Detection Of Shear Waves Research Articles

TH-A-207B-01: Basics and Current Implementations of Ultrasound Imaging of Shear Wave Speed and Elasticity

Imaging of tissue elastic properties is a relatively new and powerful approach to one of the oldest and most important diagnostic tools. Imaging of shear wave speed with ultrasound is has been added to most high-end ultrasound systems. Understanding this exciting imaging mode aiding its most effective use in medicine can be a rewarding effort for medical physicists and other medical imaging and treatment professionals. Assuring consistent, quantitative measurements across the many ultrasound systems in a typical imaging department will constitute a major step toward realizing the great potential of this technique and other quantitative imaging. This session will target these two goals with two presentations. A. Basics and Current Implementations of Ultrasound Imaging of Shear Wave Speed and Elasticity - Shigao Chen, Ph.D. Learning objectives-To understand: 1.Introduction: •Importance of tissue elasticity measurement •Strain vs. shear wave elastography (SWE), beneficial features of SWE •The link between shear wave speed and material properties, influence of viscosity 2.Generation of shear waves •External vibration (Fibroscan) •ultrasound radiation force •Point push •Supersonic push (Aixplorer) •Comb push (GE Logiq E9) 3.Detection of shear waves •Motion detection from pulse-echo ultrasound •Importance of frame rate for shear wave imaging •Plane wave imaging detection •How to achieve high effective frame rate using line-by-line scanners 4.Shear wave speed calculation •Time to peak •Random sample consensus (RANSAC) •Cross correlation 5.Sources of bias and variation in SWE •Tissue viscosity •Transducer compression or internal pressure of organ •Reflection of shear waves at boundaries B. Elasticity Imaging System Biomarker Qualification and User Testing of Systems – Brian Garra, M.D. Learning objectives-To understand: 1.Goals •Review the need for quantitative medical imaging •Provide examples of quantitative imaging biomarkers •Acquaint the participant with the purpose of the RSNA Quantitative Imaging Biomarker Alliance and the need for such an organization •Review the QIBA process for creating a quantitative biomarker •Summarize steps needed to verify adherence of site, operators, and imaging systems to a QIBA profile 2.Underlying Premise and Assumptions •Objective, quantifiable results are needed to enhance the value of diagnostic imaging in clinical practice •Reasons for quantification i.Evidence based medicine requires objective, not subjective observer data ii.Computerized decision support tools (eg CAD) generally require quantitative input. iii.Quantitative, reproducible measures are more easily used to develop personalized molecular medical diagnostic and treatment systems 3.What is quantitative imaging? •Definition from Imaging Metrology Workshop 4.The Quantitative Imaging Biomarker Alliance •Formation 2008 •Mission •Structure •Example Imaging Biomarkers Being Explored •Biomarker Selection •Groundwork •Draft Protocol for imaging and data evaluation •QIBA Profile Drafting •Equipment and Site Validation i.Technical ii.Clinical •Site and Equipment QA and Compliance Checking 5.Ultrasound Elasticity Estimation Biomarker •US Elasticity Estimation Background •Current Status and Problems •Biomarker Selection-process and outcome 6.US SWS for Liver Fibrosis Biomarker Work •Groundwork i.Literature search and analysis results ii.Phase I phantom testing-Elastic phantoms iii.Phase II phantom testing-Viscoelastic phantoms iv.Digital Simulated Data •Protocol and Profile Drafting iProtocol: based on UPICT and existing literature and standards bodies protocols ii.Profile-Current claims, Manufacturer specific appendices 7.What comes after the profile •Profile Validation iTechnical validation ii.Clinical validation •QA and Compliance i.Possible approaches 1.Site a.Operator testing b.Site protocol re-evaluation 2.Imaging system a.Manufacturer testing and attestation b.User acceptance testing and periodic QA i.Phantom Tests ii.Digital Phantom Based Testing iii.Standard QA Testing iv.Remediation Schemes 8.Profile Evolution •Towards additional applications •Towards higher accuracy and precision Supported in part by NIH contract HHSN268201300071C from NIBIB. Collaboration with GE Global Research, no personal support.; S. Chen, Some technologies described in this presentation have been licensed. Mayo Clinic and Dr. Chen have financial interests these technologies.

TH-A-207B-02: QIBA Ultrasound Elasticity Imaging System Biomarker Qualification and User Testing of Systems

Imaging of tissue elastic properties is a relatively new and powerful approach to one of the oldest and most important diagnostic tools. Imaging of shear wave speed with ultrasound is has been added to most high-end ultrasound systems. Understanding this exciting imaging mode aiding its most effective use in medicine can be a rewarding effort for medical physicists and other medical imaging and treatment professionals. Assuring consistent, quantitative measurements across the many ultrasound systems in a typical imaging department will constitute a major step toward realizing the great potential of this technique and other quantitative imaging. This session will target these two goals with two presentations. A. Basics and Current Implementations of Ultrasound Imaging of Shear Wave Speed and Elasticity - Shigao Chen, Ph.D. Learning objectives-To understand: 1. Introduction: • Importance of tissue elasticity measurement • Strain vs. shear wave elastography (SWE), beneficial features of SWE • The link between shear wave speed and material properties, influence of viscosity 2. Generation of shear waves • External vibration (Fibroscan) • ultrasound radiation force • Point push • Supersonic push (Aixplorer) • Comb push (GE Logiq E9) 3. Detection of shear waves • Motion detection from pulse-echo ultrasound • Importance of frame rate for shear wave imaging • Plane wave imaging detection • How to achieve high effective frame rate using line-by-line scanners 4. Shear wave speed calculation • Time to peak • Random sample consensus (RANSAC) • Cross correlation 5. Sources of bias and variation in SWE • Tissue viscosity • Transducer compression or internal pressure of organ • Reflection of shear waves at boundaries B. Elasticity Imaging System Biomarker Qualification and User Testing of Systems – Brian Garra, M.D. Learning objectives-To understand: 1. Goals • Review the need for quantitative medical imaging • Provide examples of quantitative imaging biomarkers • Acquaint the participant with the purpose of the RSNA Quantitative Imaging Biomarker Alliance and the need for such an organization • Review the QIBA process for creating a quantitative biomarker • Summarize steps needed to verify adherence of site, operators, and imaging systems to a QIBA profile 2. Underlying Premise and Assumptions • Objective, quantifiable results are needed to enhance the value of diagnostic imaging in clinical practice • Reasons for quantification i. Evidence based medicine requires objective, not subjective observer data ii. Computerized decision support tools (eg CAD) generally require quantitative input. iii. Quantitative, reproducible measures are more easily used to develop personalized molecular medical diagnostic and treatment systems 3. What is quantitative imaging? • Definition from Imaging Metrology Workshop 4. The Quantitative Imaging Biomarker Alliance • Formation 2008 • Mission • Structure • Example Imaging Biomarkers Being Explored • Biomarker Selection • Groundwork • Draft Protocol for imaging and data evaluation • QIBA Profile Drafting • Equipment and Site Validation i. Technical ii. Clinical • Site and Equipment QA and Compliance Checking 5. Ultrasound Elasticity Estimation Biomarker • US Elasticity Estimation Background • Current Status and Problems • Biomarker Selection-process and outcome 6. US SWS for Liver Fibrosis Biomarker Work • Groundwork i. Literature search and analysis results ii. Phase I phantom testing-Elastic phantoms iii. Phase II phantom testing-Viscoelastic phantoms iv. Digital Simulated Data • Protocol and Profile Drafting i Protocol: based on UPICT and existing literature and standards bodies protocols ii. Profile-Current claims, Manufacturer specific appendices 7. What comes after the profile • Profile Validation i Technical validation ii. Clinical validation • QA and Compliance i. Possible approaches 1. Site a. Operator testing b. Site protocol re-evaluation 2. Imaging system a. Manufacturer testing and attestation b. User acceptance testing and periodic QA i. Phantom Tests ii. Digital Phantom Based Testing iii. Standard QA Testing iv. Remediation Schemes 8. Profile Evolution • Towards additional applications • Towards higher accuracy and precision Supported in part by NIH contract HHSN268201300071C from NIBIB. Collaboration with GE Global Research, no personal support.; S. Chen, Some technologies described in this presentation have been licensed. Mayo Clinic and Dr. Chen have financial interests these technologies.

TH-A-207B-00: Shear-Wave Imaging and a QIBA US Biomarker Update

Imaging of tissue elastic properties is a relatively new and powerful approach to one of the oldest and most important diagnostic tools. Imaging of shear wave speed with ultrasound is has been added to most high-end ultrasound systems. Understanding this exciting imaging mode aiding its most effective use in medicine can be a rewarding effort for medical physicists and other medical imaging and treatment professionals. Assuring consistent, quantitative measurements across the many ultrasound systems in a typical imaging department will constitute a major step toward realizing the great potential of this technique and other quantitative imaging. This session will target these two goals with two presentations. A. Basics and Current Implementations of Ultrasound Imaging of Shear Wave Speed and Elasticity - Shigao Chen, Ph.D. Learning objectives-To understand: 1.Introduction: •Importance of tissue elasticity measurement •Strain vs. shear wave elastography (SWE), beneficial features of SWE •The link between shear wave speed and material properties, influence of viscosity 2.Generation of shear waves •External vibration (Fibroscan) •ultrasound radiation force •Point push •Supersonic push (Aixplorer) •Comb push (GE Logiq E9) 3.Detection of shear waves •Motion detection from pulse-echo ultrasound •Importance of frame rate for shear wave imaging •Plane wave imaging detection •How to achieve high effective frame rate using line-by-line scanners 4.Shear wave speed calculation •Time to peak •Random sample consensus (RANSAC) •Cross correlation 5.Sources of bias and variation in SWE •Tissue viscosity •Transducer compression or internal pressure of organ •Reflection of shear waves at boundaries B. Elasticity Imaging System Biomarker Qualification and User Testing of Systems – Brian Garra, M.D. Learning objectives-To understand: 1.Goals •Review the need for quantitative medical imaging •Provide examples of quantitative imaging biomarkers •Acquaint the participant with the purpose of the RSNA Quantitative Imaging Biomarker Alliance and the need for such an organization •Review the QIBA process for creating a quantitative biomarker •Summarize steps needed to verify adherence of site, operators, and imaging systems to a QIBA profile 2.Underlying Premise and Assumptions •Objective, quantifiable results are needed to enhance the value of diagnostic imaging in clinical practice •Reasons for quantification i.Evidence based medicine requires objective, not subjective observer data ii.Computerized decision support tools (eg CAD) generally require quantitative input. iii.Quantitative, reproducible measures are more easily used to develop personalized molecular medical diagnostic and treatment systems 3.What is quantitative imaging? •Definition from Imaging Metrology Workshop 4.The Quantitative Imaging Biomarker Alliance •Formation 2008 •Mission •Structure •Example Imaging Biomarkers Being Explored •Biomarker Selection •Groundwork •Draft Protocol for imaging and data evaluation •QIBA Profile Drafting •Equipment and Site Validation i.Technical ii.Clinical •Site and Equipment QA and Compliance Checking 5.Ultrasound Elasticity Estimation Biomarker •US Elasticity Estimation Background •Current Status and Problems •Biomarker Selection-process and outcome 6.US SWS for Liver Fibrosis Biomarker Work •Groundwork i.Literature search and analysis results ii.Phase I phantom testing-Elastic phantoms iii.Phase II phantom testing-Viscoelastic phantoms iv.Digital Simulated Data •Protocol and Profile Drafting iProtocol: based on UPICT and existing literature and standards bodies protocols ii.Profile-Current claims, Manufacturer specific appendices 7.What comes after the profile •Profile Validation iTechnical validation ii.Clinical validation •QA and Compliance i.Possible approaches 1.Site a.Operator testing b.Site protocol re-evaluation 2.Imaging system a.Manufacturer testing and attestation b.User acceptance testing and periodic QA i.Phantom Tests ii.Digital Phantom Based Testing iii.Standard QA Testing iv.Remediation Schemes 8.Profile Evolution •Towards additional applications •Towards higher accuracy and precision Supported in part by NIH contract HHSN268201300071C from NIBIB. Collaboration with GE Global Research, no personal support.; S. Chen, Some technologies described in this presentation have been licensed. Mayo Clinic and Dr. Chen have financial interests these technologies.

Non-destructive testing of stainless steel in high temperature using electromagnetic acoustic transducer

Stainless steel is widely used on the power station boiler and main steam piping, whose service temperature is generally between 300 and 650°C. Electromagnetic acoustic transducer is one of the most promising ultrasonic technologies to achieve the in-service non-destructive testing of the material and structure at high temperature. As the physical properties of the material change with temperature, ultrasonic testing signal also varies. The variations of the electromagnetic ultrasonic speed, signal amplitude and wave package shape with temperature were studied. The stainless steel of 304, 316, TP347H and aluminium were observed in the experiments. The results showed that the amplitudes and velocities of 304 and 316 stainless steel decreased monotonously as a function of temperature, while TP347H showed the opposite trend. The results imply that shear wave detection with electromagnetic acoustic transducer could be used efficiently below 500°C for the application of non-destructive testing at high temperature.

Coded excitation plane wave imaging for shear wave motion detection.

Plane wave imaging has greatly advanced the field of shear wave elastography thanks to its ultrafast imaging frame rate and the large field-of-view (FOV). However, plane wave imaging also has decreased penetration due to lack of transmit focusing, which makes it challenging to use plane waves for shear wave detection in deep tissues and in obese patients. This study investigated the feasibility of implementing coded excitation in plane wave imaging for shear wave detection, with the hypothesis that coded ultrasound signals can provide superior detection penetration and shear wave SNR compared with conventional ultrasound signals. Both phase encoding (Barker code) and frequency encoding (chirp code) methods were studied. A first phantom experiment showed an approximate penetration gain of 2 to 4 cm for the coded pulses. Two subsequent phantom studies showed that all coded pulses outperformed the conventional short imaging pulse by providing superior sensitivity to small motion and robustness to weak ultrasound signals. Finally, an in vivo liver case study on an obese subject (body mass index = 40) demonstrated the feasibility of using the proposed method for in vivo applications, and showed that all coded pulses could provide higher SNR shear wave signals than the conventional short pulse. These findings indicate that by using coded excitation shear wave detection, one can benefit from the ultrafast imaging frame rate and large FOV provided by plane wave imaging while preserving good penetration and shear wave signal quality, which is essential for obtaining robust shear elasticity measurements of tissue.

Robust Detection and Estimation for Logging While Drilling Monopole Acoustic Data

In this paper, we present methods and strategies for robust detection and slowness estimation of weak compressional (P) and shear (S) waves in borehole sonic logging in noisy environments such as while logging while drilling, by proposing methods for enhancing the semblance used in the slowness time coherence method used in the logging. In this direction our contributions are two fold. First, we propose a novel class of shrinkage estimators in the discrete Radon transform domain derived from data semblance, for waveform de-noising to combat random additive noise and reflections. In this context we also identify necessary and sufficient conditions for the optimality of the proposed estimator. Our second contribution lies in developing a novel method to cancel energy propagating at the slowness of borehole modes, chiefly Stoneley, and to a lesser extent, shear, that significantly lowers the semblance of the weaker head wave arrivals. This approach is based on representing the data using time-frequency compact space-time propagators. Finally, we present an algorithm that combines the space time shrinkage in the discrete Radon transform domain and the proposed interference cancelation strategies for enhanced compressional and shear detection via semblance processing. The algorithm is validated on synthetic data and demonstrated to enhance performance on real logging while drilling field data sets.

Fundamentals of picosecond laser ultrasonics

The aim of this article is to provide an introduction to picosecond laser ultrasonics, a means by which gigahertz–terahertz ultrasonic waves can be generated and detected by ultrashort light pulses. This method can be used to characterize materials with nanometer spatial resolution. With reference to key experiments, we first review the theoretical background for normal-incidence optical detection of longitudinal acoustic waves in opaque single-layer isotropic thin films. The theory is extended to handle isotropic multilayer samples, and is again compared to experiment. We then review applications to anisotropic samples, including oblique-incidence optical probing, and treat the generation and detection of shear waves. Solids including metals and semiconductors are mainly discussed, although liquids are briefly mentioned.

A New Kind of Water-Squirting Ultrasonic Detector

The water-squirting ultrasonic detector can not only reduce wetted area of specimen, volume of detection equipment, but also gain longitudinal wave, shear wave, and surface wave detection by changing the ultrasonic incident angle. The paper discusses the development of a new kind of water-squirting ultrasonic detector, which is based on the study of water immersion ultrasonic detector. In this detector, a removable water column replaces the fixed water container for maneuverability; a composited column replaces the water-only column for the ultrasonic coupling channel; a special optimized nozzle is used to form the composited column; an ultrasonic absorption intracavity and an air-water composited mixture are used for anti-interference. Finally, the new kind of water-squiring ultrasonic detector may replace the original water immersion detector, and can be applied to more extensive detection field.

A Hybrid Bender Element–Ultrasonic System for Measurement of Wave Velocity in Soils

In recent years, the determination of the small strain modulus of soils from laboratory measurement of the elastic wave velocity has become more common. Piezoelectric elements are used in these tests, with two types of configurations: fixed to the back face of a platen as an ultrasonic transducer, or as a bimorph that slightly protrudes out of the platen. A survey of the literature shows that bender/extender elements are more widely used than ultrasonic transducers in soil tests. However, bender/extender elements are invasive in nature. Besides introducing some degree of specimen disturbance, they need to be sufficiently robust for insertion into the soil specimen, and they also need to be properly waterproofed to avoid short-circuiting. Ultrasonic transducers can solve the above-mentioned problems. However, the detection of shear waves can be challenging in soils, as reported in the literature. The objectives of this paper are to examine the difficulties of shear wave detection by ultrasonic transducers and to propose a hybrid bender element–ultrasonic system that partially alleviates the problems associated with bender/extender elements while still providing reliable shear wave velocity measurement. The hybrid system used was calibrated with standard materials, and tests were conducted on sand and kaolin specimens. Relative to bender/extender elements and ultrasonic transducers, the hybrid system showed better performance in determining wave velocities in soil tests, especially for shear waves.

Shear wave pulse compression for dynamic elastography using phase-sensitive optical coherence tomography

Assessing the biomechanical properties of soft tissue provides clinically valuable information to supplement conventional structural imaging. In the previous studies, we introduced a dynamic elastography technique based on phase-sensitive optical coherence tomography (PhS-OCT) to characterize submillimetric structures such as skin layers or ocular tissues. Here, we propose to implement a pulse compression technique for shear wave elastography. We performed shear wave pulse compression in tissue-mimicking phantoms. Using a mechanical actuator to generate broadband frequency-modulated vibrations (1 to 5 kHz), induced displacements were detected at an equivalent frame rate of 47 kHz using a PhS-OCT. The recorded signal was digitally compressed to a broadband pulse. Stiffness maps were then reconstructed from spatially localized estimates of the local shear wave speed. We demonstrate that a simple pulse compression scheme can increase shear wave detection signal-to-noise ratio (>12 dB gain) and reduce artifacts in reconstructing stiffness maps of heterogeneous media.

Tracking mechanical wave propagation within tissue using phase-sensitive optical coherence tomography: motion artifact and its compensation

We describe theoretical and experimental investigations of motion artifacts that can arise in the detection of shear wave propagating within tissue with phase-sensitive optical coherence tomography. We find that the motion artifact is a combined product of sample surface motion and refractive index difference between sample and air, which cannot be neglected when estimating the tissue motion within tissue. A method of compensating the motion artifact is demonstrated, the results of which emphasize the need for surface motion compensation when measuring the mechanical response for elastography or other biomedical applications.

온도와 포화도의 변화에 의한 표면장력이 전단파 속도에 미치는 영향

표면장력에 의한 겉보기 점착력은 적절한 함수비를 가지고 있는 흙의 경우 생성되며 지반의 강도를 증가시킨다. 본 연구의 목적은 온도에 따라 변화하는 표면장력이 전단파 속도에 미치는 영향을 파악하는 것이다. 표면장력의 발생 유무를 조절하기 위하여 모래-실트 혼합토를 이용하여 포화도가 다른 아홉 가지의 시료 (0%, 2.5%, 5%, 10%, 20%, 40%, 60%, 80%, 100%)를 조성하였다. 전단파 속도를 측정하기 위해 나일론 재질의 셀을 제작하였으며 전단파 트랜스듀서인 벤더 엘리먼트를 크로스 홀 형상으로 부착하였다. 시료의 온도가 <TEX>$15^{\circ}C$</TEX>에서 <TEX>$1^{\circ}C$</TEX>까지 변화하는 동안 포화도가 다른 각 시료의 전단파 신호를 연속적으로 측정하였다. 실험결과, 포화도 0%인 시료와 포화도 100%인 시료는 온도변화에 의한 전단파 속도 변화가 미비하였으나, 표면장력이 발생하기에 적절한 포화도를 가진 시료는 온도가 감소함에 따라 전단파 속도는 증가하였다. 또한 완전 포화된 시료를 <TEX>$70^{\circ}C$</TEX>에서 건조시키면서 포화도에 따른 전단파 속도를 측정한 시료의 경우, <TEX>$15^{\circ}C$</TEX>에서 측정된 시료의 전단파 속도보다 더 낮은 전단파 속도가 측정되었다. 본 연구는 특정한 포화도에서 온도변화에 따라 전단파 속도가 변화하는 원인을 실험을 통해 분석하였으며, 미소변형구간에서의 전단탄성계수 측정과 같은 실내 및 현장실험 시, 온도를 동시에 평가해야 함을 보여준다. The surface tension, which is generated in the unsaturated soils, increases the stiffness of the soils. The objective of this study is to estimate the effect of the surface tension, which varies according to the temperature, on the shear wave velocity. Nine specimens, which have the different degree of saturation (0%, 2.5%, 5%, 10%, 20%, 40%, 60%, 80%, 100%), are prepared by using sand-silt mixtures. Experiments are carried out in a nylon cell designed for the measurement of shear waves. A pair of bender elements, which are used for the generation and detection of shear waves, is installed as a cross-hole type. The shear waves are continuously monitored and measured as the temperature of specimens decreases from <TEX>$15^{\circ}C$</TEX> to <TEX>$1^{\circ}C$</TEX>. The results show that shear wave velocities of the fully saturated and fully dried specimens change a little bit as the temperatures of specimens decrease. However, the shear wave velocities of the specimens with the degree of saturations of 2.5%, 5%, 10%, 20%, 40%, 60% and 80% continuously increase as temperature decreases from <TEX>$15^{\circ}C$</TEX> to <TEX>$1^{\circ}C$</TEX>. Furthermore, a fully saturated specimen is dried at the temperature of <TEX>$70^{\circ}C$</TEX> in order to observe the shear waves according to degree of saturation. The shear wave velocities measured at the temperature of <TEX>$70^{\circ}C$</TEX> are generally lower than those measured at temperature of <TEX>$15^{\circ}C$</TEX>. This study demonstrates that the dependence of shear wave velocities on the temperature according to the degree of saturation should be taken into account in both laboratory and field tests.

Very preliminary reference Moon model

The deep structure of the Moon is a missing piece to understand the formation and evolution of the Earth–Moon system. Despite the great amount of information brought by the Apollo passive seismic experiment (ALSEP), the lunar structure below deep moonquakes, which occur around 900 km depth, remains largely unknown. We construct a reference Moon model which incorporates physical constraints, and fits both geodesic (lunar mass and polar moment of inertia, and Love numbers) and seismological (body wave arrivals measured by Apollo network) data. In this model, the core radius is constrained by the detection of S waves reflected from the core. In a first step, for each core radius, a radial model of the lunar interior, including P and S wave velocities and density, is inverted from seismic and geodesic data. In a second step, the core radius is determined from the detection of shear waves reflected on the lunar core by waveform stacking of deep moonquake Apollo records. This detection has been made possible by careful data selection and processing, including a correction of the gain of horizontal sensors based on the principle of energy equipartition inside the coda of lunar seismic records, and a precise alignment of SH waveforms by a non-linear inversion method. The Very Preliminary REference MOON model (VPREMOON) obtained here has a core radius of 380 ± 40 km and an average core mass density of 5200 ± 1000 kg/m 3. The large error bars on these estimates are due to the poorly constrained S-wave velocity profile at the base of the mantle and to mislocation errors of deep moonquakes. The detection of horizontally polarized S waves reflected from the core and the absence of detection of vertically polarized S waves favour a liquid state in the outermost part of the core. All these results are consistent, within their error bars, with previous estimates based on lunar rotation dissipation ( Williams et al., 2001) and on lunar induced magnetic moment ( Hood et al., 1999).

Coherent shear phonon generation and detection with picosecond laser acoustics

Measurements on a film of silica on crystalline zinc using picosecond laser acoustics are theoretically analyzed to quantitatively explain the generation and detection of picosecond shear and longitudinal-acoustic waves. The theory encompasses the scattering of obliquely incident probe light of arbitrary polarization by a depth-dependent anisotropic permittivity modulation in a multilayer, including terms arising from the photoelastic effect, interface displacements, and local rotations. Sound velocities, ultrasonic attenuation, and photoelastic constants are experimentally derived.

Three-dimensional elasto-optical interaction for reflectometric detection of diffracted acoustic fields in picosecond ultrasonics

The three-dimensional (3D) photoelastic interaction involved in the detection mechanism of picosecond ultrasonics is investigated in micrometric metallic films. In pump-probe experiments, the laser source beam is focused to a spot size of less than $1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$. A 3D diffracted acoustic field is generated at high frequencies of several tens of gigahertz, containing longitudinal and shear waves altogether. Their propagation changes the dielectric permittivity tensor and the material becomes optically heterogeneous. Consequently, the detection process is modeled through the propagation of the laser probe beam in a material with dielectric properties varying in all directions. Thus, the solution of Maxwell's equations leads to a differential system, the source term of which is proportional to the acoustic field itself. In the frame of small perturbation theory, the latter is decomposed into a continuous sum of monochromatic plane waves. The scattered electromagnetic field is described using the matricant, and the ensuing analytical solution then allows analyzing the 3D photoelastic interaction. The contribution of acoustic diffraction and shear wave detection to the reflectometric signal is put into relief. Good agreement with experiments performed in a $1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ thick aluminum film is found.

P1-6 Excitation and Detection of Ultrasound Shear Wave by EMAR under High Pressure(Poster session 1)

P1-6 Excitation and Detection of Ultrasound Shear Wave by EMAR under High Pressure(Poster session 1)

Doppler ultrasound detection of shear waves remotely induced in tissue phantoms and tissue in vitro

In shear wave elasticity imaging (SWEI), mechanical excitation within the tissue is remotely generated using radiation force of focused ultrasound. The induced shear strain is subsequently detected to estimate visco-elastic properties of tissue and thus aid diagnostics. In this paper, the mechanical response of tissue to radiation force was detected using a modified ultrasound Doppler technique. The experiments were performed on tissue mimicking and tissue containing phantoms using a commercial diagnostic scanner. This scanner was modified to control both the pushing and probing beams. The pushing beam was fired repetitively along a single direction while interlaced probing beams swept the surrounding region of interest to detect the induced motion. The detectability of inhomogeneous inclusions using ultrasonic Doppler SWEI method has been demonstrated in this study. The displacement fields measured in elastic phantoms clearly reveal the oscillatory nature of the mechanical relaxation processes in response to impulsive load due to the boundary effects. This relaxation dynamics was also present in cooked muscle tissue, but was not detected in more viscous and less elastic phantom and raw muscles. Presence of a local heterogeneity in the vicinity of the focal region of the pushing beam results in generation of a standing wave field pattern which is manifested in the oscillatory response of the excited region of the tissue. There has been made an assumption that dynamic characteristics of the relaxation process may be used for visualization of inhomogeneities.

Increase in the efficiency of the shear wave generation in gelatin due to the nonlinear absorption of a focused ultrasonic beam

Experimental results and theoretical estimates are presented to demonstrate the prospects of using the acoustic nonlinearity of a gel-like medium for increasing the efficiency of the shear wave generation in it by a pulsed ultrasonic beam. The experiment is based on the propagation of a focused beam of longitudinal acoustic waves at a frequency of 1.1 MHz in a gelatin sample and on the detection of shear waves by the optical method [1]. It is demonstrated that the amplitude of the shear wave excited by a nonlinear acoustic pulse can be increased by an order of magnitude owing to the formation of shock fronts in the profile of this pulse.

Doppler ultrasound detection of shear waves remotely induced in tissue phantoms by focused ultrasound

Remote generation of shear waves in tissues by radiation force of focused ultrasound is the basis of shear wave elasticity imaging (SWEI), a new acoustic method of medical diagnostics. Feasibility of SWEI was previously demonstrated in the experiments with optical and NMR detection of ultrasonically induced shear waves [Sarvazyan et al., Ultrasound Med. Biol. 24, 1419 (1998)]. In the present study the SWEI system with ultrasonic pulsed Doppler detection of shear waves was designed and tested using a range of gelatin-based phantoms and muscle tissue. Radiation force was generated by a focusing transducer of 8 cm diameter and 7 cm focal length. The carrier frequency was 1 MHz with intensity 1.85 W/cm2 at the surface of the transducer. The Doppler detection transducer operating at 3.5 MHz was installed in the center of the pumping transducer. The developed procedures of tissue motion detection and Doppler signal-processing algorithms based on the autocorrelation method allowed estimation of the velocity with accuracy better than 0.2 mm/s. The waveforms of the shear wave at various distances from the pumping ultrasonic beam axis were measured and the shear wave velocities were evaluated. The oscillation character of relaxation process for some phantoms and muscle tissue was shown experimentally.

Detection of shear wave in ultrasonic range by using a laser Doppler vibrometer

A laser Doppler vibrometer is used to measure shear waves propagating through solids in the ultrasonic frequency range. The laser Doppler vibrometer detects translational motion of small spherical lenses mounted on a solid surface. Stacking of wave-form signals increases the signal-to-noise ratio. Wave motion on a solid surface can be obtained from the surface vibrations measured at different incident angles of a laser beam. The observed longitudinal and shear wave amplitudes from a thickness-dilation-mode transducer agreed fairly well with the calculated amplitudes modeled by a piston force source.