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BRL Abstracts Database |
Your search for ultrasound produced 3296 results. Page 134 out of 330
Title |
Have your scanner's acoustic output figures been tissue adjusted? |
Author |
Clark PD. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1987 |
Abstract |
No abstract available. |
Title |
Hazards of diagnostic ultrasonography-A study with mice. |
Author |
Warwick R, Pond JB, Woodward B, Connolly CC. |
Journal |
IEEE Trans Sonics Ultrason |
Volume |
|
Year |
1970 |
Abstract |
Increasing use is being made in mechanical waves in the form of ultrasound as an alternative to X radiation in a variety of diagnostic procedures. Such waves afford satisfactory visualization of soft tissues, apparently without the dangers of ionizing radiation; moreover, there are certain advantages in showing up soft tissue structures. Suitable frequencies are in the low megahertz range with high pulse repetition frequencies and common intensities of the order of 20 W/cm2 or even as high as 95 W/cm2. Mechanisms have been proposed whereby such dosage, though of low time-average intensity, could be harmful. A particular diagnostic application that is becoming more widespread is the ultrasonic irradiation of pregnant women. Developing embryos would be expected to be especially vulnerable targets in the infliction of both immediate and delayed effects. With laboratory mice (strain S.A.S.I.C.I.) as a convenient subject in a search for such hazards, experiments imitating clinical practice as far as possible have been carried out with a variety of generators and transducers to yield different modes of dosage. Peak intensities were as high as 490 W/cm2 and time-average intensities as high as 27 W/cm2. Gestation time, fetal weight, litter size, and incidence of resorptions and abnormalities were all recorded and a statistical analysis of the latter three sets revealed that the ultrasound produced no significant effect... |
Title |
Hazards of intense sound and ultrasound. |
Author |
Davis H, Parrack HO, Eldredge DH. |
Journal |
Ann Otol Rhinol Laryngol |
Volume |
|
Year |
1949 |
Abstract |
No abstract available. |
Title |
Heart wall motion studies with ultrasound. |
Author |
Schwan HP, Reid JM. |
Journal |
Rep Univ PA Moore Sch Elect Eng |
Volume |
|
Year |
1961 |
Abstract |
A complete equipment for the production and reception of pulses of ultrasonic energy has been built. This equipment locates the positions of the heart walls and septa through the closed chest wall. Special ultrasonic transducers have also been developed which allow accurate recordings to be made of the instantaneous position of these heart structures during the cardiac cycle. Studies of the propagation of sound waves through dog lung tissue have been conducted. We conclude that the loss of energy is too great to allow the determination of heart wall positions if the ultrasound must traverse lung tissue. This conclusion has been verified for the human for ultrasonic frequencies of 1 and 2 Mc. Preliminary work with human volunteers has shown that reproducible records of wall and septal motions can be obtained through the precordium. To determine the significance of the records a study is being made of the echos obtained from dog hearts through the open chest. |
Title |
Heat generated by ultrasound in an absorbing medium. |
Author |
Cavicchi TJ, O'Brien WD Jr. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
1984 |
Abstract |
Nyborg's [J. Acoust. Soc. Am. 70, 310-312 (1981)] derivation of heat generation density has been examined. An alternative approach has been developed to yield the same expression by assuming a complex wavenumber with the linear acoustic equations. |
Title |
Heat generation by ultrasound in a relaxing medium. |
Author |
Nyborg WL. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
1981 |
Abstract |
It is shown that at any point P in a continuous sound field the time-averaged rate of heat generation by relaxational absorption per unit volume is given by alpha rho /sub 0//sup 2//pc. Here p/sub 0/ is the pressure amplitude at P while alpha is the absorption coefficient arising from relaxation when the coefficient of shear viscosity eta is zero; rho and c are, respectively, the density and velocity of sound in the medium. The result, a familiar one for plane traveling waves is shown here to apply generally when eta =0. |
Title |
Heat in male contraception (hot water 60 degrees C, infrared, microwave, and ultrasound). |
Author |
Fahim MS, Fahim Z, Der R, Hall DG, Harman J. |
Journal |
Contraception |
Volume |
|
Year |
1975 |
Abstract |
Spermatogenesis in the mammalian male is disturbed by high ambient temperature. 300 male rats weighing 250-300 gm were divided into 5 groups. Group I, control; Group II, testes were exposed for 15 minutes to water at 60 C; Group III, testicular temperature was raised to 60 C for 15 minutes by infrared spot heater concentrating radiant energy from a 750 watt iodine cycle lamp focused on the testes; Group IV, testes were treated with a microwave diathermy unit radiating energy at 2450 megacycles/second for 1, 5, or 15 minutes; Group V, ultrasound 1.0 w/sq cm was applied once or twice, or 2.0 w/sq cm was applied once. The animals were mated with proestrus females 24 hours after treatment, then followed each 5 days with another female until pregnancy was documented to have occured in females. This was continued for 10 months, the duration of this experiment. Group II males impregnated females after 30-35 days, while those in Group III impregnanted females after 60-75 days. Goups IV and V impregnated females after 65-80 days, after 150-210 days, or did not impregnate females during the 10-month study - depending on the power and duration in the case of microwave, and the dosage, duration, and frequency of application in the case of ultrasound. No significant difference in blood testosterone levels occured in treated animals. Seminiferous tubules were either normal in histological appearance or showed partial degranulation, especially in Groups IV and V. Long-term effects of recurrent heat application are under investigation. This pilot study offers the possibility of reversible and irreversible sterilization for human males as well as a new method of animal population control in the U.S.A. |
Title |
Heating as a mechanism for ultrasonically-induced petechial hemorrhages in mouse intestine. |
Author |
Miller DL, Thomas RM. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1994 |
Abstract |
Anesthetized hairless mice were exposed to 1.035 MHz unfocused ultrasound in a temperature-controlled water bath. Visible petechial hemorrhages and hyperemia were produced in the intestines. Histologically, the petechiae appeared to be localized mostly to the lamina propria of the mucosa. For 2 min exposure, the number of petechiae and length of hyperemic tissue both increased with increasing spatial peak pressure amplitude above a threshold of about 0.4-0.57 MPa. The magnitude of these effects increased, and the threshold decreased, with increasing exposure duration from 1 min to 4 min. The effects also increased for increasing bath temperature from 32 degrees C to 42 degrees C. The effects decreased markedly for 1 ms burst-mode exposure with 2 ms and 4 ms repetition periods with constant pressure amplitude, but were essentially constant for constant temporal-average intensity. Both effects were also produced by heating from radio-frequency diathermy at 10.35 MHz. The effects were associated with abdominal temperatures above about 42-43 degrees C, which were estimated with a thermocouple at the end of the exposure. The hyperemia is a clearly thermal effect, while the petechiae have been previously associated with the cavitation mechanism. However, the ultrasonically-induced petechiae observed in this study do not represent an unequivocal marker for cavitation, but rather appear to be attributable to heating. These findings help to reduce the expectation of ultrasonic cavitation during medical therapy treatments.
|
Title |
Heating distribution color graphics for homogeneous lossy spheres irradiated with plane wave ultrasound. |
Author |
Cavicchi TJ, O'Brien WD Jr. |
Journal |
IEEE Trans Sonics Ultrason |
Volume |
|
Year |
1985 |
Abstract |
Color distributions of absorption of acoustic energy in spheres due to an incident plane wave are presented. The characteristics of the spheres are typical of tissue, while the lossless surrounding medium is similar to water. Effects of varying parameters such as sound velocity, density, and object size on the solution to the wave equation are discussed and demonstrated in the images. Larger objects and those with lower acoustic impedance than the surrounding medium have areas of focused and relatively more intense heating. For short duration exposure the images represent the spatial distributions of relative rates of temperature rise. |
Title |
Heating of guinea-pig fetal brain during exposure to pulsed ultrasound. |
Author |
Bosward KL Barnett SB Wood AKW Edwards MJ Kossoff G. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1993 |
Abstract |
Ultrasound-induced temperature elevations in fresh and formalin-fixed fetal guinea-pig brains were measured during in vitro insonation, with a stationary beam in a tank containing water at 38 degrees C. The pulsing regimen used 6.25 microseconds pulses, repeated at a frequency of 4 kHz emitted from a focussed transducer operating with a centre frequency of 3.2 MHz. The greatest temperature rise in brain tissue occurred close to bone and correlated with both gestational age and progression in bone development. After a 2 min insonation with a spatial peak temporal average intensity (ISPTA) of 2.9 W/cm2, a mean temperature elevation of 5.2 degrees C was recorded in fetuses of 60 days gestation (dg). The same exposure produced an increase of 2.6 degrees C in the centre of whole brains of 60 dg fetuses when the bony cranium was removed. As most of the heating occurs within 40 s, these findings have implications for the safety of pulsed Doppler examinations where dwell-time may be an important factor.
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