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BRL Abstracts Database |
Your search for ultrasound produced 3296 results. Page 112 out of 330
Title |
Enzymatic studies in foetal brain and liver of mouse following in utero exposure to ultrasound. |
Author |
Suneetha N, Kumar RPS. |
Journal |
Ultrasonics |
Volume |
|
Year |
1991 |
Abstract |
Lactate, malate and succinate dehydrogenases (LDH, MDH and SDH) were estimated in the foetal brain and liver following in utero exposure of mice to a continuous wave of unfocussed ultrasound. Enzymes in both tissues showed a significant increase (P > 0.001), indicating high energy demand due to depletion of oxygen. The increase was recorded even on the twentieth day of pregnancy. |
Title |
Epithelial and corneal thickness measurements by high-frequency ultrasound digital signal processing. |
Author |
Reinstein DZ, Silverman RH, Rondeau MJ, Coleman DJ. |
Journal |
Ophthalmology |
Volume |
|
Year |
1994 |
Abstract |
PURPOSE:
The authors determine the mean central corneal and epithelial thickness in a group of normal human subjects using a new high-frequency ultrasound technique, incorporating digital signal processing.
METHOD:
Both eyes of ten volunteers (age range, 23-44 years) were scanned through a normal saline standoff. Digitized ultrasonic echo data were mathematically transformed to produce a plot, the I-scan, which optimally localizes acoustic interfaces to provide improved measurement precision. System precision was determined by analysis of variance of repeated measures. Central epithelial thickness was obtained by averaging multiple measurements. Central corneal thickness was determined by fitting measurements of apparent corneal thickness in consecutive parallel B-scans to a mathematically modeled cornea. A speed of sound of 1640 m/second was used.
RESULTS:
Epithelial pachymetric precision using A-scan and I-scan was 4.8 and 2.0 microns (standard deviation), respectively. The mean epithelial thicknesses for the right and left eyes were 50.7 +/- 3.7 microns and 50.3 +/- 3.4 microns, respectively. The mean corneal thicknesses in the right and left eyes were 514.6 +/- 38.4 microns and 516.2 +/- 37.8 microns, respectively. The root mean-square differences in epithelial and corneal thickness between the left and right eyes of each subject were 1.3 and 7.7 microns, respectively (neither was statistically significant).
CONCLUSION:
This system provides a pachymetric precision superior to current optical and ultrasound methods. Epithelial and corneal pachymetry is obtained noninvasively by a method that is not limited to optically clear media. |
Title |
Erratum: transient pulsations of small gas bubbles in water. |
Author |
Flynn HG, Church CC. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
1988 |
Abstract |
Transient behavior of small gas bubbles in a liquid set into violent motion by ultrasonic pressure waves is of interest because of widespread use of.microsecond pulses in diagnostic ultrasound. Such pulses contain only a few pressure cycles and the transient pulsations of bubbles set in motion.by such pulses would determine the bubble-ultrasound interaction. A computer study has been made to obtain a global representation of the.pulsation amplitudes R (t) of small gas bubbles (nuclei) in water during the first few cycles of a cw ultrasonic pressure. One objective was to obtain.a better understanding of cavitation phenomena where many nuclei with initial radii Rn from 0.1-20 microns are set in motion at pressures ranging.from 0.5-5 bars and at frequencies from 0.5-10 MHz. Results allowed construction of surfaces showing the relative bubble amplitude R/Rn as a.function of Rn and of the time t/TA, where TA is the acoustic period. One finding is that, in the range of peak pressures found in diagnostic pulses,.transient cavities would be generated during the first pressure cycle from nuclei with initial radii as small as a few microns (micron). Nuclei that.grow into transient cavities in the first pressure cycle are here called "prompt" nuclei. At a specified pressure, the size range of radii Rn in which.they occur decreases with increasing frequency. At 5 bars, the range of Rn for prompt nuclei is 0.166-11.35 microns at 0.5 MHz and vanishes at.10 MHz. |
Title |
Error bounds on Doppler ultrasound blood flow measurements. |
Author |
Gilson WH, Schultheiss P, Tuteur F, Holland SK, Orphanoudakis SC. |
Journal |
Proc Twelfth Annu Northeast Bioeng Conf, IEEE - Yale Univ |
Volume |
|
Year |
1986 |
Abstract |
The attenuation coefficient of tissue is in general proportional to the acoustic frequency. If a Doppler instrument transmits short pulses, the echoes will be effectively shifted down in frequency as the high frequencies are preferentially attenuated, even without any Doppler shift. This phenomenon raises two questions. First, how well can one correct this shift, and second, since short pulses are more strongly affected, does lack of information about the attenuation place a limit on the range resolution of Doppler instruments? It is shown that by computing a Cramer-Rao bound on the variance of a velocity estimator, one should be able to correct almost completely for the attenuation, and the uncertainty about the attenuation does not influence the range resolution. |
Title |
Error bounds on ultrasonic scatterer size estimates. |
Author |
Chaturvedi P, Insana MF. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
1996 |
Abstract |
Precision errors that occur in estimating the average scatterer size from pulse-echo ultrasound waveforms are examined in.detail. The method-independent lower bound on estimation error is found from the Cramer-Rao inequality for comparison with.the predicted error for the measurement technique currently used to estimate scatterer sizes in soft biological tissues. The.probability density function for the estimate is also derived. From these statistical analyses, strategies for designing experiments.that minimize the error are discussed. It is shown that compared with biological variability, measurement errors in scatterer size.estimates are relatively large. Consequently, there is reason to continue searching for more efficient estimators. Although the.analysis and results are derived for Gaussian correlation models that have been used to study the function and structure of.kidneys, generalization to include correlation models for other tissues is straightforward. . |
Title |
Errors in biased estimators for parametric ultrasonic imaging. |
Author |
Chaturvedi P, Insana MF. |
Journal |
IEEE Trans Med Imaging |
Volume |
|
Year |
1998 |
Abstract |
Maximum likelihood (ML) methods are widely used in acoustic parameter estimation. Although ML methods are often unbiased, the variance is unacceptably large for many applications, including medical imaging. For such cases, Bayesian estimators can reduce variance and preserve contrast at the cost of an increased bias. Consequently, including prior knowledge about object and noise properties in the estimator can improve low-contrast target detectability of parametric ultrasound images by improving the precision of the estimates. In this paper, errors introduced by biased estimators are analyzed and approximate closed-form expressions are developed. The task-specific nature of the estimator performance is demonstrated through analysis, simulation, and experimentation. A strategy for selecting object priors is proposed. Acoustic scattering from kidney tissue is the emphasis of this paper, although the results are more generally applicable |
Title |
Errors involved in intensity values from the acoustic radiation force on steel spheres |
Author |
Hasegawa T, Yosioka K |
Journal |
Proc Int Congr Acoust |
Volume |
|
Year |
1968 |
Abstract |
The radiation force method in current use for the determination of ultrasound intensity utilizes a stainless steel sphere suspended by a bifilar suspension int he sound field in liquid. From the magnitude of the radiation force, which is evaluated from the deflection of the sphere, the acoustic intensity at a specific site in the field is computed using King's formula of the radiation force on rigid spheres.
Since King's theory is based upon the assumptions: (1) plane progressive sound field, (2) a rigid sphere and (3) non-viscous surrounding medium, the divergence between every just-mentioned assumption and the actual situation may lead to errors in the intensity values, thus obtained. |
Title |
Essential basic physics in diagnostic ultrasound. |
Author |
Kossoff G, Robinson DE. |
Journal |
Rep Commonw Aust |
Volume |
|
Year |
1966 |
Abstract |
No abstract available. |
Title |
Estimating acoustic attenuation from reflected ultrasound signals: Comparison of spectral-shift and spectral-difference approaches. |
Author |
Kuc R. |
Journal |
IEEE Trans ASSP |
Volume |
|
Year |
1984 |
Abstract |
The acoustic attenuation coefficient of soft biological tissue has been observed to have an increasing linear-with-frequency attenuation characteristic with a slope, denoted by ?, that varies with the disease condition of the liver. Hence, it would be diagnostically useful to estimate the value of ? from reflected ultrasound signals. Two approaches for estimating ? are examined: the spectral-shift approach, which estimates ? from the downward shift experienced by the propagating pulse spectrum with penetration into the liver, and the spectral-difference approach, which estimates ? from the slope of the log spectral differences. While the spectral-shift approach requires the propagating pulse to have a Gaussian-shaped spectrum, the spectral-difference method does not require a specific spectral form. A mathematical model is developed to simulate the random ultrasound signals reflected from the liver. The bias and variance properties of the ? estimators are determined by using the simulated signals and compared as a function of the data window size. The results indicate that, while the accuracy of both approaches is equivalent for large data windows, the frequency-shift approach is more accurate than the spectral-difference approach for most practical cases. |
Title |
Estimating attenuation in composite laminates using backscattered ultrasound. |
Author |
Blodgett ED, Johnston PH, Miller JG. |
Journal |
Proc Ultrason Symp IEEE |
Volume |
|
Year |
1984 |
Abstract |
As an approach to the nondestructive evaluation of composite laminates, we applied several techniques based on spectral analysis of backscattered ultrasound in order to evaluate a method for estimating attenuation which does not require access to both sides of a composite. The method makes use of the fact that propagation of a broadband ultrasonic pulse through a medium exhibiting a frequency-dependent attenuation results in changes in the backscattered spectrum, including changes in the lowest order moments (i.e., total backscattered energy, spectral centroid, and spectral variance or width). As a means of evaluating the accuracy of the estimate of the attenuation determined from backscattered ultrasound, attenuation was measured at the same sites using a transmission mode technique with a phase-insensitive acoustoelectric receiving transducer. Results of attenuation estimates on a test specimen consisting of an isotropic suspension of 44 micron SiC grit embedded in gelatin and on a graphite-epoxy composite laminate were in good agreement with the results of transmission mode measurements. |
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