Showing papers in "IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control in 1994"
TL;DR: In this paper, the authors extended the ultrasound speckle tracking method to allow measurement of internal displacement and strain fields over a wide dynamic range of tissue motion, which should lead to enhanced contrast resolution in strain and elasticity images.
Abstract: Previous ultrasound speckle tracking methods have been extended, permitting measurement of internal displacement and strain fields over a wide dynamic range of tissue motion. The markedly increased dynamic range of this approach should lead to enhanced contrast resolution in strain and elasticity images. Results of experiments on gelatin-based, tissue equivalent phantoms show the capabilities of the method. >
739 citations
TL;DR: In this article, the authors identify for the user community those sets of constants from which SAW design calculations can reliably be made, and discuss the constants and their reliability for langasite, lithium niobate/lithium tantalate, and dilithium tetraborate.
Abstract: Piezoelectric materials for acoustic wave applications have changed markedly over the past 20 years in terms of both the types of materials available and the quality of individual samples. The total family of acoustic wave materials now includes piezoelectric glass-ceramics having crystallographic and polar orientation and crystals having symmetry classes mm2, 32, 3m, 4mm, 6mm, and 4/spl macr/3m. The symmetry classes 6mm and 4/spl macr/3m also occur frequently in piezoelectric semiconductor materials that are now available in both bulk and thin-film configurations. In this paper, we bring together and extract the various reported values of the material constants mainly of interest for surface acoustic wave (SAW) device applications. We identify for the user community those sets of constants from which SAW design calculations can reliably be made, and discuss the constants and their reliability for langasite, lithium niobate/lithium tantalate, and dilithium tetraborate. The relevant material constants include: mass density /spl rho/, elastic stiffness c/sub ij/, piezoelectric stress e/sub ij/, dielectric permittivity /spl epsiv//sub ii/, and the thermal expansion coefficients /spl alpha//sub ii/. Except for the semiconductor materials, only data published after 1978 are included, since the reference literature (Landolt-Bornstein) amply covers those years prior to 1978. >
254 citations
TL;DR: An ultrasound synthetic aperture imaging method based on a monostatic approach was studied experimentally in this paper, where complex object data were recorded coherently in a 2D hologram using a 3.5 MHz single transducer with a fairly wide-angle beam.
Abstract: An ultrasound synthetic aperture imaging method based on a monostatic approach was studied experimentally. The proposed synthetic aperture method offers good dynamical resolution along with fast numerical reconstruction. In this study complex object data were recorded coherently in a two-dimensional hologram using a 3.5 MHz single transducer with a fairly wide-angle beam. Image reconstruction which applies the wavefront backward propagation method and the near-field curvature compensation was performed numerically in a microcomputer using the spatial frequency domain. This approach allows an efficient use of the FFT-algorithms. Because of the simple and fast scanning scheme and the efficient reconstruction algorithms the method can be made real-time. The image quality of the proposed method was studied by evaluating the spatial and dynamical resolution in a waterbath and in a typical tissue-mimicking phantom. The lateral as well as the range resolution (-6 dB) were approximately 1 mm in the depth range of 30-100 mm. The dynamical resolution could be improved considerably when the beam width was made narrower. Although it resulted in a slightly reduced spatial resolution this compromise has to be done for better resolution of low-contrast targets such as cysts. The study showed that cysts as small as 2 mm by diameter could be resolved. >
177 citations
TL;DR: In this paper, the authors proposed two methods to improve the overall efficiency of an ultrasonic pulse-echo system using nonlinear frequency modulation and square wave chirps derived from sine type chirp signals.
Abstract: Chirp pulse compression is a signal correlation technique that uses frequency modulated pulses as transmitted signals. Usually, signals with linear frequency modulation are applied. They can be generated rather easily, but their spectra are not totally matched to the transfer function of ultrasonic systems. In pulse-echo mode operation, with signal duration and consequently the time-bandwidth product being critical parameters, waveforms should be applied which make full use of the available power and bandwidth resources. We report here two methods to improve the overall efficiency of an ultrasonic pulse-echo system. Transmitter signals with constant amplitude level and nonlinear frequency modulation can be generated in such a way that they are spectrally matched to the system. A formula for the calculation of such a matched nonlinear chirp signal is presented. This modulation scheme also leads to a side-lobe level reduction of the compressed pulses. The application of square wave chirps derived from sine type chirps yields an additional gain of echo signal amplitude. Moreover, the complexity of the signal generation hardware is reduced. The methods are illustrated by an example. >
176 citations
TL;DR: In this paper, the results of measured internal strain and displacement fields from gel-based phantoms are compared with theoretical predictions of a linear elastic model, and some aspects of elasticity reconstruction based on measured displacement and strain fields are discussed.
Abstract: Evaluation of internal displacement and strain distributions in tissue under externally applied forces is a necessary step in elasticity imaging To obtain a quantitative image of the elastic modulus, strain and displacement fields must be measured with reasonable accuracy and inverted based on an accurate theoretical model of soft tissue mechanics In this paper, results of measured internal strain and displacement fields from gel-based phantoms are compared with theoretical predictions of a linear elastic model In addition, some aspects of elasticity reconstruction based on measured displacement and strain fields are discussed >
169 citations
TL;DR: In this paper, transmission line analogous circuits for piezoelectric transducers are developed which employ controlled sources rather than the traditional transformer to model the coupling between the electrical and the mechanical systems.
Abstract: Transmission line analogous circuits for piezoelectric transducers are developed which employ controlled sources rather than the traditional transformer to model the coupling between the electrical and the mechanical systems. A novel method is used to derive each model that consists of adding a term that is equal to zero to one of the device electromechanical equations. When this is done, it is shown that the equations can be cast into the form of the familiar telegraphist's equations for the voltage and current on an electrical transmission line. The circuits are derived for both the thickness-mode piezoelectric transducer and the side-electrode bar piezoelectric transducer. SPICE models of the analogous circuits are presented and an example simulation is given. >
157 citations
TL;DR: 2-D arrays made of multilayer ceramics can be used to form images at a higher frequency and greater range than single layer arrays.
Abstract: In medical ultrasound imaging, 2-D array transducers have become essential to implement dynamic focusing and phase-correction in the elevation dimension as well as real-time volumetric scanning. Unfortunately, the small size of a 2-D array element results in a small clamped capacitance and a large electrical impedance near resonance. These elements have poor sensitivity because their impedance is much higher than the electrical impedance of the transmit and receive circuitry. Sensitivity can be improved by using an N layer structure of PZT ceramic with the layers connected acoustically in series and electrically in parallel. For the multilayer ceramic (MLC), the damped capacitance is multiplied by a factor of N/sup 2/ and the electrical impedance by 1/N/sup 2/ compared to a single layer element of the same dimensions. A 3/spl times/43 phased-array transducer has been fabricated using 3 layer PZT-5H material. Each element had a thickness of 0.66 mm and an area of 0.37/spl times/3.5 mm. The MLC was manufactured using thick film technology with plated-through vias to electrically interconnect the electrode layers. The completed transducer was compared to a single layer control array of similar dimensions. With a light epoxy backing and a /spl lambda//4 matching layer, the MLC array elements had an impedance of 100 /spl Omega/ at series resonance of 2.25 MHz, compared to 800 /spl Omega/ for the control elements. The lower impedance of the MLC elements resulted in a minimum round-trip insertion loss of 24.0 dB, compared to an 34.1 dB for the control array elements. These results were consistent with KLM modeling. B-scan images were made of cysts in a tissue-mimicking phantom and of the left kidney in vivo. The images clearly showed a higher signal-to-noise ratio for the MLC array compared to the control. As a result, 2-D arrays made of multilayer ceramics can be used to form images at a higher frequency and greater range than single layer arrays. >
145 citations
TL;DR: It is shown that the magnitude of the interelement correlation is the key parameter governing phase correction performance, and techniques that utilize a small correction reference region are more susceptible to noise and missing elements than techniques which use larger reference regions.
Abstract: A common framework is presented to classify several phase correction techniques. A subset of these techniques are evaluated through simulations which utilize 2-D phase aberration profiles measured in the breast. The techniques are compared based on their ability to reduce phase errors, stability, and sensitivity to noise and missing elements in the transducer array. Significant differences are observed in these measures of performance when the size and location of the aperture area used to generate a phase reference signal are varied. Techniques that utilize a small correction reference region are more susceptible to noise and missing elements than techniques which use larger reference regions. The algorithms encounter problems in 2-D phase correction when making the transition from one row to the next, due to the low interelement correlation at the transition points. It is shown that the magnitude of the interelement correlation is the key parameter governing phase correction performance. >
135 citations
TL;DR: In this article, a transducer is fabricated by bonding a malleable backing layer onto a thin plate of PZT and then pressing the plate into a spherically shaped well.
Abstract: Difficulty in obtaining well focused efficient ultrasound transducers has limited the development of new high frequency applications of B-mode imaging. This paper describes a method for fabricating high frequency (53 MHz) spherically focused lead zirconate titanate (PZT) transducers. A transducer is fabricated by bonding a malleable backing layer onto a thin plate of PZT and then pressing the plate into a spherically shaped well. The backing layer evenly distributes stresses across the material when it is pressed into the well. Local concentrations of stress which lead to fracture are avoided and the material can be deformed without macroscopic cracking. The characteristics of a 2 mm diameter 53 MHz PZT transducer with a 4 mm focal length are described. A lateral beam width of 68 /spl mu/m and a 12 dB depth of field of 1.5 mm were obtained. The minimum two-way insertion loss of the system was /spl minus/25 dB and the 6 dB bandwidth of the pulse echo response was 30%. An image of a resolution phantom and an in vivo skin image illustrate the excellent imaging characteristics of the transducer. >
134 citations
TL;DR: In this paper, the Cramer-Rao lower bound was applied to derive analytical expressions which predict the magnitude of jitter for 1-D and 2-D problems using both radio frequency (RF) and envelope detected data.
Abstract: Cross correlation and similar operations are used in ultrasonic imaging to estimate blood or soft tissue motion in one or more dimensions and to measure echo arrival time differences for phase aberration correction. These estimates are subject to large errors known as false peaks and smaller magnitude errors known as jitter. While false peaks can sometimes be removed through nonlinear processing, jitter errors place a fundamental limit on the performance of delay estimation techniques. This paper applies the Cramer-Rao Lower Bound to derive analytical expressions which predict the magnitude of jitter for 1-D and 2-D problems using both radio frequency (RF) and envelope detected data. One-dimensional simulation results are presented which closely match theoretical predictions. These results indicate that for typical clinical conditions axial jitter for detected data is approximately five times greater than that for RF data. Lateral jitter is approximately ten times greater than axial jitter for RF data. Examples are presented which utilize these results to predict the performance of phase aberration correction and flow estimation systems. >
130 citations
TL;DR: The mechanically free open-circuited and short- circuited surface wave boundary value problems for piezoelectrics are formulated using the matrix method and illustrative numerical examples for the PSAW's reveals that low-loss orientations are quite sensitive to material constant values.
Abstract: Pseudo-surface-waves (PSAW's), or leaky SAW's, were first recognized over 25 years ago and the phase velocity (v/sub p/) and attenuation per wavelength (/spl alpha//spl lambda/) of PSAW modes for nonpiezoelectrics were calculated soon after. Since the seventies progress has been made in exploiting the higher velocities and electromechanical coupling constants (K/sup 2/=2/spl Delta/v/v) achievable with PSAW's for piezoelectric device applications; this has stimulated new interest in the search for piezoelectric materials with orientations which have low /spl alpha//spl lambda/, high K/sup 2/, high v/sub p/. Procedures for calculating the PSAW properties (v/sub p/, /spl alpha//spl lambda/, and K/sup 2/) are not very explicitly given. In light of the preceding we present in this paper a review of the basic features of SAW and Pseudo-SAW's using the matrix method. In this paper: the mechanically free open-circuited and short-circuited surface wave boundary value problems for piezoelectrics are formulated using the matrix method; two types of modes (SAW and PSAW) are described; and a number of computationally simple, frequency independent analytical functions are derived, from which /spl alpha//spl lambda/, v/sub p/, and K/sup 2/ are calculated for any direction on any material plane using commercially available PC software. The relationship of these functions to the effective permittivity concept, favoured by many researchers, is demonstrated and illustrative numerical examples for the PSAW's reveals that low-loss orientations are quite sensitive to material constant values. >
TL;DR: A fast and simple method to estimate small time delays in narrowband signals is proposed, based on using the Hilbert transform in correlation between two signals and consists of only one scalar product, which makes it fast.
Abstract: In many areas the time delay of arrival (TDOA) is desired. In the case of narrowband signals we propose a fast and simple method to estimate small time delays. This method is shown to have the same or better accuracy as the cross correlation methods for small delays in the order of fractions of the sample interval. It is based on using the Hilbert transform in correlation between two signals and consists of only one scalar product, which makes it fast. It may also be used in applications with narrowband signals where the measurements are repeatable, such as ultrasonic imaging and nondestructive testing. In ultrasonic applications, due to fluctuations in the insonified media, a small random time shift may be present causing the signals to be misaligned in time. Averaging signals under these conditions will result in a distortion of the signal shape. We propose an averaging method to avoid this and to accomplish a higher SNR without the distortion. Simulations and experiments from ultrasonic applications are presented. >
TL;DR: Results indicate that the density function of the envelope can be modeled by the K-distribution and the parameters of the K -distribution can provide information on the nature of the scattering region in terms of the number as well as the scattering cross sections of the scatterers.
Abstract: The statistics of the envelope of the backscattered signal from tissues have been known to vary from the well-known Rayleigh model. The K-distribution is used to model this non-Rayleigh behavior, since the generalized K-distribution encompasses a wide range of distributions like Rayleigh, Lognormal, and Rician. Computer simulations were conducted using a simple one-dimensional discrete scattering model to investigate the properties of the echo envelope. Significant departures from Rayleigh statistics were seen as the scattering cross sections of the scatterers became random. The validity of this model was also tested using data from tissue mimicking phantoms. Results indicate that the density function of the envelope can be modeled by the K-distribution and the parameters of the K-distribution can provide information on the nature of the scattering region in terms of the number as well as the scattering cross sections of the scatterers. >
TL;DR: In this article, the authors present a literature review concerning the existing use of stress waves for the nondestructive evaluation of concrete and present new approaches that have been successful in applications to advanced engineering materials other than concrete, where appropriate, potential benefits and pitfalls of each new technique, as applied to concrete, are discussed.
Abstract: The goal of this paper is to develop an understanding of the current state of ultrasonic nondestructive evaluation in the concrete community. Methods supplemental to the less than satisfactory procedure specified in ASTM C-597 are discussed. It is hoped that such an understanding, in conjunction with a feeling for the nature of reinforced concrete as a material, will promote research interest in this important field. Following an introductory problem statement, a literature review concerning the existing use of stress waves for the nondestructive evaluation of concrete is presented. An examination of current practice is offered. Next, new approaches are selected and reviewed from the current literature. In all cases, these are approaches that have been successful in applications to advanced engineering materials other than concrete. Where appropriate, potential benefits and pitfalls of each new technique, as applied to concrete, are discussed. >
TL;DR: In this paper, an echographic image formation model is used to study the motion artifact produced by a rotating phantom and observed by a linear scan imaging system with a Gaussian beam.
Abstract: Speckle patterns in ultrasound images may move in a way which bears no simple relationship to the motion of the corresponding tissues. In some instances the speckle motion replicates the underlying tissue motion, in others it does not. The authors name "speckle motion artifact" the difference between the speckle and the underlying tissue motion. An echographic image formation model is used to study the motion artifact produced by a rotating phantom and observed by a linear scan imaging system with a Gaussian beam. The authors propose that when the tissue is modeled as a random array of small and numerous scatterers, such motion aberration be accounted for by the 2D phase characteristics of the imaging system. An analytic prediction of this motion artifact in relation to the imaging system characteristics (beam width, transducer frequency, pulse duration) is presented. It is shown that the artifact results from the curvature of the system point spread function, which in turn determines the curvature of the 2D phase characteristics. To the authors' knowledge, it is the first time a comprehensive model of ultrasonic speckle motion artifact is presented. The model has been developed to study rotation-induced artifact; the method is however quite general and can be extended to study the effects of other tissue motion, in particular deformation and shear. >
TL;DR: The feasibility of steering limited diffraction beams with a two-dimensional array is studied, and it is shown that there will be almost no distortion of beams if the effective aperture reduction of the array is properly compensated so that the beams have a constant transverse profile as they are steered.
Abstract: The newly developed limited diffraction beams such as the Bessel beams and X waves have a large depth of field and approximate depth-independent property. They have possible applications in medical imaging, color Doppler imaging, tissue characterization, and nondestructive evaluation of materials, and in other wave related physical branches such as electromagnetics and optics. However, limited diffraction beams are currently produced with an annular array transducer that has to be steered mechanically. In this paper, we study the feasibility of steering these beams with a two-dimensional array, and show that there will be almost no distortion of beams if the effective aperture reduction of the array is properly compensated so that the beams have a constant transverse profile as they are steered. In addition, methods for reducing the complexity of the electronic multiplexing of the array elements are proposed. We also investigate the influences of the interelement distance and the size of array elements on the sidelobes and grating lobes of limited diffraction beams as the beams are steered. They are similar to those previously reported for conventional beams. >
TL;DR: In this article, a model for the signal in a multigated pulsed wave Doppler system is presented, which describes the relation between a general time-variable velocity field and the signal correlation in space and time, including the effect of movement of the ultrasonic beam for color flow imaging systems with mechanical scanning.
Abstract: A review of the scattering theory for moving blood, and a model for the signal in a multigated pulsed wave Doppler system is presented. The model describes the relation between a general time-variable velocity field and the signal correlation in space and time, including the effect of movement of the ultrasonic beam for color flow imaging systems with mechanical scanning. In the case of a constant and rectilinear velocity field, a parametric model for the autocorrelation function is deduced. General formulas for a full second order characterization of the set of autocorrelation estimates, with arbitrary lags in the spatial and temporal directions, are developed. The formulas are applied to the parametric model, and numerical results for the estimator variance are presented. A qualitative evaluation of the theoretical results has been performed by offline-processing of 2-D Doppler signals from a color flow imaging scanner. The benefit of spatial and temporal averaging is demonstrated by using different averaging filters to the same set of recorded data. >
TL;DR: In this article, a theoretical comparison of three generic sampled aperture ultrasonic imaging systems for nondestructive evaluation is presented, and the imaging systems are categorized according to their source-receiver combination for data acquisition: common-source, back-scatter and full-array imaging.
Abstract: This paper presents a theoretical comparison of three generic sampled aperture ultrasonic imaging systems for nondestructive evaluation. The imaging systems are categorized according to their source-receiver combination for data acquisition: common-source, back-scatter, and full-array imaging. First, forward modeling is performed for a point source and a point receiver. This is then used to model the received data set for each of the imaging categories. Subsequently, the inversion algorithm for each category is derived, and their performance is evaluated in terms of resolution, noise, and computation. We show that in terms of resolution, back-scatter imaging is the best, followed by full-array and common-source imaging. However, in terms of material noise, full-array imaging is the best, with back-scatter and common-source imaging having the same material noise response. Full-array imaging is the only system with inherent redundancy to reduce electronic noise, but at the expense of significantly more computation. The physical transducer is in the full-array category, allowing mechanical scanning to be traded for dynamic focusing and computational power. >
TL;DR: A physical parameter, composed of acoustic velocity, piezoelectric coupling, and /spl tau//sub 1/ is identified which aids in understanding the maximum frequency limitations of plate resonators.
Abstract: In order to compare piezoelectric materials and devices, an intrinsic parameter, the motional time constant /spl tau//sub 1//sup (m/)=(/spl omega//sub m/Q/sub m/)/sup -1/ for a particular mode m is employed. The use of /spl tau//sub 1//sup (m/) follows from the accommodation of acoustic loss in the elastic compliance/stiffness and the establishment of material coefficients that are elements of viscosity matrices. Alternative and fully equivalent definitions of /spl tau//sub 1/ are given based on the RC time constant derived from the equivalent circuit representation of a crystal resonator, acoustic attenuation, logarithmic decrement, and viscosity or damping. For quartz devices, the variation of /spl tau//sub 1/: for any simple thickness mode, for the Y'X shear mode for rotated Y-cuts, and with diameter-thickness ratio for AT-cuts is discussed. Other factors such as mounting loss and loss caused by crystal inhomogeneities (dislocations, defect positions in the resonator, and impurity migration under vibrational stress) are briefly considered with quartz devices as the model. Some new piezoelectric materials/material constants/devices are reviewed and their motional time constants are compared. A physical parameter, composed of acoustic velocity, piezoelectric coupling, and /spl tau//sub 1/ is identified which aids in understanding the maximum frequency limitations of plate resonators. >
TL;DR: In this paper, an alternative method of modeling transducers using network theory is described, based on a measurement of the transducers impedance in water and the pulse-echo response of the system for a given electrical source and load.
Abstract: Obtaining an accurate transducer model for a high-frequency transducer can be troublesome using traditional models, such as the KLM model, since it is often difficult to measure precisely the piezoelectric, dielectric, and mechanical properties of the transducer. This paper describes an alternative method of modeling transducers using network theory. The network theory model for a transducer is determined from a measurement of the transducer impedance in water and the pulse-echo response of the system for a given electrical source and load. A discussion of how this model can be used to optimize the design of an electrical matching circuit is given. This method is illustrated by designing a two-element transmission line matching circuit for a miniature 53 MHz transducer. Excellent agreement between the network model prediction and the experimental response is obtained. >
TL;DR: In this article, the quasi-static coupling coefficients for electrostrictive ceramics are computed analytically based on a three-dimensional constitutive relation that models both electrostriction and nonlinear dielectric behaviors.
Abstract: The quasi-static coupling coefficients, k/sub 13/ and k/sub 33/, for electrostrictive ceramics are computed analytically. The calculation is based on a three-dimensional constitutive relation that models both electrostriction and nonlinear dielectric behaviors. The results show that the coupling factors depend on the amplitudes of the applied ac field and the dc bias, as well as the mechanical prestress. For an actuator without bias voltage or prestress, the coupling coefficients approach an asymptotic value with increasing electric field. The primary coefficients, k/sub 13/ and k/sub 33/, for a lead magnesium niobate, Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/BaTiO/sub 3/(PMN-PT-BT), based relaxor ferroelectric are computed as an example. The results show that the coupling coefficients for PMN-PT-BT materials are roughly comparable with those of existing piezoelectrics. These coefficients are important parameters for material section and power source design for transducer devices. >
TL;DR: In this article, a technique for estimating the total velocity vector, using only two transducers, is described, making use of the fact that the bandwidth of a Doppler spectrum has been shown to be proportional to the velocity component normal to the sound beam.
Abstract: Current ultrasonic blood flow measurement systems estimate only that component of flow which is parallel to the incident ultrasound beam. This is done by relating the mean backscattered frequency shift to the axial velocity component through the classical Doppler equation. A number of ultrasonic techniques for estimating the two-dimensional (2D) blood velocity vector have been published, both Doppler and non-Doppler. Several three-dimensional (3D) blood velocity vector techniques have also been proposed, all of which require a multiplicity of transducers or lines of sight. Here a technique is described for estimating the total velocity vector, using only two transducers. This is achieved by measuring not only the frequency shifts but also the bandwidths of the backscattered spectra, making use of the fact that the bandwidth of a Doppler spectrum has been shown to be proportional to the velocity component normal to the sound beam. Partial experimental verification of the proposed vector flow estimation scheme is demonstrated by using a constant velocity thread phantom. >
TL;DR: In this paper, a simple model for B-mode image formation in diagnostic ultrasound is presented, which is used to give a general description of the effects which scattering ultrasound contrast agents have on B- or M-mode images, as long as linear propagation of ultrasound is prevailing.
Abstract: A simple model for B-mode image formation in diagnostic ultrasound is presented. It is used to give a general description of the effects, which scattering ultrasound contrast agents have on B- or M-mode images, as long as linear propagation of ultrasound is prevailing. The results of the model calculations are illustrated for the case of a homogeneous medium. It turns out that acoustical shadowing is limiting the maximum attainable backscatter enhancement. This becomes obvious when the model is also applied to the slightly more complicated case of cardiac and especially myocardial (or tissue) contrast. Conditions for optimum enhancement are derived for a number of typical diagnostic situations. Some possible pitfalls, which may prevent good results, are also called to attention. Microbubble suspensions are discussed as an important special example for contrast agents. In this case, the limits of the linear range can be estimated from the acoustically driven pulsations of a microbubble in a viscous fluid. The properties of contrast agents in the linear range described here should also provide a basis for later discussion of their nonlinear properties, which may help to overcome limitations imposed on tissue contrast in the linear range. >
TL;DR: In this article, a general technique for analyzing layered piezoelectric resonators under thickness and lateral field excitation is presented and applied to the study of zinc oxide on silicon thin film resonators.
Abstract: Exact analysis of the propagation of acoustic waves in multilayered piezoelectric plates is performed using the transfer matrix method. A general technique for analyzing layered piezoelectric resonators under thickness and lateral field excitation is presented and is applied to the study of zinc oxide on silicon thin film resonators. Both one and two-dimensional analysis with general material anisotropy is performed, and a simplified method for incorporating thin conducting electrodes on the plate's free surfaces is presented. The general methodology described is summarized into efficient algorithms to aid in the implementation of the procedures and some computational aspects are discussed. Results are presented for cutoff behavior as well as general dispersion characteristics for two and three layered plates. >
TL;DR: A Taylor series based adaptive dynamic focusing method for phased arrays based on a set of discrete hydrophones array measurements is described, which does not require any prior knowledge of the applicator geometry and all the parameters needed for correction can be measured directly at the hydrophone array sensor locations.
Abstract: A prototype 16-element needle hydrophone array has been designed, fabricated and characterized. The primary use of this array is to provide acoustic feedback during ultrasound hyperthermia treatments. This feedback can be used to compensate for patient motion and tissue inhomogeneities by controlling the phased array driving patterns. It can also be used in adaptive dynamic focusing, a procedure which enables the phased array to focus at points away from specified control points. The hydrophone array consists of a PVDF sheet, which covers a silicon substrate carrier that contains the signal electrodes of the individual acoustic sensors. A complete description of the hydrophone array and its characteristics is given in this paper. The aberration correction and motion compensation algorithms are also described, and some experimental results are shown. Finally, a Taylor series based adaptive dynamic focusing method for phased arrays based on a set of discrete hydrophone array measurements is described. This algorithm does not require any prior knowledge of the applicator geometry and all the parameters needed for correction can be measured directly at the hydrophone array sensor locations. >
TL;DR: In ultrasound hyperthermia, focal patterns generated by phased arrays can be degraded by phase errors due to tissue inhomogeneities, digitization of the driving signals, and imperfect fabrication of the transducers as discussed by the authors.
Abstract: In ultrasound hyperthermia, focal patterns generated by phased arrays can be degraded by phase errors due to tissue inhomogeneities, digitization of the driving signals, and imperfect fabrication of the transducers. The degree of degradation depends on the severity of phase aberrations. As predicted by simulation and verified by experimental results, focal degradation scales with the circular variance of phase errors. However, degraded power deposition patterns can be significantly improved after phase aberration correction, especially where patterns are complicated and the aberrations are severe. Also, as shown in motion compensation experiments, an aberration corrected pattern can be particularly sensitive to aberrator movement greater than the correlation length of the aberrator. After motion compensation, new sharply focused patterns can be accomplished, thus reducing the unwanted influence of "body" movement by stabilizing the positions of foci with respect to patient anatomy. >
TL;DR: In this article, the authors summarized the measurement data processed during 1990 and 1991 for real-time B-mode and M-mode, general pulsed Doppler, peripheral vascular (PV) pulsed doppler and color flow Dopplers.
Abstract: As part of the section 510(k) requirements of the 1976 Medical Device Amendments to the Federal Food, Drug, and Cosmetic Act, manufacturers of diagnostic ultrasound devices submit acoustic output data to the U.S. Food and Drug Administration. Because this information is pertinent to the assessment of any potential bioeffects due to ultrasound exposure, we have summarized the measurement data processed during 1990 and 1991. Exposure data were summarized for real-time B-mode and M-mode, general pulsed Doppler, peripheral vascular (PV) pulsed Doppler, and color flow Doppler. Exposure quantities included peak rarefactional and compressional pressures, spatial-peak pulse-average and spatial-peak temporal-average intensities (both water and derated values), and power. Also, where data permitted, mechanical and thermal indices were calculated. Ranges, means, medians, and standard deviations were categorized for the exposure quantities and indices. In general the temporal-average values (including indices) were higher in Doppler modes than in B/M imaging modes. Differences among the temporal-peak exposure quantities and indices were less distinct, although values tended to be higher in the PV and color flow Doppler categories. These data, along with comparable results collected by others, provide a means to relate the output of current devices to levels of exposure relevant to ultrasound induced biological effects. >
TL;DR: In this article, the non-Gaussian and non-Rayleigh properties of ultrasound echo signals are derived for the case of a pulsed transducer insonifying a medium containing randomly distributed scatterers.
Abstract: Parameters expressing the non-Gaussian and the non-Rayleigh properties of ultrasound echo signals are derived for the case of a pulsed transducer insonifying a medium containing randomly distributed scatterers. Both parameters depend on the measurement system, including the transducer field and pulse frequency content, as well as on the medium's properties. The latter is expressed in terms of the number of scatterers per unit volume and the second and fourth moments of the medium's scattering functions. A simple relationship between the parameters describing the non-Gaussian and non-Rayleigh properties is derived and verified experimentally. >
TL;DR: In this article, a volume flow estimate is made by assuming a circularly symmetric velocity field and integrating the velocity profile measured along a diameter, where the many velocity measurements made contribute to higher precision in the integrated velocity estimate.
Abstract: The direct measurement of the velocity profile of blood flowing in a vessel yields a volume flow estimate that is more accurate than single-point Doppler ultrasound. A volume flow estimate is made by assuming a circularly symmetric velocity field and integrating the velocity profile measured along a diameter. The many velocity measurements made contribute to higher precision in the integrated velocity estimate. Also, the velocity profile furnishes the functional diameter of the vessel at many points through the cardiac cycle. This algorithm, as implemented on the Philips CVI system, was tested theoretically by numerical modelling, and experimentally with a flow simulator. The effect of beamwidth, vessel size, and measurement position misalignment on the volume flow estimate were studied. Experimental and theoretical results agreed well and showed that the flow estimation algorithm can produce precise and accurate volume flow estimates. The flow estimate is sensitive to the flow angle and is inaccurate by 5% per degree error in the angle. Beamwidths of 1.0 to 1.5 mm are a good match to axial resolution and yield accurate volume flow estimates in vessels over 2 mm in diameter. Larger beamwidths give lower volume flow estimates, but are not as sensitive to misalignment. >
TL;DR: In this paper, a pulsed laser has been used to generate ultrasonic transients in samples of metal and fiber-reinforced polymer composite material using an air-coupled piezoelectric transducer.
Abstract: A pulsed laser has been used to generate ultrasonic transients in samples of metal and fiber-reinforced polymer composite material. These have been detected using an air-coupled piezoelectric transducer. It is demonstrated that such a transduction system can be used for longitudinal waves in bulk material, Rayleigh waves at solid surfaces and Lamb waves in thin plates. >