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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 280 out of 330
| Title |
Toxicity of ultrasound in mice: neonatal studies. |
| Author |
Stolzenberg SJ, Torbit CA, Pryor GT, Edmonds PD. |
| Journal |
Radiat Environ Biophys |
| Volume |
|
| Year |
1980 |
| Abstract |
Pregnant mice were exposed to ultrasound (continuous wave, 2 MHz) on Day 8 of gestation to determine effects on the progeny. The most significant finding was a decrease in mean uterine weight of the female progeny. The thresholds for this.effect were 140 s at 0.5 W/cm2 and 60 s at 1 W/cm2, which were below the thresholds previously reported for other effects in mice. We suggest that this indicates a delay or impairment of maturation of the mice exposed in utero. Exposure of the dams to spatial average intensity of 1 W/cm2 for 40 and 60 s had no effect on body weight of the progeny, compared with sham-treated controls. In this experiment the body weights of progeny from sham-treated controls were significantly lower than those from untreated controls on Days 10, 17, and 25 of age. After exposure in utero to 0.5 W/cm2 for 180 s, statistically significant decreases in mean body weights of the neonates were observed, but only on Day 25 of age, in both sexes compared with sham-treated controls. At necropsy at Day 25 of age, neonatal organ weights relative to body weights were not significantly affected for the thymus in either sex or for the seminal vesicles and tests ion comparison with.sham-treated controls. |
| Title |
Toxicity studies on the interaction of ultrasound on embryonic and adult tissues. |
| Author |
Taylor KJW, Dyson M. |
| Journal |
Proc Second World Congr Ultrason Med - Rotterdam |
| Volume |
|
| Year |
1973 |
| Abstract |
The data on toxicity are incomplete but sufficient are available to show that many deleterious effects can be produced by higher parameters of ultrasound than are currently used for diagnostic purposes. The data give some information about safety margins. Long-term irradiation at low intensities showed no effect on developing embryos. |
| Title |
Tracking and correcting for organ motion artifacts in ultrasound tomography systems. |
| Author |
Dhanantwari AC, Stergiopoulos S. |
| Journal |
J. Acoust. Soc. Am |
| Volume |
|
| Year |
1998 |
| Abstract |
Motion artifacts have been identified as a problem in medical tomography systems. This problem, however, is well known in other types of real‐time imaging systems such as radar satellites and sonars. In this case it has been found that the application of an overlap processing scheme [J. Acoust. Soc. Am. 86, 158–171 (1989)] increases the resolution of a phased array imaging system and corrects for motion artifacts as well. Reported results have shown that the problem of correcting motion artifacts in synthetic aperture applications is centered on the estimation of a phase correction factor. This correction factor is then used to compensate for the temporal phase differences between sequential sensor‐array measurements in order to synthesize the spatial information coherently. This paper describes an approach which tracks the organ motion and allows the artifacts to be isolated in ultrasound tomography systems. Two sources are utilized so that two sets of projections are generated that are identical in space but separated in time. Then the spatial overlap correlator processing scheme is used to synthesize the 2‐D projection data coherently. This provides the desired phase correction factor, which compensates for the phase fluctuations caused by the subject’s organ‐motion effects and tracks the organ motion. |
| Title |
Trade-offs between the axial resolution and the signal-to-noise ratio in elastography. |
| Author |
Srinivasan S, Righetti R, Ophir J. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2003 |
| Abstract |
Elastography involves tracking the ultrasonic A-mode signals before and after mechanical compression of tissue to form a computed image of the local strains undergone by various tissue components. The quality of the strain estimates in elastography is typically quantified using factors such as the elastographic SNR (SNRe), contrast-to-noise ratio (CNRe), and the spatial resolution. These quality factors depend on the mechanical parameters (such as the applied strain and the boundary conditions), the acoustic parameters (such as the sonographic SNR, the center frequency, and the bandwidth), and the signal-processing parameters (such as the window length and the window separation). Theoretical developments in elastography have established functional relationships between the SNRe and CNRe and these parameters. Similarly, simulations have established empirical relationships between the axial resolution and the acoustic and signal-processing parameters. We find that a trade-off exists between the achievable SNRe (CNRe) and the axial resolution in elastography and that the trade-off occurs only with respect to the signal-processing parameters. Theoretical work on the spatial resolution accompanied with simulations and experiments were used to confirm such an observation. The trade-off between the SNRe (CNRe) and the resolution was found to be nonlinear, with large improvements in the SNRe being possible at the expense of small reductions in the axial resolution. All the quality factors improve with the acoustic parameters, which suggests the preferred use of transducers with high absolute bandwidths and center frequencies. |
| Title |
Transcranial low-frequency ultrsound-mediated thrombolysis in brain ischemia:Increased risk of hemorrhage with combined ultrasound and tissue plasminogen activator:Results of a phase II clinical trial |
| Author |
Daffertshofer M,Gass A,Ringleb P,Sitzer M,Sliwka U,Els T,Sedlaczek O,Koroshetz WJ,Hennerici MG. |
| Journal |
Stroke |
| Volume |
|
| Year |
2005 |
| Abstract |
Background— Clinical studies using ultrasound at diagnostic frequencies in transcranial Doppler devices provided encouraging results in enhancing thrombolysis with tissue plasminogen activator (tPA) in acute stroke. Low-frequency ultrasound does not require complex positioning procedures, penetrates through the skull better, and has been demonstrated to accelerate thrombolysis with tPA in animal experiments in wide cerebrovascular territories without hemorrhagic side effects. We therefore conducted the first multicenter clinical trial to investigate safety of tPA plus low-frequency ultrasound (300 kHz).
Methods— Acute stroke patients within a 6-hour time window were included (National Institutes of Health Stroke Scale scores >4). Magnetic resonance imaging (MRI) was used to document vascular occlusion and to rule out cerebral hemorrhage. Patients were allocated to combination therapy alternately; the first patient received tPA only, the second patient received tPA plus ultrasound, etc. Follow-up included serial MRI directly thereafter and 24 hours later to confirm recanalization and tissue imaging. Clinical recovery was measured after treatment and 3 months later.
Results— 26 patients (70.4±9.7 years) entered the trial (12 tPA, 14 tPA plus ultrasound). The study was prematurely stopped because 5 of 12 patients from the tPA only group but 13 of 14 patients treated with the tPA plus ultrasound showed signs of bleeding in MRI (P<0.01). Within 3 days of treatment, 5 symptomatic hemorrhages occurred within the tPA plus ultrasound group. At 3 months, neither morbidity nor treatment-related mortality or recanalization rates differed between both groups.
Conclusions— This study demonstrated bioeffects from low-frequency ultrasound that caused an increased rate of cerebral hemorrhages in patients concomitantly treated with intravenous tPA.
Key Words: stroke, acute • thrombolysis • ultrasonography. |
| Title |
Transcutaneous ultrasound-facilitated coronary thrombolysis during acute myocardial infarction. |
| Author |
Cohen MG,Tuero E,Bluguermann J,Kevorkian R,Berrocal DH, Carlevaro O,Picabea E,Hudson MP,Siegel RJ,Douthat L,Greenbaum AB,Echt D,Weaver WD,Grinfeld LR. |
| Journal |
Am J Cardiol |
| Volume |
|
| Year |
2003 |
| Abstract |
In preclinical experiments, the combination of transcutaneous, low-frequency ultrasound and thrombolytic therapy has shown improved patency rates over thrombolytics alone. A total of 25 patients with myocardial infarction were treated with a thrombolytic agent and adjunctive transcutaneous ultrasound. No unanticipated major adverse events were observed. |
| Title |
Transfection of a reporter plasmid into cultured cells by sonoporation in vitro. |
| Author |
Bao S,Thrall BD,Miller DL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1997 |
| Abstract |
Cultured Chinese hamster ovary cells were exposed to 2.25-MHz ultrasound in sterile 4.5-mL polyethylene chambers and tested for cell lysis, sonoporation and DNA transfection. Ten percent of Albunex®, a gas-body-based ultrasound contrast agent, was added to ensure cavitation nucleation, and the chambers were rotated at 60 rpm to promote cavitation activity during the 1-min exposures. Uptake of large fluorescent dextran molecules by some cells was observed for spatial peak pressure amplitudes as low as 0.1 MPa, which indicates transient permeabilization and resealing, i.e., sonoporation, of these cells during exposure. Significant lysis occurred for 0.2 MPa, and increased rapidly for exposures above the apparent cavitation threshold (using the H2O2 production test) of about 0.4 MPa spatial peak pressure amplitude. In the DNA transfection tests, 20 micrograms/mL luciferase reporter plasmid was added to the suspension during exposure, and cells were assayed for proliferation ability and luciferase gene expression 2 days after exposure. Cell proliferation was greatly reduced above the cavitation threshold. Luciferase production was significant for 0.20-MPa exposure, and reached 0.33 ng per 106 cells at 0.8-MPa exposure. The luciferase production was great for cells exposed in medium supplemented with serum than for cells exposed in serum-free medium. Cells harvested for exposure either in the log phase or in the stationary phase of culture gave similar proliferation and transfection results. The effects essentially disappeared when the Albunex® was omitted from the suspension and the tube was not rotated. Thus, sonoporation by ultrasonic cavitation in the rotating tube system yields plasmid transfection with subsequent transient gene expression. |
| Title |
Transient acoustic cavitation in gallstone fragmentation: a study of gallstones.fragmented in vivo. |
| Author |
Vakil N, Everbach EC. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1993 |
| Abstract |
The mechanism of gallstone fragmentation by shock waves in vivo is uncertain. We used scanning electron microscopy to study 9.partially fragmented stones obtained from 6 patients who underwent lithotripsy and subsequently had surgery because of.incomplete fragmentation. Surface characteristics of the stone were studied using scanning electron microscopy and compared to.gallstones fragmented in degassed water in vitro and to control stones obtained from patients with uncomplicated cholelithiasis..Characteristic damage caused by transient acoustic cavitation was visible in all stones fragmented in vivo and in vitro as pits.10-100 microns diameter. In these pits, cholesterol crystals were fractured, and the symmetry of crystal boundaries was.damaged. In areas of more severe damage, individual pits coalesced to form craters on the stone surface. High magnification of.the pit walls revealed cracks, which in some instances radiated out onto the unpitted surface of the stone. We conclude that.transient acoustic cavitation plays a role in gallstone fragmentation in vivo through the mechanism of surface pitting and the.formation of cracks that radiate outward from the surface pits. Measures to enhance cavitation may improve the results of.gallstone lithotripsy. . |
| Title |
Transient cavitation in tissues during ultrasonically induced hyperthermia. |
| Author |
Sommer FG, Pounds D. |
| Journal |
Med Phys |
| Volume |
|
| Year |
1982 |
| Abstract |
An isospherical array of ultrasonic transducers designed for hyperthermia treatment of malignant tumors in humans was employed in studies of transient cavitation in tissues during ultrasonic heating. Both in vitro and in vivo studies revealed the presence of transient cavitation within tissues during ultrasonic heating, as indicated by the detection of the first half-order subharmonic of insonifying ultrasound with an interrogating transducer. The applied power to the focal region of the array required to exceed cavitation thresholds in tissue was 75 +/- 8 W/cm2, a level considerably higher than that required to heat tissues to the temperature range used for cancer treatment (43-45 degrees C). |
| Title |
Transient cavitation in tissues during.ultrasonically induced hyperthermia. |
| Author |
Sommer FG, Pounds D. |
| Journal |
Med Phys |
| Volume |
|
| Year |
1982 |
| Abstract |
An isospherical array of ultrasonic transducers designed for hyperthermia.treatment of malignant tumors in humans was employed in studies of transient.cavitation in tissues during ultrasonic heating. Both in vitro and in vivo studies.revealed the presence of transient cavitation within tissues during ultrasonic.heating, as indicated by the detection of the first half-order subharmonic of.insonifying ultrasound with an interrogating transducer. The applied power to.the focal region of the array required to exceed cavitation thresholds in tissue.was 75 +/- 8 W/cm2, a level considerably higher than that required to heat.tissues to the temperature range used for cancer treatment (43-45 degrees C). |
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