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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 190 out of 330
| Title |
On estimating the number density of random scatterers from backscattered acoustic signals. |
| Author |
Sleefe GE, Lele PP. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1988 |
| Abstract |
When an acoustic pulse interacts with an inhomogeneous, attenuating medium, the backscattered signals exhibit random fluctuations which are correlated with the physical properties of the medium. This paper proposes a robust model for characterizing the statistical nature of these backscattered signals. This model takes into account frequency-dependent attenuation, spatially varying media statistics, arbitrary beam geometries, and arbitrary pulse shapes. Based on this model, statistical estimation schemes are proposed for estimating both the attenuation coefficient and scatterer number density of the medium. Using appropriate simplifying assumptions, it is shown that this model is consistent with attenuation estimation algorithms currently used for ultrasonic tissue characterization. A statistical approach for estimating the number density of scatterers is described and its theoretical performance is evaluated. The algorithm for estimating the scatterer number density incorporates measurements of both the statistical moments of the backscattered signals and the point spread function of the acoustic system. The number density algorithm has been applied to simulated waveforms, waveforms obtained from ultrasonic phantoms with known number densities, and in vitro mammalian tissues. There is an excellent agreement between theoretical, simulation, and experimental results. The application of this technique to ultrasonic tissue characterization is also discussed. |
| Title |
On modeling biomedical ultrasound RF echoes using a power-law shot-noise model. |
| Author |
Kutay MA, Petropulu AP, Piccoli CW. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2001 |
| Abstract |
We propose a new model for the RF ultrasound echo, namely the power-law shot-noise process. Based on this model, the in-phase and quadrature components of the echo are shown to exhibit 1/f beta-type spectral behavior, in a sense that is defined in the paper. The envelope also exhibits this type of spectral behavior, but with a different exponent. This result explains the experimental observations by other researchers of the power-law trend of the RF echo spectrum. Although the shot-noise model has been used in the past for modeling the RF echo, this is the first time that a power-law impulse response filter is used and that the resulting 1/f beta-type spectral behavior of the RF echo has been investigated. The model parameters are linked to tissue characteristics, such as scatterer density and attenuation; thus, they have the potential to be used as tissue characterization features. The validity of the proposed model is tested based on a database of 100 clinical ultrasound images of the breast. |
| Title |
On the acoustic motion of fibrous networks in viscous media. |
| Author |
McQueen DH. |
| Journal |
Acustica |
| Volume |
|
| Year |
1978 |
| Abstract |
A simple acoustic theory of wave motion in two component systems consisting of a viscous fluid medium and a fibrous network is developed. Two wave equations governing the displacement of the viscous medium u(sub)m and of the fibres u(sub)t are coupled through viscous drag forces. When u(sub)t = 0 an equation describing wave propagation in a stiff fibrous network such as fibrous acoustic damping material is obtained. At the opposite extreme, when u(sub)m = 0, the motion of the fibres can be detected by inelastic laser light scattering. An illustrative example of the intermediate case is the rupture of capillary vessels in the spinal chords of rats by pulsed ultrasound. |
| Title |
On the application of ultrasonic contrast agents for blood flowmetry.and assessment of cardiac perfusion. |
| Author |
Bleeker H, Shung K, Barnhart J. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1990 |
| Abstract |
The stability, size, and ultrasonic properties of several ultrasonic microbubble contrast agents such as Albunex, SHU-454, 1% hydrogen peroxide, and sonicated solutions such as 70% and 50% dextrose, 70% sorbitol, 5% albumin, Renografin-76, and others were evaluated. Albunex was the only tested agent that was sufficiently stable over an extended period of time for in vitro ultrasonic characterization. The attenuation and backscatter coefficients of Albunex at 5 and 7.5 MHz were found to be linearly proportional to microsphere concentration at low concentrations (less than 0.01% for attenuation and less than 0.002% for backscatter). Also, Albunex was found to be more echogenic than soft tissues at 5 MHz even after being diluted to 0.0003% of the original concentration. Next, the feasibility of using this acoustic information for contrast blood flowmetry was investigated. In vitro flow estimates in a mock flow loop were made using only the ultrasonic properties of the contrast agent. Bolus injections of Albunex and indicator-dilution curves inferred from ultrasonic measurements were used to estimate calibrated flow rate ranging from 400 to 5000 mL/min. The flow estimates from attenuation measurements showed a good correlation with those from an independent method (r = 0.97), but the results from backscatter studies did not correlate well. These results demonstrate that attenuation measurement may be a feasible alternative for in vivo blood flow measurement in conjunction with the indicator dilution principle or estimation of tissue perfusion such as myocardial perfusion using a time-activity approach. |
| Title |
On the assessment of risk to ultrasound. |
| Author |
O'Brien WD Jr, Shore ML, Fred RK, Leach WM. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1972 |
| Abstract |
A reliable assessment of risks and benefits associated with exposure to ultrasound is essential because of the rapid development and increasing utilization of ultrasound in the healing arts and in industrial and consumer applications. Disproportionately low and insufficient attention has been directed to the development of information on the biological implications of exposure to ultrasound. Interactions between ultrasound and biological systems have been documented, and include degradation of biological molecules, destruction of cells and cell organelles, and formation of lesions in tissues. Much available information is based on inadequate dosimetry for purposes of realistic risk assessments. A unified concept is essential to relate exposure to energy distribution and deposition in tissues. To develop this concept, identification of biologically important physical parameters of exposure is necessary. Specific attention must be given to identify biologically significant and sensitive indicators of damage. Dose-effect relationships must be quantitated. Substantive studies are needed to answer questions about possible delayed, cumulative, and synergistic effects. Proper epidemiologic designs must be employed to evaluate the impact of ultrasound exposure on human development. Information from an effective national research effort will facilitate risk assessment as an integral part of the development of radiation safety performance standards for ultrasound generating electronic products, for which the Bureau has responsibility under Public Law 90-602. |
| Title |
On the detection of intracranial pathology by ultrasound. |
| Author |
Ballantine HT Jr, Bolt RH, Hueter TF, Ludwig GD. |
| Journal |
Science |
| Volume |
|
| Year |
1950 |
| Abstract |
No abstract available. |
| Title |
On the equivalence of pulsed and continuous ultrasound in producing temperature elevations resulting from absorption. |
| Author |
Drewniak JL, Dunn F. |
| Journal |
J Acoust Soc Jpn |
| Volume |
|
| Year |
1992 |
| Abstract |
It is commonly accepted that the temperature elevation in biological specimens resulting from ultrasonic absorption will be the same for both continuous and pulsed ultrasound fields for identical spatial-peak, temporal-average intensities. The rate of heat generation per unit volume is typically determined by time averaging the square of the pressure waveform divided by pc0 over the pulse repetition frequency. The assumption that pulsed and continuous ultrasound fields produce the same temperature elevation for identical spatial-peak, temporal-average intensities is examined from an alternate perspective and is found to be consistent with the above usual practice. |
| Title |
On the impact of vessel size on the threshold of bubble collapse. |
| Author |
Sassaroli E, Hynynen K. |
| Journal |
Appl Phys Lett |
| Volume |
|
| Year |
2006 |
| Abstract |
A series of experiments involving microbubbles in narrow tubes is presented. The threshold for bubble collapse has been investigated as a function of the applied pressure and tube diameter. The threshold has been found to be dependent not only on the applied pressure amplitude but also on the tube size with an increase for smaller tubes. The data have been interpreted in terms of a simple damped harmonic oscillator model. The motivation of this study lies in the possibility of obtaining a better understanding of microbubble behavior in blood vessels in order to optimize applications of microbubbles in medical ultrasound. |
| Title |
On the interaction of intense, noncavitating ultrasound and proteins in solution. |
| Author |
Macleod RM, Dunn F. |
| Journal |
Proc Fifth Int Congr Acoust - Liege |
| Volume |
|
| Year |
1965 |
| Abstract |
No abstract available. |
| Title |
On the measurement and specification of acoustic output generated by pulsed ultrasonic diagnostic equipment. |
| Author |
Kossoff G. |
| Journal |
J Clin Ultrasound |
| Volume |
|
| Year |
1978 |
| Abstract |
The method of describing acoustic output generated by pulsed equipment has not been fully formalized and is often inadequately specified. This paper discusses the terms that we have found useful to specify the acoustic output generated by pulsed diagnostic equipment and proposes additional terms that allow a more complete description of irradiation dosage. The application of the proposed specification is illustrated by measurements made on a typical contact echoscope. |
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