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Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on

Issue 3 • Date March 2007

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  • IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control - March 2007

    Page(s): c1 - c2
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  • IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society - list staff

    Page(s): c3
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  • IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society - info-society

    Page(s): c4
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  • Table of contents - Vol 54 No 3

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  • Information for Contributors with Multimedia Addition

    Page(s): 459 - 463
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  • A multimedia example

    Page(s): 464
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  • In this issue - Technically

    Page(s): 465
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  • In this issue - Technically

    Page(s): 466
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  • Acoustic properties of alumina colloidal/polymer nano-composite film on silicon

    Page(s): 467 - 469
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (279 KB) |  | HTML iconHTML  

    Alumina colloidal/polymer composite films on silicon substrates have been successfully fabricated using the sol-gel method, in which the crystallite sizes of alumina are between 20 and 50 nm. The density and ultrasonic phase velocities in these films with different alumina ratios from 14% to 32% were measured at the desired operating frequency. We have proved that the density, acoustic phase velocities, and hence the acoustic impedance of the nanocomposite films increase with the alumina content, which gives us another option of tailoring the acoustic impedance of the nano-composite film for making the matching layer of high-frequency medical ultrasonic transducers View full abstract»

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  • Aberration in nonlinear acoustic wave propagation

    Page(s): 470 - 479
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    Theory and simulations are presented indicating that imaging at the second-harmonic frequency does not solve the problem of ultrasonic wave aberration. The non-linearity of acoustic wave propagation in biological tissue is routinely exploited in medical imaging because the improved contrast resolution leads to better image quality in many applications. The major sources of acoustic noise in ultrasound images are aberration and multiple reflections between the transducer and tissue structures (reverberations), both of which are the result of spatial variations in the acoustic properties of the tissue. These variations mainly occur close to the body surface, i.e., the body wall. As a result, the nonlinearly generated, second harmonic is believed to alleviate both reverberation and aberration because it is assumed that the second harmonic is mainly generated after the body wall. However, in the case of aberration, the second harmonic is generated by an aberrated source. Thus the second harmonic experiences considerable aberration at all depths, originating from this source. The results in this paper show that the second harmonic experiences similar aberration as its generating source, the first harmonic. View full abstract»

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  • Stable and transient subharmonic emissions from isolated contrast agent microbubbles

    Page(s): 480 - 497
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    Ultrasound contrast agents (UCAs) have been widely studied in recent years in order to improve and develop new, sophisticated imaging techniques for clinical applications. In order to improve the understanding of microbubble-ultrasound interactions, an acoustic dynamic characterization of UCA microbubble behavior was performed in this work using a high frame-rate acquiring and processing system. This equipment is connected to a commercial scanner that provides RF beam-formed data with a frame-rate of 30 Hz. Acquired RF sequences allows us to follow the dynamics of cavitation mechanisms in its temporal evolution during different insonifying conditions. The experimental setup allowed us to keep the bubbles free in a spatial region of the supporting medium, thus avoiding boundary effects that can alter the ultrasound field and the scattered echo from bubbles. The work focuses on the study of subharmonic emission from an isolated bubble of contrast agent. In particular, the acoustic pressure threshold for a subharmonic stable emission was evaluated for a subset of 50 microbubbles at 3.3 MHz and at 5 MHz of insonation frequencies. An unexpected second pressure threshold, which caused the standstill of the subharmonic emission, was detected at 3.3 MHz and 5 MHz excitation frequencies. A transient subharmonic emission, which is hypothesized as being related to the formation of new free gas bubbles, was detected during the ultrasound-induced destruction of microbubbles. An experimental procedure was devised in order to investigate these behaviors and several sequences of RF echo signals and the related spectra, acquired from an isolated bubble in different insonation conditions, are presented and discussed in this paper View full abstract»

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  • Estimation of polyvinyl alcohol cryogel mechanical properties with four ultrasound elastography methods and comparison with gold standard testings

    Page(s): 498 - 509
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    Tissue-mimicking phantoms are very useful in the field of tissue characterization and essential in elastography for the purpose of validating motion estimators. This study is dedicated to the characterization of polyvinyl alcohol cryogel (PVA-C) for these types of applications. A strict fabrication procedure was defined to optimize the reproducibility of phantoms having a similar elasticity. Following mechanical stretching tests, the phantoms were used to compare the accuracy of four different elastography methods. The four methods were based on a one-dimensional (1-D) scaling factor estimation, on two different implementations of a 2-D Lagrangian speckle model estimator (quasistatic elastography methods), and on a 1-D shear wave transient elastography technique (dynamic method). Young's modulus was investigated as a function of the number of freeze-thaw cycles of PVA-C, and of the concentration of acoustic scatterers. Other mechanical and acoustic parameters, such as the speed of sound, shear wave velocity, mass density, and Poisson's ratio, also were assessed. The Poisson's ratio was estimated with good precision at 0.499 for all samples, and the Young's moduli varied in a range of 20 kPa for one freeze-thaw cycle to 600 kPa for 10 cycles. Nevertheless, above six freeze-thaw cycles, the results were less reliable because of sample geometry artifacts. However, for the samples that underwent less than seven freeze-thaw cycles, the Young's moduli estimated with the four elastography methods showed good matching with the mechanical tensile tests with a regression coefficient varying from 0.97 to 1.07, and correlations R2 varying from 0.93 to 0.99, depending on the method View full abstract»

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  • Attenuation estimation using spectral cross-correlation

    Page(s): 510 - 519
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    Estimation of the local attenuation coefficient in soft tissue is important both for clinical diagnosis and for further analysis of ultrasound B-mode images. However, it is difficult to extract spectral properties in a small region of interest from noisy backscattered ultrasound radio frequency (RF) signals. Diffraction effects due to transducer beam focal properties also have to be corrected for accurate estimation of the attenuation coefficient. In this paper, we propose a new attenuation estimation method using spectral cross-correlation between consecutive power spectra obtained from the backscattered RF signals at different depths. Since the spectral cross-correlation method estimates the spectral shift by comparing the entire power spectra, it is more robust and stable to the spectral noise artifacts in the backscattered RF signals. A diffraction compensation technique using a reference phantom with a known attenuation coefficient value is also presented. Local attenuation coefficient estimates obtained using spectral cross-correlation are within 2.3% of the actual value with small estimation variances, as demonstrated in the simulation results View full abstract»

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  • Contrast imaging with chirped excitation

    Page(s): 520 - 529
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    Coded excitation has been successfully used in imaging to increase the signal-to-noise ratio (SNR) and penetration depth. With a contrast agent, wideband signals have been hypothesized to increase the contrast-to-tissue ratio (CTR). However, nonlinear properties of contrast agents make decoding difficult when applying coded excitation to contrast imaging. We propose two chirped excitation methods to image contrast agents, with a mechanical index (MI) ranging from 0.05 to 0.34. In the single chirp method, one chirp is transmitted, followed by a clutter filter to reject tissue echoes, then a matched filter is used to recover range resolution. In the chirp sequence method, an increasing and decreasing chirp sequence is transmitted followed by subtraction of the compressed echoes to reject tissue echoes (assuming tissue is a linear scatterer at low MI). Ten independent acoustic experiments were performed to evaluate the CTR for chirp and tone burst insonation, with the same spatial peak temporal averaged intensity (ISPTA)A significant increase in CTR, ranging from 4 dB to 8 dB, is observed for chirped excitation as compared with tone burst insonation, at an ISPTA of 0.1 and 0.3 mW/cm2 (P les 5e-3). To achieve the same CTR of 15 dB, the spatial peak pulse averaged intensity (ISPPA) can be decreased by 6 dB for chirp insonation as compared with tone burst insonation (P < 1e-5). Additionally, an increase of more than 10 dB in tissue rejection ratio (TRR) is observed for a chirp sequence insonation compared to tone burst phase inversion for this set of parameters (P les 1e-9). Deconvolution of the linear microbubble response from the received echoes is proposed as a method to recover spatial resolution. The difference in the axial resolution resulting from chirp and three-cycle tone burst insonation is approximately 220 mum. The difference in the mainlobe width between experimental and predicted compressed echoes is less than - - 20%. The side-lobe amplitude is 9 dB to 16 dB below the mainlobe with a transmitted ISPTA from 0.1 to 6.6 mW/cm2 View full abstract»

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  • Ultrasound speckle reduction using modified gabor filters

    Page(s): 530 - 538
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    B-mode ultrasound images are characterized by speckle artifact, which may make the interpretation of images difficult. One widely used method for ultrasound speckle reduction is the split spectrum processing (SSP), but the use of one-dimensional (1-D), narrow-band filters makes the resultant image experience a significant resolution loss. In order to overcome this critical drawback, we propose a novel method for speckle reduction in ultrasound medical imaging, which uses a bank of wideband 2-D directive filters, based on modified Gabor functions. Each filter is applied to the 2-D radio-frequency (RF) data, resulting in a B-mode image filtered in a given direction. The compounding of the filters outputs give rise to a final image in which speckle is reduced and the structure is enhanced. We have denoted this method as directive filtering (DF). Because the proposed filters have effectively the same bandwidth as the original image, it is possible to avoid the resolution loss caused by the use of narrow-band filters, as with SSP. The tests were carried out with both simulated arid real clinical data. Using the signal-to-noise ratio (SNR) to quantify the amount of speckle of the ultrasound images, we have achieved an average SNR enhancement of 2.26 times with simulated data and 1.18 times with real clinical data View full abstract»

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  • Optimal velocity estimation in ultrasound color flow imaging in presence of clutter

    Page(s): 539 - 549
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    In color flow imaging (CFI), the rejection of tissue clutter signal is treated separately from blood velocity estimation by high-pass filtering the received Doppler signal. The complete suppression of clutter is then difficult to achieve without affecting the subsequent velocity estimates. In this work, a different approach to velocity estimation is investigated, based on a statistical model of the signal from both clutter and blood. An analytic expression for the Cramer-Rao lower bound (CRLB) is developed, and used to determine the existence of an efficient maximum likelihood estimator (MLE) of blood velocity in CFI when assuming full knowledge of the clutter statistics. We further simulate and compare the performance of the MLE to that of the autocorrelation method (ACM) using finite-impulse response (FIR) and polynomial regression clutter filters. Two signal scenarios are simulated, representing a central and peripheral vessel. Simulations showed that, by including 3-9 (independent) spatial points, the MLE variance approached the CRLB in both scenarios. The ACM was approximately unbiased only for the central scenario in the clutter filter pass band, then with a variance of up to four times the CRLB. The ACM suffered from a severe bias in the filter transition region, and a significant performance gain was achieved here using the MLE. For practical use, the clutter properties must be estimated. We finally replaced the known clutter statistics with an estimate obtained from low-rank approximations of the received sample correlation matrix. Used in the model-based framework, this method came close to the performance of the MLE, and it may be an important step toward a practical model-based estimator, including tissue clutter with optimal performance View full abstract»

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  • Wavelet restoration of medical pulse-echo ultrasound images in an EM framework

    Page(s): 550 - 568
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    The clinical utility of pulse-echo ultrasound images is severely limited by inherent poor resolution that impacts negatively on their diagnostic potential. Research into the enhancement of image quality has mostly been concentrated in the areas of blind image restoration and speckle removal, with little regard for accurate modeling of the underlying tissue reflectivity that is imaged. The acoustic response of soft biological tissues has statistics that differ substantially from the natural images considered in mainstream image processing: although, on a macroscopic scale, the overall tissue echogenicity does behave somewhat like a natural image and varies piecewise-smoothly, on a microscopic scale, the tissue reflectivity exhibits a pseudo-random texture (manifested in the amplitude image as speckle) due to the dense concentrations of small, weakly scattering particles. Recognizing that this pseudo-random texture is diagnostically important for tissue identification, we propose modeling tissue reflectivity as the product of a piecewise-smooth echogenicity map and a field of uncorrelated, identically distributed random variables. We demonstrate how this model of tissue reflectivity can be exploited in an expectation-maximization (EM) algorithm that simultaneously solves the image restoration problem and the speckle removal problem by iteratively alternating between Wiener filtering (to solve for the tissue reflectivity) and wavelet-based denoising (to solve for the echogenicity map). Our simulation and in vitro results indicate that our EM algorithm is capable of producing restored images that have better image quality and greater fidelity to the true tissue reflectivity than other restoration techniques based on simpler regularizing constraints. View full abstract»

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  • A real-time measure of cavitation induced tissue disruption by ultrasound imaging backscatter reduction

    Page(s): 569 - 575
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    A feedback method for obtaining real-time information on the mechanical disruption of tissue through ultrasound cavitation is presented. This method is based on a substantial reduction in ultrasound imaging backscatter from the target volume as the tissue structure is broken down. Ex-vivo samples of porcine liver were exposed to successive high-intensity ultrasound pulses at a low duty cycle to induce mechanical disruption of tissue parenchyma through cavitation (referred to as histotripsy). At the conclusion of treatment, B-scan imaging backscatter was observed to have decreased by 22.4 plusmn 2.3 dB in the target location. Treated samples of tissue were found to contain disrupted tissue corresponding to the imaged hypoechoic volume with no remaining discernable structure and a sharp boundary. The observed, substantial backscatter reduction may be an effective feedback mechanism for assessing treatment efficacy in ultrasound surgery using pulsed ultrasound to create cavitation View full abstract»

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  • Spatial variability in acoustic backscatter as an indicator of tissue homogenate production in pulsed cavitational ultrasound therapy

    Page(s): 576 - 590
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    Spatial variability in acoustic backscatter is investigated as a potential feedback metric for assessment of lesion morphology during cavitation-mediated mechanical tissue disruption ("histotripsy"). A 750-kHz annular array was aligned confocally with a 4.5 MHz passive backscatter receiver during ex vivo insonation of porcine myocardium. Various exposure conditions were used to elicit a range of damage morphologies and backscatter characteristics [pulse duration = 14 mus, pulse repetition frequency (PRF) = 0.07-3.1 kHz, average ISPPA = 22-44 kW/cm2]. Variability in backscatter spatial localization was quantified by tracking the lag required to achieve peak correlation between sequential RF A-lines received. Mean spatial variability was observed to be significantly higher when damage morphology consisted of mechanically disrupted tissue homogenate versus mechanically intact coagulation necrosis (2.35 plusmn 1.59 mm versus 0.067 plusmn 0.054 mm, p < 0.025). Statistics from these variability distributions were used as the basis for selecting a threshold variability level to identify the onset of homogenate formation via an abrupt, sustained increase in spatially dynamic backscatter activity. Specific indices indicative of the state of the homogenization process were quantified as a function of acoustic input conditions. The prevalence of backscatter spatial variability was observed to scale with the amount of homogenate produced for various PRFs and acoustic intensities View full abstract»

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  • Lord Rayleigh: John William Strutt, third Baron Rayleigh

    Page(s): 591 - 596
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    John William Strutt, first son of the second Baron Rayleigh, was born on November 12, 1842. He was a sickly boy, so his schooling was sporadic. Nevertheless, he graduated first in his year at Cambridge and subsequently was a Fellow of Trinity College until his marriage in 1871. His father died in 1873, and he succeeded to the title third Baron Rayleigh. He converted the stable block of his country house, Terling Place, into a laboratory. In 1879, he moved back to Cambridge as Professor of Experimental Physics, but he returned to Terling in 1884. He published The Theory of Sound in 1877/1878 and, in his lifetime, 466 scientific articles. He received the 1904 Nobel Prize in Physics for the discovery of argon and made numerous seminal contributions to scientific progress. In the field of acoustics, he studied scattering, the diffraction limit, surface waves, resonance phenomena, reciprocity, streaming, radiation force, cavitation, relaxation, and binaural perception. He received many honors, was President of the Royal Society, one of the founding members of the Order of Merit, and Chancellor of Cambridge University. He also was interested in psychical research. Lord Rayleigh died on June 30, 1919 View full abstract»

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  • An ultrasonically levitated noncontact stage using traveling vibrations on precision ceramic guide rails

    Page(s): 597 - 604
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1209 KB) |  | HTML iconHTML  

    This paper presents a noncontact sliding table design and measurements of its performance via ultrasonic levitation. A slider placed atop two vibrating guide rails is levitated by an acoustic radiation force emitted from the rails. A flexural traveling wave propagating along the guide rails allows noncontact transportation of the slider. Permitting a transport mechanism that reduces abrasion and dust generation with an inexpensive and simple structure. The profile of the sliding table was designed using the finite-element analysis (FEA) for high levitation and transportation efficiency. The prototype sliding table was made of alumina ceramic (Al2O3) to increase machining accuracy and rigidity using a structure composed of a pair of guide rails with a triangular cross section and piezoelectric transducers. Two types of transducers were used: bolt-clamped Langevin transducers and bimorph transducers. A 40-mm long slider was designed to fit atop the two rail guides. Flexural standing waves and torsional standing waves were observed along the guide rails at resonance, and the levitation of the slider was obtained using the flexural mode even while the levitation distance was less than 10 mum. The levitation distance of the slider was measured while increasing the slider's weight. The levitation pressure, rigidity, and vertical displacement amplitude of the levitating slider thus were measured to be 6.7 kN/m2, 3.0 kN/mum/m2, and less than 1 mum, respectively. Noncontact transport of the slider was achieved using phased drive of the two transducers at either end of the vibrating guide rail. By controlling the phase difference, the slider transportation direction could be switched, and a maximum thrust of 13 mN was obtained View full abstract»

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  • The peculiarities of energy characteristics of acoustic waves in piezoelectric materials and structures

    Page(s): 605 - 611
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    This paper is devoted to detailed theoretical investigation of energy density and power flow of homogeneous (bulk) and inhomogeneous (surface and plate) plane acoustic waves in piezoelectric materials and structures. The analysis of these waves in different materials of various crystallographic orientations allowed us to establish some energy regularities. These regularities are the same for instantaneous energy characteristics of homogeneous waves and for time-average energy characteristics on unit of aperture of inhomogeneous waves if the electrical energy and power flow in vacuum are taken into account. It has been shown that, for strong piezoactive waves, the electric energy density may exceed the mechanical energy density more than three times View full abstract»

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  • Acoustic waves in the vicinity of the normal to the surface of piezoelectric crystals

    Page(s): 612 - 620
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    The acoustic wave propagation in the vicinity of the normal to the plane surface confining a piezoelectric crystal of arbitrary symmetry is theoretically studied. An octet formalism arid a perturbation theory have been put forward to describe the wave fields in the region of concern. The developed mathematical approach has been applied to several problems. Specifically, the derivation of the transfer matrix for the normal direction to the surface has been discussed. Furthermore, we have discussed how to estimate the electric potential induced outside the piezoelectric material by a normally incident wave. In addition, an analytical expression has been derived for the numerical factor in the function describing the asymptotic behavior of quasielectrostatic Green's function for half-infinite piezoelectric substrates at small values of the wave vector View full abstract»

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  • Theoretical modeling of a thickness-shear mode circular cylinder piezoelectric transformer

    Page(s): 621 - 626
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    We propose a piezoelectric transformer operating with thickness-shear modes of a circular cylinder arid perform a theoretical analysis on the transformer. An exact solution from the three-dimensional equations of piezoelectricity is obtained. The output voltage, input admittance, and efficiency of the transformer are determined. The basic behaviors of the transformer are shown by numerical results View full abstract»

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  • Enhancing ultrasonic imaging with low transient pulse shaping

    Page(s): 627 - 635
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    This work deals with improving the resolution of ultrasonic ranging systems by means of preshaping the transmitter drive signals to achieve low transient acoustic pulses. As ultrasonic transducers are operated at a relatively high nominal frequency and quality factor, feedforward strategy is among the most efficient means to generate the low transient acoustic pulses. In this work, a digital signal processor and a field programmable gate array synthesize the transmitter drive signal to emit low transient pulses which are then applied to the detection of surface features. Both simulation and experiment results confirm an improved spatial detection resolution due to the lower acoustic transient interference. The drive signal synthesis process is also simpler than the conventional modulation method and should result in lower cost of implementation 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