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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 122 out of 330
| Title |
Experimental verification of theoretical in vivo ultrasound heating using cobalt detected magnetic resonance. |
| Author |
Smith NB, Webb AG, Ellis DS, Wilmes LJ, O'Brien WD Jr. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1995 |
| Abstract |
Conventional methods of measuring heating in vivo are invasive and therefore interfere with heat propagation. For the first time, ultrasound-induced temperature increases in living specimens have been estimated theoretically and measured experimentally using a noninvasive technique. In vivo ultrasound-induced temperature increases in the livers of rats show consistent results between: (1) a theoretical ultrasound point-source solution for a measured ultrasound source power of 4.3 W (2°C) and (2) a sensitive noninvasive magnetic resonance method with the cobalt (III) nucleus as a probe (2.0±1.2°C) |
| Title |
Experimental, ultrasonically induced lesions in the retina, choroid, and sclera. |
| Author |
Lizzi FL, Coleman DJ, Driller J, Franzen LA, Jakobiec FA. |
| Journal |
Invest Ophthalmol Vis Sci |
| Volume |
|
| Year |
1978 |
| Abstract |
Lesions of the retina, choroid, and sclera were created in the proptosed eye of the rabbit with the use of focused ultrasound at 9.8 MHz. Exposure levels greatly exceeding those encountered in diagnostic systems were required. Histological examination of selected tissue samples, analysis of lesion-producing exposures, and lesion size variations suggest that thermal mechanisms are the principal cause of permanent tissue alterations. Subthreshold lesions, which consist of transitory effects, were observed. 'Threshold" lesions first manifested tansitory effects followed.by permanent alterations which appeared within 24 hr. Suprathreshold lesions were evidenced by the immediate appearance of a highly blanched area with an overlying edema and occasional hemorrhage, appearing within 24 hr. The edema in these cases was resorbed within a few days, leaving behind a permanently blanched region. The threshold curve developed from these data is similar in shape to the threshold curve for light-induced lesions created with a commensurate.focal spot. |
| Title |
Experiments on ultra-sound osteomyletis. |
| Author |
Holland C. |
| Journal |
Z Orthop |
| Volume |
|
| Year |
1972 |
| Abstract |
In German speaking countries Grundmann's hypothesis based on experiments, is accepted, according to which akute hemotogenous osteomyelitis starts as an allergic-hyperergic reaction.
In numerous sets of experiments using the model of Grundmann's work the role of ultrasound was investigated. The model was modified in various ways. Clinical, radiologic and histologic tests showed that the role of ultra-sound at the start of "ultra-sound osteomyelitis" differs from that assumed by Grundmann. Ultra-sound produces direct tissue-damage which in turn causes a local intravenous infection and not a specific allergic-hyperergic reaction, only localized by ultrasound. The Grundmann concept of the origin of acute hematogenous osteomyelitis lacks experimental proof. |
| Title |
Exposimetry of unfocused ultrasound. |
| Author |
Zhang X, Harrison GH, Balcer-Kubiczek EK. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1994 |
| Abstract |
Therapeutic applications of unfocused pulsed ultrasound have recently been identified and require specialized exposimetry. Spatial distributions of pressure and several measures of intensity are presented for an unfocused pulsed ultrasound field produced by a PZT-4 transducer with diameter 3.8 cm and center frequency 2 MHz. Distributions of pressure Itp and Im were adequately uniform over a 4-cm2 area in a transverse plane at an axial distance of 7 cm, but not so for Ita and Ipa , which both exhibited off-axis asymmetric maxima. |
| Title |
Exposure criteria for medical diagnostic ultrasound. I. Criteria based on thermal mechanisms. |
| Author |
Barnett SB. |
| Journal |
Australas Radiol |
| Volume |
|
| Year |
1993 |
| Abstract |
No abstract available. |
| Title |
Exposure criteria for medical diagnostic ultrasound: I. Criteria based on thermal mechanisms. |
| Author |
Jago JR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1995 |
| Abstract |
No abstract available. |
| Title |
Exposure levels for ultrasonic cavitation in mammals. |
| Author |
Frizzell LA, Lee CS. |
| Journal |
Proc IEEE Annu Conf of EMBS |
| Volume |
|
| Year |
1986 |
| Abstract |
Heat and cavitation are two mechanisms by which ultrasound is known to induce biological effects. Of the two, heat is reasonably well understood, but the role of cavitation in mammalian bioeffects needs further investigation. The levels for hind limb paralysis in the neonatal mouse from 1 MHz, continuous wave unfocused ultrasound have been investigated at 1 and 16 bars ambient pressure and at 10 and 37 degrees C. Above approximately 150 W/cm2 at 10 degrees C and above approximately 60 W/cm2 at 37 degrees C the exposure duration for paralysis of 50 percent of specimens exposed increases with increased ambient pressure suggesting cavitational involvement. This temperature dependence is consistent with a cavitation mechanism. These levels are well above the time-averaged intensities employed in ultrasonic diagnosis and diathermy. |
| Title |
Exposure levels for ultrasonic cavitation in the mouse neonate. |
| Author |
Lee CS, Frizzell LA. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1988 |
| Abstract |
The levels for hind limb paralysis from 1 MHz, continuous wave, unfocused ultrasound in the neonatal mouse were determined at 1 and 16 bars hydrostatic pressure and at 10 and 37 degrees C. Above a specific intensity level at each temperature, the exposure duration for paralysis of 50% of specimens exposed (t50) was found to be greater at 16 bars than at 1 bar suggesting a threshold for cavitational involvement. Using these results, the intensity thresholds for cavitation were found to be in the ranges of 120-150 W/cm2 and 53-74 W/cm2 at10 degrees C and 37 degrees C, respectively. This temperature dependence is consistent with a cavitation mechanism. In addition, the t50 at 289 W/cm2 and 10 degrees C was measured as a function of hydrostatic pressure and showed that cavitation was suppressed at hydrostatic pressures above approximately 10 bars. This result and the intensity threshold for cavitation at 1 bar and 10 degrees C yielded similar values for the threshold negative total pressure for cavitation in the neonatal mouse. |
| Title |
Exposure to low-intensity ultrasound increases aggrecan gene expression in a rat femur fracture model. |
| Author |
Yang KH, Parvizi J, Wang SJ, Lewallen DG, Kinnick RR, Greenleaf JF, Bolander ME. |
| Journal |
J Orthop Res |
| Volume |
|
| Year |
1996 |
| Abstract |
The effects of ultrasound stimulation on various parameters of bone repair after diaphyseal injury were assessed in a standard rat femur fracture model. Bilateral closed femoral fractures were made in 79 skeletally mature male Long-Evans rats. An ultrasound signal consisting of a 200 microsecond burst sine wave of 0.5 MHz repeating at 1 kHz, with an intensity of 50 or 100 mW/cm2 spatial and temporal average, was applied to one fracture in each animal. The contralateral fracture was not exposed to ultrasound and served as a control. Mechanical testing of the healing fracture was performed 3 weeks after injury. In fractures treated with a 50 mW/cm2 ultrasound signal, the average maximum torque (223.5 +/- 50.5 Nmm compared with 172.6 +/- 54.9 Nmm, p = 0.022, paired t test) and average torsional stiffness (13.0 +/- 3.4 Nmm/degree compared with 9.5 +/- 2.9 Nmm/degree, p = 0.017) were significantly greater in treated than in control fractures. In animals treated with a 100 mW/cm2 ultrasound signal, the average maximum torque and torsional stiffness were greater in treated than in control fractures, but this trend did not reach statistical significance. Biochemical analysis of callus in ultrasound-treated and control fractures failed to demonstrate significant differences in cell number, collagen content, or calcium content. Evaluation of gene expression in fractures treated with 50 mW/cm2 ultrasound demonstrated a shift in the expression of genes associated with cartilage formation; aggrecan gene expression was significantly higher on day 7 after fracture and significantly lower on day 21 (p = 0.033 and 0.035, respectively). alpha 1(II) procollagen gene expression was similarly modified, but this trend did not reach statistical significance. Expression of genes coding for bone-related proteins, including alpha 1(I) procollagen, bone gamma-carboxyglutamic acid protein, alkaline phosphatase, and transforming growth factor-beta 1, did not differ between ultrasound-treated and control fractures. These data suggest that ultrasound stimulation increased the mechanical properties of the healing fracture callus by stimulating earlier synthesis of extracellular matrix proteins in cartilage, possibly altering chondrocyte maturation and endochondral bone formation. |
| Title |
Exposure to ultrasound decreases the recalcification time of platelet rich plasma. |
| Author |
Williams AR, O'Brien WD Jr, Coller B. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1976 |
| Abstract |
Human blood was withdrawn, anticoagulated with citrate, and centrifuged, yielding platelet rich plasma (PRP). Recalcification times (i.e., the time taken to form a clot following the addition of sufficient calcium ions) were measured with a semiautomatic device. There were no changes in the recalcification time of PRP sample immediately following exposure to continuous wave 1 MHz ultrasound at intensities in the range 0.065-2 W/cm(^-2). However, subsequent measurements showed an irreversible time dependent decrease of the recalcification time of an asymptotic value which was invariably less than that of the controls. This behavior can be interpreted as a time dependent alteration to the platelet population. |
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