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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 35 out of 330
| Title |
An assessment of ultrasonic radiation hazard.using yeast genetic systems. |
| Author |
Thacker J. |
| Journal |
Br J Radiol |
| Volume |
|
| Year |
1974 |
| Abstract |
To assess possible genetic effects of ultrasonic radiation, four different genetic systems have been established using yeast cells. The systems were especially chosen to minimize the chance of overlooking any damaging effects which might lead to hereditary change. Irradiation of the cells has been carried out at parameters similar to those used in medical applications of ultrasound (diagnosis and physiotherapy) and under more extreme (cavitational) conditions. None of these treatments showed an effect upon mutant or recombinant frequency in the yeast systems. Similarly, efforts to show any delayed or cryptic effects of ultrasonic irradiations, and to show a genetic component in lethality caused by ultrasound, were negative. Only under conditions allowing a build-up of the secondary effects of heating or peroxide formation was an effect found, in the system assaying for genetic loss of mitochondrial DNA function (respiratory deficiency). Thus, on this evidence, there seems to be only a small chance of genetic hazard from therapeutic irradiations, and no hazard is envisaged from diagnostic irradiation parameters. However, because of the difficulties inherent in extrapolation it is considered that, before this finding may be generalized, similar tests should be carried out upon genetically well-defined multicellular organisms. |
| Title |
An attempt to reconstruct the lithotriptor shock wave pulse in kidney: Possible temperature effects. |
| Author |
Filipczynski L, Etienne J, Piechocki M. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1992 |
| Abstract |
Based on measurements carried out in water in two lithotripter systems, the authors have made an attempt to reconstruct numerically amplitudes and shapes of shock wave pulses penetrating into kidney which differ from those in water. The difference between these pulses and those observed in water was analyzed and was also demonstrated experimentally. The amplitude and the steepness of the reconstructed pulse front were shown to be much lower than in water depending on the distance of the kidney stone from the patient's body surface. For a distance equal to 4 cm, the shock wave pulse amplitude of 40 MPa in water was estimated to decrease in the kidney by a factor of about two and the steepness of the positive shock pulse front to decrease several times. The analysis was carried out by considering the possible changes of absorption and attenuation in tissues which increase in an unknown way with the wave amplitude. It was shown that the temperature elevation caused by the increase of nonlinear high amplitude absorption is limited due to a corresponding increase in attenuation of the shock wave penetrating soft tissues. The temperature elevation was estimated on the basis of this work to be at most 1.8 times that one estimated in the case of two considered lithotripsy systems when assuming small amplitude absorption and attenuation coefficients. |
| Title |
An automated ultrasonic exposure system to assess the effects of in utero diagnostic ultrasound. |
| Author |
Smith NB, Vorhees CV, Meyer RA, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1990 |
| Abstract |
An ultrasound exposimetry system has been designed and constructed to expose rat embryos and fetuses to ultrasound. The unique feature of the exposure system is that it insonates pregnant rats which are not anesthetized or otherwise restrained. The rats are trained to float in a restricted area directly above the submerged ultrasound transducer. The water tank has been designed to confine the floating rat to a 15 x 10 cm region while being exposed by ultrasound. The ultrasound transducer operating at 3 MHz in either pulsed or CW mode is submerged below the animal and moved in a raster fashion to irradiate the entire abdominal area. Computer control of the exposure system and the ultrasound intensity levels allow for the experiments to be conducted in a blind fashion. Using a calibrated hydrophone, the pressure waveforms are obtained from which the free-field ISPTA and ISPTA are calculated at the distance of the rat?s abdomen. |
| Title |
An automated ultrasonic exposure system to assess the effects of in utero diagnostic ultrasound. |
| Author |
Smith NB, Vorhees CV, Meyer RA, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1990 |
| Abstract |
An ultrasound exposimetry system was designed and constructed to expose rat embryos and fetuses to ultrasound. The unique feature of the exposure system is that it insonates pregnant rats which are not anesthetized or otherwise restrained. The rats were trained to float in a restricted area directly above the submerged ultrasound transducer. The water tank was designed to confine the floating rat to a 15-cm×10-cm region while being exposed to ultrasound. The ultrasound transducer operating in either pulsed or continuous-wave (CW) mode is submerged below the animal and moved in a raster fashion to irradiate the entire abdominal area. Computer control of the exposure system and the ultrasound intensity levels allow for the experiments to be conducted in a blind fashion. Using a calibrated hydrophone, pressure waveforms are obtained from which the free-field ISPTA and ISPTP are calculated at the distance of the rat's abdomen. |
| Title |
An examination of cavitation due to short pulses of megahertz ultrasound. |
| Author |
Fowlkes JB, Crum LA. |
| Journal |
Rep Natl Cent Phys Acoust |
| Volume |
|
| Year |
1988 |
| Abstract |
The acoustic cavitation threshold of an aqueous solution was measured at megahertz frequencies as a function of pulse width and pulse repetition frequency for various combinations of these parameters. The fluid tested was a 0.1 M KOH - H(3)BO(3) buffer solution at a pH of 10.9 which contained luminol (2x10(-4)M), was saturated with argon, and filtered through a 25 micron filter. The presence of cavitation was detected by a photomultiplier tube which required the emission of visible light that was both larger in magnitude and longer in duration than a present criterion. It was observed that the cavitation threshold of water under pulse conditions decreases both when the pulse width is fixed and the pulse repetition frequency is increased, and when the pulse repetition frequency is fixed and the pulse width is increased. Acoustic cavitation thresholds in aqueous solutions, as measured in this study, are significantly less than those acoustic pressures associated with instruments that are currently in widespread use in medicine. In an attempt to explain the dependence of cavitation threshold on pulse parameters, a new solution to the problem of rectified diffusion is developed for short acoustic pulses. Results of this solution indicate that rectified diffusion is a possible source for pulse dependences observed in this work and that certain analytical theories apparently under estimate the gas diffusion into the bubble for megahertz frequencies and small bubble radii. The new formulation for rectified diffusion presented here is based on the bubble dynamics theory of Prosperetti et al. |
| Title |
An experimental neuropathological study of the effects of high-frequency focused ultrasound on the brain of the cat. |
| Author |
Astrom KE, Bell E, Ballantine HT, Heidensleben. |
| Journal |
J Neuropathol Exp Neurol |
| Volume |
|
| Year |
1961 |
| Abstract |
No Abstract Available. |
| Title |
An experimental study on the effect of low-intensity ultrasound on developing mouse embryos. |
| Author |
Shoji R, Momma E, Shimizu T, Matsuda S. |
| Journal |
J Fac Sci Hokkaido Univ Ser VI Zool |
| Volume |
|
| Year |
1971 |
| Abstract |
The Doppler effect of ultrasound waves has been recently applied to a diagnostic purpose in obstetrics on early detection of fetal life and determination of intrauterine death. Some clinical investigators have not demonstrated any untoward or toxic effect of diagnostic ultrasound on any type of tissue with the power levels which are currently used (Thompson 1968, Barton 1968). Up-to-date experimental results indicated by a few workers have differed according to different conditions (Fritz-Niggli et al 1950, Selman et al 1953, 1964, Holmes et al 1962, Andrew 1964, Pourhadi et al 1968, Takeuchi et al 1970). No evidence which is able to assure the safety, with confidence, on the normal development of embryos exposed to ultrasound waves has been established as yet, although diagnostic energy was low intensity. The present authors have projected embryological and cytogenetic studies on teratogenic action of ultrasound waves on mammalian embryos. This report indicates primary data in an animal experiment on effects of low-intensity of ultrasound waves on developing mouse embryos. |
| Title |
An experimentally obtainable heat source due to absorption of ultrasound in biological media. |
| Author |
Drewniak JL, Dunn F. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1996 |
| Abstract |
Deposition of heat as a result of loss in an ultrasonic wave may result in damage to biological tissues. The extensive use of ultrasound diagnostic purposes during pregnancy necessitates the evaluation of thermal risk to a developing fetus during routine clinical exposures. Because of the small ultrasonic absorption coefficient in soft tissues at low megahertz frequencies, temperature elevations exceeding 1 degree C are not expected from clinically employed ultrasound systems, and there is no evidence that such small temperature increases can result in deleterious effects. However, when the propagation path includes bone, which is known to be highly lossy, theoretical calculations and experimental work indicate that local heating might exceed 1 degree C for realistic clinical conditions. Thus it is imperative to obtain reasonable estimates of the temperature elevation in and around fetal properties of fetal bone, which depend on gestational age, estimates of the temperature elevation resulting from exposure to ultrasound must be based on crude models. A measured quantity for a heat source resulting from conversion of acoustic to thermal energy in an ultrasound field is suggested. The heat source is developed from theoretical considerations, and can be used in the bioheat transfer equation to obtain better estimates of the temperature increase in fetal bone and the surrounding tissues as a result of exposure to ultrasound. |
| Title |
An explanation for the decrease in cell lysis in a rotating tube with increasing ltrasound intensity. |
| Author |
Miller MW, Church CC, Brayman AA, Malcuit MS, Boyd RW. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1989 |
| Abstract |
Previous observations indicate that for in vitro mammalian cells insonated in rotating test tube the amount of cell lysis initially increases to some maximum and then decreases with further increase in ultrasound exposure. The results of the present investigation support the postulate that the reduction in cell lysis with increase in ultrasound intensity is related to the development of an ultrasonically induced "cloud" of bubbles in the fluid between the transducer and test tube; these bubbles mitigate against acoustic transmission thus reducing cell lysis in the insonated test tube. |
| Title |
An explanation of bioeffect mechanisms. |
| Author |
O'Brien WD Jr, Kuperberg I, Skelly A. |
| Journal |
In-service Rev Diagn Med Sonog |
| Volume |
|
| Year |
1987 |
| Abstract |
This issue takes a temporary departure from clinical matters to the important topic of bioeffects. Dr. William O'Brien, author of dozens of articles on bioeffects, explains the mechanisms for bioeffect production in living tissue, concentrating on thermal effects and cavitation. Irwin Kuperberg then takes a further look at cavitation for those who have never been able to understand this confusing phenomenon. The program ends with a presentation by Andrea Skelly, Director of the Diagnostic Ultrasound Program at Seattle University and Chairman of the SDMS Bioeffects Committee. She explores the major issues related to the biological effects of ultrasound. |
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