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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 29 out of 330
| Title |
Acoustic power calibrations of cylindrical intracavitary ultrasound hyperthermia applicators. |
| Author |
Hynynen K. |
| Journal |
Med Phys |
| Volume |
|
| Year |
1993 |
| Abstract |
Preliminary clinical results indicate that some tumors can be heated well utilizing cylindrical ultrasound sources placed in body cavities. In this paper a simple method for measuring the acoustic power from cylindrical intracavitary transducers will be described. The radially propagating acoustic field was converted to a beam with a single propagation direction by a brass reflector, and the radiation force generated by this beam on an absorbing target was measured. The power output of several clinical intracavitary arrays varied significantly between identically shaped transducer elements. The results show that it is important to measure the acoustic power output from each element prior to its clinical use. The radiation force technique is simple and sensitive and can be easily adapted to be used as a routine clinical quality assurance method. |
| Title |
Acoustic power measurements of Doppler.ultrasound devices used for perinatal and.infant examinations. |
| Author |
Rabe H, Grohs B, Schmidt RM, Schloo R, Bomelburg T, Jorch G. |
| Journal |
Pediatr Radiol |
| Volume |
|
| Year |
1990 |
| Abstract |
Acoustic power output levels were measured in four different pulsed Doppler.systems (transcranial, Duplex mode, colour mode, miniature for continuous.monitoring) currently used for examination of fetal and infant blood flow.velocities. The frequencies of the transducers ranged from 2 to 8 MHz. The.devices were studied at three to five different intensity settings. The.measurements were performed using the radiation force balance of the.Fraunhofer-Institut, which was especially adapted for this study. Each of the.four devices was tested while running in its commonly used mode, and.comparison showed that their acoustic power values varied widely: 96.8 mW (2.MHz, EME TC2-64B), 8.7 mW (5 MHz, ATL Mk 500), 61.9 mW (3.5 MHz,.Acuson 128) and 13.5 mW (5 MHz, HP 77020). All transducers had total power.output levels below the limits recommended by the American Institute for.Ultrasound in Medicine and Biology in the conclusions on a thermal bioeffects.mechanism, which were approved in October 1987. . |
| Title |
Acoustic propagation properties of normal, stunned, and infarcted myocardium. |
| Author |
O'Brien WD Jr, Sagar KB, Warltier DC, Rhyne TL. |
| Journal |
Circulation |
| Volume |
|
| Year |
1995 |
| Abstract |
Anesthetized open-chest dogs underwent a total occlusion of the left anterior descending coronary artery for 15 minutes (stunned, n=7) and 90 minutes (infarcted, n=8), followed by reperfusion for 3 hours. Circumflex coronary artery perfusion territory (n=15) served as normal control tissue. Regions of myocardium were quantitatively evaluated with a scanning laser acoustic microscope operating at 100 MHz and a research ultrasound system operating at 4 to 7 MHz. Four ultrasonic parameters were determined: attenuation coefficient (an index of loss per unit distance), speed of propagation, a spatial variation of propagation speed called the heterogeneity index (HI), and ultrasonic backscatter at 5 MHz (IBR5). Myocardial water, lipid, and protein contents of normal, stunned, and infarcted myocardium were also determined. The attenuation coefficient of normal myocardium (179±20 dB/cm) was significantly greater than that of stunned (136±7 dB/cm, P<.001) and infarcted (130±8 dB/cm, P<.001) myocardium. The propagation speed of normal myocardium (1597±6 m/s) was similar to that of stunned (1600±6 m/s) and significantly higher than that of infarcted (1575±7 m/s, P<.001) myocardium. The HI for specimen thicknesses of 75 to 100 µm showed an increase of 33% between normal (5.0±0.8 m/s) and stunned (7.5±2.3 m/s, P<.05) myocardium. However, for the infarcted myocardium (5.8±2.0 m/s), the HI was essentially the same as that of the normal myocardium (5.0±0.8 m/s). The IBR5 of normal (-47.1±1.0 dB) was not significantly different from that of stunned myocardium (-46.8±0.9 dB). The IBR5 of infarcted myocardium (-42.4±1.0 dB) was significantly greater than that of normal myocardium. Myocardial water and protein contents were similar in the normal and stunned myocardium. Water content in the infarcted myocardium (80.8±2%) was significantly greater (P<.05) than in the normal (72.7±1.3%), and protein content of 18.5±0.7% was significantly lower (P<.05) than the normal (21.4±0.8%). Lipid content was increased in the stunned (8.5±0.5%) and virtually absent in the infarcted myocardium (0.8±0.3%) compared with normal (5.5±0.6%). |
| Title |
Acoustic propagation properties of normal, stunned, and infarcted myocardium. Morphological and biochemical determinants. |
| Author |
O'Brien WD, Sagar KB, Warltier DC, Rhyne TL. |
| Journal |
Circulation |
| Volume |
|
| Year |
1994 |
| Abstract |
BACKGROUND:
Identification of viable but stunned myocardium remains a major problem. Since stunned myocardium results in impairment of myocardial function without any structural damage and infarcted myocardium causes major structural disruption, we postulated that acoustic properties could distinguish between the two insults.
METHODS AND RESULTS:
Anesthetized open-chest dogs underwent a total occlusion of the left anterior descending coronary artery for 15 minutes (stunned, n = 7) and 90 minutes (infarcted, n = 8), followed by reperfusion for 3 hours. Circumflex coronary artery perfusion territory (n = 15) served as normal control tissue. Regions of myocardium were quantitatively evaluated with a scanning laser acoustic microscope operating at 100 MHz and a research ultrasound system operating at 4 to 7 MHz. Four ultrasonic parameters were determined: attenuation coefficient (an index of loss per unit distance), speed of propagation, a spatial variation of propagation speed called the heterogeneity index (HI), and ultrasonic backscatter at 5 MHz (IBR5). Myocardial water, lipid, and protein contents of normal, stunned, and infarcted myocardium were also determined. The attenuation coefficient of normal myocardium (179 +/- 20 dB/cm) was significantly greater than that of stunned (136 +/- 7 dB/cm, P < .001) and infarcted (130 +/- 8 dB/cm, P < .001) myocardium. The propagation speed of normal myocardium (1597 +/- 6 m/s) was similar to that of stunned (1600 +/- 6 m/s) and significantly higher than that of infarcted (1575 +/- 7 m/s, P < .001) myocardium. The HI for specimen thicknesses of 75 to 100 microns showed an increase of 33% between normal (5.0 +/- 0.8 m/s) and stunned (7.5 +/- 2.3 m/s, P < .05) myocardium. However, for the infarcted myocardium (5.8 +/- 2.0 m/s), the HI was essentially the same as that of the normal myocardium (5.0 +/- 0.8 m/s). The IBR5 of normal (-47.1 +/- 1.0 dB) was not significantly different from that of stunned myocardium (-46.8 +/- 0.9 dB). The IBR5 of infarcted myocardium (-42.4 +/- 1.0 dB) was significantly greater than that of normal myocardium. Myocardial water and protein contents were similar in the normal and stunned myocardium. Water content in the infarcted myocardium (80.8 +/- 2%) was significantly greater (P < .05) than in the normal (72.7 +/- 1.3%), and protein content of 18.5 +/- 0.7% was significantly lower (P < .05) than the normal (21.4 +/- 0.8%). Lipid content was increased in the stunned (8.5 +/- 0.5%) and virtually absent in the infarcted myocardium (0.8 +/- 0.3%) compared with normal (5.5 +/- 0.6%).
CONCLUSIONS:
We conclude that acoustic propagation properties can identify stunned and infarcted myocardium and may be related to biochemical/morphological differences. |
| Title |
Acoustic propagation properties of normal, stunned, and infarcted myocardium: Morphological and biochemical determinants. |
| Author |
O'Brien WD Jr, Sagar KB, Warltier DC, Rhyne TL. |
| Journal |
Circulation |
| Volume |
|
| Year |
1995 |
| Abstract |
BACKGROUND: Identification of viable but stunned myocardium remains a major problem. Since stunned myocardium results in impairment of myocardial function without any structural damage and infarcted myocardium causes major.structural disruption, we postulated that acoustic properties could distinguish between the two insults. METHODS AND RESULTS: Anesthetized open-chest dogs underwent a total occlusion of the left anterior descending coronary artery for 15.minutes (stunned, n = 7) and 90 minutes (infarcted, n = 8), followed by reperfusion for 3 hours. Circumflex coronary artery perfusion territory (n = 15) served as normal control tissue. Regions of myocardium were quantitatively evaluated with a scanning laser acoustic microscope operating at 100 MHz and a research ultrasound system operating at 4 to 7 MHz. Four ultrasonic parameters were determined: attenuation coefficient (an index of loss per unit distance), speed of propagation, a spatial variation of propagation speed called the heterogeneity index (HI), and ultrasonic backscatter at 5 MHz (IBR5). Myocardial water, lipid, and protein contents of normal, stunned, and infarcted myocardium were also determined. The.attenuation coefficient of normal myocardium (179 +/- 20 dB/cm) was significantly greater than that of stunned (136 +/- 7 dB/cm, P < .001) and infarcted (130 +/- 8 dB/cm, P < .001) myocardium. The propagation speed of normal myocardium.(1597 +/- 6 m/s) was similar to that of stunned (1600 +/- 6 m/s) and significantly higher than that of infarcted (1575 +/- 7 m/s, P < .001) myocardium. The HI for specimen thicknesses of 75 to 100 microns showed an increase of 33% between.normal (5.0 +/- 0.8 m/s) and stunned (7.5 +/- 2.3 m/s, P < .05) myocardium. However, for the infarcted myocardium (5.8 +/- 2.0 m/s), the HI was essentially the same as that of the normal myocardium (5.0 +/- 0.8 m/s). The IBR5 of normal.(-47.1 +/- 1.0 dB) was not significantly different from that of stunned myocardium (-46.8 +/- 0.9 dB). The IBR5 of infarcted myocardium (-42.4 +/- 1.0 dB) was significantly greater than that of normal myocardium. Myocardial water and.protein contents were similar in the normal and stunned myocardium. Water content in the infarcted myocardium (80.8 +/- 2%) was significantly greater (P < .05) than in the normal (72.7 +/- 1.3%), and protein content of 18.5 +/- 0.7% was significantly lower (P < .05) than the normal (21.4 +/- 0.8%). Lipid content was increased in the stunned (8.5 +/- 0.5%) and virtually absent in the infarcted myocardium (0.8 +/- 0.3%) compared with normal (5.5 +/- 0.6%). CONCLUSIONS: We conclude that acoustic propagation properties can identify stunned and infarcted myocardium and may be related to biochemical/morphological differences. |
| Title |
Acoustic properties of blood and its components. |
| Author |
Carstensen EL, Schwan HP. |
| Journal |
Ultrasound Biol Med |
| Volume |
|
| Year |
1957 |
| Abstract |
No abstract available. |
| Title |
Acoustic properties of normal and cancerous human liver--II: Dependence on pathological condition. |
| Author |
Bamber JC, Hill CR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1981 |
| Abstract |
Ultrasonic speed, attenuation and backscattering were measured as a function of frequency and compared with measurements of water content, fat content and collagen content in specimens of excised human liver. It is observed that the ultrasonic velocity decreases with both increasing water and fat contents, although the water content appears to have the overriding influence. An increase in the water content correlates well with decreasing attenuation and backscattering coefficients (and the slope of their frequency dependence), but positive dependences are found between these acoustic characteristics and the fat content. It is believed that the dependences on fat content are of secondary importance to those on water content and possibly arise as a result of an inverse relationship between the fat content and the water content. For the collagen content of liver specimens, positive correlations, barely significant, were found for attenuation and backscattering only after the data had first been corrected for variations in water content, while no significant velocity dependence was seen. |
| Title |
Acoustic properties of normal and cancerous human liver--II: Dependence on tissue structure. |
| Author |
Bamber JC, Hill CR, King JA. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1981 |
| Abstract |
No abstract available. |
| Title |
Acoustic radiation force and streaming induced by focused nonlinear ultrasound in a dissipative medium. |
| Author |
Rudenko OV, Sarvazyan AP, Emelianov SY. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1996 |
| Abstract |
Based on asymptotic methods recently developed in nonlinear acoustics, analytical solutions of the equations for the radiation force induced by nonlinear focused. ultrasound in a dissipative medium are considered. Equations describing spatial structure of the radiation force field in the paraxial region of the ultrasound beam and the. spatial-temporal behavior of the induced nonlinear streaming are derived. The equations enable analytical investigation of dependencies of radiation pressure and resulting. streaming on the acoustic field and medium parameters. Estimates have shown that nonlinearity of medium can significantly enhance radiation force in the focal region at. the intensities lower than those used in ultrasound devices for medical imaging. The initiation of acoustical streaming by radiation force is considered, and the spatial and. temporal characteristics of induced flow are discussed. Both acoustic and hydrodynamic nonlinearities are taken into account. The paper concludes by discussing. possible medical and industrial applications of ultrasound radiation force and induced acoustical streaming. |
| Title |
Acoustic scattering theory apllied to soft biological tissues. |
| Author |
Insana MF,Brown DF. |
| Journal |
Book Chapter |
| Volume |
|
| Year |
1993 |
| Abstract |
Interest in quantitative ultrasound scattering measurements in biological issues stems from the belief that only a fraction of the total information available in the echo signal is visible in the gray-scale ultrasound image.Much information of potential diagnostic significance concerning tissue characterization can be made available only through sophisticated signal processing.A more fundamental understanding of the basic acoustic interactions in tissues prelude to this processing,which holds the promise for improvement in imaging technology and enhancement in the diagnostic tissues utility of the modality.
The complexity and diversity of biological tissues make it unlikely that a rigorous and generally applicable theoritical description of medical ultrasound imaging will evolve.Images are generated by complex interactions among the incident pressure field,the geometry of the detector, and fluctuations in mechanical properties within tissues.Boundaries between tissues that are large compared to the wavelength of sound produce strong specular reflections that usually dominate the image.Smaqll diffuse structures produce scattered waves that coherently interfere at the detector,generating a speckle pattern in the image that is characteristic both of the instrumentation and of the tissue.As a result of this complexity,scattering from tissues must remian an empirical science, but one requiring the guidance of a relaistic theoritical treatmet. Understanding scattering mechanisms in tissues at a fundamental level requires precise specification of the tissue characteristics and acoustic pressure fields.Difference among the various approaches to scattering measurement found in the literature are related to approximation and assumptions regarding these specifications.
In this chapter,we review the basic equations of acoustic scattering theory.Our emphasis will be on providing an intuitive "feel" for the underlying phenomena being described,so some of our arguments will be simplifed forms of more rigorous arguments referenced.The basic characteristics ( if not the precise details) of scattering follow naturally form a few easily understood physical principles,and the mathematical complexity of the derivations tends to obscure the simplicity of these relationships. On the other hand ,we will work out in detail some of the calculations which are glossed over briefly in the standard treatments of the subject in order to engender a higher degree of comfort with the final results. Special attention is given to the approximations and assumptions made when applying the results to soft tissues. |
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