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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 266 out of 330
| Title |
The role of the duty factor in ultrasound-mediated cardiac stimulation |
| Author |
Coiado OC, O'Brien William D Jr. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2014 |
| Abstract |
The role of the duty factor (DF) in ultrasound-mediated cardiac stimulation is studied. Five 3-month-old female rats were exposed transthoracically to 3.5-MHz ultrasonic pulses of 2.0-MPa peak rarefactional pressure amplitude, variable DF, and variable pulse repetition frequency. A change in the heart rate was not observed following the 0.25%-DF sequence. A decrease of about 4% in the heart rate was observed following the 0.50%-DF and 1.00%-DF sequences. Outcomes suggest a possible DF threshold for cardiac pacing. |
| Title |
The role of ultrasound operation mode for safely interfering in the heart rate. |
| Author |
Belassiano E, Miller R, O'Brien WD Jr. Buiochi F, Costa ET. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
2010 |
| Abstract |
Diagnostic ultrasound applies low intensity acoustic waves to noninvasively investigate biological tissues. Higher intensities can alter tissue characteristics, and this is of interest for therapeutic ultrasound, when the occurrence of bioeffects is – to a certain extent – desirable for tissue healing.
Relative to cardiology, diagnostic ultrasound is well established, whereas there is an unexplored potential for therapeutic applications. Ultrasound is an alternative source of energy that has different characteristics when compared to
electrical energy and so its interference in the cardiac activity might be useful for treating arrhythmias. The objective of this study is to investigate the role of operation mode (continuous / pulsed ultrasound) for interfering in the heart rate without damaging the tissue. Nine Sprague-Dawley rats were anesthetized with isoflurane and exposed to high-intensity, 1- MHz ultrasound. One animal was submitted to continuous wave application, which produced thermal damage. Two
groups of four animals were submitted to different pulsed schemes (single / variable pulse repetition frequency). Posttherapy values were divided by pre-therapy values, resulting in normalized values for heart rate and respiratory rate. These values were compared between both pulsed schemes, resulting in a statistically significant difference (p<0.05) only for the heart rate. When comparing the post-therapy and pre-therapy absolute values within the variable pulse repetition rate group, there was a heart rate drop (p<0.05), whereas there was no significant effect on the ejection fraction and end diastolic
volume, meaning that no major damage was produced. The insonification scheme used in this study excludes temperature effects, so the observed effect results from nonthermal mechanisms, possibly from radiation force. |
| Title |
The safety of clinical ultrasonic examination. Electroencephalographic examination of the. neonate subjected to pulsed ultrasound. |
| Author |
Kohorn EI, Pritchard JW, Hobbins JC. |
| Journal |
Obstet Gynecol |
| Volume |
|
| Year |
1967 |
| Abstract |
No abstract available. |
| Title |
The safety of diagnostic contineuos wave ultrasonic irradiation - a clinical study, serum hemoglobin level and scanning electron microscopic finding of maternal and cord blood in vitro. |
| Author |
Koh S. |
| Journal |
Acta Obstet Gynaecol Jpn |
| Volume |
|
| Year |
1981 |
| Abstract |
In order to check the safety of diagnostic contineous wave ultrasonic irradiation, a clinical study, serum hemoglobin level and scanning microscopic finding of ultrasound irradiated blood were studied. The following results were obtained..1. Clinical study:.Ultrasonic examinations were carried out on 6788 pregnant women at the first trimester of gestation. In test group, rate of abortion and premature delivery, fetal malformation and small for date gestation were not significantly higher than those of control group.. Neither timing of first examination nor number of examination at the first trimester seemed to increase above mentioned abnormality..2. Serum hemoglobin level:.Blood exposed 2 to 12 hours to low intensity ultrasound (20 mw/cm(^2)) showed no significantly higher serum hemoglobin level than that of control group. However, blood exposed 40 to 120 minutes to high intensity ultrasound (2.6 w/cm(^2)) have significant higher hemoglobin lever than that of control group..3. Scanning electron microscopic finding:. Erythrocyte exposed 4 to 24 hours to low intensity ultrasound have no significantly different scanning electron microscope finding when compared to that of control group. However, deformed erythrocytes were significantly higher than those of control groups after exposure 40 to 120 minutes to high intensity ultrasound.. |
| Title |
The safety of ultrasound in fetal monitoring. |
| Author |
Mannor SM, Serr DM, Tamari I, Meshorer A, Frei EH. |
| Journal |
Am J Obstet Gynecol |
| Volume |
|
| Year |
1972 |
| Abstract |
Since ultrasonic (Doppler) fetal monitoring systems are technically feasible, it is most important to establish whether repeated prolonged irradiations are safe to both the mother and the fetus. The safety of ultrasonic exposures was investigated in this study with particular regard to structural changes, congenital malformation, and chromosomal aberration. Intensity levels of 164, 272, 490, 1050 mW per square centimeter have been used at a frequency of 2.28 megahertz (MHz), for 5 or 60 minutes, either singly or for 5 consecutive exposures. At an intensity of 1050 mW per square centimeter, tissue damage was recorded proportional to the duration of exposure. Macroscopic and microscopic examinations including chromosomal analysis showed these tissue effects to be identical with those found in overheating. It has been found that an intensity level of 490 mW per square centimeter did not cause critical tissue temperature rise. There were no pathologic findings on the macroscopic and microscopic examinations in the mothers, fetuses, and neonates, and no congenital malformations were recorded. Moreover, there were no pathologic findings in neonates of the third generation produced by brother-sister cross-mating from the fetuses which had been irradiated. All of the exposed mothers were able to conceive again, producing healthy offspring. Chromotome squash preparations were done from irradiated fetuses, revealing an equal incidence of chromosome aberrations as compared with that of the control group. |
| Title |
The safety of ultrasound. |
| Author |
Dewhurst CJ. |
| Journal |
Proc R Soc Med |
| Volume |
|
| Year |
1971 |
| Abstract |
No abstract available. |
| Title |
The scattering of ultrasound by cylinders: implications for diffraction tomography. |
| Author |
Robinson BS, Greenleaf JF. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1986 |
| Abstract |
The validity of wave equations employed as system models in acoustical diffraction tomography is investigated using.simulations and measurements of the scattering of plane ultrasound waves by cylinders. It is demonstrated by simulation and.experiment that it can be appropriate to neglect density fluctuations and shear waves, implying that the commonly used form of.the wave equation suitably describes scattering by fluctuations of acoustic speed and absorption. Diffraction tomographic.reconstructions of simulated data reveal the importance of absorption, the behavior of the real and imaginary parts of the.reconstructed refractive index, and the relative advantages and limitations of the Born and Rytov approximate transformations. . |
| Title |
The scattering of ultrasound by human blood. |
| Author |
Reid JM, Sigelmann RA, Nasser MG, Baker DW. |
| Journal |
Proc Eighth ICMBE - Chicago |
| Volume |
|
| Year |
1969 |
| Abstract |
No abstract available. |
| Title |
The scattering of ultrasound by human tissues - some theoretical models. |
| Author |
Chivers RC. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1977 |
| Abstract |
Two ultrasonic scattering models for human tissue are suggested, one in which the homogeneities are discrete and the other an inhomogeneous continuum. After discussing relevant functions, the results of the literature on the two models are considered in the context of diagnosis. The results point to the parameters relevant to a description of the scattering process, emphasizing the need for more physical information about human tissue. |
| Title |
The scattering of ultrasound by red blood cells. |
| Author |
Shung KK, Sigelmann RA, Reid JM. |
| Journal |
Appl Radiol |
| Volume |
|
| Year |
1976 |
| Abstract |
This paper reviews the experimental results obtained so far on the measurement of ultrasonic scattering properties of erythrocytes. The scattering is proportional to the fourth power of the frequency predicted by Rayleigh?s scattering theory for frequencies below 15 MHz. The scattering is not linearly dependent on the hematocrit, as would be expected for the single scattering process. Twersky?s wave-scattering theories are therefore applied to describe this result. The magnitude of the monopole scattering due to compressibility and of the dipole scattering due to density is in good agreement with theory. Blood is the first tissue for which a nearly complete experimental and theoretical characterization of scattering exists. |
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