Bioacoustics Research Lab
University of Illinois at Urbana-Champaign | Department of Electrical and Computer Engineering | Department of Bioengineering
Department of Statistics | Coordinated Science Laboratory | Beckman Institute | Food Science and Human Nutrition | Division of Nutritional Sciences | College of Engineering
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William D. O'Brien, Jr. publications:

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Title Power spectral strain estimators in elastography.
Author Konofagou EE, Varghese T, Ophir J, Alam SK.
Journal Ultrasound Med Biol
Volume
Year 1999
Abstract Elastography can produce quality strain images in vitro and in vivo. Standard elastography uses a coherent cross-correlation technique to estimate tissue displacement and tissue strain using a subsequent gradient operator. Although coherent estimation methods generally have the advantage of being highly accurate and precise, even relatively small undesired motions are likely to cause enough signal decorrelation to produce significant degradation of the elastogram. For elastography to become more universally practical in such applications as hand-held, intravascular and abdominal imaging, the limitations associated with coherent strain estimation methods that require tissue and system stability, must be overcome. In this paper, we propose the use of a spectral-shift method that uses a centroid shift estimate to measure local strain directly. Furthermore, we also show theoretically that a spectral bandwidth method can also provide a direct strain estimation. We demonstrate that strain estimation using the spectral-shift technique is moderately less precise, but far more robust than the cross-correlation method. A theoretical analysis, simulations and experimental results are used to illustrate the properties associated with this method.


Title Precision and accuracy of acoustospectrographic parameters.
Author Huisman HJ, Thijssen JM.
Journal Ultrasound Med Biol
Volume
Year 1996
Abstract Theoretical estimates of the standard deviation (STD) of four acoustospectrographic parameters (the intercept and slope of attenuation and backscatter coefficient) are derived. This derivation expands and corrects existing derivations, and is confirmed using simulations based on the adopted theoretical model. A robust parameter estimation method is applied to various phantom measurements, and to in vivo liver scans of healthy human subjects. The measured STD is higher than the theoretically predicted value, and we investigated four possible factors which explain this discrepancy. First, it is shown that the STD and bias after spectrogram calculation are rather insensitive to changes in windowing function, type, length and overlap. Second, we observed that a diffraction correction spectrogram calibrated on a medium different from the one being measured insufficiently corrects the depth-dependency of the parameters, which affects both precision as well as accuracy. We therefore propose a method that constructs an organ-specific diffraction correction spectrogram from the averaged spectrogram of a set of normal organs. We show that the organ-specific correction does not affect STD even in case of previously unseen acquisitions. Third, we introduce local inhomogeneity, which predicts excess STD due to local variations of the physical parameters within an organ (i.e., intrasubject), and global inhomogeneity, which predicts variations between organs (i.e., intersubject). We conclude that our method of estimating STD predicts normal, in vivo data very well, and propose that the deviation from these estimates is a potential tissue characterization parameter.


Title Predicting the acoustic response of a microbubble population for contrast imaging in medical ultrasound.
Author Chin CT, Burns PN.
Journal Ultrasound Med Biol
Volume
Year 2000
Abstract Although the behavior of a bubble in an acoustic field has been studied extensively, few theoretical treatments to date have been applied to simulate the acoustic response of a real population of variably sized microbubbles in a finite-width sound beam. In this paper, we present a modified Trilling equation for single bubble dynamics that has been solved numerically for different conditions. Radiated waveforms from a large number of such bubbles are combined, reflecting their size distribution and location and the shape of a real acoustic beam. The resulting time-domain pressure waveforms can be compared with those obtained experimentally. The dependence of second-harmonic radiation on incident focal amplitude at different frequencies is presented. This model is particularly suited to the study of interaction between a medical ultrasound beam and microbubble contrast agents in aqueous media.


Title Prediction and comparison of in situ acoustic pressure levels for linearly derated fields and nonlinear tissue fields.
Author Gandhi DR.
Journal Thesis(MS): Univ of Illinois
Volume
Year 1993
Abstract Nonlinear wave propagation plays an important role in medical ultrasound due to the high acoustic pressure amplitude levels employed. Measurements to comply with labeling standards and FDA requirements for diagnostic equipment are performed in water, a medium readily available and easy to use. To predict the fields in tissue, an attenuating and absorbing medium, the FDA has established a derating factor of 0.3 dB/cm-MHz. This model, however, is based on a simple linear model which does not take into account the nonlinearity of the medium nor does it consider the effects of diffraction. This thesis provides some implications when these effects are taken into account.


Title Prediction of frequency-dependent ultrasonic backscatter in cancellous bone using staitstical weak scattering model.
Author Jenson F,Padilla F,Laugier P.
Journal Ultrasound Med Biol
Volume
Year 2003
Abstract The goal of this study was to propose a model for the ultrasonic frequency-dependent backscatter coefficient in cancellous bone. This model allows us to address the inverse problem and to predict the mean trabecular thickness. A weak scattering model is used and the backscatter coefficient is expressed in terms of an autocorrelation function of the medium. Different autocorrelation functions (Gaussian, exponential and densely populated media) were used to compute the backscatter coefficient and comparison is made with experimental data for 19 specimens and for frequency ranging from 0.4 to 1.2 MHz. For each specimen, a nonlinear regression was performed and the mean trabecular thickness is estimated. Experimental data and theoretical predictions were averaged over the 19 specimens. A good agreement between experimental data and predictions was found for both the magnitude and the frequency-dependence of the backscatter coefficient. We also found a good agreement between the experimental mean trabecular thickness (Tb · Th = 130 ± 6.5 μm) derived from the analysis of bone 3-D microarchitecture using high-resolution microtomography and theoretical predictions (dGauss = 140 ± 10 μm, dexponential = 153 ± 12.5 μm and ddense = 138 ± 6.5 μm). These results open interesting prospects for the estimation of the mean trabecular thickness from in vivo measurements. Keywords: Trabecular thickness; Backscatter coefficient; Cancellous bone; Weak scattering; Inverse problem; Autocorrelation function; Ultrasound.


Title Prediction of in situ exposure to ultrasound: An acoustical attenuation method.
Author Preston RC, Shaw A, Zeqiri B.
Journal Ultrasound Med Biol
Volume
Year 1991
Abstract The prediction of the acoustic levels occurring in a patient during ultrasound examination is important for the assessment of equipment safety. While considerable effort has been devoted to theoretical methods of predicting exposure levels, there is a need to develop simple experimental methods which are universally applicable to the wide range of ultrasonic fields generated by medical ultrasonic equipment. This article outlines a number of methods that have been proposed and explores in detail a new experimental method based on the use of acoustical attenuators, made of low-density polyethylene, which are placed in the ultrasound beam between the transducer and the measuring hydrophone. Measurements of important acoustical quantities have been made using a measurement system based on a multielement hydrophone and comparisons made between this new method and other methods such as electrical attenuation and linear derating theory. The acoustical attenuation technique has been systematically studied, and results are compared with reference levels obtained using tissuemimicking material. A procedure involving making measurements with the attenuator placed first at the face of the transducer and then at the hydrophone has been developed. By taking the mean value of these two measurements, it has been shown that this new method can simulate within ?10% the acoustic levels obtained using the reference. It is concluded that it could be the basis of a universally applicable method.


Title Prediction of nonlinear acoustic effects at biomedical frequencies and intensities.
Author Muir TG, Carstensen EL.
Journal Ultrasound Med Biol
Volume
Year 1980
Abstract Some fundamentals of nonlinear acoustics are reviewed to facilitate their consideration in biomedical ultrasound. The phenomena described include acoustic nonlinearity, finite amplitude distortion, shock formation, harmonic components, nonlinearly induced absorption, saturation, and the influence of these effects on ultrasonic beams. The simplified results of several theoretical derivations are presented and employed in illustrative calculations and plots. These may be used to ascertain the importance of nonlinear effects in applications involving plane waves, spherically diverging waves, and spherically converging (focused) waves. A discussion of relevant experiments is given, along with some comments on possible consequences in diagnostic, surgical, and therapeutic applications.


Title Prediction of the temporal shape of an ultrasonic pulse in a photoacoustic sensing application.
Author Oksanen M, Wu J.
Journal Ultrasonics
Volume
Year 1994
Abstract Temporal shapes of low power photoacoustic sound sources were predicted and measured. The applicability of a relatively low-power laser in generating detectable ultrasound for a sensing application was confirmed.


Title Prediction of ultrasonic scattering in blood: an historical note.
Author Ahuja AS.
Journal Ultrasound Med Biol
Volume
Year 1979
Abstract No abstract available - article is a letter to the editor.


Title Preliminary report on morphological changes to mouse testicular tissue from in vivo ultrasonic irradiation.
Author O'Brien WD Jr, Brady JK, Graves CN, Dunn F.
Journal Proc Symp Biol Eff Character Ultrasound Sour
Volume
Year 1977
Abstract Use of ultrasonic diagnostic equipment on, or in close proximity to, the male reproductive organs appears to be increasing (Miskin and Bain, 1974; Albright and Harris, 1975). At present, no data exists upon which to base risk assessment for exposure to ultrasound of the testes.A study has been initiated for the purpose of providing basic information regarding the interaction between ultrasound and mouse testicular tissue. A portion of this work concerning the ultrasonic absorption coefficient of testicular tissue has been reported (Brady et al., 1976). This paper deals with a continuation of that work in which ultrasonically induced morphological changes in the testis are examined. Testes are the principal male organ which produce spermatozoa. The production of spermatozoa is called spermatogenesis and consists of spermatocytogenesis and spermiogenesis. In the mouse spermatocytogenesis begins with a stem cell or type A spermatogonium which gives rise to a smaller type B spermatogonium through the intermediate spermatogonium. Type B spermatogonium either divide or metamorphose into primary spermatocytes which has two set of chromosomes. The first meiotic division of the primary spermatocyte yields two haploid secondary spermatocytes. The second meiotic division yields four spermatids, each with one set of monovalent chromosomes, which signals the beginning of spermiogenesis. Spermiogenesis, the transformation of a spermatid into a spermatozoon, involves no divisions. At any given cross-sectional segment of the seminiferous tubule type A spermatogonia are initiating the spermatogenesis cycle which will liberate spermatozoa some 34.5 days later. Spermatocytogenesis requires approximately 25 days and spermiogenesis is 9.5 days. This cycle is initiated every 8.6 days (Monesi, 1972; Rugh, 1968; Nalbandov, 1976).


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