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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 298 out of 330
| Title |
Ultrasonic velocity spatial distribution analysis of biological materials with the scanning laser acoustic microscope. |
| Author |
Embree PM, Foster SG, Bright G, O'Brien WD Jr. |
| Journal |
Acoust Imaging |
| Volume |
|
| Year |
1984 |
| Abstract |
The fundamental examination of biological tissue with ultrasound can lead to important diagnostic capabilities. In order to quantify tissue characteristics with ultrasound, the ultrasonic propagation properties of normal and pathological tissues must be characterized and cataloged. An important ultrasonic property is the speed of sound for characterizing tissue [1]. In this work, the Scanning Laser Acoustic Microscope (SLAM) is used to measure the spatial variation of the speed of sound in tissue, thereby providing a quantitative ultrasonic parameter for tissue characterization.
The SLAM (Sonomicroscope 100, Sonoscan, Inc.) provides three different television type images as shown in Figure 1. A laser scans the lower surface of the coverslip in order to detect mechanical disturbances induced by the 100 MHz ultrasonic energy which has passed through the specimen from below. The optical (laser scan) transmission image (Figure 1a) allows the operator to position the sample in the center of the 2 mm x 3 mm field of view. The acoustic image (Figure 1b) shows the amount of ultrasound energy passing through the sample. This signal is proportional t o the envelope of the laser detector output. In this image, dark areas correspond to high areas of ultrasonic attenuation and light areas to low attenuation areas. The third image (Figure 1c), the interference image, is produced by electronically mixing the laser detector output with a 100 MHz reference signal.
The interference image consists of approximately 39 vertical light and dark bands which represent locations of constant phase contours of the ultrasonic wave after it has traversed through the specimen. In saline solution (the normal coupling medium for tissue samples) the interference lines are straight and equally spaced. When a slice of tissue (usually 400 to 800 um thick) is placed in the saline solution, the interference lines shift to the right at the saline-tissue interface indicating the tissue has a higher speed of sound. In an area of tissue where the thickness is constant, the interference lines appearance is somewhat corrugated, that is, they do not appear straight as in the very homogeneous coupling medium. This could not represent a microscopic index of refraction gradient in tissue and may represent a microscopic index of refraction gradient in tissue and may represent a source of ultrasonic back scattering for clinical B-scan imaging systems. To quantify this gradient, the interference lines are subjected to an automated analysis technique which is described herein.
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| Title |
Ultrasonic vibrational potentials in gels and preparations of biological tissue. |
| Author |
Rosenfeld EH. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1992 |
| Abstract |
Measurements of the ultrasonic vibrational potentials (UVP) were performed at 815 kHz in agar and agarose gels as well as in several biological tissues from frog, rat and pig. The results for gels show that the magnitude of the UVP depends on the charge of the solid components of the gel, its mechanical strength and particularly on the concentration of free electrolytes present in the gel. The UVP decreases to less than 10 microV for a velocity amplitude of 1 cm/s if the salt concentrations exceed 10(-2) mol/L. The measurements in biological tissue in vitro demonstrate that the UVP are of the order of magnitude of a microV s cm-1 which is also explained by the presence of electrolytes of high concentrations in tissues. The measurements in biological tissue in vitro demonstrate that the UVP are of the order of magnitude of microV s cm-1 which is also explained by the presence of electrolytes of high concentrations in tissues. Based on these experiments, it can be concluded that the potential for harm to humans due to electrical effects of ultrasound as used in medical diagnostics is very low. |
| Title |
Ultrasonic: central nervous system changes from focused ultrasound. |
| Author |
Hueter TF, Fry WJ. |
| Journal |
Untrasonic |
| Volume |
|
| Year |
Unknown |
| Abstract |
No abstract available. |
| Title |
Ultrasonically accelerated resorption of vitreous membranes. |
| Author |
Coleman DJ, Lizzi FL, El-Mofty AAM, Driller J, Franzen LA. |
| Journal |
Am J Ophthalmol |
| Volume |
|
| Year |
1980 |
| Abstract |
A noninvasive procedure was used to treat membranes within the vitreous with controlled exposure to focused high-intensity ultrasound in rabbit eyes. Membranes were created by injecting small quantities of platelet-rich plasma into the vitreous of the intact globe of anesthetized rabbits. The average time for untreated membranes (controls and shams) to be resorbed was 34 days, whereas the average time to total resorption of membranes treated with ultrasound was 21 days. This comparison showed that high-intensity ultrasound was effective in accelerating the resorption of this type of vitreous membrane. This ultrasound technique is totally noninvasive and can be used without damage to other ocular tissues. Although this animal model.departs in some respects from human vitreous membranes, eventual clinical applications are indicated in selected cases where vitrectomy must be delayed or is contraindicated. Noninvasive disruption of vitreous membranes by therapeutic ultrasound offers great promise for reducing the visual limitations produced by such membranes, and eliminating the sequence of disease leading to permanent visual loss. |
| Title |
Ultrasonically activated gas-filled micropores release hemoglobin and antigens from human erythrocytes in vitro. |
| Author |
Miller DL, Lamore BJ. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1987 |
| Abstract |
Antigen release from human type B red blood cells was investigated by sensitive capillary-tube assay techniques after subjecting 3% suspensions to a controlled form of ultrasonic cavitation. Cells were kept suspended during the 1,000-sec exposures by an orbital motion of the sample chamber. Several spatial peak.intensities of continuous 1.7 MHz ultrasound were applied to the samples which included gas-filled 4-microns diameter micropores in hydrophobic membranes. Free hemoglobin, indicating hemolysis, and free antigenic material, indicating solubilization of antigens, were found in the supernates of suspensions.exposed to 90 mW/cm2 or 180 mW/cm2, respectively, or greater intensities. None of the free antigenic material could be attributed to antigen loss by surviving cells. For these conditions, the antigen release effect of ultrasound appears to be a byproduct of cavitation-induced cell lysis. |
| Title |
Ultrasonically induced cavitation studies of electrochemical passivity and transport mechanisms. |
| Author |
Perusich SA, Alkire RC. |
| Journal |
J Electrochem Soc |
| Volume |
|
| Year |
1991 |
| Abstract |
Focused ultrasound was used to investigate processes that influence depassivation and repassivation phenomena onpure Fe and on cast iron in 2N H2SO4 at 1.58 MHz and at intensities up to 7.8 kW/cm2. At sufficiently high intensities, ultrasoundwas found to affect significantly the time of passivation and to hinder repassivation completely. The critical acousticfocal intensity, either required for depassivation or to prevent repassivation, was found to vary exponentially with potential.Once the oxide film had formed on the metal, the acoustic focal intensity needed to break down the film dependedlogarithmically on the time of passivation. The mass transfer coefficient in the focal region was found to be proportional tothe acoustic focal intensity to the one-third power. |
| Title |
Ultrasonically induced disruption and hemolysis of vitreous hemorrhages. |
| Author |
Lucas BC Driller J Iwamoto T Silverman RH Lizzi FL Coleman DJ. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1989 |
| Abstract |
High-intensity focused ultrasound was used to insonify simulated vitreous hemorrhages in two in vitro models and one in vivo animal model. Histopathologic evaluation of the treatment effect was performed with light and electron microscopy. Ultrasonic parameters resulting in histopathologically proven disruption and hemolysis of intravitreal blood were investigated. Most important in obtaining this effect were the temporal average acoustic power and pulse repetition rate of the applied ultrasonic beam. Accurate positioning of the therapeutic beam and visualization of internal spatio-temporal response patterns in the blood during insonification were monitored via simultaneous diagnostic B-mode imaging. Results suggested that high-intensity focused ultrasound might facilitate the two major mechanisms involved in the natural resorption process of vitreous hemorrhages namely hemolysis and surface-dependent phagocytosis. |
| Title |
Ultrasonically induced fetal weight reduction in mice. |
| Author |
O'Brien WD Jr. |
| Journal |
Ultrasound Med |
| Volume |
|
| Year |
1976 |
| Abstract |
No abstract available. |
| Title |
Ultrasonically induced gas bubbles on the surface of SOAB rubber: the consequence for measurement of power output from ultrasonic instruments. |
| Author |
Quan KM, Watmough DJ. |
| Journal |
Meas Sci Technol |
| Volume |
|
| Year |
1991 |
| Abstract |
SOAB rubber has been used as the absorbing target for measuring the total power outputs from medical ultrasonic instruments. The studies described in this paper show that the ultrasound irradiation from a therapeutic instrument can generate significant temperature rises inside SOAB rubber and cause gas bubbles to form on its surface. The temperature rise is believed to be responsible for the formation of gas bubbles. The likely effects of these gas bubbles on the accuracy of measurement of power output are discussed. |
| Title |
Ultrasonically induced intravascular streaming and thrombus formation adjacent to a micropipette. |
| Author |
Frizzell LA, Miller DL, Nyborg WL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1986 |
| Abstract |
Ultrasonically induced microstreaming around bubbles of gas have been shown to cause damage to biological materials in vitro at clinical exposure levels. The potential for ultrasonically induced cavitation and microstreaming in mammalian systems is of interest with respect to the safe application of clinical ultrasound. Ultrasonically induced intravascular microstreaming and formation of thrombi at 1 MHz is demonstrated adjacent the tip of a micropipette in contact with a mesenteric vessel of the mouse. These effects occur at or above therapeutic levels. |
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