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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 5 • Date May 2004

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Displaying Results 1 - 24 of 24
  • IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control - Front cover

    Page(s): 1 - 2
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  • [Inside front cover]

    Page(s): 3
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  • [Inside back cover]

    Page(s): 4
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  • IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control - Table of contents

    Page(s): 5 - 6
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  • Information for Contributors with Multimedia Addition

    Page(s): 477 - 481
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  • A multimedia example

    Page(s): 482
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  • CALL FOR PAPERS - Special Issue on Micromachined Ultrasonic Transducers

    Page(s): 483
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  • Whispering-gallery mode technique applied to the measurement of the dielectric properties of Langasite between 4 K and 300 K

    Page(s): 484 - 490
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (558 KB) |  | HTML iconHTML  

    We report new measurements of dielectric properties of Lanthanum gallium silicate (Langasite or LGS) conducted with the whispering-gallery mode technique at microwave frequencies and between 4.2 K and 300 K. The real part of the permittivity tensor of LGS presents two components having temperature coefficients of opposite sign. This unique property enables the design of a temperature compensated resonator that may be useful in building stable microwave oscillators or filters. We report also the first measurements of the two independent components of the imaginary part of the permittivity tensor. It appears LGS is a relatively high-loss dielectric material compared with sapphire or quartz. View full abstract»

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  • Nonscanning measurements for determining in-plane mode shapes in piezoelectric devices with polished surfaces

    Page(s): 491 - 495
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (411 KB) |  | HTML iconHTML  

    A nonmechanical scanning method has been developed for the visualization of the in-plane mode shapes of piezoelectric devices with polished surfaces. By taking into account the reflection versus laser-wavelength characteristics of the material of the electrodes, the in-plane motion can be measured even if the surface of the measurement plane is polished like a mirror. This method is based on laser speckle interference and two-dimensional correlation filtering that effectively enhance the mode-shape visualization for bulk and surface acoustic wave devices. Although this method cannot directly measure absolute displacement, the simple measurement system and high speed measurement more than offset this disadvantage. The experimental results for fundamental thickness-shear and nearby inharmonic modes in a bimesa-shaped rectangular AT-cut quartz resonator have been presented. The results of the experiments and the analyses obtained by the three-dimensional finite element analyses correlate well and show the advantages and validity of the proposed technique. View full abstract»

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  • An evaluation of effective radiuses of bulk-wave ultrasonic transducers as circular piston sources for accurate velocity measurements

    Page(s): 496 - 501
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    The effective radius of a bulk-wave ultrasonic transducer as a circular piston source, fabricated on one end of a synthetic silica (SiO/sub 2/) glass buffer rod, was evaluated for accurate velocity measurements of dispersive specimens over a wide frequency range. The effective radius was determined by comparing measured and calculated phase variations due to diffraction in an ultrasonic transmission line of the SiO/sub 2/ buffer rod/water-couplant/SiO/sub 2/ standard specimen, using radio-frequency (RF) tone burst ultrasonic waves. Fourteen devices with different device parameters were evaluated. The velocities of the nondispersive standard specimen (C-7940) were found to be 5934.10 /spl plusmn/ 0.35 m/s at 70 to 290 MHz, after diffraction correction using the nominal radius (0.75 mm) for an ultrasonic device with an operating center frequency of about 400 MHz. Corrected velocities were more accurately found to be 5934.15 /spl plusmn/ 0.03 m/s by using the effective radius (0.780 mm) for the diffraction correction. Bulk-wave ultrasonic devices calibrated by this experimental procedure enable conducting extremely accurate velocity dispersion measurements. View full abstract»

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  • High-power, multioutput piezoelectric transformers operating at the thickness-shear vibration mode

    Page(s): 502 - 509
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (654 KB) |  | HTML iconHTML  

    In this study, a piezoelectric transformer operating at the thickness shear vibration mode and with dual or triple outputs is proposed. It consists of a lead zirconate titanate (PZT) ceramic plate with a high mechanical quality factor Q/sub m/ and a size of 120 /spl times/ 20 /spl times/ 4 mm/sup 3/. The PZT ceramic plate is poled along the width direction. The electrodes of input and output parts are on the top and bottom surfaces of the ceramic plate and separated by narrow gaps. A new construction of support and lead wire connection is used for the transformer. At a temperature rise less than 20/spl deg/C and efficiency of 90%, the piezoelectric transformer with dual outputs has a maximum total output power of 169.8 W, with a power of 129.5 W in one output and 40.3 W in another. The one with triple outputs has a maximum total output power of 163.1 W, with a power of 36.9 W in the first output, 13.0 W in the second output and 113.2 W in the third output. The maximum efficiency of the piezo-electric transformer with dual outputs and triple outputs is 98% and 95.7%, respectively. The voltage gains of the transformers are less than one, and different outputs have different gains. Also, there is a driving frequency range in which the load resistance of one output has little effect on the voltage gain of another output. View full abstract»

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  • Noise reduction using spatial-angular compounding for elastography

    Page(s): 510 - 520
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1290 KB) |  | HTML iconHTML  

    Ultrasound elastography has developed into an imaging modality suitable for detection and diagnosis of cancers in the breast, prostate, and thyroid and for monitoring ablative therapies in the liver, kidneys, and other sites. In this article, a new approach is described that enables the reduction of noise artifacts in elastography without a significant reduction in either the contrast or spatial resolution. The technique uses angular-weighted compounding of local angular strains estimated from echo signals scanned at different insonification angles. Strain estimated along angular insonification directions can be separated into strain tensor components along the axial (direction of compression) and lateral directions. The mechanical stimulus is applied only along one direction. Angular-weighting factors are derived from the relationship between the axial and lateral strains under the assumption of tissue incompressibility. Experimental results using a uniformly elastic, tissue-mimicking phantom demonstrate the improvement in the signal-to-noise ratio obtained with angular-weighted compounding. Variation in the signal-to-noise ratio obtained using different angular increments also is investigated. Elastograms obtained from an inclusion phantom also demonstrate the improvement in contrast detail resolution obtained using spatial-angular compounding. View full abstract»

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  • Model-based reconstructive elasticity imaging of deep venous thrombosis

    Page(s): 521 - 531
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (506 KB) |  | HTML iconHTML  

    Deep venous thrombosis (DVT) and its sequela, pulmonary embolism, is a significant clinical problem. Once detected, DVT treatment is based on the age of the clot. There are no good noninvasive methods, however, to determine clot age. Previously, we demonstrated that imaging internal mechanical strains call identify and possibly age thrombus in a deep vein. In this study the deformation geometry for DVT elasticity imaging and its effect on Young's modulus estimates is addressed. A model-based reconstruction method is presented to estimate elasticity in which the clot-containing vessel is modeled as a layered cylinder. Compared to all unconstrained approach in reconstructive elasticity imaging, the proposed model-based approach has several advantages: only one component of the strain tensor is used; the minimization procedure is very fast; the method is highly efficient because an analytic solution of the forward elastic problem is used; and the method is not very sensitive to the details of the external load pattern-a characteristic that is important for free-hand, external, surface-applied deformation. The approach was tested theoretically using a numerical model, and experimentally on both tissue-like phantoms and all animal model of DVT. Results Suggest that elasticity reconstruction may prove to be a practical adjunct to triplex scanning to detect, diagnose, and stage DVT. View full abstract»

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  • Nonlinear elasticity imaging: Theory and phantom study

    Page(s): 532 - 539
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2189 KB) |  | HTML iconHTML  

    In tissue the Young's modulus cannot be assumed constant over a wide deformation range. For example, direct mechanical measurements on human prostate show up to a threefold increase in Young's modulus over a 10% deformation. In conventional elasticity imaging, these effects produce strain-dependent elastic contrast. Ignoring these effects generally leads to suboptimal contrast (stiffer tissues at lower strain are contrasted against softer tissues at higher strain), but measuring the nonlinear behavior results in enhanced tissue differentiation. To demonstrate the methods extracting nonlinear elastic properties, both simulations and measurements were performed on an agar-gelatin phantom. Multiple frames of phase-sensitive ultrasound data are acquired as the phantom is deformed by 12%. All interframe displacement data are brought back to the geometry of the first frame to form a three-dimensional (3-D) data set (depth, lateral, and preload dimensions). Data are fit to a 3-D second order polynomial model for each pixel that adjusts for deformation irregularities. For the phantom geometry and elastic properties considered in this paper, reconstructed frame-to-frame strain images using this model result in improved contrast to noise ratios (CNR) at all preload levels, without any sacrifice in spatial resolution. From the same model, strain hardening at all preload levels can be extracted. This is an independent contrast mechanism. Its maximum CNR occurs at 5.13% preload, and it is a 54% improvement over the best case (preload 10.6%) CNR for frame-to-frame strain reconstruction. Actual phantom measurements confirm the essential features of the simulation. Results show that modeling of the nonlinear elastic behavior has the potential to both increase detectability in elasticity imaging and provide a new independent mechanism for tissue differentiation. View full abstract»

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  • Lateral speckle tracking using synthetic lateral phase

    Page(s): 540 - 550
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    In traditional speckle tracking, lateral displacement (perpendicular to the beam direction) estimates are much less accurate than axial ones (along the beam direction). The accuracy of lateral tracking is very important whenever spatial derivatives of both axial and lateral displacements are required to give a full description of a two-dimensional (2-D) strain field. A number of methods have been proposed to improve lateral tracking by increasing the sampling rate in the lateral direction. We propose an alternate method using synthetic lateral phase (SLP). The algorithm, a direct analog of the phase zero-crossing approach used in axial displacement estimation, synthesizes the lateral phase first, then performs a zero-crossing detection on this synthetic phase to obtain lateral displacement estimates. The SLP is available by simply eliminating either the positive or negative half of the lateral spectrum of the original analytic signal. No new data need to be acquired for this procedure. This new algorithm was tested on both simulations and measurements from a cardiac phantom model. Results show that the method greatly improves the accuracy of lateral tracking, especially for low strain cases (/spl les/1%). The standard deviation of the estimation error of the lateral normal strain obtained with this approach has an approximate factor of 2-3 improvement for low strain cases. The conceptual and computational simplicity of this new method makes it a practical approach to improve lateral tracking for elasticity imaging. View full abstract»

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  • On the thermal effects associated with radiation force imaging of soft tissue

    Page(s): 551 - 565
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1049 KB) |  | HTML iconHTML  

    Several laboratories are investigating the use of acoustic radiation force to image the mechanical properties of tissue. Acoustic Radiation Force Impulse (ARFI) imaging is one approach that rises brief, high-intensity, focused ultrasound pulses to generate radiation force in tissue. This radiation force generates tissue displacements that are tracked using conventional correlation-based ultrasound methods. The tissue response provides a mechanism to discern mechanical properties of the tissue. The acoustic energy that is absorbed by tissue generates radiation force and tissue heating. A finite element methods model of acoustic heating has been developed that models the thermal response of different tissues during short duration radiation force application. The beam sequences and focal configurations used during ARFI imaging are modeled herein; the results of these thermal models can be extended to the heating due to absorption associated with other radiation force-based imaging modalities. ARFI-induced thermal diffusivity patterns are functions of the transducer f-number, the tissue absorption, and the temporal and spatial spacing of adjacent ARFI interrogations. Cooling time constants are on the order of several seconds. Tissue displacement due to thermal expansion is negligible for ARFI imaging. Changes in sound speed due to temperature changes call be appreciable. These thermal models demonstrate that ARFI imaging of soft tissue is safe, although thermal response must be monitored when ARFI beam sequences are being developed. View full abstract»

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  • Acoustic intensity for a long vessel with noncircular cross section

    Page(s): 566 - 575
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    The acoustic intensity distribution around and within long vessels of noncircular cross section was investigated for parameters typical of biomedical ultrasound and blood vessels. We have developed a collocation method for finding the acoustic field when a uniform plane wave is obliquely incident on a long, not necessarily cylindrical, impedance interface. Results are presented for vessels of noncircular cross section and for vessels with thick walls of nonuniform thickness. The intensity in the vicinity of the vessel, throughout the lumen, and in the wall, is calculated for intermediate length scales, i.e., vessel radius and wall thickness in the range 1 to 10 wavelengths. The intensity distribution is an interference pattern, with complicated regions of increased and decreased intensity. These results are compared with approximate intensity obtained using ray theory. Effects not predicted by ray theory and intensity variations that will be significant in any close ultrasonic investigation of these vessels are revealed. View full abstract»

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  • Spatial coherence of backscatter for the nonlinearly produced second harmonic for specific transmit apodizations

    Page(s): 576 - 588
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (557 KB) |  | HTML iconHTML  

    To be successful, correlation-based, phase-aberration correction requires a high correlation among backscattered signals. For harmonic imaging, the spatial coherence of backscatter for the second harmonic component is different than the spatial coherence of backscatter for the fundamental component. The purpose of this work was to determine the effect of changing the transmit apodization on the spatial coherence of backscatter for the nonlinearly generated second harmonic. Our approach was to determine the effective apodizations for the fundamental and second harmonic using both experimental measurements and simulations. Two-dimensional measurements of the transverse cross sections of the finite-amplitude ultrasonic fields generated by rectangular and circular apertures were acquired with a hydrophone. Three different one-dimensional transmit apodization functions were investigated: uniform, Riesz, and trapezoidal. An effective apodization was obtained for each transmit apodization by backpropagating the values measured from within the transmit focal zone using a linear angular spectrum approach. Predictions of the spatial coherence of backscatter were obtained using the pulse-echo Van Cittert-Zernike theorem. In all cases the effective apodization at 2f was narrower than the transmit apodization. We demonstrate that certain transmit apodizations result in a greater spatial coherence of backscatter at the second harmonic than at the fundamental. View full abstract»

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  • Aperture size effect on ultrasonic wavefront distortion correction

    Page(s): 589 - 605
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1134 KB) |  | HTML iconHTML  

    The influences of aperture size on wavefront distortion correction are investigated both theoretically and numerically. A multilayer, phase-screen model is assumed to be the underlying, distorting medium. Numerical simulations were performed using three wavefront distortion correction methods: time-shift compensation (TSC), backpropagation followed by time-shift compensation (BP+TSC), and the previously proposed, multilayer, phase-screen compensation (MPSC) method. The distorted wavefronts were generated by propagating a planar wavefront through a multilayer, phase-screen model constructed with a two-dimensional (2-D) scanned map of a real abdominal slice. Performances were evaluated by L/sup 2/ errors between the corrected wavefronts and the undistorted planar wavefront. Point spread functions also were calculated to evaluate the relative image quality. Theoretical analysis shows L/sup 2/ error will decrease as aperture size grows when exact phase compensation (EPC) is applied, although finite errors will always exist along the edges of the corrected wavefront. Three different aperture sizes, 14.24 mm (64 elements), 28.48 mm (128 elements), and 56.96 mm (256 elements) are considered in this study. Numerical results Show that the quality of wavefront with EPC is essentially limited by the aperture size, and the correction methods considered are relatively robust against the aperture size. It also shows that, for low aberration, results with MPSC and EPC are comparable. However, for high aberration, MPSC significantly outperforms EPC in suppression of L/sup 2/ error kind sidelobes. This study suggests that, for most medical ultrasound imaging systems, the exact structure of the distorting medium may not be necessary to be known a priori for optimal distortion correction because of the limitation imposed by finite aperture size. View full abstract»

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  • Temperature estimation using ultrasonic spatial compound imaging

    Page(s): 606 - 615
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2021 KB) |  | HTML iconHTML  

    The feasibility of temperature estimation during high-intensity focused ultrasound therapy using pulse-echo diagnostic ultrasound data has been demonstrated. This method is based upon the measurement of thermally-induced modifications in backscattered RF echoes due to thermal expansion and local changes in the speed Of Sound. It has been shown that strong ripple artifacts due to the thermo-acoustic lens effect severely corrupt the temperature estimates behind the heated region. We propose here a new imaging technique that improves the temperature estimation behind the heated region and reduces the variance of the temperature estimates in the entire image. We replaced the conventional beamforming on transmit with multiple steered plane wave insonifications using several subapertures. A two-dimensional temperature map is estimated from axial displacement maps between consecutive RF images of identically steered plane wave insonifications. Temperature estimation is then improved by averaging the two-dimensional maps from the multiple steered plane wave insonifications. Experiments were conducted in a tissue-mimicking gelatin-based phantom and in fresh bovine liver. View full abstract»

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  • Simulation of surface acoustic wave devices

    Page(s): 616 - 623
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (313 KB) |  | HTML iconHTML  

    The Mason crossed-field circuit model is generalized to simulate apodized interdigital transducers without channel division. The apodized transducer model is based on the transmission line model, and the artificial transformer with different voltage and current coupling ratios is used to independently obtain the transfer function and radiation admittance. In addition, a heuristic expression for transformer current ratios is used to approximate the radiation admittance of apodized transducers. Through comparing with the multichannel model, this unichannel model is illustrated to successfully describe the frequency response of apodized interdigital transducers. View full abstract»

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  • Acoustic impedance matching of piezoelectric transducers to the air

    Page(s): 624 - 633
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (540 KB) |  | HTML iconHTML  

    The purpose of this work is threefold: to investigate material requirements to produce impedance matching layers for air-coupled piezoelectric transducers, to identify materials that meet these requirements, and to propose the best solution to produce air-coupled piezoelectric transducers for the low megahertz frequency range. Toward this end, design criteria for the matching layers and possible configurations are reviewed. Among the several factors that affect the efficiency of the matching layer, the importance of attenuation is pointed out. A standard characterization procedure is applied to a wide collection of candidate materials to produce matching layers. In particular, some types of filtration membranes are studied. From these results, the best materials are identified, and the better matching configuration is proposed. Four pairs of air-coupled piezoelectric transducers also are produced to illustrate the performance of the proposed solution. The lowest two-way insertion loss figure is -24 dB obtained at 0.45 MHz. This increases for higher frequency transducers up to -42 dB at 1.8 MHz and -50 at 2.25 MHz. Typical bandwidth is about 15-20%. View full abstract»

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  • Time-varying, 3-D echocardiography using a fast-rotating probe

    Page(s): 634 - 639
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB) |  | HTML iconHTML  

    A fast continuous rotating ultrasound scanhead transducer was used to perform three-dimensional (3D) echocardiography with 2-D images acquired during a single cardiac cycle. The 3-D images were reconstructed by interpolating 2-D data acquired with the probe. Two experiments were carried out to validate the image reconstructions. A dynamic cardiac phantom was used as a known reference to compare the minimal and maximal volumes estimated manually on the reconstructed 3-D images. The left ventricle (LV) volume of 30 healthy volunteers also were estimated using a semiautomatic ellipse approach and compared to measurements obtained with standard 2-D examination. Results showed a good agreement between 3-D and reference measurements. View full abstract»

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  • Transmission line model for simulation of guided-wave defect signals in piping

    Page(s): 640 - 643
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (417 KB) |  | HTML iconHTML  

    A simple transmission line model for analytically simulating the guided-wave signal reflected from a volumetric defect of arbitrary shape in piping is described. In the model, the guided-wave interaction with a defect is treated as the one-dimensional problem of plane wave reflection from a boundary of multilayered media of different acoustic impedances in a transmission line. Results of simulation show good qualitative agreement with experimentally measured signals. View full abstract»

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Aims & Scope

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control focuses on the theory, design, and application on generation, transmission, and detection of bulk and surface mechanical waves.

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Editor-in-Chief
Steven Freear
s.freear@leeds.ac.uk