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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 23 out of 330
| Title |
Aberration correction for time-domain ultrasound diffraction tomography. |
| Author |
Mast TD. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2002 |
| Abstract |
Extensions of a time-domain diffraction tomography method, which reconstructs spatially dependent sound speed variations from far-field time-domain acoustic scattering measurements, are presented and analyzed. The resulting reconstructions are quantitative images with applications including ultrasonic mammography, and can also be considered candidate solutions to the time-domain inverse scattering problem. Here, the linearized time-domain inverse scattering problem is shown to have no general solution for finite signal bandwidth. However, an approximate solution to the linearized problem is constructed using a simple delay-and-sum method analogous to "gold standard" ultrasonic beamforming. The form of this solution suggests that the full nonlinear inverse scattering problem can be approximated by applying appropriate angle- and space-dependent time shifts to the time-domain scattering data; this analogy leads to a general approach to aberration correction. Two related methods for aberration correction are presented: one in which delays are computed from estimates of the medium using an efficient straight-ray approximation, and one in which delays are applied directly to a time-dependent linearized reconstruction. Numerical results indicate that these correction methods achieve substantial quality improvements for imaging of large scatterers. The parametric range of applicability for the time-domain diffraction tomography method is increased by about a factor of 2 by aberration correction. |
| Title |
Aberration correction with OFF: the overdetermined, fan-filtering algorithm. |
| Author |
Haun MA, Jones DL, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2003 |
| Abstract |
As medical ultrasound imaging moves to larger apertures and higher frequencies, tissue sound-speed variations continue to limit resolution. In geophysical imaging, a standard approach for estimating near-surface aberrating delays is to analyze the time shifts between common-midpoint signals. This requires the collection of complete data - echoes from every combination of an individual source and receiver. Unfocused, common-midpoint signals remain highly correlated in the presence of aberration; there is also tremendous redundancy in the data. In medical ultrasound, this technique has been severely impaired by the wide-angle, random scattering nature of tissue. Until now, it has been difficult to estimate azimuth dependent aberration profiles or to harness the full redundancy in the complete data. Prefiltering the data with two-dimensional fan filters largely solves these problems, permitting highly overdetermined, least-squares solutions for the aberration profiles at many steering angles. In experiments with a tissue-mimicking phantom target and silicone rubber aberrators at non-zero stand-off distances from a 1-D array transducer, this overdetermined, fan-filtering algorithm (OFF) significantly outperformed other published algorithms. |
| Title |
Aberration correction without the need for a beacon signal. |
| Author |
O'Donnell M, Flax SW. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1988 |
| Abstract |
Phase aberrations induced by spatial inhomogeneities in the index of refraction are a major problem in all coherent imaging systems. In this paper, methods for phase aberration correction applicable to all coherent imaging systems, and especially to medical ultrasound imaging using array transducers, are discussed. In particular, a method for aberration correctio which has no need for a beacon or an ideal point reflector to act as a source for estimating phase errors is presented. The results of measurements on actual array transducers will be shown to demonstrate the utility of the method. |
| Title |
Ability of high-intensity ultrasound to ablate human.atherosclerotic plaques and minimize debris size. |
| Author |
Ernst A, Schenk EA, Gracewski SM, Woodlock TJ, Murant FG, Alliger H, Meltzer RS. University of Rochester, New York. |
| Journal |
Am J Cardiol |
| Volume |
|
| Year |
1991 |
| Abstract |
To investigate whether high-intensity ultrasound can destroy atherosclerotic plaques while.sparing the normal arterial wall, 279 normal human aortic sites and 119 fibrous and 193 calcified.plaques, obtained from 24 necropsies, were insonified in a water tank, at 20 kHz and at 5.different power intensities, ranging from 68 W/cm2 (P1) to 150 W/cm2 (P5). These intensities.were associated with a total excursion of the ultrasound irradiation apparatus tip from 90 to 268.microns, respectively. Time to perforate normal aortic sites and fibrous and calcified plaques was.recorded at each intensity. There was no difference in perforation time between normal aortic.sites and fibrous and calcified plaques when high-power levels (P2 to P5) were used. However,.at the lowest power (P1), perforation time for the normal aortic wall was significantly longer than.for fibrous and calcified plaques: 30 +/- 18 seconds (166 observations), 14 +/- 7 seconds (p less.than 0.001) (78 observations) and 12 +/- 8 seconds (p less than 0.001) (115 observations),.respectively. When perforation times for normal vessel wall versus fibrous plaque and normal.vessel wall versus calcified plaque from the same necropsy specimen were compared in a.pairwise manner, the results were: 29 +/- 13 vs 16 +/- 7 (p less than 0.001) (48 paired.observations) and 26 +/- 9 vs 10 +/- 5 seconds (p less than 0.001) (55 paired observations),.respectively. Regardless of whether paired or unpaired comparison was applied, no significant.difference was found in perforation time between fibrous and calcified plaques. The debris did.not differ in size as measured separately for normal sites and fibrous and calcified plaques by a.computer-interfaced Channelizer and Coulter Counter system. |
| Title |
Absence of a mutagenic effect of diagnostic ultrasound in the Salmonella mutagenicity test (Ames test). |
| Author |
Wegner RD, Lang R. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1986 |
| Abstract |
The mutagenic potential of diagnostic ultrasound in vitro was analyzed in the Ames test using seven major tester strains of Salmonella typhimurium: TA 1535 and TA 100 for detection of base pair substitutions; TA 1537, TA 1538, TA 97, and TA 98 for detection of frameshift mutations; and TA 102 which detects a variety of oxidative mutagens. Two commercially available ultrasound units were used in the experiments, one emitting a continuous beam with a SPTA intensity of 10.1 mW/cm2 at a frequency of 2.2 MHz, the other a pulsed beam with a SATA intensity of 0.10 mW/cm2 and a SPTP intensity of 0.54 W/cm2 at a frequency of 2.5 MHz. The tester strains were sonicated up to 60 min. No evidence for an induction of point mutations were found. |
| Title |
Absence of an effect of diagnostic ultrasound on sister-chromatid exchange induction in human lymphocytes in vitro. |
| Author |
Miller MW, Wolff S, Filly R, Cox C, Carstensen EL. |
| Journal |
Mutat Res |
| Volume |
|
| Year |
1983 |
| Abstract |
The frequency of sister-chromatid exchanges in human lymphocytes cultured in vitro was not changed after a 30-min exposure to a 2 MHz focused, diagnostic ultrasound beam with a pulse repetition rate of 1000 Hz, 1 musec burst duration, 100 W/cm(^2) temporal peak, spatial peak intensity. These results are consistent with.those obtained with a number of other cell types and are contrary to some previously reported effects for human lymphocytes. |
| Title |
Absence of an ultrasound effect on in vitro lymphocyte sister chromatid exchange. |
| Author |
Brulfert A, Ciaravino V, Miller MW, Carstensen EL. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1983 |
| Abstract |
The frequency of sister chromatid exchanges (SCEs) in human lymphocytes cultured in vitro was not affected by a 30 min exposure to 2.25 MHz focused ultrasound beam (from a clinical diagnostic unit with a pulse repetition rate of 1000 Hz, a 1 ?sec burst duration, and a 2-200 W/cm2 maximum intensity. A 30 sec exposure to CW 1 MHz 2 W/cm2 (SP) ultrasound from an experimental device lysed 10-15 percent of the lymphocytes; there was no increase in SCEs in the survivors relative to unexposed controls. Treatment of lymphocytes with 0.033 ?g/ml mitomycin-C, a known SCE inducer, increased the frequency of SCEs about 4 times above control levels. |
| Title |
Absence of mitotic reduction in regenerating rat livers exposed to ultrasound. |
| Author |
Miller MW, Kaufman GE, Cataldo FL, Carstensen EL. |
| Journal |
J Clin Ultrasound |
| Volume |
|
| Year |
1976 |
| Abstract |
The frequency of mitotic cells in surgically stimulated rat livers in vivo was not affected by one- and five-minute exposures to 2.2 MHz ultrasound at intensities ranging from 60 to 16,000 mW/cm2. These results do not confirm Kremkau and Witcofski's report on mitotic reduction in rat liver similarly exposed to ultrasound. |
| Title |
Absence of mutation following ultrasonic treatment of Bacillus subtilis cells and transforming deoxyribonucleic acid. |
| Author |
Combes RD. |
| Journal |
Br J Radiol |
| Volume |
|
| Year |
1975 |
| Abstract |
Possible mutagenic effects of ultrasound at medical dosages have been assessed using genetic systems of Bacillus subtilis. The induction of mutations, after treatment of cells and of extracted transforming DNA with ultrasound has been tested. High-frequency (2 MHz diagnostic regime and higher intensities) ultrasound was unable to increase significantly the spontaneous frequency of back-mutation of an.auxotrophic strain. Moreover, high-frequency treatments (1.5 MHz diagnostic and therapeutic regimes) were incapable of producing detectable levels of mutagenic lesions after in vitro irradiation of transforming DNA. Slight decreases in transforming activity of the treated DNA were apparent while the degree of.linkage between two contiguous markers was unaffected. It is concluded that the ultrasound treatments employed under the conditions pertaining do not result in production of detectable mutagenic effects in cells or in vitro treated DNA. Before extrapolating such results to the human hazard situation, it is suggested that.tests using genetic systems of higher organisms should be carried out. |
| Title |
Absolute hydrophone calibration. |
| Author |
Livett AJ, Bacon DR, Preston RC. |
| Journal |
Ultrasound |
| Volume |
|
| Year |
1983 |
| Abstract |
No abstract available. |
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