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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 174 out of 330
| Title |
Mechanisms for biological effects of ultrasound. |
| Author |
Carstensen EL. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1998 |
| Abstract |
No abstract available. |
| Title |
Mechanisms for hemolysis by ultrasonic cavitation in the rotating exposure system. |
| Author |
Miller DL, Thomas RM, Williams AR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1991 |
| Abstract |
The rotating chamber provides a useful system for enhancing cavitation bioeffects so that they may be more easily studied. A tube with acoustically transparent windows was rotated at 72 rpm perpendicular to its axis. The 1.61 MHz ultrasound beam was switched on and off in 42 ms bursts to expose the chamber while it was aligned with the beam. The hemolysis of 0.5% suspensions of canine erythrocytes was used as a measure of the efficacy of this rotating exposure system. Use of dialysis membrane, agar plugs, plastic sealing film or wax film for the.windows produced no differences in the results for exposure intensities above an apparent threshold of 2-2.8 W/cm2, up to 16 W/cm2, at which essentially 100% lysis was observed. Changing the tube length from 1.4 cm to 4 cm, or partitioning it into three 0.5 cm segments had little influence on the results, but a short 0.5 cm chamber had reduced efficacy. Pressurizing the suspension filled chamber at 10 MPa to reduce the population of cavitation nuclei reduced the hemolysis. Separately pressurizing the suspension or the chamber produced indistinguishable, smaller reductions in hemolysis. The results lead to the hypothesis that the hemolysis occurs primarily in the bulk of the medium (rather than on surfaces). Bubbles recycled by rotation into the medium move toward the back of the chamber at estimated speeds of 10 m/s, generating hydrodynamic stresses sufficient to cause the observed hemolysis. |
| Title |
Mechanisms for nonthermal effects of sound. |
| Author |
Nyborg WL. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1968 |
| Abstract |
Research on cell suspensions, single cells, macromolecular suspensions, and model (nonliving) systems reveal a variety of changes brought about by sound in the absence of gross-heating or transient ("collapse"-type) cavitation. Many of these phenomena are explainable in terms of acoustic streaming, radiation pressure, and other characteristics of ultrasound that arise from nonlinearity. Commonly, the sonic effect depends on nonuniformity in the sound field. Interesting results are obtained with techniques by which one can set up nonuniform vibration in the walls or membranes of individual cells. In ultrasonic beams acting on tissue, it is possible that variations may arise from gradients in the incident field, or from inhomogeneities in the tissue, which scatter sound. Gaseous pockets or bubbles would be especially effective as such inhomogeneities. |
| Title |
Mechanisms of cell and tissue damage in shock wave lithotripsy. |
| Author |
McAteer JA, Williams JC Jr, Evan AP, Willis LR, Bailey MR, Crum LA, Cleveland RO. |
| Journal |
Proc Second Int Symp Ther Ultrasound |
| Volume |
|
| Year |
2002 |
| Abstract |
Shock wave lithotripsy (SWL) is a highly effective treatment for urinary stones. Lithotripters generate an acoustic pulse in the range ~35-115 MPa P+, ~-10 MPa P-, focused to a zone only a few mn wide (estimated ISPTP~80,000 W/cm2). Lithotripter SW?s are effective at breaking stones, but collateral kidney injury can be severe. A clinical dose of SW?s (2,000 SW, 24 kV) delivered to the juvenile pig kidney using the Dorniuer-HM3 lithotripter created a hemorrhagic lesion measuring 6.1?1.7 volume percent. The same dose, but using a time-reversed SW that suppresses cavitation, produced minimal bleeding?injury too small to quantitate. Lysis of red blood cells in vitro was lower with the time-reversed waveform than with conventional SW?s, and high overpressure (>120 atm) reduced red cell lysis with convention SW?s. These observations support the idea that cell/tissue injury is related to cavitation. However, red cell lysis at high overpressure was significantly greater than untreated controls, and breakage of ~100 nm diameter phospholipid membrane vesicles was unaffected by overpressure. Overall these results suggest that cavitation plays an important role in renal injury in SWL, but in the in vitro cell and vesicle data show that SW damage may not be linked to cavitation when target dimensions are small. Thus, multiple mechanisms appear to be at play in SW damage to biological targets in SWL. |
| Title |
Mechanisms of contrast agent destruction. |
| Author |
Chomas JE, Dayton P, Allen J, Morgan K, Ferrara KW. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2001 |
| Abstract |
Various applications of contrast-assisted ultrasound, including blood vessel detection, perfusion estimation, and drug delivery, require controlled destruction of contrast agent microbubbles. The lifetime of a bubble depends on properties of the bubble shell, the gas core, and the acoustic waveform impinging on the bubble. Three mechanisms of microbubble destruction are considered: fragmentation, acoustically driven diffusion, and static diffusion. Fragmentation is responsible for rapid destruction of contrast agents on a time scale of microseconds. The primary characteristics of fragmentation are a very large expansion and subsequent contraction, resulting in instability of the bubble. Optical studies using a novel pulsed-laser optical system show the expansion and contraction of ultrasound contrast agent microbubbles with the ratio of maximum diameter to minimum diameter greater than 10. Fragmentation is dependent on the transmission pressure, occurring in over 55% of bubbles insonified with a peak negative transmission pressure of 2.4 MPa and in less than 10% of bubbles insonified with a peak negative transmission pressure of 0.8 MPa. The echo received from a bubble decorrelates significantly within two pulses when the bubble is fragmented, creating an opportunity for rapid detection of bubbles via a decorrelation-based analysis. Preliminary findings with a mouse tumor model verify the occurrence of fragmentation in vivo. A much slower mechanism of bubble destruction is diffusion, which is driven by both a concentration gradient between the concentration of gas in the bubble compared with the concentration of gas in the liquid, as well as convective effects of motion of the gas-liquid interface. The rate of diffusion increases during insonation, because of acoustically driven diffusion, producing changes in diameter on the time scale of the acoustic pulse length, thus, on the order of microseconds. Gas bubbles diffuse while they are not being insonified, termed static diffusion. An air bubble with initial diameter of 2 um in water at 37 degrees celcius is predicted to fully dissolve within 25 ms. Clinical ultrasound contrast agents are often designed with a high molecular weight core in an attempt to decreas the diffusion rate. C3F8 and C4F10 gas bubbles of the same size are predicted to fully dissolve within 400 ms and 4000 ms, respectively. Optical experiments involving gas diffusion of a contrast agent support the theoretical predictions; however, shelled agents diffuse at a much slower rate without insonation, on the order of minutes to hours. SHell properties play a significant role in the rate of static diffusion by blocking the gas-liquid interface and decreasing the transport of gas into the surrounding liquid. Static diffusion decreases the diameter of albumin-shelled agnets to a greater extent than lipid-shelled agents after insonation. |
| Title |
Mechanisms of removal of micron-sized particles by high-frequency ultrasonic waves. |
| Author |
Qi Q, Brereton GJ. |
| Journal |
Rep Univ Ill - Urbana/Champaign Dept Theor Appl Mech |
| Volume |
|
| Year |
1994 |
| Abstract |
In this paper, theories of particle removal by high-frequency ultrasonic waves are discussed and tested against recent experimental data. First, the principal adhesion forces such as van der Waals forces are briefly reviewed and the typical uncertainties in their size in particle-surface systems are assessed. The different ultrasound-induced forces-linear forces such as added mass, drag, lift, and Basset forces and nonlinear ones due to radiation pressure, and drag exerted by acoustic streaming-are discussed and their magnitudes are evaluated for typical cleaning operations. It is shown that high-frequency ultrasound can clean particles most effectively in media with properties like water because: (1) the wavelength can be made comparable to the particle radius to promote effective sound-particle interaction; (2) the viscous boundary layer is thin, minimizing particle "hide-out;" and (3) both the added mass and radiation pressure forces exceed typical adhesion forces at high frequencies. Based on these analyses, possible mechanisms of particle removal are discussed and interpreted in terms of experimental observations of particle cleaning. (25 References). |
| Title |
Medical diagnostic ultrasound : a retrospective on its 40th anniversary. |
| Author |
Unknown. |
| Journal |
Rep Kodak Health Sci |
| Volume |
|
| Year |
1988 |
| Abstract |
No abstract available. |
| Title |
Medical imaging by ultrasound -computer tomography. |
| Author |
Stotzka R, Muller TO, Wurfel J, gemmeke H. |
| Journal |
Ultrason Imaging |
| Volume |
|
| Year |
2002 |
| Abstract |
No Abstract Available. |
| Title |
Medical ultrasonics: an historical review. |
| Author |
Hill CR. |
| Journal |
Br J Radiol |
| Volume |
|
| Year |
1973 |
| Abstract |
The technology of ultrasonics has grown up over the past 50 years and, almost from the start, there has been considerable interest in applying the radiation ?like properties of ultrasound for medical purposes in modes analogous to those familiar with ionizing radiation. Until recently, at least much of the development in this field has been on a superficial level and without reference to any scientific understanding of the situation. This has been particularly the case in attempts to use ultrasound therapeutically and, in the diagnostic field, which is historically a more recent development, very considerable advances may be expected in the future as the full potential of the subject is realized. |
| Title |
Medical ultrasound visualization. |
| Author |
Heyser R, Le Croissette D, Martin B. |
| Journal |
Rep Calif Inst Technol |
| Volume |
|
| Year |
1972 |
| Abstract |
The feasibility of obtaining transmission pictures of soft biological tissue using ultrasonic radiation has been established. The method employed the use of time delay spectrometry, a novel swept-frequency technique, operating in the 2 to 3 mHz frequency range. The system used a combination of commercial and laboratory assembled equipment to produce a simple television-type raster giving images with about 1.5 mm resolution. Sample pictures in vitro and in vivo are included in the report. A comparison between conventional pulse-echo and continuous-wave transmission systems was made. By increasing the swept frequency range it is shown that the resolution of the images may be proportionally improved. A discussion of the time and frequency domain information available in the signal showed that a substantial image enhancement may be obtained if the phase information were included in the image. This work was conducted as Phase 1 of Task 151 of the Space Technology Application Project funded by the NASA Applications Technology Office. |
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