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Showing papers in "IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control in 1995"


Journal ArticleDOI
TL;DR: This paper presents a review of the main developments of the matrix techniques, and their use in response and modal models, with emphasis on ultrasonics applications.
Abstract: Research into ultrasonic NDE techniques for the inspection of multilayered structures relies strongly on the use of modeling tools which calculate dispersion curves and reflection and transmission spectra. These predictions are essential to enable the best inspection strategies to be identified and their sensitivities to be evaluated. General purpose multilayer modeling tools may be developed from a number of matrix formulations which have evolved in the latter half of this century and there is now a formidable number of publications on the subject. This paper presents a review of the main developments of the matrix techniques, and their use in response and modal models, with emphasis on ultrasonics applications. >

931 citations


Journal ArticleDOI
TL;DR: Multi-element synthetic aperture imaging methods suitable for applications with severe cost and size limitations are explored in this article, where each method uses different spatial frequencies and acquisition strategies for imaging, and therefore different sets of active transmit/receive element combinations.
Abstract: Multi-element synthetic aperture imaging methods suitable for applications with severe cost and size limitations are explored. Array apertures are synthesized using an active multi-element receive subaperture and a multi-element transmit subaperture defocused to emulate a single-element spatial response with high acoustic power. Echo signals are recorded independently by individual elements of the receive subaperture. Each method uses different spatial frequencies and acquisition strategies for imaging, and therefore different sets of active transmit/receive element combinations. Following acquisition, image points are reconstructed using the complete data set with full dynamic focus on both transmit and receive. Various factors affecting image quality have been evaluated and compared to conventional imagers through measurements with a 3.5 MHz, 128-element transducer array on different gel phantoms. Multielement synthetic aperture methods achieve higher electronic signal to noise ratio and better contrast resolution than conventional synthetic aperture techniques, approaching conventional phased array performance. >

595 citations


Journal ArticleDOI
TL;DR: In this paper, the authors apply the Cramer-Rao Lower Bound to derive an analytical expression which predicts the magnitude of jitter errors incurred when estimating delays using radio frequency (RF) data from speckle targets.
Abstract: Delay estimation is used in ultrasonic imaging to estimate blood or soft tissue motion, to measure echo arrival time differences for phase aberration correction, and to estimate displacement for tissue elasticity measurements. In each of these applications delay estimation is performed using speckle signals which are at least partially decorrelated relative to one another. Delay estimates which utilize such data 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. The authors apply the Cramer-Rao Lower Bound to derive an analytical expression which predicts the magnitude of jitter errors incurred when estimating delays using radio frequency (RF) data from speckle targets. The analytical expression presented includes the effects of signal decorrelation due to physical processes, corruption by electronic noise, and a number of other factors. Simulation results are presented which show that the performance of the normalized cross correlation algorithm closely matches theoretical predictions. These results indicate that for poor signal to noise ratios (0 dB) a small improvement in signal to noise ratio can dramatically reduce jitter magnitude. At high signal to noise ratios (30 dB) small amounts of signal decorrelation can significantly increase the magnitude of jitter errors. >

512 citations


Journal ArticleDOI
TL;DR: In this article, a 2D autocorrelator is proposed to estimate axial velocity values by evaluating the Doppler equation using explicit estimates of both the mean DoP and the mean RF frequency at each range gate location.
Abstract: This paper introduces a new velocity estimator, referred to as the 2D autocorrelator, which differs from conventional Doppler techniques in two respects: the derivation of axial velocity values by evaluating the Doppler equation using explicit estimates of both the mean Doppler and the mean RF frequency at each range gate location; and, the 2D nature (depth samples versus pulse transmissions) of processing within the range gate. The estimator's output can be calculated by evaluating the 2D autocorrelation function of the demodulated (baseband) backscattered echoes at two lags. A full derivation and mathematical description of the estimator is presented, based on the framework of the 2D Fourier transform. The same framework is adopted to analyze two other established velocity estimators (the conventional 1D autocorrelator and the crosscorrelator) in a unifying manner, and theoretical arguments as well as experimental results are used to highlight the common aspects of all three estimators. In addition, a thorough performance evaluation is carried out by means of extensive simulations, which document the effect of a number of factors (velocity spread, range gate length, ensemble length, noise level, transmitted bandwidth) and provide an insight into the optimum parameters and trade-offs associated with individual algorithms. Overall, the 2D autocorrelator is shown to offer the best performance in the context of the specific simulation conditions considered here. Its superiority over the crosscorrelator is restricted to cases of low signal-to-noise ratios. However, the 2D autocorrelator always outperforms the conventional 1D autocorrelator by a significant margin. These comparisons, when linked to the computational requirements of the proposed estimator, suggest that it combines the generally higher performance of 2D broadband time-domain techniques with the relatively modest complexity of 1D narrowband phase-domain velocity estimators. >

481 citations


Journal ArticleDOI
TL;DR: In this article, the Rayleigh-Ritz assumed mode energy method is used to model the distributed piezoceramics and the traveling wave dynamics of the stator.
Abstract: A piezoelectric rotary ultrasonic motor is modeled for the purpose of predicting, a priori, motor performance as a function of design parameters. The Rayleigh-Ritz assumed mode energy method is used to model the distributed piezoceramics and the traveling wave dynamics of the stator. Natural frequencies and modeshapes are obtained for a generally configured motor. Nonlinear normal and tangential interface forces between the rotor and stator are incorporated into the forcing function along with the linear piezoelectric forcing. Given the applied torque, applied axial loading, and piezo drive voltages as inputs to the model, general motor performance measures are obtained-namely speed, input power, output power, and efficiency. The approach presented here provides a general framework for modeling these motors as well as a design tool for optimizing prototypes with the added flexibility of allowing for a wide variety of geometries and materials. >

335 citations


Journal ArticleDOI
TL;DR: Air-coupled capacitance transducers have been manufactured using anisotropic etched silicon backplates and commercially available dielectric films (Kapton and Mylar) as discussed by the authors.
Abstract: Air-coupled capacitance transducers have been manufactured using anisotropically etched silicon backplates and commercially available dielectric films (Kapton and Mylar). The small backplate pits which result from etching, provide well ordered and highly uniform air layers between the backplate surface and thin dielectric film. Such uniformity allows the transducers to be manufactured with reproducible characteristics (a property difficult to achieve through conventional manufacturing). Impulse response studies in generation and detection, have indicated well-damped, wideband behavior, with bandwidths extending from >

284 citations


Journal ArticleDOI
TL;DR: In this article, the elastic modulus of soft tissue based on ultrasonic displacement and strain images is reconstructed using a hybrid reconstruction procedure based on numerical solution of the partial differential equations describing mechanical equilibrium of a deformed medium.
Abstract: A method is presented to reconstruct the elastic modulus of soft tissue based on ultrasonic displacement and strain images. Incompressible and compressible media are considered separately. Problems arising with this method, as well as applications to real measurements on gel-based, tissue equivalent phantoms, are given. Results show that artifacts present in strain images can be greatly reduced using a hybrid reconstruction procedure based on numerical solution of the partial differential equations describing mechanical equilibrium of a deformed medium. >

283 citations


Journal ArticleDOI
TL;DR: In this article, a theoretical analysis of the SAW properties of layered structures consisting of a piezoelectric material layer, a diamond layer and a substrate were examined by theoretical calculation, and it was shown that a SiO/sub 2/ZnO/diamond/Si structure with a high phase velocity of 8,000-9,000 m/s and a large electro-mechanical coupling coefficient of up to 4%.
Abstract: Diamond has the highest surface acoustic wave (SAW) velocity among all materials and thus can provide much advantage for fabrication of high frequency SAW devices when it is combined with a piezoelectric thin film. Basic SAW properties of layered structures consisting of a piezoelectric material layer, a diamond layer and a substrate were examined by theoretical calculation. Rayleigh mode SAW's with large SAW velocities up to 12,000 m/s and large electro-mechanical coupling coefficients from 1 to 11% were found to propagate in ZnO/diamond/Si, LiNbO/sub 3//diamond/Si and LiTaO/sub 3//diamond/Si structures. It was also found that a SiO/sub 2//ZnO/diamond/Si structure can realize a zero temperature coefficient of frequency with a high phase velocity of 8,000-9,000 m/s and a large electro-mechanical coupling coefficient of up to 4%. >

201 citations


Journal ArticleDOI
TL;DR: In this article, a 2D autocorrelator and its Doppler power estimation counterpart were evaluated in the context of ultrasound color flow mapping, and the results of the in vitro evaluation show that the proposed 2D-autocorrelation form of processing is consistently better than the corresponding 1D-based techniques, in terms of both velocity and power estimation.
Abstract: This paper evaluates experimentally the performance of a novel axial velocity estimator, the 2D autocorrelator, and its Doppler power estimation counterpart, the 2D zero-lag autocorrelator, in the context of ultrasound color flow mapping. The evaluation also encompasses the well-established 1D autocorrelation technique for velocity estimation and its corresponding power estimator (1D zero-lag autocorrelator), to allow performance comparisons under identical conditions. Clutter-suppressed in vitro data sets from a steady-flow system are used to document the effect of the range gate and ensemble length, noise level and angle of insonation on the precision of the velocity estimates. The same data sets are used to examine issues related to the estimation of the Doppler signal's power. The first-order statistics of power estimates from regions corresponding to flow and noise are determined experimentally and the ability of power-based thresholding to separate flow signals from noise is characterized by means of ROC analysis. In summary, the results of the in vitro evaluation show that the proposed 2D-autocorrelation form of processing is consistently better than the corresponding 1D-autocorrelation techniques, in terms of both velocity and power estimation. Therefore, given their relatively modest implementation requirements, the 2D-autocorrelation algorithms for velocity and power estimation appear to represent a superior, yet realistic, alternative to conventional Doppler processing for color flow mapping. >

182 citations


Journal ArticleDOI
TL;DR: Two-dimensional homomorphic deconvolution produced substantial improvement in the resolution of B-mode images of a tissue-mimicking phantom in vitro and of several human tissues in vivo.
Abstract: Describes how two-dimensional (2D) homomorphic deconvolution can be used to improve the lateral and radial resolution of medical ultrasound images recorded by a sector scanner. The recorded radio frequency ultrasound image in polar coordinates is considered as a 2D sequence of angle and depth convolved with a 2D space invariant point-spread function (PSF). Each polar coordinate sequence is transformed into the 2D complex cepstrum domain using the fast Fourier transform for Cartesian coordinates. The low-angle and low-depth portion of this sequence is taken as an estimate of the complex cepstrum representation of the PSF. It is transformed back to the Fourier frequency domain and is used to compute the deconvolved angle and depth sequence by 2D Wiener filtering. Two-dimensional homomorphic deconvolution produced substantial improvement in the resolution of B-mode images of a tissue-mimicking phantom in vitro and of several human tissues in vivo. It was better than lateral or radial homomorphic deconvolution alone, and better than 2D Wiener filtering with a PSF recorded in vitro. >

156 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show that the second harmonic signal produced by Albunex is significant and that harmonic images in which backscattered echoes from solid tissues were filtered out, but not those from albunex, can be obtained.
Abstract: Gaseous ultrasound contrast agents, such as Albunex, have been shown to be valuable clinically for the better identification of certain anatomic structures and for quantitating organ perfusion. However, the application of a contrast agent sometimes also reduces the image contrast between the blood and the surrounding tissues. This paper presents experimental results to show that this problem may be alleviated by using harmonic signals generated by nonlinear backscattering of these microbubbles. The results show that the second harmonic signal produced by Albunex is significant and that harmonic images in which backscattered echoes from solid tissues were filtered out, but not those from Albunex, can be obtained. In addition, a continuous wave Doppler arrangement has been implemented. It permits quantitative harmonic Doppler measurements at different frequencies, concentrations, and transmitted acoustic pressures. When Albunex was compared to polystyrene microsphere suspensions which possess exclusively linear behavior, Doppler power at second and subharmonic frequencies could only be detected from these microbubbles. A comparison of results on Doppler powers measured at the first harmonic from polystyrene spheres and Albunex indicates that at a transmitting frequency of 2.5 MHz, the Doppler power from Albunex is 12 dB stronger than the polystyrene spheres, whereas at 5 MHz, the Doppler power from Albunex is 3 dB weaker than that from the polystyrene spheres.

Journal ArticleDOI
TL;DR: In this paper, a blind deconvolution method was proposed to identify and remove the convolutional distortion in order to reconstruct the tissue response, thus enhancing the diagnostic quality of the ultrasonic image.
Abstract: We address the problem of improving the spatial resolution of ulrasound images through blind deconvolution. The ultrasound image formation process in the RF domain can be expressed as a spatio-temporal convolution between the tissue response and the ultrasonic system response, plus additive noise. Convolutional components of the dispersive attenuation and aberrations introduced by propagating through the object being imaged are also incorporated in the ultrasonic system response. Our goal is to identify and remove the convolutional distortion in order to reconstruct the tissue response, thus enhancing the diagnostic quality of the ultrasonic image. Under the assumption of an independent, identically distributed, zero-mean, non-Gaussian tissue response, we were able to estimate distortion kernels using bicepstrum operations on RF data. Separate 1D distortion kernels were estimated corresponding to axial and lateral image lines and used in the deconvolution process. The estimated axial kernels showed similarities to the experimentally measured pulse-echo wavelet of the imaging system. Deconvolution results from B-scan images obtained with clinical imaging equipment showed a 2.5-5.2 times gain in lateral resolution, where the definition of the resolution has been based on the width of the autocovariance function of the image. The gain in axial resolution was found to be between 1.5 and 1.9.

Journal ArticleDOI
TL;DR: The concept of thermal dose as a predictor for the size of the necrosed tissue volume during high-intensity focussed ultrasound surgery was tested and the model was found to predict well the trends of increasing power and pulse duration.
Abstract: The concept of thermal dose as a predictor for the size of the necrosed tissue volume during high-intensity focussed ultrasound surgery was tested. The sensitivity of the predicted lesion size to the uncertainties in the iso-dose constant, attenuation coefficient, and thermal dose threshold of necrosis was studied. The predicted lesion size appears to be independent of attenuation at some high attenuation values and certain depth in tissue. Thus, for a given target depth, a proper selection of frequency could minimize the lesion size variability due to uncertainty in the tissue attenuation. The predicted lesion size was less dependent on the uncertainties in the iso-dose constant and thermal dose of necrosis. The predictions of the model were compared with experimental data in rabbit muscle, and experimental data in cat and rat brain measured by others. The agreement was found to be good in most of the experiments. Similarly, the model was found to predict well the trends of increasing power and pulse duration. >

Journal ArticleDOI
TL;DR: In this paper, the frequency instabilities of precision bulk acoustic wave (BAW) quartz crystal oscillators are reviewed and the fundamental limits on the achievable frequency stabilities and the degree to which fundamental limits have been approached to date are examined.
Abstract: The frequency instabilities of precision bulk acoustic wave (BAW) quartz crystal oscillators are reviewed. The fundamental limits on the achievable frequency stabilities, and the degree to which the fundamental limits have been approached to date are examined. Included are the instabilities as a function of time, temperature, acceleration, ionizing radiation, electromagnetic fields, humidity, atmospheric pressure, power supply, and load impedance. Most of the fundamental limits are zero or negligibly small, a few are finite. We speculate about the progress which may be achievable in the future with respect to approaching the fundamental limits. Suggestions are provided about the paths that may lead to significant stability improvements. >

Journal ArticleDOI
TL;DR: A tutorial synopsis of the piezoelectric effect is presented in the context of its history, traditional uses, and relation to crystal symmetry as mentioned in this paper, and future prospects, particularly in the area of microelectromechanical systems/structures (MEMS) are discussed.
Abstract: A tutorial synopsis of the piezoelectric effect is presented in the context of its history, traditional uses, and relation to crystal symmetry. Associated effects are briefly noted. Future prospects, particularly in the area of microelectromechanical systems/structures (MEMS) are discussed. >

Journal ArticleDOI
TL;DR: Regression filters were found to offer significantly better performance than step-initialized IIR filters under heavy clutter conditions and, given their steeper roll-off, appear to be more effective clutter suppressors for power Doppler imaging.
Abstract: One of the major issues in color Doppler ultrasound is the suppression of clutter that arises from stationary or slowly moving tissue. If not adequately suppressed, clutter can severely affect the ability of color Doppler systems to accurately estimate the Doppler mean frequency and power of blood, resulting in a potentially misleading depiction of flow. In this study, the performances of two classes of clutter suppression techniques-step-initialized infinite impulse response (IIR) and regression filters-were evaluated and compared by means of extensive simulations. The performance indicators used were the accuracy and precision of the mean frequency and the power estimates after clutter filtering. In summary, the ability of both filter classes to suppress clutter was found to vary considerably depending on factors such as the clutter-to-flow-signal ratio and the ensemble length. In particular, the performance of step-initialized IIR filters was shown to be noticeably inferior to that predicted by their steady-state response. Regression filters were found to offer significantly better performance than step-initialized IIR filters under heavy clutter conditions and, given their steeper roll-off, appear to be more effective clutter suppressors for power Doppler imaging. However, it should be noted that, as demonstrated by the simulations, the performance of IIR filters is severely degraded by their transient response which, in turn, is determined by the initialization scheme used. Therefore, more elaborate schemes-with superior transient characteristics than step-initialization-could significantly improve the effectiveness of IIR filtering under heavy clutter conditions. >

Journal ArticleDOI
TL;DR: In this paper, a self-adaptive time reversal mirror is proposed to detect small defects in a noisy background, which can compensate for the distortions induced by liquid-solid interfaces of different geometries.
Abstract: In this paper, we present a novel and completely different approach to focusing on defects beneath plane or curved surfaces: the time reversal mirror method. The time reversal technique is based on the concept of time reversal of ultrasonic fields and takes into account both the phase and modulus information coming from the defect. This technique is self-adaptative and requires only the presence of a target in the solid sample. In highly scattering media, it is shown that the time reversal process allows a new approach to speckle noise reduction. Experimental results obtained with a 121-channel time reversal mirror on titanium and duralumin samples are presented. They demonstrate the ability of time reversal to compensate for the distortions induced by liquid-solid interfaces of different geometries and to detect small defects in a noisy background.

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional elastic contact model is used for estimating the friction drive between the rotor and vibrator of an ultrasonic motor and an electrical equivalent circuit is used to estimate the interaction between the electrical and mechanical parts of the vibrator.
Abstract: The purpose of the present paper is to establish a method of design for a traveling wave type ultrasonic motor. This method is based on two models for the ultrasonic motor. A two-dimensional elastic contact model is used for estimating the friction drive between the rotor and vibrator of the motor. Moreover, an electrical equivalent circuit is used to estimate the interaction between the electrical and mechanical parts of the vibrator. The proposed method is applied to the design of a prototype motor. To determine applicability of the method, the load characteristics of the prototype motor are measured. The measured characteristics agree with the required ones which are specified in advance. As a result, the validity of the proposed method is experimentally confirmed. >

Journal ArticleDOI
TL;DR: Micromachined capacitance transducers have been investigated in practical situations where air-coupled ultrasound has current application as discussed by the authors, and their /spl sim/2 MHz bandwidths lead to good performance in pulse-echo and through transmission operation at solid surfaces.
Abstract: Micromachined capacitance transducers have been investigated in practical situations where air-coupled ultrasound has current application. Their /spl sim/2 MHz bandwidths lead to good performance in pulse-echo and through transmission operation at solid surfaces. Applications in surface profiling and distance measurement have been investigated. For the transduction of waves within solid media, the devices are shown to be capable of detecting longitudinal and shear waves at solid surfaces, as well as Rayleigh and Lamb waves. Examples are also given of fully noncontact, through transmission of carbon fibre reinforced polymer plates. >

Journal ArticleDOI
TL;DR: In this paper, the authors discussed and tested theories of particle removal by high-frequency ultrasonic waves against recent experimental data and showed that highfrequency ultrasound can clean particles most effectively in media with properties like water because: (1) the wavelength can be made comparable to the particle radius to promote effective sound-particle interaction; (2) the viscous boundary layer is thin, minimizing particle hideout; and (3) both the added mass and radiation pressure forces exceed typical adhesion forces at high frequencies.
Abstract: In this paper, theories of particle removal by high-frequency ultrasonic waves are discussed and tested against recent experimental data. First, the principal adhesion forces such as van der Waals forces are briefly reviewed and the typical uncertainties in their size in particle-surface systems are assessed. The different ultrasound-induced forces-linear forces such as added mass, drag, lift, and Basset forces and nonlinear ones due to radiation pressure, and drag exerted by acoustic streaming-are discussed and their magnitudes are evaluated for typical cleaning operations. It is shown that high-frequency ultrasound can clean particles most effectively in media with properties like water because: (1) the wavelength can be made comparable to the particle radius to promote effective sound-particle interaction; (2) the viscous boundary layer is thin, minimizing particle "hide-out;" and (3) both the added mass and radiation pressure forces exceed typical adhesion forces at high frequencies. Based on these analyses, possible mechanisms of particle removal are discussed and interpreted in terms of experimental observations of particle cleaning. >

Journal ArticleDOI
TL;DR: In this article, an intrinsic fiber optic Fabry-Perot interferometric sensor embedded in a solid material for the purpose of detecting ultrasound is proposed, which is achieved by using active homodyne stabilization which tunes the laser frequency to maintain quadrature.
Abstract: A method is proposed to stabilize an intrinsic fiber optic Fabry-Perot interferometric sensor embedded in a solid material for the purpose of detecting ultrasound. Without stabilization the interferometer drifts out of quadrature due to the presence of low-frequency dynamic strains. Stabilization is achieved by using active homodyne stabilization which tunes the laser frequency to maintain quadrature. A control loop shifts the laser frequency by 10 GHz at rates less than 25 Hz in order to compensate for induced drifts. The stabilization procedure was tested for a sensor embedded in an epoxy plate. Ultrasonic pulses, generated by a 5 MHz piezoelectric transducer, were detected with the embedded fiber sensor stabilized in the presence of applied low frequency strains. Improvements in sensitivity which result from stabilization are demonstrated. Additionally, a simulated acoustic emission signal, generated by a lead pencil break (Hsu-Neilson source), was detected with the sensor stabilized in the presence of dynamic strains. >

Journal ArticleDOI
TL;DR: In this paper, a 100 MHz ultrasonic linear transducer array made from a piezoelectric zinc oxide thin film on a sapphire substrate was developed and evaluated.
Abstract: A 100-MHz ultrasonic linear transducer array made from a piezoelectric zinc oxide thin film on a sapphire substrate was developed and evaluated. Epitaxial, high-acoustic quality 10-/spl mu/m-thick ZnO film layers were produced by rf-magnetron sputter deposition onto a (111)-oriented gold film (with a chromium adhesion layer) that was vacuum-evaporated onto a (0001) sapphire surface. We found that, in well-oriented growth of gold, it is important to control the chromium sublayer thickness (less than 5 nm). An array was constructed by photolithography with an appropriate etch. V-shaped grooves between adjacent elements were formed by using an anisotropic etchant (HCl and HNO/sub 3/-based) that preferentially etched the c-plane of ZnO. Typical array elements were 90 /spl mu/m wide, 3.2 mm long, and 10 /spl mu/m thick, and the pitch of an array was typically 100 /spl mu/m. Our fine uniform array resulted in uniform ultrasonic response of individual elements throughout the array. For a 32-element array, the ultrasound beam in the azimuth plane in water could be electronically focused in the 100 MHz range to obtain a half-amplitude width of 60 /spl mu/m at the focal depth, agreeing well with theoretical predictions. Besides the use demonstrated with this present transducer, piezoelectric thin films should also lead to fabrication of various other kinds of ultrasonic transducers that can operate at high frequencies and should provide opportunities for miniaturizing transducers and making integrated ultrasonic devices. >

Journal ArticleDOI
TL;DR: In this paper, the EMCC of commonly seen piezoelectric elements is formulated and analyzed, and the results are in good agreement with those found by using Berlincourt's formula and the dynamic formula of Mason.
Abstract: An important characteristic of piezoelectric elements as energy converters is the energy conversion efficiency. The electromechanical coupling coefficient (EMCC) is commonly used as a measure of a piezoelectric elements' efficiency. The latest Standard on Piezoelectric recommends that EMCC be determined by the use of the Berlincourt et al. formula for a uniform electroelastic state, and the dynamic formula by Mason for near resonance frequencies. This paper is devoted to the analysis of these two formulas along with a third formula. The EMCC of commonly seen piezoelectric elements are formulated and analyzed. The comparison of the numerical results leads us to the following conclusions: 1. The formula of Berlincourt et al. is valid only for a uniform electroelastic state, 2. The dynamic formula of Mason gives the EMCC at a frequency equal to the arithmetic mean of resonance and the corresponding antiresonance frequencies, 3. The third formula for the EMCC is valid for both the static and dynamic electroelastic state of a piezoelement, and its results are in good agreement with those found by using Berlincourt's formula and the dynamic formula of Mason. >

Journal ArticleDOI
TL;DR: An expression for the lower bound for the strain estimation error (LBSE) is obtained, derived under the assumption that the post-compression echo signal can be reconstructed to the original shape of the echo signal before compression.
Abstract: Elastography is a technique for the estimation of tissue elasticity that is based on the estimation of strain. Tissue strain can be estimated by finite difference computations of echo time-delay. Echo time-delays are obtained by cross-correlation processing of pre- and post-compression echo signals. Errors in strain estimation can be expressed in terms of the errors in time delay estimation for given echo-signal characteristics. The smallest time delay estimation error is given by the Cramer-Rao Lower Bound (CRLB), which can be achieved when operating under the small error condition. Based on the CRLB, we obtain an expression for the lower bound for the strain estimation error (LBSE). The LBSE equation is derived under the assumption that the post-compression echo signal can be reconstructed to the original shape of the echo signal before compression. The theoretical bound given by the LBSE may or may not be achievable in practice, depending on the compliance with the requirements for echo signal reconstruction. In an example, the obtained LBSE shows that there is potential for significant reduction of the current level of noise in elastograms. >

Journal ArticleDOI
TL;DR: In this paper, a frequency-smoothed spectral autocorrelation (SAC) function was proposed to estimate the mean scatterer spacing from backscattered ultrasound signals.
Abstract: The quasiperiodicity of regularly spaced scatterers results in characteristic patterns in the spectra of backscattered ultrasonic signals from which the mean scatterer spacing can be estimated. The mean spacing has been considered for classifying certain biological tissue. This paper addresses the problem of estimating the mean scatterer spacing from backscattered ultrasound signals using the frequency-smoothed spectral autocorrelation (SAC) function. The SAC function exploits characteristic differences between the phase spectrum of the resolvable quasiperiodic scatterers and the unresolvable uniformly distributed (diffuse) scatterers to improve estimator performance over other estimators that operate directly on the magnitude spectrum. Mean scatterer spacing estimates are compared for the frequency-smoothed SAC function and a cepstral technique using an AR model. Simulation results indicate that SAC-based estimates converge more reliably over smaller amounts of data than cepstrum-based estimates. An example of computing an estimate from liver tissue scans is also presented for the SAC function and the AR cepstrum. >

Journal ArticleDOI
TL;DR: In this paper, a second-order autoregressive (AR2) model, whose parameters are estimated with the Burg algorithm, is used to estimate the center frequency on echo signals and its evolution versus depth.
Abstract: The authors deal with the application of parametric spectral analysis for attenuation estimation on the reflected ultrasound signal of biological tissues. A second-order autoregressive (AR2) model, whose parameters are estimated with the Burg algorithm, is used to estimate the center frequency on echo signals and its evolution versus depth. Data simulation of independent A-lines backscattered by a homogeneous medium of scatterers are generated by a computer model with attenuation values ranging from 1 to 5 dB/cmMHz, an ultrasonic frequency of 5 MHz and different pulse durations. The performance of the estimator is evaluated for time windows ranging from 5 to 0.3 /spl mu/s. The comparison is made with the classical short time Fourier analysis using a fast Fourier transform (FFT). It is found that the AR2 model provides a better estimation of attenuation than the Fourier technique: the relative error of attenuation is below 5% for windows between 0.6 to 2.5 /spl mu/s, while the one obtained with the Fourier technique lies between 3 and 16% for the same window sizes. However, the variance of attenuation estimate is the same with the two techniques. These results offer promises for determining attenuation in highly attenuating medium (material or biological tissue) either because of their structure or because high frequencies are used. >

Journal ArticleDOI
Shiroh Saitoh1, M. Izumi1, Y. Mine1
TL;DR: In this article, a dual frequency probe using a multilayer ceramic is proposed for simultaneously obtaining a high resolution B mode and a high sensitivity Doppler mode image, which consists of two layers in which the poling directions are opposite and the individual thicknesses are different.
Abstract: A dual frequency probe using a multilayer ceramic is proposed for simultaneously obtaining a high resolution B mode and a high sensitivity Doppler mode image. This ceramic consists of two layers in which the poling directions are opposite and the individual thicknesses are different. It is possible to control the values of relative electromechanical coupling factors in the fundamental and the second harmonic by changing the thickness ratio. A thickness ratio of 1:0.7 was decided from computer simulation based on the Mason's model. A sufficient resolution has been shown from the fact that the intima of the carotid artery could be distinguished by an actually fabricated probe with dual frequencies of 3.75 and 7.5 MHz. Also, the sensitivity of this probe in the Doppler mode at 5 cm depth from the surface has been improved as much as 5 dB over that of a conventional one. >

Journal ArticleDOI
TL;DR: The ultrasonic properties of ocular tissues including sclera, cornea, ciliary body and iris have been quantitatively evaluated over the frequency range from 50 MHz to 100 MHz at 37/spl deg/C and are qualitatively related to their histological structure and imaging characteristics.
Abstract: The ultrasonic properties of ocular tissues including sclera, cornea, ciliary body and iris have been quantitatively evaluated over the frequency range from 50 MHz to 100 MHz at 37/spl deg/C. Measurements were made with a wideband 60 MHz PVDF copolymer transducer in conjunction with a C-scan microscopy system developed in the authors' laboratory. Using this system, high resolution overview images were produced to identify homogeneous tissue regions for detailed quantitative analysis. The speed of sound for the four eye tissues ranged from 1542 m/s for iris to 1622 m/s for sclera. At 50 MHz the attenuation coefficient ranged from 1.3 dB/mm for cornea to 4.3 dB/mm for sclera. Scleral tissue also had the highest backscatter coefficient (0.0157 Sr/sup -1/ mm/sup -1/), while iris had the lowest (0.00184 Sr/sup -1/ mm/sup -1/). The measured ultrasonic properties are qualitatively related to their histological structure and imaging characteristics. >

Journal ArticleDOI
TL;DR: A method of periodic Green's functions with a propagation factor exp(i/spl beta/x), unknown in advance, was used to calculate dispersion curves and attenuation coefficients for Rayleigh- and leaky- waves propagating in a periodic system of thin electrodes on a piezoelectric surface as mentioned in this paper.
Abstract: A method of periodic Green's functions with a propagation factor exp(i/spl beta/x), unknown in advance, is used to calculate dispersion curves and attenuation coefficients for Rayleigh- and leaky- waves propagating in a periodic system of thin electrodes on a piezoelectric surface. To describe the charge distribution on the electrodes both a step approximation and Chebyshev polynomials are used, the last being more adequate in most cases. Numerically determined values of the Green's function are used and interpolated either linearly or using a modified variant of Ingebrigtsen's formula. Such basic parameters as stopband width, stopband center frequency, wave velocity and attenuation in the stopband are found. These parameters can be used in the coupling-of-modes (COM) analysis and design of SAW devices. The analysis includes bulk wave radiation and scattering. The dependence of the corresponding attenuation coefficient on frequency is determined. Results obtained allow the determination directly and properly of the COM parameters and the design of SAW devices having large number of electrodes most precisely and rapidly. Numerical results for Rayleigh waves on YZ-LiNbO/sub 3/ and leaky waves on 36/spl deg/YX-LiTaO/sub 3/ substrates are presented. >

Journal ArticleDOI
TL;DR: In this paper, the elastic constants and the mass density of isotropic and anisotropic solids and thin films were determined from the directional variation of measured SAW velocities, using a preliminary estimate of /spl rho/.
Abstract: A method is presented to determine the elastic constants and the mass density of isotropic and anisotropic solids and anisotropic thin films. The velocity and attenuation of leaky surface acoustic waves (SAWs) have been obtained for specified propagation directions from V(z) curves measured by line-focus acoustic microscopy (LFAM). The experimentally obtained velocities have been compared to velocities obtained from a measurement model for the V(z) curve which simulates the experiment. Since the measured and simulated V(z) curves have the same systemic errors, the material constants are free of such errors. For an isotropic solid, Young's modulus E, the shear modulus G and the mass density /spl rho/ have been determined from the leaky Rayleigh wave velocity and attenuation, measured by LFAM, and a longitudinal wave velocity measured by a pulse-echo transit-time technique. For a cubic-crystalline solid, the ratios of the elastic constants to the mass density (c/sub 11///spl rho/, c/sub 12///spl rho/, c/sub 44///spl rho/) have been determined from the directional variation of measured SAW velocities, using a preliminary estimate of /spl rho/. The mass density /spl rho/ has subsequently been determined by additionally using the attenuation of leaky SAWs in crystal symmetry directions. For a cubic-crystalline thin film deposited on a substrate, the elastic constants and the mass density (c/sub 11/, c/sub 12/, c/sub 44/, /spl rho/) of the film have been determined from the directional variation of the measured SAW velocities, and a comparison of the corresponding attenuation coefficient with the measured attenuation coefficient has been used to verify the results. >