Bioacoustics Research Lab
University of Illinois at Urbana-Champaign | Department of Electrical and Computer Engineering | Department of Bioengineering
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William D. O'Brien, Jr. publications:

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Your search for ultrasound produced 3296 results.

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Title Action of ultrasound on a viscoelastic solid.
Author Frost HM.
Journal Thesis(PhD): Univ of Vermont
Volume
Year 1974
Abstract A literature review of selected publications concerning the “mechanical” effects of ultrasound on bulk solids reveals that diverse media—such as metals and biological tissue—have received considerable attention, while materials intermediate in elastic or viscous properties—such as plastics—have not. Investigation of viscoeleastic solids such as plastics would help serve i) to fill a gap in our present knowledge and ii) to encourage a more unified approach in our attempts to understand the action of ultrasound on solid-like media in general. An ultrasonic composite vibrator with appropriately shaped tip was vibrated continuously at 80 to 90 kHz and at tip displacement amplitudes of 0 to 8 µm while pressed by a static force against the edge surface of a plate of strain birefingent, markedly viscoelastic epoxy. The sample was mounted on the stage of a circularly polarizing microscope. Consequently, time-averaged deformation in the epoxy plate was characterized by photographs of photoelastic fringes (chiefly isochromatics). The vibrator was driven within a negative feedback loop whose resonant frequency was sensitive to the acoustic loading effects of the epoxy sample. The combined action of the static and time-averaged sonic forces was approximately equivalent to a static line force for moderate displacement amplitudes. For a certain range of displacements, the time averaged force was a proportional to displacement. When a proportionality exists, the sonic stiffness (partial derivative of the time averaged force with respect to displacement) was found by experiment to equal the static stiffness K derived by the author. At moderate displacements, the action of ultrasound is mechanical in nature. At high large amplitude displacements, both the thermal and mechanical effects of ultrasound intervene. Sonically produced deformation in the epoxy is reversible and can be qualitatively explained in terms of a theory of linear viscoelasticity, which involves ultrasonically activated viscosity. This viscosity can be reversibly decreased by either mechanical or thermal action of the ultrasound. A solid-solid phase transition observed in the epoxy can in principle be described in terms of the ultrasonically activated viscosity. Other theory is developed for i) interpreting resonant frequency changes in terms of the material properties of the epoxy, ii) interpreting photoelastic data in terms of both the field and localized aspects of sonically induced deformation, and iii) determining by a matrix method the intensity of light emerging from the analyzer of a polarizing microscope. Some of the possible applications of this work include i) a novel test for glaucoma, ii) measurement of the elastic properties of plastics, iii) a new technique for “locking in” strain in three-dimensional photoelasticity, and iv) determination of static contact force in Mason horn studies of biological tissue such as single plant cells.


Title Action of ultrasound on nerve tissue - a review.
Author Fry WJ.
Journal J Acoust Soc Am
Volume
Year 1953
Abstract This review is concerned with (1) certain physiological and structural changes produced in tissues of the central nervous system caused by high level ultrasound and (2) investigations into the physical mechanisms underlying these changes. The cell bodies of neurons in the central nervous system are particularly susceptible to change by ultrasound. The effect of irradiation is immediately evident as a loss of function which may be reversible or irreversible depending on the dosage. Irreversible changes in function are accompanied by changes in the structure of the cell. The susceptibility of neurons studied so far is graded according to size, the larger neurons exhibiting a greater susceptibility. The dose of ultrasound can be adjusted to cause irreversible changes in neurons without causing any observable damage to the vascular and supporting components of the tissue. This selective and specific effect of ultrasound is being used as a tool in neuroanatomical studies now in progress and has considerable potential value in neurosurgery. The ultrasound alters the state of the nerve cells and, therefore, affords a basis for studying intracellular structure and function. The physical basis for the ultrasonically produced biological effects has been investigated in part. The following aspects of temperature have been analyzed and rejected: (1) High average (space) level, (2) interface heating, (3) rapid time rate of change, (4) temperature changes resulting from cavitation, (5) heating at gas nuclei. The phenomenon of cavitation is also shown to play no essential direct role in producing the effects.


Title Activation, aggregation and adhesion of platelets exposed to high-intensity focused ultrasound.
Author Poliachik SL, Chandler WL, Mourad PD, Ollos RJ, Crum LA.
Journal Ultrasound Med Biol
Volume
Year 2001
Abstract Using platelet-rich plasma, we investigated the effect of 1.1-MHz continuous wave high-intensity focused ultrasound (HIFU) on platelet activation, aggregation and adhesion to a collagen-coated surface. Platelets were exposed for durations of 10-500 s at spatial average intensities of up to 4860 W/cm(2). To avoid heating effects, the average temperature in the HIFU tank was maintained at 33.8 +/- 4.0 degrees C during platelet experiments. Flow cytometry, laser aggregometry, environmental scanning electron microscopy and passive cavitation detection were used to observe and to quantify platelet activation, aggregation, adhesion to a collagen-coated surface and associated cavitation. It was determined that HIFU can activate platelets, stimulate them to aggregate and promote their adherence to a collagen-coated surface. In principle, HIFU can stimulate primary, or platelet-related, hemostasis. Cavitation was monitored by a passive cavitation detector during aggregation trials and was quantified to provide a relative measure of the amount of cavitation that occurred in each aggregation trial. Regression analysis shows a weak correlation (r(2) = 0.11) between aggregation and ultrasound intensity, but a substantial correlation (r(2) = 0.76) between aggregation and cavitation occurrence.


Title Acute response of fetal rat telencephalon to ultrasound exposure in utero.
Author Norton S, Kimler BF, Cytacki EP, Rosenthal SJ.
Journal Exp Neurol
Volume
Year 1990
Abstract Pregnant rats were exposed to ultrasound or microwaves from transducers located over one uterine horn. Ultrasound intensity (SPTA) was 0.78 W/cm2 for 30 min at a frequency of 2.5 MHz. Microwave exposure was used to reproduce approximately the rate of rise of uterine temperature of the rats exposed to ultrasound. The average peak temperature was 40.1 degrees C for ultrasound exposure and 42.2 degrees C for microwave exposure. On Gestational Day 16, 24 h after exposure, fetuses were removed and prepared for morphological examination of the developing cerebral cortical mantle. Morphometric measurements were made of nuclear area of subventricular zone cells, number of mitoses per mm in the.ventricular zone, number of pyknotic cells in the mantle per mm, and number of ventricular macrophages per mm. Both exposures increased nuclear size and numbers of pyknotic cells and macrophages, and decreased the number of mitotic.figures. The data from the four measurements were evidence of damage from ultrasound similar to the effects produced by microwave heating. The thermal effects of ultrasound, even at relatively low levels of rise in temperature, may have been the.cause of the damage to the fetal cortex in these experiments or may have interacted with other effects of ultrasound energies to produce damage to developing neurons.


Title Adaption, development and expansion of xray mammography techniques for ultrasound mammography.
Author Kelly-Fry E, Jackson VP.
Journal J Ultrasound Med
Volume
Year 1991
Abstract New techniques for ultrasound examination of the breast have been developed and tested. These new techniques allow: 1) the whole breast to be ultrasonically imaged while it is held under the exact same compression and position orientations that are used in x-ray mammography, 2) a significant decrease in the time required for ultrasound breast examination. THere is an on-going need for improved correlation between imaging information obtained by x-ray mammography and that obtained by ultrasound mammography. Tumors and normal tissue structures can be displaced within the breast by current x-ray and ultrasound mammography techniques. However, since the type of tissue displacement for these two methods is different, correlation of the x-ray and ultrasound data is sometimes difficult. The proposed approach to ultrasound mammography should alleviate this problem. Long-term studies were carried out on materials that allow the transfer of x-ray and ultrasound energy and also provide appropriate compression of the breast. COmpression paddles fabricated from these materials were applied in an x-ray mammography unit and in an especially designed ultrasound mammograpny unit. Results indicate that the proposed method has significant potential in terms of 1) rapidly examining the breast and 2) allowing the use of higher ultrasound frequencies.


Title Adaptive filtering for reduction of speckle in ultrasonic pulse-echo.images.
Author Bamber JC, Daft C.
Journal Ultrasonics
Volume
Year 1986
Abstract Current medical ultrasonic scanning instrumentation permits the display of fine image detail (speckle) which does not transfer useful information but degrades the apparent low contrast resolution in the image. An adaptive two-dimensional filter has been developed which uses local features of image texture to recognize and maximally low-pass filter those parts of the image which correspond to fully developed speckle, while substantially preserving information associated with resolved-object structure. A first implementation of the filter is described which uses the ratio of the local variance and the local mean as the speckle recognition feature. Preliminary results of applying this form of display processing to medical ultrasound images are very encouraging; it appears that the visual perception of features such as small discrete structures, subtle fluctuations in mean echo level and changes in image texture may be enhanced relative to that for unprocessed images.


Title Adaptive focusing through layered media using the geophysical "time migration" concept.
Author Haun MA, Jones DL, O'Brien WD Jr.
Journal Proc Ultrason Symp IEEE
Volume
Year 2002
Abstract Virtually all practical algorithms for aberration correction in medical ultrasound have thus far modeled the aberrating tissues with a thin time-delay screen. While this assumption is probably reasonable for small image regions (isoplanatic patches), practical application is still difficult. In many cases, an inability to estimate the screen parameters with sufficient accuracy in the presence of aberration and speckle targets has led to disappointing performance. A new aberration correction approach is proposed, inspired by the geophysical imaging concept of time migration. This technique is motivated by considering complete, bistatic, pulse-echo data acquired from layered media, where sound speed is a function of depth only. Reflection travel times as a function of source-receiver offset in such a model are approximately hyperbolic, just as they would be if the sound speed in the medium were constant and equal to the rms speed of the layers. Seismic imaging practice has shown this approximation to be robust in the presence of minor lateral speed variations. By focusing each point in the image using a constant sound-speed assumption, but allowing this assumed speed to change from point to point, a well-focused image may be obtained. A focusing criterion is all that is needed to determine the optimum focusing speed at each image point, without a priori knowledge of the medium properties. FDTD simulations provide synthetic data acquired from a 64-element array. A simple skull model was interposed between the array and targets in one simulation; in another, a speckle-producing region with embedded cysts was imaged through a Gaussian-shaped, high-speed anomaly. In both cases, images formed using different assumed sound speeds show different parts of the image in good focus. Application of the proposed focusing criterion produces a composite image showing improvement over any single image formed assuming a constant speed of sound.


Title Adaptive speckle reduction filter for log-compressed b-scan images.
Author Dutt V, Greenleaf JF.
Journal IEEE Trans Med Imaging
Volume
Year 1996
Abstract A good statistical model of speckle formation is useful for designing a good adaptive filter for speckle reduction in ultrasound B-scan images. Previously, statistical models have been used, but they failed to account for the log compression of the echo envelope employed by clinical ultrasound systems. Log-compression helps in reducing the dynamic range of the B-scan images for display on a monitor as well as enhancing weak backscatterers. In this article, statistics of log-compressed echo images, using the K-distribution statistical model for the echo envelope, are used to derive a parameter that can be used to quantify the extent of speckle formation. This speckle quantification can be used with an unsharp masking filter to adaptively reduce speckle. The effectiveness of the filter is demonstrated on images of contrast detail phantoms and on in-vivo abdominal images obtained by clinical ultrasound system with log-compression.


Title Adult cardiology.
Author Wilde P.
Journal Ultrasound Med Biol
Volume
Year 2000
Abstract No abstract available.


Title Advance of medical application of ultrasound developed.
Author Unknown.
Journal Rep Juntendo Univ Sch Med
Volume
Year 1964
Abstract In this report, we will present the recent review of advanced medical application of ultrasound both as diagnostic and surgical tool which was developed by the Ultrasonic Research Group in Juntendo University in 1963.


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