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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 80 out of 330
| Title |
Delta-sigma oversampled ultrasound beamformer with dynamic delays. |
| Author |
Freeman SR, Quick MK, Morin MA, Anderson RC, Desilets CS, Linnenbrink TE, O'Donnell M. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1999 |
| Abstract |
The principles of oversampling are exploited in a simple beamforming architecture using a single bit delta-sigma ( Delta E) analog to digital converter (A/D) on every channel. The high sampling rate required for the single bit A/D provides adequate delay accuracy for high quality beamforming using elementary sample manipulations. Images produced with this beamformer exhibit significant artifacts directly related to dynamic focusing. However, a simple digital recording technique following delays permits dynamically focused beamforming without degrading image quality. The simplicity of this beamformer compared to conventional methods may facilitate very large channel count or low power beamformers suitable for 1.5-D arrays or portable scanners. |
| Title |
Demonstration of nonlinear acoustical effects at biomedical frequencies and intensities. |
| Author |
Carstensen EL, Law WK, McKay ND, Muir TG. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1980 |
| Abstract |
Examples of nonlinear acoustic phenomena in water in the range of frequencies and intensities of interest for biomedical ultrasound are provided. Total intensities, including all harmonics generated in the medium, have been measured with a spherical radiometer. The fundamental component of the waves have been measured with a miniature probe hydrophone and low pass filter. Simple adaptation of the theory summarized in a companion paper leads to predictions which are in excellent agreement with the observations. The illustrated phenomena must be considered in studies of the biological effects of ultrasound as well as in the applications of ultrasound in medicine. |
| Title |
Demonstration of potential noninvasive ultrasound brain therapy through an intact skull. |
| Author |
Hynynen K, Jolesz FA. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1998 |
| Abstract |
Utilization of therapeutic ultrasound in the brain has been seriously limited by the commonly accepted view that these exposures would require that a piece of the skull bone be removed to allow the ultrasound beam to propagate into the brain. In this paper, the feasibility of delivering ultrasound therapy through the intact skull was studied. Sonications were performed through a piece of human skull with focused transducers at 0.248, 0.559, 1.0 and 1.68 MHz. The skull attenuated and distorted the field; however, a sharp focal spot was created at frequencies of 1 MHz or lower. At the higher frequency, the focus was destroyed. To investigate the feasibility of compensating for the ultrasound field distortion caused by the bone, phased array experiments were performed. Two arrays with 64 elements, operating at 0.6 MHz and 1.58 MHz, were used in these experiments. The phase shifts caused by the skull were measured for each element of the arrays and then compensated for by phase-control circuitry. These phase corrections allowed a sharp focus to be generated at both frequencies. Finally, tissue destruction was induced by using pulsed sonication through a piece of human skull in a rabbit brain in vivo at the frequency of 0.559 MHz. In summary, the results showed that transcranial delivery of therapeutic ultrasound into the brain may be feasible. |
| Title |
Dental enamel: Detection of surface changes by ultrasound. |
| Author |
Lees S, Barber FE, Lobene RR. |
| Journal |
Science |
| Volume |
|
| Year |
1970 |
| Abstract |
Evidence indicates that the tooth surface differs in structure from the enamel immediately beneath it, and particularly that the enamel rod type structure is minimial in the true natural surface. Furthermore, the rod ends appear to disappear with age after the eruption of the tooth. The thickness of the surface layer may be as much as 25 micrometers. Studies of caries incidence show a peak in the attack curve 2 to 4 years after eruption and a decline thereafter for all teeth. This information indicates that the mechanical structure of the tooth surface should be carefully studied. A highly useful means appears to be ultrasound since the specific acoustic impedance of highly mineralized tissue like enamel is strongly dependent on fraction volume mineralization and since nondestructive test techniques can be based on ultrasonics. An experimental demonstration of ultrasonic detection in vitro of tooth surface demineralization is given. |
| Title |
Dependence of the electromechanical coupling coefficient on the width-to-thickness ratio of plank-shaped piezoelectric transducers used for electronically scanned ultrasound diagnostic systems. |
| Author |
Sato J, Kawabuchi M, Fukumoto A. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1979 |
| Abstract |
A finite element analysis method is used to obtain the electromechanical coupling coefficient k(sub)e for plank-shaped piezoelectric transducers with a width W to thickness T ratio of not more than two. Calculation results for typical piezoelectric ceramics show that there exist maximum values of k(sub)e at certain values of W/T. For PCM-5 material the maximum value of k(sub)e is 0.69 at a W/T of 0.6. It is shown that only one vibrational mode is very strongly coupled around this value of W/T. This vibrational mode is very useful for application to electronically scanned arrayed transducers. |
| Title |
Dependence of the electromechanical coupling coefficient on the width‐to‐thickness ratio of plank‐shaped piezoelectric transducers used for electronically scanned ultrasound diagnostic systems. |
| Author |
Sato J, Kawabuchi M, Fukumoto A. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1979 |
| Abstract |
A finite element analysis method is used to obtain the electromechanical coupling coefficient ke for plank‐shaped piezoelectric transducers with a width W to thickness T ratio of not more than two. Calculation results for typical piezoelectric ceramics show that there exist maximum values of ke at certain values of W/T. For PCM‐5R material the maximum value of ke is 0.69 at a W/T of 0.6. It is shown that only one vibrational mode is very strongly coupled around this value of W/T. This vibrational mode is very useful for application to electronically scanned arrayed transducers. |
| Title |
Dependence of the ultrasonic properties of biological tissue on constituent proteins. |
| Author |
Goss SA, Frizzell LA, Dunn F, Dines KA. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1980 |
| Abstract |
The absorption and speed of ultrasound in mammalian tissues are discussed in relation to the fractional protein content. To a first approximation, biological tissues are shown to correspond to composite materials whose ultrasonic propagation properties are determined by the individual ultrasound properties of their globular and structural protein contents. |
| Title |
Dependence of the velocity and attenuation of ultrasound in bone on the mineral content. |
| Author |
Tavakoli MB, Evans JA. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
1991 |
| Abstract |
Measurements of the attenuation and velocity of ultrasound from 0.3 to 0.8 MHz have been performed on a number of bovine cancellous bone samples. The influence of bone mineral content has been isolated by measuring the acoustic properties of the samples at various stages of demineralization resulting from controlled nitric acid attack. The correlation coefficient r, between the attenuation at different frequencies and bone density was found to be in the range 0.68-0.97. Broadband ultrasonic attenuation (BUA) was also calculated and produced r values between 0.84 and 0.99. The velocity measurements indicated a correlation greater than 0.97 in all cases. Thus velocity is the parameter most sensitive to changes in bone mineral density alone. Attenuation and BUA are less well correlated presumably because of a sensitivity to minor structural change. |
| Title |
Depression of phagocytosis by ultrasound. |
| Author |
Anderson DW, Barrett JT. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1981 |
| Abstract |
No abstract available |
| Title |
Describing small-scale structure in random media using pulse-echo ultrasound. |
| Author |
Insana MF, Wagner RF, Brown DG, Hall TJ. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1990 |
| Abstract |
A method for estimating structural properties of random media is described. The size, number density, and scattering strength of particles are estimated from an analysis of the radio frequency (rf) echo signal power spectrum. Simple correlation functions and the accurate scattering theory of Faran [J.J. Faran, J. Acoust. Soc. Am. 23, 405-418 (1951)], which includes the effects of shear waves, were used separately to model backscatter from spherical particles and thereby describe the structures of the medium. These methods were tested using both glass sphere-in-agar and polystyrene sphere-in-agar scattering media. With the appropriate correlation function, it was possible to measure glass sphere diameters with an accuracy of 20%. It was not possible to accurately estimate the size of polystyrene spheres with the simple spherical and Gaussian correlation models examined because of a significant shear wave contribution. Using the Faran scattering theory for spheres, however, the accuracy for estimating diameters was improved to 10% for both glass and polystyrene scattering media. It was possible to estimate the product of the average scattering particle number density and the average scattering strength per particle, but with lower accuracy than the size estimates. The dependence of the measurement accuracy on the inclusion of shear waves, the wavelength of sound, and medium attenuation are considered, and the implications for describing the structure of biological soft tissues are discussed. |
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