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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 208 out of 330
| Title |
Quantification of acoustic shock in routine exposure measurement. |
| Author |
Starritt HC, Duck FA. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1992 |
| Abstract |
No abstract available, letter to the editor. |
| Title |
Quantification of atherosclerotic plaque composition in cholesterol-fed rabbits with 50-MHz acoustic microscopy. |
| Author |
Shepard RK, Miller JG, Wickline SA. |
| Journal |
Arterioscler Thromb |
| Volume |
|
| Year |
1992 |
| Abstract |
To determine whether high-frequency ultrasound could distinguish normal from pathological vascular structure and to elucidate the determinants of ultrasonic backscatter in different layers of normal and atherosclerotic arteries, high-resolution acoustic microscopy at 50 MHz was used to characterize aortic plaque in six New Zealand White rabbits fed a 2% cholesterol diet for 3.5 months. Four rabbits were fed a standard diet for 3.5 months to provide normal control data. Segments of aortas were excised, fixed in formalin, opened longitudinally, and mounted flat for insonification. For each specimen, backscattered radio frequency (rf) data were acquired from 30 to 100 independent sites separated by 500 microns. Portions of rf data were gated from discrete layers of the vessel wall for computation of integrated backscatter. Results of histological and immunocytochemical analyses of vessel wall thickness and composition were compared with those of ultrasonic analysis. Normal aortas manifested prominent but homogeneous backscatter (average integrated backscatter, -28.5 +/- 2.9 dB) throughout the vessel wall, with no clear distinction between intimal and medial layers. The atherosclerotic aortas manifested substantially reduced integrated backscatter from the thickened intima (-47.5 +/- 3.2 dB, p < 0.0001) but relatively normal integrated backscatter from the media (-31.2 +/- 1.6 dB; p = NS versus normal aortas). The thickness of the media for both normal and atherosclerotic rabbits was approximately 300 microns. Histological characteristics of atherosclerotic aortas confirmed the presence of substantial intimal thickening, with prominent foam cell and lipid infiltration abutting a more normal medial layer. Two of the six cholesterol-fed rabbits did not evelop atherosclerotic plaque despite marked evaluations in blood cholesterol levels, and their aortas manifested rf backscatter patterns identical to those from normal aortas. Thus, quantitavtive high-frequency, high-resolution ultrasound differentiates normal from pathological vascular structure in diet-induced atherosclerosis. |
| Title |
Quantification of intimal and medial thickness of human coronary arteries by acoustic microscopy. |
| Author |
Wickline SA, Barzilai B, Thomas LJ III, Saffitz JE. |
| Journal |
Curr Sci |
| Volume |
|
| Year |
1990 |
| Abstract |
Real-time, ultrasonic, two-dimensional, intravascular imaging of human peripheral and coronary arteries with high-frequency ultrasound represents a promising new approach for characterization of the composition and severity of atherosclerotic plaque. The purpose of this study was to determine wheter analysis of unprocessed radiofrequency data could provide potentially useful information as an adjunct to the imaging format and to define the precision of high-frequency ultrasound for quantification of the dimensions of human coronary arterial intima and media. Accordingly, high-resolution acoustic microscopy of fresh normal and calcified human coronary arteries was performed invitro with a 50-MHz broad-band, focused (F/2) piezoelectric transducer. An objective, computer-driven algorithm was applied to the unprocessed radiofrequency data to identify endothelial, intimal-medial, and medial-adventitial boundaries by computing the magnitude of the complex analytic signal, the real part of which is the digitized ultrasonic radiofreqency trace and the imaginary part of which is the Hilbert transformation of the digitized radiofrequency data. Intimal and medial thicknesses for normal artery were determined by analyisis of ultrasonic radiofrequency data along three scan lines at 55 sites and by histologic analysis at 44 sites along the same scan lines in the fixed specimen. intima and media (+/-SE) were 65 +/-2 versus 139+/-2 micrometeres by ultrasound and 47+/-1 versus 119+/-2 by histology. The thicknesses of intima and media in calcific plaque could not be determind reliably because of ultrasonic "shadowing" or disruption of normal vessel architecture by advanced atherosclerosis or both, but these radiofrequency traces differed markedly from those of normal arteries. Thus, analysis of high-frequency radiofrequency data permits reliable quantification of the intimal and medial dimensions of normal human coronary arteries. |
| Title |
Quantification of microbubble destruction of three fluorocarbon-filled ultrasonic contrast agents. |
| Author |
Moran CM, Anderson T, Pye SD, Sboros V, McDicken WN. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2000 |
| Abstract |
The assessment of myocardial blood velocity using ultrasonic contrast agents is based on the premise that the vast majority of contrast microbubbles within a myocardial region can be destroyed by an acoustic pulse of sufficient magnitude. Determination of the period of time after destruction that a region of myocardium needs to reperfuse may be used to assess myocardial blood velocity. In this study, we investigated the acoustic pressure sensitivity of three solutions of intravenous fluorocarbon-filled contrast agents and the magnitude of acoustic pulse required to destroy the contrast agent microbubbles. A novel tissue-mimicking phantom was designed and manufactured to investigate the relationships between mean integrated backscatter, incident acoustic pressure and number of frames of insonation for three fluorocarbon-filled contrast agents (Definity?, Optison?, and Sonazoid?, formerly NC100100). Using a routine clinical ultrasound (US) scanner (Acuson XP-10), modified to allow access to the unprocessed US data, the contrast agents were scanned at the four acoustic output powers. All three agents initially demonstrated a linear relationship between mean integrated backscatter and number of frames of insonation. For all three agents, mean integrated backscatter decreased more rapidly at higher acoustic pressures, suggesting a more rapid destruction of the microbubbles. In spite of the fact that there was no movement of microbubbles into or out of the beam, only the results from Definity? suggested that a complete destruction of the contrast agent microbubbles had occurred within the total duration of insonation in this study.
|
| Title |
Quantification of optison bubble size and lifetime during sonication dominant role of secondary cavitation bubbles causing acoustic bioeffects. |
| Author |
Kamaev PP, Hutcheson JD, Wilson ML, Prausnitz MR. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2004 |
| Abstract |
Acoustic cavitation has been shown to deliver molecules into viable cells, which is of interest for drug and gene delivery applications. To address mechanisms of these acoustic bioeffects, this work measured the lifetime of albumin-stabilized cavitation bubbles (Optison) and correlated it with desirable (intracellular uptake of molecules) and undesirable (loss of cell viability) bioeffects. Optison was exposed to 500 kHz ultrasound (acoustic pressures of 0.6?3.0 MPa and energy exposures of 0.2?200 J/cm2) either with or without the presence of DU145 prostate cancer cells (106 cells/ml) bathed in calcein, a cell-impermeant tracer molecule. Bubble lifetime was determined using a Coulter counter and flow cytometer, while bioeffects were evaluated by flow cytometry. The lifetime of Optison cavitation nuclei was found to decrease and bioeffects (molecular uptake and loss of cell viability) were found to increase with increasing acoustic energy exposure. These bioeffects correlated well with the disappearance of bubbles, suggesting that contrast agent destruction either directly or indirectly affected cells, probably involving unstabilized cavitation nuclei created upon the destruction of Optison. Because Optison solutions presonicated to destroy all detectable bubbles also caused significant bioeffects, the indirect mechanism involving secondary cavitation bubbles is more likely. |
| Title |
Quantifying B-mode images of in vivo rat mammary tumors by the frequency dependence of backscatter. |
| Author |
Topp KA, Zachary JF, O'Brien WD Jr. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
2001 |
| Abstract |
OBJECTIVE: To evaluate the frequency dependence of ultrasonic backscatter for its ability to differentiate between neoplastic and healthy tissue. METHODS: Standard B-mode images were created of 5 rats with spontaneous mammary tumors, and regions of interest in the lesion and surrounding tissue were parameterized by the slope of the backscatter amplitude versus frequency. RESULTS: In 4 of the 5 rats, the averaged backscatter slope of the regions of interest in the tumor was significantly (P < .05) different from that of the surrounding tissue, and the fifth case had a moderate difference (P = .20). The consistency of the averaged slope values (1.2-1.8 dB/MHz) across all but 1 of the mammary tumors was encouraging for the prospect of identifying a tissue type by its backscatter slope. CONCLUSIONS: This work suggests that characterization and diagnosis of tissue types may be possible by using ultrasonographic images quantified by the frequency dependence of backscatter. |
| Title |
Quantifying elasticity and viscosity from measurement of shear wave speed dispersion. |
| Author |
Chen S, Fatemi M, Greenleaf JF. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2004 |
| Abstract |
The propagation speed of shear waves is related to frequency and the complex stiffness (shear elasticity and viscosity) of the medium. A method is presented to solve for shear elasticity and viscosity of a homogeneous medium by measuring shear wave speed dispersion. Harmonic radiation force, introduced by modulating the energy density of incident ultrasound, is used to generate cylindrical shear waves of various frequencies in a homogeneous medium. The speed of shear waves is measured from phase shift detected over the distance propagated. Measurements of shear wave speed at multiple frequencies are fit with the theoretical model to solve for the complex stiffness of the medium. Experiments in gelatin phantoms show promising results validated by an independent method. Practical considerations and challenges in possible medical applications are discussed. |
| Title |
Quantitation of carotid stenosis with continuous-wave (C-W) doppler ultrasound. |
| Author |
Spencer MP, Reid JM. |
| Journal |
Stroke |
| Volume |
|
| Year |
1979 |
| Abstract |
Two methods for determining the degree of stenoses developing on the origin of the internal carotid were tested using non-invasive Doppler ultrasonic imaging (DOPSCAN) of the carotid bifurcations. Spectral analysis of Doppler audio recordings was utilized in determining the maximum frequencies found within the stenosis, as well as the ratio of the frequency downstream to the stenosis, to the frequency within the stenosis. The theoretical relationships between blood flow, velocity, and pressure drop are defined for all grades of stenosis and they predict that carotid flow will not be reduced unless the lumen diameter is less than 1.5 mm. At critical diameter reductions, below 1 mm, the frequencies in human carotids do not exceed 16 KHz because turbulence limits peak velocities. If the maximum systolic frequency exceeds 5 KHZ, when 5 MHZ probes are directed at a 30? angle from the body axis, there is always present stenosis up to diameters of less than 3.5 mm by x-ray angiographic measurements. Frequency ratio studies confirm that plaque growth is not symmetrical but they did not improve x-ray angiography correlations because of the limitations of x-ray in measuring cross sectional areas from projection films and limitations of the spot |
| Title |
Quantitative analysis for ultrasound imaging. |
| Author |
Kinicki RM. |
| Journal |
Hewlett-Packard Journal |
| Volume |
|
| Year |
1983 |
| Abstract |
No abstract available. |
| Title |
Quantitative analysis of ultrasound contrast agent postexcitation collapse |
| Author |
King DA, O'Brien WD Jr. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2014 |
| Abstract |
An empirically based peak-detection technique is described for statistically analyzing single ultrasound contrast agent collapses. It is shown that microbubbles with postexcitation collapse initially exhibit a stronger principal response on average than those without postexcitation, and that lower insonifying
frequencies lead to postexcitation signals which have greater separation from their principal response and persist through more rebounds. |
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