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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 246 out of 330
| Title |
Temperature rise generated by a focussed Gaussian beam in a two-layer medium. |
| Author |
Wu J, Nyborg WL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1992 |
| Abstract |
The temperature rise is calculated at points along the axis of a focused Gaussian beam propagating through a two-layer medium; the first layer is non-attenuating and the second one consists of absorbing material simulating soft tissue. This two-layer medium is relevant to several situations encountered in medical applications of diagnostic ultrasound. These include fetal examinations via the abdominal wall, where the beam may travel a significant distance through urine or amniotic fluid before reaching the fetus. |
| Title |
Temperature rise generated by diagnostic ultrasound in a transcranial phantom. |
| Author |
Wu J, Cubberley F, Gormley G, Szabo TL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1995 |
| Abstract |
Temperature rises generated by diagnostic ultrasound from a modified commercial system (Sonos 1000 Hewlett Packard) in a transcranial phantom that consists of human temporal bone and tissue-mimicking material are measured. Significant temperature rises were found at the external and internal temporal bone surfaces. The experimental results are compared with cranial thermal.indices (TIC) developed by the American Institute of Ultrasound in Medicine and the National Electrical Manufacturers Association for various modes. For all the modes compared, TIC underestimated temperature rise at the external temporal bone surface. The differences between the data and temperature rises predicted by TIC can be attributed to transducer surface heating. |
| Title |
Temperature rise in a tissue-mimicking material generated by unfocused and focused ultrasonic transducers. |
| Author |
Wu J, Chase JD, Zhu Z, Holzapfel TP. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1992 |
| Abstract |
The temperature elevation in a homogeneous tissue-mimicking material with tissue-like thermal and acoustic properties, generated by unfocused and focused ultrasonic transducers operating at 1.0 and 3.5 MHz frequencies, was measured. It was found that in the vicinity of a transducer front face, both transducer surface heating and ultrasound absorption are important sources for tissue heating. As for heating due to ultrasound absorption, the experimental results are compared with theoretical predictions for nonperfused tissues resulting from different beam models. The experimental data are in reasonable agreement with the results calculated from a model developed by Nyborg and Steele, a Gaussian beam model and from the model used by the National Council on Radiation Protection and Measurements (NCRP). |
| Title |
Temperature-dependent differences in the nonlinear acoustic behavior of ultrasound contrast agents revealed by high-speed imaging and bulk acoustics. |
| Author |
Mulvana H, Stride E, Tang M, Hajnal JV, Eckersley R. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2011 |
| Abstract |
Previous work by the authors has established that increasing the temperature of the suspending liquid from 20°C to body temperature has a significant impact on the bulk acoustic properties and stability of an ultrasound contrast agent suspension (SonoVue, Bracco Suisse SA, Manno, Lugano, Switzerland). In this paper the influence of temperature on the nonlinear behavior of microbubbles is investigated, because this is one of the most important parameters in the context of diagnostic imaging. High-speed imaging showed that raising the temperature significantly influences the dynamic behavior of individual microbubbles. At body temperature, microbubbles exhibit greater radial excursion and oscillate less spherically, with a greater incidence of jetting and gas expulsion, and therefore collapse, than they do at room temperature. Bulk acoustics revealed an associated increase in the harmonic content of the scattered signals. These findings emphasize the importance of conducting laboratory studies at body temperature if the results are to be interpreted for in vivo applications. |
| Title |
Temperatures produced in tissues by ultrasound: Experimental study using various technics. |
| Author |
Herrick JF. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1953 |
| Abstract |
Experiments have been carried out to investigate ultrasound as a possible therapeutic agent. These show that selective heating occurs in nerves and bones treated in situ. Effects of direct heat on nerves are strikingly similar to the effects of ultrasound. Blocking of nerves by sound or heat with present techniques seems impractical because the margin of safety is too narrow. |
| Title |
Temporal and spatial evaluation of lesion reparative responses following superthreshold exposure of rat lung to pulsed ultrasound. |
| Author |
Zachary JF, Frizzell LA, Norrell KS, Blue JP Jr, Miller RJ, O'Brien WD Jr. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2001 |
| Abstract |
This study characterized the reparative responses in rat lung. Forty-five adult female rats were exposed at two sites over the left lung to 3.1-MHz superthreshold pulsed ultrasound. The repair of lung lesions was evaluated from 0 through 44 days postexposure. Macroscopic lesions at 0 days postexposure were large bright red eclipses of hemorrhage. By 1 and 3 days postexposure, lesions were the same size and dark red to red-black, but, by 3 days postexposure, lesions had a raised surface appearance. From 5-10 days postexposure, lesions grew smaller in size, progressed from red-gray to yellow-brown, and retained a raised surface appearance. From 13 through 44 days postexposure, lesions gradually decreased in size, had a faint yellow-brown discoloration, and gradually lost the raised surface appearance. By 37 and 44 days exposure, lung returned to near normal morphology, but had small areas of light yellow-brown discoloration in the areas where lung was exposed. Microscopic lesions at 0 and 1 days postexposure were areas of acute alveolar hemorrhage. By 3 days postexposure, lesions had lose of alveolar erythrocytes and the formation of hemoglobin crystals. From 5 through 44 days postexposure, iron in degraded erythrocytes was processed to hemosiderin and was negligible in quantity at 44 days postexposure. The proliferation of resident cells (likely alveolar epithelial cells, fibroblasts and endothelial cells) and the infiltration of inflammatory cells in lesions declined in intensity as the lesions aged and was minimal by 44 days postexposure. Under the superthreshold exposure conditions described, lesions induced by ultrasound do not seem to have long-term residual effects in lung. |
| Title |
Temporal peak intensity as a critical parameter in ultrasound dosimetry. |
| Author |
Barnett SB, Kossoff G. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1984 |
| Abstract |
The in vitro effect of microsecond pulses of ultrasound is studied in mammalian cells using two different biologic endpoints. The frequency of sister chromatid exchanges (SCE) is unchanged in Chinese hamster ovarian cells insonated with a stationary transducer for 1-30 minutes at an SPTA intensity of 0.1 W/cm2. Raising the temporal average intensity to 2 W/cm2 by increasing the pulse repetition frequency alone still has no effect, whereas a change in temporal peak intensity produces an increase in SCE after insonation for only 1 minute. From experiments involving aggregation of platelets in suspension around acoustically active hydrophobic pores, pulse duration is found to be a more effective factor than the pulse repetition frequency. Results of the two studies show the biologic response to be strongly dependent on temporal peak intensity and pulse duration, but weakly dependent on duration of exposure. The temporal average intensity as a singular dosage specification is considered to be a poor indicator of potential nonthermal bioeffects associated with microsecond pulses. |
| Title |
Temporally-specific modification of myelinated axon excitability in vitro following a single ultrasound pulse. |
| Author |
Mihran RT, Barnes FS, Wachtel H. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1990 |
| Abstract |
Single, short-duration, low-energy pulses of ultrasound were found to elicit distinct modifications of the electrical excitability of myelinated frog sciatic nerve in vitro in a window extending 40-50 ms after pulse termination. These modifications include both enhancement and suppression of relative excitability, the sequence of which generally follows one of two distinct temporal response patterns. The ultrasound pulses were focused, 2-7 MHz, of 500-microseconds duration, and of peak intensities of 100-800 W/cm2. Total absorbed pulse energies were generally less than 100 mJ/g, corresponding to local temperature rises of the nerve trunk of no more than 0.025 degrees C per pulse, thereby precluding bulk heating as a basis of this effect. The observed effects cannot be elicited using either a subthreshold square wave or RF electrical prestimulus, suggesting a unique form of receptivity of the nerve trunk to mechanical perturbation. We present evidence that the low-frequency radiation pressure transient accompanying the envelope of the acoustic pulse is the active parameter in this phenomenon, and postulate that it may act by the gating of stretch-sensitive channels, which have been recently reported in a variety of cell membranes. These results may demonstrate that stretch-sensitive channels in neural membrane can serve to functionally modulate neuro-electric signals normally mediated by voltage-dependent channels, a finding which could suggest new clinical applications of high peak-power, low-total-energy pulsed ultrasound. |
| Title |
Tenderization of semitendinosus muscle using high intensity ultrasound. |
| Author |
Smith NB, Cannon JE, Novakofski JE, McKeith FK, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1991 |
| Abstract |
Semitendinosis muscle specimens, approximately 2.54-cm thick and weighing 200 g, were exposed to high-intensity ultrasound for periods of 0, 2, 4, 8, and 16 min. Four specimens were used at each period for a total of 20 specimens. A magnetorestrictive transducer produced CW ultrasound at a frequency of 25.9 kHz in a stainless steel tank filled with degassed saline. The semitendinosus meat specimens were cut either cross-sectionally or longitudinally to the muscle fibers. The cross-sectional cuts of the meat specimens were exposed to the ultrasound for periods of 2, 4 and 8 min while the longitudinal cuts were exposed for periods of 2, 4, 8 and 16 min. Tenderness was measured by Warner-Bratzler shear force by removing six 1.3-cm-diameter cores from each meat sample. For the samples exposed for 2 and 4 min, there was a statistically significant decrease in Warner-Bratzler shear force, which indicates an increase in tenderness for these specimens. These results suggest that high-intensity ultrasound is capable of tenderizing meat as assessed by an objective shear force measurement. |
| Title |
Teratologic evaluation of rats prenatally exposed to pulsed-wave ultrasound. |
| Author |
Fisher JE Jr, Acuff-Smith KD, Schilling MA, Vorhees CV, Meyer RA, Smith NB,O'Brien WD Jr. |
| Journal |
Teratology |
| Volume |
|
| Year |
1994 |
| Abstract |
While there are no known risks associated with diagnostic ultrasound, uncertainty about the safety of prenatal ultrasound exposure remains. The purpose of the present experiment was to evaluate the teratogenic potential of pulsed-wave (pw) ultrasound in rats, in the absence of maternal anesthesia or restraint. Pregnant CD rats, trained to remain immobile in a water-filled ultrasound exposure tank, were scanned with 3-MHz pw ultrasound at levels of 0, 2, 20 or 30 W/cm2 ISPTA (spatial peak, temporal average intensity) on gestational days 4-19 for approximately 10 min/day. Examination of fetuses on E20 revealed no increase in skeletal or visceral malformations in groups exposed to pw ultrasound in utero. The number of implantations/dam was significantly increased in all pw ultrasound exposure groups compared to sham-exposed animals and, in a possibly related finding, resorptions were increased in the two highest exposure groups. Although significantly increased compared to controls, resorption frequencies in these groups were low (< 10%). No exposure-related changes in fetal weights were observed in offspring of rats scanned with pw ultrasound during gestation. The results indicate that, under the conditions described, no overt embryotoxicity is associated with gestational exposure to pw ultrasound intensities of up to 30 W/cm2. |
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