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1

20 MHz/40 MHz Dual Element Transducers for High Frequency Harmonic Imaging  

PubMed Central

Concentric annular type dual element transducers for second harmonic imaging at 20 MHz / 40 MHz were designed and fabricated to improve spatial resolution and depth of penetration for ophthalmic imaging applications. The outer ring element was designed to transmit the 20 MHz signal and the inner circular element was designed to receive the 40 MHz second harmonic signal. Lithium niobate (LiNbO3), with its low dielectric constant, was used as the piezoelectric material to achieve good electrical impedance matching. Double matching layers and conductive backing were used and optimized by KLM modeling to achieve high sensitivity and wide bandwidth for harmonic imaging and superior time-domain characteristics. Prototype transducers were fabricated and evaluated quantitatively and clinically. The average measured center frequency for the transmit ring element was 21 MHz and the one-way –3 dB bandwidth was greater than 50%. The 40 MHz receive element functioned at 31 MHz center frequency with acceptable bandwidth to receive attenuated and frequency downshifted harmonic signal. The lateral beam profile for the 20 MHz ring elements at the focus matched the Field II simulated results well, and the effect of outer ring diameter was also examined. Images of a posterior segment of an excised pig eye and a choroidal nevus of human eye were obtained both for single element and dual element transducers and compared to demonstrate the advantages of dual element harmonic imaging. PMID:19126492

Kim, Hyung Ham; Cannata, Jonathan M.; Liu, Ruibin; Chang, Jin Ho; Silverman, Ronald H.; Shung, K. Kirk

2009-01-01

2

A parallel adaptive finite element simplified spherical harmonics approximation solver for frequency domain fluorescence molecular imaging  

PubMed Central

Fluorescence molecular imaging/tomography may play an important future role in preclinical research and clinical diagnostics. Time- and frequency-domain fluorescence imaging can acquire more measurement information than the continuous wave (CW) counterpart, improving the image quality of fluorescence molecular tomography. Although diffusion approximation (DA) theory has been extensively applied in optical molecular imaging, high-order photon migration models need to be further investigated to match quantitation provided by nuclear imaging. In this paper, a frequency-domain parallel adaptive finite element solver is developed with simplified spherical harmonics (SPN) approximations. To fully evaluate the performance of the SPN approximations, a fast time-resolved tetrahedron-based Monte Carlo fluorescence simulator suitable for complex heterogeneous geometries is developed using a convolution strategy to realize the simulation of the fluorescence excitation and emission. The validation results show that high-order SPN can effectively correct the modeling errors of the diffusion equation, especially when the tissues have high absorption characteristics or when high modulation frequency measurements are used. Furthermore, the parallel adaptive mesh evolution strategy improves the modeling precision and the simulation speed significantly on a realistic digital mouse phantom. This solver is a promising platform for fluorescence molecular tomography using high-order approximations to the radiative transfer equation. PMID:20671350

Lu, Yujie; Zhu, Banghe; Shen, Haiou; Rasmussen, John C; Wang, Ge; Sevick-Muraca, Eva M

2010-01-01

3

Second Harmonic and Sum Frequency Generation Imaging of Fibrous Astroglial Filaments in Ex Vivo Spinal Tissues  

PubMed Central

Sum frequency generation (SFG) and second harmonic generation (SHG) were observed from helical fibrils in spinal cord white matter isolated from guinea pigs. By combining SFG with coherent anti-Stokes Raman scattering microscopy, which allows visualization of myelinated axons, these fibers were found to be distributed near the surface of the spinal cord, between adjacent axons, and along the blood vessels. Using 20-?m-thick tissue slices, the ratio of forward to backward SHG signal from large bundles was found to be much larger than that from small single fibrils, indicating a phase-matching effect in coherent microscopy. Based on the intensity profiles across fibrils and the size dependence of forward and backward signal from the same fibril, we concluded that the main SHG signal directly originates from the fibrils, but not from surface SHG effects. Further polarization analysis of the SHG signal showed that the symmetry property of the fibril could be well described with a cylindrical model. Colocalization of the SHG signal with two-photon excitation fluorescence (TPEF) from the immunostaining of glial fibrillary acidic protein demonstrated that SHG arises from astroglial filaments. This assignment was further supported by colocalization of the SHG contrast with TPEF signals from astrocyte processes labeled by a Ca2+ indicator and sulforhodamine 101. This work shows that a combination of three nonlinear optical imaging techniques—coherent anti-Stokes Raman scattering, TPEF, and SHG (SFG) microscopy—allows simultaneous visualization of different structures in a complex biological system. PMID:17293404

Fu, Yan; Wang, Haifeng; Shi, Riyi; Cheng, Ji-Xin

2007-01-01

4

Second harmonic inversion for ultrasound contrast harmonic imaging  

NASA Astrophysics Data System (ADS)

Ultrasound contrast agents (UCAs) are small micro-bubbles that behave nonlinearly when exposed to an ultrasound wave. This nonlinear behavior can be observed through the generated higher harmonics in a back-scattered echo. In past years several techniques have been proposed to detect or image harmonics produced by UCAs. In these proposed works, the harmonics generated in the medium during the propagation of the ultrasound wave played an important role, since these harmonics compete with the harmonics generated by the micro-bubbles. We present a method for the reduction of the second harmonic generated during nonlinear-propagation-dubbed second harmonic inversion (SHI). A general expression for the suppression signals is also derived. The SHI technique uses two pulses, p' and p'', of the same frequency f0 and the same amplitude P0 to cancel out the second harmonic generated by nonlinearities of the medium. Simulations show that the second harmonic is reduced by 40 dB on a large axial range. Experimental SHI B-mode images, from a tissue-mimicking phantom and UCAs, show an improvement in the agent-to-tissue ratio (ATR) of 20 dB compared to standard second harmonic imaging and 13 dB of improvement in harmonic power Doppler.

Pasovic, Mirza; Danilouchkine, Mike; Faez, Telli; van Neer, Paul L. M. J.; Cachard, Christian; van der Steen, Antonius F. W.; Basset, Olivier; de Jong, Nico

2011-06-01

5

Cover image High-harmonic generation could be  

E-print Network

Cover image High-harmonic generation could be the basis of frequency combs for vacuum­ultraviolet. Bonn 815 vacuum-ultraviolet frequency combs from below-threshold harmonics Dylan C. Yost, Thomas R-ray astronomy in the laboratory with a miniature compact object produced by laser-driven implosion Shinsuke

Loss, Daniel

6

Harmonic image reconstruction assisted by a nonlinear metmaterial surface.  

PubMed

We experimentally demonstrate a microwave far-field image reconstruction modality with the transverse resolution exceeding the diffraction limit by using a single layer of highly nonlinear metamaterial. The harmonic fields of the nonlinear metamaterial surface allow the far-field propagation of wave fronts with spatial frequencies several times higher than that of the fundamental field. Near-field images can thus be mathematically recovered from the far-field patterns of the harmonic fields. PMID:21405360

Wang, Zhiyu; Luo, Yu; Jiang, Tao; Wang, Zheng; Huangfu, Jiangtao; Ran, Lixin

2011-01-28

7

Reduced Switching-Frequency Active Harmonic Elimination for Multilevel Converters  

Microsoft Academic Search

This paper presents a reduced switching-frequency active-harmonic-elimination method (RAHEM) to eliminate any number of specific order harmonics of multilevel converters. First, resultant theory is applied to transcendental equations to eliminate low-order harmonics and to determine switching angles for a fundamental frequency-switching scheme. Next, based on the number of harmonics to be eliminated, Newton climbing method is applied to transcendental equations

Zhong Du; Leon M. Tolbert; John N. Chiasson; Burak Ozpineci

2008-01-01

8

Reduced Switching Frequency Active Harmonic Elimination for Multilevel Converters  

SciTech Connect

This paper presents a reduced switching-frequency active-harmonic-elimination method (RAHEM) to eliminate any number of specific order harmonics of multilevel converters. First, resultant theory is applied to transcendental equations to eliminate low-order harmonics and to determine switching angles for a fundamental frequency-switching scheme. Next, based on the number of harmonics to be eliminated, Newton climbing method is applied to transcendental equations to eliminate high-order harmonics and to determine switching angles for the fundamental frequency-switching scheme. Third, the magnitudes and phases of the residual lower order harmonics are computed, generated, and subtracted from the original voltage waveform to eliminate these low-order harmonics. Compared to the active-harmonic-elimination method (AHEM), which generates square waves to cancel high-order harmonics, RAHEM has lower switching frequency. The simulation results show that the method can effectively eliminate all the specific harmonics, and a low total harmonic distortion (THD) near sine wave is produced. An experimental 11-level H-bridge multilevel converter with a field-programmable gate-array controller is employed to experimentally validate the method. The experimental results show that RAHEM does effectively eliminate any number of specific harmonics, and the output voltage waveform has low switching frequency and low THD.

Du, Zhong [ORNL; Tolbert, Leon M [ORNL; Chiasson, John N [ORNL; Ozpineci, Burak [ORNL

2008-01-01

9

Superharmonic imaging with chirp coded excitation: filtering spectrally overlapped harmonics.  

PubMed

Superharmonic imaging improves the spatial resolution by using the higher order harmonics generated in tissue. The superharmonic component is formed by combining the third, fourth, and fifth harmonics, which have low energy content and therefore poor SNR. This study uses coded excitation to increase the excitation energy. The SNR improvement is achieved on the receiver side by performing pulse compression with harmonic matched filters. The use of coded signals also introduces new filtering capabilities that are not possible with pulsed excitation. This is especially important when using wideband signals. For narrowband signals, the spectral boundaries of the harmonics are clearly separated and thus easy to filter; however, the available imaging bandwidth is underused. Wideband excitation is preferable for harmonic imaging applications to preserve axial resolution, but it generates spectrally overlapping harmonics that are not possible to filter in time and frequency domains. After pulse compression, this overlap increases the range side lobes, which appear as imaging artifacts and reduce the Bmode image quality. In this study, the isolation of higher order harmonics was achieved in another domain by using the fan chirp transform (FChT). To show the effect of excitation bandwidth in superharmonic imaging, measurements were performed by using linear frequency modulated chirp excitation with varying bandwidths of 10% to 50%. Superharmonic imaging was performed on a wire phantom using a wideband chirp excitation. Results were presented with and without applying the FChT filtering technique by comparing the spatial resolution and side lobe levels. Wideband excitation signals achieved a better resolution as expected, however range side lobes as high as -23 dB were observed for the superharmonic component of chirp excitation with 50% fractional bandwidth. The proposed filtering technique achieved >50 dB range side lobe suppression and improved the image quality without affecting the axial resolution. PMID:25389159

Harput, Sevan; McLaughlan, James; Cowell, David M J; Freear, Steven

2014-11-01

10

Use of harmonic imaging without echocardiographic contrast to improve two-dimensional image quality  

Microsoft Academic Search

The aim of this study was to determine whether harmonic imaging (HI) improves endocardial visualization during 2-dimensional echocardiography without echocardiographic contrast. HI differs from fundamental imaging (FI) by transmitting ultrasound at one frequency and receiving at twice the transmitted frequency. This technique has been used in conjunction with contrast echocardiography to enhance myocardial contrast visualization. HI and FI were sequentially

KirkT Spencer; James Bednarz; PatrickG Rafter; Claudia Korcarz; RobertoM Lang

1998-01-01

11

Harmonic signal generation and frequency upconversion using selective sideband Brillouin  

E-print Network

of America OCIS codes: 350.4010, 060.2330, 070.1170, 290.5900. Signal generation and frequency upconversion be a promis- ing candidate since it can provide high RF power gain for the generated harmonic signalsHarmonic signal generation and frequency upconversion using selective sideband Brillouin

Choi, Woo-Young

12

Transmit Frequency Adaptation for Contrast to Tissue Ratio Optimization in Second Harmonic  

E-print Network

, optimal control, opti- mization, second harmonic, signal processing, transmitted pulse, ultrasound imaging of amplitude, phase or frequency of the ultrasound wave transmitted such as pulse inver- sion [10], power://www.joece.org/paperInfo.aspx?ID=115 Abstract--Conventional ultrasound contrast imaging systems use sequences of sine waves at a fixed

Boyer, Edmond

13

Frequency-resolved optical grating using third-harmonic generation  

SciTech Connect

We demonstrate the first frequency-resolved optical gating measurement of an laser oscillator without the time ambiguity using third-harmonic generation. The experiment agrees well with the phase-retrieved spectrograms.

Tsang, T. [Brookhaven National Laboratory, Upton, NY (United States); Krumbuegel, M.A.; Delong, K.W. [Sandia National Laboratories, Livermore, CA (United States)] [and others

1995-12-01

14

Dynamic nonlinearity of lung tissue: frequency dependence and harmonic distortion.  

PubMed

Harmonic distortion (HD) is a simple approach to analyze lung tissue nonlinear phenomena. This study aimed to characterize frequency-dependent behavior of HD at several amplitudes in lung tissue strips from healthy rats and its influence on the parameters of linear analysis. Lung strips (n = 17) were subjected to sinusoidal deformation at three different strain amplitudes (??) and fixed operational stress (12 hPa) among various frequencies, between 0.03 and 3 Hz. Input HD was <2% in all cases. The main findings in our study can be summarized as follows: 1) harmonic distortion of stress (HD) showed a positive frequency and amplitude dependence following a power law with frequency; 2) HD correlated significantly with the frequency response of dynamic elastance, seeming to converge to a limited range at an extrapolated point where HD=0; 3) the relationship between tissue damping (G) and HD(?=1) (the harmonic distortion at ?=1 rad/s) was linear and accounted for a large part of the interindividual variability of G; 4) hysteresivity depended linearly on ? (the power law exponent of HD with ?); and 5) the error of the constant phase model could be corrected by taking into account the frequency dependence of harmonic distortion. We concluded that tissue elasticity and tissue damping are coupled at the level of the stress-bearing element and to the mechanisms underlying dynamic nonlinearity of lung tissue. PMID:21565986

Romero, Pablo V; Faffe, Débora S; Cañete, Concepción

2011-08-01

15

Experimental characterization of fundamental and second harmonic beams for a high-frequency ultrasound transducer.  

PubMed

In the diagnostic frequency range, nonlinear imaging has been shown to improve image contrast and decrease artefacts. The extension of these techniques to high-frequency imaging (>15 MHz) was investigated. The second harmonic beam at 40 MHz of a high-frequency focused transducer (aperture 6 mm, focal distance 10 mm, f-number 1.67) was measured experimentally in water, in transmission and pulse-echo, and compared with the fundamental beams at 20 MHz and 40 MHz. Measurements were performed at peak negative pressures of 0.8 to 4.7 MPa. Transmission measurements were performed with a custom hydrophone with a 25microm spot size to limit beam averaging. Over the range of peak negative pressures, the transmitted harmonic (40 MHz) beam had an average lateral beam width (-3 dB) of 77 microm and an average depth-of-field of 0.93 mm, whereas the fundamental beam had a corresponding beam width of 137 microm and a depth-of-field of 1.59 mm. The harmonic beam showed a 3-dB decrease in side lobe levels. Preliminary second harmonic images of mouse tissue in vitro are presented and compared to fundamental imaging at 20 and 40 MHz. PMID:12079700

Cherin, Emmanuel W; Poulsen, Jens Kristian; van der Steen, A F W; Lum, Paul; Foster, F Stuart

2002-05-01

16

High frequency SAW devices based on third harmonic generation.  

PubMed

We demonstrate the third harmonic generation in a ZnO/Si layered structure to obtain high frequency SAW devices. This configuration eliminates the need of high lithography resolution and allows easy integration of such devices and electronics on the same wafer. A theoretical study was carried out for the determination of the phase velocity and the electromechanical coupling coefficient (K(2)) dispersion curves of the surface acoustic waves. These results are also in agreement with those measured on a SAW filter designed for the third harmonic generation and the operating frequency is up to 2468 MHz. PMID:17055019

Le Brizoual, L; Elmazria, O; Sarry, F; El Hakiki, M; Talbi, A; Alnot, P

2006-12-01

17

Contrast and harmonic imaging improves accuracy and efficiency of novice readers for dobutamine stress echocardiography  

NASA Technical Reports Server (NTRS)

BACKGROUND: Newer contrast agents as well as tissue harmonic imaging enhance left ventricular (LV) endocardial border delineation, and therefore, improve LV wall-motion analysis. Interpretation of dobutamine stress echocardiography is observer-dependent and requires experience. This study was performed to evaluate whether these new imaging modalities would improve endocardial visualization and enhance accuracy and efficiency of the inexperienced reader interpreting dobutamine stress echocardiography. METHODS AND RESULTS: Twenty-nine consecutive patients with known or suspected coronary artery disease underwent dobutamine stress echocardiography. Both fundamental (2.5 MHZ) and harmonic (1.7 and 3.5 MHZ) mode images were obtained in four standard views at rest and at peak stress during a standard dobutamine infusion stress protocol. Following the noncontrast images, Optison was administered intravenously in bolus (0.5-3.0 ml), and fundamental and harmonic images were obtained. The dobutamine echocardiography studies were reviewed by one experienced and one inexperienced echocardiographer. LV segments were graded for image quality and function. Time for interpretation also was recorded. Contrast with harmonic imaging improved the diagnostic concordance of the novice reader to the expert reader by 7.1%, 7.5%, and 12.6% (P < 0.001) as compared with harmonic imaging, fundamental imaging, and fundamental imaging with contrast, respectively. For the novice reader, reading time was reduced by 47%, 55%, and 58% (P < 0.005) as compared with the time needed for fundamental, fundamental contrast, and harmonic modes, respectively. With harmonic imaging, the image quality score was 4.6% higher (P < 0.001) than for fundamental imaging. Image quality scores were not significantly different for noncontrast and contrast images. CONCLUSION: Harmonic imaging with contrast significantly improves the accuracy and efficiency of the novice dobutamine stress echocardiography reader. The use of harmonic imaging reduces the frequency of nondiagnostic wall segments.

Vlassak, Irmien; Rubin, David N.; Odabashian, Jill A.; Garcia, Mario J.; King, Lisa M.; Lin, Steve S.; Drinko, Jeanne K.; Morehead, Annitta J.; Prior, David L.; Asher, Craig R.; Klein, Allan L.; Thomas, James D.

2002-01-01

18

Multimode Directional Coupler for Utilization of Harmonic Frequencies from TWTAs  

NASA Technical Reports Server (NTRS)

A novel waveguide multimode directional coupler (MDC) intended for the measurement and potential utilization of the second and higher order harmonic frequencies from high-power traveling wave tube amplifiers (TWTAs) has been successfully designed, fabricated, and tested. The design is based on the characteristic multiple propagation modes of the electrical and magnetic field components of electromagnetic waves in a rectangular waveguide. The purpose was to create a rugged, easily constructed, more efficient waveguide- based MDC for extraction and exploitation of the second harmonic signal from the RF output of high-power TWTs used for space communications. The application would be a satellitebased beacon source needed for Qband and V/W-band atmospheric propagation studies. The MDC could function as a CW narrow-band source or as a wideband source for study of atmospheric group delay effects on highdata- rate links. The MDC is fabricated from two sections of waveguide - a primary one for the fundamental frequency and a secondary waveguide for the second harmonic - that are joined together such that the second harmonic higher order modes are selectively coupled via precision- machined slots for propagation in the secondary waveguide. In the TWTA output waveguide port, both the fundamental and the second harmonic signals are present. These signals propagate in the output waveguide as the dominant and higher order modes, respectively. By including an appropriate mode selective waveguide directional coupler, such as the MDC presented here at the output of the TWTA, the power at the second harmonic can be sampled and amplified to the power level needed for atmospheric propagation studies. The important conclusions from the preliminary test results for the multimode directional coupler are: (1) the second harmonic (Ka-band) can be measured and effectively separated from the fundamental (Ku-band) with no coupling of the latter, (2) power losses in the fundamental frequency are negligible, and (3) the power level of the extracted second harmonic is sufficient for further amplification to power levels needed for practical applications. It was also demonstrated that third order and potentially higher order harmonics are measurable with this device. The design is frequency agnostic, and with the appropriate choice of waveguides, is easily scaled to higher frequency TWTs. The MDC has the same function but with a number of important advantages over the conventional diplexer.

Simmons, Rainee N.; Wintucky, Edwin G.

2013-01-01

19

Harmonic Motion Imaging (HMI) for Tumor Imaging and Treatment Monitoring  

PubMed Central

Palpation is an established screening procedure for the detection of several superficial cancers including breast, thyroid, prostate, and liver tumors through both self and clinical examinations. This is because solid masses typically have distinct stiffnesses compared to the surrounding normal tissue. In this paper, the application of Harmonic Motion Imaging (HMI) for tumor detection based on its stiffness as well as its relevance in thermal treatment is reviewed. HMI uses a focused ultrasound (FUS) beam to generate an oscillatory acoustic radiation force for an internal, non-contact palpation to internally estimate relative tissue hardness. HMI studies have dealt with the measurement of the tissue dynamic motion in response to an oscillatory acoustic force at the same frequency, and have been shown feasible in simulations, phantoms, ex vivo human and bovine tissues as well as animals in vivo. Using an FUS beam, HMI can also be used in an ideal integration setting with thermal ablation using high-intensity focused ultrasound (HIFU), which also leads to an alteration in the tumor stiffness. In this paper, a short review of HMI is provided that encompasses the findings in all the aforementioned areas. The findings presented herein demonstrate that the HMI displacement can accurately depict the underlying tissue stiffness, and the HMI image of the relative stiffness could accurately detect and characterize the tumor or thermal lesion based on its distinct properties. HMI may thus constitute a non-ionizing, cost-efficient and reliable complementary method for noninvasive tumor detection, localization, diagnosis and treatment monitoring. PMID:25364321

Maleke, Caroline; Vappou, Jonathan

2014-01-01

20

Excitation of electron Langmuir frequency harmonics in the solar atmosphere  

SciTech Connect

An alternative mechanism for the excitation of electron Langmuir frequency harmonics as a result of the development of explosive instability in a weakly relativistic beam-plasma system in the solar atmosphere is proposed. The efficiency of the new mechanism as compared to the previously discussed ones is analyzed.

Fomichev, V. V.; Fainshtein, S. M.; Chernov, G. P. [Russian Academy of Sciences, Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation (Russian Federation)

2013-05-15

21

Lens-less surface second harmonic imaging  

PubMed Central

Lens-less surface second harmonic generation imaging (SSHGI) is used to image an SHG active molecule, (S)-( + )-1,1’-bi-2-naphthol (SBN), incorporated into a lipid bilayer patterned with the 1951 United States Air Force resolution test target. Data show the coherent plane-wave nature of SHG allows direct imaging without the aid of a lens system. Lens-less SSHGI readily resolves line-widths as small as 223 ?m at an object-image distance of 7.6 cm and line-widths of 397 ?m at distances as far as 30 cm. Lens-less SSHGI simplifies the detection method, raises photon collection efficiency, and expands the field-of-view. These advantages allow greater throughput and make lens-less SSHGI a potentially valuable detection method for biosensors and medical diagnostics. PMID:23037346

Sly, Krystal L.; Nguyen, Trang T.; Conboy, John C.

2012-01-01

22

Frequency domain interpolation wavelet transform based algorithm for harmonic analysis of power system  

Microsoft Academic Search

A power system harmonic detection technique based on a frequency domain interpolation wavelet transform is proposed. Aiming at harmonic detection, a fast Fourier transform (FFT) can only detect integer harmonics; a short time Fourier transform (STFT) can detect non-integer harmonics with low resolution; a wavelet transform can detect non-integer harmonics, but it has spectral aliasing and spectral leakage phenomena, which

Tianjun Du; Guangju Chen; Yong Lei

2004-01-01

23

Second harmonic generation imaging in muscle fibers  

NASA Astrophysics Data System (ADS)

We have used second harmonic generation (SHG) imaging to quantify a strong intrinsic SHG-signal from cellular and subcellular muscle fibre preparations. In isolated single muscle cells, the intrinsic SHG-signal periodically follows the striation pattern and strongly depends on the sarcomere length and the polarization of the illuminating laser beam. At the subcellular level, the SHG signal seems to be located mainly at the overlapping region of the (thin) actin and (thick) myosin filaments. Thus, SHG imaging resolves the arrangement of the contractile structures with high resolution non-invasively and without chromophores. It may also allow to study dynamic molecular interactions of the motor protein myosin with actin filaments during force production and muscle shortening.

Both, Martin; Vogel, Martin; Fink, Rainer H.; Uttenweiler, Dietmar

2003-10-01

24

Tabletop Lensless Imaging Using Coherent High Harmonic Beams  

Microsoft Academic Search

We present the first demonstration of lensless imaging using coherent high harmonic beams. This coherent imaging technique avoids traditional diffractive optics, and is transparently extendable to shorter wavelengths without aberrations.

R. Sandberg; A. Paul; D. Raymondson; D. Gaudiosi; J. Holtsnider; M. Murnane; H. Kapteyn; Changyong Song; Janwei Miao

2007-01-01

25

Qualitative and quantitative effects of harmonic echocardiographic imaging on endocardial edge definition and side-lobe artifacts  

NASA Technical Reports Server (NTRS)

Harmonic imaging is a new ultrasonographic technique that is designed to improve image quality by exploiting the spontaneous generation of higher frequencies as ultrasound propagates through tissue. We studied 51 difficult-to-image patients with blinded side-by-side cineloop evaluation of endocardial border definition by harmonic versus fundamental imaging. In addition, quantitative intensities from cavity versus wall were compared for harmonic versus fundamental imaging. Harmonic imaging improved left ventricular endocardial border delineation over fundamental imaging (superior: harmonic = 71.1%, fundamental = 18.7%; similar: 10.2%; P <.001). Quantitative analysis of 100 wall/cavity combinations demonstrated brighter wall segments and more strikingly darker cavities during harmonic imaging (cavity intensity on a 0 to 255 scale: fundamental = 15.6 +/- 8.6; harmonic = 6.0 +/- 5.3; P <.0001), which led to enhanced contrast between the wall and cavity (1.89 versus 1.19, P <.0001). Harmonic imaging reduces side-lobe artifacts, resulting in a darker cavity and brighter walls, thereby improving image contrast and endocardial delineation.

Rubin, D. N.; Yazbek, N.; Garcia, M. J.; Stewart, W. J.; Thomas, J. D.

2000-01-01

26

Optical coherence tomography imaging based on non-harmonic analysis  

NASA Astrophysics Data System (ADS)

A new processing technique called Non-Harmonic Analysis (NHA) is proposed for OCT imaging. Conventional Fourier-Domain OCT relies on the FFT calculation which depends on the window function and length. Axial resolution is counter proportional to the frame length of FFT that is limited by the swept range of the swept source in SS-OCT, or the pixel counts of CCD in SD-OCT degraded in FD-OCT. However, NHA process is intrinsically free from this trade-offs; NHA can resolve high frequency without being influenced by window function or frame length of sampled data. In this study, NHA process is explained and applied to OCT imaging and compared with OCT images based on FFT. In order to validate the benefit of NHA in OCT, we carried out OCT imaging based on NHA with the three different sample of onion-skin,human-skin and pig-eye. The results show that NHA process can realize practical image resolution that is equivalent to 100nm swept range only with less than half-reduced wavelength range.

Cao, Xu; Hirobayashi, Shigeki; Chong, Changho; Morosawa, Atsushi; Totsuka, Koki; Suzuki, Takuya

2009-11-01

27

Multi-Channel Microstrip Transceiver Arrays Using Harmonics for High Field MR Imaging in Humans  

PubMed Central

RF transceiver array design using primary and higher order harmonics for in-vivo parallel MR imaging and spectroscopic imaging is proposed. The improved electromagnetic decoupling performance, unique magnetic field distributions and high-frequency operation capabilities of higher-order harmonics of resonators would benefit transceiver arrays for parallel MRI, especially for ultrahigh field parallel MRI. To demonstrate this technique, microstrip transceiver arrays using first and second harmonic resonators were developed for human head parallel imaging at 7T. Phantom and human head images were acquired and evaluated using the GRAPPA reconstruction algorithm. The higher-order harmonic transceiver array design technique was also assessed numerically using FDTD simulation. Compared with regular primary-resonance transceiver designs, the proposed higher-order harmonic technique provided an improved g-factor and increased decoupling among resonant elements without using dedicated decoupling circuits, which would potentially lead to a better parallel imaging performance and ultimately faster and higher quality imaging. The proposed technique is particularly suitable for densely spaced transceiver array design where the increased mutual inductance among the elements becomes problematic. In addition, it also provides a simple approach to readily upgrade the channels of a conventional primary resonator microstrip array to a larger number for faster imaging. PMID:21878410

Wu, Bing; Wang, Chunsheng; Lu, Jonathan; Pang, Yong; Nelson, Sarah J; Vigneron, Daniel B; Zhang, Xiaoliang

2012-01-01

28

Second harmonic imaging and scoring of collagen in fibrotic tissues  

E-print Network

Second harmonic imaging and scoring of collagen in fibrotic tissues M. Strupler, A.-M. Pena, and M resolution and picosecond time resolution," J. Biomed. Opt. 8, 432-439 (2003). 8. A.-M. Pena, M. Strupler, T

Paris-Sud XI, Université de

29

Harmonic Image Reconstruction Assisted by a Nonlinear Metmaterial Surface  

E-print Network

We experimentally demonstrate a microwave far-field image reconstruction modality with the transverse resolution exceeding the diffraction limit by using a single layer of highly nonlinear metamaterial. The harmonic fields ...

Wang, Zhiyu

30

Second Harmonic Generation Imaging Microscopy: Applications to Diseases Diagnostics  

PubMed Central

Second Harmonic Generation microscopy has emerged as a powerful new optical imaging modality. This Feature describes its chemical and physical principles and highlights current applications in disease diagnostics. PMID:21446646

Campagnola, Paul

2011-01-01

31

Harmonic source wavefront aberration correction for ultrasound imaging  

PubMed Central

A method is proposed which uses a lower-frequency transmit to create a known harmonic acoustical source in tissue suitable for wavefront correction without a priori assumptions of the target or requiring a transponder. The measurement and imaging steps of this method were implemented on the Duke phased array system with a two-dimensional (2-D) array. The method was tested with multiple electronic aberrators [0.39? to 1.16? radians root-mean-square (rms) at 4.17 MHz] and with a physical aberrator 0.17? radians rms at 4.17 MHz) in a variety of imaging situations. Corrections were quantified in terms of peak beam amplitude compared to the unaberrated case, with restoration between 0.6 and 36.6 dB of peak amplitude with a single correction. Standard phantom images before and after correction were obtained and showed both visible improvement and 14 dB contrast improvement after correction. This method, when combined with previous phase correction methods, may be an important step that leads to improved clinical images. PMID:21303031

Dianis, Scott W.; von Ramm, Olaf T.

2011-01-01

32

HARMONIC ACTIVE CONTOURS FOR MULTICHANNEL IMAGE SEGMENTATION Virginia Estellers1  

E-print Network

HARMONIC ACTIVE CONTOURS FOR MULTICHANNEL IMAGE SEGMENTATION Virginia Estellers1 , Dominique Zosso1 Kong SAR ABSTRACT We propose a segmentation method based on the geometric repre- sentation of images as surfaces embedded in a higher dimensional space, handling naturally multichannel images. The segmentation

Soatto, Stefano

33

Dual-frequency transducer for nonlinear contrast agent imaging.  

PubMed

Detection of high-order nonlinear components issued from microbubbles has emerged as a sensitive method for contrast agent imaging. Nevertheless, the detection of these high-frequency components, including the third, fourth, and fifth harmonics, remains challenging because of the lack of transducer sensitivity and bandwidth. In this context, we propose a new design of imaging transducer based on a simple fabrication process for high-frequency nonlinear imaging. The transducer is composed of two elements: the outer low-frequency (LF) element was centered at 4 MHz and used in transmit mode, whereas the inner high-frequency (HF) element centered at 14 MHz was used in receive mode. The center element was pad-printed using a lead zirconate titanate (PZT) paste. The outer element was molded using a commercial PZT, and curved porous unpoled PZT was used as backing. Each piezoelectric element was characterized to determine the electromechanical performance with thickness coupling factor around 45%. After the assembly of the two transducer elements, hydrophone measurements (electroacoustic responses and radiation patterns) were carried out and demonstrated a large bandwidth (70% at -3 dB) of the HF transducer. Finally, the transducer was evaluated for contrast agent imaging using contrast agent microbubbles. The results showed that harmonic components (up to the sixth harmonic) of the microbubbles were successfully detected. Moreover, images from a flow phantom were acquired and demonstrated the potential of the transducer for high-frequency nonlinear contrast imaging. PMID:24297028

Guiroy, Axel; Novell, Anthony; Ringgaard, Erling; Lou-Moeller, Rasmus; Grégoire, Jean-Marc; Abellard, André-Pierre; Zawada, Tomasz; Bouakaz, Ayache; Levassort, Franck

2013-12-01

34

Analysis of wire scatterers with nonlinear or time-harmonic loads in the frequency domain  

Microsoft Academic Search

The time-harmonic scattering properties of wire scatterers with nonlinear or time-harmonic loads are analyzed in the frequency domain. First, the scattering problem is treated as a network problem that is analyzed by the method of moments. Then, the harmonic balance technique is applied in the nonlinear load case, and the conversion matrix technique is applied in the time-harmonic load case.

Chien-Chang Huang; Tah-Hsiung Chu

1993-01-01

35

Constant frequency aircraft electric power systems with harmonic reduction  

Microsoft Academic Search

The ever-increasing number of power electronic converters connected to the aircraft electric power system significantly increases harmonic levels and voltage transients in that system. Stringent limits on harmonic current distortion and perturbation of the aircraft electric power supply demands accurate simulation and development of high performance filters for the mitigation of harmonics and minimization of system transients. This paper presents

A. Eid; H. El-Kishky; M. Abdel-Salam; T. El-Mohandes

2008-01-01

36

Second-order susceptibility imaging with polarization-resolved second harmonic generation microscopy  

E-print Network

Second harmonic generation (SHG) microscopy has become an important tool for minimally invasive biomedical imaging. However, differentiation of different second harmonic generating species is mainly provided by morphological ...

So, Peter T. C.

37

Frequency-tunable second-harmonic submillimeter-wave gyrotron oscillators  

E-print Network

This thesis reports the design and experimental demonstration of frequency-tunable submillimeter-wave gyrotrons operating in continuous wave (CW) at the second harmonic of the electron cyclotron frequency. An unprecedented ...

Sousa, Antonio C. Torrezan de (Antonio Carlos Torrezan de)

2010-01-01

38

Polarization-insensitive ultralow-power second-harmonic generation frequency-resolved  

E-print Network

Polarization-insensitive ultralow-power second-harmonic generation frequency-resolved optical-insensitive ultralow-power second-harmonic generation frequency-resolved op- tical gating (FROG) measurementsW coupled average power without control of the input polarization. © 2007 Optical Society of America OCIS

Purdue University

39

Cerebral perfusion imaging with bolus harmonic imaging (Honorable Mention Poster Award)  

NASA Astrophysics Data System (ADS)

Fast visualisation of cerebral microcirculation supports diagnosis of acute stroke. However, the commonly used CT/MRI-based methods are time consuming, costly and not applicable to every patient. The bolus perfusion harmonic imaging (BHI) method is an ultrasound imaging technique which makes use of the fact, that ultrasound contrast agents unlike biological tissues resonate at harmonic frequencies. Exploiting this effect, the contrast between perfused and non-perfused areas can be improved. Thus, BHI overcomes the low signal-to-noise ratio of transcranial ultrasound and the high impedance of the skull. By analysing image sequences, visualising the qualitative characteristics of an US contrast agent bolus injection becomes possible. The analysis consists of calculating four perfusion-related parameters, Local Peak Intensity, Time To Peak, Area Under Curve, and Average Rising, from the time/intensity curve and providing them as colour-coded images. For calculating these parameters the fundamental assumption is that image intensity corresponds to contrast agent concentration which in turn shows the perfusion of the corresponding brain region. In a clinical study on patients suffering from acute ischemic stroke it is shown that some of the parameters correlate significantly to the infarction area. Thus, BHI becomes a less time-consuming and inexpensive bedside method for diagnosis of cerebral perfusion deficits.

Kier, Christian; Toth, Daniel; Meyer-Wiethe, Karsten; Schindler, Angela; Cangur, Hakan; Seidel, Gunter; Aach, Til

2005-04-01

40

A Novel Multimode Waveguide Coupler for Accurate Power Measurement of Traveling Wave Tube Harmonic Frequencies  

NASA Technical Reports Server (NTRS)

This paper presents the design, fabrication and test results for a novel waveguide multimode directional coupler (MDC). The coupler fabricated from two dissimilar waveguides is capable of isolating the power at the second harmonic frequency from the fundamental power at the output port of a traveling-wave tube (TWT). In addition to accurate power measurements at harmonic frequencies, a potential application of the MDC is in the design of a beacon source for atmospheric propagation studies at millimeter-wave frequencies.

Wintucky, Edwin G.; Simons, Rainee N.

2014-01-01

41

Confocal Imaging of Biological Tissues Using Second Harmonic Generation  

SciTech Connect

A confocal microscopy imaging system was devised to selectively detect Second harmonic signals generated by biological tissues. Several types of biological tissues were examined using this imaging system, including human teeth, bovine blood vessels, and chicken skin. All these tissues generated strong second harmonic signals. There is considerable evidence that the source of these signals in tissue is collagen. Collagen, the predominant component of most tissues, is known to have second order nonlinear susceptibility. This technique may have diagnostic usefulness in pathophysiological conditions characterized by changes in collagen structure including malignant transformation of nevi, progression of diabetic complications, and abnormalities in wound healing.

Kim, B-M.; Stoller, P.; Reiser, K.; Eichler, J.; Yan, M.; Rubenchik, A.; Da Silva, L.

2000-03-06

42

Image enhancement by nonlinear extrapolation in frequency space.  

PubMed

A technique for enhancing the perceptual sharpness of an image is described. The enhancement algorithm augments the frequency content of the image using shape-invariant properties of edges across scale by using a nonlinearity that generates phase coherent higher harmonics. The procedure utilizes the Laplacian transform and the Laplacian pyramid image representation. Results are presented depicting the power-spectra augmentation and the visual enhancement of several images. Simplicity of computations and ease of implementation allow for real-time applications such as high-definition television (HDTV). PMID:18255474

Greenspan, H; Anderson, C H; Akber, S

2000-01-01

43

Single pulse frequency compounding protocol for superharmonic imaging  

NASA Astrophysics Data System (ADS)

Second harmonic imaging is currently accepted as the standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the third till the fifth harmonics, arising during nonlinear sound propagation. It could further enhance the resolution and quality of echographic images. To meet the bandwidth requirement for SHI a dedicated phased array has been developed: a low frequency subarray, intended for transmission, interleaved with a high frequency subarray, used in reception. As the bandwidth of the elements is limited, the spectral gaps in between the harmonics cause multiple (ghost) reflection artifacts. A dual-pulse frequency compounding method aims at suppressing those artifacts at a price of a reduced frame rate. In this study we explore a possibility of performing frequency compounding within a single transmission. The traditional frequency compounding method suppresses the ripples by consecutively emitting two short Gaussian bursts with a slightly different center frequency. In the newly proposed method, the transmit aperture is divided into two parts: the first half is used to send a pulse at the lower center frequency, while the other half simultaneously transmits at a slightly higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study with INCS and the hydrophone measurements. Moreover, an experimental study was carried out to find the optimal parameters for the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. Additionally, the images of a human heart in the parasternal projection were acquired. The scanning aperture with the developed protocol amounts to approximately 90°, which is sufficient to capture the cardiac structures in the standard anatomical projections. The theoretically estimated and experimentally measured grating lobe levels are equal to -28.3 dB and -35.9 dB, respectively. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at -6 dB in comparison with the third harmonic (2.23 mm) was observed. A similar comparison in terms of the lateral resolution slightly favored the superharmonic component by 0.2 mm. Additionally, the images of the tissue mimicking phantom exhibited the absence of the multiple reflection artifacts. The in-vivo acquisition allows one to clearly observe the dynamic of the mitral valve leaflets. The new method is equally effective in eliminating the ripple artifacts associated with SHI as the dual-pulse technique, while the full frame rate is maintained.

Danilouchkine, M. G.; van Neer, P. L. M. J.; Verweij, M. D.; Matte, G. M.; Vletter, W. B.; van der Steen, A. F. W.; de Jong, N.

2013-07-01

44

Low Switching Frequency Active Harmonic Elimination in Multilevel Converters with Unequal DC Voltages  

E-print Network

method for the cascaded H-bridges multilevel converter when supplied by unequal DC sources. FirstLow Switching Frequency Active Harmonic Elimination in Multilevel Converters with Unequal DC, the multilevel converter is decoupled into individual unipolar converters, and the low order harmonics (such

Tolbert, Leon M.

45

Vectorial second harmonic generation imaging of gold nanocones  

Microsoft Academic Search

ewas used to characterize a nanocone-tip antenna [3]. Here, we show that second harmonic generation (SHG) imaging using cylindrical vector beams permits highly sensitive mapping of the local response in a gold nanocone array. Our sample consists of gold nanocones on a silicon substrate fabricated using UV-nanoimprint lithography [4]. The nanocones, each having a base diameter of 150 nm and

Godofredo Bautista; Mikko J. Huttunen; Jouni Makitalo; Juha M. Kontio; Janne Simonen; Martti Kauranen

2011-01-01

46

Harmonic chirp imaging method for ultrasound contrast agent.  

PubMed

Coded excitation is currently used in medical ultrasound to increase signal-to-noise ratio (SNR) and penetration depth. We propose a chirp excitation method for contrast agents using the second harmonic component of the response. This method is based on a compression filter that selectively compresses and extracts the second harmonic component from the received echo signal. Simulations have shown a clear increase in response for chirp excitation over pulse excitation with the same peak amplitude. This was confirmed by two-dimensional (2-D) optical observations of bubble response with a fast framing camera. To evaluate the harmonic compression method, we applied it to simulated bubble echoes, to measured propagation harmonics, and to B-mode scans of a flow phantom and compared it to regular pulse excitation imaging. An increase of approximately 10 dB in SNR was found for chirp excitation. The compression method was found to perform well in terms of resolution. Axial resolution was in all cases within 10% of the axial resolution from pulse excitation. Range side-lobe levels were 30 dB below the main lobe for the simulated bubble echoes and measured propagation harmonics. However, side-lobes were visible in the B-mode contrast images. PMID:15801312

Borsboom, Jerome M G; Chin, Chien Ting; Bouakaz, Ayache; Versluis, Michel; de Jong, Nico

2005-02-01

47

Analysis of the second harmonic generation of a femtosecond optical frequency comb  

NASA Astrophysics Data System (ADS)

The second harmonic generation (SHG) of a femtosecond optical frequency comb (FOFC) has been studied. This work focuses on the SHG frequencies that are generated by the mixing of even-numbered frequency components from the original comb with odd-numbered components. It is observed that the generation of those frequencies is the reason the original FOFC and FOFC-based SHG signal have the same repetition frequency. The theoretical derivation agrees with the result of an optical experiment. Our results may be of use with the high-harmonic-generation process and FOFC-based SHG applications, including high-resolution spectroscopy, attosecond pulse generation, and precision length measurement.

Wei, Dong; Aketagawa, Masato

2014-12-01

48

Lensless diffractive imaging using tabletop, coherent, high harmonic soft x  

Microsoft Academic Search

We present the first experimental demonstration of lensless imaging using a tabletop, coherent soft-x-rays source. A 29 nm high harmonic beam illuminates an object, and the diffraction is collected on an x-ray CCD camera. High dynamic range diffraction patterns are obtained by taking multiple exposures while blocking small-angle diffraction using beam blocks of varying size. These patterns reconstruct to images

Richard L. Sandberg; Daisy Raymondson; David Gaudiosi; Jim Holtsnider; Ron Tobey; Oren Cohen; M. Murnane; Henry C. Kapteyn; Changyong Song; Jianwei Miao

49

Coherent states and uncertainty relations for the damped harmonic oscillator with time-dependent frequency  

NASA Technical Reports Server (NTRS)

Starting with evaluations of propagator and wave function for the damped harmonic oscillator with time-dependent frequency, exact coherent states are constructed. These coherent states satisfy the properties which coherent states should generally have.

Yeon, Kyu-Hwang; Um, Chung-In; George, Thomas F.; Pandey, Lakshmi N.

1993-01-01

50

Frequency-resolved optical grating using surface third-harmonic generation  

SciTech Connect

We demonstrate the frequency-resolved optical grating technique using third-harmonic generation on the surface of a cover glass with ultra-short optical pulses and compare that with the phase-retrieved spectrogram.

Tsang, T. [Brookhaven National Lab., Upton, NY (United States); Krumbuegel, M.A.; Delong, K.W.; Fittinghoff, D.N.; Trebino, R. [Sandia National Labs., Livermore, CA (United States)

1995-11-01

51

Active optoelectronic system for stabilizing pulsed laser output energy at the fourth-harmonic frequency  

NASA Astrophysics Data System (ADS)

A feedback loop using an optoelectronic system has been tested successfully for the stabilization of the output energy at the fourth-harmonic frequency of a Nd-YAG laser (266 nm). The system presented includes an optical device to monitor the laser output energy at the nonconverted wavelengths and an electronic circuitry to optimize the laser output energy at the fourth-harmonic frequency, via real-time correction of the frequency quadrupling laser crystal angle with respect to the input beam. Results show that the present system provides a laser output energy stability better than +/- 15 percent for a long-term operation at the fourth-harmonic frequency, and keeps the locking even during the warming phase, immediately after the laser turning on. This system was designed for automatic lidar operations in field experiments, but its principle of operation is applicable to any type of harmonic generator for either solid-state or dye laser.

Papayannis, A.; Ancellet, G.; Conrad, J. L.; Laqui, C.; Pelon, J.

1993-03-01

52

Accurate, explicit formulae for higher harmonic force spectroscopy by frequency modulation-AFM  

PubMed Central

Summary The nonlinear interaction between an AFM tip and a sample gives rise to oscillations of the cantilever at integral multiples (harmonics) of the fundamental resonance frequency. The higher order harmonics have long been recognized to hold invaluable information on short range interactions but their utilization has thus far been relatively limited due to theoretical and experimental complexities. In particular, existing approximations of the interaction force in terms of higher harmonic amplitudes generally require simultaneous measurements of multiple harmonics to achieve satisfactory accuracy. In the present letter we address the mathematical challenge and derive accurate, explicit formulae for both conservative and dissipative forces in terms of an arbitrary single harmonic. Additionally, we show that in frequency modulation-AFM (FM-AFM) each harmonic carries complete information on the force, obviating the need for multi-harmonic analysis. Finally, we show that higher harmonics may indeed be used to reconstruct short range forces more accurately than the fundamental harmonic when the oscillation amplitude is small compared with the interaction range.

Kuchuk, Kfir

2015-01-01

53

Imaging collagen orientation using polarization-modulated second harmonic generation  

NASA Astrophysics Data System (ADS)

We use polarization-modulated second harmonic generation to image fiber orientation in collagen tissues, with an axial resolution of about 10 micrometers and a transverse resolution of up to 1 micrometers . A linearly polarized ultra-short pulse (200 fs) Ti:Sapphire laser beam is modulated using an electro-optic modulator and quarter-wave plate combination and focused onto a translation stage mounted sample using a microscope objective. The generated second harmonic light is collected using a photomultiplier tube and demodulated using phase sensitive detection to obtain signal intensity and fiber orientation information. In order to obtain second harmonic generation images of different types of collagen organization, we analyze several different tissues, including rat-tail tendon, mouse aorta, mouse fibrotic liver, and porcine skin. We can use our technique to image fibrotic tissue in histological sections of damaged liver and to identify burned tissue in porcine skin to a depth of a few hundred microns. Polarization-modulated second harmonic generation potentially could be a useful clinical technique for diagnosing collagen related disease or damage, especially in the skin.

Stoller, Patrick C.; Celliers, Peter M.; Reiser, Karen M.; Rubenchik, Alexander M.

2002-06-01

54

Acoustic imaging by second harmonic of phase-conjugate wave in inhomogeneous medium  

NASA Astrophysics Data System (ADS)

Application of the supercritical magnetoelastic wave phase conjugation to harmonic imaging in acoustic C-scan microscopy is demonstrated. Second-harmonic generation by phase-conjugate wave is used for improvement of resolution of an imaging system. Possibility to compensate phase aberrations introduced in harmonic image by inhomogeneity of propagation medium is shown experimentally and explained theoretically.

Pyl'nov, Yu.; Pernod, P.; Preobrazhensky, V.

2001-01-01

55

[Harmonic imaging analysis for assessment of morphological changes in mini-pig alveolar bone by normal and increased functional load].  

PubMed

The aim of the study was to reveal the mastication forces effect on the microstructure of mandible bone tissue of mini-pigs by Fouirier harmonic imaging analysis of bone sections images of back scattered electrons and assessment of calcium and phosphorous distribution maps obtained by roentgenofluorescence technique. The results showed that by higher functional loads not only the total content of mineral elements in the bone matrix increased but also the of the low-frequency harmonics in the image spectrum indicating structural heterogeneity decrease in bone mineralization. PMID:25588332

Guseva, I E; Zhitkov, M Iu; Loginova, N K; Mokhov, A V

2014-01-01

56

Dual-Frequency Piezoelectric Transducers for Contrast Enhanced Ultrasound Imaging  

PubMed Central

For many years, ultrasound has provided clinicians with an affordable and effective imaging tool for applications ranging from cardiology to obstetrics. Development of microbubble contrast agents over the past several decades has enabled ultrasound to distinguish between blood flow and surrounding tissue. Current clinical practices using microbubble contrast agents rely heavily on user training to evaluate degree of localized perfusion. Advances in separating the signals produced from contrast agents versus surrounding tissue backscatter provide unique opportunities for specialized sensors designed to image microbubbles with higher signal to noise and resolution than previously possible. In this review article, we describe the background principles and recent developments of ultrasound transducer technology for receiving signals produced by contrast agents while rejecting signals arising from soft tissue. This approach relies on transmitting at a low-frequency and receiving microbubble harmonic signals at frequencies many times higher than the transmitted frequency. Design and fabrication of dual-frequency transducers and the extension of recent developments in transducer technology for dual-frequency harmonic imaging are discussed. PMID:25375755

Martin, K. Heath; Lindsey, Brooks D.; Ma, Jianguo; Lee, Mike; Li, Sibo; Foster, F. Stuart; Jiang, Xiaoning; Dayton, Paul A.

2014-01-01

57

Dual-frequency piezoelectric transducers for contrast enhanced ultrasound imaging.  

PubMed

For many years, ultrasound has provided clinicians with an affordable and effective imaging tool for applications ranging from cardiology to obstetrics. Development of microbubble contrast agents over the past several decades has enabled ultrasound to distinguish between blood flow and surrounding tissue. Current clinical practices using microbubble contrast agents rely heavily on user training to evaluate degree of localized perfusion. Advances in separating the signals produced from contrast agents versus surrounding tissue backscatter provide unique opportunities for specialized sensors designed to image microbubbles with higher signal to noise and resolution than previously possible. In this review article, we describe the background principles and recent developments of ultrasound transducer technology for receiving signals produced by contrast agents while rejecting signals arising from soft tissue. This approach relies on transmitting at a low-frequency and receiving microbubble harmonic signals at frequencies many times higher than the transmitted frequency. Design and fabrication of dual-frequency transducers and the extension of recent developments in transducer technology for dual-frequency harmonic imaging are discussed. PMID:25375755

Martin, K Heath; Lindsey, Brooks D; Ma, Jianguo; Lee, Mike; Li, Sibo; Foster, F Stuart; Jiang, Xiaoning; Dayton, Paul A

2014-01-01

58

Second harmonic imaging and scoring of collagen in fibrotic tissues  

Microsoft Academic Search

We compare second harmonic generation (SHG) to histological and immunohistochemical techniques for the visualization and scoring of collagen in biological tissues. We show that SHG microscopy is highly specific for fibrillar collagens and that combined SHG and two-photon excited fluorescence (2PEF) imaging can provide simultaneous three-dimensional visualization of collagen synthesis and assembly sites in transgenic animal models expressing GFP constructs.

M. Strupler; A.-M. Pena; M. Hernest; P.-L. Tharaux; J.-L. Martin; E. Beaurepaire; M.-C. Schanne-Klein

2007-01-01

59

Ka Band Broadband Fourth Harmonic Image Rejection Mixer  

Microsoft Academic Search

This paper presents the design and implementation of Ka band broadband hybrid integrated image rejection mixer with a fourth\\u000a harmonic mixer as unit mixer. Detailed design and analysis have been carried out. The mixer was fabricated by hybrid microwave\\u000a integrated circuit (HMIC) process based on the thin film ceramic substrate which can reduce the cost compared to monolithic\\u000a microwave integrated

Fang Fang Fan; Ze Hong Yan

2008-01-01

60

3D Harmonic Mapping and Tetrahedral Meshing of Brain Imaging Data  

E-print Network

3D Harmonic Mapping and Tetrahedral Meshing of Brain Imaging Data Yalin Wang1 , Xianfeng Gu2 , Paul algorithm finds a harmonic map from a 3-manifold to a 3D solid sphere and the second is a novel sphere of magnetic resonance images (MRI). A heat flow method is used to solve the volumetric harmonic mapping

Thompson, Paul

61

Joint Entropy of the Harmonic Oscillator with Time Dependent Mass and Frequency  

E-print Network

Time dependent entropy of harmonic oscillator with time dependent mass and frequency are investigated. The joint entropy so called Leipnik's entropy is calculated by using time dependent wave function obtained by the Feynman path integral method. It is shown that, Leipnik's entropy fluctuates with time. However in constant mass and time dependent frequency case, entropy increases monotonically with time.

E. Akturk; O. Ozcan; R. Sever

2007-03-15

62

Modulation extension control for multilevel converters using triplen harmonic injection with low switching frequency  

Microsoft Academic Search

This paper presents a modulation extension control method for multilevel converters with low switching frequency. The disadvantage of the fundamental frequency switching control method for multilevel converters is its narrow range of modulation indices where solutions exist. To address this problem, a triplen harmonic compensation method is proposed. First, the resultant method and\\/or Newton climbing method are used to find

Zhong Du; Leon M. Tolbert; John N. Chiasson

2005-01-01

63

Effects of ion cyclotron harmonic damping on current drive in the lower hybrid frequency range  

SciTech Connect

We investigate the ion cyclotron harmonic damping effects on slow and fast waves in the lower hybrid frequency range for tokamak reactor parameters. Inclusion of the higher order terms in the hot plasma dielectric tensor introduces ion cyclotron harmonic damping; these terms also contribute to the real part of the dispersion relation and affect the wave trajectories. However, wave absorption by 15 keV deuterium and tritium ions can be avoided by choosing the slow wave frequency above the lower hybrid frequency and the fast wave frequency below the lower hybrid frequency. But preliminary estimates show that energetic alpha particles tend to absorb both the slow and the fast waves. This absorption may become a serious obstacle for fusion-reactor current drive in the lower hybrid frequency range.

Wong, K.L.; Ono, M.

1983-11-01

64

Electron cyclotron harmonic resonances in high-frequency heating of the ionosphere  

SciTech Connect

Electron acceleration by upper hybrid waves under cyclotron harmonic resonance interaction is studied. Theory is formulated; the analytical solutions in the second and fourth harmonic cyclotron resonance cases are obtained, and in the third harmonic case, a first order differential equation governing the evolution of the electron energy is derived. The theory is applied for explaining the generation of artificial ionization layers observed in high-frequency (HF) ionospheric heating experiments. The upper hybrid waves are assumed to be excited parametrically by the O-mode HF heating wave. As the decay mode is the lower hybrid wave, the excited upper hybrid waves have wavelengths ranging from 0.25 to 0.5 m, which are short enough to effectively incorporate the finite Larmour radius effect for the harmonic cyclotron resonance interactions as well as have a frequency bandwidth of about 20 kHz, which provides an altitude region of about 10 km for continuous harmonic cyclotron resonance interaction between electrons and descending waves in the slightly inhomogeneous geomagnetic field. The numerical results on electron acceleration show that electron fluxes with energies larger than 14 eV are generated in the three harmonic cases. These energetic electrons cause impact ionizations, which are descending to form artificial ionization layers at the bottom of the ionospheric F region.

Kuo, Spencer P. [Polytechnic Institute of New York University, 6 MetroTech Center, Brooklyn, New York 11201 (United States)] [Polytechnic Institute of New York University, 6 MetroTech Center, Brooklyn, New York 11201 (United States)

2013-09-15

65

Localized, Non-Harmonic Active Flap Motions for Low Frequency In-Plane Rotor Noise Reduction  

NASA Technical Reports Server (NTRS)

A first-of-its-kind demonstration of the use of localized, non-harmonic active flap motions, for suppressing low frequency, in-plane rotor noise, is reported in this paper. Operational feasibility is verified via testing of the full-scale AATD/Sikorsky/UTRC active flap demonstration rotor in the NFAC's 40- by 80-Foot anechoic wind tunnel. Effectiveness of using localized, non-harmonic active flap motions are compared to conventional four-per-rev harmonic flap motions, and also active flap motions derived from closed-loop acoustics implementations. All three approaches resulted in approximately the same noise reductions over an in-plane three-by-three microphone array installed forward and near in-plane of the rotor in the nearfield. It is also reported that using an active flap in this localized, non-harmonic manner, resulted in no more that 2% rotor performance penalty, but had the tendency to incur higher hub vibration levels.

Sim, Ben W.; Potsdam, Mark; Kitaplioglu, Cahit; LeMasurier, Philip; Lorber, Peter; Andrews, Joseph

2012-01-01

66

Research of second harmonic generation images based on texture analysis  

NASA Astrophysics Data System (ADS)

Texture analysis plays a crucial role in identifying objects or regions of interest in an image. It has been applied to a variety of medical image processing, ranging from the detection of disease and the segmentation of specific anatomical structures, to differentiation between healthy and pathological tissues. Second harmonic generation (SHG) microscopy as a potential noninvasive tool for imaging biological tissues has been widely used in medicine, with reduced phototoxicity and photobleaching. In this paper, we clarified the principles of texture analysis including statistical, transform, structural and model-based methods and gave examples of its applications, reviewing studies of the technique. Moreover, we tried to apply texture analysis to the SHG images for the differentiation of human skin scar tissues. Texture analysis method based on local binary pattern (LBP) and wavelet transform was used to extract texture features of SHG images from collagen in normal and abnormal scars, and then the scar SHG images were classified into normal or abnormal ones. Compared with other texture analysis methods with respect to the receiver operating characteristic analysis, LBP combined with wavelet transform was demonstrated to achieve higher accuracy. It can provide a new way for clinical diagnosis of scar types. At last, future development of texture analysis in SHG images were discussed.

Liu, Yao; Li, Yan; Gong, Haiming; Zhu, Xiaoqin; Huang, Zufang; Chen, Guannan

2014-09-01

67

Imaging morphodynamics of human blood cells in vivo with video-rate third harmonic generation microscopy.  

PubMed

With a video-rate third harmonic generation (THG) microscopy system, we imaged the micro-circulation beneath the human skin without labeling. Not only the speed of circulation but also the morpho-hydrodynamics of blood cells can be analyzed. Lacking of nuclei, red blood cells (RBCs) shows typical parachute-like and hollow-core morphology under THG microscopy. Quite different from RBCs, every now and then, round and granule rich blood cells with strong THG contrast appear in circulation. The corresponding volume densities in blood, evaluated from their frequencies of appearance and the velocity of circulation, fall within the physiological range of human white blood cell counts. PMID:23162724

Chen, Chien-Kuo; Liu, Tzu-Ming

2012-11-01

68

Quantifying thermodynamics of collagen thermal denaturation by second harmonic generation imaging  

NASA Astrophysics Data System (ADS)

Time-lapse second harmonic generation (SHG) microscopy was applied for the extraction of thermodynamic parameters of collagen thermal denaturation. We found that at sufficiently high temperatures, temporal dependence of SHG intensity from the isothermal treatment of chicken dermal collagen was single exponential and can be modeled by the Arrhenius equation. Activation energy and the frequency factor of chicken dermal collagen thermal denaturation were determined using temporal decays of SHG intensity at different temperatures. Our results show that time-lapse, high temperature SHG imaging can be used to quantify kinetic properties of collagen thermal denaturation within a microscopic volume of 1 nl.

Hovhannisyan, Vladimir A.; Su, Ping-Jung; Lin, Sung-Jan; Dong, Chen-Yuan

2009-06-01

69

Increased efficiency of ion acceleration by using femtosecond laser pulses at higher harmonic frequency  

SciTech Connect

The influence of laser frequency on laser-driven ion acceleration is investigated by means of two-dimensional particle-in-cell simulations. When ultrashort intense laser pulse at higher harmonic frequency irradiates a thin solid foil, the target may become re lativistically transparent for significantly lower laser pulse intensity compared with irradiation at fundamental laser frequency. The relativistically induced transparency results in an enhanced heating of hot electrons as well as increased maximum energies of accelerated ions and their numbers. Our simulation results have shown the increase in maximum proton energy and increase in the number of high-energy protons by a factor of 2 after the interaction of an ultrashort laser pulse of maximum intensity 7?×?10{sup 21?}W/cm{sup 2} with a fully ionized plastic foil of realistic density and of optimal thickness between 100?nm and 200?nm when switching from the fundamental frequency to the third harmonics.

Psikal, J., E-mail: jan.psikal@fjfi.cvut.cz [FNSPE, Czech Technical University in Prague, 11519 Prague (Czech Republic); Klimo, O. [FNSPE, Czech Technical University in Prague, 11519 Prague (Czech Republic); ELI-Beamlines Project, Institute of Physics of the ASCR, 18221 Prague (Czech Republic); Weber, S.; Margarone, D. [ELI-Beamlines Project, Institute of Physics of the ASCR, 18221 Prague (Czech Republic)

2014-07-15

70

Harmonics, interharmonics and unbalances of arc furnaces: a new frequency domain approach  

Microsoft Academic Search

The complexity of nonlinear models for simulating the dynamic behavior of arc furnaces is well known. For this reason, previous works are based on time domain solutions. In this paper, a new frequency domain approach for obtaining harmonics, interharmonics and unbalances of arc furnaces is proposed. The model assumes a dynamic and nonlinear u-i characteristic of the electric arc as

Luis F. Beites; Julio G. Mayordomo; Araceli Hernández; Rafael Asensi

2001-01-01

71

A Finite Element Method with Lagrange Multipliers for Low-Frequency Harmonic Maxwell Equations  

Microsoft Academic Search

The aim of this paper is to analyze a finite element method to solve the low-frequency harmonic Maxwell equations in a bounded domain containing conductors and dielectrics. This system of partial differential equations is a model for the so-called eddy currents problem. After writing this problem in terms of the magnetic field, it is discretized by Nedelec edge finite elements

Alfredo Bermúdez; Rodolfo Rodríguez; Pilar Salgado

2002-01-01

72

Value of tissue harmonic imaging (THI) and contrast harmonic imaging (CHI) in detection and characterisation of breast tumours  

PubMed Central

The purpose of this study was to investigate the extent to which tissue harmonic imaging (THI), speckle reduction imaging (SRI), spatial compounding (SC) and contrast can improve detection and differentiation of breast tumours. We examined 38 patients (14 benign, 24 malignant tumours) with different combinations of THI, SRI and SC. The effect on delineation, margin, tissue differentiation and posttumoral phenomena was evaluated with a three-point score. Additionally, 1oo not palpable tumours (diameters: 4–15 mm) were examined by contrast harmonic imaging (CHI) with power Doppler. After bolus injection (0.5 ml Optison), vascularisation and enhancement were observed for 20 min. The best combination for detection of margin, infiltration, echo pattern and posterior lesion boundary was the combination of SRI level 2 with SC low. THI was helpful for lesions OF more than 1 cm depth. In native Power Doppler, vessels were found in 54 of 100 lesions. Within 5 min after contrast medium (CM) injection, marginal and penetrating vessels increased in benign and malignant tumours and central vessels mostly in carcinomas (p<0.05). A diffuse CM accumulation was observed up to 20 min after injection in malignant tumours only (p<0.05). THI, SRI and SC improved delineation and tissue differentiation. Second-generation contrast agent allowed detection of tumour vascularisation with prolonged enhancement. PMID:16823568

Jung, E. M.; Jungius, K.-P.; Ertan, K.

2006-01-01

73

Second-harmonic reflector type high-gain FET frequency doubler operating in K-band  

Microsoft Academic Search

A high-gain FET frequency doubler with a second-harmonic reflector in the input circuit has been developed. The reflector position which gives maximum multiplication gain depends on line loss. The relation between multiplication gain and the reflector position varies with line loss. A K-band frequency doubler designed on this basis was fabricated, showing a multiplication gain of 6 dB

Y. Iyama; A. Iida; T. Takagi; S. Urasaki

1989-01-01

74

Second harmonic imaging and scoring of collagen in fibrotic tissues.  

PubMed

We compare second harmonic generation (SHG) to histological and immunohistochemical techniques for the visualization and scoring of collagen in biological tissues. We show that SHG microscopy is highly specific for fibrillar collagens and that combined SHG and two-photon excited fluorescence (2PEF) imaging can provide simultaneous three-dimensional visualization of collagen synthesis and assembly sites in transgenic animal models expressing GFP constructs. Finally, we propose several scores for characterizing collagen accumulation based on SHG images and appropriate for different types of collagen distributions. We illustrate the sensitivity of these scores in a murine model of renal fibrosis using a morphological segmentation of the tissue based on endogenous 2PEF signals. PMID:19532649

Strupler, M; Pena, A-M; Hernest, M; Tharaux, P-L; Martin, J-L; Beaurepaire, E; Schanne-Klein, M-C

2007-04-01

75

Variable Frequency Motor Drives: Harmonics, Power Factor, and Energy Efficiency  

E-print Network

the inverter output as a three-phase sine wave. Variable frequency drives are typically classified according voltage and horsepower, based upon the motor they will serve (8). Small, low voltage motors generally are rated 250 horsepower or less and operate... at or below 600 volts AC. Medium voltage motors are larger than 250 horsepower and operate above 600 volts AC. Where a motor is large but operates at low voltage, the horsepower rating typically dictates its classification. ENERGY EmCIENCY The main...

Massey, G. W.

76

Light transport in biological tissue using three-dimensional frequency-domain simplified spherical harmonics equations  

NASA Astrophysics Data System (ADS)

The accuracy of the commonly used diffusion approximation as used in diffuse optical tomography is known to be limited in cases involving strong absorption and in these situations a higher ordered approximation is necessary. In this study, a light transport model has been developed based upon the three-dimensional frequency-domain simplified spherical harmonics (SPN) approximation for orders up to N = 7. The SPN data are tested against a semi-infinite multi-layered Monte Carlo model. It has been shown that the SPN approximation for higher orders (N >1) provides an increase in accuracy over the diffusion equation specifically near sources and at boundaries of regions with increased optical absorption. It is demonstrated that the error of fluence calculated near the sources between the diffusion approximation and the SPN model (N = 7) can be as large as 60%, therefore limiting the use of the diffusion approximation for small animal imaging and in situations where optical changes near sources are critical for tomographic reconstructions.

Chu, Michael; Vishwanath, Karthik; Klose, Alexander D.; Dehghani, Hamid

2009-04-01

77

Statistical phase-screen model for second-harmonic beam distortion by body wall tissue in tissue harmonic imaging  

NASA Astrophysics Data System (ADS)

In certain clinical situations, tissue harmonic imaging reduces distortion due to phase aberrations introduced by the body wall layer. A statistical model was developed to describe the effects of random inhomogeneity in the body wall on the second-harmonic beam structure. This inhomogeneity is represented by a thin random phase screen located close to the source. Phase variations across the screen are characterized statistically. An analytical solution was derived for the expected value of the intensity of the second-harmonic field for a source that radiates a focused Gaussian beam. The focal beam pattern for the second-harmonic field is compared with that of the fundamental field as a function of correlation length and variance of the phase screen, for values based on measured human abdominal wall statistics.

Yan, X.; Hamilton, M. F.

2006-05-01

78

Single pulse frequency compounding protocol for superharmonic imaging  

NASA Astrophysics Data System (ADS)

Second harmonic imaging is currently adopted as standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the 3rd till the 5th harmonics, arising during nonlinear sound propagation. It could further enhance resolution and quality of echographic images. To meet the bandwidth requirement for SHI a dedicated phased array has been developed: a low frequency subarray, intended for transmission, interleaved with a high frequency subarray, used in reception. As the bandwidth of the elements is limited, the spectral gaps in between the harmonics cause multiple reflection artifacts. Recently, we introduce a dual-pulse frequency compounding (DPFC) method to suppress those artifacts at price of a reduced frame rate. In this study we investigate the feasibility of performing the frequency compounding protocol within a single transmission. The traditional DPFC method constructs each trace in a post-processing stage by summing echoes from two emitted pulses, the second slightly frequency-shifted compared to the first. In the newly proposed method, the transmit aperture is divided into two parts: the first half is used to send a pulse at the lower center frequency, while the other half simultaneously transmits at the higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study using the FIELD II toolkit. Moreover, an experimental study was performed to deduce the optimal parametric set for implementation of the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. For in-vitro acquisitions the SHI probe with interleaved phased array (44 odd elements at 1MHz and 44 even elements at 3.7MHz elements, optimized for echocardiography) was connected to a fully programmable ultrasound system. The results of the Field II simulations demonstrated that the angle between the main and grating lobe amounted to 90°. The difference in the fundamental pressure level between those lobes was equal to -26.8 dB. Those results suggest that the superharmonic content in the grating lobe was acceptably low. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at -6 dB in comparison with the 3rd harmonic (2.23 mm) was observed. A similar comparison in terms of the lateral resolution slightly favored the superharmonic component by 0.2 mm. Additionally, the images of the tissue mimicking phantom exhibited an absence of the multiple reflection artifacts in the focal and post-focal regions. The new method is equally effective in eliminating the ripple artifacts associated with SHI as the dual pulse technique, while the full frame rate is maintained.

Danilouchkine, Mikhail G.; van Neer, Paul L. M. J.; Matte, Guillaume M.; Verweij, Martin D.; de Jong, Nico

2011-03-01

79

Differential near-edge coherent diffractive imaging using a femtosecond high-harmonic  

E-print Network

-ray imaging; (340.7480) X-rays, soft X-rays, extreme ultraviolet (EUV); (190.2620) Harmonic generation, "Lensless imaging of magnetic nanostructures by X-ray spectro-holography," Nature 432(7019), 885­888 (2004

Neumark, Daniel M.

80

Simulations of Localized Harmonic Motion Imaging for Ultrasound Surgery Monitoring  

NASA Astrophysics Data System (ADS)

During the past few years, many noninvasive ultrasound techniques have been developed to explore mechanical properties of soft tissues. Some of these methods have been proposed to be useable for ultrasound surgery monitoring. In Localized Harmonic Motion Imaging (LHMI), a dynamic ultrasound radiation force stimulation is used to cause displacements in a target which are measured and used in the estimation of elastic properties of the target. In this study, we simulated displacements in soft tissue using different stimulation configurations while elastic parameters and absorption coefficients were varied as a function of temperature. The displacements were computed using a finite element method in an inhomogeneous domain that consisted of a spherical target surrounded by soft tissue. From the vibration simulations, it can be seen that displacements in LHMI are dependent on the stimulation technique and on the properties of the target when temperature changes. The results indicate that the method was able to determine the temperature elevation and the threshold for thermal coagulation.

Heikkilä, Janne; Hynynen, Kullervo

2006-05-01

81

Improved Shear Wave Motion Detection Using Pulse-Inversion Harmonic Imaging with a Phased Array Transducer.  

PubMed

Ultrasound tissue harmonic imaging is widely used to improve ultrasound B-mode imaging quality thanks to its effectiveness in suppressing imaging artifacts associated with ultrasound reverberation, phase aberration, and clutter noise. In ultrasound shear wave elastography (SWE), because the shear wave motion signal is extracted from the ultrasound signal, these noise sources can significantly deteriorate the shear wave motion tracking process and consequently result in noisy and biased shear wave motion detection. This situation is exacerbated in in vivo SWE applications such as heart, liver, and kidney. This paper, therefore, investigated the possibility of implementing harmonic imaging, specifically pulse-inversion harmonic imaging, in shear wave tracking, with the hypothesis that harmonic imaging can improve shear wave motion detection based on the same principles that apply to general harmonic B-mode imaging. We first designed an experiment with a gelatin phantom covered by an excised piece of pork belly and show that harmonic imaging can significantly improve shear wave motion detection by producing less underestimated shear wave motion and more consistent shear wave speed measurements than fundamental imaging. Then, a transthoracic heart experiment on a freshly sacrificed pig showed that harmonic imaging could robustly track the shear wave motion and give consistent shear wave speed measurements of the left ventricular myocardium while fundamental imaging could not. Finally, an in vivo transthoracic study of seven healthy volunteers showed that the proposed harmonic imaging tracking sequence could provide consistent estimates of the left ventricular myocardium stiffness in end-diastole with a general success rate of 80% and a success rate of 93.3% when excluding the subject with Body Mass Index (BMI) higher than 25. These promising results indicate that pulse-inversion harmonic imaging can significantly improve shear wave motion tracking and thus potentially facilitate more robust assessment of tissue elasticity by SWE. PMID:24021638

Song, Pengfei; Zhao, Heng; Urban, Matthew; Manduca, Armando; Pislaru, Sorin; Kinnick, Randall; Pislaru, Cristina; Greenleaf, James; Chen, Shigao

2013-09-01

82

Molecular Expressions: Digital Image Sampling Frequency  

NSDL National Science Digital Library

This item is an interactive Java simulation relating to digital imaging with optical microscopes. The "sampling interval" is the spatial resolution of a digital image, as determined by the distance between pixels. Analog signals must be digitized at an appropriate sampling frequency to produce acceptable image resolution. This simulation allows users to explore how variations in the sampling frequency affect the final image. This item is part of a larger collection of materials on optics and microscopy developed by the National High Magnetic Field Laboratory and Florida State University.

Davidson, Michael; Spring, Kenneth R.; Parry-Hill, Matthew J.; Russ, John C.

2008-08-16

83

Application of frequency-domain interferometry in the extreme-ultraviolet range by use of high-order harmonics  

Microsoft Academic Search

We apply the frequency-domain interferometry technique in the extreme-ultraviolet (XUV) range using high-order harmonics. The technique is first used to study the influence of ionization of the generating gas on the harmonic emission. We report a thorough study of the fringe contrast as a function of the generating parameters: gas pressure, laser intensity and focus position, harmonic order, delay, and

Jean-Francois Hergott; Thierry Auguste; Pascal Salières; Laurent Le Déroff; Pascal Monot; Pascal D'Oliveira; David Campo; Hamed Merdji; Bertrand Carré

2003-01-01

84

Frequency-resolved optical-gating measurements of ultrashort pulses using surface third-harmonic generation  

SciTech Connect

We demonstrate what is to our knowledge the first frequency-resolved optical gating (FROG) technique to measure ultrashort pulses from an unamplified Ti:sapphire laser oscillator without direction-of-time ambiguity. This technique utilizes surface third-harmonic generation as the nonlinear-optical effect and, surprisingly, is the most sensitive third-order FROG geometry yet. {copyright} {ital 1996 Optical Society of America.}

Tsang, T. [Brookhaven National Laboratory, Upton, New York 11973 (United States); Krumbuegel, M.A.; DeLong, K.W.; Fittinghoff, D.N.; Trebino, R. [Combustion Research Facility, MS9057, Sandia National Laboratories, Livermore, California 94551-0969 (United States)

1996-09-01

85

Distinction between harmonic and structural components in ambient excitation tests using the time-frequency domain decomposition technique  

NASA Astrophysics Data System (ADS)

The time-frequency domain decomposition technique has been proposed for modal identification in ambient vibration testing. In the presence of harmonic excitations, the modal identification process can provide not only structural modes but also non-structural ones relative to harmonic components. It is thus important to distinguish between them. In this study, by using the time-frequency domain decomposition technique, it is demonstrated that the distinction between non-structural harmonic components and those of the structural responses can be possible, and it is merged into the general procedure of the time-frequency domain decomposition method. This proposition is then verified by numerical examples and by a laboratory test.

Le, Thien-Phu; Argoul, Pierre

2015-02-01

86

Harmonic imaging with fresnel beamforming in the presence of phase aberration.  

PubMed

Fresnel beamforming is a beamforming method with a delay profile similar in shape to a physical Fresnel lens. The advantage of Fresnel beamforming is the reduced channel count, which consists of four to eight transmit and two analog-to-digital receive channels. Fresnel beamforming was found to perform comparably to conventional delay-and-sum beamforming. However, the performance of Fresnel beamforming is highly dependent on focal errors. These focal errors result in high side-lobe levels and further reduce the performance of Fresnel beamforming in the presence of phase aberration. With the advantages of lower side-lobe levels and suppression of aberration effects, harmonic imaging offers an effective solution to the limitations of Fresnel beamforming. We describe the implementation of tissue harmonic imaging and pulse inversion harmonic imaging in Fresnel beamforming, followed by dual apodization with cross-correlation, to improve image quality. Compared with conventional delay-and-sum beamforming, experimental results indicated contrast-to-noise ratio improvements of 10%, 49% and 264% for Fresnel beamforming using tissue harmonic imaging in the cases of no aberrator, 5-mm pork aberrator and 12-mm pork aberrator, respectively. These improvements were 22%, 57% and 352% for Fresnel beamforming using pulse inversion harmonic imaging. Moreover, dual apodization with cross-correlation was found to further improve the contrast-to-noise ratios in all cases. Harmonic imaging was also found to narrow the lateral beamwidth and shorten the axial pulse length by at least 25% and 21%, respectively, for Fresnel beamforming at different aberration levels. These results suggest the effectiveness of harmonic imaging in improving image quality for Fresnel beamforming, especially in the presence of phase aberration. Even though this combination of Fresnel beamforming and harmonic imaging does not outperform delay-and-sum beamforming combined with harmonic imaging, it provides the benefits of reduced channel count and potentially reduced cost and size of ultrasound systems. PMID:25018027

Nguyen, Man Minh; Shin, Junseob; Yen, Jesse

2014-10-01

87

Second harmonic generation imaging microscopy of cellular structure and function  

NASA Astrophysics Data System (ADS)

Second harmonic generation (SHG) imaging microscopy is an important emerging technique for biological research, with many advantages over existing one- or two-photon fluorescence techniques. A non-linear phenomenon employing mode-locked Ti:sapphire or fiber-based lasers, SHG results in intrinsic optical sectioning without the need for a confocal aperture. Furthermore, as a second-order process SHG is confined to loci lacking a center of symmetry. Many important structural proteins such as collagen and cellulose show intrinsic SHG, thus providing access to sub-resolution information on symmetry. However, we are particularly interested here in "resonance-enhanced" SHG from styryl dyes. In general SHG is a combination of a true second-order process and a third-order process dependent on a static electric field, such that SHG from membrane-bound dyes depends on a cell's trans-membrane potential. With simultaneous patch-clamping and non-linear imaging of cells, we have found that SHG is a sensitive probe of trans-membrane potential with sensitivities that are up to four times better than those obtained under optimal conditions using one-photon fluorescence imaging. With the sensitivity of SHG to local electric fields from other sources such as the membrane dipole potential as well as the quadratic dependence of SHG on concentration, we have found that SHG imaging of styryl dyes is also a powerful technique for the investigation of lipid phases and rafts and for the visualization of the dynamics of membrane-vesicle fusion following fertilization of an ovum.

Millard, Andrew C.; Jin, Lei; Loew, Leslie M.

2005-03-01

88

IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 55, NO. 4, APRIL 2008 1761 Reduced Switching-Frequency Active Harmonic  

E-print Network

) near sine wave is produced. An experimental 11-level H-bridge multilevel converter with a field-Frequency Active Harmonic Elimination for Multilevel Converters Zhong Du, Member, IEEE, Leon M. Tolbert, Senior number of specific order harmonics of multilevel converters. First, resultant theory is applied

Tolbert, Leon M.

89

Polarization-insensitive ultralow-power second-harmonic generation frequency-resolved optical gating  

NASA Astrophysics Data System (ADS)

We demonstrate polarization-insensitive ultralow-power second-harmonic generation frequency-resolved optical gating (FROG) measurements with a fiber-pigtailed, aperiodically poled lithium niobate waveguide. By scrambling the polarization much faster than the measurement integration time, we eliminate the impairment that frequency-independent random polarization fluctuations induce in FROG measurements. As a result we are able to retrieve intensity and phase profiles of few hundred femtosecond optical pulses with 50 MHz repetition rates at 5.2 nW coupled average power without control of the input polarization.

Miao, Houxun; Weiner, Andrew M.; Langrock, Carsten; Roussev, Rostislav V.; Fejer, Martin M.

2007-04-01

90

A Preliminary Engineering Design of Intravascular Dual-Frequency Transducers for Contrast-Enhanced Acoustic Angiography and Molecular Imaging  

PubMed Central

Current intravascular ultrasound (IVUS) probes are not optimized for contrast detection because of their design for high-frequency fundamental-mode imaging. However, data from transcutaneous contrast imaging suggests the possibility of utilizing contrast ultrasound for molecular imaging or vasa vasorum assessment to further elucidate atherosclerotic plaque deposition. This paper presents the design, fabrication, and characterization of a small-aperture (0.6 × 3 mm) IVUS probe optimized for high-frequency contrast imaging. The design utilizes a dual-frequency (6.5 MHz/30 MHz) transducer arrangement for exciting microbubbles at low frequencies (near their resonance) and detecting their broadband harmonics at high frequencies, minimizing detected tissue backscatter. The prototype probe is able to generate nonlinear microbubble response with more than 1.2 MPa of rarefractional pressure (mechanical index: 0.48) at 6.5 MHz, and is also able to detect microbubble response with a broadband receiving element (center frequency: 30 MHz, ?6-dB fractional bandwidth: 58.6%). Nonlinear super-harmonics from microbubbles flowing through a 200-?m-diameter micro-tube were clearly detected with a signal-to-noise ratio higher than 12 dB. Preliminary phantom imaging at the fundamental frequency (30 MHz) and dual-frequency super-harmonic imaging results suggest the promise of small aperture, dual-frequency IVUS transducers for contrast-enhanced IVUS imaging. PMID:24801226

Ma, Jianguo; Martin, K. Heath; Dayton, Paul A.; Jiang, Xiaoning

2014-01-01

91

Generation and coherent control of even-order harmonics driven by intense frequency-comb and cavity-mode fields inside a fsEC  

E-print Network

Generation and coherent control of even-order harmonics driven by intense frequency-comb and cavity) doi:10.1088/0953-4075/46/14/145403 Generation and coherent control of even-order harmonics driven, resulting in the generation of even-order harmonics. The high-order harmonic generation (HHG) from a two

Chu, Shih-I

92

Extracting tidal frequencies using multivariate harmonic analysis of sea level height time series  

NASA Astrophysics Data System (ADS)

This contribution is seen as a first attempt to extract the tidal frequencies using a multivariate spectral analysis method applied to multiple time series of tide-gauge records. The existing methods are either physics-based in which the ephemeris of Moon, Sun and other planets are used, or are observation-based in which univariate analysis methods—Fourier and wavelet for instance—are applied to tidal observations. The existence of many long tide-gauge records around the world allows one to use tidal observations and extract the main tidal constituents for which efficient multivariate methods are to be developed. This contribution applies the multivariate least-squares harmonic estimation (LS-HE) to the tidal time series of the UK tide-gauge stations. The first 413 harmonics of the tidal constituents and their nonlinear components are provided using the multivariate LS-HE. A few observations of the research are highlighted: (1) the multivariate analysis takes information of multiple time series into account in an optimal least- squares sense, and thus the tidal frequencies have higher detection power compared to the univariate analysis. (2) Dominant tidal frequencies range from the long-term signals to the sixth-diurnal species interval. Higher frequencies have negligible effects. (3) The most important tidal constituents (the first 50 frequencies) ordered from their amplitudes range from 212 cm (M2) to 1 cm (OQ2) for the data set considered. There are signals in this list that are not available in the 145 main tidal frequencies of the literature. (4) Tide predictions using different lists of tidal frequencies on five different data sets around the world are compared. The prediction results using the first significant 50 constituents provided promising results on these locations of the world.

Amiri-Simkooei, A. R.; Zaminpardaz, S.; Sharifi, M. A.

2014-10-01

93

Harmonic optical microscopy and fluorescence lifetime imaging platform for multimodal imaging.  

PubMed

In this work, we proposed and built a multimodal optical setup that extends a commercially available confocal microscope (Olympus VF300) to include nonlinear second harmonic generation (SHG) and third harmonic generation (THG) optical (NLO) microscopy and fluorescence lifetime imaging microscopy (FLIM). We explored all the flexibility offered by this commercial confocal microscope to include the nonlinear microscopy capabilities. The setup allows image acquisition with confocal, brightfield, NLO/multiphoton and FLIM imaging. Simultaneously, two-photon excited fluorescence (TPEF) and SHG are well established in the biomedical imaging area, because one can use the same ultrafast laser and detectors set to acquire both signals simultaneously. Because the integration with FLIM requires a separated modulus, there are fewer reports of TPEF+SHG+FLIM in the literature. The lack of reports of a TPEF+SHG+THG+FLIM system is mainly due to difficulties with THG because the present NLO laser sources generate THG in an UV wavelength range incompatible with microscope optics. In this article, we report the development of an easy-to-operate platform capable to perform two-photon fluorescence (TPFE), SHG, THG, and FLIM using a single 80 MHz femtosecond Ti:sapphire laser source. We described the modifications over the confocal system necessary to implement this integration and verified the presence of SHG and THG signals by several physical evidences. Finally, we demonstrated the use of this integrated system by acquiring images of vegetables and epithelial cancer biological samples. PMID:22648907

Pelegati, Vitor B; Adur, Javier; De Thomaz, André A; Almeida, Diogo B; Baratti, Mariana O; Andrade, Liliana A L A; Bottcher-Luiz, Fátima; Cesar, Carlos L

2012-10-01

94

Infrared-pumped third-harmonic and sum-frequency generation in diatomic molecules  

NASA Technical Reports Server (NTRS)

Using molecular hydrogen as a model system, we present a calculation which demonstrates the feasibility of efficient third-harmonic and sum-frequency generation of IR laser radiation by diatomic molecular gases. A conversion efficiency of 10% without phase matching is achievable with a modest laser intensity of about 20 MW/sq cm. In addition to a two-photon resonance, the efficient conversion depends on a mechanism which makes use of virtual vibronic transitions exclusively. Possible methods for phase matching are also suggested.

She, C. Y.; Billman, K. W.

1975-01-01

95

Third and second harmonic generation imaging of human articular cartilage  

NASA Astrophysics Data System (ADS)

Cartilage matrix is damaged in diseased states such as osteoarthritis, while adult articular cartilage does not have the capacity to repair structural damage. A least invasive mean to diagnose these diseased states of human articular cartilage with a high spatial resolution is thus highly desired. In this paper, we present our harmonic generation microscopic studies on the human articular cartilage samples. Without any staining, third and second harmonic generation can provide strong contrast in chondrocytes and collagen matrix, respectively. Our study indicates the high capability of harmonic generation microscopy for future articular cartilage disease diagnosis.

Tsai, Ming-Rung; Chen, Chih-Hwa; Sun, Chi-Kuang

2009-02-01

96

Uniform polarity microtubule assemblies imaged in native brain tissue by second-harmonic  

E-print Network

Uniform polarity microtubule assemblies imaged in native brain tissue by second-harmonic generation the mixed polarity in dendrites leads to destructive interference. SHG imaging provides a tool- m imaging depth) that is capable of recording MT ensemble polarity information is described here

Dombeck, Daniel

97

Second Harmonic Imaging improves Echocardiograph Quality on board the International Space Station  

NASA Technical Reports Server (NTRS)

Ultrasound (US) capabilities have been part of the Human Research Facility (HRF) on board the International Space Station (ISS) since 2001. The US equipment on board the ISS includes a first-generation Tissue Harmonic Imaging (THI) option. Harmonic imaging (HI) is the second harmonic response of the tissue to the ultrasound beam and produces robust tissue detail and signal. Since this is a first-generation THI, there are inherent limitations in tissue penetration. As a breakthrough technology, HI extensively advanced the field of ultrasound. In cardiac applications, it drastically improves endocardial border detection and has become a common imaging modality. U.S. images were captured and stored as JPEG stills from the ISS video downlink. US images with and without harmonic imaging option were randomized and provided to volunteers without medical education or US skills for identification of endocardial border. The results were processed and analyzed using applicable statistical calculations. The measurements in US images using HI improved measurement consistency and reproducibility among observers when compared to fundamental imaging. HI has been embraced by the imaging community at large as it improves the quality and data validity of US studies, especially in difficult-to-image cases. Even with the limitations of the first generation THI, HI improved the quality and measurability of many of the downlinked images from the ISS and should be an option utilized with cardiac imaging on board the ISS in all future space missions.

Garcia, Kathleen; Sargsyan, Ashot; Hamilton, Douglas; Martin, David; Ebert, Douglas; Melton, Shannon; Dulchavsky, Scott

2008-01-01

98

Three-dimensional tooth imaging using multiphoton and second harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

Detailed morphological and cellular information relating to the human tooth have traditionally been obtained through histological studies that required decalcification, staining, and fixation. With the recent invention of multiphoton microscopy, it has become possible to acquire high resolution images without histological procedures. Using an epiilluminated multiphoton microscope, we obtained two-photon excited autofluorescence and second harmonic generation (SHG) images of ex vivo human tooth. By combining these two imaging modalities we obtained submicron resolution images of the enamel, dentin, and the periodontal ligaments. The enamel emits endogenous two-photon autofluorescence. The structure of the dentin is visible from both the autofluorescence and second harmonic generation signals. The periodontal ligament composed mostly of collagen can be visualized by SHG imaging. We also constructed three dimensional images of the enamel, dentin, and periodontal ligament. The effectiveness of using multiphoton and second harmonic generation microscopy to obtain structural information of teeth suggest its potential use in dental diagnostics.

Chen, Min-Huey; Chen, Wei-Liang; Sun, Yen; Fwu, Peter Tramyeon; Lin, Ming-Gu; Dong, Chen-Yuan

2007-02-01

99

High-resolution harmonic motion imaging (HR-HMI) for tissue biomechanical property characterization  

PubMed Central

Background Elastography, capable of mapping the biomechanical properties of biological tissues, serves as a useful technique for clinicians to perform disease diagnosis and determine stages of many diseases. Many acoustic radiation force (ARF) based elastography, including acoustic radiation force impulse (ARFI) imaging and harmonic motion imaging (HMI), have been developed to remotely assess the elastic properties of tissues. However, due to the lower operating frequencies of these approaches, their spatial resolutions are insufficient for revealing stiffness distribution on small scale applications, such as cancerous tumor margin detection, atherosclerotic plaque composition analysis and ophthalmologic tissue characterization. Though recently developed ARF-based optical coherence elastography (OCE) methods open a new window for the high resolution elastography, shallow imaging depths significantly limit their usefulness in clinics. Methods The aim of this study is to develop a high-resolution HMI method to assess the tissue biomechanical properties with acceptable field of view (FOV) using a 4 MHz ring transducer for efficient excitation and a 40 MHz needle transducer for accurate detection. Under precise alignment of two confocal transducers, the high-resolution HMI system has a lateral resolution of 314 µm and an axial resolution of ?147 µm with an effective FOV of 2 mm in depth. Results The performance of this high resolution imaging system was validated on the agar-based tissue mimicking phantoms with different stiffness distributions. These data demonstrated the imaging system’s improved resolution and sensitivity on differentiating materials with varying stiffness. In addition, ex vivo imaging of a human atherosclerosis coronary artery demonstrated the capability of high resolution HMI in identifying layer-specific structures and characterizing atherosclerotic plaques based on their stiffness differences. Conclusions All together high resolution HMI appears to be a promising ultrasound-only technology for characterizing tissue biomechanical properties at the microstructural level to improve the image-based diseases diagnosis in multiple clinical applications.

Ma, Teng; Qian, Xuejun; Chiu, Chi Tat; Yu, Mingyue; Jung, Hayong; Tung, Yao-Sheng; Shung, K. Kirk

2015-01-01

100

Rapid vibrational imaging with sum frequency generation microscopy  

E-print Network

Rapid vibrational imaging with sum frequency generation microscopy Varun Raghunathan,1, Yang Han,1, 2011 We demonstrate rapid vibrational imaging based on sum frequency generation (SFG) microscopy parametric oscillator, vibrationally selective imaging of collagen fibers is achieved with submicrometer

Potma, Eric Olaf

101

High-order harmonic generation by chirped and self-guided femtosecond laser pulses. II. Time-frequency analysis  

SciTech Connect

We present a time-dependent analysis of high-order harmonics generated by a self-guided femtosecond laser pulse propagating through a long gas jet. A three-dimensional model is used to calculate the harmonic fields generated by laser pulses, which only differ by the sign of their initial chirp. The time-frequency distributions of the single-atom dipole and harmonic field reveal the dynamics of harmonic generation in the cutoff. A time-dependent phase-matching calculation was performed, taking into account the self-phase modulation of the laser field. Good phase matching holds for only few optical cycles, being dependent on the electron trajectory. When the cutoff trajectory is phase matched, emitted harmonics are locked in phase and the emission intensity is maximized.

Tosa, V. [Department of Physics, KAIST, Yuseong-gu, Daejeon, 305-701 (Korea, Republic of); National Institute for R and D of Isotopic and Molecular Technologies, Cluj-Napoca (Romania); Kim, H.T.; Kim, I.J.; Nam, C.H. [Department of Physics, KAIST, Yuseong-gu, Daejeon, 305-701(Korea, Republic of)

2005-06-15

102

Protection of VHF international distress frequencies from harmonic radiation due to digital television equipment  

NASA Astrophysics Data System (ADS)

Digital television picture processing equipment uses a luminance sampling frequency of 13.5 MHz, which can give rise to harmonics at 121.5 and 243 MHz. If such equipment becomes sufficiently widespread as will probably be the case with MAC/packet receivers, it is possible that the cumulative radiation could become significantly high. Since these frequencies are used by the international distress services there is a potential for interference if this unwanted radiation is not controlled at the point of manufacture. Over the last two years this problem was studied by the BBC in conjunction with the EBU. The conclusion is that the distress services will be protected provided that digital television picture processing equipment meets existing electromagnetic compatibility (EMC) standards for information technology equipment. In the case of domestic television this should not present a problem, but for studio equipment, because of its size and complexity, EMC compliance may not be so easy.

Middleton, J.

103

Optical frequency comb generation based on electro-optical modulation with high-order harmonic of a sine RF signal  

NASA Astrophysics Data System (ADS)

By using cascaded intensity and phase modulators, optical frequency comb (OFC) is generated. In the OFC generation scheme, high-order harmonic of a RF signal is used for driving intensity modulator (IM) or phase modulator (PM). Experimental and theoretical results indicate when IM is driven by high-order harmonic, lower RF driving power for PM is required to generate an OFC with the best flatness.

Wei, Renjie; Yan, JuanJuan; Peng, Yichao; Yao, Xiayuan; Bai, Ming; Zheng, Zheng

2013-03-01

104

Inelastic neutron scattering analysis of low-frequency motions in proteins: Harmonic and damped harmonic models of bovine pancreatic tryspin inhibitor  

NASA Astrophysics Data System (ADS)

Inelastic neutron scattering spectra are calculated from harmonic and damped harmonic models of the internal dynamics of a small protein, the bovine pancreatic trypsin inhibitor (BPTI). Numerical Fourier transformation of the intermediate scattering function Fvibinc (q, t) is used to calculate the inelastic scattering. This permits the inclusion of multiphonon scattering and frictional damping effects. Although for a typical experimental configuration, the multiphonon contribution does not significantly alter the form of the scattering at frequencies below about 30 cm-1, it does have a significant effect on the scattering intensity at higher frequencies. Frictional damping is introduced into the harmonic model by assuming that each mode acts as an independent damped Langevin oscillator. With this model and the assumption that the lowest frequency modes are overdamped while the higher frequency modes are underdamped, improved agreement with the experimental BPTI powder results is obtained. The measured scattering from BPTI in solution shows increased intensity at frequencies below 50 cm-1 relative to the powder results. The solution scattering profile can be reproduced approximately by the addition of overdamped Langevin oscillator normal modes to the dynamic model in best agreement with the powder data. Several other aspects of neutron scattering from proteins are examined. Anisotropy in the harmonic resolution broadened scattering is demonstrated. Spectra calculated assuming classical equations of motion are shown to agree with those calculated with the full quantum-mechanical dynamical model. Translational diffusion broadening is found to be small compared to the instrumental resolution broadening for the range of scattering wave vectors of interest. The contribution of the coherent scattering to the measured intensity is calculated for the case of a partially hydrated protein. Under typical experimental conditions, the measured cross sections are dominated by the incoherent scattering and the self part of the coherent scattering, a result that justifies the comparison of experimental data with calculated incoherent scattering spectra.

Smith, Jeremy; Cusack, Stephen; Tidor, Bruce; Karplus, Martin

1990-09-01

105

High throughput second harmonic imaging for label-free biological applications.  

PubMed

Second harmonic generation (SHG) is inherently sensitive to the absence of spatial centrosymmetry, which can render it intrinsically sensitive to interfacial processes, chemical changes and electrochemical responses. Here, we seek to improve the imaging throughput of SHG microscopy by using a wide-field imaging scheme in combination with a medium-range repetition rate amplified near infrared femtosecond laser source and gated detection. The imaging throughput of this configuration is tested by measuring the optical image contrast for different image acquisition times of BaTiO3 nanoparticles in two different wide-field setups and one commercial point-scanning configuration. We find that the second harmonic imaging throughput is improved by 2-3 orders of magnitude compared to point-scan imaging. Capitalizing on this result, we perform low fluence imaging of (parts of) living mammalian neurons in culture. PMID:25607059

Macias-Romero, Carlos; Didier, Marie E P; Jourdain, Pascal; Marquet, Pierre; Magistretti, Pierre; Tarun, Orly B; Zubkovs, Vitalijs; Radenovic, Aleksandra; Roke, Sylvie

2014-12-15

106

Mosquito (Aedes aegypti) flight tones: Frequency, harmonicity, spherical spreading, and phase relationships  

PubMed Central

Mosquito flight produces a tone as a side effect of wing movement; this tone is also a communication signal that is frequency-modulated during courtship. Recordings of tones produced by tethered flying male and female Aedes aegypti were undertaken using pairs of pressure-gradient microphones above and below, ahead and behind, and to the left and right over a range of distances. Fundamental frequencies were close to those previously reported, although amplitudes were lower. The male fundamental frequency was higher than that of the female and males modulated it over a wider range. Analysis of harmonics shows that the first six partials were nearly always within 1?Hz of integer multiples of the fundamental, even when the fundamental was being modulated. Along the front-back axis, amplitude attenuated as a function of distance raised to the power 2.3. Front and back recordings were out of phase, as were above and below, while left and right were in phase. Recordings from ahead and behind showed quadratic phase coupling, while others did not. Finally, two methods are presented for separating simultaneous flight tones in a single recording and enhancing their frequency resolution. Implications for mosquito behavior are discussed. PMID:25234901

Arthur, Benjamin J.; Emr, Kevin S.; Wyttenbach, Robert A.; Hoy, Ronald R.

2014-01-01

107

Frequency domain analysis of knock images  

NASA Astrophysics Data System (ADS)

High speed imaging-based knock analysis has mainly focused on time domain information, e.g. the spark triggered flame speed, the time when end gas auto-ignition occurs and the end gas flame speed after auto-ignition. This study presents a frequency domain analysis on the knock images recorded using a high speed camera with direct photography in a rapid compression machine (RCM). To clearly visualize the pressure wave oscillation in the combustion chamber, the images were high-pass-filtered to extract the luminosity oscillation. The luminosity spectrum was then obtained by applying fast Fourier transform (FFT) to three basic colour components (red, green and blue) of the high-pass-filtered images. Compared to the pressure spectrum, the luminosity spectra better identify the resonant modes of pressure wave oscillation. More importantly, the resonant mode shapes can be clearly visualized by reconstructing the images based on the amplitudes of luminosity spectra at the corresponding resonant frequencies, which agree well with the analytical solutions for mode shapes of gas vibration in a cylindrical cavity.

Qi, Yunliang; He, Xin; Wang, Zhi; Wang, Jianxin

2014-12-01

108

MREIT conductivity imaging based on the local harmonic Bz algorithm: Animal experiments  

NASA Astrophysics Data System (ADS)

From numerous numerical and phantom experiments, MREIT conductivity imaging based on harmonic Bz algorithm shows that it could be yet another useful medical imaging modality. However, in animal experiments, the conventional harmonic Bz algorithm gives poor results near boundaries of problematic regions such as bones, lungs, and gas-filled stomach, and the subject boundary where electrodes are not attached. Since the amount of injected current is low enough for the safety for in vivo animal, the measured Bz data is defected by severe noise. In order to handle such problems, we use the recently developed local harmonic Bz algorithm to obtain conductivity images in our ROI(region of interest) without concerning the defected regions. Furthermore we adopt a denoising algorithm that preserves the ramp structure of Bz data, which informs of the location and size of anomaly. Incorporating these efficient techniques, we provide the conductivity imaging of post-mortem and in vivo animal experiments with high spatial resolution.

Jeon, Kiwan; Lee, Chang-Ock; Woo, Eung Je; Kim, Hyung Joong; Seo, Jin Keun

2010-04-01

109

Imaging lipid bodies in cells and tissues using third-harmonic generation microscopy  

E-print Network

Imaging lipid bodies in cells and tissues using third-harmonic generation microscopy Delphine De­2 orders of magnitude larger than other structures, which allows one to image them with high specificity in a variety of unstained samples including insect embryos, plant seeds and intact mammalian tissue (liver

Cai, Long

110

Simultaneous acquisition of spatial harmonics (SMASH): Fast imaging with radiofrequency coil arrays  

Microsoft Academic Search

This report presents a fast-imaging technique that al- lows some fraction of signal data points to be acquired in parallel, rather than sequentially in time. Previously, several fast imaging schemes have been proposed using simultaneous data acquisition in multiple RF coils (8- 13). The technique described here, dubbed simultaneous acquisition of spatial harmonics (SMASH), reduces im- age acquisition times by

Daniel K. Sodickson; Warren J. Manning

1997-01-01

111

Conductivity and current density image reconstruction using harmonic Bz algorithm in magnetic resonance electrical impedance tomography  

Microsoft Academic Search

Magnetic resonance electrical impedance tomography (MREIT) is to provide cross-sectional images of the conductivity distribution ? of a subject. While injecting current into the subject, we measure one component Bz of the induced magnetic flux density B = (Bx, By, Bz) using an MRI scanner. Based on the relation between ?2Bz and ??, the harmonic Bz algorithm reconstructs an image

Suk Hoon Oh; Byung Il Lee; Eung Je Woo; Soo Yeol Lee; Min Hyoung Cho; Ohin Kwon; Jin Keun Seo

2003-01-01

112

Measurement of sound velocity made easy using harmonic resonant frequencies with everyday mobile technology  

NASA Astrophysics Data System (ADS)

Recent articles about smartphone experiments have described their applications as experimental tools in different physical contexts.1-4 They have established that smartphones facilitate experimental setups, thanks to the small size and diverse functions of mobile devices, in comparison to setups with computer-based measurements. In the experiment described in this article, the experimental setup is reduced to a minimum. The objective of the experiment is to determine the speed of sound with a high degree of accuracy using everyday tools. An article published recently proposes a time-of-flight method where sound or acoustic pulses are reflected at the ends of an open tube.5 In contrast, the following experiment idea is based on the harmonic resonant frequencies of such a tube, simultaneously triggered by a noise signal.

Hirth, Michael; Kuhn, Jochen; Müller, Andreas

2015-02-01

113

Definitions of non-stationary vibration power for time-frequency analysis and computational algorithms based upon harmonic wavelet transform  

NASA Astrophysics Data System (ADS)

While the vibration power for a set of harmonic force and velocity signals is well defined and known, it is not as popular yet for a set of stationary random force and velocity processes, although it can be found in some literatures. In this paper, the definition of the vibration power for a set of non-stationary random force and velocity signals will be derived for the purpose of a time-frequency analysis based on the definitions of the vibration power for the harmonic and stationary random signals. The non-stationary vibration power, defined as the short-time average of the product of the force and velocity over a given frequency range of interest, can be calculated by three methods: the Wigner-Ville distribution, the short-time Fourier transform, and the harmonic wavelet transform. The latter method is selected in this paper because band-pass filtering can be done without phase distortions, and the frequency ranges can be chosen very flexibly for the time-frequency analysis. Three algorithms for the time-frequency analysis of the non-stationary vibration power using the harmonic wavelet transform are discussed. The first is an algorithm for computation according to the full definition, while the others are approximate. Noting that the force and velocity decomposed into frequency ranges of interest by the harmonic wavelet transform are constructed with coefficients and basis functions, for the second algorithm, it is suggested to prepare a table of time integrals of the product of the basis functions in advance, which are independent of the signals under analysis. How to prepare and utilize the integral table are presented. The third algorithm is based on an evolutionary spectrum. Applications of the algorithms to the time-frequency analysis of the vibration power transmitted from an excitation source to a receiver structure in a simple mechanical system consisting of a cantilever beam and a reaction wheel are presented for illustration.

Heo, YongHwa; Kim, Kwang-joon

2015-02-01

114

Multiscale image features analysis with circular harmonic wavelets  

NASA Astrophysics Data System (ADS)

In this contribution we introduce a new family of wavelets named Circular Harmonic Wavelets (CHW), suited for multiscale feature-based representations, that constitute a basis for general steerable wavelets. The family is based on Circular Harmonic Functions (CHF) derived by the Fourier expansion of local Radial Tomographic Projections. A multiscale general feature analysis can be performed by linearly combining the outputs of CHW operators of different order. After a survey on the general properties of the CHFs, we investigate the relationship between CHF and the wavelet expansion, stating the basic admissibility and stability conditions with reference to the Hankel transform of the radial profiles and describing some fundamental mathematical properties. Finally some applications are illustrated through examples.

Jacovitti, Giovanni; Neri, Alessandro

1995-09-01

115

Imaging of Fatigue Damage in CFRP Composite Laminates Using Nonlinear Harmonic Generation  

NASA Astrophysics Data System (ADS)

In this paper, experimental evidence is presented that suggests a strong nonlinear interaction between acoustic wave and micro-structural damage before the onset of delaminations in fatigued CFRP samples. Sample used were 32 plies quasi-isotropic graphite/epoxy laminate fatigued with a four point bending fatigue. First harmonic images were constructed from the amplitude of the first harmonic normalized by the amplitude of the fundamental. Harmonic imaging technique (HIT) shows a much higher sensitivity to micro-damage than amplitude C-scan. Correlations are established between the image zone where the nonlinear parameter is high and the region where a high density of micro-delamination and matrix cracks is observed.

Mattei, Christophe; Marty, Pierre

2003-03-01

116

Harmonic oscillator model of early visual image processing  

NASA Astrophysics Data System (ADS)

To characterize how the human visual system responds to spatial patterns, a 'black box' method was adopted, in which visual evoked potentials (VEPs) were taken as outputs and visual patterned stimuli were taken as inputs. The stimuli were gratings whose function profiles were weighted Hermite polynomials (WHPs). A model, mathematically analogous to harmonic oscillators in quantum mechanics, was developed to describe the black box and the quantitative relationships between the VEPs and the WHPs.

Yang, Jian; Reeves, Adam J.

1991-11-01

117

Ultrasonic imaging of static objects through an aberrating layer using harmonic phase conjugation approach.  

PubMed

The main goal of this study is to develop a new image reconstruction approach for the ultrasonic detection of small objects (comparable to or smaller than the ultrasonic wavelength) behind an aberrating layer. Instead of conventional pulse-echo experimental setup we used through transmission, as the backscattered field after going twice through the layer becomes much weaker than the through-transmitted field. The proposed solution is based on the Harmonic Phase Conjugation (HPC) technique. The developed numerical model allows to calculate the amplitude and phase distributions of the through-transmitted acoustic field interacting with the objects and received by a linear transducer array either directly or after passing through an additional aberrating layer. Then, the digitized acoustic field received by the array is processed, phase-conjugated, and finally, numerically propagated back through the medium in order to reconstruct the image of the target objects. The reconstruction quality of the algorithm was systematically tested on a numerical model, which included a barrier, a medium behind it, and a group of three scatterers, by varying scatterer distances from the source transducer, their mutual arrangement, and the angle of the incident field. Subsequently, a set of laboratory experiments was conducted (at transmit frequency of 2MHz) to verify the accuracy of the developed simulation. The results demonstrate feasibility of imaging multiple scattering objects through a barrier using the HPC method with better than 1mm accuracy. The results of these tests are presented, and the feasibility of implementing this approach for various biomedical and NDT imaging applications is discussed. PMID:25553713

Mirzania, Raheleh; Shapoori, Kiyanoosh; Malyarenko, Eugene; Maev, Roman Gr

2015-04-01

118

Imaging the bipolarity of myosin filaments with Interferometric Second Harmonic Generation microscopy  

PubMed Central

We report that combining interferometry with Second Harmonic Generation (SHG) microscopy provides valuable information about the relative orientation of noncentrosymmetric structures composing tissues. This is confirmed through the imaging of rat medial gastrocnemius muscle. The inteferometric Second Harmonic Generation (ISHG) images reveal that each side of the myosin filaments composing the A band of the sarcomere generates ? phase shifted SHG signal which implies that the myosin proteins at each end of the filaments are oriented in opposite directions. This highlights the bipolar structural organization of the myosin filaments and shows that muscles can be considered as a periodically poled biological structure. PMID:24156065

Rivard, Maxime; Couture, Charles-André; Miri, Amir K.; Laliberté, Mathieu; Bertrand-Grenier, Antony; Mongeau, Luc; Légaré, François

2013-01-01

119

A high frequency electromagnetic impedance imaging system  

SciTech Connect

Non-invasive, high resolution geophysical mapping of the shallow subsurface is necessary for delineation of buried hazardous wastes, detecting unexploded ordinance, verifying and monitoring of containment or moisture contents, and other environmental applications. Electromagnetic (EM) techniques can be used for this purpose since electrical conductivity and dielectric permittivity are representative of the subsurface media. Measurements in the EM frequency band between 1 and 100 MHz are very important for such applications, because the induction number of many targets is small and the ability to determine the subsurface distribution of both electrical properties is required. Earlier workers were successful in developing systems for detecting anomalous areas, but quantitative interpretation of the data was difficult. Accurate measurements are necessary, but difficult to achieve for high-resolution imaging of the subsurface. We are developing a broadband non-invasive method for accurately mapping the electrical conductivity and dielectric permittivity of the shallow subsurface using an EM impedance approach similar to the MT exploration technique. Electric and magnetic sensors were tested to ensure that stray EM scattering is minimized and the quality of the data collected with the high-frequency impedance (HFI) system is good enough to allow high-resolution, multi-dimensional imaging of hidden targets. Additional efforts are being made to modify and further develop existing sensors and transmitters to improve the imaging capability and data acquisition efficiency.

Tseng, Hung-Wen; Lee, Ki Ha; Becker, Alex

2003-01-15

120

Experimental and simulation studies on the behavior of signal harmonics in magnetic particle imaging.  

PubMed

Our purpose in this study was to investigate the behavior of signal harmonics in magnetic particle imaging (MPI) by experimental and simulation studies. In the experimental studies, we made an apparatus for MPI in which both a drive magnetic field (DMF) and a selection magnetic field (SMF) were generated with a Maxwell coil pair. The MPI signals from magnetic nanoparticles (MNPs) were detected with a solenoid coil. The odd- and even-numbered harmonics were calculated by Fourier transformation with or without background subtraction. The particle size of the MNPs was measured by transmission electron microscopy (TEM), dynamic light-scattering, and X-ray diffraction methods. In the simulation studies, the magnetization and particle size distribution of MNPs were assumed to obey the Langevin theory of paramagnetism and a log-normal distribution, respectively. The odd- and even-numbered harmonics were calculated by Fourier transformation under various conditions of DMF and SMF and for three different particle sizes. The behavior of the harmonics largely depended on the size of the MNPs. When we used the particle size obtained from the TEM image, the simulation results were most similar to the experimental results. The similarity between the experimental and simulation results for the even-numbered harmonics was better than that for the odd-numbered harmonics. This was considered to be due to the fact that the odd-numbered harmonics were more sensitive to background subtraction than were the even-numbered harmonics. This study will be useful for a better understanding, optimization, and development of MPI and for designing MNPs appropriate for MPI. PMID:23589334

Murase, Kenya; Konishi, Takashi; Takeuchi, Yuki; Takata, Hiroshige; Saito, Shigeyoshi

2013-07-01

121

Calculation and analysis of the harmonic vibrational frequencies in molecules at extreme pressure: Methodology and diborane as a test case  

NASA Astrophysics Data System (ADS)

We present a new quantum chemical method for the calculation of the equilibrium geometry and the harmonic vibrational frequencies of molecular systems in dense medium at high pressures (of the order of GPa). The new computational method, named PCM-XP, is based on the polarizable continuum model (PCM), amply used for the study of the solvent effects at standard condition of pressure, and it is accompanied by a new method of analysis for the interpretation of the mechanisms underpinning the effects of pressure on the molecular geometries and the harmonic vibrational frequencies. The PCM-XP has been applied at the density functional theory level to diborane as a molecular system under high pressure. The computed harmonic vibrational frequencies as a function of the pressure have shown a satisfactory agreement with the corresponding experimental results, and the parallel application of the method of analysis has reveled that the effects of the pressure on the equilibrium geometry can be interpreted in terms of direct effects on the electronic charge distribution of the molecular solutes, and that the effects on the harmonic vibrational frequencies can be described in terms of two physically distinct effects of the pressure (curvature and relaxation) on the potential energy for the motion of the nuclei.

Cammi, R.; Cappelli, C.; Mennucci, B.; Tomasi, J.

2012-10-01

122

Calculation and analysis of the harmonic vibrational frequencies in molecules at extreme pressure: methodology and diborane as a test case.  

PubMed

We present a new quantum chemical method for the calculation of the equilibrium geometry and the harmonic vibrational frequencies of molecular systems in dense medium at high pressures (of the order of GPa). The new computational method, named PCM-XP, is based on the polarizable continuum model (PCM), amply used for the study of the solvent effects at standard condition of pressure, and it is accompanied by a new method of analysis for the interpretation of the mechanisms underpinning the effects of pressure on the molecular geometries and the harmonic vibrational frequencies. The PCM-XP has been applied at the density functional theory level to diborane as a molecular system under high pressure. The computed harmonic vibrational frequencies as a function of the pressure have shown a satisfactory agreement with the corresponding experimental results, and the parallel application of the method of analysis has reveled that the effects of the pressure on the equilibrium geometry can be interpreted in terms of direct effects on the electronic charge distribution of the molecular solutes, and that the effects on the harmonic vibrational frequencies can be described in terms of two physically distinct effects of the pressure (curvature and relaxation) on the potential energy for the motion of the nuclei. PMID:23083153

Cammi, R; Cappelli, C; Mennucci, B; Tomasi, J

2012-10-21

123

Efficient procedure for the numerical calculation of harmonic vibrational frequencies based on internal coordinates  

SciTech Connect

We propose a general procedure for the numerical calculation of the harmonic vibrational frequencies that is based on internal coordinates and Wilson’s GF methodology via double differentiation of the energy. The internal coordinates are defined as the geometrical parameters of a Z-matrix structure, thus avoiding issues related to their redundancy. Linear arrangements of atoms are described with a dummy atom of infinite mass. The procedure has been automated in FORTRAN90 and its main advantage lies in the nontrivial reduction of the number of single point energy calculations needed for the construction of the Hessian matrix when compared to the corresponding number using double differentiation in Cartesian coordinates. For molecules of C1 symmetry the computational savings amount to 36! ? 30, where N is the number of atoms, with additional savings when symmetry is present. Typical applications for small and medium size molecules in their minimum and transition state geometries as well as hydrogen bonded clusters are presented. In all cases the frequencies based on internal coordinates differ on average by < 1 cm-1 from those obtained from Cartesian coordinates.

Miliordos, Evangelos; Xantheas, Sotiris S.

2013-08-15

124

Real-Time Monitoring Of Regional Tissue Elasticity During FUS Focused Ultrasound Therapy Using Harmonic Motion Imaging  

NASA Astrophysics Data System (ADS)

The feasibility of the Harmonic Motion Imaging (HMI) technique for simultaneous monitoring and generation of focused ultrasound therapy using two separate focused ultrasound transducer elements has previously been shown. In this study, a new HMI technique is described that images tissue displacement induced by a harmonic radiation force induced using a single focused ultrasound element. First, wave propagation simulation models were used to compare the use of a single Amplitude-Modulated (AM) focused beam versus two overlapping focused beams as previously implemented for HMI. Simulation results indicated that, unlike in the two-beam configuration, the AM beam produced a consistent, stable focus for the applied harmonic radiation force. The AM beam thus offered the unique advantage of sustaining the application of the spatially-invariant radiation force. Experiments were then performed on gelatin gel phantoms and tissue in vitro bovine liver. The radiation force was generated by a 4.68 MHz focused transducer using a low-frequency Amplitude-Modulated (AM) RF-signal. RF data were acquired at 7.5 MHz with a PRF of 6.5 kHz and displacements were estimated using a 1D cross-correlation algorithm on successive RF signals. Furthermore, taking advantage of the real-time capability of our method, the change in the elastic properties was monitored during focused ultrasound (FUS) ablation of tissue in vitro bovine liver. Based on the harmonic displacements, their temperature-dependence, and the calculated acoustic radiation force, the change in the relative, regional stiffness could be monitored during heating and ablation, both using the displacement amplitude and the resulting phase shift change of the displacement relative to the radiation force temporal profile. In conclusion, the feasibility of using an AM radiation force for HMI for simultaneous monitoring and treatment during ultrasound therapy was demonstrated in phantoms and tissues in vitro. Further study of this method will include, ex vivo and in vivo, stiffness and temperature.

Maleke, Caroline; Pernot, Mathieu; Konofagou, Elisa

2006-05-01

125

Comparison of fundamental and wideband harmonic contrast imaging of liver tumors.  

PubMed

Wideband harmonic imaging (with phase inversion for improved tissue suppression) was compared to fundamental imaging in vivo. Four woodchucks with naturally occurring liver tumors were injected with Imagent (Alliance Pharmaceutical Corp., San Diego, CA). Randomized combinations of dose (0.05, 0.2 and 0.4 ml/kg) and acoustic output power (AO; 5, 25 and 63% or MI < or = 0.9) were imaged in gray scale using a Sonoline Elegra scanner (Siemens Medical Systems, Issaquah, WA). Tumor vascularity, conspicuity and contrast enhancement were rated by three independent observers. Imagent produced marked tumor enhancement and improved depiction of neovascularity at all dosages and AO settings in both modes. Tumor vascularity and enhancement correlated with mode, dose and AO (P < 0.002). Fundamental imaging produced more enhancement (P < 0.05), but tumor vascularity and conspicuity were best appreciated in harmonic mode (P < 0.05). Under the conditions studied here, the best approach was wideband harmonic imaging with 0.2 ml/kg of Imagent at an AO of 25%. PMID:10829639

Forsberg, F; Liu, J B; Chiou, H J; Rawool, N M; Parker, L; Goldberg, B B

2000-03-01

126

Imaging Jupiter Radiation Belts At Low Frequencies  

NASA Astrophysics Data System (ADS)

The ultra-relativistic electrons, trapped in the inner radiation belts of Jupiter, generates a strong synchrotron radio emission (historically known as the jovian decimeter radiation (DIM)) which is beamed, polarized (~20% linear, ~1% circular) and broadband. It has been extensively observed by radio telescopes/ probes and imaged by radio interferometers over a wide frequency spectrum (from >300 MHz up to 22 GHz). This extended emission presents two main emission peaks constantly located on both sides of the planet close to the magnetic plane. High latitude emissions were also regularly observed at particular frequencies, times and in particular observational configurations. This region of the magnetosphere is "frozen" due to the strong magnetic field (~4.2 G as the equator) and therefore is forced to rotate at the planetary period (T?9h55m). Due to the tilt (~ 10o) between the spin axis of the planet and the magnetic axis (which can be seen as dipolar in first approximation), the belts and the associated radio emission wobble around the planet center. The analysis of the flux at different frequencies highlighted spatial, temporal and spectral variabilities which origins are now partly understood. The emission varies at different time scales (short-time variations of hours to long-term variation over decades) due to the combination of visibility effect (wobbling, beaming, position of the observer in the magnetic rotating reference frame) [1], [2] and intrinsic local variations (interaction between relativistic electrons and satellites/dust, delayed effect of the solar wind ram pressure, impacts events) [3], [4], [5]. A complete framework is necessary to fully understand the source, loss and transport processes of the electrons originating from outside the belt, migrating by inward diffusion and populating the inner region of the magnetosphere. Only a few and unresolved measurements were made below 300 MHz and the nonsystematic observation of this radio emission, at different epochs only provided, each time, glimpses of the spectral content in different observational configurations. As the synchrotron emission frequency peaks at Vmax / E2B (with max in MHz, E, the electron energy in MeV and B, the magnetic field in Gauss), the low frequency content of this emission is associated with low energy electron populations inside the inner belt and the energetic electrons located in regions of weaker magnetic field (at few jovian radii). Therefore, there is much interest in extending and completing the current knowledge of the synchrotron emission from the belts, with low frequency resolved observations. LOFAR, the LOw Frequency ARray (LOFAR) [6], is a giant flexible and digital ground-based radio interferometer operating in the 30-250 MHz band. It brings very high time (~ ?s), frequency (~ kHz) and angular resolutions (~1") and huge sensitivity (mJy). In November 2011, a single 10-hour track enabled to cover an entire planetary rotation and led to the first resolved image of the radiation belts between 127- 172 MHz [7,8]. In Feb 2013, an 2×5h30 joint LOFAR/ WSRT observing campaign seized the state of the radiation belts from 45 MHz up to 5 GHz. We will present the current state of the study (imaging, reconstruction method and modeling) of the radiation belts dynamic with this current set of observations. LOFAR can contribute to the understanding of the physics taking place in the inner belt as well as possibly providing a fast and a systematic "diagnostic" of the state of the belts. The latter represents an opportunity to give context and ground-based support for the arrival of JUNO (NASA) scheduled in July 2016 and also for future missions, such as JUICE (ESA), at the vicinity of Jupiter by the exploration of its icy satellites.

Girard, J. N.; de Pater, I.; Zarka, P.; Santos-Costa, D.; Sault, R.; Hess, S.; Cecconi, B.; Fender, R.; Pewg, Lofar

2014-04-01

127

Pulse-modulated second harmonic imaging microscope quantitatively demonstrates marked increase of collagen in tumor after chemotherapy  

E-print Network

Pulse-modulated second harmonic imaging microscopes (PM-SHIMs) exhibit improved signal-to-noise ratio (SNR) over conventional SHIMs on sensitive imaging and quantification of weak collagen signals inside tissues. We quantify ...

Raja, Anju M.

128

Frequency-domain interpretation of the plateaus in laser-assisted recombination and high-order harmonic generation  

NASA Astrophysics Data System (ADS)

The plateaus in laser-assisted recombination and high-order harmonic generation are investigated in the frequency domain. It is found that the probability amplitude of finding an electron with a given energy is given by a generalized Bessel function, which can be represented as a coherent superposition of contributions from a few electronic quantum trajectories. This concept is illustrated by comparing the spectral density of the electron with the laser-assisted recombination spectrum. On the other hand, the plateau of high-order harmonic generation reflects the spectral density of the electron at the location of the nucleus after above-threshold ionization.

Cheng, Taiwang; Li, Xiaofeng; Ao, Shuyan; Wu, Ling-An; Fu, Panming

2003-09-01

129

Contrast-enhanced harmonic endoscopic ultrasound imaging: Basic principles, present situation and future perspectives  

PubMed Central

Over the last decade, the development of stabilised microbubble contrast agents and improvements in available ultrasonic equipment, such as harmonic imaging, have enabled us to display microbubble enhancements on a greyscale with optimal contrast and spatial resolution. Recent technological advances made contrast harmonic technology available for endoscopic ultrasound (EUS) for the first time in 2008. Thus, the evaluation of microcirculation is now feasible with EUS, prompting the evolution of contrast-enhanced EUS from vascular imaging to images of the perfused tissue. Although the relevant experience is still preliminary, several reports have highlighted contrast-enhanced harmonic EUS (CH-EUS) as a promising noninvasive method to visualise and characterise lesions and to differentiate benign from malignant focal lesions. Even if histology remains the gold standard, the combination of CH-EUS and EUS fine needle aspiration (EUS-FNA) can not only render EUS more accurate but may also assist physicians in making decisions when EUS-FNA is inconclusive, increasing the yield of EUS-FNA by guiding the puncture with simultaneous imaging of the vascularity. The development of CH-EUS has also opened up exciting possibilities in other research areas, including monitoring responses to anticancer chemotherapy or to ethanol-induced pancreatic tissue ablation, anticancer therapies based on ultrasound-triggered drug and gene delivery, and therapeutic adjuvants by contrast ultrasound-induced apoptosis. Contrast harmonic imaging is gaining popularity because of its efficacy, simplicity and non-invasive nature, and many expectations are currently resting on this technique. If its potential is confirmed in the near future, contrast harmonic imaging will become a standard practice in EUS. PMID:25400439

Alvarez-Sánchez, María-Victoria; Napoléon, Bertrand

2014-01-01

130

Three-dimensional high-resolution second-harmonic generation imaging of endogenous structural proteins in biological tissues.  

PubMed

We find that several key endogenous protein structures give rise to intense second-harmonic generation (SHG)-nonabsorptive frequency doubling of an excitation laser line. Second-harmonic imaging microscopy (SHIM) on a laser-scanning system proves, therefore, to be a powerful and unique tool for high-resolution, high-contrast, three-dimensional studies of live cell and tissue architecture. Unlike fluorescence, SHG suffers no inherent photobleaching or toxicity and does not require exogenous labels. Unlike polarization microscopy, SHIM provides intrinsic confocality and deep sectioning in complex tissues. In this study, we demonstrate the clarity of SHIM optical sectioning within unfixed, unstained thick specimens. SHIM and two-photon excited fluorescence (TPEF) were combined in a dual-mode nonlinear microscopy to elucidate the molecular sources of SHG in live cells and tissues. SHG arose not only from coiled-coil complexes within connective tissues and muscle thick filaments, but also from microtubule arrays within interphase and mitotic cells. Both polarization dependence and a local symmetry cancellation effect of SHG allowed the signal from species generating the second harmonic to be decoded, by ratiometric correlation with TPEF, to yield information on local structure below optical resolution. The physical origin of SHG within these tissues is addressed and is attributed to the laser interaction with dipolar protein structures that is enhanced by the intrinsic chirality of the protein helices. PMID:11751336

Campagnola, Paul J; Millard, Andrew C; Terasaki, Mark; Hoppe, Pamela E; Malone, Christian J; Mohler, William A

2002-01-01

131

High-resolution imaging of a corneal incision by second- and third-harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

We demonstrate high spatial resolution imaging of a stromal cut in the ex-vivo pig cornea, using second- and third-harmonic generation microscopy. From these images, we see in detail how the cut affects the corneal layers. In the beginning of the cut, the anterior layers, in which the blade is passing through, are disorganized, which could explain the shadows observed on the images. In the stroma, the cut can be imaged by third harmonic microscopy, probably due to the ?3 contrast. Although the current results were obtained from the healthy ex-vivo cornea, it already allows one to understand the effects of the cut on the tissue characteristics (such as scattering).

Jay, L.; Dion, C.; Brocas, A.; Singh, K.; Kieffer, J.-C.; Brunette, I.; Ozaki, T.

2010-02-01

132

Image enhancement by non-linear extrapolation in frequency space  

NASA Technical Reports Server (NTRS)

An input image is enhanced to include spatial frequency components having frequencies higher than those in an input image. To this end, an edge map is generated from the input image using a high band pass filtering technique. An enhancing map is subsequently generated from the edge map, with the enhanced map having spatial frequencies exceeding an initial maximum spatial frequency of the input image. The enhanced map is generated by applying a non-linear operator to the edge map in a manner which preserves the phase transitions of the edges of the input image. The enhanced map is added to the input image to achieve a resulting image having spatial frequencies greater than those in the input image. Simplicity of computations and ease of implementation allow for image sharpening after enlargement and for real-time applications such as videophones, advanced definition television, zooming, and restoration of old motion pictures.

Anderson, Charles H. (Inventor); Greenspan, Hayit K. (Inventor)

1998-01-01

133

The effect of Neel relaxation on the properties of the third harmonic signal of magnetic nanoparticles for use in narrow-band magnetic nanoparticle imaging  

NASA Astrophysics Data System (ADS)

We study the third harmonic signal of magnetic nanoparticles (MNPs) for use in narrow-band magnetic nanoparticle imaging. We measured the properties of the third harmonic signal, such as frequency and magnetic field dependencies, when the behavior of MNPs was dominated by Neel relaxation. It was shown that the third harmonic signal had both real and imaginary parts, although only the real part is expected from the conventional Langevin function. The real and imaginary parts exhibited different dependences on the frequency and magnetic field. The dynamic behavior of MNPs was analyzed by taking into account the Neel relaxation of MNPs. It was shown that the imaginary part was generated due to Neel relaxation. We obtain an analytical expression for the third harmonic signal, in which distributions of magnetic moment and anisotropic energy of MNPs in the sample were also considered. We show that the analytical results quantitatively explain the experimental results. Our results indicate that the properties of the third harmonic signal of immobilized MNPs are significantly affected by Neel relaxation.

Enpuku, Keiji; Bai, Shi; Hirokawa, Aiki; Tanabe, Kazuhiro; Sasayama, Teruyoshi; Yoshida, Takashi

2014-10-01

134

Low switching frequency active harmonic elimination in multilevel converters with unequal DC voltages  

Microsoft Academic Search

This paper presents an active harmonic elimination modulation control method for the cascaded H-bridges multilevel converter when supplied by unequal DC sources. First, the multilevel converter is decoupled into individual unipolar converters, and the low order harmonics (such as the 5th, 7th, 11th, and 13th) are eliminated by using resultant theory while at the same time the minimum specified harmonic

Zhong Du; Leon M. Tolbert; John N. Chiasson; Hui Li

2005-01-01

135

Graphics processing unit-based quantitative second-harmonic generation imaging.  

PubMed

We adapt a graphics processing unit (GPU) to dynamic quantitative second-harmonic generation imaging. We demonstrate the temporal advantage of the GPU-based approach by computing the number of frames analyzed per second from SHG image videos showing varying fiber orientations. In comparison to our previously reported CPU-based approach, our GPU-based image analysis results in ?10× improvement in computational time. This work can be adapted to other quantitative, nonlinear imaging techniques and provides a significant step toward obtaining quantitative information from fast in vivo biological processes. PMID:25223706

Kabir, Mohammad Mahfuzul; Jonayat, A S M; Patel, Sanjay; Toussaint, Kimani C

2014-09-01

136

Graphics processing unit-based quantitative second-harmonic generation imaging  

NASA Astrophysics Data System (ADS)

We adapt a graphics processing unit (GPU) to dynamic quantitative second-harmonic generation imaging. We demonstrate the temporal advantage of the GPU-based approach by computing the number of frames analyzed per second from SHG image videos showing varying fiber orientations. In comparison to our previously reported CPU-based approach, our GPU-based image analysis results in ˜10× improvement in computational time. This work can be adapted to other quantitative, nonlinear imaging techniques and provides a significant step toward obtaining quantitative information from fast in vivo biological processes.

Kabir, Mohammad Mahfuzul; Jonayat, ASM; Patel, Sanjay; Toussaint, Kimani C., Jr.

2014-09-01

137

Long-term imaging of mouse embryos using adaptive harmonic generation microscopy  

PubMed Central

We present a detailed description of an adaptive harmonic generation (HG) microscope and culture techniques that permit long-term, three-dimensional imaging of mouse embryos. HG signal from both pre- and postimplantation stage (0.5–5.5 day-old) mouse embryos are fully characterized. The second HG images reveal central spindles during cytokinesis whereas third HG images show several features, such as lipid droplets, nucleoli, and plasma membranes. The embryos are found to develop normally during one-day-long discontinuous HG imaging, permitting the observation of several dynamic events, such as morula compaction and blastocyst formation. PMID:21529087

Thayil, Anisha; Watanabe, Tomoko; Jesacher, Alexander; Wilson, Tony; Srinivas, Shankar; Booth, Martin

2012-01-01

138

Sum frequency and second harmonic generation from the surface of a liquid microjet.  

PubMed

The use of a liquid microjet as a possible source of interest for Second Harmonic Generation (SHG) and Sum Frequency Generation (SFG) spectroscopy is examined. We measured non-resonant SHG scattering patterns from the air/water interface of a microjet of pure water and observe a strong enhancement of the SHG signal for certain scattering angles. These enhancements can be explained by the optical properties and the shape of the liquid microjet. SFG experiments at the surface of a liquid microjet of ethanol in air show that it is also possible to measure the coherent vibrational SFG spectrum of the ethanol/air interface in this way. Our findings are useful for future far-UV or X-ray based nonlinear optical surface experiments on liquid jets. In addition, combined X-ray photoelectron spectroscopy and SHG/SFG measurements are feasible, which will be very useful in improving our understanding of the molecular foundations of electrostatic and chemical surface properties and phenomena. PMID:25399189

Smolentsev, Nikolay; Chen, Yixing; Jena, Kailash C; Brown, Matthew A; Roke, Sylvie

2014-11-14

139

A Spectral Finite Element Approach to Modeling Soft Solids Excited with High-Frequency Harmonic Loads  

PubMed Central

An approach for efficient and accurate finite element analysis of harmonically excited soft solids using high-order spectral finite elements is presented and evaluated. The Helmholtz-type equations used to model such systems suffer from additional numerical error known as pollution when excitation frequency becomes high relative to stiffness (i.e. high wave number), which is the case, for example, for soft tissues subject to ultrasound excitations. The use of high-order polynomial elements allows for a reduction in this pollution error, but requires additional consideration to counteract Runge's phenomenon and/or poor linear system conditioning, which has led to the use of spectral element approaches. This work examines in detail the computational benefits and practical applicability of high-order spectral elements for such problems. The spectral elements examined are tensor product elements (i.e. quad or brick elements) of high-order Lagrangian polynomials with non-uniformly distributed Gauss-Lobatto-Legendre nodal points. A shear plane wave example is presented to show the dependence of the accuracy and computational expense of high-order elements on wave number. Then, a convergence study for a viscoelastic acoustic-structure interaction finite element model of an actual ultrasound driven vibroacoustic experiment is shown. The number of degrees of freedom required for a given accuracy level was found to consistently decrease with increasing element order. However, the computationally optimal element order was found to strongly depend on the wave number. PMID:21461402

Brigham, John C.; Aquino, Wilkins; Aguilo, Miguel A.; Diamessis, Peter J.

2010-01-01

140

Sum frequency and second harmonic generation from the surface of a liquid microjet  

NASA Astrophysics Data System (ADS)

The use of a liquid microjet as a possible source of interest for Second Harmonic Generation (SHG) and Sum Frequency Generation (SFG) spectroscopy is examined. We measured non-resonant SHG scattering patterns from the air/water interface of a microjet of pure water and observe a strong enhancement of the SHG signal for certain scattering angles. These enhancements can be explained by the optical properties and the shape of the liquid microjet. SFG experiments at the surface of a liquid microjet of ethanol in air show that it is also possible to measure the coherent vibrational SFG spectrum of the ethanol/air interface in this way. Our findings are useful for future far-UV or X-ray based nonlinear optical surface experiments on liquid jets. In addition, combined X-ray photoelectron spectroscopy and SHG/SFG measurements are feasible, which will be very useful in improving our understanding of the molecular foundations of electrostatic and chemical surface properties and phenomena.

Smolentsev, Nikolay; Chen, Yixing; Jena, Kailash C.; Brown, Matthew A.; Roke, Sylvie

2014-11-01

141

Imaging nanometer-thick patterned self-assembled monolayers via second-harmonic generation microscopy  

SciTech Connect

We have used the inherent surface sensitivity of second-harmonic generation to develop an instrument for nonlinear optical microscopy of surfaces and interfaces. This optical technique is ideal for imaging nanometer-thick, chromophoric self-assembled monolayers (SAMs), which have been patterned using photolithographic techniques. In this paper, we demonstrate the application of second-harmonic generation microscopy to patterned SAMs of the noncentrosymmetric molecule calixarene and discuss the resolution and sensitivity limits of the technique. {copyright} {ital 1997 American Institute of Physics.}

Smilowitz, L.; Jia, Q.X.; Yang, X.; Li, D.Q.; McBranch, D.; Buelow, S.J.; Robinson, J.M. [Chemical Sciences and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Chemical Sciences and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1997-03-01

142

Towards Real-Time High Frequency Ultrasound Imaging of Cells  

E-print Network

-thinning of lithium Niobate wafers for devices for high-frequency medical ultrasound imaging Srikanta Sharma, Jim McTowards Real-Time High Frequency Ultrasound Imaging of Cells Srikanta Sharma Academic supervisor;Research Aims · To develop a real time high frequency (up to 500 MHz) ultrasound scanning Bio

Greenaway, Alan

143

Application of frequency-domain interferometry in the extreme-ultraviolet range by use of high-order harmonics  

NASA Astrophysics Data System (ADS)

We apply the frequency-domain interferometry technique in the extreme-ultraviolet (XUV) range using high-order harmonics. The technique is first used to study the influence of ionization of the generating gas on the harmonic emission. We report a thorough study of the fringe contrast as a function of the generating parameters: gas pressure, laser intensity and focus position, harmonic order, delay, and relative intensity of the two laser pulses. We show that two phase-locked time-delayed harmonic pulses can be produced under optimal conditions. However, a strong distortion of the fringe pattern (low contrast and large asymmetry) can be induced by the deleterious effects of the medium ionization, i.e., depletion of the emitters, laser defocusing, and loss of mutual coherence that is due to free-electron dispersion. XUV frequency-domain interferometry is then applied to the measurement of the electron density of a plasma created by optical field-induced ionization of a high-pressure helium jet by use of an intense short-pulse laser. The measured temporal evolution of the electron density shows that the resolution of our experimental setup was of the order of 200 fs, which, to our knowledge, provides the first XUV interferometry measurement on a femtosecond time scale.

Hergott, Jean-Francois; Auguste, Thierry; Salières, Pascal; Le Déroff, Laurent; Monot, Pascal; D'Oliveira, Pascal; Campo, David; Merdji, Hamed; Carré, Bertrand

2003-01-01

144

High-order harmonic spectroscopy for molecular imaging of polyatomic molecules.  

PubMed

High-order harmonic generation is a powerful and sensitive tool for probing atomic and molecular structures, combining in the same measurement an unprecedented attosecond temporal resolution with a high spatial resolution of the order of an angstrom. Imaging of the outermost molecular orbital by high-order harmonic generation has been limited for a long time to very simple molecules, like nitrogen. Recently we demonstrated a technique that overcame several of the issues that have prevented the extension of molecular orbital tomography to more complex species, showing that molecular imaging can be applied to a triatomic molecule like carbon dioxide. Here we report on the application of such a technique to nitrous oxide (N2O) and acetylene (C2H2). This result represents a first step towards the imaging of fragile compounds, a category which includes most of the fundamental biological molecules. PMID:25415258

Negro, M; Devetta, M; Faccialá, D; De Silvestri, S; Vozzi, C; Stagira, S

2014-01-01

145

Design of Active Integrated Antenna for Dual Frequency Image Rejection  

Microsoft Academic Search

This paper is discusses a new configuration of integrated antenna for dual frequency operations and image frequency rejection. Microstrip patch antenna is design in such away to operate in dual frequencies band. The RF 90° hybrid, LNA's, mixers, LO and IF coupler are integrated to a dual frequency microstrip patch antenna to produce a single module of integrated antenna system

Sohiful Anuar Zainol Murad; Widad Ismail

2006-01-01

146

Label-free three-dimensional imaging of cell nucleus using third-harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

We report the implementation of the combined third-harmonic generation (THG) and two-photon excited fluorescence (TPEF) microscopy for label-free three-dimensional (3-D) imaging of cell nucleus morphological changes in liver tissue. THG imaging shows regular spherical shapes of normal hepatocytes nuclei with inner chromatin structures while revealing the condensation of chromatins and nuclear fragmentations in hepatocytes of diseased liver tissue. Colocalized THG and TPEF imaging provides complementary information of cell nuclei and cytoplasm in tissue. This work suggests that 3-D THG microscopy has the potential for quantitative analysis of nuclear morphology in cells at a submicron-resolution without the need for DNA staining.

Lin, Jian; Zheng, Wei; Wang, Zi; Huang, Zhiwei

2014-09-01

147

Application of abstract harmonic analysis to the high-speed recognition of images  

NASA Technical Reports Server (NTRS)

Methods are constructed for rapidly computing correlation functions using the theory of abstract harmonic analysis. The theory developed includes as a particular case the familiar Fourier transform method for a correlation function which makes it possible to find images which are independent of their translation in the plane. Two examples of the application of the general theory described are the search for images, independent of their rotation and scale, and the search for images which are independent of their translations and rotations in the plane.

Usikov, D. A.

1979-01-01

148

Frequency-resolved optical gating with the use of second-harmonic generation  

SciTech Connect

We discuss the use of second-harmonic generation (SHG) as the nonlinearity in the technique of frequency-resolved optical gating (FROG) for measuring the full intensity and phase evolution of an arbitrary ultrashort pulse. FROG that uses a third-order nonlinearity in the polarization-gate geometry has proved extremely successful, and the algorithm required for extraction of the intensity and the phase from the experimental data is quite robust. However, for pulse intensities less than [similar to] 1 MW, third-order nonlinearities generate insufficient signal strength, and therefore SHG FROG appears necessary. We discuss the theoretical, algorithmic, and experimental considerations of SHG FROG in detail. SHG FROG has an ambiguity in the direction of time, and its traces are somewhat unintuitive. Also, previously published algorithms are generally ineffective at extracting the intensity and the phase of an arbitrary laser pulse from the SHG FROG trace. We present an improved pulse-retrieval algorithm, based on the method of generalized projections, that is far superior to the previously published algorithms, although it is still not so robust as the polarization-gate algorithm. We discuss experimental sources of error such as pump depletion and group-velocity mismatch. We also present several experimental examples of pulses measured with SHG FROG and show that the derived intensities and phases are in agreement with more conventional diagnostic techniques, and we demonstrate the high-dynamic-range capability of SHG FROG. We conclude that, despite the above drawbacks, SHG FROG should be useful in measuring low-energy pulses.

DeLong, K.W.; Trebino, R. (Combustion Research Facility, MS-9057, Sandia National Laboratories, Livermore, California 94551-0969 (United States)); Hunter, J.; White, W.E. (Lawrence Livermore National Laboratory, Livermore, California 94550 (United States))

1994-11-01

149

Spectral imaging of breast fibroadenoma using second-harmonic generation  

NASA Astrophysics Data System (ADS)

Fibroadenoma (FA), typically composed of stroma and epithelial cells, is a very common benign breast disease. Women with FA are associated with an increased risk of future breast cancer. The objective of this study was to demonstrate the potential of multiphoton laser scanning microscopy (MPLSM) for characterizing the morphology of collagen in the human breast fibroadenomas. In the study, high-contrast SHG images of human normal breast tissues and fibroadenoma tissues were obtained for comparison. The morphology of collagen was different between normal breast tissue and fibroadenoma. This study shows that MPLSM has the ability to distinguish fibroadenoma tissues from the normal breast tissues based on the noninvasive SHG imaging. With the advent of the clinical portability of miniature MPLSM, we believe that the technique has great potential to be used in vivo studies and for monitoring the treatment responses of fibroadenomas in clinical.

Zheng, Liqin; Wang, Yuhua

2014-09-01

150

A Multivariate, Multitaper Approach to Detecting and Estimating Harmonic Response in Cortical Optical Imaging Data  

PubMed Central

The efficiency and accuracy of cortical maps from optical imaging experiments have been improved using periodic stimulation protocols. The resulting data analysis requires the detection and estimation of periodic information in a multivariate dataset. To date, these analyses have relied on discrete Fourier transform (DFT) sinusoid estimates. Multitaper methods have become common statistical tools in the analysis of univariate time series that can give improved estimates. Here, we extend univariate multitaper harmonic analysis methods to the multivariate, imaging context. Given the hypothesis that a coherent oscillation across many pixels exists within a specified bandwidth, we investigate the problem of its detection and estimation in noisy data by constructing Hotelling’s generalized T2-test. We then extend the investigation of this problem in two contexts, that of standard Canonical Variate Analysis (CVA) and that of Generalized Indicator Function Analysis (GIFA) which is often more robust in extracting a signal in spatially correlated noise. We provide detailed information on the fidelities of the mean estimates found with our methods and comparison with DFT estimates. Our results indicate that GIFA provides particularly good estimates of harmonic signals in spatially correlated noise and is useful for detecting small amplitude harmonic signals in applications such as biological imaging measurements where spatially correlated noise is common. We demonstrate the power of our methods with an optical imaging dataset of the periodic response to a periodically rotating oriented drifting grating stimulus experiment in cat visual cortex. PMID:21970814

Sornborger, A.T.; Yokoo, T.

2011-01-01

151

Assessment of harmonic source correction for ultrasound medical imaging  

NASA Astrophysics Data System (ADS)

Tissue velocity and attenuation inhomogeneities reduce ultrasound image quality in many patients. Over the years a number of methods have been developed to estimate the corrective delays necessary for phase aberration correction. Past methods were based on assumptions of the target or required a separate transducer acting as a transponder point source. A method is proposed which creates a known acoustical source in the tissue suitable for wavefront correction without a priori assumptions of the target or requiring a point source transponder. This method was tested with multiple electronically produced aberrations with RMS focusing errors of 0.25? radians, 0.44? radians, and 0.87? radians at 4.17 MHz. These aberrators were corrected using excised pork kidneys and on the left kidney of human volunteers as targets. Waveform correction on pork kidney led to an improvement in imaging beam amplitude and side-lobe level. Waveform correction on human subjects for a 0.87? radians RMS error aberrator led to a 15.4 dB improvement in imaging beam amplitude and an 11.8 dB improvement in side-lobe level. This method shows promise of overcoming the limitations of previous phase correction methods.

Dianis, Scott W.; von Ramm, Olaf T.

2010-03-01

152

Spatial and energy parameters of laser radiation and second harmonic upon self-frequency doubling  

SciTech Connect

The intracavity second-harmonic generation of laser radiation in an active nonlinear crystal is studied. The spatial distributions of the intensity and power of laser radiation and its second harmonic are calculated by the method of numerical simulations as functions of the parameters of the resonator, active nonlinear crystal, and pump. The analysis is performed for a periodically poled Nd:Mg:LiNbO{sub 3} crystal taking diffraction into account. (active media. lasers)

Laptev, G D [International Laser Center, M. V. Lomonosov Moscow State University, Moscow (Russian Federation); Novikov, Aleksei A; Chirkin, Anatolii S [Department of Physics, M.V. Lomonosov Moscow State University, Moscow (Russian Federation)

2005-01-31

153

Standing Waves and Harmonics In this laboratory exercise you will explore how the frequency of a wave and the stretching force applied to a  

E-print Network

Standing Waves and Harmonics Purpose In this laboratory exercise you will explore how the frequency of a wave and the stretching force applied to a string affects the speed of the wave in a vibrating string

Yu, Jaehoon

154

Coherent control and giant enhancement of multiphoton ionization and high-order-harmonic generation driven by intense frequency-comb laser fields: An ab initio theoretical investigation  

E-print Network

We present an ab initio theoretical investigation of the coherent control and significant enhancement of multiphoton ionization (MPI) and high-order-harmonic generation (HHG) of atoms and molecules by means of intense frequency-comb laser fields. We...

Chu, Shih-I; Zhao, Di; Li, Fu-li

2013-04-11

155

Analyzing Image Structure by Multidimensional Frequency Modulation  

E-print Network

images. Previous papers have detailed methods for achiev- ing relevant AM-FM demodulation, namely-Modu- lation (AM-FM) image model, which models nonstationary image content using an AM-FM expansion. By way shows a woodgrain. Both images are excellent examples of emergent AM-FM patterns. Nonstationarity

Texas at Austin, University of

156

Lensless Diffractive Imaging Using Tabletop Coherent High-Harmonic Soft-X-Ray Beams  

SciTech Connect

We present the first experimental demonstration of lensless diffractive imaging using coherent soft x rays generated by a tabletop soft-x-ray source. A 29 nm high harmonic beam illuminates an object, and the subsequent diffraction is collected on an x-ray CCD camera. High dynamic range diffraction patterns are obtained by taking multiple exposures while blocking small-angle diffraction using beam blocks of varying size. These patterns reconstruct to images with 214 nm resolution. This work demonstrates a practical tabletop lensless microscope that promises to find applications in materials science, nanoscience, and biology.

Sandberg, Richard L.; Paul, Ariel; Raymondson, Daisy A.; Haedrich, Steffen; Gaudiosi, David M.; Holtsnider, Jim; Tobey, Ra'anan I.; Cohen, Oren; Murnane, Margaret M.; Kapteyn, Henry C.; Song, Changyong; Miao Jianwei; Liu Yanwei; Salmassi, Farhad [JILA and Department of Physics, University of Colorado and NSF Engineering Research Center in Extreme Ultraviolet Science and Technology, Boulder, Colorado 80309 (United States); Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States); Center for X-Ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2007-08-31

157

Chiral imaging of collagen by second-harmonic generation circular dichroism  

PubMed Central

We provide evidence that the chirality of collagen can give rise to strong second-harmonic generation circular dichroism (SHG-CD) responses in nonlinear microscopy. Although chirality is an intrinsic structural property of collagen, most of the previous studies ignore that property. We demonstrate chiral imaging of individual collagen fibers by using a laser scanning microscope and type-I collagen from pig ligaments. 100% contrast level of SHG-CD is achieved with sub-micrometer spatial resolution. As a new contrast mechanism for imaging chiral structures in bio-tissues, this technique provides information about collagen morphology and three-dimensional orientation of collagen molecules. PMID:23761852

Lee, H.; Huttunen, M. J.; Hsu, K.-J.; Partanen, M.; Zhuo, G.-Y.; Kauranen, M.; Chu, S.-W.

2013-01-01

158

Texture analysis applied to second harmonic generation image data for ovarian cancer classification  

NASA Astrophysics Data System (ADS)

Remodeling of the extracellular matrix has been implicated in ovarian cancer. To quantitate the remodeling, we implement a form of texture analysis to delineate the collagen fibrillar morphology observed in second harmonic generation microscopy images of human normal and high grade malignant ovarian tissues. In the learning stage, a dictionary of "textons"-frequently occurring texture features that are identified by measuring the image response to a filter bank of various shapes, sizes, and orientations-is created. By calculating a representative model based on the texton distribution for each tissue type using a training set of respective second harmonic generation images, we then perform classification between images of normal and high grade malignant ovarian tissues. By optimizing the number of textons and nearest neighbors, we achieved classification accuracy up to 97% based on the area under receiver operating characteristic curves (true positives versus false positives). The local analysis algorithm is a more general method to probe rapidly changing fibrillar morphologies than global analyses such as FFT. It is also more versatile than other texture approaches as the filter bank can be highly tailored to specific applications (e.g., different disease states) by creating customized libraries based on common image features.

Wen, Bruce L.; Brewer, Molly A.; Nadiarnykh, Oleg; Hocker, James; Singh, Vikas; Mackie, Thomas R.; Campagnola, Paul J.

2014-09-01

159

Theory of electron cyclotron maser interaction in a cavity at the harmonic frequencies  

Microsoft Academic Search

A theory of the cyclotron maser interaction between an annular electron beam and the standing electromagnetic wave in a cavity structure is formulated on the basis of the relativistic Vlasov equation and the Maxwell equations. Detailed analytical expressions for the beam-wave coupling coefficient, beam energy gain, and threshold beam power have been derived for the fundamental and higher cyclotron harmonics.

K. R. Chu

1978-01-01

160

Extra Low-Frequency Terrestrial Radio-Wave Field Calculations with the Zonal Harmonics Series  

Microsoft Academic Search

Use of the zonal harmonics series for calculating the terrestrial wave guide fields directly is described. The analysis is extended to include radio waves propagating into sea water or below the earth's surface. A sample calculation of ELF radio waves is analyzed into a direct wave and a wave that has traveled the circumference of the earth. The location of

J. Ralph Johler; Richard L. Lewis

1969-01-01

161

Modulation Extension Control for Multilevel Converters Using Triplen Harmonic Injection with Low Switching Frequency  

E-print Network

was implemented with an 11-level H-bridge multilevel converter and an 8µs control resolution to demonstrateModulation Extension Control for Multilevel Converters Using Triplen Harmonic Injection with Low@utk.edu Abstract--This paper presents a modulation extension control method for multilevel converters with low

Tolbert, Leon M.

162

Harmonic wave analysis of conductor corona current based on wide frequency band measurement  

Microsoft Academic Search

Corona current is one of important corona characteristic research contents. In order to analyze conductor corona current harmonic wave characteristic, a corona current measurement system is developed. The synchronous collect of the voltage and current signal is realized by the GPS technology. The corona current signal is transmitted to the lower computer through the wireless network. And the current signal

Fangcheng Lu; Shaohua You; Yunpeng Liu; Lei Zhu

2011-01-01

163

The utilization of the bubble pressure dependent harmonic resonance frequency for enhanced heating during high intensity focused ultrasound treatments  

NASA Astrophysics Data System (ADS)

The use of bubbles in High Intensity Focused Ultrasound (HIFU) enhances tissue heating; however, localization of the treatment is difficult due to harmful effects at non-focal regions. In this study the bubble dynamics were studied through the utilization of resonance curves and bifurcation diagrams of the normalized bubble oscillation amplitude (NBOA) (time varying radius/initial radius) by solving the Hoff model. This method allowed us to study the bubble dynamics in wide ranges of control parameters. Results indicate that, by sonicating the bubbles with their pressure dependent harmonic resonance frequency (e.g. 3.1 MHz for a 5 micron bubble with shell shear modulus of 50 MPa and 100nm thickness), the (NBOA) is negligible below a threshold pressure (PT) (˜1.5 MPa). For pressures above the PT, the NBOA increases and remains constant for a large pressure range concomitant with a significant increase in higher harmonic emissions. Because of the steep spatial pressure gradient of the HIFU transducer, the non-focal bubbles will be non-resonant as the non-focal pressure is below the PT. Therefore, the undesirable effects of non-focal bubbles will be minimized. The resonant bubbles at the focal region are stable (NBOA<1.4) and radiate significant harmonics thus providing a long lasting controllable enhanced heating.

Sojahrood, Amin Jafari; Kolios, Michael C.

2012-10-01

164

[Second- and third-harmonic generation microscopies for the structural imaging of intact tissues].  

PubMed

One principal advantage of multiphoton excitation microscopy is that it preserves its three-dimensional micrometer resolution when imaging inside light-scattering samples. For that reason two-photon-excited fluorescence microscopy has become an invaluable tool for cellular imaging in intact tissue, with applications in many fields of physiology. This success has driven increasing interest in other forms of nonlinear microscopy that can provide additional information on cells and tissues, such as second- (SHG) and third- (THG) harmonic generation microscopies. In recent years, significant progress has been made in understanding the contrast mechanisms of these recent methodologies, and high-resolution imaging based on intrinsic sources of signal has been demonstrated in cells and tissues. Harmonic generation exhibits structural rather than chemical specificity and can be obtained from a variety of non-fluorescent samples. SHG is observed specifically in dense, non-centrosymmetric arrangements of polarizable molecules, such as collagen fibrils, myofilaments, and polarized microtubule bundles. SHG imaging is therefore emerging as a novel approach for studying processes such as the physiopathological remodelling of the collagen matrix and myofibrillogenesis in intact tissue. THG does not require a non-centrosymmetric system ; however no signal can be obtained from a homogeneous medium. THG imaging therefore provides maps of sub-micrometer heterogeneities (interfaces, inclusions) in unstained samples, and can be used as a general purpose structural imaging tool. Recent studies showed that this technique can be used to image embryo development in small organisms and to characterize the accumulation of large lipid bodies in specialized cells. SHG and THG microscopy both rely on femtosecond laser technology and are easily combined with two-photon microscopy. PMID:17026938

Débarre, Delphine; Pena, Ana-Maria; Supatto, Willy; Boulesteix, Thierry; Strupler, Mathias; Sauviat, Martin-Pierre; Martin, Jean-Louis; Schanne-Klein, Marie-Claire; Beaurepaire, Emmanuel

2006-10-01

165

Time and structural crosscorrelation image analysis of microscopic volumes, simultaneously recorded with second harmonic generation, third harmonic generation, and multiphoton excitation fluorescence microscopy  

NASA Astrophysics Data System (ADS)

Our newly developed multimodal microscope enables simultaneous collection of second harmonic generation (SHG), third harmonic generation (THG) and multiphoton excitation fluorescence (MPF) signals. The signals can be generated within different or the same intercellular structures. In comparing two signals, traditional methods of image crosscorrelation analysis using Pearson's coefficient provide a general parameter as to whether the images are similar, however it does not give detailed information about correlation of different structures inside the images. We present here a new technique that employs a pixel by pixel analysis over an entire area or volume that is used to correlate the structures appearing in the images. The result of the analysis reveals structures within the sample that are generated by both nonlinear signals as well as highlighting the structures that are generated by only one of the nonlinear signals. The algorithm provides a means to colocalize different structures revealed by the different nonlinear contrast mechanisms. Structural correlation maps are useful in identifying the origin of structures in one nonlinear contrast mechanism when the origin of structures in another is known. Image analysis has also been exploited for sequences of images taken in time. The intensity fluctuations in time for each pixel reveal regions of intense physiological activity in biological samples. Correlation of time dependent fluctuations from different pixels in the image time series allows construction of the structural map that undergoes similar time behavior or appears out of phase. These structural correlation analysis techniques are demonstrated based on polystyrene beads and cardiomyocytes.

Greenhalgh, Catherine; Cisek, Richard; Prent, Nicole; Major, Arkady; Aus de Au, Juerg; Squier, Jeff; Barzda, Virginijus

2005-09-01

166

Sonographic Evaluation of Breast Nodules: Comparison of Conventional, Real-Time Compound, and Pulse-Inversion Harmonic Images  

PubMed Central

Objective To compare the use of conventional, real-time compound, and pulse-inversion harmonic imaging in the evaluation of breast nodules. Materials and Methods Fifty-two breast nodules were included in this study, conducted between May and December 2000, in which conventional, real-time compound, and pulse-inversion harmonic images were obtained in the same plane. Three radiologists, each blinded to the interpretations of the other two, evaluated the findings, characterizing the lesions and ranking the three techniques from grade 1, the worst, to grade 3, the best. Lesion conspicuity was assessed, and lesions were also characterized in terms of their margin, clarity of internal echotexture, and clarity of posterior echo pattern. The three techniques were compared using Friedman's test, and interobserver agreement in image interpretation was assessed by means of the intraclass correlation coefficient. Results With regard to lesion conspicuity, margin, and internal echotexture of the nodules, real-time compound imaging was the best technique (p < 0.05); in terms of posterior echo pattern, the best was pulse-inversion harmonic imaging (p < 0.05). Real-time compound and pulse inversion harmonic imaging were better than conventional sonography in all evaluative aspects. Interobserver agreement was greater than moderate. Conclusion Real-time compound and pulse-inversion harmonic imaging procedures are superior to conventional sonography in terms of both lesion conspicuity and the further characterization of breast nodules. Real-time compound imaging is the best technique for evaluation of the margin and internal echotexture of nodules, while pulse-inversion harmonic imaging is very effective for the evaluation of the posterior echo patterns. PMID:11919477

Seo, Bo-Kyoung; Oh, Yu Whan; Kim, Hyung Rae; Kim, Hong Weon; Kang, Chang Ho; Lee, Nam Joon; Kim, Jung Hyuk; Park, Bum Jin; Cho, Kyu Ran; Lee, June Young; Lee, Ki Yeoul; Bae, Jeoung Won

2002-01-01

167

Frequency Synthesizers and Oscillator Architectures Based on Multi-Order Harmonic Generation  

E-print Network

present new techniques and architectures for implementing high speed frequency synthesizers which fulfill the aforementioned requirements. We propose a new architecture and design approach for the realization of wideband millimeter-wave frequency...

Abdul-Latif, Mohammed

2012-02-14

168

Noncollinear Second-Harmonic Generation with Compensation of Phase Mismatch by Controlling Frequency Chirp and Tilted Pulse Fronts of Femtosecond Laser Pulses  

NASA Astrophysics Data System (ADS)

In order to achieve the efficient second-harmonic generation with femtosecond laser pulses, we studied a noncollinear second-harmonic generation with tilted pulse fronts and a suitableproper frequency chirp of fundamental pulses. We discussed the compensation of a phase-mismatch by controlling thea frequency chirp of fundamental pulses and an improvement of thea energy conversion efficiency usingwith our method. When the energy conversion efficiency was less than 0.4% under a phase-mismatch condition, we experimentally obtained a 30% energy conversion efficiency with a proper frequency chirp of fundamental pulses.

Aoyama, Makoto; Zhang, Tiejun; Tsukakoshi, Motowo; Yamakawa, Koichi

2000-06-01

169

Multi-frequency Polarization Imaging of Blazars with Cyclic Activity  

E-print Network

Results of multi-frequency VLBA polarization imaging for sources showing evidence of quasi-periodic variations in their total flux density are discussed. Possible origins of the observed behavior are proposed.

T. B. Pyatunina; D. C. Gabuzda; S. G. Jorstad; M. F. Aller; H. D. Aller; H. Terasranta

2005-02-08

170

Interferometric Backward Third Harmonic Generation Microscopy for Axial Imaging with Accuracy Beyond the Diffraction Limit  

PubMed Central

A new nonlinear microscopy technique based on interference of backward-reflected third harmonic generation (I-THG) from multiple interfaces is presented. The technique is used to measure height variations or changes of a layer thickness with an accuracy of up to 5 nm. Height variations of a patterned glass surface and thickness variations of fibroblasts are visualized with the interferometric epi-THG microscope with an accuracy at least two orders of magnitude better than diffraction limit. The microscopy technique can be broadly applied for measuring distance variations between membranes or multilayer structures inside biological tissue and for surface height variation imaging. PMID:24710103

Coelho, Nuno M.; McCulloch, Christopher; Barzda, Virginijus

2014-01-01

171

Far-field imaging of optical second-harmonic generation in single GaN nanowires.  

PubMed

Means for assessing the nonlinear optical properties of nanoscale materials are of key importance for the advancement of active nanophotonics. By correlating second-harmonic generation (SHG) with electron backscattered diffraction from single GaN nanowires (NWs), we demonstrate that far-field microscopic imaging of SHG offers an approach for distinguishing crystallographic orientations of NWs lying on a substrate. The quasi-static approximation, which should prove useful in describing many nanophotonic behaviors, is shown to satisfactorily account for the SHG data. PMID:17326689

Long, J P; Simpkins, B S; Rowenhorst, D J; Pehrsson, P E

2007-03-01

172

Ab initio theoretical investigation of the frequency comb structure and coherence in the vuv-xuv regimes via high-order harmonic generation  

E-print Network

We present a fully ab initio quantum investigation of the frequency comb structure and coherence within each order of the high-order harmonic generation (HHG) spectrum in the high-frequency vuv-xuv regime. The HHG spectrum driven by a train of equal...

Chu, Shih-I; Carrera, Juan J.; Son, Sang-Kil

2008-03-03

173

Biomechanical assessment and monitoring of thermal ablation using Harmonic Motion Imaging for Focused Ultrasound (HMIFU)  

NASA Astrophysics Data System (ADS)

Cancer remains, one of the major public health problems in the United States as well as many other countries worldwide. According to According to the World Health Organization, cancer is currently the leading cause of death worldwide, accounting for 7.6 million deaths annually, and 25% of the annual death was due to Cancer during the year of 2011. In the long history of the cancer treatment field, many treatment options have been established up to date. Traditional procedures include surgical procedures as well as systemic therapies such as biologic therapy, chemotherapy, hormone therapy, and radiation therapy. Nevertheless, side-effects are often associated with such procedures due to the systemic delivery across the entire body. Recently technologies have been focused on localized therapy under minimally or noninvasive procedure with imaging-guidance, such as cryoablation, laser ablation, radio-frequency (RF) ablation, and High Intensity F-ocused Ultrasound (HIFU). HIFU is a non-invasive procedure aims to coagulate tissue thermally at a localized focal zone created with noninvasively emitting a set of focused ultrasound beams while the surrounding healthy tissues remain relatively untreated. Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a dynamic, radiation-force-based imaging technique, which utilizes a single HIFU transducer by emitting an Amplitude-modulated (AM) beam to both thermally ablate the tumor while inducing a stable oscillatory tissue displacement at its focal zone. The oscillatory response is then estimated by a cross-correlation based motion tracking technique on the signal collected by a confocally-aligned diagnostic transducer. HMIFU addresses the most critical aspect and one of the major unmet needs of HIFU treatment, which is the ability to perform real-time monitoring and mapping of tissue property change during the HIFU treatment. In this dissertation, both the assessment and monitoring aspects of HMIFU have been investigated fundamentally and experimentally through development of both a 1-D and 2-D based system. The performance assessment of HMIFU technique in depicting the lesion size increase as well as the lesion-to-background displacement contrast was first demonstrated using a 3D, FE-based interdisciplinary simulation framework. Through the development of 1-D HMIFU system, a multi-parametric monitoring approach was presented where presented where the focal HMI displacement, phase shift (Delta?), and correlation coefficients were monitored along with thermocouple and PCD under the HIFU treatment sequence with boiling and slow denaturation. For HIFU treatments with slow denaturation, consistent displacement increase-then-decrease trend was observed, indicating tissue softening-then-stiffening and phase shift increased with treatment time in agreement with mechanical testing outcomes. The correlation coefficient remained high throughout the entire treatment time under a minimized broadband energy and boiling mechanism. Contrarily, both displacement and phase shift changes lacked consistency under HIFU treatment sequences with boiling due to the presence of strong boiling mechanism confirmed by both PCD and thermocouple monitoring. In order to facilitate its clinical translation, a fully-integrated, clinically 2D real-time HMIFU system was also developed, which is capable of providing 2D real-time streaming during HIFU treatment up to 15 Hz without interruption. Reproducibility studies of the system showed consistent displacement estimation on tissue-mimicking phantoms as well as monitoring of tissue-softening-then-stiffening phase change across 16 out of 19 liver specimens (Increasing rate in phase shift (Delta?): 0.73+/-0.69 %/s, Decreasing rate in phase shift (Delta?): 0.60+/-0.19 %/s) along with thermocouple monitoring (Increasing: 0.84+/-1.15 %/ °C, Decreasing: 2.03+/- 0.93%/ °C) and validation of tissue stiffening using mechanical testing. In addition, the 2-D HMIFU system feasibility on preclinical pancreatic tumor mice model was also demonstrated in vivo, where HMI displa

Hou, Gary Yi

174

Inter- and Intra-Observer Variability in Prostate Definition With Tissue Harmonic and Brightness Mode Imaging  

SciTech Connect

Purpose: The objective of this study was to compare the relative utility of tissue harmonic (H) and brightness (B) transrectal ultrasound (TRUS) images of the prostate by studying interobserver and intraobserver variation in prostate delineation. Methods and Materials: Ten patients with early-stage disease were randomly selected. TRUS images of prostates were acquired using B and H modes. The prostates on all images were contoured by an experienced radiation oncologist (RO) and five equally trained observers. The observers were blinded to information regarding patient and imaging mode. The volumes of prostate glands and areas of midgland slices were calculated. Volumes contoured were compared among the observers and between observer group and RO. Contours on one patient were repeated five times by four observers to evaluate the intraobserver variability. Results: A one-sample Student t-test showed the volumes outlined by five observers are in agreement (p > 0.05) with the RO. Paired Student t-test showed prostate volumes (p = 0.008) and midgland areas (p = 0.006) with H mode were significantly smaller than that with B mode. Two-factor analysis of variances showed significant interobserver variability (p < 0.001) in prostate volumes and areas. Inter- and intraobserver consistency was quantified as the standard deviation of mean volumes and areas, and concordance indices. It was found that for small glands ({<=}35 cc) H mode provided greater interobserver consistency; however, for large glands ({>=}35 cc), B mode provided more consistent estimates. Conclusions: H mode provided superior inter- and intraobserver agreement in prostate volume definition for small to medium prostates. In large glands, H mode does not exhibit any additional advantage. Although harmonic imaging has not proven advantageous for all cases, its utilization seems to be judicious for small prostates.

Sandhu, Gurpreet Kaur, E-mail: Gurpreet.Sandhu2@albertahealthservices.ca [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, Alberta (Canada); Dunscombe, Peter [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, Alberta (Canada); Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Alberta (Canada); Meyer, Tyler [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, Alberta (Canada); Pavamani, Simon [Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Alberta (Canada); Department of Radiation Oncology, Christian Medical College, Vellore (India); Khan, Rao [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta (Canada); Department of Physics and Astronomy, University of Calgary, Calgary, Alberta (Canada); Department of Oncology, Faculty of Medicine, University of Calgary, Calgary, Alberta (Canada)

2012-01-01

175

Computational segmentation of collagen fibers from second-harmonic generation images of breast cancer  

NASA Astrophysics Data System (ADS)

Second-harmonic generation (SHG) imaging can help reveal interactions between collagen fibers and cancer cells. Quantitative analysis of SHG images of collagen fibers is challenged by the heterogeneity of collagen structures and low signal-to-noise ratio often found while imaging collagen in tissue. The role of collagen in breast cancer progression can be assessed post acquisition via enhanced computation. To facilitate this, we have implemented and evaluated four algorithms for extracting fiber information, such as number, length, and curvature, from a variety of SHG images of collagen in breast tissue. The image-processing algorithms included a Gaussian filter, SPIRAL-TV filter, Tubeness filter, and curvelet-denoising filter. Fibers are then extracted using an automated tracking algorithm called fiber extraction (FIRE). We evaluated the algorithm performance by comparing length, angle and position of the automatically extracted fibers with those of manually extracted fibers in twenty-five SHG images of breast cancer. We found that the curvelet-denoising filter followed by FIRE, a process we call CT-FIRE, outperforms the other algorithms under investigation. CT-FIRE was then successfully applied to track collagen fiber shape changes over time in an in vivo mouse model for breast cancer.

Bredfeldt, Jeremy S.; Liu, Yuming; Pehlke, Carolyn A.; Conklin, Matthew W.; Szulczewski, Joseph M.; Inman, David R.; Keely, Patricia J.; Nowak, Robert D.; Mackie, Thomas R.; Eliceiri, Kevin W.

2014-01-01

176

An introduction to medical imaging with coherent terahertz frequency radiation  

Microsoft Academic Search

Methods have recently been developed that make use of electromagnetic radiation at terahertz (THz) frequencies, the region of the spectrum between millimetre wavelengths and the infrared, for imaging purposes. Radiation at these wavelengths is non-ionizing and subject to far less Rayleigh scatter than visible or infrared wavelengths, making it suitable for medical applications. This paper introduces THz pulsed imaging and

A J Fitzgerald; E Berry; N N Zinovev; G C Walker; M A Smith; J M Chamberlain

2002-01-01

177

Extracting Cardiac Myofiber Orientations from High Frequency Ultrasound Images  

PubMed Central

Cardiac myofiber plays an important role in stress mechanism during heart beating periods. The orientation of myofibers decides the effects of the stress distribution and the whole heart deformation. It is important to image and quantitatively extract these orientations for understanding the cardiac physiological and pathological mechanism and for diagnosis of chronic diseases. Ultrasound has been wildly used in cardiac diagnosis because of its ability of performing dynamic and noninvasive imaging and because of its low cost. An extraction method is proposed to automatically detect the cardiac myofiber orientations from high frequency ultrasound images. First, heart walls containing myofibers are imaged by B-mode high frequency (>20 MHz) ultrasound imaging. Second, myofiber orientations are extracted from ultrasound images using the proposed method that combines a nonlinear anisotropic diffusion filter, Canny edge detector, Hough transform, and K-means clustering. This method is validated by the results of ultrasound data from phantoms and pig hearts. PMID:24392208

Qin, Xulei; Cong, Zhibin; Jiang, Rong; Shen, Ming; Wagner, Mary B.; Kishbom, Paul; Fei, Baowei

2013-01-01

178

Extracting Cardiac Myofiber Orientations from High Frequency Ultrasound Images.  

PubMed

Cardiac myofiber plays an important role in stress mechanism during heart beating periods. The orientation of myofibers decides the effects of the stress distribution and the whole heart deformation. It is important to image and quantitatively extract these orientations for understanding the cardiac physiological and pathological mechanism and for diagnosis of chronic diseases. Ultrasound has been wildly used in cardiac diagnosis because of its ability of performing dynamic and noninvasive imaging and because of its low cost. An extraction method is proposed to automatically detect the cardiac myofiber orientations from high frequency ultrasound images. First, heart walls containing myofibers are imaged by B-mode high frequency (>20 MHz) ultrasound imaging. Second, myofiber orientations are extracted from ultrasound images using the proposed method that combines a nonlinear anisotropic diffusion filter, Canny edge detector, Hough transform, and K-means clustering. This method is validated by the results of ultrasound data from phantoms and pig hearts. PMID:24392208

Qin, Xulei; Cong, Zhibin; Jiang, Rong; Shen, Ming; Wagner, Mary B; Kishbom, Paul; Fei, Baowei

2013-03-29

179

Second harmonic generation microscopy as a powerful diagnostic imaging modality for human ovarian cancer.  

PubMed

In this study we showed that second-harmonic generation (SHG) microscopy combined with precise methods for images evaluation can be used to detect structural changes in the human ovarian stroma. Using a set of scoring methods (alignment of collagen fibers, anisotropy, and correlation), we found significant differences in the distribution and organization of collagen fibers in the stroma component of serous, mucinous, endometrioid and mixed ovarian tumors as compared with normal ovary tissue. This methodology was capable to differentiate between cancerous and healthy tissue, with clear cut distinction between normal, benign, borderline, and malignant tumors of serous type. Our results indicated that the combination of different image-analysis approaches presented here represent a powerful tool to investigate collagen organization and extracellular matrix remodeling in ovarian tumors. PMID:23024013

Adur, Javier; Pelegati, Vitor B; de Thomaz, Andre A; Baratti, Mariana O; Andrade, Liliana A L A; Carvalho, Hernandes F; Bottcher-Luiz, Fátima; Cesar, Carlos Lenz

2014-01-01

180

Coherent EUV light from high-order harmonic generation: Enhancement and applications to lensless diffractive imaging  

NASA Astrophysics Data System (ADS)

The first half of this thesis presents the first demonstration of quasi-phase matching in the coherent high-order harmonic conversion of ultrafast laser pulses into the EUV region of the spectrum. To achieve this quasi-phase matching, a novel method of fabricating hollow waveguides with a modulated inner diameter was developed. This technique lead to significant enhancements of EUV flux at wavelengths shorter than were previously accessible by known phase-matching techniques. In the second half of this thesis, the first tabletop demonstration of lensless diffractive imaging with EUV light is presented using HHG in a gas-filled hollow waveguide to provide coherent illumination. This tabletop microscope shows a spatial resolution of ˜ 200 nm and a large depth of field. Furthermore, the technique is easily scalable to shorter wavelengths of interest to biological imaging.

Paul, Ariel J.

2007-12-01

181

Frequency-difference electrical impedance tomography: Phantom imaging experiments  

NASA Astrophysics Data System (ADS)

Frequency-difference electrical impedance tomography (fdEIT) using a weighted voltage difference has been proposed as a means to provide images of admittivity changes at different frequencies. This weighted difference method is an effective way to extract anomaly information while eliminating background effects by unknown boundary geometry, uncertainty in electrode positions and other systematic measurement artefacts. It also properly handles the interplay between conductivity and permittivity in measured boundary voltage data. Though the proposed fdEIT algorithm is promising for applications such as detection of hemorrhagic stroke and breast cancer, more validation studies are needed. In this paper, we performed two-and three-dimensional numerical simulations and phantom experiments. Backgrounds of imaging objects were either saline or carrot pieces suspended in saline. We used carrot pieces to simulate a more realistic frequency-dependent admittivity distribution. Test objects were banana, potato or conductive gel with known admittivity spectra. When the background was saline, both simple and weighted difference approaches produced reasonably accurate images. The weighted difference method yielded better images from two-dimensional imaging objects with background of carrot pieces. For the three-dimensional head-shaped phantom, the advantage of the weighted frequency difference method over the simple difference method is not as obvious as in the case of the two-dimensional phantom. It is unclear if this is due to measurement errors or limitations in the linear algorithm. Further refinement and validation of the frequency difference image reconstructions are currently in progress.

Ahn, Sujin; Jun, Sung Chan; Seo, Jin Keun; Lee, Jeehyun; Woo, Eung Je; Holder, David

2010-04-01

182

Low-power analog processing for sensing applications: low-frequency harmonic signal classification.  

PubMed

A low-power analog sensor front-end is described that reduces the energy required to extract environmental sensing spectral features without using Fast Fouriér Transform (FFT) or wavelet transforms. An Analog Harmonic Transform (AHT) allows selection of only the features needed by the back-end, in contrast to the FFT, where all coefficients must be calculated simultaneously. We also show that the FFT coefficients can be easily calculated from the AHT results by a simple back-substitution. The scheme is tailored for low-power, parallel analog implementation in an integrated circuit (IC). Two different applications are tested with an ideal front-end model and compared to existing studies with the same data sets. Results from the military vehicle classification and identification of machine-bearing fault applications shows that the front-end suits a wide range of harmonic signal sources. Analog-related errors are modeled to evaluate the feasibility of and to set design parameters for an IC implementation to maintain good system-level performance. Design of a preliminary transistor-level integrator circuit in a 0.13 µm complementary metal-oxide-silicon (CMOS) integrated circuit process showed the ability to use online self-calibration to reduce fabrication errors to a sufficiently low level. Estimated power dissipation is about three orders of magnitude less than similar vehicle classification systems that use commercially available FFT spectral extraction. PMID:23892765

White, Daniel J; William, Peter E; Hoffman, Michael W; Balkir, Sina

2013-01-01

183

Harmonic Vibrational Frequencies:  An Evaluation of Hartree?Fock, Møller?Plesset, Quadratic Configuration Interaction, Density Functional Theory, and Semiempirical Scale Factors  

Microsoft Academic Search

Scaling factors for obtaining fundamental vibrational frequencies, low-frequency vibrations, zero-point vibrational energies (ZPVE), and thermal contributions to enthalpy and entropy from harmonic frequencies determined at 19 levels of theory have been derived through a least-squares approach. Semiempirical methods (AM1 and PM3), conventional uncorrelated and correlated ab initio molecular orbital procedures (Hartree- Fock (HF), Møller-Plesset (MP2), and quadratic configuration interaction including

Anthony P. Scott; Leo Radom

1996-01-01

184

Observations of high-frequency harmonic tremor in Fogo, Cape Verde Islands  

Microsoft Academic Search

We report observations of high-frequency (HF) volcanic tremor, with spectral peaks in the band 5 20 Hz, recorded in Fogo Island, Cape Verde archipelago. Several occurrences are characterized by regularly spaced spectral peaks, but the fundamental frequency is missing. The signal is strong enough to be weakly detected on the southern islands of the archipelago, at distances of 20, 80

Sandra I. N. Heleno; Bruno V. E. Faria; Zuleyka Bandomo; João F. B. D. Fonseca

2006-01-01

185

Ex vivo imaging and quantification of liver fibrosis using second-harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

Conventionally, liver fibrosis is diagnosed using histopathological techniques. The traditional method is time-consuming in that the specimen preparation procedure requires sample fixation, slicing, and labeling. Our goal is to apply multiphoton microscopy to efficiently image and quantitatively analyze liver fibrosis specimens bypassing steps required in histological preparation. In this work, the combined imaging modality of multiphoton autofluorescence (MAF) and second-harmonic generation (SHG) was used for the qualitative imaging of liver fibrosis of different METAVIR grades under label-free, ex vivo conditions. We found that while MAF is effective in identifying cellular architecture in the liver specimens, it is the spectrally distinct SHG signal that allows the characterization of the extent of fibrosis. We found that qualitative SHG imaging can be used for the effective identification of the associated features of liver fibrosis specimens graded METAVIR 0 to 4. In addition, we attempted to associate quantitative SHG signal to the different METAVIR grades and found that an objective determination of the extent of disease progression can be made. Our approach demonstrates the potential of using multiphoton imaging in rapid classification of ex vivo liver fibrosis in the clinical setting and investigation of liver fibrosis-associated physiopathology in animal models in vivo.

Sun, Tzu-Lin; Liu, Yuan; Sung, Ming-Chin; Chen, Hsiao-Ching; Yang, Chun-Hui; Hovhannisyan, Vladimir; Lin, Wei-Chou; Jeng, Yung-Ming; Chen, Wei-Liang; Chiou, Ling-Ling; Huang, Guan-Tarn; Kim, Ki-Hean; So, Peter T. C.; Chen, Yang-Fang; Lee, Hsuan-Shu; Dong, Chen-Yuan

2010-05-01

186

Observations of high-frequency harmonic tremor in Fogo, Cape Verde Islands  

Microsoft Academic Search

We report observations of high-frequency (HF) volcanic tremor, with spectral peaks in the band 5–20 Hz, recorded in Fogo Island, Cape Verde archipelago. Several occurrences are characterized by regularly spaced spectral peaks, but the fundamental frequency is missing. The signal is strong enough to be weakly detected on the southern islands of the archipelago, at distances of 20, 80 and 120 km

Sandra I. N. Heleno; Bruno V. E. Faria; Zuleyka Bandomo; João F. B. D. Fonseca

2006-01-01

187

Polarization second harmonic generation by image correlation spectroscopy on collagen type I hydrogels.  

PubMed

Successful engineering of biomimetic tissue relies on an accurate quantification of the mechanical properties of the selected scaffold. To improve this quantification, typical bulk rheological measurements are often complemented with microscopic techniques, including label-free second harmonic generation (SHG) imaging. Image correlation spectroscopy (ICS) has been applied to obtain quantitative information from SHG images of fibrous scaffolds. However, the typical polarization SHG (P-SHG) effect, which partly defines the shape of the autocorrelation function (ACF), has never been taken into account. Here we propose a new and flexible model to reliably apply ICS to P-SHG images of fibrous structures. By starting from a limited number of straightforward assumptions and by taking into account the P-SHG effect, we were able to cope with the typically observed ACF particularities. Using simulated datasets, the resulting model was thoroughly evaluated and compared with models previously described in the literature. We showed that our new model has no restrictions concerning the fibre length for the density retrieval. For certain length ranges, the model can additionally be used to obtain the average fibre length and the P-SHG related non-zero susceptibility tensor element ratios. From experimental data on collagen type I hydrogels, values of SHG tensor element ratios and fibre thickness were determined which match values reported in the literature, thereby underpinning the validity and applicability of our new model. PMID:24444774

Paesen, Rik; Sanen, Kathleen; Smisdom, Nick; Michiels, Luc; Ameloot, Marcel

2014-05-01

188

Theoretical analysis of dynamic chemical imaging with lasers using high-order harmonic generation  

SciTech Connect

We report theoretical investigations of the tomographic procedure suggested by Itatani et al. [Nature (London) 432, 867 (2004)] for reconstructing highest occupied molecular orbitals (HOMOs) using high-order harmonic generation (HHG). Due to the limited range of harmonics from the plateau region, we found that even under the most favorable assumptions, it is still very difficult to obtain accurate HOMO wave functions using the tomographic procedure, but the symmetry of the HOMOs and the internuclear separation between the atoms can be accurately extracted, especially when lasers of longer wavelengths are used to generate the HHG. Since the tomographic procedure relies on approximating the continuum wave functions in the recombination process by plane waves, the method can no longer be applied upon the improvement of the theory. For future chemical imaging with lasers, we suggest that one may want to focus on how to extract the positions of atoms in molecules instead, by developing an iterative method such that the theoretically calculated macroscopic HHG spectra can best fit the experimental HHG data.

Van-Hoang Le [J. R. Macdonald Laboratory, Department of Physics, Cardwell Hall, Kansas State University, Manhattan, Kansas 66506 (United States); Department of Physics, University of Pedagogy, 280 An Duong Vuong, Ward 5, Ho Chi Minh City (Viet Nam); Anh-Thu Le; Xie Ruihua; Lin, C. D. [J. R. Macdonald Laboratory, Department of Physics, Cardwell Hall, Kansas State University, Manhattan, Kansas 66506 (United States)

2007-07-15

189

Devices for low frequency stroboscopic x-ray diffraction imaging  

NASA Astrophysics Data System (ADS)

Two stroboscopic shutters, adapted for the study of periodic phenomena in the 1-400 Hz range, were developed and tested. The principle, advantages and drawbacks of these devices are pointed out. Results obtained by x-ray diffraction imaging (topography) on a vibrating silicon crystal, and on the investigation of defects produced in KTiOPO4 by the application of an electric field, illustrate the possibilities of this stroboscopic imaging technique at low frequencies.

Lorut, F.; Pernot, E.; Pernot-Rejmánková, P.; Baruchel, J.

2003-05-01

190

Swept-frequency feedback interferometry using terahertz frequency QCLs: a method for imaging and materials analysis.  

PubMed

The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of high-power radiation with a narrow intrinsic linewidth. As such, THz QCLs are extremely promising sources for applications including high-resolution spectroscopy, heterodyne detection, and coherent imaging. We exploit the remarkable phase-stability of THz QCLs to create a coherent swept-frequency delayed self-homodyning method for both imaging and materials analysis, using laser feedback interferometry. Using our scheme we obtain amplitude-like and phase-like images with minimal signal processing. We determine the physical relationship between the operating parameters of the laser under feedback and the complex refractive index of the target and demonstrate that this coherent detection method enables extraction of complex refractive indices with high accuracy. This establishes an ultimately compact and easy-to-implement THz imaging and materials analysis system, in which the local oscillator, mixer, and detector are all combined into a single laser. PMID:24104111

Raki?, Aleksandar D; Taimre, Thomas; Bertling, Karl; Lim, Yah Leng; Dean, Paul; Indjin, Dragan; Ikoni?, Zoran; Harrison, Paul; Valavanis, Alexander; Khanna, Suraj P; Lachab, Mohammad; Wilson, Stephen J; Linfield, Edmund H; Davies, A Giles

2013-09-23

191

Detection of Myocardial Perfusion in Multiple Echocardiographic Windows With One Intravenous Injection of Microbubbles Using Transient Response Second Harmonic Imaging  

Microsoft Academic Search

Objectives. The purpose of this study was to prove that transient response harmonic imaging could detect normal and abnormal myocardial perfusion in multiple echocardiographic windows with one intravenous injection of microbubbles in humans.Background. Myocardial ultrasound contrast can be produced from intravenous perfluorocarbon-exposed sonicated dextrose albumin, and ultrasound can be significantly improved by briefly suspending the interval between frame rates. Whether

Thomas R. Porter; Shouping Li; David Kricsfeld; Robert W. Armbruster

1997-01-01

192

High-frequency ultrasonic imaging of thickly sliced specimens  

NASA Astrophysics Data System (ADS)

It has been reported that a mechanical scanning reflection acoustic microscope (hereinafter called simply "SAM"), using high frequency ultrasonic tone-burst waves, can form a horizontal cross-sectional image (i.e., c-scan image) showing a highly resolved cellular structure of biological tissue. However, the tissue prepared for the SAM has been mostly a thinly sectioned specimen. In this study, the SAM images of specimens thickly sectioned from the tissue were analyzed. Optical and scanning acoustic microscopies were used to evaluate tissues of human small intestine and esophagus. For preparing thin specimens, the tissue was embedded in paraffin, and substantially sectioned at 5-10?m by the microtome. For optical microscopy, the tissue was stained with hematoxylin and eosin, and affixed onto glass substrates. For scanning acoustic microscopy, two types of specimens were prepared: thinly sectioned specimens affixed on the glass substrate, wherein the specimens were deparaffinized in xylene, but not stained, and thickely sectioned specimens. Images of the thick specimens obtained with frequency at 200 MHz revealed cellular structures. The morphology was very similar to that seen in the thinly sectioned specimens with optical and scanning acoustic microscopy. In addition, scanning electron microscopy was used to compare the images of biological tissue. An acoustic lens with frequency at 200 MHz permitted the imaging of surface and/or subsurface of microstructures in the thick sections of small intestine and esophagus.

Miyasaka, Chiaki; Tittmann, Bernhard R.; Chandraratna, Premindra A. N.

2003-07-01

193

Imaging elastic and collagen fibers with sulforhodamine B and second-harmonic generation  

NASA Astrophysics Data System (ADS)

Since the early nineties, multiphoton microscopy has become a powerful tool to investigate morphological and physiological parameters in vivo or on thick ex vivo sections. To stain structures of interest many dyes have been developed and two-photon properties (cross section, excitation and emission spectra) of existing ones have been characterized. Recently, our team has shown a new property of sulforhodamine B (SRB). This dye has the ability to bind specifically elastic fibers. The observation of elastin using its endofluorescence properties was already widely described but required long exposition delays up to 10s and the imaging depth was limited to approximately 50 ?m. With a multiphoton microscope and SRB, it is possible to observe elastic fibers directly in the living animal or on thick tissue sections with a micrometric spatial resolution in less than one second per image with an imaging depth of ~ 200 ?m. Moreover, with an appropriate set of filters, we can acquire simultaneously the SRB and the second harmonic generation (SHG) signals of collagen fibers. Here, we report various applications of this new staining method on different arterial rings. The layers of the arterial wall, as well as, the elastic lamellae are observed and are numbered. With the addition of a nuclear stain such as the Hoechst 33342, a more accurate morphological study of the arterial walls can be accomplished. Finally, an intravital observation of the saphenous artery morphology is presented.

Ricard, Clément; Vial, Jean-Claude; Douady, Julien; van der Sanden, Boudewijn

2008-02-01

194

Computationally Efficient Steady-State Solution of the Bloch Equations for Rapid Sinusoidal Scans Based on Fourier Expansion in Harmonics of the Scan Frequency  

PubMed Central

Rapid-scan EPR has been shown to improve the signal-to-noise ratio relative to conventional continuous wave spectroscopy. Equations are derived for the steady-state solution to the Bloch equations as a Fourier expansion in the harmonics of the scan frequency. This simulation method is about two orders of magnitude faster than time-domain numerical integration. PMID:24678142

Tseitlin, Mark; Eaton, Gareth R.; Eaton, Sandra S.

2014-01-01

195

Harmonic nanoparticles for regenerative research.  

PubMed

In this visualized experiment, protocol details are provided for in vitro labeling of human embryonic stem cells (hESC) with second harmonic generation nanoparticles (HNPs). The latter are a new family of probes recently introduced for labeling biological samples for multi-photon imaging. HNPs are capable of doubling the frequency of excitation light by the nonlinear optical process of second harmonic generation with no restriction on the excitation wavelength. Multi-photon based methodologies for hESC differentiation into cardiac clusters (maintained as long term air-liquid cultures) are presented in detail. In particular, evidence on how to maximize the intense second harmonic (SH) emission of isolated HNPs during 3D monitoring of beating cardiac tissue in 3D is shown. The analysis of the resulting images to retrieve 3D displacement patterns is also detailed. PMID:24836220

Ronzoni, Flavio; Magouroux, Thibaud; Vernet, Remi; Extermann, Jérôme; Crotty, Darragh; Prina-Mello, Adriele; Ciepielewski, Daniel; Volkov, Yuri; Bonacina, Luigi; Wolf, Jean-Pierre; Jaconi, Marisa

2014-01-01

196

Tomographic imaging via spectral encoding of spatial frequency  

PubMed Central

Three-dimensional optical tomographic imaging plays an important role in biomedical research and clinical applications. We introduce spectral tomographic imaging (STI) via spectral encoding of spatial frequency principle that not only has the capability for visualizing the three-dimensional object at sub-micron resolution but also providing spatially-resolved quantitative characterization of its structure with nanoscale accuracy for any volume of interest within the object. The theoretical basis and the proof-of-concept numerical simulations are presented to demonstrate the feasibility of spectral tomographic imaging. PMID:23546131

Uttam, Shikhar; Alexandrov, Sergey A.; Bista, Rajan K.; Liu, Yang

2013-01-01

197

High frequency ultrasound imaging in pupillary block glaucoma.  

PubMed Central

BACKGROUND--The diagnosis of pupillary block glaucoma requires sufficient clarity of the ocular media. This is particularly important for assessment of both the presence and patency of an iridotomy, and the determination of central anterior chamber depth. METHODS--High frequency ultrasonography was used in three patients with suspected pupillary block to determine iris configuration, posterior chamber volume, and ciliary body conformation. RESULTS--All patients demonstrated high frequency ultrasonographic findings consistent with pupillary block: iris bombé, a formed posterior chamber, and a lack of anterior rotation of the ciliary processes. CONCLUSION--High frequency ultrasound imaging appears to be a valuable adjunct in making or corroborating the diagnosis of pupillary block glaucoma. Images PMID:8534666

Aslanides, I M; Libre, P E; Silverman, R H; Reinstein, D Z; Lazzaro, D R; Rondeau, M J; Harmon, G K; Coleman, D J

1995-01-01

198

Generating high-frequency, rotating magnetic fields with low harmonic content  

SciTech Connect

The future electron-ion collider (eRHIC) at Brookhaven National Laboratory demands a high-current, polarized, bunched electron beam [http://www.bnl.gov/cad/eRhic]. One of the challenges here is to combine the bunched beams generated by multiple cathodes so to address the issue of designing and prototyping a combiner with high-frequency (700 kHz) rotational magnetic fields. This article presents its design, and simulation, and details some of the test results from this unprecedented device.

Ben-Zvi, I.; Chang, X.; Litvinenko, V.; Meng, W.; Pikin, A.; Skaritka, J.

2011-09-13

199

Imaging radio-frequency fields using a scanning SQUID microscope  

SciTech Connect

Using a liquid-nitrogen-cooled scanning SQUID magnetic microscope, we have developed a technique for broadband imaging of radio-frequency (rf) and microwave fields with a spatial resolution of about 15 [mu]m. We have produced images of the amplitude of 50 MHz fields with an rms noise of 2.6 nT and a 300 [mu]m/s scan rate. Detection is accomplished by using the nonlinearity of the voltage-flux characteristic of the SQUID to rectify the rf fields. Our present technique is limited by cavity mode resonances in the SrTiO[sub 3] substrate of our SQUID sensor. Using a small excitation probe, we have directly imaged these resonances at frequencies up to about 12.5 GHz.

Black, R.C.; Wellstood, F.C. (Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (United States)); Dantsker, E.; Miklich, A.H.; Koelle, D.; Ludwig, F.; Clarke, J. (Department of Physics, University of California and Materials Sciences Division, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States))

1995-03-06

200

The Calculation of Accurate Harmonic Frequencies of Large Molecules: The Polycyclic Aromatic Hydrocarbons, a Case Study  

NASA Technical Reports Server (NTRS)

The vibrational frequencies and infrared intensities of naphthalene neutral and cation are studied at the self-consistent-field (SCF), second-order Moller-Plesset (MP2), and density functional theory (DFT) levels using a variety of one-particle basis sets. Very accurate frequencies can be obtained at the DFT level in conjunction with large basis sets if they are scaled with two factors, one for the C-H stretches and a second for all other modes. We also find remarkably good agreement at the B3LYP/4-31G level using only one scale factor. Unlike the neutral PAHs where all methods do reasonably well for the intensities, only the DFT results are accurate for the PAH cations. The failure of the SCF and MP2 methods is caused by symmetry breaking and an inability to describe charge delocalization. We present several interesting cases of symmetry breaking in this study. An assessment is made as to whether an ensemble of PAH neutrals or cations could account for the unidentified infrared bands observed in many astronomical sources.

Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Arnold, James O. (Technical Monitor)

1996-01-01

201

Observations of high-frequency harmonic tremor in Fogo, Cape Verde Islands  

NASA Astrophysics Data System (ADS)

We report observations of high-frequency (HF) volcanic tremor, with spectral peaks in the band 5-20 Hz, recorded in Fogo Island, Cape Verde archipelago. Several occurrences are characterized by regularly spaced spectral peaks, but the fundamental frequency is missing. The signal is strong enough to be weakly detected on the southern islands of the archipelago, at distances of 20, 80 and 120 km from Fogo. This widespread detection of the HF tremor suggests that the propagation of the energy is made as T-waves propagating in the ocean sound channel. After correcting for site effects, the spatial pattern of amplitudes in Fogo and Brava Islands clearly indicates an offshore source. Active seamounts recently discovered in the vicinity of Fogo and Brava Islands [Hansteen, T.H., Grevemeyer, I., Hanel, K., Kraus, G., Schneider, J., Masson, D.G., Le Bas, T., Faria, B., 2006. Seamounts at the Cape Verde Islands: the geosphere-hydrosphere-biosphere connection, Seamount Biogeosciences Network, Workshop volume, La Jolla, March 24-25, 2006, 27-29.] are proposed to be the source of the HF tremor.

Heleno, Sandra I. N.; Faria, Bruno V. E.; Bandomo, Zuleyka; Fonseca, João F. B. D.

2006-11-01

202

Continuous-wave coherent imaging with terahertz quantum cascade lasers using electro-optic harmonic sampling  

NASA Astrophysics Data System (ADS)

We demonstrate a coherent imaging system based on a terahertz (THz) frequency quantum cascade laser (QCL) phase-locked to a near-infrared fs-laser comb. The phase locking enables coherent electro-optic sampling of the continuous-wave radiation emitted by the QCL through the generation of a heterodyne beat-note signal. We use this beat-note signal to demonstrate raster scan coherent imaging using a QCL emitting at 2.5 THz. At this frequency the detection noise floor of our system is of 3 pW/Hz and the long-term phase stability is <3°/h, limited by the mechanical stability of the apparatus.

Ravaro, M.; Jagtap, V.; Santarelli, G.; Sirtori, C.; Li, L. H.; Khanna, S. P.; Linfield, E. H.; Barbieri, S.

2013-03-01

203

Continuous-wave coherent imaging with terahertz quantum cascade lasers using electro-optic harmonic sampling  

E-print Network

We demonstrate a coherent imaging system based on a terahertz (THz) frequency quantum cascade laser (QCL) phase-locked to a near-infrared fs-laser comb. The phase locking enables coherent electro-optic sampling of the continuous-wave radiation emitted by the QCL through the generation of a heterodyne beat-note signal. We use this beat-note signal to demonstrate raster scan coherent imaging using a QCL emitting at 2.5 THz. At this frequency the detection noise floor of our system is of 3 pW/Hz and the long-term phase stability is <3 degrees/h, limited by the mechanical stability of the apparatus.

Ravaro, Marco; Santarelli, Giorgio; Sirtori, Carlo; Li, Lianhe; Khanna, S P; Linfield, Edmund H; Barbieri, Stefano; 10.1063/1.4793424

2013-01-01

204

Label-free imaging of Schwann cell myelination by third harmonic generation microscopy.  

PubMed

Understanding the dynamic axon-glial cell interaction underlying myelination is hampered by the lack of suitable imaging techniques. Here we demonstrate third harmonic generation microscopy (THGM) for label-free imaging of myelinating Schwann cells in live culture and ex vivo and in vivo tissue. A 3D structure was acquired for a variety of compact and noncompact myelin domains, including juxtaparanodes, Schmidt-Lanterman incisures, and Cajal bands. Other subcellular features of Schwann cells that escape traditional optical microscopies were also visualized. We tested THGM for morphometry of compact myelin. Unlike current methods based on electron microscopy, g-ratio could be determined along an extended length of myelinated fiber in the physiological condition. The precision of THGM-based g-ratio estimation was corroborated in mouse models of hypomyelination. Finally, we demonstrated the feasibility of THGM to monitor morphological changes of myelin during postnatal development and degeneration. The outstanding capabilities of THGM may be useful for elucidation of the mechanism of myelin formation and pathogenesis. PMID:25453108

Lim, Hyungsik; Sharoukhov, Denis; Kassim, Imran; Zhang, Yanqing; Salzer, James L; Melendez-Vasquez, Carmen V

2014-12-16

205

Functional imaging of skeletal muscle fiber in different physiological states by second harmonic generation  

NASA Astrophysics Data System (ADS)

The intrinsically ordered arrays of proteins in skeletal muscle allows imaging of this tissue by Second Harmonic Generation (SHG). Biochemical and colocalization studies have gathered an increasing wealth of clues for the attribution of the molecular origin of the muscle SHG signal to the motor protein myosin. Thus, SHG represents a potentially very powerful tool in the investigation of structural dynamics occurring in muscle during active production of force. A full characterization of the polarization-dependence of the SHG signal represents a very selective information on the orientation of the emitting proteins and their dynamics during contraction, provided that different physiological states of muscle (relaxed, rigor and active) exhibit distinct patterns of SHG polarization dependence. Here polarization data are obtained from single frog muscle fibers at rest and during isometric contraction and interpreted, by means of a model, in terms of an average orientation of the SHG emitters which are structured with a cylindrical symmetry about the fiber axis. Optimizing the setup for accurate polarization measurements with SHG, we developed a line scan imaging method allowing measurement of SHG polarization curves in different physiological states. We demonstrate that muscle fiber displays a measurable variation of the orientation of SHG emitters with the transition from rest to isometric contraction.

Nucciotti, V.; Stringari, C.; Sacconi, L.; Vanzi, F.; Tesi, C.; Piroddi, N.; Poggesi, C.; Castiglioni, C.; Milani, A.; Linari, M.; Piazzesi, G.; Lombardi, V.; Pavone, F. S.

2007-07-01

206

Second harmonic generation imaging as a potential tool for staging pregnancy and predicting preterm birth  

NASA Astrophysics Data System (ADS)

We use second harmonic generation (SHG) microscopy to assess changes in collagen structure of murine cervix during cervical remodeling of normal pregnancy and in a preterm birth model. Visual inspection of SHG images revealed substantial changes in collagen morphology throughout normal gestation. SHG images collected in both the forward and backward directions were analyzed quantitatively for changes in overall mean intensity, forward to backward intensity ratio, collagen fiber size, and porosity. Changes in mean SHG intensity and intensity ratio take place in early pregnancy, suggesting that submicroscopic changes in collagen fibril size and arrangement occur before macroscopic changes become evident. Fiber size progressively increased from early to late pregnancy, while pores between collagen fibers became larger and farther apart. Analysis of collagen features in premature cervical remodeling show that changes in collagen structure are dissimilar from normal remodeling. The ability to quantify multiple morphological features of collagen that characterize normal cervical remodeling and distinguish abnormal remodeling in preterm birth models supports future studies aimed at development of SHG endoscopic devices for clinical assessment of collagen changes during pregnancy in women and for predicting risk of preterm labor which occurs in 12.5% of all pregnancies.

Akins, Meredith L.; Luby-Phelps, Katherine; Mahendroo, Mala

2010-03-01

207

Harmonic oscillator with time-dependent effective-mass and frequency with a possible application to 'chirped tidal' gravitational waves forces affecting interferometric detectors  

E-print Network

The general theory of time-dependent frequency and time-dependent mass ('effective mass') is described.The general theory for time-dependent harmonic- oscillator is applied in the present research for studying certain quantum effects in the interferometers for detecting gravitational waves.When an astronomical binary system approaches its point of coalescence the gravitational wave intensity and frequency are increasing and this can lead to strong deviations from the simple description of harmonic-oscillations for the interferometric masses on which the mirrors are placed.It is shown that under such condtions the harmonic-oscillations of these masses can be described by mechanical harmonic-oscillators with time-dependent frequency and effective-mass. In the present theoretical model the effective-mass is decreasing with time describing pumping phenomena in which the oscillator amplitude is increasing with time . The quantization of this system is analyzed by the use of the adiabatic approximation. It is found that the increase of the gravitational wave intensity, within the adiabatic approximation, leads to squeezing phenomena where the quantum noise in one quadrature is increased and in the other quadrature is decreased.

Yacob Ben-Aryeh

2008-07-29

208

Methods for estimating selected low-flow frequency statistics and harmonic mean flows for streams in Iowa  

USGS Publications Warehouse

A statewide study was conducted to develop regression equations for estimating six selected low-flow frequency statistics and harmonic mean flows for ungaged stream sites in Iowa. The estimation equations developed for the six low-flow frequency statistics include: the annual 1-, 7-, and 30-day mean low flows for a recurrence interval of 10 years, the annual 30-day mean low flow for a recurrence interval of 5 years, and the seasonal (October 1 through December 31) 1- and 7-day mean low flows for a recurrence interval of 10 years. Estimation equations also were developed for the harmonic-mean-flow statistic. Estimates of these seven selected statistics are provided for 208 U.S. Geological Survey continuous-record streamgages using data through September 30, 2006. The study area comprises streamgages located within Iowa and 50 miles beyond the State's borders. Because trend analyses indicated statistically significant positive trends when considering the entire period of record for the majority of the streamgages, the longest, most recent period of record without a significant trend was determined for each streamgage for use in the study. The median number of years of record used to compute each of these seven selected statistics was 35. Geographic information system software was used to measure 54 selected basin characteristics for each streamgage. Following the removal of two streamgages from the initial data set, data collected for 206 streamgages were compiled to investigate three approaches for regionalization of the seven selected statistics. Regionalization, a process using statistical regression analysis, provides a relation for efficiently transferring information from a group of streamgages in a region to ungaged sites in the region. The three regionalization approaches tested included statewide, regional, and region-of-influence regressions. For the regional regression, the study area was divided into three low-flow regions on the basis of hydrologic characteristics, landform regions, and soil regions. A comparison of root mean square errors and average standard errors of prediction for the statewide, regional, and region-of-influence regressions determined that the regional regression provided the best estimates of the seven selected statistics at ungaged sites in Iowa. Because a significant number of streams in Iowa reach zero flow as their minimum flow during low-flow years, four different types of regression analyses were used: left-censored, logistic, generalized-least-squares, and weighted-least-squares regression. A total of 192 streamgages were included in the development of 27 regression equations for the three low-flow regions. For the northeast and northwest regions, a censoring threshold was used to develop 12 left-censored regression equations to estimate the 6 low-flow frequency statistics for each region. For the southern region a total of 12 regression equations were developed; 6 logistic regression equations were developed to estimate the probability of zero flow for the 6 low-flow frequency statistics and 6 generalized least-squares regression equations were developed to estimate the 6 low-flow frequency statistics, if nonzero flow is estimated first by use of the logistic equations. A weighted-least-squares regression equation was developed for each region to estimate the harmonic-mean-flow statistic. Average standard errors of estimate for the left-censored equations for the northeast region range from 64.7 to 88.1 percent and for the northwest region range from 85.8 to 111.8 percent. Misclassification percentages for the logistic equations for the southern region range from 5.6 to 14.0 percent. Average standard errors of prediction for generalized least-squares equations for the southern region range from 71.7 to 98.9 percent and pseudo coefficients of determination for the generalized-least-squares equations range from 87.7 to 91.8 percent. Average standard errors of prediction for weighted-least-squares equations developed for estimating the harmonic-mean-flow statistic for each of the thr

Eash, David A.; Barnes, Kimberlee K.

2012-01-01

209

Acoustical imaging of high-frequency elastic responses of targets  

NASA Astrophysics Data System (ADS)

Acoustical imaging was used to investigate high-frequency elastic responses to sound of two targets in water. The backscattering of broadband bipolar acoustic pulses by a truncated cylindrical shell was recorded over a wide range of tilt angles [S. F. Morse and P. L. Marston, ``Backscattering of transients by tilted truncated cylindrical shells: time-frequency identification of ray contributions from measurements,'' J. Acoust. Soc. Am. (in press)]. This data set was used to form synthetic aperture images of the target based on the data within different angular apertures. Over a range of viewing angles, the visibility of the cylinder's closest rear corner was significantly enhanced by the meridional flexural wave contribution to the backscattering. In another experiment, the time evolution of acoustic holographic images was used to explore the response of tilted elastic circular disks to tone bursts having frequencies of 250 and 300 kHz. For different tilt angles, specific responses that enhance the backscattering were identified from the time evolution of the images [B. T. Hefner and P. L. Marston, Acoust. Res. Lett. Online 2, 55-60 (2001)]. [Work supported by ONR.

Morse, Scot F.; Hefner, Brian T.; Marston, Philip L.

2002-05-01

210

High-frequency ultrasonic arrays for ocular imaging  

NASA Astrophysics Data System (ADS)

High-resolution ultrasound imaging of the anterior portion of the eye has been shown to provide important information for sizing of intraocular lens implants, diagnosis of pathological conditions, and creation of detailed maps of corneal topography to guide refractive surgery. Current ultrasound imaging systems rely on mechanical scanning of a single acoustic element over the surface of the eye to create the three-dimensional information needed by clinicians. This mechanical scanning process is time-consuming and subject to errors caused by eye movement during the scanning period. This paper describes development of linear ultrasound imaging arrays intended to increase the speed of image acquisition and reduce problems associated with ocular motion. The arrays consist of a linear arrangement of high-frequency transducer elements designed to operate in the 50 - 75 MHz frequency range. The arrays are produced using single-crystal lithium niobate piezoelectric material, thin film electrodes, and epoxy-based acoustic layers. The array elements have been used to image steel test structures and bovine cornea.

Jaeger, M. D.; Kline-Schoder, R. J.; Douville, G. M.; Gagne, J. R.; Morrison, K. T.; Audette, W. E.; Kynor, D. B.

2007-03-01

211

High-speed optical frequency-domain imaging  

PubMed Central

We demonstrate high-speed, high-sensitivity, high-resolution optical imaging based on optical frequency-domain interferometry using a rapidly-tuned wavelength-swept laser. We derive and show experimentally that frequency-domain ranging provides a superior signal-to-noise ratio compared with conventional time-domain ranging as used in optical coherence tomography. A high sensitivity of ?110 dB was obtained with a 6 mW source at an axial resolution of 13.5 µm and an A-line rate of 15.7 kHz, representing more than an order-of-magnitude improvement compared with previous OCT and interferometric imaging methods. PMID:19471415

Yun, S. H.; Tearney, G. J.; de Boer, J. F.; Iftimia, N.; Bouma, B. E.

2009-01-01

212

High-speed polarization sensitive optical frequency domain imaging with frequency multiplexing  

PubMed Central

Polarization sensitive optical coherence tomography (PS-OCT) provides a cross-sectional image of birefringence in biological samples that is complementary in many applications to the standard reflectance-based image. Recent ex vivo studies have demonstrated that birefringence mapping enables the characterization of collagen and smooth muscle concentration and distribution in vascular tissues. Instruments capable of applying these measurements percutaneously in vivo may provide new insights into coronary atherosclerosis and acute myocardial infarction. We have developed a polarization sensitive optical frequency domain imaging (PS-OFDI) system that enables high-speed intravascular birefringence imaging through a fiber-optic catheter. The novel design of this system utilizes frequency multiplexing to simultaneously measure reflectance of two incident polarization states, overcoming concerns regarding temporal variations of the catheter fiber birefringence and spatial variations in the birefringence of the sample. We demonstrate circular cross-sectional birefringence imaging of a human coronary artery ex vivo through a flexible fiber-optic catheter with an A-line rate of 62 kHz and a ranging depth of 6.2 mm. PMID:18542183

Yun, S.H.; Vakoc, B.J.; Shishkov, M.; Desjardins, A.E.; Park, B.H.; de Boer, J.F.; Tearney, G.J.; Bouma, B.E.

2009-01-01

213

Tenth-order rational-harmonic frequency multiplication and detuning of optical pulse injection-locked erbium-doped fiber laser  

NASA Astrophysics Data System (ADS)

The jitter and frequency-detuning dynamics of a 10-GHz rational-harmonic frequency-multiplied pulse train generated from an erbium-doped fiber laser (EDFL) is studied. The EDFL is self-feedback seeded and optically injection locked by a gain-switched laser diode (GSLD) with a pulse width and an average power of 17.6 ps and 0.2 mW, respectively, at a repetition frequency of 1 GHz. The repetition frequency of the optical pulse train can be tenth-order multiplied by a slight detuning of the repetition frequency of the GSLD to match the rational-harmonic injection-locked condition of the EDFL. As the repetition frequency is multiplied from 1 to 10 GHz, the peak power, the pulse width, and the frequency-detuning bandwidth of the injection-locked EDFL pulses decrease from 1.2 to 0.3 W, from 40 to 21 ps, and from 40 to 9 kHz, respectively. The timing jitter of the injection-locked EDFL repeated at 1 GHz remains unchanged (<0.5 ps) within the detuning bandwidth, which inevitably increases to 1.2 ps after tenth-order multiplication.

Lin, Gong-Ru; Wu, Jung-Rung

2005-04-01

214

Evidence for Harmonic Content and Frequency Evolution of Oscillations During the Rising Phase of X-ray Bursts From 4U 1636-536  

NASA Technical Reports Server (NTRS)

We report on a study of the evolution of burst oscillation properties during the rising phase of X-ray bursts from 4U 1636-536 observed with the proportional counter array (PCA) on board the Rossi X-Ray Timing Explorer (RXTE) . We present evidence for significant harmonic structure of burst oscillation pulses during the early rising phases of bursts. This is the first such detection in burst rise oscillations, and is very important for constraining neutron star structure parameters and the equation of state models of matter at the core of a neutron star. The detection of harmonic content only during the initial portions of the burst rise is consistent with the theoretical expectation that with time the thermonuclear burning region becomes larger, and hence the fundamental and harmonic amplitudes both diminish. We also find, for the first time from this source, strong evidence of oscillation frequency increase during the burst rise. The timing behavior of harmonic content, amplitude, and frequency of burst rise oscillations may be important in understanding the spreading of thermonuclear flames under the extreme physical conditions on neutron star surfaces.

Bgattacharyya, Sudip; Strohmayer, E.

2005-01-01

215

Optimization of high-order harmonic generation by genetic algorithm and wavelet time-frequency analysis of quantum dipole emission  

E-print Network

Optimization of high-order harmonic generation by genetic algorithm and wavelet time laser fields by means of the genetic algorithm optimization of the laser-pulse amplitude and phase of the coherent control and enhancement of high-harmonic emission by means of the genetic algo- rithm GA

Chu, Shih-I

216

Imaging skeletal muscle using second harmonic generation and coherent anti-Stokes Raman scattering microscopy  

PubMed Central

We describe experimental results on label free imaging of striated skeletal muscle using second harmonic generation (SHG) and coherent anti-Stokes Raman scattering (CARS) microscopy. The complementarity of the SHG and CARS data makes it possible to clearly identify the main sarcomere sub-structures such as actin, myosin, acto-myosin, and the intact T-tubular system as it emanates from the sarcolemma. Owing to sub-micron spatial resolution and the high sensitivity of the CARS microscopy technique we were able to resolve individual myofibrils. In addition, key organelles such as mitochondria, cell nuclei and their structural constituents were observed revealing the entire structure of the muscle functional units. There is a noticeable difference in the CARS response of the muscle structure within actin, myosin and t-tubule areas with respect to laser polarization. We attribute this to a preferential alignment of the probed molecular bonds along certain directions. The combined CARS and SHG microscopy approach yields more extensive and complementary information and has a potential to become an indispensable method for live skeletal muscle characterization. PMID:21559148

Pfeffer, Christian P.; Olsen, Bjorn R.; Ganikhanov, Feruz; Légaré, François

2011-01-01

217

Quantitative second harmonic generation imaging of the diseased state osteogenesis imperfecta: experiment and simulation.  

PubMed

We report the integrated use of 3D second harmonic generation (SHG) imaging microscopy and Monte Carlo simulation as a combined metric to quantifiably differentiate normal and diseased tissues based on the physical properties of the respective extracellular matrix. To achieve this, we have identified a set of parameters comprised of the SHG creation attributes and the bulk optical parameters, which are used collectively via comparative analysis. Monte Carlo simulations of the SHG axial directional and attenuation responses allow their decomposition into the underlying factors that are not readily obtainable through experimental techniques. Specifically, this approach allows for estimation of the SHG creation attributes (directionality and relative conversion efficiency) and separation of primary and secondary filter effects, collectively that form the observed SHG contrast. The quantitative metric is shown for the connective tissue disorder Osteogenesis Imperfecta (characterized by abnormal assembly of type I collagen) using a murine model that expresses the disease in the dermis layer of skin. Structural dissimilarities between the osteogenesis imperfecta mouse and wild-type tissues lead to significant differences in the SHG depth-dependent directionality and signal attenuation. The Monte Carlo simulations of these responses using measured bulk optical parameters reproduce the experimental data trends, and the extracted emission directionality and conversion efficiencies are consistent with independent determinations. The simulations also illustrate the dominance of primary filter affects on overall SHG generation and attenuation. Thus, the combined method of 3D SHG imaging and modeling forms an essential foundation for parametric description of the matrix properties that are not distinguishable by sole consideration of either bulk optical parameters or SHG alone. Moreover, due to the quasi-coherence of the SHG process in tissues, we submit that this approach contains unique information not possible by purely scattering based methods and that these methods will be applicable in the general case where the complex fibrillar structure is difficult to fully quantify via morphological analysis. PMID:18281387

Lacomb, Ronald; Nadiarnykh, Oleg; Campagnola, Paul J

2008-06-01

218

Design of variable frequency endoscope ultrasonic digital imaging system  

NASA Astrophysics Data System (ADS)

This paper presented a real-time endoscope ultrasonic digital imaging system, which was based on FPGA and applied for gastrointestinal examination. Four modules, scan-line data processing module, coordinate transformation and interpolation algorithm module, cache reading and writing control module and transmitting and receiving control module were included in this FPGA based system. Through adopting different frequency ultrasound probes in a single insertion of endoscope, the system showed a high speed data processing mechanism capable of achieving images with various display effects. A high-precision modified coordinate calibration CORDIC (HMCC-CORDIC) algorithm was employed to realize coordinate transformation and interpolation simultaneously, while the precision and reliability of the algorithm could be greatly improved through utilizing the pipeline structure based on temporal logic. Also, system real-time control by computer could be achieved through operating under the condition of USB2.0 interface. The corresponding experimental validations proved the feasibility and the correctness of the proper data processing mechanism, the HMCC-CORDIC algorithm and the USB real-time control. Finally, the specific experimental sample, a tissue mimicking phantom, was imaged in real-time (25 frames per second) by an endoscope ultrasonic imaging system with image size 1024×1024. The requirements for clinical examination could be well satisfied with the imaging parameters discussed above.

Li, Ya-nan; Bai, Bao-ping; Chen, Xiao-dong; Zhao, Qiang; Deng, Hao-ran; Wang, Yi; Yu, Dao-yin

2013-12-01

219

Concealed weapons detection using low-frequency magnetic imaging  

NASA Astrophysics Data System (ADS)

Military personnel, law-enforcement officers, and civilians face ever-increasing dangers from persons carrying concealed handguns and other weapons. In direct correspondence with this danger is a need for more sophisticated means of detecting concealed weapons. We have developed a novel concealed-weapons detector based on the principle of low- frequency magnetic imaging. The detector is configured as a portal, and constructs an image of electrically conductive objects transported through it with a potential spatial resolution of approximately 1 inch. Measurements on a breadboard version of the weapons detector have, to date, yielded a resolution of 2 inches. In operation, magnetic dipole radiation, emitted by transmitting antennas in the perimeter of the portal, is scattered from conductive objects and is picked up by receive antennas, also positioned around the portal. With sufficient measurements, each with a different geometry, a solution to the inverse scattering problem can be found. The result is an image of conductive objects in the detector. The detector is sensitive to all metals, semiconductors, and conductive composites. The measured conductivity image formed by the detector is combined with the video signal from a visible CCD camera to form a composite image of persons transiting the detector portal and the conductive objects they are carrying. Accompanying image recognition software could be used to determine the threat level of objects based upon shape, conductivity, and placement on the person of the carrier, and provide cueing, logging, or alarm functions to the operator if suspect weapons are identified. The low- power, low-frequency emissions from the detector are at levels considered safe to humans and medical implants..

Zollars, Byron G.; Sallee, Bradley; Durrett, Michael G.; Cruce, Clay; Hallidy, William

1997-02-01

220

Frequency Identification of Vibration Signals Using Video Camera Image Data  

PubMed Central

This study showed that an image data acquisition system connecting a high-speed camera or webcam to a notebook or personal computer (PC) can precisely capture most dominant modes of vibration signal, but may involve the non-physical modes induced by the insufficient frame rates. Using a simple model, frequencies of these modes are properly predicted and excluded. Two experimental designs, which involve using an LED light source and a vibration exciter, are proposed to demonstrate the performance. First, the original gray-level resolution of a video camera from, for instance, 0 to 256 levels, was enhanced by summing gray-level data of all pixels in a small region around the point of interest. The image signal was further enhanced by attaching a white paper sheet marked with a black line on the surface of the vibration system in operation to increase the gray-level resolution. Experimental results showed that the Prosilica CV640C CMOS high-speed camera has the critical frequency of inducing the false mode at 60 Hz, whereas that of the webcam is 7.8 Hz. Several factors were proven to have the effect of partially suppressing the non-physical modes, but they cannot eliminate them completely. Two examples, the prominent vibration modes of which are less than the associated critical frequencies, are examined to demonstrate the performances of the proposed systems. In general, the experimental data show that the non-contact type image data acquisition systems are potential tools for collecting the low-frequency vibration signal of a system. PMID:23202026

Jeng, Yih-Nen; Wu, Chia-Hung

2012-01-01

221

Experimental investigation of the ionospheric hysteresis effect on the threshold excitation level of the Stimulated Electromagnetic Emission (SEE) during heating at the second electron gyro-harmonic frequency  

NASA Astrophysics Data System (ADS)

Recent experimental observations of the stimulated electromagnetic emission (SEE) spectrum during heating at the second electron gyro-harmonic show structures ordered by ion gyro-frequency. The proposed generation mechanism considers parametric decay of a pump upper hybrid/electron Bernstein (UH/EB) wave into another UH/EB and a group of neutralized ion Bernstein waves. The presumption of the proposed mechanism is that the pump electromagnetic wave is converted into the UH/EB wave. This conversion process generates field aligned irregularity which exhibits hysteresis effect. The predicted ionospheric hysteresis effect is studied during the PARS 2012 at HAARP. The preliminary results are presented for the first time. Also, experimental study of the effects of 1) the transmitter beam angle and 2) the transmitter frequency offset relative to the second electron gyro-harmonic frequency on the ion gyro-harmonic structures in the SEE spectrum are provided. The aforementioned observations are compared to the predictions of the analytical model. Possible connection of the SEE spectral features and artificially generated ionospheric descending layer is also discussed

Samimi, A.; Scales, W.; Cruz, M.; Isham, B.; Bernhardt, P. A.

2012-12-01

222

Harmonic reduction in thyristor converters by harmonic current injection  

Microsoft Academic Search

The paper describes analytical and experimental results for a new method of current harmonic reduction in thyristor converters. The principle of the method is to modify the current waveforms on the d.c. windings of the converter transformer by injecting harmonic currents at a particular frequency. In practice, third harmonic currents of the power frequency is most efficient. Experimental results carried

A. Ametani

1976-01-01

223

Coherent Raman spectro-imaging with laser frequency combs  

NASA Astrophysics Data System (ADS)

Advances in optical spectroscopy and microscopy have had a profound impact throughout the physical, chemical and biological sciences. One example is coherent Raman spectroscopy, a versatile technique interrogating vibrational transitions in molecules. It offers high spatial resolution and three-dimensional sectioning capabilities that make it a label-free tool for the non-destructive and chemically selective probing of complex systems. Indeed, single-colour Raman bands have been imaged in biological tissue at video rates by using ultra-short-pulse lasers. However, identifying multiple, and possibly unknown, molecules requires broad spectral bandwidth and high resolution. Moderate spectral spans combined with high-speed acquisition are now within reach using multichannel detection or frequency-swept laser beams. Laser frequency combs are finding increasing use for broadband molecular linear absorption spectroscopy. Here we show, by exploring their potential for nonlinear spectroscopy, that they can be harnessed for coherent anti-Stokes Raman spectroscopy and spectro-imaging. The method uses two combs and can simultaneously measure, on the microsecond timescale, all spectral elements over a wide bandwidth and with high resolution on a single photodetector. Although the overall measurement time in our proof-of-principle experiments is limited by the waiting times between successive spectral acquisitions, this limitation can be overcome with further system development. We therefore expect that our approach of using laser frequency combs will not only enable new applications for nonlinear microscopy but also benefit other nonlinear spectroscopic techniques.

Ideguchi, Takuro; Holzner, Simon; Bernhardt, Birgitta; Guelachvili, Guy; Picqué, Nathalie; Hänsch, Theodor W.

2013-10-01

224

Optimum frequency for subsurface-imaging synthetic-aperture radar  

SciTech Connect

A subsurface-imaging synthetic-aperture radar (SISAR) has potential for application in areas as diverse as non-proliferation programs for nuclear weapons to environmental monitoring. However, most conventional synthetic-aperture radars operate at higher microwave frequencies which do not significantly penetrate below the soil surface. This study attempts to provide a basis for determining optimum frequencies and frequency ranges which will allow synthetic-aperture imaging of buried targets. Since the radar return from a buried object must compete with the return from surface clutter, the signal-to-clutter ratio is an appropriate measure of performance for a SISAR. A parameter-based modeling approach is used to model the complex dielectric constant of the soil from measured data obtained from the literature. Theoretical random-surface scattering models, based on statistical solutions to Maxwell`s equations, are used to model the clutter. These models are combined to estimate the signal-to-clutter ratio for canonical targets buried in several soil configurations. Initial results indicate that the HF spectrum (3--30 MHz), although it could be used to detect certain targets under some conditions, has limited practical value for use with SISAR, while the upper vhf through uhf spectrum ({approximately}100 MHz--1 GHz) shows the most promise for a general purpose SISAR system. Recommendations are included for additional research.

Brock, B.C.; Patitz, W.E.

1993-05-01

225

Optimum frequency for subsurface-imaging synthetic-aperture radar  

SciTech Connect

A subsurface-imaging synthetic-aperture radar (SISAR) has potential for application in areas as diverse as non-proliferation programs for nuclear weapons to environmental monitoring. However, most conventional synthetic-aperture radars operate at higher microwave frequencies which do not significantly penetrate below the soil surface. This study attempts to provide a basis for determining optimum frequencies and frequency ranges which will allow synthetic-aperture imaging of buried targets. Since the radar return from a buried object must compete with the return from surface clutter, the signal-to-clutter ratio is an appropriate measure of performance for a SISAR. A parameter-based modeling approach is used to model the complex dielectric constant of the soil from measured data obtained from the literature. Theoretical random-surface scattering models, based on statistical solutions to Maxwell's equations, are used to model the clutter. These models are combined to estimate the signal-to-clutter ratio for canonical targets buried in several soil configurations. Initial results indicate that the HF spectrum (3--30 MHz), although it could be used to detect certain targets under some conditions, has limited practical value for use with SISAR, while the upper vhf through uhf spectrum ([approximately]100 MHz--1 GHz) shows the most promise for a general purpose SISAR system. Recommendations are included for additional research.

Brock, B.C.; Patitz, W.E.

1993-05-01

226

High-Frequency Quantitative Ultrasound Imaging of Cancerous Lymph Nodes  

NASA Astrophysics Data System (ADS)

High-frequency ultrasound (HFU) offers a means of investigating biological tissue at the microscopic level. High-frequency, quantitative-ultrasound (QUS) methods were developed to characterize freshly-dissected lymph nodes of cancer patients. Three-dimensional (3D) ultrasound data were acquired from lymph nodes using a 25.6-MHz center-frequency transducer. Each node was inked prior to 3D histological fixation to recover orientation after sectioning. Backscattered echo signals were processed to yield two QUS estimates associated with tissue microstructure: scatterer size and acoustic concentration. The QUS estimates were computed following established methods using a Gaussian scattering model. Four lymph nodes from a patient with stage-3 colon cancer were evaluated as an illustrative case. QUS images were generated for this patient by expressing QUS estimates as color-encoded pixels and overlaying them on conventional gray-scale B-mode images. The single metastatic node had an average scatterer size that was significantly larger than the average scatterer size of the other nodes, and the statistics of both QUS estimates in the metastatic node showed greater variance than the statistics of the other nodes. Results indicate that the methods may provide a useful means of identifying small metastatic foci in dissected lymph nodes that might not be detectable using current standard pathology procedures.

Mamou, Jonathan; Coron, Alain; Hata, Masaki; Machi, Junji; Yanagihara, Eugene; Laugier, Pascal; Feleppa, Ernest J.

2009-07-01

227

Frequency-radial duality based photoacoustic image reconstruction.  

PubMed

Photoacoustic image reconstruction algorithms are usually slow due to the large sizes of data that are processed. This paper proposes a method for exact photoacoustic reconstruction for the spherical geometry in the limiting case of a continuous aperture and infinite measurement bandwidth that is faster than existing methods namely (1) backprojection method and (2) the Norton-Linzer method [S. J. Norton and M. Linzer, "Ultrasonic reflectivity imaging in three dimensions: Exact inverse scattering solution for plane, cylindrical and spherical apertures," Biomedical Engineering, IEEE Trans. BME 28, 202-220 (1981)]. The initial pressure distribution is expanded using a spherical Fourier Bessel series. The proposed method estimates the Fourier Bessel coefficients and subsequently recovers the pressure distribution. A concept of frequency-radial duality is introduced that separates the information from the different radial basis functions by using frequencies corresponding to the Bessel zeros. This approach provides a means to analyze the information obtained given a measurement bandwidth. Using order analysis and numerical experiments, the proposed method is shown to be faster than both the backprojection and the Norton-Linzer methods. Further, the reconstructed images using the proposed methodology were of similar quality to the Norton-Linzer method and were better than the approximate backprojection method. PMID:22779464

Akramus Salehin, S M; Abhayapala, Thushara D

2012-07-01

228

Continuous-wave operation of a frequency-tunable 460-GHz second-harmonic gyrotron for enhanced nuclear magnetic resonance  

E-print Network

The design, operation, and characterization of a continuous-wave (CW) tunable second-harmonic 460-GHz gyrotron are reported. The gyrotron is intended to be used as a submillimeter-wave source for 700-MHz nuclear magnetic ...

Torrezan de Sousa, Antonio Carlos

229

Multiphoton fluorescence and second harmonic generation microscopy for imaging corneal edema  

NASA Astrophysics Data System (ADS)

The purpose of this study is to investigate the structural features of corneal edema by multiphoton fluorescence and second harmonic generation (SHG) microscopy and the potential of this technique as a clinical in vivo monitoring technique for cornea disease diagnosis.

Hsueh, Chiu-Mei; Lo, Wen; Tan, Hsin-Yuan; Dong, Chen-Yuan

2008-02-01

230

High Frequency Quantitative Ultrasound Imaging of Solid Tumors in Mice  

NASA Astrophysics Data System (ADS)

A mammary carcinoma and a sarcoma were grown in mice and imaged with ultrasound transducers operating with a center frequency of 20 MHz. Quantitative ultrasound (QUS) analysis was used to characterize the tumors using the bandwidth of 10 to 25 MHz. Initial QUS estimates of the scatterer properties (average scatterer diameter and acoustic concentration) did not reveal differences between the two kinds of tumors. Examination of the tumors using light microscopy indicated definite structural differences between the two kinds of tumors. In order to draw out the structural differences with ultrasound, a higher frequency probe (center frequency measured at 70 MHz) was used to interrogate the two kinds of tumors and new models were applied to the QUS analysis. QUS scatterer diameter images of the tumors were constructed using the high frequency probe. Several models for scattering were implemented to obtain estimates of scatterer properties in order to relate estimated scatterer properties to real tissue microstructure. The Anderson model for scattering from a fluid-filled sphere differentiated the two kinds of tumors but did not yield scatterer property estimates that resembled underlying structure. Using the Anderson model, the average estimated scatterer diameters were 25.5 ± 0.14 ?m for the carcinoma and 57.5 ± 2.90 for the sarcoma. A new cell model was developed, which was based on scattering from a cell by incorporating the effects of the cytoskeleton and nucleus. The new cell model yielded estimates that appeared to reflect underlying structure more accurately but did not separate the two kinds of tumors. Using the new cell model, the average estimated scatterer diameters were 15.6 ± 2.2 ?m for the carcinoma and 16.8 ± 3.82 ?m for the sarcoma. The new cell model yielded estimates close to the actual nuclear diameter of the cell (13 ?m)

Oelze, M. L.; O'Brien, W. D.; Zachary, J. F.

231

Focused high frequency needle transducer for ultrasonic imaging and trapping  

NASA Astrophysics Data System (ADS)

A miniature focused needle transducer (<1 mm) was fabricated using the press-focusing technique. The measured pulse-echo waveform showed the transducer had center frequency of 57.5 MHz with 54% bandwidth and 14 dB insertion loss. To evaluate the performance of this type of transducer, invitro ultrasonic biomicroscopy imaging on the rabbit eye was obtained. Moreover, a single beam acoustic trapping experiment was performed using this transducer. Trapping of targeted particle size smaller than the ultrasonic wavelength was observed. Potential applications of these devices include minimally invasive measurements of retinal blood flow and single beam acoustic trapping of microparticles.

Hsu, Hsiu-Sheng; Zheng, Fan; Li, Ying; Lee, Changyang; Zhou, Qifa; Kirk Shung, K.

2012-07-01

232

Monitoring electrical and thermal burns with Spatial Frequency Domain Imaging  

NASA Astrophysics Data System (ADS)

Thermal and electrical injuries are devastating and hard-to-treat clinical lesions. The pathophysiology of these injuries is not fully understood to this day. Further elucidating the natural history of this form of tissue injury could be helpful in offering stage-appropriate therapy. Spatial Frequency Domain Imaging (SFDI) is a novel non-invasive technique that can be used to determine optical properties of biological media. We have developed an experimental apparatus based on SFDI aimed at monitoring parameters of clinical interest such as tissue oxygen saturation, methemoglobin volume fraction, and hemoglobin volume fraction. Co- registered Laser Doppler images of the lesions are also acquired to assess tissue perfusion. Results of experiments conducted on a rat model and discussions on the systemic changes in tissue optical properties before and after injury will be presented.

Ramella-Roman, Jessica

2011-10-01

233

Image transmission in tactical radio frequency shared network propagation environments  

NASA Astrophysics Data System (ADS)

The need to transmit images across tactical radio frequency (rf) links has been identified in army digitization applications. For example, military doctrine requires that tactical functions like identification of battlefield entities as potential targets and battle damage assessment be performed by the soldier. Currently, a key input to these processes is imagery. Therefore, the quality and timeliness of the image directly impact tactical performance. The military is investigating the employment of remote sensors and advanced communications systems to meet this requirement as part of its digitization effort. Army communications systems exist that partially meet this requirement. However, many existing solutions employ these legacy systems in the context of a point-to-point communications architecture. Solutions to the problem of transmitting images across a rf network have not been fully explored. The term network implies that the rf transmission media is common to and shared by multiple subscribers. It is a suite of capabilities that collectively manage media access and information transfer for its subscribers thus providing substantial improvements in effectiveness, efficiency, and robustness. This paper discusses the challenges of transmitting images using one army legacy communications system in a tactical rf network, presents a conceptual framework for attacking the problem, and discusses one solution.

White, Kent H.; Wagner, Kerry A.; O'Hanian, Scott

1997-06-01

234

Estimation methods for flow imaging with high frequency ultrasound.  

PubMed

This article proposes to estimate slow blood flow with high frequency ultrasound imaging. The proposed technique combines 2 methods. First, a statistical method, called Speckle Flow Imaging (SFI) based on the analysis of changes in the speckle pattern along time, gives an index directly related to the total velocity vector. Secondly, a block matching approach estimates the in-plane velocity components. Results on calibrated flow sequences of blood mimicking fluid have shown good agreement with the statistical model. The quantification of flow is achieved with pulsed flow and is also angle independent when the flow is perpendicular to the ultrasound beam. Speckle Tracking has been evaluated on the same data and has shown good estimation of the in-plane velocity vector when the component of velocity perpendicular to the imaging plane is inferior to 1mm/s. The results of these two methods permit the evaluation of the total 3D velocity field and the orthogonal velocity component relative to the imaging plane. This allows the quantification of blood flow (volumetric per time unit across the sequence). PMID:16844170

Aoudi, W; Liebgott, H; Needles, A; Yang, V; Foster, F S; Vray, D

2006-12-22

235

High Harmonic Generation Physics 208A Presentation  

E-print Network

High Harmonic Generation Physics 208A Presentation October 11, 2004 Tom Allison UC Berkeley #12 to Fourier components of the polarization at harmonics of the laser frequency, creating radiation at harmonics of the laser frequency. #12;· First demonstration of second harmonic generation by P.A. Franken et

Budker, Dmitry

236

Harmonic engine  

DOEpatents

A high efficiency harmonic engine based on a resonantly reciprocating piston expander that extracts work from heat and pressurizes working fluid in a reciprocating piston compressor. The engine preferably includes harmonic oscillator valves capable of oscillating at a resonant frequency for controlling the flow of working fluid into and out of the expander, and also preferably includes a shunt line connecting an expansion chamber of the expander to a buffer chamber of the expander for minimizing pressure variations in the fluidic circuit of the engine. The engine is especially designed to operate with very high temperature input to the expander and very low temperature input to the compressor, to produce very high thermal conversion efficiency.

Bennett, Charles L. (Livermore, CA)

2009-10-20

237

Feasibility of High Frequency Acoustic Imaging for Inspection of Containments  

SciTech Connect

The Nuclear Regulatory Commission has a program at the Oak Ridge National Laboratory to provide assistance in their assessment of the effects of potential degradation on the structural integrity and Ieaktightness of metal containment vessels and steel liners of concrete containment in nuclear power plants. One of the program objectives is to identify a technique(s) for inspection of inaccessible portions of the containment pressure boundary. Acoustic imaging has been identified as one of these potential techniques. A numerical feasibility study investigated the use of high-frequency bistatic acoustic imaging techniques for inspection of inaccessible portions of the metallic pressure boundary of nuclear power plant containment. The range-dependent version of the OASES Code developed at the Massachusetts Institute of Technology was utilized to perform a series of numerical simulations. OASES is a well developed and extensively tested code for evaluation of the acoustic field in a system of stratified fluid and/or elastic layers. Using the code, an arbitrary number of fluid or solid elastic layers are interleaved, with the outer layers modeled as halfspaces. High frequency vibrational sources were modeled to simulate elastic waves in the steel. The received field due to an arbitrary source array can be calculated at arbitrary depth and range positions. In this numerical study, waves that reflect and scatter from surface roughness caused by modeled degradations (e.g., corrosion) are detected and used to identify and map the steel degradation. Variables in the numerical study included frequency, flaw size, interrogation distance, and sensor incident angle.Based on these analytical simulations, it is considered unlikely that acoustic imaging technology can be used to investigate embedded steel liners of reinforced concrete containment. The thin steel liner and high signal losses to the concrete make this application difficult. Results for portions of steel containment embedded in concrete are more encouraging in that they indicate that the intrinsic backscatter from degradations representing thickness reductions from 10 to 80% the shell thickness are sufficient to permit detection. It is recommended that a controlled experimental program be conducted in which sensor levels are calibrated against degradations to determine if current sensor technology can input sufficient power into the system to provide return levels within the dynamic range of the receivers.

C.N. Corrado; J.E. Bondaryk; V. Godino

1998-08-01

238

Three-frequency RF coil designed for optimized imaging of hyperpolarized, 13C-labeled compounds.  

PubMed

Imaging exams involving hyperpolarized, (13)C-labeled compounds require novel RF coils for efficient signal utilization. While (13)C coils are required for mapping the spatial distribution of the hyperpolarized compounds, imaging/pulsing at different frequencies is also needed for scan setup steps prior to the image acquisition. Imaging/pulsing at the (1)H frequency is typically used for anatomical localization and shimming. Flip angle (FA) calibration, which is difficult or impossible to achieve at the (13)C frequency, can be accurately performed at the (23)Na frequency using the natural abundance signal that exists in any living tissue. We demonstrate here a single RF resonant structure that is capable of operating linearly at the (1)H and (23)Na frequencies for scan setup steps, and in quadrature at the (13)C frequency for imaging. Images at the three resonant frequencies of this coil are presented from an exam involving hyperpolarized (13)C compounds in vivo. PMID:18816813

Hancu, Ileana; Wood, S James; Piel, Joseph; Whitt, David B; Fish, Kenneth M; Rutt, Brian K; Tropp, James; Dixon, W Thomas

2008-10-01

239

In vivo imaging of dermal collagen in skin burn by collagen-sensitive second-harmonic-generation microscopy  

NASA Astrophysics Data System (ADS)

Optical assessment of skin burns is possible with second-harmonic-generation (SHG) microscopy due to its high sensitivity to thermal denaturation of collagen molecules. In contrast to previous studies that were performed using excised tissue specimens ex vivo, in this study, we demonstrated in vivo observation of dermal collagen fibers in living rat burn models with SHG microscopy. We confirmed that changes in SHG vanishing patterns in the SHG images depended on the burn degree. The results imply that SHG microscopy can be used as a low-invasiveness, highly quantitative tool for skin burn assessment.

Yasui, Takeshi; Tanaka, Ryosuke; Hase, Eiji; Fukushima, Shu-ichiro; Araki, Tsutomu

2013-02-01

240

Linewidth of the harmonics in a microwave frequency comb generated by focusing a mode-locked ultrafast laser on a tunneling junction  

SciTech Connect

Previous analyses suggest that microwave frequency combs (MFCs) with harmonics having extremely narrow linewidths could be produced by photodetection with a mode-locked ultrafast laser. In the MFC generated by focusing a passively mode-locked ultrafast laser on a tunneling junction, 200 harmonics from 74.254?MHz to 14.85?GHz have reproducible measured linewidths approximating the 1?Hz resolution bandwidth (RBW) of the spectrum analyzer. However, in new measurements at a RBW of 0.1?Hz, the linewidths are distributed from 0.12 to 1.17?Hz. Measurements and analysis suggest that, because the laser is not stabilized, the stochastic drift in the pulse repetition rate is the cause for the distribution in measured linewidths. It appears that there are three cases in which the RBW is (1) greater than, (2) less than, or (3) comparable with the intrinsic linewidth. The measured spectra in the third class are stochastic and may show two or more peaks at a single harmonic.

Hagmann, Mark J. [Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112 (United States); Stenger, Frank S. [School of Computing, University of Utah, Salt Lake City, Utah 84112 (United States); Yarotski, Dmitry A. [Center for Integrated Nanotechnologies, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2013-12-14

241

Cassini/RPWS: A low frequency radio imager at Saturn  

NASA Astrophysics Data System (ADS)

The High Frequency Receiver (HFR) of the Radio and Plasma Waves Science experiment (RPWS) onboard Cassini is a sensitive, and versatile radio instrument. Although the radio antenna connected to this instrument have no intrinsic directivity, the HFR measurements can provide instantaneous direction of arrival, flux density and polarization degree of the observed radio waves. Hence, the HFR can be described as an full-sky radio imager. As the instrument provides direction of arrival, radio sources can be located with some assumption on the propagation between the source and the observer. Hence, it is possible to produce radio source maps and correlate them with observations at other wavelengths, such as UV or IR observations of the auroral regions of Saturn. The flux and polarization measurements together with the time-frequency shape of the radio emissions can also be used to identify the radio emission processes. We present a review of the results of the Cassini/RPWS/HFR observations since its arrival at Saturn in 2004: interpretation of the radio arc shapes and equatorial shadow zones; in-situ observations in the radio source region; comparison with other wavelengths and particle measurements; confirmation of the Cyclotron Maser Instability (CMI) as the main emission mechanism for auroral radio emissions; monitoring of the radio emission variability in time and location, etc.

Cecconi, Baptiste; Lamy, Laurent; Zarka, Philippe

2014-05-01

242

Four-frequency polarizing microscope for recording plasma images in the wavelength range 0.4-1.1 {mu}m  

SciTech Connect

The optical scheme and design of a four-frequency polarizing microscope intended for simultaneous recording of plasma images in the wavelength range 0.4-1.1 {mu}m with the spatial resolution 12 {mu}m in the entire spectral range are described. The effectiveness of such a microscope in studies of plasmas produced on interaction of laser radiation with a target is demonstrated. The plasma images are obtained at the frequencies {omega}{sub 0}, (3/2){omega}{sub 0}, 2{omega}{sub 0}, and (5/2){omega}{sub 0}, where {omega}{sub 0} corresponds to the frequency of heating radiation. The transformation coefficient that characterizes the efficiency of conversion of heating radiation into the 2{omega}{sub 0}, (3/2){omega}{sub 0}, and (5/2){omega}{sub 0} harmonics generated in the plasma is determined.

Vasin, B. L.; Mal'kova, S. V.; Osipov, M. V.; Puzyrev, V. N.; Saakyan, A. T.; Starodub, A. N.; Fedotov, S. I.; Fronya, A. A.; Shutyak, V. G. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

2010-12-15

243

Estimating the low-frequency (0.1-1 kHz) sound speed in marine sediments using the harmonics from the propeller of a light aircraft  

NASA Astrophysics Data System (ADS)

During ONR's Sediment Acoustics Experiment 1999 (SAX99) in the northeastern Gulf of Mexico, several research groups made high-precision, in situ measurements of dispersion in the medium-sand sediment at frequencies greater than 20 kHz. Comparable precision at lower frequencies is difficult to achieve with in situ time-of-flight techniques because of wavelength issues which, inter alia, dictate an inconveniently large and costly acoustic source. Yet low-frequency (1 kHz) sound speed measurements are sorely needed to distinguish between competing theoretical predictions. An alternative to the traditional travel-time approach employs a single hydrophone buried in the sediment and, instead of an in situ sound source, the low-frequency harmonics from the propeller of a light aircraft. Essentially, the airborne-source technique relies on the difference between the Doppler-shifted frequencies on aircraft approach and departure, as detected on the buried hydrophone, to yield a direct measure of the local sound speed at the detector. Experiments recently conducted about 1.5 km north of Scripps pier, using a single-engine Tobago TB10 aircraft with a two-blade propeller, will be described and the resultant estimates of the low-frequency sound speed in the fine-sand sediment at the site will be presented. [Work supported by ONR.

Buckingham, Michael J.; Giddens, Eric M.

2003-04-01

244

Visible spatial frequency domain imaging with a digital light microprojector  

PubMed Central

Abstract. There is a need for cost effective, quantitative tissue spectroscopy and imaging systems in clinical diagnostics and pre-clinical biomedical research. A platform that utilizes a commercially available light-emitting diode (LED) based projector, cameras, and scaled Monte Carlo model for calculating tissue optical properties is presented. These components are put together to perform spatial frequency domain imaging (SFDI), a model-based reflectance technique that measures and maps absorption coefficients (?a) and reduced scattering coefficients (?s?) in thick tissue such as skin or brain. We validate the performance of the flexible LED and modulation element (FLaME) system at 460, 530, and 632 nm across a range of physiologically relevant ?a values (0.07 to 1.5??mm?1) in tissue-simulating intralipid phantoms, showing an overall accuracy within 11% of spectrophotometer values for ?a and 3% for ?s?. Comparison of oxy- and total hemoglobin fits between the FLaME system and a spectrophotometer (450 to 1000 nm) is differed by 3%. Finally, we acquire optical property maps of a mouse brain in vivo with and without an overlying saline well. These results demonstrate the potential of FLaME to perform tissue optical property mapping in visible spectral regions and highlight how the optical clearing effect of saline is correlated to a decrease in ?s? of the skull. PMID:24005154

Lin, Alexander J.; Ponticorvo, Adrien; Konecky, Soren D.; Cui, Haotian; Rice, Tyler B.; Choi, Bernard; Durkin, Anthony J.; Tromberg, Bruce J.

2013-01-01

245

Radio-frequency energy quantification in magnetic resonance imaging  

NASA Astrophysics Data System (ADS)

Mapping of radio frequency (RF) energy deposition has been challenging for 50+ years, especially, when scanning patients in the magnetic resonance imaging (MRI) environment. As result, electromagnetic simulation software is often used for estimating the specific absorption rate (SAR), the rate of RF energy deposition in tissue. The thesis work presents challenges associated with aligning information provided by electromagnetic simulation and MRI experiments. As result of the limitations of simulations, experimental methods for the quantification of SAR were established. A system for quantification of the total RF energy deposition was developed for parallel transmit MRI (a system that uses multiple antennas to excite and image the body). The system is capable of monitoring and predicting channel-by-channel RF energy deposition, whole body SAR and capable of tracking potential hardware failures that occur in the transmit chain and may cause the deposition of excessive energy into patients. Similarly, we demonstrated that local RF power deposition can be mapped and predicted for parallel transmit systems based on a series of MRI temperature mapping acquisitions. Resulting from the work, we developed tools for optimal reconstruction temperature maps from MRI acquisitions. The tools developed for temperature mapping paved the way for utilizing MRI as a diagnostic tool for evaluation of RF/microwave emitting device safety. Quantification of the RF energy was demonstrated for both MRI compatible and non-MRI-compatible devices (such as cell phones), while having the advantage of being noninvasive, of providing millimeter resolution and high accuracy.

Alon, Leeor

246

A new image cipher in time and frequency domains  

NASA Astrophysics Data System (ADS)

Recently, various encryption techniques based on chaos have been proposed. However, most existing chaotic encryption schemes still suffer from fundamental problems such as small key space, weak security function and slow performance speed. This paper introduces an efficient encryption scheme for still visual data that overcome these disadvantages. The proposed scheme is based on hybrid Linear Feedback Shift Register (LFSR) and chaotic systems in hybrid domains. The core idea is to scramble the pixel positions based on 2D chaotic systems in frequency domain. Then, the diffusion is done on the scrambled image based on cryptographic primitive operations and the incorporation of LFSR and chaotic systems as round keys. The hybrid compound of LFSR, chaotic system and cryptographic primitive operations strengthen the encryption performance and enlarge the key space required to resist the brute force attacks. Results of statistical and differential analysis show that the proposed algorithm has high security for secure digital images. Furthermore, it has key sensitivity together with a large key space and is very fast compared to other competitive algorithms.

Abd El-Latif, Ahmed A.; Niu, Xiamu; Amin, Mohamed

2012-10-01

247

Quantification of collagen fiber organization in biological tissues at cellular and molecular scales using second-harmonic generation imaging  

NASA Astrophysics Data System (ADS)

Collagen is the most abundant structural protein found in the human body, and is responsible for providing structure and function to tissues. Collagen molecules organize naturally into structures called fibers on the scale of the wavelength of light and lack inversion symmetry, thus allowing for the process of second harmonic generation (SHG) when exposed to intense incident light. We have developed two quantitative techniques: Fourier transform-second-harmonic generation (FT-SHG) imaging and generalized chi2 second-harmonic generation (chi2-SHG) imaging. In order to show that FT-SHG imaging can be used as a valuable diagnostic tool for real-world biological problems, we first investigate collagenase-induced injury in horse tendons. Clear differences in collagen fiber organization between normal and injured tendon are quantified. In particular, we observe that the regularly oriented organization of collagen fibers in normal tendons is disrupted in injured tendons leading to a more random organization. We also observe that FT-SHG microscopy is more sensitive in assessing tendon injury compared to the conventional polarized light microscopy. The second study includes quantifying collagen fibers in cortical bone using FT-SHG imaging and comparing it with scanning electron microscopy (SEM). Further, as an example study, we show how FT-SHG imaging could be used to quantify changes in bone structure as a function of age. Some initial work and future directions for extending FT-SHG to 3D are also discussed. The second technique, chi2-SHG imaging, takes advantage of the coherent nature of SHG and utilizes polarization to extract the second-order susceptibility (d elements) which provides information on molecular organization, i.e., it provides access to sub-diffractional changes "optically". We use chi2-SHG in combination with FT-SHG imaging to investigate a couple of biological problems. First, we quantify differences in collagen fiber organization between cornea and sclera of the eye in order to investigate their properties of transparency and opacity, respectively. We find from chi2-SHG imaging that there is no statistical difference in the values of d elements between cornea and sclera, indicating that the underlying collagen structure generating SHG from the two is similar at the level of detection of SHG microscopy. However, the difference lies in the spatial organization of these collagen fibers as observed from FT-SHG imaging. We find that cornea contains lamellae with patches of ordered and uniform diameter collagen fibers with axial order, which could be the reason for its transparent behavior. Conversely, there are no lamellae in sclera (i.e., no axial order), and fibers are thicker, denser, have inconsistent diameters, and possess relatively inhomogeneous orientations, leading to its opaque nature. We also utilized the two techniques to assess differences in stromal collagen fibers for several human breast tissue conditions: normal, hyperplasia, dysplasia, and malignant. Using FT-SHG imaging, we note differences between malignant and other pathological conditions through the metric A.I. ratio. Using generalized chi2-SHG imaging, we observe structural changes in collagen at the molecular scale, and a particular d element showed a more sensitive differentiation between breast tissue conditions, except between hyperplasia and normal/dysplasia. We also find that the trigonal symmetry (3m) is a more appropriate model to describe collagen fibers in malignant tissues as opposed to the conventionally used hexagonal symmetry (C6). Furthermore, the percentage of abnormal collagen fibers could potentially be used as a metric for differentiating breast tissue conditions. We also introduce a technique for extending chi2-SHG to fibers with curvature which is useful for generating chi2-image maps (in terms of d elements) instead of the conventional SHG intensity images. The spatial variations in d elements will provide additional information. For example, in breast cancer tissues, it may help in observing how fibers chang

Ambekar Ramachandra Rao, Raghu

248

Femtosecond two-photon LIF imaging of atomic species using a frequency-quadrupled Ti:sapphire laser  

NASA Astrophysics Data System (ADS)

Femtosecond (fs)-duration laser pulses are well suited for two-photon laser-induced-fluorescence (TPLIF) imaging of key atomic species such as H, N, and O in gas-phase reacting flows. Ultrashort pulses enable efficient nonlinear excitation, while reducing interfering photochemical processes. Furthermore, amplified fs lasers enable high-repetition-rate imaging (typically 1-10 kHz) for capturing the dynamics of turbulent flow fields. However, two-dimensional (2D), single-laser-shot fs-TPLIF imaging of the above species is challenging in most practical flow fields because of the limited ultraviolet pulse energy available in commercial optical parametric amplifier (OPA)-based tunable laser sources. In this work, we report the development of an efficient, fs frequency-quadrupling unit [i.e., fourth-harmonic generator (FHG)] with overall conversion efficiency more than six times greater than that of commercial OPA-based systems. The development, characterization, and application of the fs-FHG system for 2D imaging of H atoms in flames are described in detail. The potential application of the same laser system for 2D imaging of N and O atoms is also discussed.

Kulatilaka, Waruna D.; Gord, James R.; Roy, Sukesh

2014-07-01

249

Single-Shot Diffractive Imaging with a Table-Top Femtosecond Soft X-Ray Laser-Harmonics Source  

SciTech Connect

Coherent x-ray diffractive imaging is a powerful method for studies on nonperiodic structures on the nanoscale. Access to femtosecond dynamics in major physical, chemical, and biological processes requires single-shot diffraction data. Up to now, this has been limited to intense coherent pulses from a free electron laser. Here we show that laser-driven ultrashort x-ray sources offer a comparatively inexpensive alternative. We present measurements of single-shot diffraction patterns from isolated nano-objects with a single 20 fs pulse from a table-top high-harmonic x-ray laser. Images were reconstructed with a resolution of 119 nm from the single shot and 62 nm from multiple shots.

Ravasio, A.; Gauthier, D.; Billon, M.; Caumes, J-P.; Garzella, D.; Geleoc, M.; Gobert, O.; Hergott, J-F.; Pena, A-M.; Perez, H.; Carre, B. [Commissariat a l'Energie Atomique, Service des Photons, Atomes et Molecules, Batiment 522, Centre d'Etude de Saclay, 91191 Gif-sur-Yvette (France); Maia, F. R. N. C. [Laboratory of Molecular Biophysics, Department of Cell and Molecular Biology, Uppsala University, Husargatan 3 (Box 596), SE-751 24 Uppsala (Sweden); Bourhis, E.; Gierak, J.; Madouri, A.; Mailly, D.; Schiedt, B. [Laboratoire de Photonique et Nanostructures, CNRS-UPR20, Route de Nozay, F-91460 Marcoussis (France); Fajardo, M. [Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, Avenue Rovisco Pais, 1049-001 Lisboa (Portugal); Gautier, J.; Zeitoun, P. [Laboratoire d'Optique Appliquee, Ecole Nationale Superieure de Technique Avancees, Ecole Polytechnique, CNRS UMR7639, Chemin de la Huniere, 91761 Palaiseau Cedex (France)

2009-07-10

250

Extended Finite Element Method with Simplified Spherical Harmonics Approximation for the Forward Model of Optical Molecular Imaging  

PubMed Central

An extended finite element method (XFEM) for the forward model of 3D optical molecular imaging is developed with simplified spherical harmonics approximation (SPN). In XFEM scheme of SPN equations, the signed distance function is employed to accurately represent the internal tissue boundary, and then it is used to construct the enriched basis function of the finite element scheme. Therefore, the finite element calculation can be carried out without the time-consuming internal boundary mesh generation. Moreover, the required overly fine mesh conforming to the complex tissue boundary which leads to excess time cost can be avoided. XFEM conveniences its application to tissues with complex internal structure and improves the computational efficiency. Phantom and digital mouse experiments were carried out to validate the efficiency of the proposed method. Compared with standard finite element method and classical Monte Carlo (MC) method, the validation results show the merits and potential of the XFEM for optical imaging. PMID:23227108

Li, Wei; Yi, Huangjian; Zhang, Qitan; Chen, Duofang; Liang, Jimin

2012-01-01

251

Molecular structure, Normal Coordinate Analysis, harmonic vibrational frequencies, Natural Bond Orbital, TD-DFT calculations and biological activity analysis of antioxidant drug 7-hydroxycoumarin  

NASA Astrophysics Data System (ADS)

In this work, we report harmonic vibrational frequencies, molecular structure, NBO and HOMO, LUMO analysis of Umbelliferone also known as 7-hydroxycoumarin (7HC). The optimized geometric bond lengths and bond angles obtained by computation (monomer and dimmer) shows good agreement with experimental XRD data. Harmonic frequencies of 7HC were determined and analyzed by DFT utilizing 6-311+G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of Normal Coordinate Analysis (NCA) following the Scaled Quantum Mechanical Force Field Methodology (SQMFF). The change in electron density (ED) in the ?* and ?* antibonding orbitals and stabilization energies E(2) have been calculated by Natural Bond Orbital (NBO) analysis to give clear evidence of stabilization originating in the hyperconjugation of hydrogen-bonded interaction. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. The simulated spectra satisfactorily coincides with the experimental spectra. Microbial activity of studied compounds was tested against Staphylococcus aureus, Streptococcus pyogenes, Bacillus subtilis, Escherichia coli, Psuedomonas aeruginosa, Klebsiella pneumoniae, Proteus mirabilis, Shigella flexneri, Salmonella typhi and Enterococcus faecalis.

Sebastian, S.; Sylvestre, S.; Jayarajan, D.; Amalanathan, M.; Oudayakumar, K.; Gnanapoongothai, T.; Jayavarthanan, T.

2013-01-01

252

Molecular structure, Normal Coordinate Analysis, harmonic vibrational frequencies, Natural Bond Orbital, TD-DFT calculations and biological activity analysis of antioxidant drug 7-hydroxycoumarin.  

PubMed

In this work, we report harmonic vibrational frequencies, molecular structure, NBO and HOMO, LUMO analysis of Umbelliferone also known as 7-hydroxycoumarin (7HC). The optimized geometric bond lengths and bond angles obtained by computation (monomer and dimmer) shows good agreement with experimental XRD data. Harmonic frequencies of 7HC were determined and analyzed by DFT utilizing 6-311+G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of Normal Coordinate Analysis (NCA) following the Scaled Quantum Mechanical Force Field Methodology (SQMFF). The change in electron density (ED) in the ?* and ?* antibonding orbitals and stabilization energies E(2) have been calculated by Natural Bond Orbital (NBO) analysis to give clear evidence of stabilization originating in the hyperconjugation of hydrogen-bonded interaction. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. The simulated spectra satisfactorily coincides with the experimental spectra. Microbial activity of studied compounds was tested against Staphylococcus aureus, Streptococcus pyogenes, Bacillus subtilis, Escherichia coli, Psuedomonas aeruginosa, Klebsiella pneumoniae, Proteus mirabilis, Shigella flexneri, Salmonella typhi and Enterococcus faecalis. PMID:23123244

Sebastian, S; Sylvestre, S; Jayarajan, D; Amalanathan, M; Oudayakumar, K; Gnanapoongothai, T; Jayavarthanan, T

2013-01-15

253

Label-free and real-time imaging of dehydration-induced DNA conformational changes in cellular nucleus using second harmonic microscopy  

NASA Astrophysics Data System (ADS)

Dehydration-induced DNA conformational changes have been probed for the first time with the use of second harmonic microscopy. Unlike conventional approaches, second harmonic microscopy provides a label-free and real-time approach to detect DNA conformational changes. Upon dehydration, cellular DNA undergoes a transition from B- to A-form, whereas cellular nuclei change from invisible to visible under second harmonic microscopy. These results showed that DNA is a second order nonlinear optical material. We further confirmed this by characterizing the nonlinear optical properties of extracted DNA from human cells. Our findings open a new path for SHG imaging. DNA can change its conformations under many circumstances. For example: normal cells turning into cancerous cells and drug molecules binding with DNA. Therefore, the detection of DNA conformational changes with second harmonic microscopy will be a useful tool in cancer therapy and new drug discovery.

Zhuo, Shuangmu; Ni, Ming

2014-12-01

254

Laser speckle imaging in the spatial frequency Amaan Mazhar,1,2  

E-print Network

Laser speckle imaging in the spatial frequency domain Amaan Mazhar,1,2 David J. Cuccia,3 Tyler B Beckman Laser Institute, University of California, Irvine, California 92612, USA 3 Modulated Imaging Inc, USA *bjtrombe@uci.edu Abstract: Laser Speckle Imaging (LSI) images interference patterns produced

Choi, Bernard

255

Laser speckle imaging in the spatial frequency domain  

E-print Network

A. Martinos Center for Biomedical Imaging, Charlestown,speckle contrast imaging in biomedical optics,” J. Biomed.Biomedical Engineering, University of California, Irvine, California 92612, USA Beckman Laser Institute, University of California, Irvine, California 92612, USA Modulated Imaging

2011-01-01

256

Spatial and frequency-based super-resolution of ultrasound images  

PubMed Central

Modern ultrasound systems can output video images containing more spatial and temporal information than still images. Super-resolution techniques can exploit additional information but face two challenges: image registration and complex motion. In addition, information from multiple available frequencies is unexploited. Herein, we utilised these information sources to create better ultrasound images and videos, extending existing technologies for image capture. Spatial and frequency-based super-resolution processing using multiple motion estimation and frequency combination was applied to ultrasound videos of deforming models. Processed images are larger, have greater clarity and detail, and less variability in intensity between frames. Significantly, strain measurements are more accurate and precise than those from raw videos, and have a higher contrast ratio between ‘tumour’ and ‘surrounding tissue’ in a phantom model. We attribute improvements to reduced noise and increased resolution in processed images. Our methods can significantly improve quantitative and qualitative assessments of ultrasound images when compared assessments of standard images. PMID:25191631

Wu, Mon-Ju; Karls, Joseph; Duenwald-Kuehl, Sarah; Vanderby, Ray; Sethares, William

2014-01-01

257

Advanced Reservoir Imaging Using Frequency-Dependent Seismic Attributes  

SciTech Connect

Our report concerning advanced imaging and interpretation technology includes the development of theory, the implementation of laboratory experiments and the verification of results using field data. We investigated a reflectivity model for porous fluid-saturated reservoirs and demonstrated that the frequency-dependent component of the reflection coefficient is asymptotically proportional to the reservoir fluid mobility. We also analyzed seismic data using different azimuths and offsets over physical models of fractures filled with air and water. By comparing our physical model synthetics to numerical data we have identified several diagnostic indicators for quantifying the fractures. Finally, we developed reflectivity transforms for predicting pore fluid and lithology using rock-property statistics from 500 reservoirs in both the shelf and deep-water Gulf of Mexico. With these transforms and seismic AVO gathers across the prospect and its down-dip water-equivalent reservoir, fluid saturation can be estimated without a calibration well that ties the seismic. Our research provides the important additional mechanisms to recognize, delineate, and validate new hydrocarbon reserves and assist in the development of producing fields.

Fred Hilterman; Tad Patzek; Gennady Goloshubin; Dmitriy Silin; Charlotte Sullivan; Valeri Korneev

2007-12-31

258

2D harmonic filtering of MR phase images in multicenter clinical setting: Toward a magnetic signature of cerebral microbleeds.  

PubMed

Cerebral microbleeds (CMBs) have emerged as a new imaging marker of small vessel disease. Composed of hemosiderin, CMBs are paramagnetic and can be detected with MRI sequences sensitive to magnetic susceptibility (typically, gradient recalled echo T2* weighted images). Nevertheless, their identification remains challenging on T2* magnitude images because of confounding structures and lesions. In this context, T2* phase image may play a key role in better characterizing CMBs because of its direct relationship with local magnetic field variations due to magnetic susceptibility difference. To address this issue, susceptibility-based imaging techniques were proposed, such as Susceptibility Weighted Imaging (SWI) and Quantitative Susceptibility Mapping (QSM). But these techniques have not yet been validated for 2D clinical data in multicenter settings. Here, we introduce 2DHF, a fast 2D phase processing technique embedding both unwrapping and harmonic filtering designed for data acquired in 2D, even with slice-to-slice inconsistencies. This method results in internal field maps which reveal local field details due to magnetic inhomogeneity within the region of interest only. This technique is based on the physical properties of the induced magnetic field and should yield consistent results. A synthetic phantom was created for numerical simulations. It simulates paramagnetic and diamagnetic lesions within a 'brain-like' tissue, within a background. The method was evaluated on both this synthetic phantom and multicenter 2D datasets acquired in standardized clinical setting, and compared with two state-of-the-art methods. It proved to yield consistent results on synthetic images and to be applicable and robust on patient data. As a proof-of-concept, we finally illustrate that it is possible to find a magnetic signature of CMBs and CMCs on internal field maps generated with 2DHF on 2D clinical datasets that give consistent results with CT-scans in a subsample of 10 subjects acquired with both modalities. PMID:25149849

Kaaouana, Takoua; de Rochefort, Ludovic; Samaille, Thomas; Thiery, Nathalie; Dufouil, Carole; Delmaire, Christine; Dormont, Didier; Chupin, Marie

2015-01-01

259

Investigation of Photonic Devices using Second-Harmonic-Generation Frequency-Resolved Optical Gating (SHG-FROG)  

E-print Network

Gating (SHG-FROG) Brian R. Washburn The heart of an experiment in ultrafast optics is the pulsed laser be used to determine the pulse duration. Frequency-resolved optical gating (FROG) is a technique autocorrelation. Plus, due to the overdetermination of the pulse in the time- frequency domain, FROG has built

Washburn, Brian

260

Advanced imaging and spectroscopy of biological and chemical agents at terahertz frequencies  

Microsoft Academic Search

We are developing hot electron bolometer (HEB) mixer receivers for heterodyne detection at terahertz frequencies. HEB detectors provide unprecedented sensitivity and spectral resolution at terahertz frequencies. Terahertz imagers based on HEB technology have sufficient sensitivity to operate in a passive imaging mode, thus eliminating the need for active illumination. HEB mixers have, therefore, become the detectors of choice for applications

E. Gerecht; D. Gu; L. You; S. Yngvesson

2007-01-01

261

Orbital-optimized coupled-electron pair theory and its analytic gradients: Accurate equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions  

NASA Astrophysics Data System (ADS)

Orbital-optimized coupled-electron pair theory [or simply "optimized CEPA(0)," OCEPA(0), for short] and its analytic energy gradients are presented. For variational optimization of the molecular orbitals for the OCEPA(0) method, a Lagrangian-based approach is used along with an orbital direct inversion of the iterative subspace algorithm. The cost of the method is comparable to that of CCSD [O(N6) scaling] for energy computations. However, for analytic gradient computations the OCEPA(0) method is only half as expensive as CCSD since there is no need to solve the ?2-amplitude equation for OCEPA(0). The performance of the OCEPA(0) method is compared with that of the canonical MP2, CEPA(0), CCSD, and CCSD(T) methods, for equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions between radicals. For bond lengths of both closed and open-shell molecules, the OCEPA(0) method improves upon CEPA(0) and CCSD by 25%-43% and 38%-53%, respectively, with Dunning's cc-pCVQZ basis set. Especially for the open-shell test set, the performance of OCEPA(0) is comparable with that of CCSD(T) (?R is 0.0003 Å on average). For harmonic vibrational frequencies of closed-shell molecules, the OCEPA(0) method again outperforms CEPA(0) and CCSD by 33%-79% and 53%-79%, respectively. For harmonic vibrational frequencies of open-shell molecules, the mean absolute error (MAE) of the OCEPA(0) method (39 cm-1) is fortuitously even better than that of CCSD(T) (50 cm-1), while the MAEs of CEPA(0) (184 cm-1) and CCSD (84 cm-1) are considerably higher. For complete basis set estimates of hydrogen transfer reaction energies, the OCEPA(0) method again exhibits a substantially better performance than CEPA(0), providing a mean absolute error of 0.7 kcal mol-1, which is more than 6 times lower than that of CEPA(0) (4.6 kcal mol-1), and comparing to MP2 (7.7 kcal mol-1) there is a more than 10-fold reduction in errors. Whereas the MAE for the CCSD method is only 0.1 kcal mol-1 lower than that of OCEPA(0). Overall, the present application results indicate that the OCEPA(0) method is very promising not only for challenging open-shell systems but also for closed-shell molecules.

Bozkaya, U?ur; Sherrill, C. David

2013-08-01

262

Orbital-optimized coupled-electron pair theory and its analytic gradients: accurate equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions.  

PubMed

Orbital-optimized coupled-electron pair theory [or simply "optimized CEPA(0)," OCEPA(0), for short] and its analytic energy gradients are presented. For variational optimization of the molecular orbitals for the OCEPA(0) method, a Lagrangian-based approach is used along with an orbital direct inversion of the iterative subspace algorithm. The cost of the method is comparable to that of CCSD [O(N(6)) scaling] for energy computations. However, for analytic gradient computations the OCEPA(0) method is only half as expensive as CCSD since there is no need to solve the ?2-amplitude equation for OCEPA(0). The performance of the OCEPA(0) method is compared with that of the canonical MP2, CEPA(0), CCSD, and CCSD(T) methods, for equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions between radicals. For bond lengths of both closed and open-shell molecules, the OCEPA(0) method improves upon CEPA(0) and CCSD by 25%-43% and 38%-53%, respectively, with Dunning's cc-pCVQZ basis set. Especially for the open-shell test set, the performance of OCEPA(0) is comparable with that of CCSD(T) (?R is 0.0003 A? on average). For harmonic vibrational frequencies of closed-shell molecules, the OCEPA(0) method again outperforms CEPA(0) and CCSD by 33%-79% and 53%-79%, respectively. For harmonic vibrational frequencies of open-shell molecules, the mean absolute error (MAE) of the OCEPA(0) method (39 cm(-1)) is fortuitously even better than that of CCSD(T) (50 cm(-1)), while the MAEs of CEPA(0) (184 cm(-1)) and CCSD (84 cm(-1)) are considerably higher. For complete basis set estimates of hydrogen transfer reaction energies, the OCEPA(0) method again exhibits a substantially better performance than CEPA(0), providing a mean absolute error of 0.7 kcal mol(-1), which is more than 6 times lower than that of CEPA(0) (4.6 kcal mol(-1)), and comparing to MP2 (7.7 kcal mol(-1)) there is a more than 10-fold reduction in errors. Whereas the MAE for the CCSD method is only 0.1 kcal mol(-1) lower than that of OCEPA(0). Overall, the present application results indicate that the OCEPA(0) method is very promising not only for challenging open-shell systems but also for closed-shell molecules. PMID:23927240

Bozkaya, U?ur; Sherrill, C David

2013-08-01

263

Time domain simulation of harmonic ultrasound images and beam patterns in 3D using the k-space pseudospectral method.  

PubMed

A k-space pseudospectral model is developed for the fast full-wave simulation of nonlinear ultrasound propagation through heterogeneous media. The model uses a novel equation of state to account for nonlinearity in addition to power law absorption. The spectral calculation of the spatial gradients enables a significant reduction in the number of required grid nodes compared to finite difference methods. The model is parallelized using a graphical processing unit (GPU) which allows the simulation of individual ultrasound scan lines using a 256 x 256 x 128 voxel grid in less than five minutes. Several numerical examples are given, including the simulation of harmonic ultrasound images and beam patterns using a linear phased array transducer. PMID:22003638

Treeby, Bradley E; Tumen, Mustafa; Cox, B T

2011-01-01

264

Microscopic imaging of glyceraldehyde-induced tissue glycation with intrinsic second harmonic generation and two-photon fluorescence contrasts  

NASA Astrophysics Data System (ADS)

The bioinspired approaches to tissue strengthening and preservation rely on non-toxic cross-linking agents one of which is glyceraldehyde. In this study we used multiphoton microscopy that employs second harmonic generation (SHG) contrast to evaluate collagen microstructures and two-photon fluorescence (TPF) contrast to monitor progression of cross-linking upon treatment of tissues with glyceraldehyde. We examined collagen hydrogels assembled at 37 °C and 27 °C, bovine scleral and corneal tissues, skin as well as rat tail tendons. The results show a different effect of glyceraldehyde on collagen microstructures within the above tissues. This effect depends on the original microstructural assembly of collagen within a specific tissue. Our data suggests that epidermis (in skin and cornea) will protect collagen from cross-linking with glyceraldehyde. The work highlights benefits of monitoring progression of collagen cross-linking and effects of cross-linking on fiber microstructures as imaged with SHG and TPF signals.

Hwang, Yu Jer; Granelli, Joseph; Tirumalasetty, Manasa; Lyubovitsky, Julia

2013-02-01

265

Imaging in electrically conductive porous media without frequency encoding  

NASA Astrophysics Data System (ADS)

Understanding multi-phase fluid flow and transport processes under various pressure, temperature, and salinity conditions is a key feature in many remote monitoring applications, such as long-term storage of carbon dioxide (CO2) or nuclear waste in geological formations. We propose a low-field NMR tomographic method to non-invasively image the water-content distribution in electrically conductive formations in relatively large-scale experiments (˜1 m3 sample volumes). Operating in the weak magnetic field of Earth entails low Larmor frequencies at which electromagnetic fields can penetrate electrically conductive material. The low signal strengths associated with NMR in Earth's field are enhanced by pre-polarization before signal recording. To localize the origin of the NMR signal in the sample region we do not employ magnetic field gradients, as is done in conventional NMR imaging, because they can be difficult to control in the large sample volumes that we are concerned with, and may be biased by magnetic materials in the sample. Instead, we utilize the spatially dependent inhomogeneity of fields generated by surface coils that are installed around the sample volume. This relatively simple setup makes the instrument inexpensive and mobile (it can be potentially installed in remote locations outside of a laboratory), while allowing spatial resolution of the order of 10 cm. We demonstrate the general feasibility of our approach in a simulated CO2 injection experiment, where we locate and quantify the drop in water content following gas injection into a water-saturated cylindrical sample of 0.45 m radius and 0.9 m height. Our setup comprises four surface coils and an array consisting of three volume coils surrounding the sample. The proposed tomographic NMR methodology provides a more direct estimate of fluid content and properties than can be achieved with acoustic or electromagnetic methods alone. Therefore, we expect that our proposed method is relevant for geophysical applications, such as for monitoring CO2 injections in saline aquifers or detecting water leakage into nuclear waste deposit sites installed in electrically conductive formations.

Lehmann-Horn, J. A.; Walbrecker, J. O.

2012-07-01

266

Even harmonic lasing  

SciTech Connect

Operation of a free-electron laser at harmonics of the fundamental frequency is explored with the numerical simulation code HELEX. This code includes coupling to the harmonics caused by misalignment of the electrons with the optical beam and coupling due to transverse gradients. Albeit weak, the transverse gradients produce the dominant coupling of the electrons to the even-harmonic light. Even-harmonic lasing occurs in a TEM{sub 0,2m+1}-like mode where the field on axis is zero. As bunching of the electron beam progresses, radiation at the higher odd harmonics is suppressed owing to the absence of higher-order odd-harmonic Fourier components in the bunch. Growth of the even-harmonic power from small signal requires suppression of competing harmonics (including the fundamental) that have higher gain. Lasing at an even harmonic has yet to be experimentally demonstrated in an open resonator (i.e. optical cavity). Strategies to make such an experiment possible are discussed. 9 refs., 5 figs., 1 tab.

Schmitt, M.J.

1991-01-01

267

Harmonic analysis of electrical distribution systems  

SciTech Connect

This report presents data pertaining to research on harmonics of electric power distribution systems. Harmonic data is presented on RMS and average measurements for determination of harmonics in buildings; fluorescent ballast; variable frequency drive; georator geosine harmonic data; uninterruptible power supply; delta-wye transformer; westinghouse suresine; liebert datawave; and active injection mode filter data.

NONE

1996-03-01

268

Polarization-resolved second-harmonic generation imaging for liver fibrosis assessment without labeling  

NASA Astrophysics Data System (ADS)

We apply the polarization-resolved second-harmonic generation (PR-SHG) microscopy to investigate the changes of collagen typings (type I vs type III) and collagen fibril orientations of liver tissue in bile-duct-ligation (BDL) rat models. The PR-SHG results show that the second-order susceptibility tensor ratios (?31/?15 and ?33/?15) of collagen fibers increase with liver fibrotic progression after BDL surgery, reflecting an increase of the type III collagen component with the severity of liver fibrosis; and the square root of the collagen type III to type I ratio linearly correlates (R2 = 0.98) with histopathological scores. Furthermore, the collagen fibril orientations become more random with liver fibrosis transformation as compared to normal liver tissue. This work demonstrates that PR-SHG microscopy has the potential for label-free diagnosis and characterization of liver fibrosis based on quantitative analysis of collagen typings and fibril orientations.

Lin, Jian; Pan, Shiying; Zheng, Wei; Huang, Zhiwei

2013-10-01

269

Inclusion of frequency shifts in the treatment of N-photon vibronic processes involving uncoupled harmonic surfaces: A simple and exact prescription  

NASA Astrophysics Data System (ADS)

An exact prescription is given for averaging an n propagator string involving single mode harmonic oscillator Hamiltonians ?1,?2,...,?n over a Boltzmann distribution of the eigenstates of ?1. Such averages govern finite temperature multiphoton vibronic spectra, and we calculate the averages relevant to (one photon) electronic absorption and (two photon) Raman scattering in the case where only two electronic surfaces are involved. Our solution is compact and computationally mechanizable. It is valid for arbitrary upper and lower surface frequencies ?u,?1, and in the ?u=?1 (``displaced oscillator'') limit agrees with previous solutions of this special case. An extension to systems moving according to arbitrary quadratic potentials is sketched. A sum rule connecting electronic absorption and Raman spectra of finite temperature samples is given.

Coalson, Rob D.

1984-09-01

270

Three-dimensional simulations of harmonic radiation and harmonic lasing  

SciTech Connect

Characteristics of the harmonic emission from free-electron lasers (FELs) are examined in the spontaneous, coherent-spontaneous and stimulated emission regimes. The radiation at both odd and even harmonic frequencies is treated for electron beams with finite emittance and energy spread. In the spontaneous emission regime, the transverse radiation patterns including the transverse frequency dependences, are given. How this expression is modified to include energy spread and emittance is described. In the coherent-spontaneous emission and stimulated emission regimes, the interaction of the radiation fields with the electrons must be treated self-consistently. Here, a single-frequency distributed transverse source function for each electron is used in the harmonic version of the 3-D code FELEX to model the harmonic radiation. The code has recently been modified to simultaneously model the fundamental and harmonic interactions for multiple-pass oscillator simulations. These modifications facilitate the examination of FELs under various operating conditions. When the FEL is lasing at the fundamental, the evolution of the harmonic fields can be examined. This evolution is unique in the sense that the electron beam radiates at the harmonic frequencies in the presence of the harmonic radiation circulating in the cavity. As a result, enhancements of the harmonic emission can be observed. Finally, harmonic lasing can occur in cases where there is sufficient gain to overcome cavity losses and lasing at the fundamental can be suppressed. The characteristics and efficiency of these interactions are explored. 11 refs., 9 figs.

Schmitt, M.J.; McVey, B.D.

1990-01-01

271

Imaging cells and extracellular matrix in vivo by using second-harmonic generation and two-photon excited fluorescence  

NASA Astrophysics Data System (ADS)

Multiphoton microscopy relies on nonlinear light-matter interactions to provide contrast and optical sectioning capability for high-resolution imaging. Most multiphoton microscopy studies in biological systems have relied on two-photon excited fluorescence (TPEF) to produce images. With increasing applications of multiphoton microscopy to thick-tissue "intravital" imaging, second-harmonic generation (SHG) from structural proteins has emerged as a potentially important new contrast mechanism. However, SHG is typically detected in transmission mode, thus limiting TPEF/SHG coregistration and its practical utility for in vivo thick-tissue applications. In this study, we use a broad range of excitation wavelengths (730-880 nm) to demonstrate that TPEF/SHG coregistration can easily be achieved in unstained tissues by using a simple backscattering geometry. The combined TPEF/SHG technique was applied to imaging a three-dimensional organotypic tissue model (RAFT). The structural and molecular origin of the image-forming signal from the various tissue constituents was determined by simultaneous spectroscopic measurements and confirming immunofluorescence staining. Our results show that at shorter excitation wavelengths (<800 nm), the signal emitted from the extracellular matrix (ECM) is a combination of SHG and TPEF from collagen, whereas at longer excitation wavelengths the ECM signal is exclusively due to SHG. Endogenous cellular signals are consistent with TPEF spectra of cofactors NAD(P)H and FAD at all excitation wavelengths. The reflected SHG intensity follows a quadratic dependence on the excitation power, decays exponentially with depth, and exhibits a spectral dependence in accordance with previous theoretical studies. The use of SHG and TPEF in combination provides complementary information that allows noninvasive, spatially localized in vivo characterization of cell-ECM interactions in unstained thick tissues.

Zoumi, Aikaterini; Yeh, Alvin; Tromberg, Bruce J.

2002-08-01

272

High speed full range imaging with harmonic detection swept source optical coherence tomography  

Microsoft Academic Search

A complication of Fourier domain optical coherence tomography (OCT) methods, such as spectral domain and swept source OCT, is the complex conjugate ambiguity due to inverse Fourier transform of real-valued data. As a result, the image is symmetric to the zero plane, and only half of the theoretical imaging depth range is used to avoid overlapping \\

Chuanyong Huang; Steven M. Massick; Kristen A. Peterson; Andrei B. Vakhtin

2010-01-01

273

Combination of images with diverse focuses using the spatial frequency  

E-print Network

, feature extraction and object recognition. The simplest image fusion method just takes the pixel everywhere can be obtained [11]. In this paper, an ecient pixel level image fusion algorithm based Received 18 July 2000; received in revised form 24 May 2001; accepted 15 June 2001 Abstract Image fusion

Kwok, James Tin-Yau

274

A compact frequency-domain photon migration system for integration into commercial hybrid small animal imaging scanners for fluorescence tomography  

PubMed Central

The work presented herein describes system design and performance evaluation of a miniaturized near-infrared fluorescence (NIRF) frequency-domain photon migration (FDPM) system with non-contact excitation and homodyne detection capability for small animal fluorescence tomography. The FDPM system was developed specifically for incorporation into a Siemens microPET/CT commercial scanner for hybrid small animal imaging, but could be adapted to other systems. Operating at 100 MHz, the system noise was minimized and the associated amplitude and phase errors were characterized to be ±0.7% and ±0.3°, respectively. To demonstrate the tomographic ability, a commercial mouse-shaped phantom with 50 ?M IRDye800CW and 68Ga containing inclusion was used to associate PET and NIRF tomography. 3-D mesh generation and anatomical referencing was accomplished through CT. A simplified spherical harmonics approximation (SP3) algorithm, for efficient prediction of light propagation in small animals, was tailored to incorporate FDPM approach. Finally, PET-NIRF target co-localization accuracy was analyzed in vivo with a dual-labeled imaging agent targeting orthotopic growth of human prostate cancer. The results obtained validate the integration of time-dependent fluorescence tomography system within a commercial microPET/CT scanner for multimodality small animal imaging. PMID:23171509

Darne, Chinmay D.; Lu, Yujie; Tan, I-Chih; Zhu, Banghe; Rasmussen, John C.; Smith, Anne M.; Yan, Shikui; Sevick-Muraca, Eva M

2012-01-01

275

A compact frequency-domain photon migration system for integration into commercial hybrid small animal imaging scanners for fluorescence tomography  

NASA Astrophysics Data System (ADS)

The work presented herein describes the system design and performance evaluation of a miniaturized near-infrared fluorescence (NIRF) frequency-domain photon migration (FDPM) system with non-contact excitation and homodyne detection capability for small animal fluorescence tomography. The FDPM system was developed specifically for incorporation into a Siemens micro positron emission tomography/computed tomography (microPET/CT) commercial scanner for hybrid small animal imaging, but could be adapted to other systems. Operating at 100 MHz, the system noise was minimized and the associated amplitude and phase errors were characterized to be ±0.7% and ±0.3°, respectively. To demonstrate the tomographic ability, a commercial mouse-shaped phantom with 50 µM IRDye800CW and 68Ga containing inclusion was used to associate PET and NIRF tomography. Three-dimensional mesh generation and anatomical referencing was accomplished through CT. A third-order simplified spherical harmonics approximation (SP3) algorithm, for efficient prediction of light propagation in small animals, was tailored to incorporate the FDPM approach. Finally, the PET-NIRF target co-localization accuracy was analyzed in vivo with a dual-labeled imaging agent targeting orthotopic growth of human prostate cancer. The obtained results validate the integration of time-dependent fluorescence tomography system within a commercial microPET/CT scanner for multimodality small animal imaging.

Darne, Chinmay D.; Lu, Yujie; Tan, I.-Chih; Zhu, Banghe; Rasmussen, John C.; Smith, Anne M.; Yan, Shikui; Sevick-Muraca, Eva M.

2012-12-01

276

Experimental images of heterogeneous turbid media by frequency-domain diffusing-photon tomography  

Microsoft Academic Search

We present images of heterogeneous turbid media derived from measurements of diffuse photon-density waves traveling through highly scattering tissue phantoms. To our knowledge, the images are the first experimental reconstruction based on data collected in the frequency domain. We demonstrate images of both absorbing and scattering heterogeneities and show that this method is sensitive to the optical properties of the

M. A. O'Leary; D. A. Boas; B. Chance; A. G. Yodh

277

Three-dimensional imaging of extended defects in 4H-SiC by optical second-harmonic generation and two-photon-excited photoluminescence  

NASA Astrophysics Data System (ADS)

We demonstrate three-dimensional (3D) defect imaging in 4H-SiC epilayers by optical second-harmonic generation (SHG) and two-photon-excited photoluminescence (2PPL). The SHG method provides clear 3D images of 3C inclusions because 3C-SiC is SHG-active, but not 4H-SiC host crystal in c-axis incidence. The 2PPL method also yields 3D images of 3C inclusions, 8H stacking faults, and single Shockley stacking faults in the epilayers. The spectra obtained by the SHG and 2PPL imaging methods are investigated, and the emission mechanisms discussed.

Tanuma, Ryohei; Tsuchida, Hidekazu

2014-02-01

278

Harmonic engine  

DOEpatents

An engine based on a reciprocating piston engine that extracts work from pressurized working fluid. The engine includes a harmonic oscillator inlet valve capable of oscillating at a resonant frequency for controlling the flow of working fluid into of the engine. In particular, the inlet valve includes an inlet valve head and a spring arranged together as a harmonic oscillator so that the inlet valve head is moveable from an unbiased equilibrium position to a biased closed position occluding an inlet. Upon releasing the inlet valve the inlet valve head undergoes a single oscillation past the equilibrium positio to a maximum open position and returns to a biased return position close to the closed position to choke the flow and produce a pressure drop across the inlet valve causing the inlet valve to close. Protrusions carried either by the inlet valve head or piston head are used to bump open the inlet valve from the closed position and initiate the single oscillation of the inlet valve head, and protrusions carried either by the outlet valve head or piston head are used to close the outlet valve ahead of the bump opening of the inlet valve.

Bennett, Charles L.; Sewall, Noel; Boroa, Carl

2014-08-19

279

A novel dual-frequency imaging method for intravascular ultrasound applications.  

PubMed

Intravascular ultrasound (IVUS), which is able to delineate internal structures of vessel wall with fine spatial resolution, has greatly enriched the knowledge of coronary atherosclerosis. A novel dual-frequency imaging method is proposed in this paper for intravascular imaging applications. A probe combined two ultrasonic transducer elements with different center frequencies (36MHz and 78MHz) is designed and fabricated with PMN-PT single crystal material. It has the ability to balance both imaging depth and resolution, which are important imaging parameters for clinical test. A dual-channel imaging platform is also proposed for real-time imaging, and this platform has been proven to support programmable processing algorithms, flexible imaging control, and raw RF data acquisition for IVUS applications. Testing results show that the -6dB axial and lateral imaging resolutions of low-frequency ultrasound are 78 and 132?m, respectively. In terms of high-frequency ultrasound, axial and lateral resolutions are determined to be as high as 34 and 106?m. In vitro intravascular imaging on healthy swine aorta is conducted to demonstrate the performance of the dual-frequency imaging method for IVUS applications. PMID:25454093

Qiu, Weibao; Chen, Yan; Wong, Chi-Man; Liu, Baoqiang; Dai, Jiyan; Zheng, Hairong

2015-03-01

280

Motion compensated frequency modulated continuous wave 3D coherent imaging ladar with scannerless architecture.  

PubMed

A principal difficulty of long dwell coherent imaging ladar is its extreme sensitivity to target or platform motion. This paper describes a motion compensated frequency modulated continuous wave 3D coherent imaging ladar method that overcomes this motion sensitivity, making it possible to work with nonstatic targets such as human faces, as well as imaging of targets through refractive turbulence. Key features of this method include scannerless imaging and high range resolution. The reduced motion sensitivity is shown with mathematical analysis and demonstration 3D images. Images of static and dynamic targets are provided demonstrating up to 600×800 pixel imaging with millimeter range resolution. PMID:23262614

Krause, Brian W; Tiemann, Bruce G; Gatt, Philip

2012-12-20

281

Combined nonlinear laser imaging (two-photon excitation fluorescence, second and third-harmonic generation, and fluorescence lifetime imaging microscopies) in ovarian tumors  

NASA Astrophysics Data System (ADS)

We applied Two-photon Excited Fluorescence (TPEF), Second/Third Harmonic Generation (SHG and THG) and Fluorescence Lifetime Imaging (FLIM) Non Linear Optics (NLO) Laser-Scanning Microscopy within the same imaging platform to evaluate their use as a diagnostic tool in ovarian tumors. We assess of applicability of this multimodal approach to perform a pathological evaluation of serous and mucinous tumors in human samples. The combination of TPEF-SHG-THG imaging provided complementary information about the interface epithelium/stromal, such as the transformation of epithelium surface (THG) and the overall fibrillar tissue architecture (SHG). The fact that H&E staining is the standard method used in clinical pathology and that the stored samples are usually fixed makes it important a re-evaluation of these samples with NLO microscopy to compare new results with a library of already existing samples. FLIM, however, depends on the chemical environment around the fluorophors that was completely changed after fixation; therefore it only makes sense in unstained samples. Our FLIM results in unstained samples demonstrate that it is possible to discriminate healthy epithelia from serous or mucinous epithelia. Qualitative and quantitative analysis of the different imaging modalities used showed that multimodal nonlinear microscopy has the potential to differentiate between cancerous and healthy ovarian tissue.

Adur, J.; Pelegati, V. B.; de Thomaz, A. A.; Bottcher-Luiz, F.; Andrade, L. A. L. A.; Almeida, D. B.; Carvalho, H. F.; Cesar, C. L.

2012-03-01

282

Model-based frequency response characterization of a digital-image analysis system for epifluorescence microscopy  

NASA Technical Reports Server (NTRS)

Consideration is given to a model-based method for estimating the spatial frequency response of a digital-imaging system (e.g., a CCD camera) that is modeled as a linear, shift-invariant image acquisition subsystem that is cascaded with a linear, shift-variant sampling subsystem. The method characterizes the 2D frequency response of the image acquisition subsystem to beyond the Nyquist frequency by accounting explicitly for insufficient sampling and the sample-scene phase. Results for simulated systems and a real CCD-based epifluorescence microscopy system are presented to demonstrate the accuracy of the method.

Hazra, Rajeeb; Viles, Charles L.; Park, Stephen K.; Reichenbach, Stephen E.; Sieracki, Michael E.

1992-01-01

283

Ab initio time-dependent density-functional-theory study of the frequency comb structure, coherence, and dephasing of multielectron systems in the vuv-xuv regimes via high-order harmonic generation  

E-print Network

We present an ab initio nonperturbative investigation of the frequency comb structure and coherence within each order of the high-order harmonic generation (HHG) of rare-gas atoms by means of the time-dependent density-functional theory (TDDFT...

Chu, Shih-I; Carrera, Juan J.

2009-06-17

284

Acoustoelectric Harmonic Generation in a Photoconductive Piezoelectric Semiconductor  

E-print Network

Acoustoelectric Harmonic Generation in a Photoconductive Piezoelectric Semiconductor W. Arthur, R harmonics in the low frequency regime (. Piezoelectric semiconductors can exhibit harmonic generation because of interactions between the acoustic

285

Ultrasonic imaging based on frequency-domain optimization form  

E-print Network

], such as the TDTE (Time Domain Topological Energy) [1, 2, 3]. The preliminar topo- logical sensitivity analysis The Fast Topological IMaging method 2.1 The direct and adjoint problems First, the experimental data presents the FTIM (Fast Topological IMaging) method which is based on an optimization method, called

Paris-Sud XI, Université de

286

Ultralow-power second-harmonic generation frequency-resolved optical gating using aperiodically poled lithium niobate waveguides [Invited  

Microsoft Academic Search

mW 2 in a collinear SHG FROG geometry, approximately 5 orders of magnitude better than previously reported for any FROG measurement modality. We also discuss asymmetric Y-junction A-PPLN waveguides that permit background-free SHG FROG and a polarization-insensitive SHG FROG tech- nique that eliminates the impairment that frequency-independent random polarization fluctuations induce in the FROG measurement. Finally, we applied these SHG

Houxun Miao; Shang-Da Yang; Carsten Langrock; Rostislav V. Roussev; M. M. Fejer; Andrew M. Weiner

2008-01-01

287

The response of phospholipid-encapsulated microbubbles to chirp-coded excitation: Implications for high-frequency nonlinear imaging  

PubMed Central

The current excitation strategy for harmonic and subharmonic imaging (HI and SHI) uses short sine-bursts. However, alternate pulsing strategies may be useful for enhancing nonlinear emissions from ultrasound contrast agents. The goal of this study was to corroborate the hypothesis that chirp-coded excitation can improve the performance of high-frequency HI and SHI. A secondary goal was to understand the mechanisms that govern the response of ultrasound contrast agents to chirp-coded and sine-burst excitation schemes. Numerical simulations and acoustic measurements were conducted to evaluate the response of a commercial contrast agent (Targestar-P®) to chirp-coded and sine-burst excitation (10?MHz frequency, peak pressures 290 kPa). The results of the acoustic measurements revealed an improvement in signal-to-noise ratio by 4 to 14?dB, and a two- to threefold reduction in the subharmonic threshold with chirp-coded excitation. Simulations conducted with the Marmottant model suggest that an increase in expansion-dominated radial excursion of microbubbles was the mechanism responsible for the stronger nonlinear response. Additionally, chirp-coded excitation detected the nonlinear response for a wider range of agent concentrations than sine-bursts. Therefore, chirp-coded excitation could be a viable approach for enhancing the performance of HI and SHI. PMID:23654417

Shekhar, Himanshu; Doyley, Marvin M.

2013-01-01

288

Experimental 0.22 THz Stepped Frequency Radar System for ISAR Imaging  

NASA Astrophysics Data System (ADS)

High resolution inverse synthetic aperture radar (ISAR) imaging is demonstrated by using a 0.22 THz stepped-frequency (SF) imaging radar system. The synthesis bandwidth of the terahertz (THz) SF radar is 12 GHz, which are beneficial for high resolution imaging. The resolution of ISAR image can reach centimeter-scale with the use of Range-Doppler algorithm (RDA). Results indicate that high resolution ISAR imaging is realized by using 0.22THz SF radar coupled with turntable scanning, which can provide foundations for further research on high-resolution radar image in the THz band.

Liang, Mei Yan; Zhang, Cun Lin; Zhao, Ran; Zhao, Yue Jin

2014-09-01

289

In vivo time-lapse imaging of skin burn wound healing using second-harmonic generation microscopy  

NASA Astrophysics Data System (ADS)

Wound healing is a process to repair the damaged tissue caused by thermal burn, incised wound, or stab wound. Although the wound healing has many aspects, it is common for dynamics of collagen fiber, such as decomposition, production, or growth, to be closely related with wound healing. If such the healing process can be visualized as a timelapse image of the collagen fiber in the same subject, one may obtain new findings regarding biological repairing mechanisms in the healing process. In this article, to investigate the temporal modoification of dermal collagen fiber in the burn wound healing, we used second-harmonic-generation (SHG) microscopy, showing high selectivity and good image contrast to collagen molecules as well as high spatial resolution, optical three-dimensional sectioning, minimal invasiveness, deep penetration, the absence of interference from background light, and in vivo measurement without additional staining. Since SHG light arises from a non-centrosymmetric triple helix of three polypeptide chains in the collagen molecule, SHG intensity sensitively reflects the structure maturity of collagen molecule and its aggregates. A series of time-lapse SHG images during the wound healing process of 2 weeks clearly indicated that condensation and melting of dermal collagen fibers by the deep dermal burn, decomposition of the damaged collagen fibers in the inflammation phase, production of new collagen fibers in the proliferation phase, and the growth of the new collagen fibers in the remodeling phase. These results show a high potential of SHG microscopy for optical assessment of the wound healing process in vivo.

Yasui, Takeshi; Tanaka, Ryosuke; Hase, Eiji; Fukushima, Shu-ichiro; Araki, Tsutomu

2014-02-01

290

Extending the ICRF to Higher Radio Frequencies: Imaging and Source Structure  

NASA Technical Reports Server (NTRS)

We present imaging results and source structure analysis of extragalactic radio sources observed using the Very Long Baseline Array (VLBA) at 24 GHz and 43 GHz as part of an ongoing NASA, USNO, NRAO and Bordeaux Observatory collaboration to extend the International Celestial Reference Frame (ICRF) to higher radio frequencies. The K/Q-band image database now includes images of 108 sources at 43 GHz (Q-braid) and images of 230 sources at 24 GHz (K-band). Preliminary analysis of the observations taken to date shows that the sources are generally more compact as one goes from the ICRF frequency of 8.4 GHz to 24 GHz. This result is consistent with the standard theory of compact extragalactic radio sources and suggests that reference frames defined at these higher radio frequencies will be less susceptible to the effects of intrinsic source structure than those defined at lower frequencies.

Boboltz, David A.; Fey, Alan L.; Charlot, Patrick; Fomalont, Edward B.; Lanyi, Gabor E.; Zhang, Li-Wei

2004-01-01

291

Multispectral imaging of tissue absorption and scattering using spatial frequency domain imaging and a computed-tomography imaging spectrometer  

PubMed Central

We present an approach for rapidly and quantitatively mapping tissue absorption and scattering spectra in a wide-field, noncontact imaging geometry by combining multifrequency spatial frequency domain imaging (SFDI) with a computed-tomography imaging spectrometer (CTIS). SFDI overcomes the need to spatially scan a source, and is based on the projection and analysis of periodic structured illumination patterns. CTIS provides a throughput advantage by simultaneously diffracting multiple spectral images onto a single CCD chip to gather spectra at every pixel of the image, thus providing spatial and spectral information in a single snapshot. The spatial-spectral data set was acquired 30 times faster than with our wavelength-scanning liquid crystal tunable filter camera, even though it is not yet optimized for speed. Here we demonstrate that the combined SFDI-CTIS is capable of rapid, multispectral imaging of tissue absorption and scattering in a noncontact, nonscanning platform. The combined system was validated for 36 wavelengths between 650–1000 nm in tissue simulating phantoms over a range of tissue-like absorption and scattering properties. The average percent error for the range of absorption coefficients (?a) was less than 10% from 650–800 nm, and less than 20% from 800–1000 nm. The average percent error in reduced scattering coefficients (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}\\mu_{\\rm s}^{\\prime}\\end{equation*} \\end{document}?s?) was less than 5% from 650–700 nm and less than 3% from 700–1000 nm. The SFDI-CTIS platform was applied to a mouse model of brain injury in order to demonstrate the utility of this approach in characterizing spatially and spectrally varying tissue optical properties. PMID:21280902

Weber, Jessie R.; Cuccia, David J.; Johnson, William R.; Bearman, Gregory H.; Durkin, Anthony J.; Hsu, Mike; Lin, Alexander; Binder, Devin K.; Wilson, Dan; Tromberg, Bruce J.

2011-01-01

292

Multispectral imaging of tissue absorption and scattering using spatial frequency domain imaging and a computed-tomography imaging spectrometer.  

PubMed

We present an approach for rapidly and quantitatively mapping tissue absorption and scattering spectra in a wide-field, noncontact imaging geometry by combining multifrequency spatial frequency domain imaging (SFDI) with a computed-tomography imaging spectrometer (CTIS). SFDI overcomes the need to spatially scan a source, and is based on the projection and analysis of periodic structured illumination patterns. CTIS provides a throughput advantage by simultaneously diffracting multiple spectral images onto a single CCD chip to gather spectra at every pixel of the image, thus providing spatial and spectral information in a single snapshot. The spatial-spectral data set was acquired 30 times faster than with our wavelength-scanning liquid crystal tunable filter camera, even though it is not yet optimized for speed. Here we demonstrate that the combined SFDI-CTIS is capable of rapid, multispectral imaging of tissue absorption and scattering in a noncontact, nonscanning platform. The combined system was validated for 36 wavelengths between 650-1000 nm in tissue simulating phantoms over a range of tissue-like absorption and scattering properties. The average percent error for the range of absorption coefficients (?a) was less than 10% from 650-800 nm, and less than 20% from 800-1000 nm. The average percent error in reduced scattering coefficients (?s') was less than 5% from 650-700 nm and less than 3% from 700-1000 nm. The SFDI-CTIS platform was applied to a mouse model of brain injury in order to demonstrate the utility of this approach in characterizing spatially and spectrally varying tissue optical properties. PMID:21280902

Weber, Jessie R; Cuccia, David J; Johnson, William R; Bearman, Gregory H; Durkin, Anthony J; Hsu, Mike; Lin, Alexander; Binder, Devin K; Wilson, Dan; Tromberg, Bruce J

2011-01-01

293

Second-order fractional Talbot effect induced frequency-doubling optical pulse injection for 40 GHz rational-harmonic mode-locking of an SOA fiber laser  

NASA Astrophysics Data System (ADS)

A second-order fractional Talbot effect induced frequency-doubling of a 10 GHz optical pulse-train is demonstrated to backward injection mode-lock a semiconductor optical amplifier fiber laser (SOAFL) for 40 GHz rational-harmonic mode-locking (RHML). That is, a real all-optical gain-modulation of the SOAFL can be created by injecting such a time-multiplexed but pseudo-frequency-doubled pulse-train into the cavity. The time-multiplexing pulse-train can thus be transformed into a frequency-multiplied pulse-train via cross-gain modulation (XGM). The optical pulse-train at 10 GHz is generated by nonlinearly driving an electro-absorption modulator (EAM), which experiences the second-order fractional Talbot effect after propagating through a 4 km long dispersion compensation fiber (DCF). The DCF not only plays the role of frequency-doubler but also compensates the frequency chirp of the 10 GHz optical pulse-train. The pulsewidth broadening from 22 to 60 ps for initiating the time-domain Talbot effect is simulated by the nonlinear Schrödinger equation. With careful detuning of the RF modulation power of the EAM at 5 dBm, the generated 20 GHz optical pulse-train exhibits a positive frequency chirp with minimum peak-to-peak value of 2 GHz, and the peak-amplitude fluctuation between adjacent pulses is below 1.4%. In comparison with the SOAFL pulse-train repeated at 40 GHz generated by the fourth-order purely RHML process, the optimized second-order fractional Talbot effect in combination with the second-order RHML mechanism significantly enhances the modulation-depth of RHML, thus improving the on/off extinction ratio of the 40 GHz SOAFL pulse-train from 1.8 to 5.6 dB. Such a new scheme also provides a more stable 40 GHz RHML pulse-train from the SOAFL with its timing jitter reducing from 0.51 to 0.23 ps.

Kang, Jung-Jui; Lin, Yung-Hsiang; Lee, Chao-Kuei; Lin, Gong-Ru

2013-09-01

294

Simultaneous sum-frequency and vibro-acoustography imaging for nondestructive evaluation and testing applications  

SciTech Connect

High-resolution ultrasound imaging systems for inspection of defects and flaws in materials are of great demand in many industries. Among these systems, Vibro-acoustography (VA) has shown excellent capabilities as a noncontact method for nondestructive high-resolution imaging applications. This method consists of mixing two confocal ultrasound beams, slightly shifted in frequency, to produce a dynamic (oscillatory) radiation force in the region of their intersection. This force vibrates the object placed at the focus of the confocal transducer. As a result of the applied force, an acoustic emission field at the difference frequency of the primary incident ultrasound beams is produced. In addition to the difference frequency acoustic emission signal, there exists another signal at the sum frequency, formed in the intersection region of the two primary beams. The goal of this study is to investigate the formation of high-resolution images using the sum frequency of ultrasound waves in VA while concurrently forming the conventional difference-frequency VA image, thereby increasing the amount of information acquired during a single scan. A theoretical model describing the sum-frequency wave propagation, including beam forming and image formation in the confocal configuration, is developed and verified experimentally. Moreover, sample experiments are performed on a flawed fiber-reinforced ceramic composite plate. Images at both the difference and sum frequencies are compared and discussed. Results show that the sum-frequency image produces a high-resolution C scan of the plate by which the flaws and structural details of the plate can be detected.

Mitri, F. G.; Silva, G. T.; Greenleaf, J. F.; Fatemi, M. [Department of Physiology and Biomedical Engineering, Ultrasound Research Laboratory, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, Minnesota 55905 (United States); Instituto Nacional de Matematica Pura e Aplicada-IMPA, Rio de Janeiro, RJ 22460-320 (Brazil); Department of Physiology and Biomedical Engineering, Ultrasound Research Laboratory, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, Minnesota 55905 (United States)

2007-12-01

295

Wavelet-based progressive image and video coding using trellis-coded space-frequency quantization  

E-print Network

WAVELET-BASED PROGRESSIVE IMAGE AND VIDEO CODING USING TRELLIS-CODED SPACE-FREQUENCY QUANTIZATION A Thesis by PIERRE SEIGNEURBIEUX Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements... for the degree of MASTER OF SCIENCE December 2000 Major Subject: Electrical Engineering WAVELET-BASED PROGRESSIVE IMAGE AND VIDEO CODING USING TRELLIS-CODED SPACE-FREQUENCY QUANTIZATION A Thesis by PIERRE SEIGNEURBIEUX Submitted to Texas A&M University...

Seigneurbieux, Pierre

2012-06-07

296

Electrical tissue property imaging at low frequency using MREIT.  

PubMed

The tomographic imaging of tissue's electrical properties (e.g., conductivity and permittivity) has been greatly improved by recent developments in magnetic resonance (MR) imaging techniques, which include MR electrical impedance tomography (MREIT) and electrical property tomography. When the biological material is subjected to an external electric field, local changes in its electrical properties become sources of magnetic field perturbations, which are detectable by the MR signals. Controlling the external excitation and measuring the responses using an MRI scanner, we can formulate the imaging problem as an inverse problem in which unknown tissue properties are recovered from the acquired MR signals. This inverse problem is nonlinear; it involves the incorporation of Maxwell's equations and Bloch equations during data acquisition. Each method for visualizing internal conductivity and permittivity distributions has its own methodological limitations, and is restricted to imaging only a part of the ensemble or mean tissue structures or states. Therefore, imaging methods can be improved by developing complementary methods that can employ the beneficial aspects of various existing techniques. This paper focuses on recent progress in MREIT and discusses its distinct features in comparison with other imaging methods. PMID:24759274

Seo, Jin Keun; Woo, Eung Je

2014-05-01

297

Effects of density functionals and dispersion interactions on geometries, bond energies and harmonic frequencies of Etbnd UX3 (E = N, P, CH; X = H, F, Cl)  

NASA Astrophysics Data System (ADS)

Quantum-chemical calculations have been performed to evaluate the geometries, bonding nature and harmonic frequencies of the compounds [Etbnd UX3] at DFT, DFT-D3, DFT-D3(BJ) and DFT-dDSc levels using different density functionals BP86, BLYP, PBE, revPBE, PW91, TPSS and M06-L. The stretching frequency of Utbnd N bond in [Ntbnd UF3] calculated with DFT/BLYP closely resembles with the experimental value. The performance of different density functionals for accurate Utbnd N vibrational frequencies follows the order BLYP > revPBE > BP86 > PW91 > TPSS > PBE > M06-L. The BLYP functional gives accurate value of the Utbnd E bond distances. The uranium atom in the studied compounds [Etbnd UX3] is positively charged. Upon going from [Etbnd UF3] to [Etbnd UCl3], the partial Hirshfeld charge on uranium atom decreases because of the lower electronegativity of chlorine compared to flourine. The Gopinathan-Jug bond order for Utbnd E bonds ranges from 2.90 to 3.29. The Utbnd E bond dissociation energies vary with different density functionals as M06-L < TPSS < BLYP < revPBE < BP86 < PBE ? PW91. The orbital interactions ?Eorb, in all studied compounds [Etbnd UX3] are larger than the electrostatic interaction ?Eelstat, which means the Utbnd N bonds in these compound have greater degree of covalent character (in the range 63.8-77.2%). The Usbnd E ?-bonding interaction is the dominant bonding interaction in the nitride and methylidyne complexes while it is weaker in [Ptbnd UX3]. The dispersion energy contributions to the total bond dissociation energies are rather small. Compared to the Grimme's D3(BJ) corrections, the Corminboeuf's dispersion corrections are larger with metaGGA functionals (TPSS, M06-L) while smaller with GGA functionals.

Pandey, Krishna Kumar; Patidar, Pankaj; Patidar, Sunil Kumar; Vishwakarma, Ravi

2014-12-01

298

A parameter identification method of high frequency vibration model on TDI image  

NASA Astrophysics Data System (ADS)

To accurately discern the parameters of high frequency vibration blur model on a single TDI image, the research analyzes the imaging function when high frequency vibration occurs in TDI mode. The method of simplifying the vibration model is offered and verified, which promises the MTF will be only related with motion angle and vibration amplitude. Three algorithms for motion direction discerning are compared with one another, which are Radon transform, autocorrelation analysis and cepstral method. The conclusion reveals that cepstral method can measure the most accurate motion angle. Four algorithms for vibration amplitude discerning are compared, which are the quadratic Radon transform, cepstral analysis, autocorrelation analysis and direct analysis on frequency spectrum. It reveals that direct analysis on Log frequency spectrum is the most accurate for vibration amplitude. The research suggests that composition of cesptral method and direct analysis on log frequency spectrum could obtain the highly accurate parameters in high frequency vibration model.

Liang, Jiong; Xu, Ting fa; Shi, Ming zhu; Feng, Liang; Ni, Guo qiang

2013-12-01

299

Optical correlation of spatial-frequency-shifted images in a photorefractive BSO correlator.  

PubMed

The optical cross correlation of an image with another image that was spatial-frequency shifted in one dimension was demonstrated in a photorefractive VanderLugt correlator. The first image was stored as a Fourier-transform hologram in a photorefractive Bi12SiO20 crystal (BSO) and was successively correlated with different spatial-frequency-shifted versions of a second image. We implemented the spatial-frequency shift by rotating a galvanometer mirror in an image plane, causing the Fourier transform to be shifted laterally in the BSO. We verified that the resulting operation in the BSO was an accurate complex multiplication of the shifted and the stored Fourier transforms. As many as 20 successive readouts were conducted without measurable erasure of the stored hologram. The dynamic range, saturation behavior, and other performance parameters were measured and are discussed. PMID:15046173

Tavassoli, Abtine; Becker, Michael F

2004-03-10

300

Use of low frequencies for sub-basalt imaging Anton Ziolkowski,1  

E-print Network

Use of low frequencies for sub-basalt imaging Anton Ziolkowski,1 * Peter Hanssen,2 Robert Gatliff,2 margins are covered by large areas of basalts. These basalts are often extremely heterogeneous and scatter that the acquisition system for sub-basalt targets should be modified to emphasize the low frequencies, using much

Edinburgh, University of

301

Digital parallel frequency-domain spectroscopy for tissue imaging  

PubMed Central

Abstract. Near-infrared (NIR) (650 to 1000 nm) optical properties of turbid media can be quantified accurately and noninvasively using methods based on diffuse reflectance or transmittance, such as frequency-domain photon migration (FDPM). Conventional FDPM techniques based on white-light steady-state (SS) spectral measurements in conjunction with the acquisition of frequency-domain (FD) data at selected wavelengths using laser diodes are used to measure broadband NIR scattering-corrected absorption spectra of turbid media. These techniques are limited by the number of wavelength points used to obtain FD data and by the sweeping technique used to collect FD data over a relatively large range. We have developed a method that introduces several improvements in the acquisition of optical parameters, based on the digital parallel acquisition of a comb of frequencies and on the use of a white laser as a single light source for both FD and SS measurements. The source, due to the high brightness, allows a higher penetration depth with an extremely low power on the sample. The parallel acquisition decreases the time required by standard serial systems that scan through a range of modulation frequencies. Furthermore, all-digital acquisition removes analog noise, avoids the analog mixer, and does not create radiofrequency interference or emission. PMID:23085915

Arnesano, Cosimo; Santoro, Ylenia; Gratton, Enrico

2012-01-01

302

Harmonic multiplication using resonant tunneling  

NASA Technical Reports Server (NTRS)

This paper demonstrates the use of resonant-tunneling diodes as varistors for harmonic multiplication. It is shown that efficient odd-harmonic conversion is possible and that even harmonics do not appear because of the antisymmetry of the current-voltage (I-V) curve. It is also shown that, with the proper choice of resonant-tunneling structure and pump amplitude, most of the harmonic output power can be confined to a single odd-harmonic frequency. Fifth-harmonic multiplication was demonstrated with an output at 21.75 GHz and a power conversion efficiency of 0.5 percent, and a fifth-harmonic efficiency of 2.7 percent was achieved in a circuit simulation using an improved I-V curve.

Sollner, T. C. L. G.; Brown, E. R.; Goodhue, W. D.; Correa, C. A.

1988-01-01

303

High-frequency ultrasound miniature transducers for tissue imaging  

NASA Astrophysics Data System (ADS)

We have fabricated a miniature 120-MHz transducer for imaging the internal structure of living samples, and mounted it in a 3-mm-diameter rod-shaped probe which ensures contact with a tissue to evaluate the tissue imaging capability of the transducer. The transducer consists of a thin film of 12.5-micrometer thick ZnO sandwiched between two metal electrodes, the bottom one deposited on a sapphire substrate whose other face has a polished concave-sphere acoustic lens. Both the lens diameter and the sphere radius are 0.5 mm; that is, the F number of the lens is 1. The lens of the transducer faces outwards in the probe so that the ultrasound can be transmitted and received directly by it in the radial direction of the rod without any mirrors. As the probe rotates mechanically around its axis and shifts in the direction of the axis, a cylindrical plane created by the locus of the beam focus is located inside of the tissue. Using this scanning, we form tissue images in the C-scan mode in a cylindrical plane within the target tissue. Preliminary results for imaging an in vitro bovine kidney sample into which the probe was inserted demonstrate that the fabricated probe can image microscopic structure inside tissue samples.

Yokosawa, Koichi; Ito, Yukio; Sano, Syuzo; Shinomura, Ryuichi; Sato, Yutaka

1997-04-01

304

EFFICIENT AND ACCURATE IMPLEMENTATION OF IMAGE SCALING IN THE FREQUENCY DOMAIN  

Microsoft Academic Search

Image scaling, particularly by powers of two, has previously been shown as implemented efficiently by direct manipulation of coefficients in the frequency domain. Typically, these coefficients are computed via the 8x8 DCT, or other block transforms, for their compressed storage in popular standard formats such as JPEG or MPEG. Many existing implementations of these image scaling algorithms use coarse fixed-point

Arianne T. Hinds; Nenad Rijavec; Joan L. Mitchell

305

Coherence Holography and Spatial Frequency Comb for 3-D Coherence Imaging  

E-print Network

Coherence Holography and Spatial Frequency Comb for 3-D Coherence Imaging Mitsuo Takeda, Wei Wang holography technique, called coherence holography, and a related technique for dispersion-free 3-D coherence: (090.0090) Holography; (030.1640) Coherence; (100.3010) Image reconstruction techniques; (110

Rosen, Joseph

306

OBJECTIVE: Investigate the use of microbolometer infrared technology for real time imaging at THz frequencies.  

E-print Network

OBJECTIVE: Investigate the use of microbolometer infrared technology for real time imaging at THz microbolometer pixels for sensing at THz frequencies. PHASE 1: During the initial phase of research, a detailed study of real-time THz imaging character- istics of a microbolometer infrared camera will be carried out

307

ADAPTIVE TIME-FREQUENCY DETECTION AND FILTERING FOR IMAGING IN HEAVY CLUTTER  

E-print Network

ADAPTIVE TIME-FREQUENCY DETECTION AND FILTERING FOR IMAGING IN HEAVY CLUTTER L. BORCEA, G with extensive numerical simulations that this approach to detection and imaging works well in heavy clutter the detection and filtering algorithm presented here works well in general clutter it has been analyzed

Papanicolaou, George C.

308

Dual aperture dipole magnet with second harmonic component  

DOEpatents

An improved dual aperture dipole electromagnet includes a second-harmonic frequency magnetic guide field winding which surrounds first harmonic frequency magnetic guide field windings associated with each aperture. The second harmonic winding and the first harmonic windings cooperate to produce resultant magnetic waveforms in the apertures which have extended acceleration and shortened reset portions of electromagnet operation.

Praeg, W.F.

1983-08-31

309

Dual aperture dipole magnet with second harmonic component  

DOEpatents

An improved dual aperture dipole electromagnet includes a second-harmonic frequency magnetic guide field winding which surrounds first harmonic frequency magnetic guide field windings associated with each aperture. The second harmonic winding and the first harmonic windings cooperate to produce resultant magnetic waveforms in the apertures which have extended acceleration and shortened reset portions of electromagnet operation.

Praeg, Walter F. (Palos Park, IL)

1985-01-01

310

Sparse matrix beamforming and image reconstruction for 2-D HIFU monitoring using harmonic motion imaging for focused ultrasound (HMIFU) with in vitro validation.  

PubMed

Harmonic motion imaging for focused ultrasound (HMIFU) utilizes an amplitude-modulated HIFU beam to induce a localized focal oscillatory motion simultaneously estimated. The objective of this study is to develop and show the feasibility of a novel fast beamforming algorithm for image reconstruction using GPU-based sparse-matrix operation with real-time feedback. In this study, the algorithm was implemented onto a fully integrated, clinically relevant HMIFU system. A single divergent transmit beam was used while fast beamforming was implemented using a GPU-based delay-and-sum method and a sparse-matrix operation. Axial HMI displacements were then estimated from the RF signals using a 1-D normalized cross-correlation method and streamed to a graphic user interface with frame rates up to 15 Hz, a 100-fold increase compared to conventional CPU-based processing. The real-time feedback rate does not require interrupting the HIFU treatment. Results in phantom experiments showed reproducible HMI images and monitoring of 22 in vitro HIFU treatments using the new 2-D system demonstrated reproducible displacement imaging, and monitoring of 22 in vitro HIFU treatments using the new 2-D system showed a consistent average focal displacement decrease of 46.7 ±14.6% during lesion formation. Complementary focal temperature monitoring also indicated an average rate of displacement increase and decrease with focal temperature at 0.84±1.15%/(°)C, and 2.03±0.93%/(°)C , respectively. These results reinforce the HMIFU capability of estimating and monitoring stiffness related changes in real time. Current ongoing studies include clinical translation of the presented system for monitoring of HIFU treatment for breast and pancreatic tumor applications. PMID:24960528

Hou, Gary Y; Provost, Jean; Grondin, Julien; Wang, Shutao; Marquet, Fabrice; Bunting, Ethan; Konofagou, Elisa E

2014-11-01

311

Appearance-based exercise motivation moderates the relationship between exercise frequency and positive body image.  

PubMed

Individuals with a positive body image appreciate their bodies, hold an internal perspective of their bodies, and are satisfied with the functionality of their bodies. Research shows that positive body image is more complex than the absence of body dissatisfaction. Although exercise reduces women's body dissatisfaction, very little research has explored how, or even whether, exercise is associated with positive body image. Therefore, we examined whether exercise frequency was positively related to three aspects of positive body image (body appreciation, internal body orientation, and functional body satisfaction) among 321 college women. Appearance-based exercise motivation (the extent exercise is pursued to influence weight or shape) was hypothesized to moderate these associations. Hierarchical moderated regression analyses showed that exercise frequency was related to higher positive body image, but high levels of appearance-based exercise motivation weakened these relationships. Thus, messages promoting exercise need to de-emphasize weight loss and appearance for positive body image. PMID:24529336

Homan, Kristin J; Tylka, Tracy L

2014-03-01

312

High frequency ultrasound imaging in pupillary block glaucoma  

Microsoft Academic Search

BACKGROUND--The diagnosis of pupillary block glaucoma requires sufficient clarity of the ocular media. This is particularly important for assessment of both the presence and patency of an iridotomy, and the determination of central anterior chamber depth. METHODS--High frequency ultrasonography was used in three patients with suspected pupillary block to determine iris configuration, posterior chamber volume, and ciliary body conformation. RESULTS--All

I M Aslanides; P E Libre; R H Silverman; D Z Reinstein; D R Lazzaro; M J Rondeau; G K Harmon; D J Coleman

1995-01-01

313

Imaging of buried objects by low frequency SAS  

Microsoft Academic Search

Search for buried objects are normally done by normal incidence sonar, working with wide-band low frequency signals. Especially the parametric sonar has proven to be a reliable tool to detect buried objects, as well as for mapping of internal stratification in sub-bottom layers. However, due to the small foot-print searching with normal incidence sonar is tedious. Also, in a mine

M. Jonsson; Jorgen Pihl; M. Aklint

2005-01-01

314

Frequency-domain photothermoacoustics: Alternative imaging modality of biological tissues  

E-print Network

spatial resolution typical of ultrasonic imaging. Since the physical process responsible for generation Engineering, Centre for Advanced Diffusion-Wave Technologies (CADIFT), University of Toronto, Toronto M5S 3G8 the necessity to employ short-pulse and high peak-power laser systems to generate acoustic transients

Mandelis, Andreas

315

High frequency resonant waveguide grating imager for assessing drug-induced cardiotoxicity  

NASA Astrophysics Data System (ADS)

We report a high-frequency resonant waveguide grating imager for assessing compound-induced cardiotoxicity. The imager sweeps the wavelength range from 823 nm to 838 nm every 3 s to identify and monitor compound-induced shifts in resonance wavelength and then switch to the intensity-imaging mode to detect the beating rhythm and proarrhythmic effects of compounds on induced pluripotent stem cell-derived cardiomyocytes. This opens possibility to study cardiovascular biology and compound-induced cardiotoxicity.

Ferrie, Ann M.; Wu, Qi; Deichmann, Oberon D.; Fang, Ye

2014-05-01

316

High Frequency Methods for Simulation of High Resolution Imaging in Terahertz Regime  

NASA Astrophysics Data System (ADS)

High resolution imaging in the terahertz (THz) frequency range is investigated theoretically in this paper through the use of the high frequency methods in computational electromagnetics (CEM). Physical optics (PO), shooting and bouncing ray (SBR) and truncated-wedge incremental length diffraction coefficients (TW-ILDCs) methods are combined together to compute the scattered fields, which are then used to construct the inverse synthetic aperture radar (ISAR) images through two dimensional fast Fourier transform (2D-FFT). The corresponding ISAR images clearly show that high range and bearing resolution can be easily realized for THz carrier waves with broad bandwidth.

Li, Zhuo; Cui, Tie Jun

2010-03-01

317

Pump-probe spectroscopy in potassium using an AlGaAs laser and the second-harmonic generation of an InGaAsP laser for frequency stabilization and linking  

NASA Astrophysics Data System (ADS)

Pump-probe spectroscopy in K-41 by using a grating-feedback 0.77-micron AlGaAs laser and the second-harmonic wave of a 1.54-micron InGaAsP laser for providing a frequency reference in the 1.5 micron region was performed. The Doppler-free absorption spectra in both co- and counter-propagating schemes were obtained, and the feasibility of simultaneous frequency stabilization and linking for two diode lasers with a frequency difference as large as 200 THz was demonstrated.

Wang, W.; Akulshin, A. M.; Ohtsu, M.

1994-01-01

318

Microwave Frequency Ferroelectric Domain Imaging of Deuterated Triglycine Sulfate Crystals  

NASA Astrophysics Data System (ADS)

We have used a near-field scanning microwave microscope(D. E. Steinhauer, C. P. Vlahacos, F. C. Wellstood, Steven M. Anlage, C. Canedy, R. Ramesh, A. Stanishevsky, and J. Melngailis, "Quantitative Imaging of Dielectric Permittivity and Tunability with a Near-Field Scanning Microwave Microscope," Rev. Sci. Instrum. 71), 2751-2758 (2000). to image domain structure and quantitatively measure dielectric permittivity and nonlinearity in ferroelectric crystals at 8.1 GHz with a spatial resolution of 1 ?m. We imaged ferroelectric domains in periodically-poled LiNbO_3, BaTiO_3, and deuterated triglycine sulfate (DTGS) with a signal-to-noise ratio of 7. Measurement of the permittivity and nonlinearity of DTGS in the temperature range 300--400 K shows a peak at the Curie temperature, TC ? 340 K, as well as reasonable agreement with thermodynamic theory. In addition, the domain growth relaxation time shows a minimum near T_C. We observe coarsening of ferroelectric domains in DTGS after a temperature quench from 360 K to 330 K, and evaluate the structure factor.

Steinhauer, David E.; Anlage, Steven M.

2001-03-01

319

Optimal modulation frequencies for small-tissue imaging based on the equation of radiative transfer  

NASA Astrophysics Data System (ADS)

The frequency-domain experimental data is typically corrupted by noise and the measurement accuracy is compromised. Assuming the widely used shot-noise model, it is well-known that the signal-to-noise ratio (SNR) of the amplitude signal decreases with increasing frequency, whereas the SNR of phase measurement reaches a peak value in the range between 400 MHz and 800 MHz in tissue volumes typical for small animal imaging studies. As a consequence, it can be assumed that there exists an optimal frequency for which the reconstruction accuracy would be best. To determine optimal frequencies for FDOT, we investigate here the frequency dependence of optical tomographic reconstruction results using the frequency-domain equation of radiative transfer. We present numerical and experimental studies with a focus on small tissue geometries as encountered in small animal imaging and imaging of human finger joints affected by arthritis. Best results were achieved in the 400-800 MHz frequency range, depending on the particular optical properties.

Kim, Hyun Keol; Netz, Uwe J.; Beuthan, j.; Hielscher, Andreas H.

2009-02-01

320

Optimal geometries and harmonic vibrational frequencies of the global minima of water clusters (H2O)n, n=2-6, and several hexamer local minima at the CCSD(T) level of theory  

SciTech Connect

We report the first optimum geometries and harmonic vibrational frequencies for the ring pentamer and several water hexamer (prism, cage, cyclic and two book) at the CCSD(T)/aug-cc-pVDZ level of theory. All five hexamer isomer minima previously reported by MP2 are also minima on the CCSD(T) potential energy surface (PES). In addition, all CCSD(T) minimum energy structures for the n=2-6 cluster isomers are quite close to the ones previously obtained by MP2 on the respective PESs, as confirmed by a modified Procrustes analysis that quantifies the difference between any two cluster geometries. The CCSD(T) results confirm the cooperative effect of the homodromic ring networks (systematic contraction of the nearest-neighbor (nn) intermolecular separations with cluster size) previously reported by MP2, albeit with O-O distances shorter by ~0.02 Å, indicating that MP2 overcorrects this effect. The harmonic frequencies at the minimum geometries were obtained by the double differentiation of the CCSD(T) energy using an efficient scheme based on internal coordinates that reduces the number of required single point energy evaluations by ~15% when compared to the corresponding double differentiation using Cartesian coordinates. Negligible differences between MP2 and CCSD(T) are found for the librational modes, while uniform increases of ~15 and ~25 cm-1 are observed for the bending and “free” OH harmonic frequencies. The largest differences between MP2 and CCSD(T) are observed for the harmonic hydrogen bonded frequencies. The CCSD(T) red shifts from the monomer frequencies (??) are smaller than the MP2 ones, due to the fact that the former produces shorter elongations (?R) of the respective hydrogen bonded OH lengths from the monomer value with respect to the latter. Both the MP2 and CCSD(T) results for the hydrogen bonded frequencies were found to closely follow the relation - ?? = s ? ?R, with a rate of s = 20.3 cm-1 / 0.001 Å. The CCSD(T) harmonic frequencies, when corrected using the MP2 anharmonicities obtained from second order vibrational perturbation theory (VPT2), produce anharmonicCCSD(T) estimates that are within < 60 cm-1 from the measured infrared (IR) active bands of the n=2-6 clusters and furthermore trace the observed red shifts with respect to the monomer (??) quite accurately. The energetic order between the various hexamer isomers on the PES (prism has the lowest energy) previously reported at MP2 was found to be preserved at the CCSD(T) level, whereas the inclusion of anharmonic corrections further stabilizes the cage among the hexamer isomers.

Miliordos, Evangelos; Apra, Edoardo; Xantheas, Sotiris S.

2013-09-21

321

Towards spatial frequency domain optical imaging of neurovascular coupling in a mouse model of Alzheimer's disease  

NASA Astrophysics Data System (ADS)

Early neurovascular coupling (NVC) changes in Alzheimer's disease can potentially provide imaging biomarkers to assist with diagnosis and treatment. Previous efforts to quantify NVC with intrinsic signal imaging have required assumptions of baseline optical pathlength to calculate changes in oxy- and deoxy-hemoglobin concentrations during evoked stimuli. In this work, we present an economical spatial frequency domain imaging (SFDI) platform utilizing a commercially available LED projector, camera, and off-the-shelf optical components suitable for imaging dynamic optical properties. The fast acquisition platform described in this work is validated on silicone phantoms and demonstrated in neuroimaging of a mouse model.

Lin, Alexander J.; Konecky, Soren D.; Rice, Tyler B.; Green, Kim N.; Choi, Bernard; Durkin, Anthony J.; Tromberg, Bruce J.

2012-02-01

322

An image reconstruction method from Fourier data with uncertainties on the spatial frequencies  

NASA Astrophysics Data System (ADS)

In this paper the reconstruction of a two-dimensional image from a nonuniform sampling of its Fourier transform is considered, in the presence of uncertainties on the frequencies corresponding to the measured data. The problem therefore becomes a blind deconvolution, in which the unknowns are both the image to be reconstructed and the exact frequencies. The availability of information on the image and the frequencies allows to reformulate the problem as a constrained minimization of the least squares functional. A regularized solution of this optimization problem is achieved by early stopping an alternating minimization scheme. In particular, a gradient projection method is employed at each step to compute an inexact solution of the minimization subproblems. The resulting algorithm is applied on some numerical examples arising in a real-world astronomical application.

Cornelio, Anastasia; Bonettini, Silvia; Prato, Marco

2013-10-01

323

Metamaterial fibres for subdiffraction imaging and focusing at terahertz frequencies over optically long distances.  

PubMed

Using conventional materials, the resolution of focusing and imaging devices is limited by diffraction to about half the wavelength of light, as high spatial frequencies do not propagate in isotropic materials. Wire array metamaterials, because of their extreme anisotropy, can beat this limit; however, focusing with these has only been demonstrated up to microwave frequencies and using propagation over a few wavelengths only. Here we show that the principle can be scaled to frequencies orders of magnitudes higher and to considerably longer propagation lengths. We demonstrate imaging through straight and tapered wire arrays operating in the terahertz spectrum, with unprecedented propagation of near field information over hundreds of wavelengths and focusing down to 1/28 of the wavelength with a net increase in power density. Applications could include in vivo terahertz-endoscopes with resolution compatible with imaging individual cells. PMID:24162458

Tuniz, Alessandro; Kaltenecker, Korbinian J; Fischer, Bernd M; Walther, Markus; Fleming, Simon C; Argyros, Alexander; Kuhlmey, Boris T

2013-01-01

324

Imaging of collagen matrix remodeling in three-dimensional space using second harmonic generation and two photon excitation fluorescence  

NASA Astrophysics Data System (ADS)

Second harmonic generation (SHG), a nonlinear optical phenomenon, exhibits several in-common characteristics of twophoton excited fluorescence (TPEF) microscopy. These characteristics include identical equipment requirements from experiment to experiment and the intrinsic capability of generating 3-dimensional (D) high resolution images. Structural protein arrays that are highly ordered, such as collagen, produce strong SHG signals without the need for any exogenous label (stain). SHG and TPEF can be used together to provide information on structural rearrangements in 3D space of the collagen matrix associated with various physiological processes. In this study, we used SHG and TPEF to detect cellmediated structural reorganization of the extracellular collagen matrix in 3D space triggered by dimensional changes of embedded fibroblasts. These fibroblasts were cultured in native type I collagen gels and were stimulated to contract for a period of 24 hours. The gels were stained for cell nuclei with Hoechst and for actin with phalloidin conjugated to Alexa Fluor 488. We used non-de-scanned detectors and spectral scanning mode both in the reflection geometry for generating the 3D images and for SHG spectra, respectively. We used a tunable infrared laser with 100-fs pulses at a repetition rate of 80-MHz tuned to 800-nm for Hoechst and Alexa 488 excitations. We employed a broad range of excitation wavelengths (800 to 880-nm) with a scan interval of 10 nm to detect the SHG signal. We found that spectrally clean SHG signal peaked at 414-nm with excitation wavelength of 830-nm. The SHG spectrum has a full width half maximum (FWHM) bandwidth of 6.60-nm, which is consistent with its scaling relation to FWHM bandwidth 100-fs excitation pulses. When stimulated to contract, we found the fibroblasts to be highly elongated as well as interconnected in 2D space, and the collagen matrix, in the form of a visibly clear fibril structure, accumulated around the cells. In the absence of contraction, on the other hand, the cells were predominantly round in shape and no sign of collagen accumulation around the cell was evident despite the presence of SHG signal as well as the fibrillar collagen morphology in the collagen matrix. We here conclude that SHG in conjunction with TPEF can serve as a noninvasive method to provide spatially resolved 3D structural reorganization of collagen matrices triggered by various physiological processes.

Abraham, Thomas; Carthy, Jon; McManus, Bruce

2009-02-01

325

Automatic classification of sleep stages based on the time-frequency image of EEG signals.  

PubMed

In this paper, a new method for automatic sleep stage classification based on time-frequency image (TFI) of electroencephalogram (EEG) signals is proposed. Automatic classification of sleep stages is an important part for diagnosis and treatment of sleep disorders. The smoothed pseudo Wigner-Ville distribution (SPWVD) based time-frequency representation (TFR) of EEG signal has been used to obtain the time-frequency image (TFI). The segmentation of TFI has been performed based on the frequency-bands of the rhythms of EEG signals. The features derived from the histogram of segmented TFI have been used as an input feature set to multiclass least squares support vector machines (MC-LS-SVM) together with the radial basis function (RBF), Mexican hat wavelet, and Morlet wavelet kernel functions for automatic classification of sleep stages from EEG signals. The experimental results are presented to show the effectiveness of the proposed method for classification of sleep stages from EEG signals. PMID:24008250

Bajaj, Varun; Pachori, Ram Bilas

2013-12-01

326

Multibeam single frequency synthetic aperture radar processor for imaging separate range swaths  

NASA Technical Reports Server (NTRS)

A method and apparatus are described for single frequency multibeam imaging of multiple strips of range swath at high range intervals for those applications where it is desirable to cover a range swath much greater than is possible for a given interpulse interval. Data from a single frequency synthetic aperture radar (in which beam parameters are adjusted so that the return from each successive swath is received during successive interpulse periods) are separated in Dopple frequency for the return from each beam at the frequency plane of the processor. Alternatively, the image formed by each beam may be spatially separated in the azimuth direction and successively selected by positioning an appropriate slit in the recording plane of the processor.

Jain, A. (inventor)

1979-01-01

327

Tip-induced deformation of a phospholipid bilayer: Theoretical perspective of sum frequency generation imaging  

NASA Astrophysics Data System (ADS)

The paper addresses theory of Sum Frequency Generation imaging of an atomic force microscopy tip-induced deformation of a bilayer phospholipid membrane deposited over a pore: known as a nano-drum system. Image modeling employed nonlinearities of the normal modes specific to hydrocarbon terminal methyls, which are distributed about the deformed surfaces of inner and outer leaflets. The deformed profiles are according to the solutions of shape equation for Canham-Helfrich Hamiltonian accounting properties of four membranes, which differ in elasticity and adhesion. The results indicate that in continuous deformed surfaces, the difference in the curvature of the outer and inner leaflets dominates in the imaged nonlinearity. This is different comparing to the results for a perfect bilayer spherical cap system (the subject of previous study), where nonlinear image response is dominated by the mismatch of the inner and outer leaflets' surface areas (as projected to the image plane) at the edge of perfectly spherical structure. The results of theoretical studies, here, demonstrate that Sum Frequency Generation imaging in continuous and deformed bilayer surfaces are helpful to address curvature locally and anticipate mechanical properties of membrane. The articles discuss applicability and practical limitations of the approach. Combination of Atomic Force Microscopy and Sum Frequency Generation imaging under controlled tip-induced deformation provides a good opportunity to probe and test membranes physical properties with rigor of adopted theory.

Volkov, Victor

2014-10-01

328

Tip-induced deformation of a phospholipid bilayer: theoretical perspective of sum frequency generation imaging.  

PubMed

The paper addresses theory of Sum Frequency Generation imaging of an atomic force microscopy tip-induced deformation of a bilayer phospholipid membrane deposited over a pore: known as a nano-drum system. Image modeling employed nonlinearities of the normal modes specific to hydrocarbon terminal methyls, which are distributed about the deformed surfaces of inner and outer leaflets. The deformed profiles are according to the solutions of shape equation for Canham-Helfrich Hamiltonian accounting properties of four membranes, which differ in elasticity and adhesion. The results indicate that in continuous deformed surfaces, the difference in the curvature of the outer and inner leaflets dominates in the imaged nonlinearity. This is different comparing to the results for a perfect bilayer spherical cap system (the subject of previous study), where nonlinear image response is dominated by the mismatch of the inner and outer leaflets' surface areas (as projected to the image plane) at the edge of perfectly spherical structure. The results of theoretical studies, here, demonstrate that Sum Frequency Generation imaging in continuous and deformed bilayer surfaces are helpful to address curvature locally and anticipate mechanical properties of membrane. The articles discuss applicability and practical limitations of the approach. Combination of Atomic Force Microscopy and Sum Frequency Generation imaging under controlled tip-induced deformation provides a good opportunity to probe and test membranes physical properties with rigor of adopted theory. PMID:25338888

Volkov, Victor

2014-10-21

329

Current collapse imaging of Schottky gate AlGaN/GaN high electron mobility transistors by electric field-induced optical second-harmonic generation measurement  

SciTech Connect

Two-dimensional current collapse imaging of a Schottky gate AlGaN/GaN high electron mobility transistor device was achieved by optical electric field-induced second-harmonic generation (EFISHG) measurements. EFISHG measurements can detect the electric field produced by carriers trapped in the on-state of the device, which leads to current collapse. Immediately after (e.g., 1, 100, or 800??s) the completion of drain-stress voltage (200?V) in the off-state, the second-harmonic (SH) signals appeared within 2??m from the gate edge on the drain electrode. The SH signal intensity became weak with time, which suggests that the trapped carriers are emitted from the trap sites. The SH signal location supports the well-known virtual gate model for current collapse.

Katsuno, Takashi, E-mail: e1417@mosk.tytlabs.co.jp; Ishikawa, Tsuyoshi; Ueda, Hiroyuki; Uesugi, Tsutomu [Toyota Central R and D Laboratories Inc., Nagakute, Aichi 480-1192 (Japan); Manaka, Takaaki; Iwamoto, Mitsumasa [Department of Physical Electronics, Tokyo Institute of Technology, Meguro, Tokyo 152-8552 (Japan)

2014-06-23

330

High frame-rate intravascular optical frequency-domain imaging in vivo  

PubMed Central

Intravascular optical frequency-domain imaging (OFDI), a second-generation optical coherence tomography (OCT) technology, enables imaging of the three-dimensional (3D) microstructure of the vessel wall following a short and nonocclusive clear liquid flush. Although 3D vascular visualization provides a greater appreciation of the vessel wall and intraluminal structures, a longitudinal imaging pitch that is several times bigger than the optical imaging resolution of the system has limited true high-resolution 3D imaging, mainly due to the slow scanning speed of previous imaging catheters. Here, we demonstrate high frame-rate intravascular OFDI in vivo, acquiring images at a rate of 350 frames per second. A custom-built, high-speed, and high-precision fiber-optic rotary junction provided uniform and high-speed beam scanning through a custom-made imaging catheter with an outer diameter of 0.87 mm. A 47-mm-long rabbit aorta was imaged in 3.7 seconds after a short contrast agent flush. The longitudinal imaging pitch was 34 ?m, comparable to the transverse imaging resolution of the system. Three-dimensional volume-rendering showed greatly enhanced visualization of tissue microstructure and stent struts relative to what is provided by conventional intravascular imaging speeds. PMID:24466489

Cho, Han Saem; Jang, Sun-Joo; Kim, Kyunghun; Dan-Chin-Yu, Alexey V.; Shishkov, Milen; Bouma, Brett E.; Oh, Wang-Yuhl

2013-01-01

331

Compressive sensing imaging with optical Fourier frequency spectrum coding and optical wavelet transform  

NASA Astrophysics Data System (ADS)

In traditional signal sampling process, Shannon - Nyquist (Shoon-Nyquist) sampling theorem is a fundamental principle that must be followed, in that the sampling frequency must be at least twice the highest frequency of the sampled signal. However, with the increasing of data acquisition capabilities of sensing systems, acquisition of high-resolution images will inevitably lead to a flood of sampling data according to Shoon-Nyquist sampling theorem, which increases the cost of data transport and storage, and also the demand for the resolution of the detector. Donoho and Candes proposed the compressed sensing theory which is considered as a revolutionary breakthrough in that it breaks Shoon-Nyquist sampling frequency requirements. For compressible or sparse signals, signal sampling can be implemented with the sampling frequency that is less than that of Shoon-Nyquist sampling theorem, and the signal is also compressed meanwhile. This paper studied compressive coding imaging based on optical wavelet transform coupled with the frequency spectrum coding. The imaging quality can be enhanced by introducing optical wavelet transform for pre-treatment of the target image before the compression coding on the frequency spectrum plane. Simulation results show that higher quality images can be obtained with the pre-treatment of optical wavelet transform than that of purely optical Fourier transform without any increasing of the transmitted data. With the proposed method, we have conducted the numerical simulations. The results show that the proposed compression sampling method can achieve the real-time compression sampling of the images without distortion, and a compression ratio of 4:1 can be obtained.

Han, Jiyu; Xu, Feng; Wang, Chinhua

2013-08-01

332

High Frequency Methods for Simulation of High Resolution Imaging in Terahertz Regime  

Microsoft Academic Search

High resolution imaging in the terahertz (THz) frequency range is investigated theoretically in this paper through the use\\u000a of the high frequency methods in computational electromagnetics (CEM). Physical optics (PO), shooting and bouncing ray (SBR)\\u000a and truncated-wedge incremental length diffraction coefficients (TW-ILDCs) methods are combined together to compute the scattered\\u000a fields, which are then used to construct the inverse synthetic

Zhuo Li; Tie Jun Cui

2010-01-01

333

Multi-frequency time-reversal-based imaging for ultrasonic nondestructive evaluation using full matrix capture.  

PubMed

In this paper, two multi-frequency time-reversal (TR)-based imaging algorithms are explored for application to the nondestructive evaluation (NDE) imaging of defects in solids: time reversal with multiple signal classification (TRMUSIC) and a related phase-coherent form (PC-MUSIC). These algorithms are tested with simulated and experimental ultrasonic array data acquired using the full matrix capture (FMC) process. The performance of these algorithms is quantified in terms of their spatial resolution and robustness to noise. The effect of frequency bandwidth is investigated and the results are compared with the single-frequency versions of these algorithms. It is shown that both TR-MUSIC and PCMUSIC are capable of resolving lateral targets spaced closer than the Rayleigh limit, achieving super-resolution imaging. TR-MUSIC can locate the positions of scatterers correctly, whereas the results from PC-MUSIC are less clear because of the presence of multiple peaks in the vicinity of target. However, an advantage of PC-MUSIC is that it can overcome the elongated point spread function that appears in TR-MUSIC images, and hence provide enhanced axial resolution. For high noise levels, TR-MUSIC and PC-MUSIC are shown to provide stable images and suppress the presence of artifacts seen in their single-frequency equivalents. PMID:25474781

Fan, Chengguang; Pan, Mengchun; Luo, Feilu; Drinkwater, Bruce

2014-12-01

334

A multi-scale multi-frequency deconvolution algorithm for synthesis imaging in radio interferometry  

NASA Astrophysics Data System (ADS)

Aims: We describe MS-MFS, a multi-scale multi-frequency deconvolution algorithm for wide-band synthesis-imaging, and present imaging results that illustrate the capabilities of the algorithm and the conditions under which it is feasible and gives accurate results. Methods: The MS-MFS algorithm models the wide-band sky-brightness distribution as a linear combination of spatial and spectral basis functions, and performs image-reconstruction by combining a linear-least-squares approach with iterative ?2 minimization. This method extends and combines the ideas used in the MS-CLEAN and MF-CLEAN algorithms for multi-scale and multi-frequency deconvolution respectively, and can be used in conjunction with existing wide-field imaging algorithms. We also discuss a simpler hybrid of spectral-line and continuum imaging methods and point out situations where it may suffice. Results: We show via simulations and application to multi-frequency VLA data and wideband EVLA data, that it is possible to reconstruct both spatial and spectral structure of compact and extended emission at the continuum sensitivity level and at the angular resolution allowed by the highest sampled frequency.

Rau, U.; Cornwell, T. J.

2011-08-01

335

Multiple images storage and frequency conversion in a cold atomic ensemble  

E-print Network

The strong demand for quantum memory, a key building block of quantum network, has inspired new methodologies and led to experimental progress for quantum storage. The use of quantum memory for spatial multimode or image storage could dramatically increase the channel bit-rate. Furthermore, quantum memory that can store multiple optical modes would lead to higher efficiencies in quantum communication and computation. Here, by using resonant tripod electromagnetically induced transparency in a cold atomic ensemble, we experimentally demonstrate multiple probes storage in frequency domain, where two probe fields have discrete wavelengths and different spatial information. In addition, by using different read-light, we realize frequency conversion of retrieved images with high efficiency. Besides, our method could be used to create a superposition of the images by realizing the function of a beamsplitter. All advantages make our method useful in many fields including quantum information, detection, imaging, sensing and even astrophysical observation.

Dong-Sheng Ding; Jing-Hui Wu; Zhi-Yuan Zhou; Bao-Sen Shi; Xu-Bo Zou; Guang-Can Guo

2012-09-10

336

An approach for images with low-frequency noise denoising via pre-emphasis and high-pass filter  

NASA Astrophysics Data System (ADS)

Wavelet-based denoising methods have been successfully applied in processing images with high-frequency noise, such as salt noise, Gausian noise, Poisson noise, etc. However, it is less effective when processing images with low-frequency noise. Seemingly, we can consider using high-pass filter directly to remove the low-frequency noise, but it turns out that when the noise is removed, the useful low-frequency information is also weakened during the process. In this paper, we proposed a new approach to denoise the images with low-frequency noise via pre-emphasis and high-pass filtration. Thereby we removed the low-frequency noise effectively without losing useful low-frequency information. The approach can be well applied in decreasing the interference of low-frequency noise in image transmission.

Zhang, Qi; Ma, Shaobo; Cao, Li

2013-03-01

337

High frequency atmospheric gravity-wave properties using Fe-lidar and OH-imager observations  

NASA Astrophysics Data System (ADS)

Simultaneous iron resonance lidar density profiles, OH intensity images and MF-radar wind measurements have been used to determine the horizontal and vertical components of high-frequency (<=~1 hour) atmospheric gravity waves (AGW). Previous investigations predicted that AGW information from lidars and imagers could only be combined over a limited range. Here, a novel approach to increasing the utility of the simultaneous lidar and OH imager measurement are presented. By temporally high-pass filtering each altitude-bin of the lidar profiles, the vertical wavelengths of AGW typically observed with the OH imager become apparent. Measured OH imager horizontal wavelengths were converted into vertical wavelengths using the dispersion relationship and background winds, showing that the instruments were able to observe the same waves. Hence, the lidar-imager combination is able to access the intrinsic wave components to allow investigation of AGW propagation and an assessment of the chemical waves effects on minor species chemistry.

Diettrich, J. C.; Nott, G. J.; Espy, P. J.; Swenson, G. R.; Chu, X.; Taylor, M. J.; Riggin, D. M.; Fritts, D. C.

2005-05-01

338

Three-dimensional ground penetrating radar imaging using multi-frequency diffraction tomography  

SciTech Connect

In this paper we present results from a three-dimensional image reconstruction algorithm for impulse radar operating in monostatic pulse-echo mode. The application of interest to us is the nondestructive evaluation of civil structures such as bridge decks. We use a multi-frequency diffraction tomography imaging technique in which coherent backward propagations of the received reflected wavefield form a spatial image of the scattering interfaces within the region of interest. This imaging technique provides high-resolution range and azimuthal visualization of the subsurface region. We incorporate the ability to image in planarly layered conductive media and apply the algorithm to experimental data from an offset radar system in which the radar antenna is not directly coupled to the surface of the region. We present a rendering in three-dimensions of the resulting image data which provides high-detail visualization.

Mast, J.E.; Johansson, E.M.

1994-07-01

339

Effect of spectral shaping on defect detection in frequency modulated thermal wave imaging  

NASA Astrophysics Data System (ADS)

This manuscript highlights a novel data processing approach for active infrared non-destructive testing and evaluation of carbon fibre reinforced polymers (CFRP). This is accomplished by performing spectral reshaping on a captured pre-processed linear frequency modulated thermal profile over the specimen. Results obtained from the Gaussian windowed frequency modulated thermal wave imaging (GWFMTWI) clearly shows better detection capabilities with improved test resolution and sensitivity. Further multi-transform techniques have been introduced both in time and frequency in order to test subsurface defect capabilities of the proposed approach.

Dua, Geetika; Mulaveesala, Ravibabu; Siddique, Juned A.

2015-02-01

340

DeStripe: frequency-based algorithm for removing stripe noises from AFM images  

PubMed Central

Background Atomic force microscopy (AFM) is a relatively recently developed technique that shows a promising impact in the field of structural biology and biophysics. It has been used to image the molecular surface of membrane proteins at a lateral resolution of one nanometer or less. An immediate obstacle of characterizing surface features in AFM images is stripe noise. To better interpret structures at a sub-domain level, pre-processing of AFM images for removing stripe noises is necessary. Noise removal can be performed in either spatial or frequency domain. However, denoising processing in the frequency domain is a better solution for preserving edge sharpness. Results We have developed a denoising protocol, called DeStripe, for AFM bio-molecular images that are contaminated with heavy and fine stripes. This program adopts a divide-and-conquer approach by dividing the Fourier spectrum of the image into central and off-center regions for noisy pixels detection and intensity restoration; it is also applicable to other images interfered with high-density stripes such as those acquired by the scanning electron microscope. The denoising effect brought by DeStripe provides better visualization for image objects without introducing additional artifacts into the restored image. Conclusions The DeStripe denoising effect on AFM images is illustrated in the present work. It allows extracting extended information from the topographic measurements and implicitly enhances the molecular features in the image. All the presented images were processed by DeStripe with the raw image as the only input without any requirement for other prior information. A web service, http://biodev.cea.fr/destripe, is available for running DeStripe. PMID:21281524

2011-01-01

341

Electrical tissue property imaging using MRI at dc and Larmor frequency  

NASA Astrophysics Data System (ADS)

Cross-sectional imaging of conductivity and permittivity distributions inside the human body has been actively investigated in impedance imaging areas such as electrical impedance tomography (EIT) and magnetic induction tomography (MIT). Since the conductivity and permittivity values exhibit frequency-dependent changes, it is worthwhile to perform spectroscopic imaging from almost dc to hundreds of MHz. To probe the human body, we may inject current using surface electrodes or induce current using external coils. In EIT and MIT, measured data are only available on the boundary or exterior of the body unless we invasively place sensors inside the body. Their image reconstruction problems are nonlinear and ill-posed to result in images with a relatively low spatial resolution. Noting that an MRI scanner can noninvasively measure magnetic fields inside the human body, electrical tissue property imaging methods using MRI have lately been proposed. Magnetic resonance EIT (MREIT) performs conductivity imaging at dc or below 1 kHz by externally injecting current into the human body and measuring induced internal magnetic flux density data using an MRI scanner. Magnetic resonance electrical property tomography (MREPT) produces both conductivity and permittivity images at the Larmor frequency of an MRI scanner based on B1-mapping techniques. Since internal data are only available in MREIT and MREPT, we may formulate well-posed inverse problems for image reconstructions. To develop related imaging techniques, we should clearly understand the basic principles of MREIT and MREPT, which are based on coupled physics of bioelectromagnetism and MRI as well as associated mathematical methods. In this paper, we describe the physical principles of MREIT and MREPT in a unified way and associate measurable quantities with the conductivity and permittivity. Clarifying the key relations among them, we examine existing image reconstruction algorithms to reveal their capabilities and limitations. We discuss technical issues in MREIT and MREPT and suggest future research directions to improve the quality of cross-sectional images of the electrical tissue properties.

Seo, Jin Keun; Kim, Dong-Hyun; Lee, Joonsung; In Kwon, Oh; Sajib, Saurav Z. K.; Woo, Eung Je

2012-08-01

342

Frequency-modulated atomic force microscopy operation by imaging at the frequency shift minimum: The dip-df mode  

SciTech Connect

In frequency modulated non-contact atomic force microscopy, the change of the cantilever frequency (?f) is used as the input signal for the topography feedback loop. Around the ?f(z) minimum, however, stable feedback operation is challenging using a standard proportional-integral-derivative (PID) feedback design due to the change of sign in the slope. When operated under liquid conditions, it is furthermore difficult to address the attractive interaction regime due to its often moderate peakedness. Additionally, the ?f signal level changes severely with time in this environment due to drift of the cantilever frequency f{sub 0} and, thus, requires constant adjustment. Here, we present an approach overcoming these obstacles by using the derivative of ?f with respect to z as the input signal for the topography feedback loop. Rather than regulating the absolute value to a preset setpoint, the slope of the ?f with respect to z is regulated to zero. This new measurement mode not only makes the minimum of the ?f(z) curve directly accessible, but it also benefits from greatly increased operation stability due to its immunity against f{sub 0} drift. We present isosurfaces of the ?f minimum acquired on the calcite CaCO{sub 3}(101{sup ¯}4) surface in liquid environment, demonstrating the capability of our method to image in the attractive tip-sample interaction regime.

Rode, Sebastian; Schreiber, Martin; Kühnle, Angelika; Rahe, Philipp, E-mail: rahe@uni-mainz.de [Institut für Physikalische Chemie, Fachbereich Chemie, Johannes Gutenberg-Universität Mainz, Duesbergweg 10-14, 55099 Mainz (Germany)] [Institut für Physikalische Chemie, Fachbereich Chemie, Johannes Gutenberg-Universität Mainz, Duesbergweg 10-14, 55099 Mainz (Germany)

2014-04-15

343

Frequency-modulated atomic force microscopy operation by imaging at the frequency shift minimum: The dip-df mode  

NASA Astrophysics Data System (ADS)

In frequency modulated non-contact atomic force microscopy, the change of the cantilever frequency (?f) is used as the input signal for the topography feedback loop. Around the ?f(z) minimum, however, stable feedback operation is challenging using a standard proportional-integral-derivative (PID) feedback design due to the change of sign in the slope. When operated under liquid conditions, it is furthermore difficult to address the attractive interaction regime due to its often moderate peakedness. Additionally, the ?f signal level changes severely with time in this environment due to drift of the cantilever frequency f0 and, thus, requires constant adjustment. Here, we present an approach overcoming these obstacles by using the derivative of ?f with respect to z as the input signal for the topography feedback loop. Rather than regulating the absolute value to a preset setpoint, the slope of the ?f with respect to z is regulated to zero. This new measurement mode not only makes the minimum of the ?f(z) curve directly accessible, but it also benefits from greatly increased operation stability due to its immunity against f0 drift. We present isosurfaces of the ?f minimum acquired on the calcite CaCO3(10overline{1}4) surface in liquid environment, demonstrating the capability of our method to image in the attractive tip-sample interaction regime.

Rode, Sebastian; Schreiber, Martin; Kühnle, Angelika; Rahe, Philipp

2014-04-01

344

Room temperature terahertz wave imaging at 60 fps by frequency up-conversion in DAST crystal  

NASA Astrophysics Data System (ADS)

Terahertz imaging has attracted a lot of interests for more than 10 years. But real time, high sensitive, low cost THz imaging in room temperature, which is widely needed by fields such as biology, biomedicine and homeland security, has not been fully developed yet. A lot of approaches have been reported on electro-optic (E-O) imaging and THz focal plane arrays with photoconductive antenna or micro-bolometer integrated. In this paper, we report high sensitive realtime THz image at 60 frames per second (fps) employing a commercial infrared camera, using nonlinear optical frequency up-conversion technology. In this system, a flash-lamp pumped nanosecond pulse green laser is used to pump two optical parametric oscillator systems with potassium titanyl phosphate crystals (KTP-OPO). One system with dual KTP crystals is used to generate infrared laser for the pumping of THz difference frequency generation (DFG) in a 4- Dimethylamino-N-Methyl-4-Stilbazolium Tosylate (DAST) crystal. The other one is for generation of pumping laser for THz frequency up-conversion in a second DAST crystal. The THz frequency can be tuned continuously from a few THz to less than 30 THz by controlling the angle of KTP crystals. The frequency up-converted image in infrared region is recorded by a commercial infrared camera working at 60 Hz. Images and videos are presented to show the feasibility of this technique and the real-time ability. Comparison with a general micro-bolometer THz camera shows the high sensitivity of this technique.

Fan, Shuzhen; Qi, Feng; Notake, Takashi; Nawata, Kouji; Matsukawa, Takeshi; Takida, Yuma; Minamide, Hiroaki

2014-02-01

345

Accumulated source imaging of brain activity with both low and high-frequency neuromagnetic signals  

PubMed Central

Recent studies have revealed the importance of high-frequency brain signals (>70 Hz). One challenge of high-frequency signal analysis is that the size of time-frequency representation of high-frequency brain signals could be larger than 1 terabytes (TB), which is beyond the upper limits of a typical computer workstation's memory (<196 GB). The aim of the present study is to develop a new method to provide greater sensitivity in detecting high-frequency magnetoencephalography (MEG) signals in a single automated and versatile interface, rather than the more traditional, time-intensive visual inspection methods, which may take up to several days. To address the aim, we developed a new method, accumulated source imaging, defined as the volumetric summation of source activity over a period of time. This method analyzes signals in both low- (1~70 Hz) and high-frequency (70~200 Hz) ranges at source levels. To extract meaningful information from MEG signals at sensor space, the signals were decomposed to channel-cross-channel matrix (CxC) representing the spatiotemporal patterns of every possible sensor-pair. A new algorithm was developed and tested by calculating the optimal CxC and source location-orientation weights for volumetric source imaging, thereby minimizing multi-source interference and reducing computational cost. The new method was implemented in C/C++ and tested with MEG data recorded from clinical epilepsy patients. The results of experimental data demonstrated that accumulated source imaging could effectively summarize and visualize MEG recordings within 12.7 h by using approximately 10 GB of computer memory. In contrast to the conventional method of visually identifying multi-frequency epileptic activities that traditionally took 2–3 days and used 1–2 TB storage, the new approach can quantify epileptic abnormalities in both low- and high-frequency ranges at source levels, using much less time and computer memory. PMID:24904402

Xiang, Jing; Luo, Qian; Kotecha, Rupesh; Korman, Abraham; Zhang, Fawen; Luo, Huan; Fujiwara, Hisako; Hemasilpin, Nat; Rose, Douglas F.

2014-01-01

346

A novel radio frequency coil for veterinary magnetic resonance imaging system  

NASA Astrophysics Data System (ADS)

In this article, a novel designed radio frequency (RF) coil is designed and built for the imaging of puppies in a V-shape permanent magnetic resonance imaging (MRI) system. Two sets of Helmholtz coil pairs with a V-shape structure are used to improve the holding of an animal in the coil. The homogeneity and the sensitivity of the RF field in the coil are analysed by theoretical calculation. The size and the shape of the new coil are optimized and validated by simulation through using the finite element method (FEM). Good magnetic resonance (MR) images are achieved on a shepherd dog.

Meng, Bin; Huang, Kai-Wen; Wang, Wei-Min

2010-07-01

347

High-frequency ex vivo ultrasound imaging of the auditory system.  

PubMed

A 50MHz array-based imaging system was used to obtain high-resolution images of the ear and auditory system. This previously described custom built imaging system (Brown et al. 2004a, 2004b; Brown and Lockwood 2005) is capable of 50 microm axial resolution, and lateral resolution varying from 80 microm to 130 microm over a 5.12 mm scan depth. The imaging system is based on a 2mm diameter, seven-element equal-area annular array, and a digital beamformer that uses high-speed field programmable gate arrays (FPGAs). The images produced by this system have shown far superior depth of field compared with commercially available single-element systems. Ex vivo, three-dimensional (3-D) images were obtained of human cadaveric tissues including the ossicles (stapes, incus, malleus) and the tympanic membrane. In addition, two-dimensional (2-D) images were obtained of an intact cochlea by imaging through the round window membrane. The basilar membrane inside the cochlea could clearly be visualized. These images demonstrate that high-frequency ultrasound imaging of the middle and inner ear can provide valuable diagnostic information using minimally invasive techniques that could potentially be implemented in vivo. PMID:19679390

Brown, Jeremy A; Torbatian, Zahra; Adamson, Robert B; Van Wijhe, Rene; Pennings, Ronald J; Lockwood, Geoffrey R; Bance, Manohar L

2009-11-01

348

LOW FREQUENCY SOUND SPEED MEASUREMENTS PAIRED WITH COMPUTED X-RAY TOMOGRAPHY IMAGING IN GAS-  

E-print Network

LOW FREQUENCY SOUND SPEED MEASUREMENTS PAIRED WITH COMPUTED X-RAY TOMOGRAPHY IMAGING IN GAS the overall void fraction (VF) and the bubble size distribution (BSD), both of which greatly effect varying fractions of biogenic gas bubbles or air bubbles. The acoustic resonator operated between 100

Wilson, Preston S.

349

Sum frequency generation image reconstruction: aliphatic membrane under spherical cap geometry.  

PubMed

The article explores an opportunity to approach structural properties of phospholipid membranes using Sum Frequency Generation microscopy. To establish the principles of sum frequency generation image reconstruction in such systems, at first approach, we may adopt an idealistic spherical cap uniform assembly of hydrocarbon molecules. Quantum mechanical studies for decanoic acid (used here as a representative molecular system) provide necessary information on transition dipole moments and Raman tensors of the normal modes specific to methyl terminal - a typical moiety in aliphatic (and phospholipid) membranes. Relative degree of localization and frequencies of the normal modes of methyl terminals make nonlinearities of this moiety to be promising in structural analysis using Sum Frequency Generation imaging. Accordingly, the article describes derivations of relevant macroscopic nonlinearities and suggests a mapping procedure to translate amplitudes of the nonlinearities onto microscopy image plane according to geometry of spherical assembly, local molecular orientation, and optical geometry. Reconstructed images indicate a possibility to extract local curvature of bilayer envelopes of spherical character. This may have practical implications for structural extractions in membrane systems of practical relevance. PMID:25296798

Volkov, Victor

2014-10-01

350

High-sensitivity vibrational imaging with frequency modulation coherent anti-Stokes  

E-print Network

High-sensitivity vibrational imaging with frequency modulation coherent anti-Stokes Raman vibrational os- cillators than possible through existing CARS microscopy methods. © 2006 Optical Society information about the intrinsic vibrational resonances of a sample, allowing for label-free, chemically

Xie, Xiaoliang Sunney

351

Sum frequency generation image reconstruction: Aliphatic membrane under spherical cap geometry  

NASA Astrophysics Data System (ADS)

The article explores an opportunity to approach structural properties of phospholipid membranes using Sum Frequency Generation microscopy. To establish the principles of sum frequency generation image reconstruction in such systems, at first approach, we may adopt an idealistic spherical cap uniform assembly of hydrocarbon molecules. Quantum mechanical studies for decanoic acid (used here as a representative molecular system) provide necessary information on transition dipole moments and Raman tensors of the normal modes specific to methyl terminal - a typical moiety in aliphatic (and phospholipid) membranes. Relative degree of localization and frequencies of the normal modes of methyl terminals make nonlinearities of this moiety to be promising in structural analysis using Sum Frequency Generation imaging. Accordingly, the article describes derivations of relevant macroscopic nonlinearities and suggests a mapping procedure to translate amplitudes of the nonlinearities onto microscopy image plane according to geometry of spherical assembly, local molecular orientation, and optical geometry. Reconstructed images indicate a possibility to extract local curvature of bilayer envelopes of spherical character. This may have practical implications for structural extractions in membrane systems of practical relevance.

Volkov, Victor

2014-10-01

352

Near field focusing algorithm for high frequency ground penetration imaging radar  

Microsoft Academic Search

Ground penetrating radar has been successfully used for imaging stratigraphic structures. The goal of our ground penetrating radar program is to provide a capability for strategic subsurface target detection for military applications. This paper describes an experimental approach to high frequency (HF) radar sub-surface profiling, and the results obtained from signal and data processing for deep tunnel detection. Ongoing experiments

Russell D. Brown; E. Douglas Lynch; David W. Mokry; James M. VanDamme; Richard A. Schneible; Michael C. Wicks

1999-01-01

353

Interactions of magnetic resonance imaging radio frequency magnetic fields with elongated medical implants  

Microsoft Academic Search

Magnetic resonance imaging (MRI) is a well established diagnostic technique, one from which all patients should be able to benefit, including those with implanted medical devices. This paper describes an experimental and numerical study of the temperature rise near the ends of wires by the radio frequency (rf) field in MRI. These wires simulate long wires which may be part

Chris D. Smith; Alexander V. Kildishev; John A. Nyenhuis; Kirk S. Foster; Joe D. Bourland

2000-01-01

354

Image Segmentation Using Fuzzy Region Competition and Spatial\\/Frequency Information  

Microsoft Academic Search

This paper presents a multiphase fuzzy region com- petition model that takes into account spatial and frequency infor- mation for image segmentation. In the proposed energy functional, each region is represented by a fuzzy membership function and a data fidelity term that measures the conformity of spatial and fre- quency data within each region to (generalized) Gaussian densities whose parameters

S. K. Choy; M. L. Tang; C. S. Tong

2011-01-01

355

Stepped-frequency continuous-wave microwave-induced thermoacoustic imaging  

SciTech Connect

Microwave-induced thermoacoustic (TA) imaging combines the dielectric contrast of microwave imaging with the resolution of ultrasound imaging. Prior studies have only focused on time-domain techniques with short but powerful microwave pulses that require a peak output power in excess of several kilowatts to achieve sufficient signal-to-noise ratio (SNR). This poses safety concerns as well as to render the imager expensive and bulky with requiring a large vacuum radio frequency source. Here, we propose and demonstrate a coherent stepped-frequency continuous-wave (SFCW) technique for TA imaging which enables substantial improvements in SNR and consequently a reduction in peak power requirements for the imager. Constructive and destructive interferences between TA signals are observed and explained. Full coherency across microwave and acoustic domains, in the thermo-elastic response, is experimentally verified and this enables demonstration of coherent SFCW microwave-induced TA imaging. Compared to the pulsed technique, an improvement of 17?dB in SNR is demonstrated.

Nan, Hao, E-mail: haonan@stanford.edu; Arbabian, Amin [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States)

2014-06-02

356

Stepped-frequency continuous-wave microwave-induced thermoacoustic imaging  

NASA Astrophysics Data System (ADS)

Microwave-induced thermoacoustic (TA) imaging combines the dielectric contrast of microwave imaging with the resolution of ultrasound imaging. Prior studies have only focused on time-domain techniques with short but powerful microwave pulses that require a peak output power in excess of several kilowatts to achieve sufficient signal-to-noise ratio (SNR). This poses safety concerns as well as to render the imager expensive and bulky with requiring a large vacuum radio frequency source. Here, we propose and demonstrate a coherent stepped-frequency continuous-wave (SFCW) technique for TA imaging which enables substantial improvements in SNR and consequently a reduction in peak power requirements for the imager. Constructive and destructive interferences between TA signals are observed and explained. Full coherency across microwave and acoustic domains, in the thermo-elastic response, is experimentally verified and this enables demonstration of coherent SFCW microwave-induced TA imaging. Compared to the pulsed technique, an improvement of 17 dB in SNR is demonstrated.

Nan, Hao; Arbabian, Amin

2014-06-01

357

Final Scientific/Technical Report for DE-FG03-02NA00063 Coherent imaging of laser-plasma interactions using XUV high harmonic radiation  

SciTech Connect

The objective of this project was to develop experimental techniques for using coherent extreme-ultraviolet (EUV) radiation generated using the high-order harmonic generation technique, as an illumination source for studies of high-density plasmas relevant to the stockpile stewardship mission. In this project, we made considerable progress, including the first demonstration of imaging of dynamic processes using this coherent ultrashort pulse light. This work also stimulated considerable progress in the development of the required ultrashort EUV pulses, and in the development of new laser technologies that have been commercialized. We also demonstrated the first EUV sources that exhibit full intrinsic optical coherence. This work resulted in 12 publications.

Henry Kapteyn

2006-06-06

358

Optical frequency domain imaging with a rapidly swept laser in the 815-870 nm range  

NASA Astrophysics Data System (ADS)

Optical frequency domain imaging (OFDI) in the 800-nm biological imaging window is demonstrated by using a novel wavelength-swept laser source. The laser output is tuned continuously from 815 to 870 nm at a 43.2-kHz repetition rate with 7-mW average power. Axial resolution of 10-?m in biological tissue and peak sensitivity of 96 dB are achieved. In vivo imaging of Xenopus laevis is demonstrated with an acquisition speed of 84 frames per second (512 axial lines per frame). This new imaging technique may prove useful in comprehensive retinal screening for medical diagnosis and contrast-agent-based imaging for biological investigations.

Lim, H.; de Boer, J. F.; Park, B. H.; Lee, E. C.; Yelin, R.; Yun, S. H.

2006-06-01

359

Imaging weak zones in the foundation using frequency domain attenuation tomography  

NASA Astrophysics Data System (ADS)

Cross-hole imaging method using Time Domain (TD) and Frequency Domain (FD) parts of cross-hole radar tomography data acquired using Step Frequency Ground Penetrating Radar (SFGPR) was implemented. This method was adopted for imaging foundation of a dam to check if the foundation was free of geological weak zones. The dam site is characterised by massive and jointed-phyllites associated with major and minor shears. The cross-hole radar tomography data was acquired in the frequency bandwidth of 250 MHz, from the deepest level gallery up to a depth of 40 m in the foundation. In TD, first arrival time and amplitudes of radio waves were inverted using Simultaneous Iterative Reconstruction Technique (SIRT) resulting in velocity and attenuation tomograms. The tomograms showed nearly uniform velocity or attenuation structure in the respective tomographic plane. Subsequently, cross-hole radar tomography data was analysed in FD for a variation of spectrum-amplitude at different frequencies. Amplitudes picked at each single frequency were then inverted using SIRT for obtaining frequency domain attenuation tomogram (FDAT). The FDAT clearly showed presence of anomalous high attenuation zones in the depth range of 23-33 m of the tomographic plane. The anomalous zones in the attenuation tomogram are weak zones in the foundation. To validate the above observations, cross-hole seismic tomography was also done in the same boreholes. Cross-hole seismic tomography results showed low velocity (p-wave) zones around the same location corresponding to the high attenuation zone in FDAT, bringing the dormant weak zone to light. This enabled fine-tuning of the reinforcement design and strengthening the weak zone. This paper discusses the cross-hole radar tomography imaging method, the results of its application in imaging weak zones in the foundation and the comparison of cross-hole radar tomography results (in TD and FD) with the cross-hole seismic tomography results.

Balasubramaniam, V. R.; Jha, P. C.; Chandrasekhar, E.; Babu, B. Butchi; Sivaram, Y. V.; Sandeep, N.

2013-10-01

360

Multi-band frequency encoding method for metabolic imaging with hyperpolarized [1- 13C]pyruvate  

NASA Astrophysics Data System (ADS)

A new method was developed for simultaneous spatial localization and spectral separation of multiple compounds based on a single echo, by designing the acquisition to place individual compounds in separate frequency encoding bands. This method was specially designed for rapid and robust metabolic imaging of hyperpolarized 13C substrates and their metabolic products, and was investigated in phantom studies and studies in normal mice and transgenic models of prostate cancer to provide rapid metabolic imaging of hyperpolarized [1- 13C]pyruvate and its metabolic products [1- 13C]lactate and [1- 13C]alanine at spatial resolutions up to 3 mm in-plane. Elevated pyruvate and lactate signals in the vicinity of prostatic tissues were observed in transgenic tumor mice. The multi-band frequency encoding technique enabled rapid metabolic imaging of hyperpolarized 13C compounds with important advantages over prior approaches, including less complicated acquisition and reconstruction methods.

von Morze, Cornelius; Reed, Galen; Shin, Peter; Larson, Peder E. Z.; Hu, Simon; Bok, Robert; Vigneron, Daniel B.

2011-08-01

361

High-frequency imaging radar for robotic navigation and situational awareness  

NASA Astrophysics Data System (ADS)

With increasingly available high frequency radar components, the practicality of imaging radar for mobile robotic applications is now practical. Navigation, ODOA, situational awareness and safety applications can be supported in small light weight packaging. Radar has the additional advantage of being able sense through aerosols, smoke and dust that can be difficult for many optical systems. The ability to directly measure the range rate of an object is also an advantage in radar applications. This paper will explore the applicability of high frequency imaging radar for mobile robotics and examine a W-band 360 degree imaging radar prototype. Indoor and outdoor performance data will be analyzed and evaluated for applicability to navigation and situational awareness.

Thomas, David J.; Luo, Changan; Knox, Robert

2011-05-01

362

Optimal geometries and harmonic vibrational frequencies of the global minima of water clusters (H2O)n, n = 2-6, and several hexamer local minima at the CCSD(T) level of theory  

NASA Astrophysics Data System (ADS)

We report the first optimum geometries and harmonic vibrational frequencies for the ring pentamer and several water hexamer (prism, cage, cyclic and two book) at the coupled-cluster including single, double, and full perturbative triple excitations (CCSD(T))/aug-cc-pVDZ level of theory. All five examined hexamer isomer minima previously reported by Møller-Plesset perturbation theory (MP2) are also minima on the CCSD(T) potential energy surface (PES). In addition, all CCSD(T) minimum energy structures for the n = 2-6 cluster isomers are quite close to the ones previously obtained by MP2 on the respective PESs, as confirmed by a modified Procrustes analysis that quantifies the difference between any two cluster geometries. The CCSD(T) results confirm the cooperative effect of the homodromic ring networks (systematic contraction of the nearest-neighbor (nn) intermolecular separations with cluster size) previously reported by MP2, albeit with O-O distances shorter by ˜0.02 Å, indicating that MP2 overcorrects this effect. The harmonic frequencies at the minimum geometries were obtained by the double differentiation of the CCSD(T) energy using an efficient scheme based on internal coordinates that reduces the number of required single point energy evaluations by ˜15% when compared to the corresponding double differentiation using Cartesian coordinates. Negligible differences between MP2 and CCSD(T) frequencies are found for the librational modes, while uniform increases of ˜15 and ˜25 cm-1 are observed for the bending and "free" OH harmonic frequencies. The largest differences between CCSD(T) and MP2 are observed for the harmonic hydrogen bonded frequencies, for which the former produces larger absolute values than the latter. Their CCSD(T) redshifts from the monomer values (??) are smaller than the MP2 ones, due to the fact that CCSD(T) produces shorter elongations (?R) of the respective hydrogen bonded OH lengths from the monomer value with respect to MP2. Both the MP2 and CCSD(T) results for the hydrogen bonded frequencies were found to closely follow the relation -?? = s . ?R, with a rate of s = 20.2 cm-1/0.001 Å for hydrogen bonded frequencies with IR intensities >400 km/mol. The CCSD(T) harmonic frequencies, when corrected using the MP2 anharmonicities obtained from second order vibrational perturbation theory, produce anharmonic CCSD(T) estimates that are within <60 cm-1 from the measured infrared (IR) active bands of the n = 2-6 clusters. Furthermore, the CCSD(T) harmonic redshifts (with respect to the monomer) trace the measured ones quite accurately. The energetic order between the various hexamer isomers on the PES (prism has the lowest energy) previously reported at MP2 was found to be preserved at the CCSD(T) level, whereas the inclusion of anharmonic corrections further stabilizes the cage among the hexamer isomers.

Miliordos, Evangelos; Aprà, Edoardo; Xantheas, Sotiris S.

2013-09-01

363

Modifying the size distribution of microbubble contrast agents for high-frequency subharmonic imaging  

PubMed Central

Purpose: Subharmonic imaging is of interest for high frequency (>10 MHz) nonlinear imaging, because it can specifically detect the response of ultrasound contrast agents (UCA). However, conventional UCA produce a weak subharmonic response at high frequencies, which limits the sensitivity of subharmonic imaging. We hypothesized that modifying the size distribution of the agent can enhance its high-frequency subharmonic response. The overall goal of this study was to investigate size-manipulated populations of the agent to determine the range of sizes that produce the strongest subharmonic response at high frequencies (in this case, 20 MHz). A secondary goal was to assess whether the number or the volume-weighted size distribution better represents the efficacy of the agent for high-frequency subharmonic imaging. Methods: The authors created six distinct agent size distributions from the native distribution of a commercially available UCA (Targestar-P®). The median (number-weighted) diameter of the native agent was 1.63 ?m, while the median diameters of the size-manipulated populations ranged from 1.35 to 2.99 ?m. The authors conducted acoustic measurements with native and size-manipulated agent populations to assess their subharmonic response to 20 MHz excitation (pulse duration 1.5 ?s, pressure amplitudes 100–398 kPa). Results: The results showed a considerable difference between the subharmonic response of the agent populations that were investigated. The subharmonic response peaked for the agent population with a median diameter of 2.15 ?m, which demonstrated a subharmonic signal that was 8 dB higher than the native agent. Comparing the subharmonic response of different UCA populations indicated that microbubbles with diameters between 1.3 and 3 ?m are the dominant contributors to the subharmonic response at 20 MHz. Additionally, a better correlation was observed between the subharmonic response of the agent and the number-weighted size-distribution (R2 = 0.98) than with the volume-weighted size distribution (R2 = 0.53). Conclusions: Modifying the size distribution of the agent appears to be a viable strategy to improve the sensitivity of high-frequency subharmonic imaging. In addition, when the size distribution of the UCA has not been suitably modified, the number-weighted size distribution is a useful parameter to accurately describe the efficacy of the agent for high-frequency subharmonic imaging. PMID:23927358

Shekhar, Himanshu; Rychak, Joshua J.; Doyley, Marvin M.

2013-01-01

364

Tree Image Growth Analysis Using the Instantaneous Phase and Frequency Modulation  

SciTech Connect

We propose the use of Amplitude-Modulation Frequency-Modulation (AM-FM) methods for tree growth analysis. Tree growth is modeled using phase modulation. For adapting AM-FM methods to different images, we introduce the use of fast filterbank filter coefficient computation based on piecewise linear polynomials and radial frequency magnitude estimation using integer-based Savitzky-Golay filters for derivative estimation. For a wide range of images, a simple filterbank design with only 4 channel filters is used. Filterbank specification is based on two different methods. For each input image, the FM image is estimated using dominant component analysis. A tree growthmodel is developed to characterize and depict quarterly and half-seasonal growth of trees using instantaneous phase. Qualitative evaluation of inter- and intraring reconstruction is performed on 20 aspen images and a mixture of 12 tree images of various types. Qualitative scores indicate that the results were mostly of good to excellent quality (4.4/5.0 and 4.0/5.0 for the two databases, resp.).

Ramachandran, Janakiramanan [ORNL; Pattichis, Marios S. [University of New Mexico, Albuquerque; Scuderi, Louis A. [University of New Mexico, Albuquerque; Baba, Justin S [ORNL

2011-01-01

365

High-speed camera with real time processing for frequency domain imaging.  

PubMed

We describe a high-speed camera system for frequency domain imaging suitable for applications such as in vivo diffuse optical imaging and fluorescence lifetime imaging. 14-bit images are acquired at 2 gigapixels per second and analyzed with real-time pipeline processing using field programmable gate arrays (FPGAs). Performance of the camera system has been tested both for RF-modulated laser imaging in combination with a gain-modulated image intensifier and a simpler system based upon an LED light source. System amplitude and phase noise are measured and compared against theoretical expressions in the shot noise limit presented for different frequency domain configurations. We show the camera itself is capable of shot noise limited performance for amplitude and phase in as little as 3 ms, and when used in combination with the intensifier the noise levels are nearly shot noise limited. The best phase noise in a single pixel is 0.04 degrees for a 1 s integration time. PMID:21750770

Shia, Victor; Watt, David; Faris, Gregory W

2011-07-01

366

High-speed camera with real time processing for frequency domain imaging  

PubMed Central

We describe a high-speed camera system for frequency domain imaging suitable for applications such as in vivo diffuse optical imaging and fluorescence lifetime imaging. 14-bit images are acquired at 2 gigapixels per second and analyzed with real-time pipeline processing using field programmable gate arrays (FPGAs). Performance of the camera system has been tested both for RF-modulated laser imaging in combination with a gain-modulated image intensifier and a simpler system based upon an LED light source. System amplitude and phase noise are measured and compared against theoretical expressions in the shot noise limit presented for different frequency domain configurations. We show the camera itself is capable of shot noise limited performance for amplitude and phase in as little as 3 ms, and when used in combination with the intensifier the noise levels are nearly shot noise limited. The best phase noise in a single pixel is 0.04 degrees for a 1 s integration time. PMID:21750770

Shia, Victor; Watt, David; Faris, Gregory W.

2011-01-01

367

Small infrared target detection using frequency-spatial cues in a single image  

NASA Astrophysics Data System (ADS)

This paper describes an approach for small infrared (IR) target detection using frequency-spatial cues. We model the background as spikes of the amplitude spectrum in the frequency domain. Target regions are highlighted through background suppression, and the suppression is realized via convoluting the amplitude spectrum with a low-pass Gaussian kernel of an appropriate scale. A theoretical analysis of the convoluting process in the frequency domain is presented. We note that the high values are attributed to sharp gradients in the IR image. In order to uniformly highlight the target region, the proposed algorithm introduces cues of image segmentation in the spatial domain. Targets are completely preserved in the final result. An image database is built, which is used to test the proposed algorithm. Results show that our algorithm detects small IR targets effectively with a competitive performance over some state-of-the-art techniques, even for images with cluttered backgrounds. In addition, we show that it is able to detect multiple targets with varied sizes, which are challenges for existing algorithms.

Sun, Xiaoliang; Hou, Wang; Yu, Qifeng; Liu, Xiaolin; Shang, Yang

2014-07-01

368

3D imaging of tomato seeds using frequency domain optical coherence tomography  

NASA Astrophysics Data System (ADS)

A fast imaging system that can reveal internal sample structures is important for research and quality controls of seeds. Optical coherence tomography (OCT) is a non-invasive optical imaging technique that can acquire high speed, high resolution depth-resolved images in scattering samples. It has found numerous applications in studying various biological tissues and other materials in vivo. A few studies have reported the use of OCT in studying seed morphology. However, 3D imaging of internal seed structure has not been reported before. In this study, we used a frequency domain OCT system to image tomato seeds. The system has a central wavelength of 844nm with a 46.8 nm FWHM bandwidth. The requirement for depth scan was eliminated by using a Fourier domain implementation. The B-scan imaging speed was limited by the spectroscopic imaging CCD at 52 kHz. The calibrated system has a 6.7?m depth resolution and a 15.4?m lateral resolution. Our results show that major seed structures can be clearly visualized in OCT images.

Fan, Chuanmao; Yao, Gang

2012-05-01

369

Full-range imaging of eye accommodation by high-speed long-depth range optical frequency domain imaging  

PubMed Central

We describe a high-speed long-depth range optical frequency domain imaging (OFDI) system employing a long-coherence length tunable source and demonstrate dynamic full-range imaging of the anterior segment of the eye including from the cornea surface to the posterior capsule of the crystalline lens with a depth range of 12 mm without removing complex conjugate image ambiguity. The tunable source spanned from 1260 to 1360 nm with an average output power of 15.8 mW. The fast A-scan rate of 20,000 per second provided dynamic OFDI and dependence of the whole anterior segment change on time following abrupt relaxation from the accommodated to the relaxed status, which was measured for a healthy eye and that with an intraocular lens. PMID:21258564

Furukawa, Hiroyuki; Hiro-Oka, Hideaki; Satoh, Nobuyuki; Yoshimura, Reiko; Choi, Donghak; Nakanishi, Motoi; Igarashi, Akihito; Ishikawa, Hitoshi; Ohbayashi, Kohji; Shimizu, Kimiya

2010-01-01

370

Compensation of motion artifacts in catheter-based optical frequency domain imaging  

PubMed Central

A novel heterodyne Doppler interferometer method for compensating motion artifacts caused by cardiac motion in intracoronary optical frequency domain imaging (OFDI) is demonstrated. To track the relative motion of a catheter with regard to the vessel, a motion tracking system is incorporated with a standard OFDI system by using wavelength division multiplexing (WDM) techniques. Without affecting the imaging beam, dual WDM monochromatic beams are utilized for tracking the relative radial and longitudinal velocities of a catheter-based fiber probe. Our results demonstrate that tracking instantaneous velocity can be used to compensate for distortion in the images due to motion artifacts, thus leading to accurate reconstruction and volumetric measurements with catheter-based imaging. PMID:20589002

Ha, J. Y.; Shishkov, M.; Colice, M.; Oh, W. Y.; Yoo, H.; Liu, L.; Tearney, G. J.; Bouma, B. E.

2010-01-01

371

Atomic-Resolution Imaging of Graphite-Water Interface by Frequency Modulation Atomic Force Microscopy  

NASA Astrophysics Data System (ADS)

Atomic-resolution images of a graphite (0001) surface in water were successfully obtained by frequency modulation atomic force microscopy. Atomic scale features with a periodicity of 0.25 nm were resolved with an interaction force of less than 100 pN using a stiff cantilever and a very small oscillation amplitude of 0.11 nm (0.21 nm peak-to-peak). Furthermore, structured-water layers on a hydrophobic graphite surface were visualized by two-dimensional frequency shift mapping. The results were compared with a molecular-scale hydration structure at an interface between a hydrophilic mica surface and water.

Suzuki, Kazuhiro; Oyabu, Noriaki; Kobayashi, Kei; Matsushige, Kazumi; Yamada, Hirofumi

2011-12-01

372

Multi-parametric monitoring and assessment of high-intensity focused ultrasound (HIFU) boiling by harmonic motion imaging for focused ultrasound (HMIFU): an ex vivo feasibility study.  

PubMed

Harmonic motion imaging for focused ultrasound (HMIFU) is a recently developed high-intensity focused ultrasound (HIFU) treatment monitoring method with feasibilities demonstrated in vitro and in vivo. Here, a multi-parametric study is performed to investigate both elastic and acoustics-independent viscoelastic tissue changes using the Harmonic Motion Imaging (HMI) displacement, axial compressive strain and change in relative phase shift during high energy HIFU treatment with tissue boiling. Forty three (n = 43) thermal lesions were formed in ex vivo canine liver specimens (n = 28). Two-dimensional (2D) transverse HMI displacement maps were also obtained before and after lesion formation. The same method was repeated in 10 s, 20 s and 30 s HIFU durations at three different acoustic powers of 8, 10, and 11 W, which were selected and verified as treatment parameters capable of inducing boiling using both thermocouple and passive cavitation detection (PCD) measurements. Although a steady decrease in the displacement, compressive strain, and relative change in the focal phase shift (??) were obtained in numerous cases, indicating an overall increase in relative stiffness, the study outcomes also showed that during boiling, a reverse lesion-to-background displacement contrast was detected, indicating potential change in tissue absorption, geometrical change and/or, mechanical gelatification or pulverization. Following treatment, corresponding 2D HMI displacement images of the thermal lesions also mapped consistent discrepancy in the lesion-to-background displacement contrast. Despite the expectedly chaotic changes in acoustic properties with boiling, the relative change in phase shift showed a consistent decrease, indicating its robustness to monitor biomechanical properties independent of the acoustic property changes throughout the HIFU treatment. In addition, the 2D HMI displacement images confirmed and indicated the increase in the thermal lesion size with treatment duration, which was validated against pathology. In conclusion, multi-parametric HMIFU was shown capable of monitoring and mapping tissue viscoelastic response changes during and after HIFU boiling, some of which were independent of the acoustic parameter changes. PMID:24556974

Hou, Gary Y; Marquet, Fabrice; Wang, Shutao; Konofagou, Elisa E

2014-03-01

373

Multi-parametric monitoring and assessment of high-intensity focused ultrasound (HIFU) boiling by harmonic motion imaging for focused ultrasound (HMIFU): an ex vivo feasibility study  

NASA Astrophysics Data System (ADS)

Harmonic motion imaging for focused ultrasound (HMIFU) is a recently developed high-intensity focused ultrasound (HIFU) treatment monitoring method with feasibilities demonstrated in vitro and in vivo. Here, a multi-parametric study is performed to investigate both elastic and acoustics-independent viscoelastic tissue changes using the Harmonic Motion Imaging (HMI) displacement, axial compressive strain and change in relative phase shift during high energy HIFU treatment with tissue boiling. Forty three (n = 43) thermal lesions were formed in ex vivo canine liver specimens (n = 28). Two-dimensional (2D) transverse HMI displacement maps were also obtained before and after lesion formation. The same method was repeated in 10 s, 20 s and 30 s HIFU durations at three different acoustic powers of 8, 10, and 11 W, which were selected and verified as treatment parameters capable of inducing boiling using both thermocouple and passive cavitation detection (PCD) measurements. Although a steady decrease in the displacement, compressive strain, and relative change in the focal phase shift (??) were obtained in numerous cases, indicating an overall increase in relative stiffness, the study outcomes also showed that during boiling, a reverse lesion-to-background displacement contrast was detected, indicating potential change in tissue absorption, geometrical change and/or, mechanical gelatification or pulverization. Following treatment, corresponding 2D HMI displacement images of the thermal lesions also mapped consistent discrepancy in the lesion-to-background displacement contrast. Despite the expectedly chaotic changes in acoustic properties with boiling, the relative change in phase shift showed a consistent decrease, indicating its robustness to monitor biomechanical properties independent of the acoustic property changes throughout the HIFU treatment. In addition, the 2D HMI displacement images confirmed and indicated the increase in the thermal lesion size with treatment duration, which was validated against pathology. In conclusion, multi-parametric HMIFU was shown capable of monitoring and mapping tissue viscoelastic response changes during and after HIFU boiling, some of which were independent of the acoustic parameter changes.

Hou, Gary Y.; Marquet, Fabrice; Wang, Shutao; Konofagou, Elisa E.

2014-03-01

374

Spectral discrimination of breast pathologies in situ using spatial frequency domain imaging  

PubMed Central

Introduction Nationally, 25% to 50% of patients undergoing lumpectomy for local management of breast cancer require a secondary excision because of the persistence of residual tumor. Intraoperative assessment of specimen margins by frozen-section analysis is not widely adopted in breast-conserving surgery. Here, a new approach to wide-field optical imaging of breast pathology in situ was tested to determine whether the system could accurately discriminate cancer from benign tissues before routine pathological processing. Methods Spatial frequency domain imaging (SFDI) was used to quantify near-infrared (NIR) optical parameters at the surface of 47 lumpectomy tissue specimens. Spatial frequency and wavelength-dependent reflectance spectra were parameterized with matched simulations of light transport. Spectral images were co-registered to histopathology in adjacent, stained sections of the tissue, cut in the geometry imaged in situ. A supervised classifier and feature-selection algorithm were implemented to automate discrimination of breast pathologies and to rank the contribution of each parameter to a diagnosis. Results Spectral parameters distinguished all pathology subtypes with 82% accuracy and benign (fibrocystic disease, fibroadenoma) from malignant (DCIS, invasive cancer, and partially treated invasive cancer after neoadjuvant chemotherapy) pathologies with 88% accuracy, high specificity (93%), and reasonable sensitivity (79%). Although spectral absorption and scattering features were essential components of the discriminant classifier, scattering exhibited lower variance and contributed most to tissue-type separation. The scattering slope was sensitive to stromal and epithelial distributions measured with quantitative immunohistochemistry. Conclusions SFDI is a new quantitative imaging technique that renders a specific tissue-type diagnosis. Its combination of planar sampling and frequency-dependent depth sensing is clinically pragmatic and appropriate for breast surgical-margin assessment. This study is the first to apply SFDI to pathology discrimination in surgical breast tissues. It represents an important step toward imaging surgical specimens immediately ex vivo to reduce the high rate of secondary excisions associated with breast lumpectomy procedures. PMID:23915805

2013-01-01

375

Application of image analysis and time-frequency analysis for tracking the rotating blades vibration  

NASA Astrophysics Data System (ADS)

The objective of this paper is to investigate the application of the photogrammetric approach to measuring the vibration of a research-scale wind turbine blade model (both damage and undamaged blade). In order to control the excitation (rotation of the wind turbine blade), a motor was used to spin the blades at controlled angular velocities. Two cameras are set in front of the turbine to tape the video images. Through a sequence of stereo image pairs acquired by high speed camera, the images are studied. The camera we used is the BASLER acA2000-340km (2048x1088, 340FPS). Before taking the photos camera calibration was conducted which include lens distortion and skew factor is examined. To analyze the displacement of the motion target on the turbine blade, after loading the 3D calibration, the 3D positions are calculated by using a stereo triangulation technique. Then the displacement fields by image template matching can be calculated. Application of the technique to track the 3D motion of the rotating wind turbine blade is demonstrated by using data from the research-scale wind turbine. Different from the image processing technique data from the contact sensors (accelerometers) is also used. Through Rodrigues' rotation formula to remove the rotation frequency it is easy to extract the out-of-plane motion of the blade, from which the model frequency of the blade can be identified.

Huang, Yu-Ting; Hsiung, Wan-Ying; Yang, Yuan-Shen; Loh, Chin-Hsiung

2014-03-01

376

Three-dimensional phantoms for curvature correction in spatial frequency domain imaging  

PubMed Central

The sensitivity to surface profile of non-contact optical imaging, such as spatial frequency domain imaging, may lead to incorrect measurements of optical properties and consequently erroneous extrapolation of physiological parameters of interest. Previous correction methods have focused on calibration-based, model-based, and computation-based approached. We propose an experimental method to correct the effect of surface profile on spectral images. Three-dimensional (3D) phantoms were built with acrylonitrile butadiene styrene (ABS) plastic using an accurate 3D imaging and an emergent 3D printing technique. In this study, our method was utilized for the correction of optical properties (absorption coefficient ?a and reduced scattering coefficient ?s?) of objects obtained with a spatial frequency domain imaging system. The correction method was verified on three objects with simple to complex shapes. Incorrect optical properties due to surface with minimum 4 mm variation in height and 80 degree in slope were detected and improved, particularly for the absorption coefficients. The 3D phantom-based correction method is applicable for a wide range of purposes. The advantages and drawbacks of the 3D phantom-based correction methods are discussed in details. PMID:22741068

Nguyen, Thu T. A.; Le, Hanh N. D.; Vo, Minh; Wang, Zhaoyang; Luu, Long; Ramella-Roman, Jessica C.

2012-01-01

377

Discrete frequency infrared microspectroscopy and imaging with a tunable quantum cascade laser  

PubMed Central

Fourier-transform infrared imaging (FT-IR) is a well-established modality but requires the acquisition of a spectrum over a large bandwidth, even in cases where only a few spectral features may be of interest. Discrete frequency infrared (DF-IR) methods are now emerging in which a small number of measurements may provide all the analytical information needed. The DF-IR approach is enabled by the development of new sources integrating frequency selection, in particular of tunable, narrow-bandwidth sources with enough power at each wavelength to successfully make absorption measurements. Here, we describe a DF-IR imaging microscope that uses an external cavity quantum cascade laser (QCL) as a source. We present two configurations, one with an uncooled bolometer as a detector and another with a liquid nitrogen cooled Mercury Cadmium Telluride (MCT) detector and compare their performance to a commercial FT-IR imaging instrument. We examine the consequences of the coherent properties of the beam with respect to imaging and compare these observations to simulations. Additionally, we demonstrate that the use of a tunable laser source represents a distinct advantage over broadband sources when using a small aperture (narrower than the wavelength of light) to perform high-quality point mapping. The two advances highlight the potential application areas for these emerging sources in IR microscopy and imaging. PMID:23113653

Kole, Matthew R.; Reddy, Rohith K.; Schulmerich, Matthew V.; Gelber, Matthew K.; Bhargava, Rohit

2012-01-01

378

Generalized frequency-domain synthetic aperture focusing technique for ultrasonic imaging of irregularly layered objects.  

PubMed

In ultrasonic nondestructive testing (NDT), the phase shift migration (PSM) technique, as a frequency-domain implementation of the synthetic aperture focusing technique (SAFT), can be adopted for imaging of regularly layered objects that are inhomogeneous only in depth but isotropic and homogeneous in the lateral direction. To deal with irregularly layered objects that are anisotropic and inhomogeneous in both the depth and lateral directions, a generalized frequency- domain SAFT, called generalized phase shift migration (GPSM), is proposed in this paper. Compared with PSM, the most significant innovation of GPSM is that the phase shift factor is generalized to handle anisotropic media with lateral velocity variations. The generalization is accomplished by computer programming techniques without modifying the PSM model. In addition, SRFFT (split-radix fast Fourier transform) input/output pruning algorithms are developed and employed in the GPSM algorithm to speed up the image reconstructions. The experiments show that the proposed imaging techniques are capable of reconstructing accurate shapes and interfaces of irregularly layered objects. The computing time of the GPSM algorithm is much less than the time-domain SAFT combined with the ray-tracing technique, which is, at present, the common method used in ultrasonic NDT industry for imaging layered objects. Furthermore, imaging regularly layered objects can be regarded as a special case of the presented technique. PMID:24402900

Qin, Kaihuai; Yang, Chun; Sun, Feng

2014-01-01

379

Brain connectivity study of joint attention using frequency-domain optical imaging technique  

NASA Astrophysics Data System (ADS)

Autism is a socio-communication brain development disorder. It is marked by degeneration in the ability to respond to joint attention skill task, from as early as 12 to 18 months of age. This trait is used to distinguish autistic from nonautistic populations. In this study, diffuse optical imaging is being used to study brain connectivity for the first time in response to joint attention experience in normal adults. The prefrontal region of the brain was non-invasively imaged using a frequency-domain based optical imager. The imaging studies were performed on 11 normal right-handed adults and optical measurements were acquired in response to joint-attention based video clips. While the intensity-based optical data provides information about the hemodynamic response of the underlying neural process, the time-dependent phase-based optical data has the potential to explicate the directional information on the activation of the brain. Thus brain connectivity studies are performed by computing covariance/correlations between spatial units using this frequency-domain based optical measurements. The preliminary results indicate that the extent of synchrony and directional variation in the pattern of activation varies in the left and right frontal cortex. The results have significant implication for research in neural pathways associated with autism that can be mapped using diffuse optical imaging tools in the future.

Chaudhary, Ujwal; Zhu, Banghe; Godavarty, Anuradha

2010-02-01

380

Clinical combination of multiphoton tomography and high frequency ultrasound imaging for evaluation of skin diseases  

NASA Astrophysics Data System (ADS)

For the first time, high frequency ultrasound imaging, multiphoton tomography, and dermoscopy were combined in a clinical study. Different dermatoses such as benign and malign skin cancers, connective tissue diseases, inflammatory skin diseases and autoimmune bullous skin diseases have been investigated with (i) state-of-the-art and highly sophisticated ultrasound systems for dermatology, (ii) the femtosecond-laser multiphoton tomograph DermaInspectTM and (iii) dermoscopes. Dermoscopy provides two-dimensional color imaging of the skin surface with a magnification up to 70x. Ultrasound images are generated from reflections of the emitted ultrasound signal, based on inhomogeneities of the tissue. These echoes are converted to electrical signals. Depending on the ultrasound frequency the penetration depth varies from about 1 mm to 16 mm in dermatological application. The 100-MHz-ultrasound system provided an axial resolution down to 16 ?m and a lateral resolution down to 32 ?m. In contrast to the wide-field ultrasound images, multiphoton tomography provided horizontal optical sections of 0.36×0.36 mm2 down to 200 ?m tissue depth with submicron resolution. The autofluorescence of mitochondrial coenzymes, melanin, and elastin as well as the secondharmonic- generation signal of the collagen network were imaged. The combination of ultrasound and multiphoton tomography provides a novel opportunity for diagnostics of skin disorders.

König, K.; Speicher, M.; Koehler, M. J.; Scharenberg, R.; Elsner, P.; Kaatz, M.

2010-02-01

381

Extremely High-Frequency Holographic Radar Imaging of Personnel and Mail  

SciTech Connect

The awareness of terrorists covertly transporting chemical warfare (CW) and biological warfare (BW) agents into government, military, and civilian facilities to harm the occupants has increased dramatically since the attacks of 9/11. Government and civilian security personnel have a need for innovative surveillance technology that can rapidly detect these lethal agents, even when they are hidden away in sealed containers and concealed either under clothing or in hand-carried items such as mailed packages or handbags. Sensor technology that detects BW and CW agents in mail or sealed containers carried under the clothing are under development. One promising sensor technology presently under development to defeat these threats is active millimeter-wave holographic radar imaging, which can readily image concealed items behind paper, cardboard, and clothing. Feasibility imaging studies at frequencies greater than 40 GHz have been conducted to determine whether simulated biological or chemical agents concealed in mail packages or under clothing could be detected using this extremely high-frequency imaging technique. The results of this imaging study will be presented in this paper.

McMakin, Douglas L.; Sheen, David M.; Griffin, Jeffrey W.; Lechelt, Wayne M.

2006-08-01

382

Extremely high-frequency holographic radar imaging of personnel and mail  

NASA Astrophysics Data System (ADS)

The awareness of terrorists covertly transporting chemical warfare (CW) and biological warfare (BW) agents into government, military, and civilian facilities to harm the occupants has increased dramatically since the attacks of 9/11. Government and civilian security personnel have a need for innovative surveillance technology that can rapidly detect these lethal agents, even when they are hidden away in sealed containers and concealed either under clothing or in hand-carried items such as mailed packages or handbags. Sensor technology that detects BW and CW agents in mail or sealed containers carried under the clothing are under development. One promising sensor technology presently under development to detect these threats is active millimeter-wave holographic radar imaging, which can readily image concealed items behind paper, cardboard, and clothing. Feasibility imaging studies at frequencies greater than 40 GHz have been conducted to determine whether simulated biological or chemical agents concealed in mail packages or under clothing could be detected using this extremely high-frequency imaging technique. The results of this imaging study will be presented in this paper.

McMakin, Douglas L.; Sheen, David M.; Griffin, Jeffery W.; Lechelt, Wayne M.

2006-05-01

383

Development and Testing of a Single Frequency Terahertz Imaging System for Breast Cancer Detection  

PubMed Central

The ability to discern malignant from benign tissue in excised human breast specimens in Breast Conservation Surgery (BCS) was evaluated using single frequency terahertz radiation. Terahertz (THz) images of the specimens in reflection mode were obtained by employing a gas laser source and mechanical scanning. The images were correlated with optical histological micrographs of the same specimens, and a mean discrimination of 73% was found for five out of six samples using Receiver Operating Characteristic (ROC) analysis. The system design and characterization is discussed in detail. The initial results are encouraging but further development of the technology and clinical evaluation is needed to evaluate its feasibility in the clinical environment. PMID:25055306

St. Peter, Benjamin; Yngvesson, Sigfrid; Siqueira, Paul; Kelly, Patrick; Khan, Ashraf; Glick, Stephen; Karellas, Andrew

2013-01-01

384

Imaging Defects in Thin DLC Coatings Using High Frequency Scanning Acoustic Microscopy  

NASA Astrophysics Data System (ADS)

In this work high frequency scanning acoustic microscopy was employed to nondestructively characterize subsurface defects in chromium containing DLC (Cr-DLC) coatings. Subsurface defects as small as one micron were successfully detected in a flat Cr-DLC coated steel coupon. Depth of the imaged subsurface defects was estimated using a simple geometrical acoustics model. The nature of the subsurface defects was investigated by using FIB/SEM technique. Curved Cr-DLC coated components including a roller and gear tooth were also imaged, and the encountered challenges were addressed.

Fei, Dong; Rebinsky, Douglas A.; Zinin, Pavel; Koehler, Bernd

2004-02-01

385

Development and testing of a single frequency terahertz imaging system for breast cancer detection.  

PubMed

The ability to discern malignant from benign tissue in excised human breast specimens in Breast Conservation Surgery (BCS) was evaluated using single frequency terahertz radiation. Terahertz (THz) images of the specimens in reflection mode were obtained by employing a gas laser source and mechanical scanning. The images were correlated with optical histological micrographs of the same specimens, and a mean discrimination of 73% was found for five out of six samples using Receiver Operating Characteristic (ROC) analysis. The system design and characterization is discussed in detail. The initial results are encouraging but further development of the technology and clinical evaluation is needed to evaluate its feasibility in the clinical environment. PMID:25055306

St Peter, Benjamin; Yngvesson, Sigfrid; Siqueira, Paul; Kelly, Patrick; Khan, Ashraf; Glick, Stephen; Karellas, Andrew

2013-07-01

386

Limitations on squeezing and formation of the superposition of two macroscopically distinguishable states at fundamental frequency in the process of second harmonic generation  

NASA Technical Reports Server (NTRS)

The results of numerical simulations of quantum state evolution in the process of second harmonic generation (SHG) are discussed. It is shown that at a particular moment of time in the fundamental mode initially coherent state turns into a superposition of two macroscopically distinguished states. The question of whether this superposition exhibits quantum interference is analyzed.

Nikitin, S. P.; Masalov, A. V.

1992-01-01

387

Second-harmonic optical coherence tomography  

Microsoft Academic Search

Second-harmonic optical coherence tomography, which uses coherence gating of second-order nonlinear optical responses of biological tissues for imaging, is described and demonstrated. Femtosecond laser pulses were used to excite second-harmonic waves from collagen harvested from rat tail tendon and a reference nonlinear crystal. Second-harmonic interference fringe signals were detected and used for image construction. Because of the strong dependence of

Yi Jiang; Ivan Tomov; Yimin Wang; Zhongping Chen

2004-01-01

388

Real-time processing for frequency domain optical imaging based on field programmable gated arrays.  

PubMed

Frequency domain optical imaging (OFDI) provides high resolution and sensitivity. However, the speed of the data processing program in C language limits its application. A real-time imaging system of OFDI based on field programmable gate arrays (FPGAs) is proposed. It adopts a high-speed digitizer board PXI14400 from Signatec for interferometric data acquisition. The acquired data is processed in the user defined FPGA on board in real-time with a pipeline data processing algorithm. The algorithm eliminates the complex conjugate ambiguity, overcomes the swept laser source's nonlinearity in k-space, and allows the data to be processed continuously. We also provide an economic method of IQ demodulation for FPGA data processing. The design breaks through the speed bottleneck of data processing, and allows the system to process each sample point at a frequency of 200 MHz. PMID:25321669

Tang, Hongying

2014-09-10

389

Imaging fall Chinook salmon redds in the Columbia River with a dual-frequency identification sonar  

USGS Publications Warehouse

We tested the efficacy of a dual-frequency identification sonar (DIDSON) for imaging and enumeration of fall Chinook salmon Oncorhynchus tshawytscha redds in a spawning area below Bonneville Dam on the Columbia River. The DIDSON uses sound to form near-video-quality images and has the advantages of imaging in zero-visibility water and possessing a greater detection range and field of view than underwater video cameras. We suspected that the large size and distinct morphology of a fall Chinook salmon redd would facilitate acoustic imaging if the DIDSON was towed near the river bottom so as to cast an acoustic shadow from the tailspill over the redd pocket. We tested this idea by observing 22 different redds with an underwater video camera, spatially referencing their locations, and then navigating to them while imaging them with the DIDSON. All 22 redds were successfully imaged with the DIDSON. We subsequently conducted redd searches along transects to compare the number of redds imaged by the DIDSON with the number observed using an underwater video camera. We counted 117 redds with the DIDSON and 81 redds with the underwater video camera. Only one of the redds observed with the underwater video camera was not also documented by the DIDSON. In spite of the DIDSON's high cost, it may serve as a useful tool for enumerating fall Chinook salmon redds in conditions that are not conducive to underwater videography.

Tiffan, K.F.; Rondorf, D.W.; Skalicky, J.J.

2004-01-01

390

In vivo spin-label murine pharmacodynamics using low-frequency electron paramagnetic resonance imaging.  

PubMed Central

A novel, very-low-frequency electron paramagnetic resonance (EPR) technique is used to image the distribution of several nitroxides with distinct pharmacologic compartment affinities in the abdomens of living mice. Image acquisition is sufficiently rapid to allow a time sequence of the distribution for each compound. The spectra and concentrations of these nitroxides are imaged with the use of spectral-spatial imaging to distinguish a single spatial dimension. Liver and bladder of the mouse anatomy are distinguished by this technique. After an intraperitoneal injection of the spin-label probes, a shift in the distribution of the compounds from the upper abdomen (primarily liver) to the lower abdomen (primarily bladder) is observed. The time dependence of the shift in regional distribution depends on the structural properties of the side chain attached to the spin label. These results indicate that this application of in vivo electron paramagnetic resonance imaging will provide a new method of magnetic resonance imaging for determination of pharmacodynamics in the body of an intact animal. Images FIGURE 1 FIGURE 4 FIGURE 5 PMID:8804623

Halpern, H J; Peric, M; Yu, C; Barth, E D; Chandramouli, G V; Makinen, M W; Rosen, G M

1996-01-01

391

Duality of log-polar image representations in the space and spatial-frequency domains  

Microsoft Academic Search

In this paper, we study the result of applying a lowpass variant filtering using scaling-rotating kernels to both the spatial and spatial-frequency representations of a two-dimensional (2-D) signal (image). It is shown that if we apply this transformation to a Fourier pair, the two resulting signals can also form a Fourier pair when the filters used in each domain maintain

Antonio Tabernero; Javier Portilla; Rafael Navarro

1999-01-01

392

Safety and reliability of Radio Frequency Identification Devices in Magnetic Resonance Imaging and Computed Tomography  

Microsoft Academic Search

BACKGROUND: Radio Frequency Identification (RFID) devices are becoming more and more essential for patient safety in hospitals. The purpose of this study was to determine patient safety, data reliability and signal loss wearing on skin RFID devices during magnetic resonance imaging (MRI) and computed tomography (CT) scanning. METHODS: Sixty RFID tags of the type I-Code SLI, 13.56 MHz, ISO 18000-3.1

Thomas Steffen; Roger Luechinger; Simon Wildermuth; Christian Kern; Christian Fretz; Jochen Lange; Franc H Hetzer

2010-01-01

393

Children's Computation of Complex Linguistic Forms: A Study of Frequency and Imageability Effects  

PubMed Central

This study investigates the storage vs. composition of inflected forms in typically-developing children. Children aged 8–12 were tested on the production of regular and irregular past-tense forms. Storage (vs. composition) was examined by probing for past-tense frequency effects and imageability effects – both of which are diagnostic tests for storage – while controlling for a number of confounding factors. We also examined sex as a factor. Irregular inflected forms, which must depend on stored representations, always showed evidence of storage (frequency and/or imageability effects), not only across all children, but also separately in both sexes. In contrast, for regular forms, which could be either stored or composed, only girls showed evidence of storage. This pattern is similar to that found in previously-acquired adult data from the same task, with the notable exception that development affects which factors influence the storage of regulars in females: imageability plays a larger role in girls, and frequency in women. Overall, the results suggest that irregular inflected forms are always stored (in children and adults, and in both sexes), whereas regulars can be either composed or stored, with their storage a function of various item- and subject-level factors. PMID:24040318

Dye, Cristina D.; Walenski, Matthew; Prado, Elizabeth L.; Mostofsky, Stewart; Ullman, Michael T.

2013-01-01

394

Children's computation of complex linguistic forms: a study of frequency and imageability effects.  

PubMed

This study investigates the storage vs. composition of inflected forms in typically-developing children. Children aged 8-12 were tested on the production of regular and irregular past-tense forms. Storage (vs. composition) was examined by probing for past-tense frequency effects and imageability effects--both of which are diagnostic tests for storage--while controlling for a number of confounding factors. We also examined sex as a factor. Irregular inflected forms, which must depend on stored representations, always showed evidence of storage (frequency and/or imageability effects), not only across all children, but also separately in both sexes. In contrast, for regular forms, which could be either stored or composed, only girls showed evidence of storage. This pattern is similar to that found in previously-acquired adult data from the same task, with the notable exception that development affects which factors influence the storage of regulars in females: imageability plays a larger role in girls, and frequency in women. Overall, the results suggest that irregular inflected forms are always stored (in children and adults, and in both sexes), whereas regulars can be either composed or stored, with their storage a function of various item- and subject-level factors. PMID:24040318

Dye, Cristina D; Walenski, Matthew; Prado, Elizabeth L; Mostofsky, Stewart; Ullman, Michael T

2013-01-01

395

Imaging of the interaction of low frequency electric fields with biological tissues by optical coherence tomography  

NASA Astrophysics Data System (ADS)

We report the use of conventional Optical Coherence Tomography (OCT) for visualization of propagation of low frequency electric field in soft biological tissues ex vivo. To increase the overall quality of the experimental images an adaptive Wiener filtering technique has been employed. Fourier domain correlation has been subsequently applied to enhance spatial resolution of images of biological tissues influenced by low frequency electric field. Image processing has been performed on Graphics Processing Units (GPUs) utilizing Compute Unified Device Architecture (CUDA) framework in the frequencydomain. The results show that variation in voltage and frequency of the applied electric field relates exponentially to the magnitude of its influence on biological tissue. The magnitude of influence is about twice more for fresh tissue samples in comparison to non-fresh ones. The obtained results suggest that OCT can be used for observation and quantitative evaluation of the electro-kinetic changes in biological tissues under different physiological conditions, functional electrical stimulation, and potentially can be used non-invasively for food quality control.

Peña, Adrian F.; Devine, Jack; Doronin, Alexander; Meglinski, Igor

2014-03-01

396

Harmonic Noise-Induced Resonant Passing in an Inverse Harmonic Potential  

NASA Astrophysics Data System (ADS)

The problem of a Brownian particle driven by harmonic noise passing over the saddle point in an inverse harmonic potential is studied. The passing probability over the saddle point is obtained analytically. The stationary passing probability is found to arrive at its maximal value when the frequency parameter of the harmonic noise is close to the frequency of the inverse harmonic potential, which results in a resonance phenomenon. With an increase in the frequency parameter of noise, the Brownian particle will recross the barrier, thereby increasing the escape rate and resulting in a decrease in the passing probability.

Han, Jie; Bao, Jing-Dong

2014-12-01

397

A quasi-local method for instantaneous frequency estimation with application to structural magnetic resonance images.  

PubMed

Spatially-varying signal content can be effectively modeled using amplitude modulation-frequency modulation (AM-FM) representations. The AM-FM representation allow us to extract instantaneous amplitude (IA) and instantaneous frequency (IF) components that can be used to measure non-stationary content in biomedical images and videos. This paper introduces a new method for estimating the IA and the IF based on a quasi-local method (QLM). We provide an extensive comparison of AM-FM demodulation approaches based on QLM and a quasi-eigenfunction approximation method using three different filter-banks: (i) a separable, equiripple design, (ii) a Gabor filter bank, and (iii) a directional filter bank approach based on the Contourlet transform. The results document that the use of the new QLM method with an equiripple filter bank design gave the best IF magnitude estimates for a synthetic image. The new QLM method is then applied to a multi-site schizophrenia dataset (N=307). The dataset included structure magnetic resonance images from healthy controls and patients diagnosed with schizophrenia. The IF magnitude is shown to be less sensitive to variations across sites as opposed to the standard use of SMRI images that suffered from significant dependency on the scanner configurations on different collection sites. Furthermore, the regions of interest identified through the use of the IF magnitude are in agreement with previous studies. PMID:25570248

Ulloa, Alvaro; Rodriguez, Paul; Jingyu Liu; Calhoun, Vince; Pattichis, Marios

2014-08-01

398

High-contrast coherent terahertz imaging of porcine tissue via swept-frequency feedback interferometry  

PubMed Central

There is considerable interest in the interrogation of biological tissue at terahertz (THz) frequencies, largely due to the contrast in the optical properties of different biological tissues which occur in this electro-magnetic radiation band. Of particular interest are THz biomedical images, which have the potential to highlight different information than those acquired in other frequency bands, thereby providing an augmented picture of biological structures. In this work, we demonstrate the feasibility of an interferometric biological imaging technique using a THz quantum cascade laser (QCL) operating at 2.59 THz to perform coherent imaging of porcine tissue samples. We show the potential of this new THz biomedical imaging technique for in vivo studies, by virtue of its reflection geometry and useful tissue penetration depth enabled by the large THz powers emitted by the quantum cascade laser used in this work. The observed clustering of interferometric tissue signatures opens a pathway towards automatic techniques for the discrimination of healthy tissue types for the study of normal physiology and possible therapeutic approaches. PMID:25426324

Lim, Yah Leng; Taimre, Thomas; Bertling, Karl; Dean, Paul; Indjin, Dragan; Valavanis, Alexander; Khanna, Suraj P.; Lachab, Mohammad; Schaider, Helmut; Prow, Tarl W.; Peter Soyer, H.; Wilson, Stephen J.; Linfield, Edmund H.; Giles Davies, A.; Raki?, Aleksandar D.

2014-01-01

399

High-contrast coherent terahertz imaging of porcine tissue via swept-frequency feedback interferometry.  

PubMed

There is considerable interest in the interrogation of biological tissue at terahertz (THz) frequencies, largely due to the contrast in the optical properties of different biological tissues which occur in this electro-magnetic radiation band. Of particular interest are THz biomedical images, which have the potential to highlight different information than those acquired in other frequency bands, thereby providing an augmented picture of biological structures. In this work, we demonstrate the feasibility of an interferometric biological imaging technique using a THz quantum cascade laser (QCL) operating at 2.59 THz to perform coherent imaging of porcine tissue samples. We show the potential of this new THz biomedical imaging technique for in vivo studies, by virtue of its reflection geometry and useful tissue penetration depth enabled by the large THz powers emitted by the quantum cascade laser used in this work. The observed clustering of interferometric tissue signatures opens a pathway towards automatic techniques for the discrimination of healthy tissue types for the study of normal physiology and possible therapeutic approaches. PMID:25426324

Lim, Yah Leng; Taimre, Thomas; Bertling, Karl; Dean, Paul; Indjin, Dragan; Valavanis, Alexander; Khanna, Suraj P; Lachab, Mohammad; Schaider, Helmut; Prow, Tarl W; Peter Soyer, H; Wilson, Stephen J; Linfield, Edmund H; Giles Davies, A; Raki?, Aleksandar D

2014-11-01

400

Development of a 64 channel ultrasonic high frequency linear array imaging system.  

PubMed

In order to improve the lateral resolution and extend the field of view of a previously reported 48 element 30 MHz ultrasound linear array and 16-channel digital imaging system, the development of a 256 element 30 MHz linear array and an ultrasound imaging system with increased channel count has been undertaken. This paper reports the design and testing of a 64 channel digital imaging system which consists of an analog front-end pulser/receiver, 64 channels of Time-Gain Compensation (TGC), 64 channels of high-speed digitizer as well as a beamformer. A Personal Computer (PC) is used as the user interface to display real-time images. This system is designed as a platform for the purpose of testing the performance of high frequency linear arrays that have been developed in house. Therefore conventional approaches were taken it its implementation. Flexibility and ease of use are of primary concern whereas consideration of cost-effectiveness and novelty in design are only secondary. Even so, there are many issues at higher frequencies but do not exist at lower frequencies need to be solved. The system provides 64 channels of excitation pulsers while receiving simultaneously at a 20-120 MHz sampling rate to 12-bits. The digitized data from all channels are first fed through Field Programmable Gate Arrays (FPGAs), and then stored in memories. These raw data are accessed by the beamforming processor to re-build the image or to be downloaded to the PC for further processing. The beamformer that applies delays to the echoes of each channel is implemented with the strategy that combines coarse (8.3 ns) and fine delays (2 ns). The coarse delays are integer multiples of the sampling clock rate and are achieved by controlling the write enable pin of the First-In-First-Out (FIFO) memory to obtain valid beamforming data. The fine delays are accomplished with interpolation filters. This system is capable of achieving a maximum frame rate of 50 frames per second. Wire phantom images acquired with this system show a spatial resolution of 146 ?m (lateral) and 54 ?m (axial). Images with excised rabbit and pig eyeball as well as mouse embryo were also acquired to demonstrate its imaging capability. PMID:21684568

Hu, ChangHong; Zhang, Lequan; Cannata, Jonathan M; Yen, Jesse; Shung, K Kirk

2011-12-01

401

Magnetically-coated silica nanospheres for dual-mode imaging at low ultrasound frequency  

PubMed Central

AIM: To experimentally investigate the acoustical behavior of different dual-mode nanosized contrast agents (NPCAs) for echographic medical imaging at low ultrasound (US) frequency. METHODS: We synthesized three different nanosized structures: (1) Pure silica nanospheres (SiNSs); (2) FePt-iron oxide (FePt-IO)-coated SiNSs; and (3) IO-coated SiNSs, employing three different diameter of SiNS-core (160, 330 and 660 nm). Tissue mimicking phantoms made of agarose gel solution containing 5 mg of different NPCAs in 2 mL-Eppendorf tubes, were insonified by a commercial echographic system at three different low US pulse values (2.5, 3.5 and 4.5 MHz). The raw radiofrequency signal, backscattered from each considered NPCA containing sample, has been processed in order to calculate the US average backscatter intensity and compare the acoustic behavior of the different NPCA types. RESULTS: The highest US contrast was exhibited by pure SiNSs; FePt-IO-coated SiNSs acoustical behavior followed a similar trend of pure SiNSs with a slight difference in terms of brightness values. The acoustic response of the examined NPCAs resulted function of both SiNS diameter and US frequency. Specifically, higher US frequencies determined higher value of the backscatter for a given SiNS diameter. Frequency-dependent enhancement was marked for pure SiNSs and became less remarkable for FePt-IO-coated SiNSs, whereas IO-coated SiNSs resulted almost unaffected by such frequency variations. Pure and FePt-IO-coated SiNSs evidenced an image backscatter increasing with the diameter up to 330 nm. Conversely, among the types of NPCA tested, IO-coated SiNSs showed the lowest acoustical response for each synthesized diameter and employed US frequency, although a diameter-dependent raising trend was evidenced. CONCLUSION: The US characterization of magnetically covered SiNS shows that FePt-IO, rather than IO, was the best magnetic coating for realizing NPCAs suitable for dual mode imaging of deep organs, combining US and magnetic resonance imaging. PMID:24349645

Chiriacò, Fernanda; Soloperto, Giulia; Greco, Antonio; Conversano, Francesco; Ragusa, Andrea; Menichetti, Luca; Casciaro, Sergio

2013-01-01

402

Image watermarking based on the space/spatial-frequency analysis and Hermite functions expansion  

NASA Astrophysics Data System (ADS)

An image watermarking scheme that combines Hermite functions expansion and space/spatial-frequency analysis is proposed. In the first step, the Hermite functions expansion is employed to select busy regions for watermark embedding. In the second step, the space/spatial-frequency representation and Hermite functions expansion are combined to design the imperceptible watermark, using the host local frequency content. The Hermite expansion has been done by using the fast Hermite projection method. Recursive realization of Hermite functions significantly speeds up the algorithms for regions selection and watermark design. The watermark detection is performed within the space/spatial-frequency domain. The detection performance is increased due to the high information redundancy in that domain in comparison with the space or frequency domains, respectively. The performance of the proposed procedure has been tested experimentally for different watermark strengths, i.e., for different values of the peak signal-to-noise ratio (PSNR). The proposed approach provides high detection performance even for high PSNR values. It offers a good compromise between detection performance (including the robustness to a wide variety of common attacks) and imperceptibility.

Stankovi?, Srdjan; Orovi?, Irena; Chabert, Marie; Mobasseri, Bijan

2013-01-01

403

Extraction of small boat harmonic signatures from passive sonar.  

PubMed

This paper investigates the extraction of acoustic signatures from small boats using a passive sonar system. Noise radiated from a small boats consists of broadband noise and harmonically related tones that correspond to engine and propeller specifications. A signal processing method to automatically extract the harmonic structure of noise radiated from small boats is developed. The Harmonic Extraction and Analysis Tool (HEAT) estimates the instantaneous fundamental frequency of the harmonic tones, refines the fundamental frequency estimate using a Kalman filter, and automatically extracts the amplitudes of the harmonic tonals to generate a harmonic signature for the boat. Results are presented that show the HEAT algorithms ability to extract these signatures. PMID:21682400

Ogden, George L; Zurk, Lisa M; Jones, Mark E; Peterson, Mary E

2011-06-01

404

Low-frequency quantitative ultrasound imaging of cell death in vivo  

SciTech Connect

Purpose: Currently, no clinical imaging modality is used routinely to assess tumor response to cancer therapies within hours to days of the delivery of treatment. Here, the authors demonstrate the efficacy of ultrasound at a clinically relevant frequency to quantitatively detect changes in tumors in response to cancer therapies using preclinical mouse models.Methods: Conventional low-frequency and corresponding high-frequency ultrasound (ranging from 4 to 28 MHz) were used along with quantitative spectroscopic and signal envelope statistical analyses on data obtained from xenograft tumors treated with chemotherapy, x-ray radiation, as well as a novel vascular targeting microbubble therapy.Results: Ultrasound-based spectroscopic biomarkers indicated significant changes in cell-death associated parameters in responsive tumors. Specifically changes in the midband fit, spectral slope, and 0-MHz intercept biomarkers were investigated for different types of treatment and demonstrated cell-death related changes. The midband fit and 0-MHz intercept biomarker derived from low-frequency data demonstrated increases ranging approximately from 0 to 6 dBr and 0 to 8 dBr, respectively, depending on treatments administrated. These data paralleled results observed for high-frequency ultrasound data. Statistical analysis of ultrasound signal envelope was performed as an alternative method to obtain histogram-based biomarkers and provided confirmatory results. Histological analysis of tumor specimens indicated up to 61% cell death present in the tumors depending on treatments administered, consistent with quantitative ultrasound findings indicating cell death. Ultrasound-based spectroscopic biomarkers demonstrated a good correlation with histological morphological findings indicative of cell death (r{sup 2}= 0.71, 0.82; p < 0.001).Conclusions: In summary, the results provide preclinical evidence, for the first time, that quantitative ultrasound used at a clinically relevant frequency, in addition to high-frequency ultrasound, can detect tissue changes associated with cell death in vivo in response to cancer treatments.

Sadeghi-Naini, Ali; Falou, Omar; Czarnota, Gregory J. [Imaging Research – Physical Science, Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5 (Canada) [Imaging Research – Physical Science, Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5 (Canada); Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5 (Canada); Department of Medical Biophysics, Faculty of Medicine, University of Toronto, Toronto, Ontario M4N 3M5 (Canada); Department of Radiation Oncology, Faculty of Medicine, University of Toronto, Toronto, Ontario M4N 3M5 (Canada); Papanicolau, Naum; Tadayyon, Hadi [Imaging Research – Physical Science, Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5, Canada and Department of Medical Biophysics, Faculty of Medicine, University of Toronto, Toronto, Ontario M4N 3M5 (Canada)] [Imaging Research – Physical Science, Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5, Canada and Department of Medical Biophysics, Faculty of Medicine, University of Toronto, Toronto, Ontario M4N 3M5 (Canada); Lee, Justin [Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5, Canada and Department of Radiation Oncology, Faculty of Medicine, University of Toronto, Toronto, Ontario M4N 3M5 (Canada)] [Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5, Canada and Department of Radiation Oncology, Faculty of Medicine, University of Toronto, Toronto, Ontario M4N 3M5 (Canada); Zubovits, Judit [Department of Pathology, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5 (Canada)] [Department of Pathology, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5 (Canada); Sadeghian, Alireza [Department of Computer Science, Ryerson University, Toronto, Ontario M5B 2K3 (Canada)] [Department of Computer Science, Ryerson University, Toronto, Ontario M5B 2K3 (Canada); Karshafian, Raffi [Department of Physics, Ryerson University, Toronto, Ontario M5B 2K3 (Canada)] [Department of Physics, Ryerson University, Toronto, Ontario M5B 2K3 (Canada); Al-Mahrouki, Azza; Giles, Anoja [Imaging Research – Physical Science, Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5, Canada and Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5 (Canada)] [Imaging Research – Physical Science, Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5, Canada and Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Ontario M4N 3M5 (Canada); Kolios, Michael C. [Department of Medical Biophysics, Faculty of Medicine, University of Toronto, Toronto, Ontario M4N 3M5, Canada and Department of Physics, Ryerson University, Toronto, Ontario M5B 2K3 (Canada)] [Department of Medical Biophysics, Faculty of Medicine, University of Toronto, Toronto, Ontario M4N 3M5, Canada and Department of Physics, Ryerson University, Toronto, Ontario M5B 2K3 (Canada)

2013-08-15

405

The impact of spatial and spectral frequencies in structured light imaging of thick tissues  

NASA Astrophysics Data System (ADS)

This research focuses on development of structured light imaging (SLI), a new optical imaging technique based on spatial frequency domain modulation. The goal of this method is to quantitatively measure and map tissue optical properties, absorption and scattering, to determine tissue biochemical structure and composition. The work presented here extends the technology's spatial and spectral frequency impact. First, to expand the depth sectioning capability of spatial frequency modulation, a layered tissue model was developed, validated and shown to accurately recover in vivo parameters in skin (epidermis and dermis), effectively filtering out signal from the underlying subcutaneous tissue. Next, to expand the impact of spectral frequency information, the SLI system was combined with a Computed Tomography Imaging Spectrometer (CTIS), which eliminates the need to scan through wavelengths when gathering multispectral information. A single SLI-CTIS measurement gathers 36 absorption maps and 36 scattering maps, with a resulting measurement speed ˜30 times faster than the liquid crystal tunable filter method currently employed in multispectral SLI systems. The multispectral information can be used to determine the concentrations of multiple tissue chromophores and the relative density of the tissue. This is immediately useful for monitoring the brain for signs of trauma, including monitoring of oxygen delivery across the brain, mapping of hemoglobin concentration to detect hemorrhage, mapping of water content to monitor edema, and mapping of tissue density to monitor swelling. A simple in vivo brain injury example is presented to demonstrate recovery of these parameters. Finally, to demonstrate the spatial, spectral and temporal resolution of the SLI-CTIS system, measurements were performed on in vivo mouse brain during seizure with electroencephalography (EEG) confirmation.

Weber, Jessie Ruth

406

2D Seismic Imaging of Elastic Parameters by Frequency Domain Full Waveform Inversion  

NASA Astrophysics Data System (ADS)

Thanks to recent advances in parallel computing, full waveform inversion is today a tractable seismic imaging method to reconstruct physical parameters of the earth interior at different scales ranging from the near- surface to the deep crust. We present a massively parallel 2D frequency-domain full-waveform algorithm for imaging visco-elastic media from multi-component seismic data. The forward problem (i.e. the resolution of the frequency-domain 2D PSV elastodynamics equations) is based on low-order Discontinuous Galerkin (DG) method (P0 and/or P1 interpolations). Thanks to triangular unstructured meshes, the DG method allows accurate modeling of both body waves and surface waves in case of complex topography for a discretization of 10 to 15 cells per shear wavelength. The frequency-domain DG system is solved efficiently for multiple sources with the parallel direct solver MUMPS. The local inversion procedure (i.e. minimization of residuals between observed and computed data) is based on the adjoint-state method which allows to efficiently compute the gradient of the objective function. Applying the inversion hierarchically from the low frequencies to the higher ones defines a multiresolution imaging strategy which helps convergence towards the global minimum. In place of expensive Newton algorithm, the combined use of the diagonal terms of the approximate Hessian matrix and optimization algorithms based on quasi-Newton methods (Conjugate Gradient, LBFGS, ...) allows to improve the convergence of the iterative inversion. The distribution of forward problem solutions over processors driven by a mesh partitioning performed by METIS allows to apply most of the inversion in parallel. We shall present the main features of the parallel modeling/inversion algorithm, assess its scalability and illustrate its performances with realistic synthetic case studies.

Brossier, R.; Virieux, J.; Operto, S.

2008-12-01

407

Molecular structure, normal coordinate analysis, harmonic vibrational frequencies, NBO, HOMO-LUMO analysis and detonation properties of (S)-2-(2-oxopyrrolidin-1-yl) butanamide by density functional methods  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) computations have become an efficient tool in the prediction of molecular structure, harmonic force fields, vibrational wave numbers as well as the IR and Raman intensities of pharmaceutically important molecule. In this work, we report harmonic vibrational frequencies, molecular structure, NBO and HOMO, LUMO analysis and detonation properties of (S)-2-(2-oxopyrrolidin-1-yl) butanamide. The solid phase FT-IR and FT-Raman spectra of (S)-2-(2-oxopyrrolidin-1-yl) butanamide were recorded in the region 4000-450 cm-1 and 4000-50 cm-1 respectively. Harmonic frequencies of this compound were determined and analyzed by DFT utilizing 6-31G(d,p), 6-31+G(d,p) basis sets. The assignments of the vibrational spectra have been carried out with the help of Normal Coordinate Analysis (NCA) following the Scaled Quantum Mechanical Force Field Methodology (SQMFF). The calculated infrared and Raman spectra of the title compounds were also stimulated utilizing the scaled force fields and the computed dipole derivatives for IR intensities and polarizability derivatives for Raman intensities. The change in electron density (ED) in the ?* and ?* antibonding orbital's and stabilization energies E(2) have been calculated by Natural Bond Orbital (NBO) analysis to give clear evidence of stabilization originating in the hyperconjugation of hydrogen-bonded interaction. Heat of formation (HOF) and calculated density were estimated to evaluate detonation properties using Kamlet-Jacobs equations. The linear polarizability (?) and the first order hyperpolarizability (?) values of the investigated molecule have been computed using DFT calculations. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The observed and calculated wave numbers are found to be in good agreement. On the basis of vibrational analyses, the thermodynamic properties of title compound at different temperatures have been calculated.

Renuga, S.; Muthu, S.

2014-01-01

408

Factors governing selection of operating frequency for subsurface- imaging synthetic-aperture radar  

SciTech Connect

A subsurface-imaging synthetic-aperture radar (SISAR) has potential for application in areas as diverse as non-proliferation programs for nuclear weapons to environmental monitoring. However, subsurface imaging is complicated by propagation loss in the soil and surface-clutter response. Both the loss and surface-clutter response depend on the operating frequency. This paper examines several factors which provide a basis for determining optimum frequencies and frequency ranges which will allow synthetic-aperture imaging of buried targets. No distinction can be made between objects at different heights when viewed with a conventional imaging radar (which uses a one-dimensional synthetic aperture), and the return from a buried object must compete with the return from the surface clutter. Thus, the signal-to-clutter ratio is an appropriate measure of performance for a SISAR. A parameter-based modeling approach is used to model the complex dielectric constant of the soil from measured data obtained from the literature. Theoretical random-surface scattering models, based on statistical solutions to Maxwell`s equations, are used to model the clutter. These models are combined to estimate the signal-to-clutter ratio for canonical targets buried in several soil configurations. Results indicate that the HF spectrum (3--30), although it could be used to detect certain targets under some conditions, has limited practical value for use with SISAR, while the upper VIHF through UHF spectrum ({approximately}100 MHz - 1 GHz) shows the most promise for a general purpose SISAR system. Recommendations are included for additional research.

Brock, B.C.; Patitz, W.E.

1993-12-31

409

Intramolecular Dynamics Probed using High Harmonic Generation  

NASA Astrophysics Data System (ADS)

We observed intramolecular dynamics as a modulation in high harmonic emission. We excite coherent vibrations in CF3Cl using impulsive Raman scattering with a short laser pulse. A second laser pulse generates high harmonics. The harmonic yield is observed to oscillate at frequencies corresponding to three vibrational modes of CF3Cl. In a second experiment, we used UV light to excite and dissociate CF3I, and follow the dynamic evolution by monitoring the harmonic yield. We observe a large modulation of the harmonic yield, likely due to resonance excitation and subsequent dissociation of the molecule. We speculate that the less-than full baseline recovery after the UV pulse is due to ionization, and that the harmonic yield is sensitive to the bond length during dissociation. By these two experiments, we confirm that high harmonic generation is a sensitive probe of intramolecular dynamics and may yield more information simultaneously than conventional ultrafast spectroscopic techniques.

Hooper, Robynne; Zhou, Xibin; Li, Wen; Wagner, Nick; Kapteyn, Henry; Murnane, Margaret

2007-06-01

410

High range resolution ultrasonographic vascular imaging using frequency domain interferometry with the Capon method.  

PubMed

For high range resolution ultrasonographic vascular imaging, we apply frequency domain interferometry with the Capon method to a single frame of in-phase and quadrature (IQ) data acquired using a commercial ultrasonographic device with a 7.5 MHz linear array probe. In order to tailor the adaptive beam forming algorithm for ultrasonography we employ four techniques: frequency averaging, whitening, radio-frequency data oversampling, and the moving average. The proposed method had a range resolution of 0.05 mm in an ideal condition, and experimentally detected the boundary couple 0.17 mm apart, where the boundary couple was indistinguishable from a single boundary utilizing a B-mode image. Further, this algorithm could depict a swine femoral artery with a range beam width of 0.054 mm and an estimation error for the vessel wall thickness of 0.009 mm, whereas using a conventional method the range beam width and estimation error were 0.182 and 0.021 mm, respectively. The proposed method requires 7.7 s on a mobile PC with a single CPU for a 1×3 cm region of interest. These findings indicate the potential of the proposed method for the improvement of range resolution in ultrasonography without deterioration in temporal resolution, resulting in enhanced detection of vessel stenosis. PMID:21984496

Taki, Hirofumi; Taki, Kousuke; Sakamoto, Takuya; Yamakawa, Makoto; Shiina, Tsuyoshi; Kudo, Motoi; Sato, Toru

2012-02-01

411

Effect of driving frequency on non-linear coupling between ultrasound transducer and target under inspection in Sonic Infrared Imaging  

NASA Astrophysics Data System (ADS)

Sonic Infrared (IR) Imaging, also referred as vibrothermography, is a novel Nondestructive Evaluation (NDE) technology to find cracks through infrared imaging of vibration-induced crack heating. The vibration source plays an important role in the detection of cracks. In this paper, the effect of driving frequency on the ultrasound vibration to the thermal