanding of supernovae. As part of our collaborative campaign for studying the emission of supernovae at late epochs, we have added two light echoes to a small sample size of Type Ia supernova light echo detections: SN 2009ig in NGC 1015 and a dual echo from SN 2007af in NGC 5584. Both echoes were observed with the Hubble Space Telescope and allow for the most detailed images of Type Ia supernova light echoes to date. Three filters (F555W, F814W, and F350LP) captured the echoes obtained with the Wide Field Camera 3, and since both host galaxies were imaged as part of the same observing program, these cases will be the best comparable light echo pairs. We also further investigate the light echoes from SN 2006X in NGC 4321 and SN 1998bu in NGC 3368 from Hubble Space Telescope archival images. Analyses performed on the images gives crucial insight into the dusty environment of the host galaxy and the surroundings of the supernova. The outer echo from SN 2007af was created from an interstellar dust sheet located ~800 pc in front of the supernova, while the inner echo could be from interstellar or circumstellar origin. A circumstellar light echo could imply a single degenerate

  4. Generalized conjugate gradient squared

    SciTech Connect

    Fokkema, D.R.; Sleijpen, G.L.G.

    1994-12-31

    In order to solve non-symmetric linear systems of equations, the Conjugate Gradient Squared (CGS) is a well-known and widely used iterative method. In practice the method converges fast, often twice as fast as the Bi-Conjugate Gradient method. This is what you may expect, since CGS uses the square of the BiCG polynomial. However, CGS may suffer from its erratic convergence behavior. The method may diverge or the approximate solution may be inaccurate. BiCGSTAB uses the BiCG polynomial and a product of linear factors in an attempt to smoothen the convergence. In many cases, this has proven to be very effective. Unfortunately, the convergence of BiCGSTAB may stall when a linear factor (nearly) degenerates. BiCGstab({ell}) is designed to overcome this degeneration of linear factors. It generalizes BiCGSTAB and uses both the BiCG polynomial and a product of higher order factors. Still, CGS may converge faster than BiCGSTAB or BiCGstab({ell}). So instead of using a product of linear or higher order factors, it may be worthwhile to look for other polynomials. Since the BiCG polynomial is based on a three term recursion, a natural choice would be a polynomial based on another three term recursion. Possibly, a suitable choice of recursion coefficients would result in method that converges faster or as fast as CGS, but less erratic. It turns out that an algorithm for such a method can easily be formulated. One particular choice for the recursion coefficients leads to CGS. Therefore one could call this algorithm generalized CGS. Another choice for the recursion coefficients leads to BiCGSTAB. It is therefore possible to mix linear factors and some polynomial based on a three term recursion. This way one may get the best of both worlds. The authors will report on their findings.

  5. Clinical ultrashort echo time imaging of bone and other connective tissues.

    PubMed

    Robson, Matthew D; Bydder, Graeme M

    2006-11-01

    The background underpinning the clinical use of ultrashort echo time, SPRITE and other pulse sequences for imaging bone and other connective tissues with short T2 is reviewed. Features of the basic physics relevant to UTE imaging are described, including the consequences when the radiofrequency pulse duration is of the order of T2 so that rotation of tissue magnetization into the transverse plane is incomplete. Consequences of the broad linewidth of short T2 components are also discussed, including partial saturation by off-resonance fat suppression pulses as well as those used in multislice and multiecho imaging. The need for rapid data acquisition of the order of T2 is explained. The basic two-dimensional UTE pulse sequence with its half excitation pulse and radial imaging from the centre of k-space is described, together with options that suppress fat and/or reduce the signal from long T2 components. The basic features of SPRITE and other sequences with very short TE are described. Image interpretation is discussed. Clinical features of the imaging of cortical bone, tendons, ligaments, menisci, periosteum and the spine are illustrated. The source of the short T2 signal in these tissues is predominantly collagen and water tightly bound to collagen. Short T2 components in all of these tissues are detectible and may show high signals. Possible future developments are outlined, as are technical limitations of clinical magnetic resonance systems. PMID:17075960

  6. Volume localized spin echo correlation spectroscopy with suppression of 'diagonal' peaks.

    PubMed

    Banerjee, Abhishek; Chandrakumar, N

    2014-02-01

    Two dimensional homonuclear (1)H correlation spectroscopy is of considerable interest for volume localized spectral studies, both in vivo and in vitro, of biological as well as material objects. The information principally sought from correlation spectra resides in the cross-peaks, which are often masked however by the presence of diagonal peaks in COSY, or 'pseudo-diagonal' peaks at F1=0 in SECSY. It has therefore been a concern to suppress these diagonal or 'pseudo-diagonal' peaks, in order to ensure that cross-peak information is fully discernible. We present here a report of our work on volume localized DIagonal Suppressed Spin Echo Correlation specTroscopy (LDISSECT) and demonstrate its performance in comparison to the standard volume localized SECSY experiment, employing brain metabolite phantoms in a gel. The sequence works in the inhomogeneous, multi-component environment by exploiting the short acquisition time to suppress undesired information by employing an additional rf pulse. A brief description of the pulse sequence, its theory, and simulations are also included, besides experimental benchmarking on two brain metabolite phantoms in gel phase.

  7. Use of earth field spin echo NMR to search for liquid minerals

    DOEpatents

    Stoeffl, Wolfgang

    2001-01-01

    An instrument for measuring the spatial, qualitative and quantitative parameters of an underground nuclear magnetic resonance (NMR) active liquid mineral deposit, including oil and water. A phased array of excitation and receiver antennas on the surface and/or in a borehole excites the NMR active nuclei in the deposit, and using known techniques from magnetic resonance imaging (MRI), the spatial and quantitative distribution of the deposit can be measured. A surface array may utilize, for example, four large (50-500 diameter) diameter wire loops laid on the ground surface, and a weak (1.5-2.5 kHz) alternating current (AC) field applied, matching the NMR frequency of hydrogen in the rather flat and uniform earth magnetic field. For a short duration (a few seconds) an additional gradient field can be generated, superimposed to the earth field, by applying direct current (DC) to the grid (wire loops), enhancing the position sensitivity of the spin-echo and also suppressing large surface water signals by shifting them to a different frequency. The surface coil excitation can be combined with downhole receivers, which are much more radio-quiet compared to surface receivers, and this combination also enhances the position resolution of the MRI significantly. A downhole receiver module, for example, may have a 5.5 inch diameter and fit in a standard six inch borehole having a one-quarter inch thick stainless steel casing. The receiver module may include more than one receiver units for improved penetration and better position resolution.

  8. Spatio-temporal learning with the online finite and infinite echo-state Gaussian processes.

    PubMed

    Soh, Harold; Demiris, Yiannis

    2015-03-01

    Successful biological systems adapt to change. In this paper, we are principally concerned with adaptive systems that operate in environments where data arrives sequentially and is multivariate in nature, for example, sensory streams in robotic systems. We contribute two reservoir inspired methods: 1) the online echostate Gaussian process (OESGP) and 2) its infinite variant, the online infinite echostate Gaussian process (OIESGP) Both algorithms are iterative fixed-budget methods that learn from noisy time series. In particular, the OESGP combines the echo-state network with Bayesian online learning for Gaussian processes. Extending this to infinite reservoirs yields the OIESGP, which uses a novel recursive kernel with automatic relevance determination that enables spatial and temporal feature weighting. When fused with stochastic natural gradient descent, the kernel hyperparameters are iteratively adapted to better model the target system. Furthermore, insights into the underlying system can be gleamed from inspection of the resulting hyperparameters. Experiments on noisy benchmark problems (one-step prediction and system identification) demonstrate that our methods yield high accuracies relative to state-of-the-art methods, and standard kernels with sliding windows, particularly on problems with irrelevant dimensions. In addition, we describe two case studies in robotic learning-by-demonstration involving the Nao humanoid robot and the Assistive Robot Transport for Youngsters (ARTY) smart wheelchair. PMID:25720008

  9. Complimentary use of epicardial echo imaging and Doppler in quantification of coronary artery stenoses

    NASA Astrophysics Data System (ADS)

    Richards, Kent L.; Cannon, Scott R.

    1990-08-01

    As more advanced therapeutic procedures are performed on coronary arteries during open chest surgery more advanced diagnostic procedures will be required to define the location and severity of coronary artery disease. This manuscript describes our preliminary experiences in identifying human coronary artery stenoses using epicardial two-dimensional color flow Doppler. Once the lesions were identified we used standard echo Doppler and imaging techniques to define their severity. The accuracy of stenotic cross sectional area calculated using the continuity equation and pressure gradient calculated using the Bernoulli equation were defined using a pulsatile flow model of the coronary circulation. Suggestions about further hardware development required to allow easy clinical application of this technique are described. 1 - CLINICAL NEED FOR INTRA-OPERATIVE EVAUJATION OFCORONARY ARTERIES The severity of coronary artery disease in adults who require coronary bypass surgery has changed significantly in the last ten years. More effective medications used to control angina pectoris and the wide use of percutaneous y artery angioplasty have delayed the timing of surgery until atherosclerotic involvement is more extensive. In addition patients who have had initial coronary bypass operations are now reaching ages at which atherosclerotic involvement of their bypass grafts and native vessels has progressed and reoperation is required. To meet the challenge of coronary arteries with multiple lesions or diffuse disease intraoperative angioplasty devices are being developed. Whether bypass surgery for advanced lesions or reoperation of

  10. STIS target acquisition

    NASA Technical Reports Server (NTRS)

    Kraemer, Steve; Downes, Ron; Katsanis, Rocio; Crenshaw, Mike; McGrath, Melissa; Robinson, Rich

    1997-01-01

    We describe the STIS autonomous target acquisition capabilities. We also present the results of dedicated tests executed as part of Cycle 7 calibration, following post-launch improvements to the Space Telescope Imaging Spectrograph (STIS) flight software. The residual pointing error from the acquisitions are < 0.5 CCD pixels, which is better than preflight estimates. Execution of peakups show clear improvement of target centering for slits of width 0.1 sec or smaller. These results may be used by Guest Observers in planning target acquisitions for their STIS programs.

  11. Interactive knowledge acquisition tools

    NASA Technical Reports Server (NTRS)

    Dudziak, Martin J.; Feinstein, Jerald L.

    1987-01-01

    The problems of designing practical tools to aid the knowledge engineer and general applications used in performing knowledge acquisition tasks are discussed. A particular approach was developed for the class of knowledge acquisition problem characterized by situations where acquisition and transformation of domain expertise are often bottlenecks in systems development. An explanation is given on how the tool and underlying software engineering principles can be extended to provide a flexible set of tools that allow the application specialist to build highly customized knowledge-based applications.

  12. Spatially resolved solid-state 1H NMR for evaluation of gradient-composition polymeric libraries.

    PubMed

    Leisen, Johannes; Gomez, Ismael J; Roper, John A; Meredith, J Carson; Beckham, Haskell W

    2012-07-01

    Polyurethane libraries consisting of films with composition gradients of aliphatic polyisocyanate and hydroxy-terminated polyacrylate resin were characterized using methods of (1)H NMR microimaging (i.e., magnetic resonance imaging, (MRI)) and solid-state NMR. Molecular mobilities and underlying structural information were extracted as a function of the relative content of each of the two components. Routine NMR microimaging using the spin-echo sequence only allows investigations of transverse relaxation of magnetization at echo times >2 ms. A single-exponential decay was found, which is likely due to free, noncross-linked polymer chains. The mobility of these chains decreases with increasing content of the aliphatic polyisocyanate. The concept of a 1D NMR profiler is introduced as a novel modality for library screening, which allows the convenient measurement of static solid-state NMR spectra as a function of spatial location along a library sample that is repositioned in the rf coil between experiments. With this setup the complete transverse relaxation function was measured using Bloch decays and spin echoes. For all positions within the gradient-composition film, relaxation data consisted of at least three components that were attributed to a rigid highly cross-linked resin, an intermediate cross-linked but mobile constituent, and the highly mobile free polymer chains (the latter is also detectable by MRI). Analysis of this overall relaxation function measured via Bloch decays and spin echoes revealed only minor changes in the mobilities of the individual fractions. Findings with respect to the most mobile components are consistent with the results obtained by NMR microimaging. The major effect is the significant increase in the rigid-component fraction with the addition of the hydroxy-terminated polyacrylate resin. PMID:22676634

  13. Analysis of the temporal structure of fish echoes using the dolphin broadband sonar signal.

    PubMed

    Matsuo, Ikuo; Imaizumi, Tomohito; Akamatsu, Tomonari; Furusawa, Masahiko; Nishimori, Yasushi

    2009-07-01

    Behavioral experiments indicate that dolphins detect and discriminate prey targets through echolocating broadband sonar signals. The fish echo contains components from multiple reflections, including those from the swim bladder and other organs, and can be used for the identification of fish species and the estimation of fish abundance. In this paper, temporal structures were extracted from fish echoes using the cross-correlation function and the lowpass filter. First, the echo was measured from an anesthetized fish in a water tank. The number, reflector intensity, and echo duration were shown to be dependent on the species, individual, and orientation of the fish. In particular, the echo duration provided useful information on the fish body height and for species identification. Second, the echo was measured from the live fish suspended by nylon monofilament lines in the open sea. It was shown that this duration could be estimated regardless of whether or not the fish were moving.

  14. Photon echo transients from an inhomogeneous ensemble of semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Poltavtsev, S. V.; Salewski, M.; Kapitonov, Yu. V.; Yugova, I. A.; Akimov, I. A.; Schneider, C.; Kamp, M.; Höfling, S.; Yakovlev, D. R.; Kavokin, A. V.; Bayer, M.

    2016-03-01

    An ensemble of quantum dot excitons may be used for coherent information manipulation. Due to the ensemble inhomogeneity any optical information retrieval occurs in the form of a photon echo. We show that the inhomogeneity can lead to a significant deviation from the conventional echo timing sequence. Variation of the area of the initial rotation pulse, which generates excitons in a dot subensemble only, reveals this complex picture of photon echo formation. We observe a retarded echo for π /2 pulses, while for 3 π /2 the echo is advanced in time as evidenced through monitoring the Rabi oscillations in the time-resolved photon echo amplitude from (In,Ga)As/GaAs self-assembled quantum dot structures and confirmed by detailed calculations.

  15. Acquisition signal transmitter

    NASA Technical Reports Server (NTRS)

    Friedman, Morton L. (Inventor)

    1989-01-01

    An encoded information transmitter which transmits a radio frequency carrier that is amplitude modulated by a constant frequency waveform and thereafter amplitude modulated by a predetermined encoded waveform, the constant frequency waveform modulated carrier constituting an acquisition signal and the encoded waveform modulated carrier constituting an information bearing signal, the acquisition signal providing enhanced signal acquisition and interference rejection favoring the information bearing signal. One specific application for this transmitter is as a distress transmitter where a conventional, legislated audio tone modulated signal is transmitted followed first by the acquisition signal and then the information bearing signal, the information bearing signal being encoded with, among other things, vehicle identification data. The acquistion signal enables a receiver to acquire the information bearing signal where the received signal is low and/or where the received signal has a low signal-to-noise ratio in an environment where there are multiple signals in the same frequency band as the information bearing signal.

  16. Defense acquisition programs

    SciTech Connect

    Not Available

    1990-06-01

    The continuing instability in the overall defense budget and the recent changes in Eastern Europe are forcing DOD and the military services to reexamine the need, priority, and annual funding levels for many weapon system acquisition programs. GAO reviewed six weapon system acquisition programs that DOD was scheduled to make an acquisition milestone decision on during fiscal year 1991. Under milestone authorization, up to five years funding can be approved to cover the entire acquisition phase for either full-scale development or full-rate production. This report examines the Non-Line-of-Sight Missile, the Light Helicopter, the MK-50 Torpedo, the Sensor Fuzed Weapon, the Advanced Tactical Fighter, and the Joint Tactical Information Distribution System Class 2 Terminals.

  17. Documentation and knowledge acquisition

    NASA Technical Reports Server (NTRS)

    Rochowiak, Daniel; Moseley, Warren

    1990-01-01

    Traditional approaches to knowledge acquisition have focused on interviews. An alternative focuses on the documentation associated with a domain. Adopting a documentation approach provides some advantages during familiarization. A knowledge management tool was constructed to gain these advantages.

  18. Airborne data acquisition techniques

    SciTech Connect

    Arro, A.A.

    1980-01-01

    The introduction of standards on acceptable procedures for assessing building heat loss has created a dilemma for the contractor performing airborne thermographic surveys. These standards impose specifications on instrumentation, data acquisition, recording, interpretation, and presentation. Under the standard, the contractor has both the obligation of compliance and the requirement of offering his services at a reasonable price. This paper discusses the various aspects of data acquisition for airborne thermographic surveys and various techniques to reduce the costs of this operation. These techniques include the calculation of flight parameters for economical data acquisition, the selection and use of maps for mission planning, and the use of meteorological forecasts for flight scheduling and the actual execution of the mission. The proper consideration of these factors will result in a cost effective data acquisition and will place the contractor in a very competitive position in offering airborne thermographic survey services.

  19. Data acquisition system

    DOEpatents

    Shapiro, Stephen L.; Mani, Sudhindra; Atlas, Eugene L.; Cords, Dieter H. W.; Holbrook, Britt

    1997-01-01

    A data acquisition circuit for a particle detection system that allows for time tagging of particles detected by the system. The particle detection system screens out background noise and discriminate between hits from scattered and unscattered particles. The detection system can also be adapted to detect a wide variety of particle types. The detection system utilizes a particle detection pixel array, each pixel containing a back-biased PIN diode, and a data acquisition pixel array. Each pixel in the particle detection pixel array is in electrical contact with a pixel in the data acquisition pixel array. In response to a particle hit, the affected PIN diodes generate a current, which is detected by the corresponding data acquisition pixels. This current is integrated to produce a voltage across a capacitor, the voltage being related to the amount of energy deposited in the pixel by the particle. The current is also used to trigger a read of the pixel hit by the particle.

  20. Pseudo LRM waveforms from CryoSat SARin acquisition

    NASA Astrophysics Data System (ADS)

    Scagliola, Michele; Fornari, Marco; Bouffard, Jerome; Parrinello, Tommaso; Féménias, Pierre

    2016-04-01

    CryoSat was launched on the 8th April 2010 and is the first European ice mission dedicated to the monitoring of precise changes in the thickness of polar ice sheets and floating sea ice. The main payload of CryoSat is a Ku-band pulsewidth limited radar altimeter, called SIRAL (Synthetic interferometric radar altimeter). When commanded in SARIn (synthetic aperture radar interferometry) mode, through coherent along-track processing of the returns received from two antennas, the interferometric phase related to the first arrival of the echo is used to retrieve the angle of arrival of the scattering in the across-track direction. When SIRAL operates in SAR or SARin mode, the obtained waveforms have an along-track resolution and a speckle reduction which is increased with respect to the pulse-limited waveforms. Anyway, in order to analyze the continuity of the geophysical retrieved parameters among different acquisition modes, techniques to transform SARin mode data to pseudo-LRM mode data are welcome. The transformation process is known as SAR reduction and it is worth recalling here that only approximate pseudo-LRM waveforms can be obtained in case of closed burst acquisitions, as SIRAL operates. A SAR reduction processing scheme has been developed to obtain pseudo-LRM waveforms from CryoSat SARin acquisition. As a trade-off between the along-track length on Earth surface contributing to one SARin pseudo-LRM waveform and the noisiness of the waveform itself, it has been chosen a SAR reduction approach based on the averaging of all the SARin echoes received each 20Hz, resulting in one pseudo-LRM waveform for each SARin burst given the SARin burst repetition period. SARin pseudo-LRM waveforms have been produced for CryoSat acquisition both on ice and sea surfaces, aiming at verifying the continuity of the retracked surface height over the ellipsoid between genuine LRM products and pseudo-LRM products. Moreover, the retracked height from the SARin pseudo-LRM has been

  1. Gradient boosting machines, a tutorial

    PubMed Central

    Natekin, Alexey; Knoll, Alois

    2013-01-01

    Gradient boosting machines are a family of powerful machine-learning techniques that have shown considerable success in a wide range of practical applications. They are highly customizable to the particular needs of the application, like being learned with respect to different loss functions. This article gives a tutorial introduction into the methodology of gradient boosting methods with a strong focus on machine learning aspects of modeling. A theoretical information is complemented with descriptive examples and illustrations which cover all the stages of the gradient boosting model design. Considerations on handling the model complexity are discussed. Three practical examples of gradient boosting applications are presented and comprehensively analyzed. PMID:24409142

  2. Optimization of magnetic flux density measurement using multiple RF receiver coils and multi-echo in MREIT.

    PubMed

    Jeong, Woo Chul; Chauhan, Munish; Sajib, Saurav Z K; Kim, Hyung Joong; Serša, Igor; Kwon, Oh In; Woo, Eung Je

    2014-09-01

    Magnetic Resonance Electrical Impedance Tomography (MREIT) is an MRI method that enables mapping of internal conductivity and/or current density via measurements of magnetic flux density signals. The MREIT measures only the z-component of the induced magnetic flux density B = (Bx, By, Bz) by external current injection. The measured noise of Bz complicates recovery of magnetic flux density maps, resulting in lower quality conductivity and current-density maps. We present a new method for more accurate measurement of the spatial gradient of the magnetic flux density gradient (∇ Bz). The method relies on the use of multiple radio-frequency receiver coils and an interleaved multi-echo pulse sequence that acquires multiple sampling points within each repetition time. The noise level of the measured magnetic flux density Bz depends on the decay rate of the signal magnitude, the injection current duration, and the coil sensitivity map. The proposed method uses three key steps. The first step is to determine a representative magnetic flux density gradient from multiple receiver coils by using a weighted combination and by denoising the measured noisy data. The second step is to optimize the magnetic flux density gradient by using multi-echo magnetic flux densities at each pixel in order to reduce the noise level of ∇ Bz and the third step is to remove a random noise component from the recovered ∇ Bz by solving an elliptic partial differential equation in a region of interest. Numerical simulation experiments using a cylindrical phantom model with included regions of low MRI signal to noise ('defects') verified the proposed method. Experimental results using a real phantom experiment, that included three different kinds of anomalies, demonstrated that the proposed method reduced the noise level of the measured magnetic flux density. The quality of the recovered conductivity maps using denoised ∇ Bz data showed that the proposed method reduced the conductivity

  3. Triple-echo steady-state T2 relaxometry of the human brain at high to ultra-high fields.

    PubMed

    Heule, Rahel; Bär, Peter; Mirkes, Christian; Scheffler, Klaus; Trattnig, Siegfried; Bieri, Oliver

    2014-09-01

    Quantitative MRI techniques, such as T2 relaxometry, have demonstrated the potential to detect changes in the tissue microstructure of the human brain with higher specificity to the underlying pathology than in conventional morphological imaging. At high to ultra-high field strengths, quantitative MR-based tissue characterization benefits from the higher signal-to-noise ratio traded for either improved resolution or reduced scan time, but is impaired by severe static (B0 ) and transmit (B1 ) field heterogeneities. The objective of this study was to derive a robust relaxometry technique for fast T2 mapping of the human brain at high to ultra-high fields, which is highly insensitive to B0 and B1 field variations. The proposed method relies on a recently presented three-dimensional (3D) triple-echo steady-state (TESS) imaging approach that has proven to be suitable for fast intrinsically B1 -insensitive T2 relaxometry of rigid targets. In this work, 3D TESS imaging is adapted for rapid high- to ultra-high-field two-dimensional (2D) acquisitions. The achieved short scan times of 2D TESS measurements reduce motion sensitivity and make TESS-based T2 quantification feasible in the brain. After validation in vitro and in vivo at 3 T, T2 maps of the human brain were obtained at 7 and 9.4 T. Excellent agreement between TESS-based T2 measurements and reference single-echo spin-echo data was found in vitro and in vivo at 3 T, and T2 relaxometry based on TESS imaging was proven to be feasible and reliable in the human brain at 7 and 9.4 T. Although prominent B0 and B1 field variations occur at ultra-high fields, the T2 maps obtained show no B0 - or B1 -related degradations. In conclusion, as a result of the observed robustness, TESS T2 may emerge as a valuable measure for the early diagnosis and progression monitoring of brain diseases in high-resolution 2D acquisitions at high to ultra-high fields.

  4. Discrete echo signal modeling of ultrasound imaging systems

    NASA Astrophysics Data System (ADS)

    Chen, Ming; Zhang, Cishen

    2008-03-01

    In this paper, a discrete model representing the pulse-tissue interaction in the medical ultrasound scanning and imaging process is developed. The model is based on discretizing the acoustical wave equation and is in terms of convolution between the input ultrasound pulses and the tissue mass density variation. Such a model can provide a useful means for ultrasound echo signal processing and imaging. Most existing models used for ultrasound imaging are based on frequency domain transform. A disadvantage of the frequency domain transform is that it is only applicable to shift-invariant models. Thus it has ignored the shift-variant nature of the original acoustic wave equation where the tissue compressibility and mass density distributions are spatial-variant factors. The discretized frequency domain model also obscures the compressibility and mass density representations of the tissue, which may mislead the physical understanding and interpretation of the image obtained. Moreover, only the classical frequency domain filtering methods have been applied to the frequency domain model for acquiring some tissue information from the scattered echo signals. These methods are non-parametric and require a prior knowledge of frequency spectra of the transmitted pulses. Our proposed model technique will lead to discrete, multidimensional, shift-variant and parametric difference or convolution equations with the transmitted pulse pressure as the input, the measurement data of the echo signals as the output, and functions of the tissue compressibility and mass density distributions as shift-variant parameters that can be readily identified from input-output measurements. The proposed model represents the entire multiple scattering process, and hence overcomes the key limitation in the current ultrasound imaging methods.

  5. Susceptibility-resistant variable-flip-angle turbo spin echo imaging for reliable estimation of cortical thickness: a feasibility study.

    PubMed

    Lee, Hyunyeol; Kim, Eung-Yeop; Yang, Kyung-Sook; Park, Jaeseok

    2012-01-01

    The thickness of the human cerebral cortex, which provides valuable information in the studies of normal and abnormal neuroanatomy, is commonly estimated using high-resolution, volumetric magnetization-prepared rapid gradient echo (MP-RAGE) magnetic resonance imaging due to its strong T1-weighted contrast and high signal-to-noise ratio. However, the accuracy of cortical thickness estimates using MP-RAGE is potentially contaminated by susceptibility-induced signal loss particularly at regions in close proximity to air-filled cavities. The purpose of this work is to investigate the feasibility of susceptibility-resistant variable-flip-angle (VFA) three-dimensional turbo/fast spin echo imaging for reliable estimation of cortical thickness of the human brain, wherein 1) radio-frequency (RF) pulse refocuses susceptibility-induced spin de-phasing, 2) the VFA refocusing pulse train is applied for a tissue-specific prescribed signal evolution along the echo train, 3) the desired T1-weighted contrast is achieved by composite restore pulses at the end of the refocusing pulse train, and 4) blood signals are suppressed using the VFA scheme combined with increasing moments of flow-sensitizing gradients while dura mater signals are attenuated due to short T2 relaxation time, which alleviates potential failure in brain segmentation. Numerical simulations of the Bloch equation are performed in both MP-RAGE and the proposed method for comparison. In vivo studies are performed in 14 healthy volunteers at 3 T. Image processing is then performed using the Freesurfer, resulting in mean and standard deviations of cortical thickness for the entire cortical surfaces. Statistical analysis demonstrates that particularly in the inferior prefrontal and temporal regions heavily affected by susceptibility-induced signal loss conventional MP-RAGE, if compared with the proposed method, significantly under-estimates cortical thickness. It is expected that the proposed pulse sequence, which is

  6. Connection between decoherence and fidelity decay in echo dynamics

    NASA Astrophysics Data System (ADS)

    Gorin, T.; Prosen, T.; Seligman, T. H.; Strunz, W. T.

    2004-10-01

    Entanglement between a quantum system and its environment leads to loss of coherence in the former. In general, the temporal fate of coherences is complicated. Here, we establish the connection between decoherence of a central system and fidelity decay in the environment for a variety of situations, including both energy conserving and dissipative couplings. We show how properties of unitary time evolution of the environment can be inferred from the nonunitary evolution of coherences in the central system. This opens up promising ways for measuring Loschmidt echoes in a variety of situations.

  7. First Experimental Evidence for Quantum Echoes in Scattering Systems

    NASA Astrophysics Data System (ADS)

    Dembowski, C.; Dietz, B.; Friedrich, T.; Gräf, H.-D.; Heine, A.; Mejía-Monasterio, C.; Miski-Oglu, M.; Richter, A.; Seligman, T. H.

    2004-09-01

    A self-pulsing effect termed quantum echoes has been observed in experiments with an open superconducting and a normal conducting microwave billiard whose geometry provides soft chaos, i.e., a mixed phase space portrait with a large stable island. For such systems a periodic response to an incoming pulse has been predicted. Its period has been associated with the degree of development of a horseshoe describing the topology of the classical dynamics. The experiments confirm this picture and reveal the topological information.

  8. Correlation between cosmic noise absorption and VHF coherent echo intensity

    NASA Astrophysics Data System (ADS)

    Makarevitch, R. A.; Honary, F.

    2005-07-01

    We present examples and statistical analysis of the events with statistically significant correlation between the cosmic noise absorption (CNA) and the signal-to-noise ratio (SNR) of the VHF coherent echo intensity in the area monitored simultaneously by an imaging riometer and two oblique-sounding coherent VHF radars in Northern Scandinavia. By only considering the observations from the narrow riometer beams comparable (in terms of the intersection with the ionosphere) with the VHF radar cells, we identify ~200 one-hour high correlation periods (HCPs) for 2 years near the solar cycle maximum, 2000 2001. The HCP occurrence is maximized in the afternoon (12:00 17:00 UT, MLT≅UT+3), with the secondary peak near the midnight (21:00 02:00 UT). Relative to the VHF echo occurrence, HCPs occur more frequently from 11:00 to 20:00 UT. The diurnal variation of HCP occurrence is similar to that of the 1-h intervals with the lowest mean absorption A<0.25dB.

    The HCPs are observed more frequently during the winter months, which, combined with the fact that VHF echoes observed during HCPs exhibit features typical for field-aligned E-region irregularities, makes their association with the polar mesospheric echoes (for which some positive CNA/SNR correlation has been reported in the past) very unlikely. Instead, we attribute the high positive CNA/SNR correlation to the synchronous, to a first approximation, variation of the particle fluxes for two different but close sets of energies.

    By considering the dependence of the CNA/SNR correlation coefficients for both VHF radars (CA1 and CA2) upon the correlation between SNRs for two radars (C12), we show that both coefficients, CA1 and CA2, and the agreement between them decrease drastically with a C12 decrease, which we interpreted through the progressively increasing role of the spatial inhomogeneity of the processes leading to the enhanced CNA and SNR. In this situation

  9. The wide-angle neutron spin echo spectrometer project WASP

    SciTech Connect

    Ehlers, Georg

    2007-01-01

    This paper describes design and optimization for the wide angle spin-echo spectrometer (WASP) presently being planned at the ILL. The spectrometer will be a replacement for the high intensity spectrometer IN11 and will enhance its signal by more than one order of magnitude while maintaining the resolution of the present spectrometer. The paper outlines the magnetic field calculations and the considerations about possible limitations. The projected performance has been verified carefully by Monte Carlo raytracing and Biot-Savart magnetic field calculations. The maximum momentum transfer of the new spectrometer is to be extended to 4 angstroms {sup -1}.

  10. Echo scintillation Index affected by cat-eye target's caliber with Cassegrain lens

    NASA Astrophysics Data System (ADS)

    Shan, Cong-miao; Sun, Hua-yan; Zhao, Yan-zhong; Zheng, Yong-hui

    2015-10-01

    The optical aperture of cat-eye target has the aperture averaging effect to the active detecting laser of active laser detection system, which can be used to identify optical targets. The echo scintillation characteristics of the transmission-type lens target have been studied in previous work. Discussing the differences of the echo scintillation characteristics between the transmission-type lens target and Cassegrain lens target can be helpful to targets classified. In this paper, the echo scintillation characteristics of Cat-eye target's caliber with Cassegrain lens has been discussed . By using the flashing theory of spherical wave in the weak atmospheric turbulence, the annular aperture filter function and the Kolmogorov power spectrum, the analytic expression of the scintillation index of the cat-eye target echo of the horizontal path two-way transmission was given when the light is normal incidence. Then the impact of turbulence inner and outer scale to the echo scintillation index and the analytic expression of the echo scintillation index at the receiving aperture were presented using the modified Hill spectrum and the modified Von Karman spectrum. Echo scintillation index shows the tendency of decreasing with the target aperture increases and different ratios of the inner and outer aperture diameter show the different echo scintillation index curves. This conclusion has a certain significance for target recognition in the active laser detection system that can largely determine the target type by largely determining the scope of the cat-eye target which depending on echo scintillation index.

  11. Examining the robustness of automated aural classification of active sonar echoes.

    PubMed

    Murphy, Stefan M; Hines, Paul C

    2014-02-01

    Active sonar systems are used to detect underwater man-made objects of interest (targets) that are too quiet to be reliably detected with passive sonar. Performance of active sonar can be degraded by false alarms caused by echoes returned from geological seabed structures (clutter) in shallow regions. To reduce false alarms, a method of distinguishing target echoes from clutter echoes is required. Research has demonstrated that perceptual-based signal features similar to those employed in the human auditory system can be used to automatically discriminate between target and clutter echoes, thereby reducing the number of false alarms and improving sonar performance. An active sonar experiment on the Malta Plateau in the Mediterranean Sea was conducted during the Clutter07 sea trial and repeated during the Clutter09 sea trial. The dataset consists of more than 95,000 pulse-compressed echoes returned from two targets and many geological clutter objects. These echoes were processed using an automatic classifier that quantifies the timbre of each echo using a number of perceptual signal features. Using echoes from 2007, the aural classifier was trained to establish a boundary between targets and clutter in the feature space. Temporal robustness was then investigated by testing the classifier on echoes from the 2009 experiment.

  12. Whole-brain quantitative mapping of metabolites using short echo 3D-proton- MRSI

    PubMed Central

    Lecocq, Angèle; Le Fur, Yann; Maudsley, Andrew A; Le Troter, Arnaud; Sheriff, Sulaiman; Sabati, Mohamad; Donnadieu, Maxime; Confort-Gouny, Sylviane; Cozzone, Patrick J.; Guye, Maxime; Ranjeva, Jean-Philippe

    2014-01-01

    Purpose To improve the extent over which whole brain quantitative 3D-MRSI maps can be obtained and be used to explore brain metabolism in a population of healthy volunteers. Materials and Methods Two short TE (20 ms) acquisitions of 3D Echo Planar Spectroscopic Imaging at two orientations, one in the anterior commissure – posterior commissure (AC-PC) plane and the second tilted in the AC-PC +15° plane were obtained at 3T in a group of ten healthy volunteers. B1+, B1−, and B0 correction procedures and normalization of metabolite signals with quantitative water proton density measurements were performed. A combination of the two spatially normalized 3D-MRSI, using a weighted mean based on the pixel wise standard deviation metabolic maps of each orientation obtained from the whole group, provided metabolite maps for each subject allowing regional metabolic profiles of all parcels of the automated anatomical labeling (AAL) atlas to be obtained. Results The combined metabolite maps derived from the two acquisitions reduced the regional inter-subject variance. The numbers of AAL regions showing NAA SD/Mean ratios lower than 30% increased from 17 in the AC-PC orientation and 41 in the AC-PC+15° orientation, to a value of 76 regions out of 116 for the combined NAA maps. Quantitatively, regional differences in absolute metabolite concentrations (mM) over the whole brain were depicted such as in the GM of frontal lobes (cNAA=10.03+1.71, cCho=1.78±0.55, cCr=7.29±1.69; cmIns=5.30±2.67) and in cerebellum (cNAA=5.28±1.77, cCho=1.60±0.41, cCr=6.95±2.15; cmIns=3.60±0.74). Conclusion A double-angulation acquisition enables improved metabolic characterization over a wide volume of the brain. PMID:25431032

  13. Density Gradients in Chemistry Teaching

    ERIC Educational Resources Information Center

    Miller, P. J.

    1972-01-01

    Outlines experiments in which a density gradient might be used to advantage. A density gradient consists of a column of liquid, the composition and density of which varies along its length. The procedure can be used in analysis of solutions and mixtures and in density measures of solids. (Author/TS)

  14. Empirical equation estimates geothermal gradients

    SciTech Connect

    Kutasov, I.M. )

    1995-01-02

    An empirical equation can estimate geothermal (natural) temperature profiles in new exploration areas. These gradients are useful for cement slurry and mud design and for improving electrical and temperature log interpretation. Downhole circulating temperature logs and surface outlet temperatures are used for predicting the geothermal gradients.

  15. Multilayer High-Gradient Insulators

    SciTech Connect

    Harris, J R

    2006-08-16

    Multilayer High-Gradient Insulators are vacuum insulating structures composed of thin, alternating layers of dielectric and metal. They are currently being developed for application to high-current accelerators and related pulsed power systems. This paper describes some of the High-Gradient Insulator research currently being conducted at Lawrence Livermore National Laboratory.

  16. The research of data acquisition system for Raman spectrometer

    NASA Astrophysics Data System (ADS)

    Cui, Xiao; Guo, Pan; Zhang, Yinchao; Chen, Siying; Chen, He; Chen, Wenbo

    2011-11-01

    Raman spectrometer has been widely used as an identification tool for analyzing material structure and composition in many fields. However, Raman scattering echo signal is very weak, about dozens of photons at most in one laser plus signal. Therefore, it is a great challenge to design a Raman spectrum data acquisition system which could accurately receive the weak echo signal. The system designed in this paper receives optical signals with the principle of photon counter and could detect single photon. The whole system consists of a photoelectric conversion module H7421-40 and a photo counting card including a field programmable gate array (FPGA) chip and a PCI9054 chip. The module H7421-40 including a PMT, an amplifier and a discriminator has high sensitivity on wavelength from 300nm to 720nm. The Center Wavelength is 580nm which is close to the excitation wavelength (532nm), QE 40% at peak wavelength, Count Sensitivity is 7.8*105(S-1PW-1) and Count Linearity is 1.5MHZ. In FPGA chip, the functions are divided into three parts: parameter setting module, controlling module, data collection and storage module. All the commands, parameters and data are transmitted between FPGA and computer by PCI9054 chip through the PCI interface. The result of experiment shows that the Raman spectrum data acquisition system is reasonable and efficient. There are three primary advantages of the data acquisition system: the first one is the high sensitivity with single photon detection capability; the second one is the high integrated level which means all the operation could be done by the photo counting card; and the last one is the high expansion ability because of the smart reconfigurability of FPGA chip.

  17. An energetic stellar outburst accompanied by circumstellar light echoes.

    PubMed

    Bond, Howard E; Henden, Arne; Levay, Zoltan G; Panagia, Nino; Sparks, William B; Starrfield, Sumner; Wagner, R Mark; Corradi, R L M; Munari, U

    2003-03-27

    Some classes of stars, including novae and supernovae, undergo explosive outbursts that eject stellar material into space. In 2002, the previously unknown variable star V838 Monocerotis brightened suddenly by a factor of approximately 10(4). Unlike a supernova or nova, it did not explosively eject its outer layers; rather, it simply expanded to become a cool supergiant with a moderate-velocity stellar wind. Superluminal light echoes were discovered as light from the outburst propagated into the surrounding, pre-existing circumstellar dust. Here we report high-resolution imaging and polarimetry of those light echoes, which allow us to set direct geometric distance limits to the object. At a distance of >6 kpc, V838 Mon at its maximum brightness was temporarily the brightest star in the Milky Way. The presence of the circumstellar dust implies that previous eruptions have occurred, and spectra show it to be a binary system. When combined with the high luminosity and unusual outburst behaviour, these characteristics indicate that V838 Mon represents a hitherto unknown type of stellar outburst, for which we have no completely satisfactory physical explanation. PMID:12660776

  18. Emergence of metapopulations and echo chambers in mobile agents

    PubMed Central

    Starnini, Michele; Frasca, Mattia; Baronchelli, Andrea

    2016-01-01

    Multi-agent models often describe populations segregated either in the physical space, i.e. subdivided in metapopulations, or in the ecology of opinions, i.e. partitioned in echo chambers. Here we show how both kinds of segregation can emerge from the interplay between homophily and social influence in a simple model of mobile agents endowed with a continuous opinion variable. In the model, physical proximity determines a progressive convergence of opinions but differing opinions result in agents moving away from each others. This feedback between mobility and social dynamics determines the onset of a stable dynamical metapopulation scenario where physically separated groups of like-minded individuals interact with each other through the exchange of agents. The further introduction of confirmation bias in social interactions, defined as the tendency of an individual to favor opinions that match his own, leads to the emergence of echo chambers where different opinions coexist also within the same group. We believe that the model may be of interest to researchers investigating the origin of segregation in the offline and online world. PMID:27572928

  19. Emergence of metapopulations and echo chambers in mobile agents.

    PubMed

    Starnini, Michele; Frasca, Mattia; Baronchelli, Andrea

    2016-01-01

    Multi-agent models often describe populations segregated either in the physical space, i.e. subdivided in metapopulations, or in the ecology of opinions, i.e. partitioned in echo chambers. Here we show how both kinds of segregation can emerge from the interplay between homophily and social influence in a simple model of mobile agents endowed with a continuous opinion variable. In the model, physical proximity determines a progressive convergence of opinions but differing opinions result in agents moving away from each others. This feedback between mobility and social dynamics determines the onset of a stable dynamical metapopulation scenario where physically separated groups of like-minded individuals interact with each other through the exchange of agents. The further introduction of confirmation bias in social interactions, defined as the tendency of an individual to favor opinions that match his own, leads to the emergence of echo chambers where different opinions coexist also within the same group. We believe that the model may be of interest to researchers investigating the origin of segregation in the offline and online world. PMID:27572928

  20. Quantum and classical correlations in electron-nuclear spin echo

    SciTech Connect

    Zobov, V. E.

    2014-11-15

    The quantum properties of dynamic correlations in a system of an electron spin surrounded by nuclear spins under the conditions of free induction decay and electron spin echo have been studied. Analytical results for the time evolution of mutual information, classical part of correlations, and quantum part characterized by quantum discord have been obtained within the central-spin model in the high-temperature approximation. The same formulas describe discord in both free induction decay and spin echo although the time and magnetic field dependences are different because of difference in the parameters entering into the formulas. Changes in discord in the presence of the nuclear polarization β{sub I} in addition to the electron polarization β{sub S} have been calculated. It has been shown that the method of reduction of the density matrix to a two-spin electron-nuclear system provides a qualitatively correct description of pair correlations playing the main role at β{sub S} ≈ β{sub I} and small times. At large times, such correlations decay and multispin correlations ensuring nonzero mutual information and zero quantum discord become dominant.

  1. Echo-Enabled Harmonic Generation for Seeded FELs

    SciTech Connect

    Stupakov, G.; /SLAC

    2011-05-19

    In the x-ray wavelengths, the two leading FEL concepts are the self-amplified spontaneous emission (SASE) configuration and the high-gain harmonic generation (HGHG) scheme. While the radiation from a SASE FEL is coherent transversely, it typically has rather limited temporal coherence. Alternatively, the HGHG scheme allows generation of fully coherent radiation by up-converting the frequency of a high-power seed laser. However, due to the relatively low up-frequency conversion efficiency, multiple stages of HGHG FEL are needed in order to generate x-rays from a UV laser. The up-frequency conversion efficiency can be greatly improved with the recently proposed echo-enabled harmonic generation (EEHG) technique. In this work we will present the concept of EEHG, and address some practically important issues that affect the performance of the seeding. We show how the EEHG can be incorporated in the FEL scheme and what is the expected performance of the EEHG seeded FEL. We will then briefly describe the first proof-of-principle EEHG experiment carried out at the Next Linear Collider Test Accelerator (NLCTA) at SLAC. We will also discuss latest advances in the echo-scheme approach, and refer to subsequent modifications of the original concept.

  2. Volumetric Echocardiographic Particle Image Velocimetry (V-Echo-PIV)

    NASA Astrophysics Data System (ADS)

    Falahatpisheh, Ahmad; Kheradvar, Arash

    2015-11-01

    Measurement of 3D flow field inside the cardiac chambers has proven to be a challenging task. Current laser-based 3D PIV methods estimate the third component of the velocity rather than directly measuring it and also cannot be used to image the opaque heart chambers. Modern echocardiography systems are equipped with 3D probes that enable imaging the entire 3D opaque field. However, this feature has not yet been employed for 3D vector characterization of blood flow. For the first time, we introduce a method that generates velocity vector field in 4D based on volumetric echocardiographic images. By assuming the conservation of brightness in 3D, blood speckles are tracked. A hierarchical 3D PIV method is used to account for large particle displacement. The discretized brightness transport equation is solved in a least square sense in interrogation windows of size 163 voxels. We successfully validate the method in analytical and experimental cases. Volumetric echo data of a left ventricle is then processed in the systolic phase. The expected velocity fields were successfully predicted by V-Echo-PIV. In this work, we showed a method to image blood flow in 3D based on volumetric images of human heart using no contrast agent.

  3. Plasma Density and Radio Echoes in the Magnetosphere

    NASA Technical Reports Server (NTRS)

    Calvert, W.

    1995-01-01

    This project provided a opportunity to study a variety of interesting topics related to radio sounding in the magnetosphere. The results of this study are reported in two papers which have been submitted for publication in the Journal of Geophysical Research and Radio Science, and various aspects of this study were also reported at meetings of the American Geophysical Union (AGU) at Baltimore, Maryland and the International Scientific Radio Union (URSI) at Boulder, Colorado. The major results of this study were also summarized during a one-day symposium on this topic sponsored by Marshall Space Flight Center in December 1994. The purpose of the study was to examine the density structure of the plasmasphere and determine the relevant mechanisms for producing radio echoes which can be detected by a radio sounder in the magnetosphere. Under this study we have examined density irregularities, biteouts, and outliers of the plasmasphere, studied focusing, specular reflection, ducting, and scattering by the density structures expected to occur in the magnetosphere, and predicted the echoes which can be detected by a magnetospheric radio sounder.

  4. EChO fine guidance sensor design and architecture

    NASA Astrophysics Data System (ADS)

    Ottensamer, Roland; Rataj, Miroslaw; Schrader, Jan-Rutger; Ferstl, Roman; Güdel, Manuel; Kerschbaum, Franz; Luntzer, Armin

    2014-08-01

    EChO, the Exoplanet Characterization Observatory, is an M-class candidate in the ESA Comic Vision programme. It will provide high resolution, multi-wavelength spectroscopic observations of exoplanets, measure their atmospheric composition, temperature and albedo. The scientific payload is a spectrometer covering the 0.4-11 micron waveband. High photometric stability over a time scale of about 10 hours is one of the most stringent requirements of the EChO mission. As a result, fine pointing stability relative to the host star is mandatory. This will be achieved through a Fine Guidance Sensor (FGS), a separate photometric channel that uses a fraction of the target star signal from the optical channel. The main task of the FGS is to ensure the centering, focusing and guiding of the satellite, but it will also provide supplemental high-precision astrometry and photometry of the target to ground for de-trending the spectra and complementary science. In this paper we give an overview of the current architectural design of the FGS subsystem and discuss related requirements as well as the expected performance.

  5. An energetic stellar outburst accompanied by circumstellar light echoes.

    PubMed

    Bond, Howard E; Henden, Arne; Levay, Zoltan G; Panagia, Nino; Sparks, William B; Starrfield, Sumner; Wagner, R Mark; Corradi, R L M; Munari, U

    2003-03-27

    Some classes of stars, including novae and supernovae, undergo explosive outbursts that eject stellar material into space. In 2002, the previously unknown variable star V838 Monocerotis brightened suddenly by a factor of approximately 10(4). Unlike a supernova or nova, it did not explosively eject its outer layers; rather, it simply expanded to become a cool supergiant with a moderate-velocity stellar wind. Superluminal light echoes were discovered as light from the outburst propagated into the surrounding, pre-existing circumstellar dust. Here we report high-resolution imaging and polarimetry of those light echoes, which allow us to set direct geometric distance limits to the object. At a distance of >6 kpc, V838 Mon at its maximum brightness was temporarily the brightest star in the Milky Way. The presence of the circumstellar dust implies that previous eruptions have occurred, and spectra show it to be a binary system. When combined with the high luminosity and unusual outburst behaviour, these characteristics indicate that V838 Mon represents a hitherto unknown type of stellar outburst, for which we have no completely satisfactory physical explanation.

  6. Echoes of Historical Supernovae in the Milky Way Galaxy

    NASA Astrophysics Data System (ADS)

    Rest, Armin; Badenes, Carles; Blondin, Stephane; Challis, Peter; Clocchiatti, Alejandro; Filippenko, Alex; Foley, Ryan; Huber, Mark E.; Matheson, Thomas; Mazzali, Paolo; Olsen, Knut; Sauer, Daniel; Sinnott, Brendan; Smith, R. Chris; Suntzeff, Nicholas; Welch, Doug; Bergmann, Marcel

    2010-08-01

    We propose to discover the first light echoes (LEs) associated with the historical Galactic supernovae SN 1181 (3C 58) and SN 1054 (Crab), and to locate additional LE complexes from SN 1680 (Cas A) and SN 1572 (Tycho). Using other facilities, we will obtain spectra of the LEs to determine the nature and properties of these important events. This is a continuation of a previously approved NOAO program to obtain images of regions of significant dust concentration near these Galactic supernova remnants. With data from previous semesters, we found LEs from the Cas A and Tycho supernovae teRest08b. We then used the rich set of LEs from Cas A to examine the Cas A SN from different viewing angles teRest10_casaspec, Rest10_leprofile, finding that in one direction the He I (lambda) 5876 and H(alpha) features are blue-shifted by an additional about 4000 km/s relative to the other directions teRest10_casaspec, which is direct evidence that the SN was asymmetric. The study of scattered-light echoes from Galactic supernovae provides a host of newly-recognized observational benefits which have only just begun to be exploited including (1) a direct comparison of a supernova and its remnant, (2) a three-dimensional view of a supernova, and (3) a Galactic network of absolute distance differences.

  7. Echo Park controversy and the American conservation movement

    SciTech Connect

    Harvey, M.W.T.

    1986-01-01

    During the twentieth century, a few conservation battles have pitted in as classic a fashion the foes of preservation and development as that waged during the 1950s over Dinosaur National Monument. The issue was whether to build the proposed Echo Park Dam within Dinosaur National Monument. The Monument spans the Utah-Colorado border, and comprises the confluence of the Green and Yampa Rivers. Echo Park, a lovely, peaceful meadow flanked by massive sandstone walls at the rivers' confluence, became the storm-center of controversy when the Bureau of Reclamation made plans to dam the Green River just two miles to the south. The dam would have flooded a hundred miles of this canyon country, and the proposal startled the nation's major conservation organizations and occupied their attention for several years. Their effort to prevent the dam ultimately succeeded, and their story is critical in tracing the roots of contemporary conservation. In the end, pressure from conservation groups helped to delete the dam from the legislation, and Dinosaur's river canyons were preserved.

  8. Emergence of metapopulations and echo chambers in mobile agents

    NASA Astrophysics Data System (ADS)

    Starnini, Michele; Frasca, Mattia; Baronchelli, Andrea

    2016-08-01

    Multi-agent models often describe populations segregated either in the physical space, i.e. subdivided in metapopulations, or in the ecology of opinions, i.e. partitioned in echo chambers. Here we show how both kinds of segregation can emerge from the interplay between homophily and social influence in a simple model of mobile agents endowed with a continuous opinion variable. In the model, physical proximity determines a progressive convergence of opinions but differing opinions result in agents moving away from each others. This feedback between mobility and social dynamics determines the onset of a stable dynamical metapopulation scenario where physically separated groups of like-minded individuals interact with each other through the exchange of agents. The further introduction of confirmation bias in social interactions, defined as the tendency of an individual to favor opinions that match his own, leads to the emergence of echo chambers where different opinions coexist also within the same group. We believe that the model may be of interest to researchers investigating the origin of segregation in the offline and online world.

  9. Meteoroid mass determination using head echoes detected at multiple frequencies

    NASA Astrophysics Data System (ADS)

    Close, Sigrid; Oppenheim, Meers; Hunt, Stephen; McKeen, Fred; Coster, Anthea

    2002-11-01

    Meteor data collected at the Kwajalein Missile Range (KMR) during the peak of the 1998 Leonid storm comprise the only simultaneous data collection of meteor head echoes and trails using seven frequencies (VHF, UHF, L-, S-, C-, Ka- and W-band). The primary sensor was the ALTAIR radar operating at 160 MHz with 30-m range resolution and 422 MHz with 7.5-m range resolution, which has both interferometric and polarization capabilities. This paper presents an alaysis of these high-resolution data in support of the following ideas: First, head echo scattering appears to arise from an ionized region with a density sufficiently high that its plasma frequency exceeds the radar frequency (overdense reflection). Second, the Radar-cross-section (RCS) values, which decrease with decreasing wavelength, peak near 105 km altitude at the point where the meteoroid gives up the most kinetic energy during its descent. Third, these RCS measurements were used to compute electron line densities, which provide estimates of a meteoroid's mass. By combining these data and simple ablation models, we can constrain meteoroid mass as it loses material during its passage through the atmosphere.

  10. Sum-frequency generation echo and grating from interface

    SciTech Connect

    Volkov, Victor

    2014-10-14

    The work addresses spectroscopy of fourth-order Sum Frequency Generation Echo and Grating responses as an experimental tool to study structure and dynamics at interfaces. First, it addresses experimental geometry to extract background-free fourth-order Echo and Grating responses. Further, the article provides the analytical expressions of the response functions for these nonlinearities. The derived expressions are used to model the χ{sup (4)} two-dimensional spectral responses of a hydrated methyl acetate, which resembles a hydrated carbonyl moiety at the polar outer side of a phospholipid membrane. Orientation, transition dipole moments, and Raman tensors are obtained from the results of classical and quantum calculations, respectively. The numerical studies for the nonlinear responses under different polarization schemes and timings suggest the possibility of securely factoring of spectral contributions of χ{sub YYYZX} and χ{sub YYYZY} macroscopic susceptibilities. As such, the nonlinearities provide an experimental perspective on orientation of a generic (low-symmetry) molecular system at interfaces. Besides, the spectral properties of the tensors may reflect correlations of the in-plane and out-of-plane field components specific to the interface. For the case of a phospholipid membrane, the experiment would address in-plane and out-of-plane anisotropy of hydrogen bonding and related dynamics.

  11. Gradient elution in capillary electrochromatography

    SciTech Connect

    Anex, D.; Rakestraw, D.J.; Yan, Chao; Dadoo, R.; Zare, R.N.

    1997-08-01

    In analogy to pressure-driven gradient techniques in high-performance liquid chromatography, a system has been developed for delivering electroosmotically-driven solvent gradients for capillary electrochromatography (CEC). Dynamic gradients with sub-mL/min flow rates are generated by merging two electroosmotic flows that are regulated by computer-controlled voltages. These flows are delivered by two fused-silica capillary arms attached to a T-connector, where they mix and then flow into a capillary column that has been electrokinetically packed with 3-mm reversed-phase particles. The inlet of one capillary arm is placed in a solution reservoir containing one mobile phase and the inlet of the other is placed in a second reservoir containing a second mobile phase. Two independent computer-controlled programmable high-voltage power supplies (0-50 kV)--one providing an increasing ramp and the other providing a decreasing ramp--are used to apply variable high-voltage potentials to the mobile phase reservoirs to regulate the electroosmotic flow in each arm. The ratio of the electroosmotic flow rates between the two arms is changed with time according to the computer-controlled voltages to deliver the required gradient profile to the separation column. Experiments were performed to confirm the composition of the mobile phase during a gradient run and to determine the change of the composition in response to the programmed voltage profile. To demonstrate the performance of electroosmotically-driven gradient elution in CEC, a mixture of 16 polycyclic aromatic hydrocarbons (PAHs) was separated in less than 90 minutes. This gradient technique is expected to be well-suited for generating not only solvent gradients in CEC, but also other types of gradients such as pH- and ionic-strength gradients in capillary electrokinetic separations and analyses.

  12. An ultrasound tomography system with polyvinyl alcohol (PVA) moldings for coupling: in vivo results for 3-D pulse-echo imaging of the female breast.

    PubMed

    Koch, Andreas; Stiller, Florian; Lerch, Reinhard; Ermert, Helmut

    2015-02-01

    Full-angle spatial compounding (FASC) is a concept for pulse-echo imaging using an ultrasound tomography (UST) system. With FASC, resolution is increased and speckles are suppressed by averaging pulse-echo data from 360°. In vivo investigations have already shown a great potential for 2-D FASC in the female breast as well as for finger-joint imaging. However, providing a small number of images of parallel cross-sectional planes with enhanced image quality is not sufficient for diagnosis. Therefore, volume data (3-D) is needed. For this purpose, we further developed our UST add-on system to automatically rotate a motorized array (3-D probe) around the object of investigation. Full integration of external motor and ultrasound electronics control in a custom-made program allows acquisition of 3-D pulse-echo RF datasets within 10 min. In case of breast cancer imaging, this concept also enables imaging of near-thorax tissue regions which cannot be achieved by 2-D FASC. Furthermore, moldings made of polyvinyl alcohol hydrogel (PVA-H) have been developed as a new acoustic coupling concept. It has a great potential to replace the water bath technique in UST, which is a critical concept with respect to clinical investigations. In this contribution, we present in vivo results for 3-D FASC applied to imaging a female breast which has been placed in a PVA-H molding during data acquisition. An algorithm is described to compensate time-of-flight and consider refraction at the water-PVA-H molding and molding-tissue interfaces. Therefore, the mean speed of sound (SOS) for the breast tissue is estimated with an image-based method. Our results show that the PVA-H molding concept is applicable and feasible and delivers good results. 3-D FASC is superior to 2-D FASC and provides 3-D volume data at increased image quality.

  13. Gradient zone boundary control in salt gradient solar ponds

    DOEpatents

    Hull, John R.

    1984-01-01

    A method and apparatus for suppressing zone boundary migration in a salt gradient solar pond includes extending perforated membranes across the pond at the boundaries, between the convective and non-convective zones, the perforations being small enough in size to prevent individual turbulence disturbances from penetrating the hole, but being large enough to allow easy molecular diffusion of salt thereby preventing the formation of convective zones in the gradient layer. The total area of the perforations is a sizable fraction of the membrane area to allow sufficient salt diffusion while preventing turbulent entrainment into the gradient zone.

  14. Multi-site study of diffusion metric variability: characterizing the effects of site, vendor, field strength, and echo time using the histogram distance

    NASA Astrophysics Data System (ADS)

    Helmer, K. G.; Chou, M.-C.; Preciado, R. I.; Gimi, B.; Rollins, N. K.; Song, A.; Turner, J.; Mori, S.

    2016-03-01

    MRI-based multi-site trials now routinely include some form of diffusion-weighted imaging (DWI) in their protocol. These studies can include data originating from scanners built by different vendors, each with their own set of unique protocol restrictions, including restrictions on the number of available gradient directions, whether an externally generated list of gradient directions can be used, and restrictions on the echo time (TE). One challenge of multi-site studies is to create a common imaging protocol that will result in a reliable and accurate set of diffusion metrics. The present study describes the effect of site, scanner vendor, field strength, and TE on two common metrics: the first moment of the diffusion tensor field (mean diffusivity, MD), and the fractional anisotropy (FA). We have shown in earlier work that ROI metrics and the mean of MD and FA histograms are not sufficiently sensitive for use in site characterization. Here we use the distance between whole brain histograms of FA and MD to investigate within- and between-site effects. We concluded that the variability of DTI metrics due to site, vendor, field strength, and echo time could influence the results in multi-center trials and that histogram distance is sensitive metrics for each of these variables.

  15. The elimination of a class of pseudo echoes by an improved T/R switch technique

    NASA Technical Reports Server (NTRS)

    Green, J. L.; Ecklund, W. L.

    1986-01-01

    An annoying class of pseudo echoes are described that evidently occur occasionally in a number of ST (stratosphere troposphere) radars. The origin of these signals are located in the output circuitry of the radar transmitter. Two methods for the elimination of the radar echoes are suggested and briefly desscrib.

  16. Time-domain Fresnel-to-Fraunhofer diffraction with photon echoes.

    PubMed

    Ménager, L; Lorgeré, I; Gouët, J L; Mohan, R K; Kröll, S

    1999-07-15

    A photon echo experiment in Tm(3+):YAG is reported that shows, for the first time to the authors' knowledge, the time-domain equivalent of the transition from near- to far-field diffraction, including Talbot self-imaging effects. The experiment demonstrates the huge dispersion capability of photon echoes and opens the way to further exploration of space-time duality.

  17. Echo-level compensation and delay tuning in the auditory cortex of the mustached bat.

    PubMed

    Macías, Silvio; Mora, Emanuel C; Hechavarría, Julio C; Kössl, Manfred

    2016-06-01

    During echolocation, bats continuously perform audio-motor adjustments to optimize detection efficiency. It has been demonstrated that bats adjust the amplitude of their biosonar vocalizations (known as 'pulses') to stabilize the amplitude of the returning echo. Here, we investigated this echo-level compensation behaviour by swinging mustached bats on a pendulum towards a reflective surface. In such a situation, the bats lower the amplitude of their emitted pulses to maintain the amplitude of incoming echoes at a constant level as they approach a target. We report that cortical auditory neurons that encode target distance have receptive fields that are optimized for dealing with echo-level compensation. In most cortical delay-tuned neurons, the echo amplitude eliciting the maximum response matches the echo amplitudes measured from the bats' biosonar vocalizations while they are swung in a pendulum. In addition, neurons tuned to short target distances are maximally responsive to low pulse amplitudes while neurons tuned to long target distances respond maximally to high pulse amplitudes. Our results suggest that bats dynamically adjust biosonar pulse amplitude to match the encoding of target range and to keep the amplitude of the returning echo within the bounds of the cortical map of echo delays. PMID:27037932

  18. Analysis of tissue changes, measurement system effects, and motion artifacts in echo decorrelation imaging.

    PubMed

    Hooi, Fong Ming; Nagle, Anna; Subramanian, Swetha; Douglas Mast, T

    2015-02-01

    Echo decorrelation imaging, a method for mapping ablation-induced ultrasound echo changes, is analyzed. Local echo decorrelation is shown to approximate the decoherence spectrum of tissue reflectivity. Effects of the ultrasound measurement system, echo signal windowing, electronic noise, and tissue motion on echo decorrelation images are determined theoretically, leading to a method for reduction of motion and noise artifacts. Theoretical analysis is validated by simulations and experiments. Simulated decoherence of the scattering medium was recovered with root-mean-square error less than 10% with accuracy dependent on the correlation window size. Motion-induced decorrelation measured in an ex vivo pubovisceral muscle model showed similar trends to theoretical motion-induced decorrelation for a 2.1 MHz curvilinear array with decorrelation approaching unity for 3-4 mm elevational displacement or 1-1.6 mm range displacement. For in vivo imaging of porcine liver by a 7 MHz linear array, theoretical decorrelation computed using image-based motion estimates correlated significantly with measured decorrelation (r = 0.931, N = 10). Echo decorrelation artifacts incurred during in vivo radiofrequency ablation in the same porcine liver were effectively compensated based on the theoretical echo decorrelation model and measured pre-treatment decorrelation. These results demonstrate the potential of echo decorrelation imaging for quantification of heat-induced changes to the scattering tissue medium during thermal ablation.

  19. Echo strength and density structure of Hawaiian mesopelagic boundary community patches.

    PubMed

    Benoit-Bird, Kelly J; Au, Whitlow W L

    2003-10-01

    A broadband sonar system and digital camera with strobe lights were mounted on a vertically profiling frame with a depth sensor. The echo strengths and densities of animals within individual mesopelagic boundary community patches were investigated as a function of depth. Time and distance from shore were also investigated. Simultaneous surface echosounder surveys permitted comparison of density estimates from two techniques. Echo strength values suggest nearshore boundary community animals are primarily myctophid fishes, which was confirmed by preliminary photographic evidence. Echo strength varied significantly as a function of distance from the shoreline and time. These measures of echo strength are important for estimating density from a surface echosounder. Density estimates from these revised echo strengths compare well with those made with echo highlight counting, which is independent of echo strength. These density measures suggest that previous density estimates were too low but do not change the conclusions of these studies. Vertical microstructure in density was apparent but animal size and compositional structure was not evident within a patch. Patch edges were abrupt, with no differences in the density or echo strength from patch interiors. These edges were generally straight, with a sharp drop in density to the background density of zero. Estimates of animal size as a function of time provide information about the diel migration patterns of these mesopelagic animals.

  20. Analysis of tissue changes, measurement system effects, and motion artifacts in echo decorrelation imaging

    PubMed Central

    Hooi, Fong Ming; Nagle, Anna; Subramanian, Swetha; Douglas Mast, T.

    2015-01-01

    Echo decorrelation imaging, a method for mapping ablation-induced ultrasound echo changes, is analyzed. Local echo decorrelation is shown to approximate the decoherence spectrum of tissue reflectivity. Effects of the ultrasound measurement system, echo signal windowing, electronic noise, and tissue motion on echo decorrelation images are determined theoretically, leading to a method for reduction of motion and noise artifacts. Theoretical analysis is validated by simulations and experiments. Simulated decoherence of the scattering medium was recovered with root-mean-square error less than 10% with accuracy dependent on the correlation window size. Motion-induced decorrelation measured in an ex vivo pubovisceral muscle model showed similar trends to theoretical motion-induced decorrelation for a 2.1 MHz curvilinear array with decorrelation approaching unity for 3–4 mm elevational displacement or 1–1.6 mm range displacement. For in vivo imaging of porcine liver by a 7 MHz linear array, theoretical decorrelation computed using image-based motion estimates correlated significantly with measured decorrelation (r = 0.931, N = 10). Echo decorrelation artifacts incurred during in vivo radiofrequency ablation in the same porcine liver were effectively compensated based on the theoretical echo decorrelation model and measured pre-treatment decorrelation. These results demonstrate the potential of echo decorrelation imaging for quantification of heat-induced changes to the scattering tissue medium during thermal ablation. PMID:25697993