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BRL Abstracts Database |
Your search for ultrasound produced 3296 results. Page 267 out of 330
Title |
The search for cavitation in vivo. |
Author |
Carstensen EL, Gracewski S, Dalecki D. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
2000 |
Abstract |
Until the mid 1970s, it was generally assumed that, with the short pulses of ultrasound (US) used in medical diagnosis, there was little need for concern about the possibility of inertial cavitation in vivo. This assumption came into question when experimental evidence indicated that killing of fruit fly larvae by diagnostically relevant US was associated with the presence of gas in the respiratory apparatus of the organisms. Independent theoretical contributions by Flynn and Apfel in the early 1980s made it clear that complacency in regard to cavitation was not warranted. Later, the mammalian lung, as with larva, was shown to be particularly vulnerable when it contained air. Yet, overall evidence suggests that lung hemorrhage is not consistent with the classical picture of inertial cavitation. Most recently, however, hemolysis and hemorrhage associated with the use of contrast agents have provided nearly incontrovertible evidence of the occurrence of cavitation in vivo. |
Title |
The sensitivity and specificity of subjective and a semi-quantitative technique of amniotic fluid volume assessment in predicting intrapartum morbidity. |
Author |
Williams K Wittmann BK. |
Journal |
Ultrasound Obstet Gynecol |
Volume |
|
Year |
1993 |
Abstract |
The aim of this study was to evaluate the ability of two techniques of amniotic fluid volume assessment to predict intrapartum morbidity in a high-risk population. A total of 213 pregnant women at the Grace Maternity Hospital, Vancouver, Canada were examined ultrasonically and the amniotic fluid volume was assessed subjectively and using the amniotic fluid index. Both techniques showed high specificity and negative predictive values for all outcome measures, but had an associated poor sensitivity and positive predictive value. Both techniques were similar in their ability to identify situations involving intrapartum morbidity. It is concluded that amniotic fluid assessment is a weak predictor of intrapartum morbidity but may be useful in certain conditions such as when the pregnancy is post-dates. |
Title |
The sensitivity of Drosophila larvae to continuous-wave ultrasound. |
Author |
Child SZ, Raeman CH, Walters E, Carstensen EL. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1992 |
Abstract |
The threshold for killing of freshly hatched Drosophila larvae exposed to continuous-wave (CW) ultrasound shows a minimum at approximately 0.3 MHz. This suggests that the stiffness of the material surrounding the gas bodies in the organism is comparable to water. From this, it is apparent that the gas bodies in three-day-old larvae that we have used in earlier studies are far larger than resonance size at the frequencies (1-5 MHz) used. Yet, these larvae were killed by short exposures to low-temporal-average-intensity pulsed ultrasound with peak intensities of the order of 10 W/cm2. Hence, it appears that "large" bubbles cannot be ignored in considerations of the biological effects of pulsed ultrasound and lithotripsy. |
Title |
The significance of cavitation in interpreting the biological effects of ultrasound. |
Author |
Hill CR, Joshi GP. |
Journal |
Proc Conf Ultrason Biol Med - Warsaw |
Volume |
|
Year |
1970 |
Abstract |
No abstract available. |
Title |
The significance of membrane changes in the safe and effective use of therapeutic and diagnostic ultrasound. |
Author |
Dinno MA, Dyson M, Young SR, Mortimer AJ, Hart J, Crum LA. |
Journal |
Phys Med Biol |
Volume |
|
Year |
1989 |
Abstract |
The cellular changes, such as alterations in motility and the stimulation of synthesis and secretion, induced by relatively low intensities of therapeutic ultrasound (e.g. 500 mW cm-2, SAPA; 100 mW cm-2 SATA) are primarily non-thermal in origin. They appear to be associated with changes in the permeability of the cell (plasma) membrane and in the transport of ions and molecules across it, effects which have been demonstrated in cells irradiated in suspension. In epithelial tissues, both in vitro and in vivo, it has been demonstrated that not only the cellular membrane transport pathways but also the paracellular or intercellular pathways are affected..Although membrane-mediated effects can be of value therapeutically, they could produce adverse effects if they were to occur during development, for the reception and transmission by the membrane of environmental signals are involved in determination of the fate of each cell. Determination is followed by selective gene expression and differentiation, that is, by the progressive increase in structural complexity brought about by the acquisition of specialised characteristics by various cell groups. Most cells of early embryos are ionically coupled via gap junctions which provide an intercellular pathway for electrochemical signalling and the.maintenance of the concentration gradients which provide the cells with positional information. Differentiation of the cells varies according to their location with respect to these gradients. Increase in the intracellular concentration of calcium ions, which has been shown to occur after exposure to therapeutic levels of ultrasound, can decrease the permeability of gap junctions and uncouple cells, in the manner which occurs when they differentiate. Ultrasonically induced increases in calcium ion concentration are thus of considerable clinical significance, since they could affect differentiation and consequently histogenesis. Modification of plasma membrane.permeability and transport properties, resulting in changes in the availability and activity of second messengers such as free calcium ions, can have profound effects on cell behaviour. Calcium channels appear to be the first channels to develop in the cell membranes of embryos, and internal calcium ion concentration is known to affect the synthesis of fetal proteins. Although generally reversible at intensities of less than 500 mW cm-2, changes in membrane permeability, particularly to calcium ions, could, if prolonged, have undesirable side effects not only on embryogenesis but on late prenatal and postnatal development. It is therefore recommended that.the environmental conditions, thresholds, and mechanisms involved in the production of such changes be determined, so that they can be avoided when ultrasound is used diagnostically on sensitive targets such as embryos and fetuses. |
Title |
The sonomicroscope. |
Author |
Kessler LW. |
Journal |
Proc Ultrason Symp IEEE |
Volume |
|
Year |
1974 |
Abstract |
The Sonomicroscope is an apparatus for real time visualization of microstructure with acoustic energy. The technique is based upon detecting VHF/UHF ultrasound after interaction with a specimen by means of a scanning focused laser beam probe. In addition to producing an acoustic micrograph, an optical image of the specimen is provided simultaneously. This is of considerable aid in interpreting the results since the experimental conditions of the specimen need not be disturbed. Resolution has been achieved in the range of 0.7 ? 1.3 wavelengths of sound at frequencies thusfar employed, viz., 100-500 MHz and thus "micron" size detail may be visualized. . Whereas acoustic visualization may be familiar to workers in medical diagnosis and non-destructive testing, acoustic microscopy is entirely new to the community of microscopists. Therefore, this paper is intended to serve as a general guide to concepts and applications of this new technique to the biomedical and material science communities. |
Title |
The stimulation of bone formation in vitro by therapeutic ultrasound. |
Author |
Reher P,Elbeshir EI,Harvey W,Megjhi S,Harris M. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1997 |
Abstract |
A controlled study was performed to evaluate the effects of different ultrasound (US) intensities on 5-day-old mouse calvaria bone in tissue culture. A special technique to apply the US was developed, and the following parameters were measured: collagen and noncollagenous protein (NCP) synthesis (bone formation), and temperature change. It was found that ultrasound at 0.1 W/cm2 (SATA), pulsed 1:4, 3 MHz, 5 min, significantly stimulates bone formation (i.e., the synthesis of collagen and NCP) (p < 0.001 and p < 0.01). However, pulsed ultrasound at higher doses (1.0-2.0 W/cm2 (SATA), pulsed 1:4, 3 MHz, 5 min) significantly inhibited the synthesis of both collagen and NCP (p < 0.05). The temperature measurements showed a maximum rise of 1.8 degrees C [at 2.0 W/cm2 (SATA)] and no detected rise at 0.1 W/cm2 (SATA), suggesting that the effects in this study were primarily nonthermal. These results may reflect the healing effect of US on fractures and osteoradionecrosis and reinforces the use of low intensity US regimens [0.1 W/cm2 (SATA)] in clinical practice. |
Title |
The stimulation of bone growth by ultrasound. |
Author |
Duarte LR. |
Journal |
Arch Orthop Trauma Surg |
Volume |
|
Year |
1983 |
Abstract |
The ultrasonic stimulation of bone growth was investigated in a experimental work in which a set of 45 rabbits were studied according to the following procedure:
a)bilateral osteotomy of fibula (23 animals) and bilateral drilled holes on the cortex of femur (22 animals);
b)exposure of ultrasound for 15 min per day;
c)Radiological and histological evaluations of the progress of the callus;
d)photography and measurements of the area of the callus;
e)graphical comparisons using the results between controls and stimulated limbs. Pulsed ultrasound, in the form of short bursts, was used at low intensities (below cavitation threshold) so that the temperature variation, at the osteotomy site, was of the order of 0.01° C (constant) a fact that reinforces the assumption that the stimulation mechanism due to the appearence of electric potentials is of non-thermal origin such as that caused by piezoelectricity. |
Title |
The stimulation of tissue regeneration by means of ultrasound. |
Author |
Dyson M, Pond JB, Joseph J, Warwick R. |
Journal |
Clin Sci |
Volume |
|
Year |
1968 |
Abstract |
No abstract available. |
Title |
The temperature dependence of ultrasound-stimulated acoustic emission. |
Author |
Konofagou EE, Thierman J, Karjalainen, Hynynen K. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
2002 |
Abstract |
Given the high variability of tissue properties during sonication, temperature monitoring is one of the most crucial components for accurate thermal treatment of tissues with focused ultrasound and other thermotherapy devices. Recently, the method of ultrasound-stimulated acoustic emission (USAE) has been introduced as a potential method for measurements of mechanical properties of tissues. In this paper, the dependence of USAE on tissue temperature is determined. Because USAE depends on the acoustic and mechanical properties, both of which vary with temperature, it is hypothesized that the USAE signal is also temperature-dependent and in such a way that it can be used to guide thermal therapy. In a series of experiments, ex vivo porcine muscle and fat samples were exposed to ultrasound at power levels that induce temperature elevation. In both tissue types, below the coagulation threshold, the USAE amplitude was found to vary linearly with temperature. However, at higher powers, the correlation with temperature was lost due mainly to the irreversible nature of the changes in the tissue properties. Theoretical simulations were used to interpret the USAE response change with temperature involving both reversible and irreversible changes and during both heating and cooling. These results indicate that USAE may have important promise as a potential method for localizing temperature elevation and, thus, thermal surgery monitoring, as well as detection of irreversible changes in tissues. |
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