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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 39 out of 330
| Title |
Analysis of low-order autoregressive models for ultrasonic grain signal characterization. |
| Author |
Wang T, Saniie J, Jin X. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1991 |
| Abstract |
In testing materials nondestructively with ultrasound, the grain scattering signal provides information that may be correlated to regional microstructure variation. In the Rayleigh scattering domain, grain scattering results in an upward shift in the expected frequency of broadband echoes, while attenuation caused by scattering and absorption affects the shift in a downward direction. Both upward and downward shifts are known to be dependent on grain size distribution. In this paper, the second- and third-order autoregressive (AR) models are used to evaluate the spectral shift in grain signals by utilizing features such as resonating frequency, maximum energy frequency or AR coefficients. Then, Euclidean distance, based on these features, is applied to classify grain scattering characteristics. Using both computer stimulated data and experimental results, the probability of correct classifications is found to be about 75% for the second-order AR model and 88% for the third order AR model, when the conditions are such that the expected shift between the center frequency of echoes is less than 4%. |
| Title |
Analysis of speckle in ultrasound images using fractional order statistics and the homodyned κ-distribution. |
| Author |
Prager RW,Gee AH,Treece GM,Berman LH. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
2002 |
| Abstract |
It is necessary to identify speckled regions in ultrasound images to control adaptive speckle suppression algorithms, for tissue characterisation, and to estimate the elevational separation of B-scans by speckle decorrelation. Previous authors have proposed classification techniques based on second order powers of the homodyned κ-distribution, or lower order powers of the more limited κ-distribution. In this paper we explore the speckle discrimination properties of statistics based on arbitrary powers of the ultrasound echo envelope signal using a combination of simulations and theoretical results from the homodyned κ-distribution. We conclude that statistics based on powers less than one are surprisingly less effective than some higher powers. A simple discriminant function for speckle is evaluated quantitatively in simulation and qualitatively on sample B-scan images.©2002 Elseiver Science B.V. All rights reserved.
Keywords: Homodyned κ-distribution; Speckle; Fractional-order statistics
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| Title |
Analysis of temperature responses to diffused ultrasound focal fields produced by a sector-vortex phased array. |
| Author |
Umemura SI, Cain CA. |
| Journal |
Int J Hyperthermia |
| Volume |
|
| Year |
1990 |
| Abstract |
The sector-vortex applicator, a disc-shaped ultrasound phased array with a geometric focus having multiple sectors and tracks, can directly synthesize, without scanning, diffuse focal patterns useful for hyperthermia. Temperature distribution patterns resulting from these acoustic fields have been simulated by solving a steady-state bioheat equation numerically for a wide range of blood perfusion rates. These results suggest that the sector-vortex array will be particularly suitable for heating non-superficial small tumours. The temperature distribution pattern changes due to variations in blood perfusion are interpreted based on spatial frequency domain Fourier analysis of temperature responses to different power deposition patterns. The system behaves like a low-pass spatial frequency filter. |
| Title |
Analysis of two quantitative ultrasound approaches |
| Author |
Muleki-Seya P, Han A, Andre MP, Erdman JW Jr, O'Brien WD Jr. |
| Journal |
Ultrasonic Imaging |
| Volume |
|
| Year |
2018 |
| Abstract |
There are two well-known ultrasonic approaches to extract sets of quantitative parameters: Lizzi–Feleppa (LF) parameters: slope, intercept, and midband; and quantitative ultrasound (QUS)–derived parameters: effective scatterer diameter (ESD) and effective acoustic concentration (EAC). In this study, the relation between the LF and QUS-derived parameters is studied theoretically and experimentally on ex vivo mouse livers. As expected from the theory, LF slope is correlated to ESD (R2=1.00), and from experimental data, LF midband is correlated to EAC (R2=0.76). However, LF intercept is not correlated to ESD (R2=0.25) nor EAC (R2=0.07). The unexpected correlation observed between LF slope and EAC (R2=0.94) results likely from the high correlation between ESD and EAC due to the inversion process. For a liver fat percentage estimation, an important potential medical application, the parameters presenting the better correlation are EAC (R2=0.78) and LF midband (R2=0.70).
KEYWORDS:
Lizzi–Feleppa parameters; QUS parameters; mouse livers; quantitative ultrasound technique |
| Title |
Analytical modelling of ultrasonically induced tissue heating. |
| Author |
Lizzi FL, Ostromogilsky M. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1987 |
| Abstract |
Ultrasonically induced heating in biological tissues has been studied for decades because of its implications for the safety of diagnostic systems and for possible therapeutic applications. Analytical models have been developed to study heating for short-term, ablative exposures and for long-term hyperthermia exposures. These models account for many of the acoustic and thermal phenomena implicated in heating but several factors remain to be fully included. Excellent agreement has been found between model results and experimental lesions in the brain and eye. Future developments may provide new capabilities for computer simulations related to safety and therapy. |
| Title |
Angle scan and frequency-sewpt ultrasonic scattering characterization of tissue. |
| Author |
Waag RC, Lee PP, Lerner RM, Hunter LP, Gramiak R, Schenk EA. |
| Journal |
Proc Second Int Symp Ultrason Tissue Character |
| Volume |
|
| Year |
1977 |
| Abstract |
Ultrasonic wave interference has been applied to characterize tissue by measuring scattered wave intensity as a function of frequency and angle. A theory of acoustic wave propagation and scattering in an inhomogeneous medium has been employed to show that received ultrasound may be expressed in terms of medium refractive index variations via a Fourier transform. Using a computer-based system, measurements were made on model targets and post-mortem liver specimens. Model studies demonstrate that regular scatterer spacing can be inferred from measured diffraction data by Fourier inversion and that scattering differences can be observed from random media consisting of particles of different average sizes. Scattering from liver indicates there is significantly more energy scattered at small angles than is backscattered. Correlation of ultrasound scattering with structure observed through a microscope has been obtained by computing the diffraction pattern of the two-dimensional optical transmittance images acquired through a microscope-TV chain attached to the computer. Average particle sizes of the model random media determined by Fourier analysis that exhibited diffraction rings of the digitized cross-sections yielded scattering predictions which were in agreement with measured acoustic data. |
| Title |
Angular dependence of scattering of ultrasound from blood. |
| Author |
Shung KK, Sigelmann RA, Reid JM. |
| Journal |
IEEE Trans Biomed Eng |
| Volume |
|
| Year |
1977 |
| Abstract |
The angular scattering of 5-MHz ultrasonic waves by blood was measured in the range from 60 to 150. Experimental and theoretical results agree very well. A discussion on the use of angular scattering for determining the mechanical properties of the erythrocyte is presented. |
| Title |
Angular distribution of scattered ultrasound from a single steel sphere in agar gelatin: A comparison between theory and experiment. |
| Author |
Burke TM, Goodsitt MM, Madsen EL, Zagzebski JA. |
| Journal |
Ultrason Imaging |
| Volume |
|
| Year |
1984 |
| Abstract |
Experimental results for the angular distribution of scattered ultrasound in water from a 0.635 mm diameter steel sphere embedded in agar were obtained for interrogating frequencies of 1.0, 2.25, 3.5 and 5.0 MHz. The experimental results compared favorably with theoretical predictions based on the work of Faran. The results for both theory and experiment are presented in the form of the Differential Scattering Cross Section (DSC) for scattering angles from 170 degrees to 44 degrees. The implications of this study on calculating the expected scattering behavior of gelatin based ultrasound phantoms are briefly discussed. |
| Title |
Angular response of miniature ultrasonic hydrophones. |
| Author |
Shombert DG, Smith SW, Harris GR. |
| Journal |
Med Phys |
| Volume |
|
| Year |
1982 |
| Abstract |
The voltage response of ceramic and polyvinylidene fluoride (PVDF) hydrophones was measured in the receive mode for angles of incidence ranging from 0 - 90 degrees. The measurements were performed at 2.5, 3.5, 5.0, and 8.0 MHz; these frequencies are typical of those used in medical diagnosis. The results are compared to three theoretical models based on diffraction theory; correlation between the measured response and theoretical models is evident for some PVDF hydrophones but not for others, and not for any ceramic hydrophone. The effective radius, as defined in the AIUM-NEMA standard for diagnostic ultrasound, is calculated and compared to the test criteria established in that standard. All of the ceramic hydrophones and two of the five PVDF hydrophones failed to meet that criteria. |
| Title |
Animal toxicity studies with ultrasound at diagnostic power levels. |
| Author |
Smyth MG Jr. |
| Journal |
Proc First Int Conf Diagn Ultrasound |
| Volume |
|
| Year |
1965 |
| Abstract |
No abstract available. |
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