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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 259 out of 330
| Title |
The feasibility of using electrically focused ultrasound arrays to induce deep hyperthermia via body cavities. |
| Author |
Diederich CJ, Hynynen K. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1991 |
| Abstract |
The results of a simulation study and subsequent experimental verification on the feasibility of using electrically focused arrays for intracavitary ultrasound hyperthermia are presented. The relative acoustic pressure fields from these cylindrical phased arrays were calculated for different dimensions and acoustic parameters to determine relevant design criteria. A thermal model based on the bioheat transfer equation was used to compute the resulting steady-state temperature distributions in tissue for various array configurations. This study has shown that cylindrical arrays of a practical size (75 mm long, 15 mm O.D.), resonating at 0.5 MHz with individual elements that are 1.5-mm wide, can preferentially heat regions that are between 20 and 50 mm from the surface of the array. In addition, it was shown that the temperature distribution can be further controlled by varying the focal position within the target volume, producing heated regions up to 40 mm wide. If practical constraints (i.e. number of amplifiers available or minimum element size attainable) become a limiting factor, arrays with wider elements would also be functional, but with certain restrictions applied to their flexible heating patterns. Thus, these electrically focused ultrasound arrays appear to offer a significant improvement over the existing intracavitary hyperthermia methods by producing a deeper and more controlled energy deposition. |
| Title |
The feasibility of using focused ultrasound for transmyocardial revascularization. |
| Author |
Smith NB, Hynynen K. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1998 |
| Abstract |
Transmyocardial laser revascularization (TMR) is used for improving the blood supply to damaged myocardium due to advanced.heart disease. We hypothesize that focused ultrasound can be used to generate channels through the cardiac muscle by vaporizing.the tissue at the focal spot. The purpose of this study was to evaluate the effects of varying the ultrasound exposure parameters.(frequency, amplitude, pulse period, duty cycle, focal depth and exposure time) on the vaporized tissue size and to determine the.feasibility of using ultrasound for creating cavities and/or channels in the left ventricular wall for transmyocardial revascularization..Based on in vitro experiments using bovine myocardium, the experiments indicate that a 1 mm diameter channel could be created.by using, for example, a focused transducer with a diameter of 10 cm and a radius of curvature of 8 cm operating at a frequency.of 2.52 MHz. The required spatial peak intensity during the 0.5-s sonications was found to be 2300 W/cm2 with a pulse repetition.period of 40 ms and a 50% duty cycle. These parameters have been used to create cavities during in vivo tests using canine.myocardium. The results demonstrated that ultrasound could be used to create small channels through myocardium. The most.important potential for ultrasound is its ability to generate these channels completely noninvasively. . |
| Title |
The fluid and elastic nature of nucleated cells: Implications from the cellular backscatter response. |
| Author |
Baddour RE, Kolios MC. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2007 |
| Abstract |
In a previous experiment [Baddour et al., J. Acoust. Soc. Am. 117(2), 934-943 (2005)] it was shown that it is possible to deduce the ultrasound backscatter transfer function from single, subresolution cells in vitro, across a broad, continuous range of frequencies. Additional measurements have been performed at high frequencies (10-65 MHz) on cells with different relative nucleus sizes. It was found that for cells with a nucleus to cell volume ratio of 0.50, the backscatter response was better modeled as an elastic sphere. For the cells in which the ratio was 0.33, the backscatter showed good agreement with the theoretical solution for a fluid sphere. |
| Title |
The future of ultrasonics in diagnostic medicine. |
| Author |
Hill CR. |
| Journal |
Philos Trans R Soc Lond A |
| Volume |
|
| Year |
1979 |
| Abstract |
Ultrasonics has been the poor relation of twentieth century physics and it is only recently that thought has been given to investigating the scientific basis of ultrasonic diagnostic methods. The physics of acoustic wave interactions with human tissues is complex but suggests the existence of a rich supply of diagnostically useful information. Static imaging technology may now be approaching a resolution limit imposed by variability of refractive index in overlying tissues, but advances are to be expected in the direction of quantification of the imaging process. Supplementary information on fine structure of tissues is also to be expected from the application of analytical techniques, of which frequency dependence of backscattering and diffraction pseudo-crystallography are two examples in which there is current research interest. Recent rapid advances in dynamic or 'real time' imaging reflect the potential of ultrasound for providing hitherto unobtainable information on patterns of tissue movement both in health and disease. Major advances in application will come, in many areas of medicine, simply as good equipment, experience and expertise become more generally available but particular impact from scientific advances may occur in the diagnosis and management of both cardiovascular disease and cancer, with effective early detection of breast cancer being one of a number of distant but compelling prospects. |
| Title |
The impact of nonlinear propagation effects in water on ultrasound used in industrial nondestructive evaluation. |
| Author |
Slotwinski JA. |
| Journal |
Thesis(PhD): Catholic Univ of America |
| Volume |
|
| Year |
1997 |
| Abstract |
No Abstract Available. |
| Title |
The impact of sound speed errors on medical ultrasound imaging. |
| Author |
Anderson ME, McKeag MS, Trahey GE. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2000 |
| Abstract |
The results of a quantitative study of the impact of sound speed errors on the spatial resolution and amplitude sensitivity of a commercial medical ultrasound scanner are presented in the context of their clinical significance. The beamforming parameters of the scanner were manipulated to produce sound speed errors ranging over +/-8% while imaging a wire target and an attenuating, speckle-generating phantom. For the wire target, these errors produced increases in lateral beam width of up to 320% and reductions in peak echo amplitude of up to 10.5 dB. In the speckle-generating phantom, these errors produced increases in speckle intensity correlation cell area of up to 92% and reductions in mean speckle brightness of up to 5.6 dB. These results are applied in statistical analyses of two detection tasks of clinical relevance. The first is of low contrast lesion detectability, predicting the changes in the correct decision probability as a function of lesion size, contrast, and sound speed error. The second is of point target detectability, predicting the changes in the correct decision probability as function of point target reflectivity and sound speed error. Representative results of these analyses are presented and their implications for clinical imaging are discussed. In general, sound speed errors have a more significant impact on point target detectability over lesion detectability by these analyses, producing up to a 22% reduction in correct decisions for a typical error. |
| Title |
The in vivo diagnosis of early-stage aortic valve sclerosis using magnetic resonance imaging in a rabbit model. |
| Author |
Hamilton AM, Rogers KA, Drangova M, Khan Z, Ronald JA, Rutt BK, Maclean KA, Lacefield JC, Boughner DR. |
| Journal |
J Magn Reson Imaging |
| Volume |
|
| Year |
2009 |
| Abstract |
PURPOSE: To use magnetic resonance imaging (MRI) to identify and monitor early aortic valve sclerosis (AVS) induced by cholesterol feeding in rabbits. AVS is a highly prevalent disease process, affecting more than 25% of the population over age 65. A major obstacle to early stage medical management of AVS has been the lack of an objective noninvasive technique to identify its presence and monitor its progress. MATERIALS AND METHODS: Retrospectively gated CINE fast spoiled gradient echo (fSPGR) images of aortic valve cusps were collected at 3-month intervals starting at 6 months using a 1.5 T MR scanner interfaced with a customized surface radiofrequency coil. At 16 months a subset of animals was sacrificed and excised cusps were examined with both high frequency ultrasound (US) and histopathological techniques to validate the MRI method. RESULTS: MR and US analysis identified significant thickening of diseased AV cusps when compared to control (P < 0.05). Histopathological analysis confirmed the presence of human-like AVS in diseased rabbit valves. CONCLUSION: Early AVS, exemplified by increased valve thickness, can be identified in vivo using high-resolution MRI. |
| Title |
The inactivation of enzymes by ultrasonic cavitation at 20 kHz. |
| Author |
Coakley WT, Brown C, James CJ, Gould RK. |
| Journal |
Arch Biochem Biophys |
| Volume |
|
| Year |
1973 |
| Abstract |
Alcohol dehydrogenase, lysozyme, and catalase were assayed after exposure to cavitating 20 kHz ultrasound for varying times. Catalase was little affected, but alcohol dehydrogenase and lysozyme were both inactivated at an exponential rate, the rate of enzyme inactivation decreased with increasing protein concentration and was inhibited by the presence of 2-mercaptoethanol. The presence of stainless steel in the sonication vessel accelerated enzyme inactivation. On the basis of the results obtained, it is suggested that the mechanism of inactivation is chemical rather than mechanical, and a comparison is made between the rate of inactivation and the yield of free radicals as measured with a radiochemical dosimeter. Suggestions are offered to minimize the sonochemical effects on proteins isolated from cells with an ultrasonic disintegrator. |
| Title |
The influence of agent delivery mode on cardiomyocyte injury induced by myocardial contrast echocardiography in rats. |
| Author |
Miller DL, Dou C, Armstrong WF. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2005 |
| Abstract |
Myocardial contrast echocardiography (MCE) can induce bioeffects in rat hearts by local activation of the contrast agent gas bodies. This study was designed to examine the influence of agent delivery mode on the magnitude of cardiomyocyte injury. A total of 69 hairless rats were anesthetized and mounted vertically in a water bath. Evans blue dye was injected as vital stain for cardiomyocyte injury. Definity contrast agent was diluted in saline and injected via tail vein at 20 or 80 microL/kg in bolus or infusion mode. In 12 rats, 0.57 mg/kg dipyridamole was given to simulate a stress test. MCE in a short axis view with 1:4 or 1:16 ECG triggering was performed at 1.5 MHz for 5 or 20 min. The peak rarefactional pressure amplitude was set to 1.1 or 2.0 MPa. Premature beats were counted from the ECG record. Evans blue fluorescent cells were counted on frozen sections from the center of the scan plane of heart samples obtained 24 h postMCE. Infusion of the contrast agent led to more cardiomyocyte injury than did bolus injection. Dipyridamole stress also increased the effect. Varying the infusion rate or trigger interval was less important than the overall dosage during scanning. Exposure at 1.1 MPa and 80 microL/kg yielded significant cell killing relative to shams. Premature beats generally followed the same trends as cell injury, except that lower infusion rates tended to increase this effect. Contrast agent delivery mode, as well as dose and peak rarefactional pressure amplitude, has a significant influence on the bioeffects potential of MCE. |
| Title |
The influence of carrier frequency on the killing of drosophila larvae by microsecond pulses of ultrasound. |
| Author |
Berg RB, Child SZ, Carstensen EL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1983 |
| Abstract |
Letter to the editor. |
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