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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 118 out of 330
| Title |
Evidence that ultrasonically-induced microbubbles carry a negative electrical charge. |
| Author |
Watmough DJ, Shiran MB, Quan KM, Sarvazyan AP, Khizhnyak EP, Pashovkin TN. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1992 |
| Abstract |
When ultrasound, propagating in a cationic dye solution, is incident on a porous material such as paper, the diffraction pattern of the sound field is recorded by virtue of variations of dye concentration retained on the paper surface. By examining such patterns formed with "Methylene Blue" dye and comparing with those obtained with "Direct Sky Blue" dye, it is concluded that the mechanism of pattern formation requires the presence of an electric field to be induced "close to the paper surface." Using light directed at grazing incidence to illuminate the sonicated paper surface it is possible to demonstrate and record photographically a mapping of microscopic bubbles caused by sonication which has, broadly, the geometric features of a diffraction pattern. Theoretical arguments are adduced to show that such bubbles should generate a significant electric field close to the paper. In order to confirm that this field will alter dye deposition on paper, electrodes were affixed to the underside of the same paper as used to make the dye patterns. When an externally generated potential (1 kV) was applied, the Methylene Blue and Sky Blue dyes were deposited on the paper close to the negative and positive electrodes respectively. We therefore conclude that acoustically-induced gas bubbles carry a negative electric charge and for micrometre-sized bubbles we estimate the field to be about 7 x 10(exp)5 V/m. There is no a priori reason to expect acoustically excited bubbles to have the same charge as that on comparatively stable bubbles mechanically introduced into water. These findings raise again the question of whether phenomena such as sonoluminescence are caused by microscopic electrical discharges and whether inter-bubble forces are adequately described by current theories. |
| Title |
Evolving applications for contrast ultrasound. |
| Author |
Lindner JR. |
| Journal |
Am J Cardiol |
| Volume |
|
| Year |
2002 |
| Abstract |
Future clinical applications for contrast-enhanced ultrasound will likely expand beyond perfusion imaging. There has been considerable progress in the past few years in the development of site-targeted microbubbles, such that instead of passing unimpeded through the circulation, they attach to specific markers of disease. Accumulation of targeted microbubbles in diseased tissue can allow noninvasive ultrasound imaging of molecular and cellular processes. In this review, the strategies for designing site-targeted microbubbles and the early experience with molecular imaging will be discussed. The use of microbubbles and ultrasound for therapeutic purposes is also just now being realized. A promising development is the ability to package either drugs or genes into or onto microbubble contrast agents. Conceptually, ultrasound-mediated destruction of microbubble vehicles will provide focal release in a tissue of interest and may facilitate extravascular sojourn of the therapeutic agent. Preliminary experience using microbubbles as vectors for gene delivery is also reviewed. |
| Title |
Ex vivo study of quantitative ultrasound parameters in fatty rabbit livers. |
| Author |
Ghoshal G, Lavarello RJ, Kemmerer JP, Miller RJ, Oelze ML. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2012 |
| Abstract |
Nonalcoholic fatty liver disease (NAFLD) affects more than 30% of Americans, and with increasing problems of obesity in the United States, NAFLD is poised to become an even more serious medical concern. At present, accurate classification of steatosis (fatty liver) represents a significant challenge. In this study, the use of high-frequency (8 to 25 MHz) quantitative ultrasound (QUS) imaging to quantify fatty liver was explored. QUS is an imaging technique that can be used to quantify properties of tissue giving rise to scattered ultrasound. The changes in the ultrasound properties of livers in rabbits undergoing atherogenic diets of varying durations were investigated using QUS. Rabbits were placed on a special fatty diet for 0, 3, or 6 weeks. The fattiness of the livers was quantified by estimating the total lipid content of the livers. Ultrasonic properties, such as speed of sound, attenuation, and backscatter coefficients, were estimated in ex vivo rabbit liver samples from animals that had been on the diet for varying periods. Two QUS parameters were estimated based on the backscatter coefficient: effective scatterer diameter (ESD) and effective acoustic concentration (EAC), using a spherical Gaussian scattering model. Two parameters were estimated based on the backscattered envelope statistics (the k parameter and the m parameter) according to the homodyned K distribution. The speed of sound decreased from 1574 to 1565 m/s and the attenuation coefficient increased from 0.71 to 1.27 B/cm/MHz, respectively, with increasing fat content in the liver. The ESD decreased from 31 to 17 mm and the EAC increased from 38 to 63 dB/cm3 with increasing fat content in the liver. A significant increase in the m parameter from 0.18 to 0.93 scatterers/mm3 was observed with increasing fat content in the liver samples. The results of this study indicate that QUS parameters are sensitive to fat content in the liver. (E-mail: oelze@illinois.edu) 2012 World Federation for Ultrasound
in Medicine & Biology. |
| Title |
Ex-vivo studies of the effect of high‐intensity focused ultrasound on whole human blood. |
| Author |
Poliachik S, Chandler W, Mourad PD, Bloch S, bailey M, Cleveland R, Crum LA, Kaczkowski P, keilman G, Porter T. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1998 |
| Abstract |
No Abstract Available. |
| Title |
Exact evaluation of an ultrasonic scattering formula for a rigid immovable sphere. |
| Author |
Jafari F, Madsen EL, Zagzebski JA, Goodsitt MM. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1981 |
| Abstract |
It has been discovered that three theoretically derived plots of acoustic scattering for rigid immovable spheres appearing in two standard reference works are only qualitatively correct and therefore could be misleading. The reason for the inaccuracy is shown to be premature truncation of the infinite series resulting from the theory. Quantitative plots resulting from exact computations and those corresponding to premature truncations are displayed. The main purpose of this note is to alert others, who may wish to check their programming of theoretical expressions for scattering of ultrasonic waves from spheres, to the error of using the plots in the standard reference works and to suggest that they use the exact results presented here. |
| Title |
Examination of inertial cavitation of Optison in producing sonoporation of chinese hamster ovary cells. |
| Author |
Forbes MM, Steinberg RL, O'Brien WD Jr. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2008 |
| Abstract |
The objective of this project was to elucidate the relationship between ultrasound contrast agents (UCAs) and sonoporation. Sonoporation is an ultrasound-induced, transient cell membrane permeability change that allows for the uptake of normally impermeable macromolecules. Specifically, this study will determine the role that inertial cavitation plays in eliciting sonoporation. The inertial cavitation thresholds of the UCA, Optison, are compared directly with the results of sonoporation to determine the involvement of inertial cavitation in sonoporation. Chinese hamster ovary (CHO) cells were exposed as a monolayer in a solution of Optison, 500,000 Da fluorescein isothiocyanate-dextran (FITC-dextran), and phosphate-buffered saline (PBS) to 30 s of pulsed ultrasound at 3.15-MHz center frequency, 5-cycle pulse duration and 10-Hz pulse repetition frequency. The peak rarefactional pressure (P(r)) was varied over a range from 120 kPa-3.5 MPa, and five independent replicates were performed at each pressure. As the P(r) was increased, from 120 kPa-3.5 MPa, the fraction of sonoporated cells among the total viable population increased from 0.63-10.21%, with the maximum occurring at 2.4 MPa. The inertial cavitation threshold for Optison at these exposure conditions has previously been shown to be in the range 0.77-0.83 MPa, at which sonoporation activity was found to be 50% of its maximum level. Furthermore, significant sonoporation activity was observed at pressure levels below the threshold for inertial cavitation of Optison. Above 2.4 MPa, a significant drop in sonoporation activity occurred, corresponding to pressures where >95% of the Optison was collapsing. These results demonstrate that sonoporation is not directly a result of inertial cavitation of the UCA, rather that the effect is related to linear and/or nonlinear oscillation of the UCA occurring at pressure levels below the inertial cavitation threshold. |
| Title |
Examination of lymphocytes for chromosome aberrations after ultrasonic irradiation. |
| Author |
Coakley WT, Slade JS, Braeman JM, Moore JL. |
| Journal |
Br J Radiol |
| Volume |
|
| Year |
1972 |
| Abstract |
The chromosomes of human lymphocytes have been irradiated with ultrasound at frequencies used in medical diagnostic equipment. Examination of over 1,000 lymphocytes irradiated in whole blood under different ultrasonic regimes did not show a significant incidence of chromosome aberrations. In early experiments on irradiating cells in tissue culture medium chromosome and chromatid gaps were observed. The damage showed no detectable dependence on sonic intensity and time of irradiation and the control cells also showed a high incidence of aberrations. It was considered that the damage did not arise from sonication. No acentric fragments, ring or dicentric chromosomes were observed in any of the experiments. |
| Title |
Excess risk thresholds in ultrasound safety studies: Statistical methods for data on occurrence and size of lesions. |
| Author |
Simpson DG, Ho M-H, Yang Y, Zhou J, Zachary JF, O'Brien WD Jr. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2004 |
| Abstract |
Concerns about the safe use of clinical ultrasound (US) at diagnostic pressure levels (below a mechanical index, or MI, = 1.9) have stimulated considerable research in US risk assessment. The objective of the present study was to develop probability-based risk thresholds for US safety studies, to present statistical methods for estimating the thresholds and their standard errors and to compare these methods with the analysis based on a piecewise linear (“hockey stick”) model. The excess risk at exposure level x > 0 was defined as the relative increase in the probability of a lesion at that level compared with the background probability of a lesion at exposure x = 0. The risk threshold was then defined as the exposure level at which the excess risk exceeded a specified level (e.g. 5% or 50%). Thus, given pressure-dependent estimates of the excess risk, the thresholds were estimated by solving the risk equation to obtain the pressure at which the target level of excess risk occurs. Threshold estimates of this type have been developed extensively in the literature for incidence (presence or absence) data. Only recently, however, have excess risk threshold estimates been derived for data in which lesion size (depth, surface area) is measured if present and a zero is recorded if the lesion is absent. Tobit regression was used to estimate pressure-dependent percentiles of the size distribution, and the excess risks were estimated from the tobit probability of a positive-valued response. The tobit model provides a well-established approach to modeling data constrained to be nonnegative. Solving the risk equation for the tobit model leads to risk threshold estimates that incorporate the information on size of observed lesions. Results using these probability-based risk estimates were compared with results for a piecewise linear (“hockey stick”) model, which has also been used in the US safety literature, although it does not explicitly address the nonnegativity constraint in the sampling model. The comparisons were carried out for data from two previously published studies, from different laboratories, on US-induced lung hemorrhage. The thresholds derived from logistic regression of lesion occurrence and tobit regression of lesion size were quite consistent with each other and within sampling error. The hockey stick thresholds, defined as the exposure level at which the piecewise linear model for the probability of the expected size of a lesion bends upward, corresponded to quite different excess risk values for incidence (lesion occurrence) compared with size (lesion surface area or depth), although these methods have been developed previously for both types of data. The use of probability-based excess risk thresholds is recommended to obtain consistent incidence vs. size thresholds and to ensure that the thresholds are well-defined and interpretable independent of the details of the statistical model. |
| Title |
Excitation of polymer-shelled contrast agents with high-frequency ultrasound. |
| Author |
Ketterling JA, Mamou J, Allen JS III, Aristizabal O, Williamson RG, Turnbull DH. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2007 |
| Abstract |
Few experimental and complementary theoretical studies have investigated high-frequency (>20 MHz) nonlinear responses from polymer-shelled ultrasound contrast agents. Three polymer agents with different shell properties were examined for their single-bubble backscatter when excited with a 40 MHz tone burst. Higher-order harmonic responses were observed for the three agents; however, their occurrence was at least partly due to nonlinear propagation. Only one of the agents (1.1 microm mean diameter) showed a subharmonic response for longer excitations (approximately 10-15 cycles) and midlevel pressure excitations ( 2.5 MPa). Theoretical calculations of the backscattered spectrum revealed behavior similar to the experimental results in specific parameter regimes. |
| Title |
Experiences in the treatment of menieres disease with ultrasound. |
| Author |
Angell JJ. |
| Journal |
HNO |
| Volume |
|
| Year |
1970 |
| Abstract |
No abstract available |
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