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BRL Abstracts Database |
Your search for ultrasound produced 3296 results. Page 57 out of 330
Title |
Bounds on estimating the acoustic attenuation of small tissue regions from reflected ultrasound. |
Author |
Kuc R. |
Journal |
Proc IEEE |
Volume |
|
Year |
1985 |
Abstract |
The acoustic attenuation coefficient of most soft biological tissues has an approximately linear-with-frequency attenuation characteristic. The slope of the attenuation coefficient with frequency, denoted by ?, has been observed to vary with the severity of liver disease. Two approaches for estimating the ? value from reflected ultrasound signals are examined: the spectral-difference approach, which estimates ? from the slope of the difference between log-spectra from two locations within the liver, and the spectral-shift approach, which estimates ? from the downward shift experienced by the propagating pulse spectrum with penetration into the liver. This paper considers signals reflected from a small tissue region, defined by a cell measuring D by D centimeters in the plane of the sonogram, thus determining the feasibility of producing attenuation images. Lower bounds on the variance of the two ? estimators are calculated by deriving maximum-likelihood estimators and by locating the tissue cell in the focal plane of the transducer. If W denotes the usable bandwidth in the reflected signals, the bounds are shown to be proportional to (WD)(exp)(-3) for ? estimates calculated from individual reflected signals, and (WD)(exp)(-4) for estimates from all the signals reflected from the tissue region. With currently available technology, clinically useful results can be obtained for cell sizes measuring approximately 2.0 cm on a side. |
Title |
Bragg diffraction scanner for ultrasonic tissue characterisation in vivo. |
Author |
Huggins RW, Phelps JV. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1977 |
Abstract |
An ultrasonic scanner, which exploits the concept of Bragg diffraction of ultrasound for tissue characterisation, has been constructed for in vivo operation. A Grey-Scale B-scan is produced, and the ultrasonic transducer can be mechanically constrained to point at one specific volume of tissue, first identified on the B-scan, throughout an angular movement of 50 degrees. Compensation for variations in the attenuation and time delay of echoes from the interrogated volume due to the changing ultrasonic path length is performed electronically. Qualitative results have been obtained in vivo from human calf muscle, liver parenchyma, and a metastatic deposit in liver, and are similar in many respects to results from in vitro measurements. The ultrasonic exposure is identical to that normally delivered in conventional ultrasonic examinations. |
Title |
Breast imaging in coronal planes with simultaneous pulse echo and transmission ultrasound. |
Author |
Carson PL, Meyer CR, Scherzinger AL, Oughton TV. |
Journal |
Science |
Volume |
|
Year |
1981 |
Abstract |
Clear delineation of breast architecture was achieved with compound pulse echo ultrasound imaging in which the images were acquired in the coronal planes used for quantitative transmission ultrasonic computed tomography. Since most connective tissue planes in the breast radiate toward the nipple, compound scans from the sides of the breast record normal interfaces more consistently and reveal greater symmetries in normal portions of relatively full breasts than do conventional scans in sagittal or transverse planes. Simultaneous acquisition of the pulse echo images and images representing the local ultrasound attenuation coefficient and speed of ultrasound suggested complementary role for reflection and through-transmission images in breast cancer detection. The high quality of pulse echo images in coronal planes provides the potential for more complete pulse echo diagnosis and the basis for spatial correlation of lesions viewed in pulse echo and ultrasonic computed tomograms. These observations may permit routine ultrasonic computed tomography of the breast in the clinical setting. |
Title |
Breast phantoms for ultrasound imaging. |
Author |
Kelly-Fry E, Madsen EL, Zagzebski JA. |
Journal |
Radiology |
Volume |
|
Year |
1983 |
Abstract |
No abstract available. |
Title |
Breast ultrasound: report of a 5 year combined clinical research program. |
Author |
Harper P, Kelly-Fry E. |
Journal |
J Fr Echogr |
Volume |
|
Year |
1984 |
Abstract |
None |
Title |
Bubble cycling and standing waves in ultrasonic cell lysis. |
Author |
Brayman AA, Miller MW. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1992 |
Abstract |
Two quite different but potentially complementary hypothetical mechanisms.have been proposed to explain the dependence of ultrasonic cell lysis in vitro on exposure vessel rotation. One mechanism proposes that resonant-size bubbles are trapped in planar arrays by standing waves in the sample and that exposure vessel rotation sweeps cells through the bubble arrays. The other mechanism, for which there is now considerable support, proposes that exposure vessel rotation simply allows bubbles to recycle after having been driven through the medium by the ultrasound. We report here the results of efforts to further discriminate between, and quantify, the relative contributions of these two mechanisms. Murine P388 cells were exposed to 1.07 MHz continuous-wave.(CW) ultrasound for 5 min at 5 W/cm2 (ISP) using various exposure vessel compositions and exposure configurations. Experimental treatments were designed either to minimize or maximize standing waves in the sample tube, or to minimize the potential for bubble recycling while maximizing standing wave formation. The results of these experiments indicate that bubble cycling is responsible for the majority of cell lysis occurring in the rotating exposure vessels, but that a significant contribution to total lysis is provided by trapped bubbles under some conditions. |
Title |
Bubble cycling as the explanation of the promotion of ultrasonic cavitation in a rotating tube exposure system. |
Author |
Miller DL, Williams AR. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1989 |
Abstract |
The cavitation-promotion effect of rotating a sample tube during ultrasound exposure is not yet fully understood. Cavitation-induced hemolysis was observed in 0.5% hematocrit suspensions of erythrocytes exposed for 5 min at 37 degrees C. For 1.61 MHz unfocused exposure an apparent threshold of 4 W/cm2 spatial-peak intensity was obtained for hemolysis in a 72 rpm rotating exposure chamber which was made of dialysis tubing. If the tube was not rotated, then no hemolysis was observed up to 16 W/cm2. Creation of standing waves in the sample by using a thick-walled culture tube, or by placing a styrofoam reflector behind the dialysis tube did not change the apparent threshold. Focused 1.45.MHz exposure gave the same apparent threshold in a rotating dialysis tube, but this increased to about 128 W/cm2 for the nonrotating case. When the focused ultrasound was turned on for half a rotation and off for half, results were similar to those for a nonrotating CW case, while on-off cycles synchronized to a quarter rotation gave results similar to the rotating CW case. A plausible explanation of the rotation effect, given these results, is that rotation brings bubbles on the rear wall, where the beam exits the tube, back around to the front again, where the bubbles may then re-nucleate the suspension, and thereby promote cavitation bioeffects in the rotating tube. |
Title |
Bubble dynamics of ultrasound contrast agents. |
Author |
Averkiou MA, Bruce MF, powers JE. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
1998 |
Abstract |
The bubble dynamics involved with microbubble contrast agents under insonification is investigated. The acoustic field of an ATL HDI‐3000 diagnostic ultrasound system in a contrast specific harmonic imaging mode is reviewed first, and its major features that are related with microbubble behavior are discussed. Issues relating to sound attenuation, mechanical index, and bubble destruction are addressed. The nonlinear oscillatory behavior of contrast microbubbles is modeled with the Gilmore equation. The acoustic pressure field of a short pulse utilized in harmonic imaging is measured with a hydrophone and used as the driving pressure of the Gilmore model. Radius‐time [R(t)] and bubble wall velocity‐time [U(t)] curves are shown. Frequency domain analysis of U(t) indicates transient resonance characteristics in both the fundamental and second harmonic components that are somewhat different from what one would expect with a continuous‐wave steady‐state response. The times for complete solution of microbubbles in water are calculated and correlated to observations seen in ultrasound images with contrast agents. Radio frequency (rf) data of scattered pulses from contrast agent microbubbles in an in‐vitro experiment were collected with a phased array. This data is used to support and explain the contrast microbubble behavior. |
Title |
Bulk ablation of soft tissue with intense ultrasound: modeling and experiments. |
Author |
Mast TD, Makin IR, Faidi W, Runk MM, Barthe PG, Slayton MH. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
2005 |
Abstract |
Methods for the bulk ablation of soft tissue using intense ultrasound, with potential applications in the thermal treatment of focal tumors, are presented. An approximate analytic model for bulk ablation predicts the progress of ablation based on tissue properties, spatially averaged ultrasonic heat deposition, and perfusion. The approximate model allows the prediction of threshold acoustic powers required for ablation in vivo as well as the comparison of cases with different starting temperatures and perfusion characteristics, such as typical in vivo and ex vivo experiments. In a full three-dimensional numerical model, heat deposition from array transducers is computed using the Fresnel approximation and heat transfer in tissue is computed by finite differences, accounting for heating changes caused by boiling and thermal dose-dependent absorption. Similar ablation trends due to perfusion effects are predicted by both the simple analytic model and the full numerical model. Comparisons with experimental results show the efficacy of both models in predicting tissue ablation effects. Phenomena illustrated by the simulations and experiments include power thresholds for in vivo ablation, differences between in vivo and ex vivo lesioning for comparable source conditions, the effect of tissue boiling and absorption changes on ablation depth, and the performance of a continuous rotational scanning method suitable for interstitial bulk ablation of soft tissue. |
Title |
Bursts of focused ultrasound energy three orders of magnitude more intense than diagnostic ultrasound are emerging as a noninvasive option for treating cancer and other medical procedures. |
Author |
Haar G. |
Journal |
Phys Today |
Volume |
|
Year |
2001 |
Abstract |
No abstract available. |
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