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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 262 out of 330
| Title |
The mechanism of the absorption of ultrasound in biological materials. |
| Author |
Carstensen EL. |
| Journal |
IRE Trans Med Electron |
| Volume |
|
| Year |
1960 |
| Abstract |
1) Absorption of sound in solutions of macromolecules has been found to be comparable in magnitude and similar in frequency dependence to that of tissues and blood. The absorption has been shown to arise through a relaxation process. Several experimental observations suggest that the relaxation may be related to the protein-water interactions. (2) The absorption of sound in normal blood, although predominantly a molecular process, has in addition a component arising form the relative motion between the cells and the plasma. (3) In certain tissues, the experimental evidence points out again the importance of direct molecular absorption. This may be modified to some extent in inhomogeneous tissues where there is the possibility of selective absorption arising at macroscopic discontinuities. |
| Title |
The mode of action of surgical tissue removing devices. |
| Author |
Chan KK, Watmough DJ, Hope DT, Moir K, Chan F. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1985 |
| Abstract |
It is believed that the surgical ultrasound in the frequency range of 20-50 KHz exploits the direct effects of mechanical vibrations. Based on the assumptions that the behavior of soft tissue is viscoelastic, a model with a liner spring and a dashspot connected in parallel is employed to explain theoretically that mechanism of tissue fragmentation produced by ultrasonic magnetostrictively driven probes. In addition a prototype motor-driven vibrating probe had been developed in our laboratory to investigate experimentally the mode of ultrasonic surgical devises. |
| Title |
The modulus of elasticity of human cortical bone: an in vivo.measurement and its clinical implications. |
| Author |
Greenfield MA, Craven JD, Wishko DS, Huddleston AL, Friedman R, Stern R. |
| Journal |
Radiology |
| Volume |
|
| Year |
1975 |
| Abstract |
The modulus of elasticity was derived by combining the velocity of ultrasound measurements and photon absorption (Norland-Cameron method) in human cortical bone (proximal radius) in vivo. The results compare favorably with published values of the elasticity modulus obtained in vitro. Values obtained for a heterogeneous group of patients with bone and joint complaints differed from those of normal volunteers. |
| Title |
The monopole-source solution for estimating tissue temperature increases for focused ultrasound fields. |
| Author |
Ellis DS, O'Brien WD Jr. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1996 |
| Abstract |
The monopole-source solution to the problem of estimating tissue temperature rise generated by a focused ultrasound beam is presented. The acoustic pressure field generated by a focused, continuous-wave ultrasound source using the acoustic monopole-source method is developed. The point-source solution to the linear bio-heat transfer equation is used to calculate the axial, steady-state temperature increase for both circular and rectangular apertures. The results of the circular aperture are compared with the temperature increase calculated using the heated-disc method and are shown to be in substantial agreement. Finally, the temperature increase generated by the circular aperture is compared to that of the rectangular aperture for the same source power, aperture surface area, operating frequency, and medium properties, and it is shown that the rectangular source generates temperature increases less than those of the circular source under these conditions. |
| Title |
The negative chronotropic effect in rat heart stimulated by ultrasonic pulses |
| Author |
Coiado AC, O'Brien WD Jr. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
2017 |
| Abstract |
Objectives—The goal of this study is to investigate the role of sex and age of the
negative chronotropic effect after exposure of 3.5-MHz pulsed ultrasound (US) to
the rat heart.
Methods—Forty F344 rats were exposed transthoracically to ultrasonic pulses at a
duty factor of approximately 1.0% at 2.0-MPa peak rarefactional pressure amplitude. The transthoracic ultrasonic bursts were delivered consecutively in five 10-s intervals, that is, 10 s of 6-Hz pulse repetition frequency (PRF), 10 s of 5-Hz PRF, 10 s of 4-Hz PRF, 10 s of 5-Hz PRF, and 10 s of 6-Hz, for a 50-s total exposure duration. The rats were divided into 8 groups (n55 each): US young male, control young male, US young female, control young female, US old male, control old male, US old female, and control old female.
Results—Two-way ANOVA for repeated measures was used to compare heart rate,
cardiac output, arterial pressure, and other hemodynamic values (baseline) before
and after US stimulation. Sex versus age versus US interaction was detected for heart rate. Cardiac output showed an age effect, and ejection fraction showed age and US effects. The arterial pressure showed a sex effect. A negative chronotropic effect (30% decrease in heart rate) was observed for young female rats. An hypothesis is that the US effect is weight (menopause) dependent, because the young (premenopausal) female rats weighed approximately 40 to 60% less than other groups of rats.
Conclusions—It is likely that the ovarian hormones are responsible for different
US-induced cardiac bioeffects in different ages and sexes.
Key Words—age; biological effects; chronotropic effect; heart; sex; ultrasound |
| Title |
The non-thermal inhibition of growth and the detection of acoustic emissions from bean roots exposed to 1 MHz ultrasound. |
| Author |
Morris JV, Coakley WT. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1980 |
| Abstract |
High amplitude modulated subharmonic and white noise emissions were detected, after a time delay, at intensities in excess of 22 W/sq cm when bean root tips were exposed to ultrasound in either plane or focused fields at 1 MHz. The temperature rise in the root tips on initiating exposure was 8 C at 10 W/sq cm and 15 C at 40 W/sq cm. A further temperature increase ranging from 5 to 20 C was observed if subharmonic emission began during the exposure. Growth inhibition occurred in root tips heated to 40 C for 3 min in the absence of sound. The temperature of the ultrasound treatment tank was maintained at about 8 C to avoid damaging temperature rises during sonication. Root growth inhibition occurred in the plane field in the absence of strong subharmonic emission at intensities as low as 3 W/sq cm following 80-min treatment. These was a detectable increase in second harmonic emission when roots were treated in the focused field at 15 W/sq cm for 6 min. |
| Title |
The nonlinearity parameter B/A of biological media. |
| Author |
Dunn F, Law W, Frizzell L. |
| Journal |
Proc Tenth ISNA - Kobe |
| Volume |
|
| Year |
1984 |
| Abstract |
In the diagnostic use of ultrasound, deeper understanding of nonlinear phenomena in mammalian tissue should lead to improved accuracy of, and provide more precise information on, the state of the organ being examined. Imaging a function of the nonlinearity parameter has already been suggested (Ichida et al., 1983). In the therapeutic use of ultrasound, the detailed understanding should lead to better control of, for example, the heat deposition of ultrasonic energy during hyperthermic treatment of cancer. For both applications it is important to determine whether the nonlinear phenomena could involve harmful effects to patients. Thus, it is desirable to be able to estimate the amount of acoustic nonlinearity which may occur in a biological medium. For this reason the authors undertook a project of determining the nonlinearity parameter B/A of biological media. They first summarize the empirically observed ultrasonic properties of tissues and tissue models, then mention briefly the methods used to determine B/A, and lastly present the resulting findings. |
| Title |
The NPL ultrasound measurement service and comments on the measurement and specification of the acoustic output of medical ultrasonic equipment. |
| Author |
Preston RC. |
| Journal |
Proc Ultrason Int Conf |
| Volume |
|
| Year |
1985 |
| Abstract |
The National Physical Laboratory (NPL) in the UK provides an Ultrasound Measurement Service whereby the acoustic output of medical ultrasonic equipment may be determined, the results being directly traceable to National Measurement Standards. Many of the measurements are made using calibrated miniature hydrophones made from polyvinylidene fluoride with both the hydrophone and ultrasonic transducer mounted in a versatile ultrasonic beam plotting facility. This facility is described together with the data acquisition system for recording and storing the measured signals. Some of the problems involved with the determination of pulse-average, temporal-average, and spatial-average acoustical quantities are described together with illustrations of sources of uncertainty. |
| Title |
The output of pulse-echo ultrasound equipment: A survey of.powers, pressures and intensities. |
| Author |
Duck FA, Starritt HC, Aindow JD, Perkins MA, Hawkins AJ. |
| Journal |
Br J Radiol |
| Volume |
|
| Year |
1985 |
| Abstract |
A survey of the powers, pressures and intensities generated by ultrasonic pulse-echo equipment in.clinical use has been carried out. Three conventional B-scanners, four linear-array scanners and four.mechanically sectored scanners were included in the study. Measurements were made on a total of 22.transducers covering the nominal frequency range 2.25-7.5 MHz. On those instruments where an output.power control was provided, two measurements were made: one at the maximum available power and a.second at a lower power. On arrays with a variable transmit focus control, measurements were made at.all available focus settings. In all, measurements were made on 38 separate focused pulsed ultrasonic.fields. The measurements were carried out using a calibrated ultrasonic force balance, and a calibrated.polyvinylidene difluoride (PVdF) membrane hydrophone. A very wide range of maximum powers,.pressures and intensities were found. Powers from 0.5-80 mW were measured; spatial-average.temporal-peak positive pressures at the transducer varied between 30 kPa and 1.15 MPa, and.spatial-peak pulse-average intensities were in the range 3.6 X 10(3)-1.1 X 10(7) Wm-2. |
| Title |
The performance of different pressure pulse generators for extracorporeal lithotripsy: A comparison based on commercial lithotripters for kidney stones. |
| Author |
Buizza A, Dell'Aquila T, Giribona P, Spagno C. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1995 |
| Abstract |
By using needle hydrophones and a PC-controlled experimental set-up, the acoustic output of 10 commercial extracorporeal shock-wave lithotripters has been measured. The pressure field was measured in the focus, along the beam axis, in the focal plane and "at the skin level" (a plane orthogonal to the beam axis, 5 cm backward from the focus, assumed as the entrance site of the pressure pulse into the patient's body). The set of tested instruments included the three technologies nowadays in use to generate the pressure pulse, namely electrohydraulic, electromagnetic and piezoelectric. Notwithstanding large intratechnology variability, the results indicate that electrohydraulic and electromagnetic generators can provide comparable performances. Piezoelectric generators produced pressure pulses with less energy than the others. Possible implications of the experimental results on treatment safety and effectiveness of kidney stone destruction are discussed. |
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