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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Your search for ultrasound produced 3296 results.

Page 196 out of 330

Title Performance of the mean frequency doppler modulator.
Author Gill RW.
Journal Ultrasound Med Biol
Volume
Year 1979
Abstract The mean frequency Doppler demodulator is of interest of quantitative measurement of blood flow, particularly in small or deep-lying vessels. It is thus desirable that the various potential sources of error be considered, and that their effects on its performance be quantified where possible. This paper analyzes the effects of interfering noise, more than one vessel falling within the Doppler sample volume, Doppler filtering, frequency aliasing, and double-sidebanding of the Doppler signal. The analysis applies to either frequency offset or non-offset Doppler systems, and a variety of blood velocity distributions is considered. It is shown that, in a number of instances, the errors can be predicted and therefore corrected. Experimental results are presented confirming the theoretical analysis.


Title Performance of the ultrasound microscope.
Author Jacobs JE.
Journal Mater Eval
Volume
Year 1967
Abstract The resolution capability of the Ultrasound Microscope, whose operation depends upon the use of a piezoelectric acoustic to charge pattern converter, is limited by the electro-acoustic properties of that layer. The minimum resolvable detail of the system when operating a maximum sensitivity and maximum resolution is set by the thickness of the piezoelectric converter surface. Maximum resolution is only obtained if the incident sound pattern does not deviate more than 2 degrees from the normal to the piezoelectric surface. This requirement severely limits the permissible aperture of the optics that may be used with the system. Due to this characteristic, the use of optics will result in a degrading of the maximum obtainable resolution by a factor of approximately two times. Performance characteristics of the overall system are calculated and demonstrated by means of standard microscopy resolution tests.


Title Performance of ultrasonic speckle tracking in various tissues.
Author Chen EJ, Jenkins WK, O'Brien WD Jr.
Journal J Acoust Soc Am
Volume
Year 1995
Abstract The purpose of this study was to investigate the accuracy of ultrasound speckle tracking in various tissues. Results from two-dimensional tissue speckle tracking in liver, muscle, fat, and sponge samples are presented, while keeping other speckle tracking parameters constant. Speckle tracking performance was characterized both in terms of the magnitude of tracking errors and in terms of the percentage of correctly tracked displacement vectors. Speckle tracking in muscle tissue, which contains myofibrils and significant tissue microstructure, produced the highest percentage of correctly tracked vectors and smallest tracking errors relative to other tissues.


Title Peripheral pulmonary lesions: Ultrasonic features and ultrasonically guided fine needle.aspiration biopsy.
Author Targhetta R, Bourgeois JM, Marty-Double C, Coste E, Proust A,.Balmes P, Pourcelot L.
Journal J Ultrasound Med
Volume
Year 1993
Abstract When transthoracic biopsy is required for diagnosing lung diseases, radiographic procedures are the methods of choice, sonographic application being still limited. Sixty-four consecutive patients with pulmonary lesions adjacent to the chest wall underwent sonography. Findings showed hypoechoic homogeneous lesions (56 cases) with posterior regular margin (57 cases). Increasing echoes deep to the mass and sonographic interruption of hyperechoic surface were seen in all patients. In two cases, chest wall invasion had been diagnosed. Histologic diagnosis was made in 55 of the 64 patients (85.9%). Two pneumothoraces occurred. Sonography is a useful, accurate, and safe technique for diagnosing selected pulmonary lesions.


Title Perspective on biomedical quantitative ultrasound imaging.
Author Mamou J, Oelze ML, O'Brien WD Jr., Zachary JF.
Journal IEEE Signal Process Mag
Volume
Year 2006
Abstract This paper discusses the recent advances in the highly multidisciplinary field of quantitative ultrasound (QUS) imaging. QUS relies heavily on signal processing techniques to extract information about underlying tissue microstructure. As such, modern signal processing strategies will prove to be critical in further improving and refining QUS techniques.


Title Perspectives in clinical uses of high-intensity focused ultrasound.
Author Clement GT.
Journal Ultrasonics
Volume
Year 2004
Abstract Focused ultrasound holds promise in a large number of therapeutic applications. It has long been known that high intensity focused ultrasound can kill tissue through coagulative necrosis. However, it is only in recent years that practical clinical applications are becoming possible, with the development of high power ultrasound phased arrays and noninvasive monitoring methods. These technologies, combined with more sophisticated treatment planning methods allow noninvasive focusing in areas such as the brain, that were once thought to be unreachable. Meanwhile, exciting investigations are underway in microbubble-enhanced heating which could significantly reduce treatment times. These developments have promoted an increase in the number of potential applications by providing valuable new tools for medical research. This paper provides an overview of the scientific and engineering advances that are allowing the growth in clinical focused ultrasound applications. It also discusses some of these prospective applications, including the treatment of brain disorders and targeted drug delivery.


Title Phase aberration correction and motion compensation for ultrasonic hyperthermia phased arrays: Experimental Results.
Author Wang H Ebbini ES O'Donnell M Cain CA.
Journal IEEE Trans UFFC
Volume
Year 1994
Abstract In ultrasound hyperthermia, focal patterns generated by phased arrays can be degraded by phase errors due to tissue inhomogeneities, digitization of the driving signals, and imperfect fabrication of the transducers. The degree of degradation depends on the severity of phase aberrations. As predicted by simulation and verified by experimental results, focal degradation scales with the circular variance of phase errors. However, degraded power deposition patterns can be significantly improved after phase aberration correction, especially where patterns are complicated and the aberrations are severe. Also, as shown in motion compensation experiments, an aberration corrected pattern can be particularly sensitive to aberrator movement greater than the correlation length of the aberrator. After motion compensation, new sharply focused patterns can be accomplished, thus reducing the unwanted influence of ?body? movement by stabilizing the positions of foci with respect to patient anatomy.


Title Phase aberration correction in medical ultrasound using speckle brightness as a quality factor.
Author Nock L, Trahey GE, Smith SW.
Journal J Acoust Soc Am
Volume
Year 1989
Abstract Medical ultrasonic images are degraded by tissues with inhomogeneous acoustic velocities. The resulting phase aberration raises the off-peak response of the imaging system's point spread function (PSF), decreasing dynamic range. In extreme cases, multiple images of a single target are displayed. Phase aberration may become a limiting factor to image quality as ultrasonic frequency and aperture size are increased in order to improve spatial resolution. A method is proposed to correct for unknown phase aberration, which uses speckle brightness as a quality factor. The phase delays of a phased array transducer are modified, element by element, to maximize mean speckle brightness in a region of interest. The technique proposed is analogous to the correction technique used by Muller and Buffington [J. Opt. Soc. Am. 64 (9), 1200-1209 (1974)] to adaptively focus incoherent optical telescopes. The method is demonstrated using a computer model with several different simulated aberration profiles. With this model, mean speckle brightness is calculated using the two-dimensional PSF. Experiments have also been conducted in which speckle brightness is shown to increase as the phase delays of an ultrasonic scanner are modified in order to compensate for a rippled aberrating layer made of silicone rubber. The characteristics of the proposed method, and the possibility of employing it clinically to correct for unknown inhomogeneities in acoustic velocity, are discussed.


Title Phase aberration correction using echo signals from moving targets. II: Experimental system and results.
Author Bohs LN, Zhao D, Trahey GE.
Journal Ultrason Imaging
Volume
Year 1992
Abstract A method for correcting errors due to near-field tissue inhomogeneities in phased array ultrasound images is evaluated experimentally. The method uses the brightness of a moving speckle-generating target, such as blood, as a quality factor to correct for unknown phase aberrations. A real time experimental system utilizing the technique has been constructed and is described. Initial results from in vitro studies using a flow phantom are compared to theoretical predictions. The results indicate that the technique can provide significant improvements in image quality when imaging through aberrating media, and may find application in clinical imaging through skull and fatty layers.


Title Phase aberration measurements in medical ultrasound: Human studies.
Author O'Donnell, Flax SW.
Journal Ultrason Imaging
Volume
Year 1988
Abstract Using a modified real-time phased array sector scanner, phase aberrations and amplitude fluctuations across the imaging aperture have been measured in a number of human subjects. Data from these subjects were classified into two categories based on the quality of conventional longitudinal images of the liver. Measured phase aberrations were very small in all subjects exhibiting high quality images. In contrast, large phase aberrations were measured in subjects producing low quality images. However, there were no significant amplitude variations across the array for all subjects studied. These results suggest that the absence of significant phase aberrations is a necessary condition for high quality phased array imaging. If so, improvements in clinical image quality in such subjects may be possible.


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