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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 20 out of 330
| Title |
A study of various parameters of spherically curved phased arrays for noninvasive ultrasound surgery. |
| Author |
Fan X, Hynynen K. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
1996 |
| Abstract |
The spherically curved square element phased array design for ultrasound surgery was studied in several of its important aspects. A method for determining the spatial limitations of the multiple-foci region was developed for spherically curved phased arrays. The effects on the ultrasound fields of varying the phases and the amplitudes at control points were investigated. It was found that the phases and the magnitudes of control points have an impact on the ultrasound field distributions. The effects of multiple-foci spacing, pulse duration, and maximum temperature on the size and shape of necrosed tissue were investigated. For a spherically curved phased array with an 8 cm radius of curvature, an 8.8 x 8.8 cm2 projected area, and a 1.5 MHz operating frequency, the minimum number of phased array elements that could produce the largest acceptable necrosed tissue volume was 256. The tissue volume necrosed during the sonication could be increased to approximately 1 x 1 x 3 cm3 with this array. |
| Title |
A study on the reconstruction of moderate contrast targets using the distorted born iterative method. |
| Author |
Lavarello R, Oelze M. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2008 |
| Abstract |
Previous tomographic methods using ultrasound for reconstructing sound speed and attenuation images suffered from convergence issues for targets with moderate speed of sound contrast. Convergence problems can be overcome by the use of the multiple frequency, distorted Born iterative method (DBIM). The implementation of DBIM for measurement configurations in which receiver positions are fixed was studied, and a novel regularization scheme was developed. The regularization parameter needed to stabilize the inversion process initially was found through the Rayleigh quotient iteration, then relaxed according to the relative residual error between the measured and estimated scattered fields. The DBIM was successfully stabilized for both full and partial receiver angular coverage without a significant loss in spatial resolution. The effects of variable density in the reconstructions were briefly explored through simulations. The ability to reconstruct targets with moderate contrast was validated through experimental measurements. Speed of sound profiles for balloons filled with saline in a background of water were reconstructed using multiple frequency DBIM techniques. The mean squared error for speed of sound reconstructions of the balloon phantoms with 16.4% sound speed contrast was 1.1%. |
| Title |
A survey of the output of diagnostic ultrasound equipment. |
| Author |
Duck FA, Starritt HC, Hawkins AJ. |
| Journal |
Book Chapter |
| Volume |
|
| Year |
1986 |
| Abstract |
No abstract available. |
| Title |
A systems design approach: Non-invasive ultrasound gallstone dissolution device. |
| Author |
Sanghvi NT,Griffith SF,Fry FJ,Burney BT,Franklin TD Jr. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1990 |
| Abstract |
Recently, shockwave biliary lithotripsy has been undergoing clinical studies utilizing the modified renal shockwave devices. Also, few scientific papers have been published on the effectiveness of gallstone fragmentation by this method. However, stone fragments and remains are a major problem with this technology and require adjunct pharmaceutical therapy for a log period post shockwave treatment. To overcome this problem, we have developed and designed a non-invasive ultrasound Gallstone Dissolution Device (GDD). When the GDD is used in the presence of a selected solvent, dissolution of gallstones is achieved in a much more rapid fashion which could provide a stone-free gallbladder in less time,thus reducing the hospital stay and making the whole procedure cost effective.
The GDD utilizes conventional therapeutic ultrasound energy which differs from the unipolar, sharply focused, high energy shockwaves. The GDD incorporates ultrasound imaging and therapy transducers in a single plastic head to provide direct visualization of gallstones and treatment, reducing focusing and critical targeting requirements. The computer-controlled electronics allow the user to select therapy parameters during the operating procedure. The device has a built-in closed loop feedback system to continuously monitor ultrasound energy and adjust the power level for any mismatch of impedance.
The device has undergone extensive animal study to establish its efficacy and risk factors. Based on this study, we have met appropriate FDA and local institution regulatory requirements to use it for human clinical testing. This paper will describe operation, design specifications, animal study results, and advantages/disadvantages of the ultrasound therapy system. |
| Title |
A tapered phased array ultrasound transducer for hyperthermia treatment. |
| Author |
Benkeser PJ, Frizzell LA, Ocheltree KB, Cain CA. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1987 |
| Abstract |
An ultrasonic tapered array transducer, consisting of a linear phased array employing elements with a tapered thickness, was developed to study the feasibility of its use for hyperthermic treatment of deep-seated tumors. The cylindrical focal region is generated and steered in two dimensions by controlling the phases of the driving signals on each element and moved in the third dimension by changing the driving frequency. Experimentally obtained field intensity distributions are in good agreement with theoretical predictions. Acoustical power output measurements indicate that tapered phased arrays are capable if providing the intensities necessary for producing therapeutic temperatures in tumors. |
| Title |
A technique with reference points image for in vivo measurement of sound velocity. |
| Author |
Ohtsuki S, Soetanto K, Okujima M. |
| Journal |
Proc Fourth Meet World Fed Ultrasound Med Biol - Sidney |
| Volume |
|
| Year |
1985 |
| Abstract |
Sound velocity in human body provides useful information for tissue differentiation. A measurement technique of this sound velocity using linear scanning of ultrasonic beam is presented here. |
| Title |
A temporal study of ultrasound contrast agent-induced changes in capillary density. |
| Author |
Johnson CA, Sarwate S, Miller RJ, O'Brien WD Jr. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
2010 |
| Abstract |
OBJECTIVE: The ability of ultrasound (US) and ultrasound contrast agents (UCAs) to induce angiogenesis has been explored as a means of restoring blood flow to ischemic muscle. Because UCAs demonstrate an increasing percentage of collapse cavitation with increasing US pressure (Pr), this study sought to explore the effects of a US Pr that produces 100% collapse cavitation, determine the capillary density changes, and determine the time point of angiogenic rebound in a normal animal model.
METHODS: Using a 1-MHz focused transducer and a peak rarefactional US Pr of 3.8 MPa, rat gracilis muscles were exposed to US, and bioeffects were assessed. Capillary density, as a measure of angiogenesis, was examined. As an additional measure, inflammatory cells were quantified via a color threshold analysis to detect the presence of CD31 and CD34 as a percentage of the total section on stained slides. Six groups (0, 3, 6, 13, 20, and 27 days postexposure [DPE]; n = 3 each) and 5 cage controls were used to characterize the angiogenic response.
RESULTS: Ultrasound-UCA treatment caused the capillary density to decrease acutely (0 DPE) by 70% and inflammatory cells to increase by up to 250%. The angiogenic rebound was observed at 3 DPE but did not return to control levels by 27 DPE, suggesting an incomplete healing response.
CONCLUSIONS: Capillary destruction and inflammation played an important role in the angiogenic response induced by US-UCA. Exposure that causes 100% collapse cavitation causes capillary destruction from which normal rats are unable to recover and suggests a nontherapeutic effect. |
| Title |
A temporal view of soft tissue quantitative ultrasound |
| Author |
O'Brien, WD Jr. |
| Journal |
Phys Procedia |
| Volume |
|
| Year |
2015 |
| Abstract |
The objective of soft tissue quantitative ultrasound (QUS) is to improve diagnostic ultrasound imaging capabilities via quantitative outcomes. Over the past three or so decades, there have been an increasing number of QUS successes. A
temporal view moves us back in history almost six decades when techniques and theoretical developments were in their earliest stages that impacted modern QUS successes. The earliest theoretical developments and techniques some six decades
ago can be attributed to Lev Chernov, Philip Morse, Herman Feshbach, Uno Ingard, John Wild and Jack Reid. Later, Floyd Dunn developed important views as to how connective tissue affected the interaction between ultrasound and soft tissue.
Then, as the theory of wave propagation in soft tissues with random inhomogeneities was extended and applied by Fred Lizzi, Jim Zagzebski and Mike Insana (and their colleagues), contemporary QUS successes started to emerge. |
| Title |
A teratologic evaluation of continuous-wave, daily ultrasound exposure in unanesthetized pregnant rats. |
| Author |
Vorhees CV, Acuff-Smith KD, Weisenburger WP, Meyer RA, Smith NB, O'Brien WD Jr. |
| Journal |
Teratology |
| Volume |
|
| Year |
1991 |
| Abstract |
Pregnant Sprague-Dawley rats were trained to remain immobile when placed in water in an ultrasound exposure tank and exposed to 0, 0.1, 2.0, or 30.0 W/cm2 ISPTA (spatial peak, temporal average), 3.0-MHz continuous wave (cw) ultrasound on embryonic (E) days 4-19 for approximately 15 min/day. On E20 fetuses were removed; weighed; examined for external, skeletal, and visceral malformations; and uteri were examined for resorptions. Analyses revealed no increase in pre-implantation loss and no effects on maternal body weight, food, or water consumption. No increase in skeletal or visceral malformations was found, in fact exposed groups had a lower incidence of defects than controls. A significant increase in resorptions in the lowest exposure group (0.1 W/cm2) was obtained, but the effect was isolated, non-dose dependent and not credible as a treatment-related effect. No reduction in fetal weight was obtained, in fact the lowest (0.1-W/cm2) and middle (2.0-W/cm2) exposure level groups weighed slightly more than controls. The immobility procedure succeeded in avoiding anesthetization or forced restraint of the dams, thereby eliminating these factors as potential confounders. The results demonstrated that in unanesthetized, unrestrained rats in utero exposure to incident intensities of ultrasound of up to 30.0 W/cm2 cw ultrasound (or estimated internal exposures of 4-21 W/cm2, depending on body orientation to the incident beam) produced no evidence of embryotoxicity based on fetal necropsy data. |
| Title |
A test for cavitation as a mechanism for intestinal hemorrhage in mice exposed to a.piezoelectric lithotripter. |
| Author |
Dalecki D, Raeman CH, Child SZ, Carstensen EL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1996 |
| Abstract |
This study tested the hypothesis that intestinal hemorrhage produced by exposure.to lithotripter fields depends upon the presence of gas in the intestine. The extent.of hemorrhage in the gas-containing intestines of pregnant mice was compared to.the amount of hemorrhage in the bubble-free intestines of their fetuses. On day 18.of gestation, the abdominal regions of pregnant C3H mice (n = 6) were exposed.to 200 pulses from a piezoelectric lithotripter. Acoustic pulses had a peak.pressure amplitude of 10 MPa and were administered at a rate of approximately 1.Hz. All maternal intestines showed hemorrhagic regions extending several.centimeters in length. In contrast, only 1 of 43 exposed fetuses showed an.intestinal hemorrhage and this one lesion was less than 1 mm in diameter. These.results support the hypothesis of the study and are consistent with a.cavitation-related mechanism for the production of intestinal hemorrhage by.exposure to acoustic fields. |
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