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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 203 out of 330
| Title |
Pressure-dependent attenuation in ultrasound contrast agents. |
| Author |
Chen Q, Zagzebski J, Wilson T, Stiles T. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2002 |
| Abstract |
Although microbubble contrast agents are believed to respond differently under different driving-pressure amplitudes, few studies have been performed to extensively study the pressure-dependence of their properties. In this paper, attenuation coefficients of two contrast agents (Optison? and Definity?) were measured under different driving-pressure amplitudes using a narrowband incident pulse. The attenuation of both contrast agents was found to increase with increasing driving pressure. Simulations using the Rayleigh, Plesset, Noltingk, Neppiras, Poritsky (RPNNP) equation were performed to study this behavior. Simulation results show that significant harmonic generation at high driving-pressure amplitudes contributes to the higher attenuation. Other possible explanations for this behavior were also examined. Attenuation coefficients of two contrast agents were also measured using a broadband method. The results showed great inconsistency when the center frequency of the incident broadband pulse was changed, indicating that broadband techniques may not be suitable for contrast-agent attenuation measurements.
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| Title |
Pressure-mediated reduction of ultrasonically induced cell lysis. |
| Author |
Ciaravino V, Miller MW, Carstensen EL. |
| Journal |
Radiat Res |
| Volume |
|
| Year |
1981 |
| Abstract |
Chinese hamster V-79 cells, exposed in polystyrene tubes for 5 min to 1-MHz continuous-wave ultrasound, were lysed more by a 10 than a 5 W/cm(^2) intensity. Higher atmospheric pressure was needed to eliminate lysis with the former relative to the latter intensity, but lysis by 10 W/cm2 was completely eliminated with 2 atm of hydrostatic pressure. The reduction in lysis per unit increase in atmospheric pressure was comparable for both ultrasound intensities. |
| Title |
Principles and applications of ultrasound backscatter microscopy. |
| Author |
Foster FS, Pavlin CJ, Lockwood GR, Ryan LK, Harasiewicz KA, Berube L, Rauth AM. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1993 |
| Abstract |
Current medical diagnostic imaging methods generally aimed at structures that are larger than 1mm. Nevertheless, there are numerous important clinical applications for submillimeter or microscopic resolution of superficial structures and structures accessible by endoscopic means. In this regard optical, ultrasonic, and magnetic resonance microscopy may have important, as yet unexplored clinical applications. In this paper, the development of ultrasound backscatter microscopy (UBM) is described together with initial clinical and biological applications. UBM is essentially an extension of the powerful B-mode backscatter methods developed for clinical imaging in the 3-10-MHz frequency range. The development of new high sensitivity transducers in the 40-100-MHz range now permits visualization of tissue structures with resolution approaching 20 mu m and a maximum penetration of approximately 4 mm. The performance characteristics and trade-offs of these new polymer and ceramic devices are reviewed, and the implementation of high-frequency imaging systems is described. Initial clinical applications of UBM include ophthalmic, skin, and intravascular imaging. Examples of images and progress in these areas are presented. The biological application of UBM is illustrated by studies of drug uptake in living tumor spheroids. Significant increases in backscatter levels resulting from drugs targeting oxic and hypoxic cell populations are demonstrated. |
| Title |
Probleme der Ultrashallubertragung. (Problems of ultrasound transmission.) Article in German. |
| Author |
Pohlman R. |
| Journal |
Proc Third Int Congr Acoust - Stuttgart |
| Volume |
|
| Year |
1959 |
| Abstract |
No abstract available. |
| Title |
Proceedings of the British Medical Ultrasound Society. |
| Author |
Unknown. |
| Journal |
Br J Radiol |
| Volume |
|
| Year |
1985 |
| Abstract |
Abstracts of papers presented at the Fifteenth Annual Meeting of the British Medical Ultrasound Society held at the University of Manchester Institute of Science and Technology, December 18-21, 1983. |
| Title |
Processing of diagnostic ultrasound signals. |
| Author |
Kuc R. |
| Journal |
IEEE ASSP Mag |
| Volume |
|
| Year |
1984 |
| Abstract |
Ultrasound signals reflected from the human liver contain significant information about its condition. Several techniques have been developed to process such signals. In this paper, two approaches are described for estimating the slope of the acoustic attenuation coefficient, denoted by ?, which provides important cues about the condition of diffuse liver disease. The first is a nonparametric approach which determines the ? value from the slope of log periodogram differences. The second is a parametric approach which requires a Gaussian-shaped spectrum and determines the ? value from a shift in the spectral center-frequency. A zero-crossing count procedure allows the parametric approach to be implemented with minimal hardware and in real-time. Simulated and actual signals illustrate the two approaches. |
| Title |
Processing radio frequency ultrasound images: A robust method for local spectral features estimation by a spatiality constrained parametric approach. |
| Author |
Gorce J,Friboulet D,Dydenko I,D'hooge J,Bijnens BH,Magnin IE. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2002 |
| Abstract |
Spectral estimation is a major component in studies aiming at characterizing biological tissues through the analysis of backscattered radio frequency (RF) ultrasonic signals and images. However, conventional spectral estimation techniques yield a well-known trade-off between spatial resolution and variance. The backscattered signals are stochastic by nature, so short-term local analysis results in a high variance of the estimates, which cannot efficiently be reduced through conventional spatial averaging. We address this issue by describing a spectral estimation technique that reduces the variance of the estimates (by smoothing the local estimates in spectrally homogeneous regions) while preserving spectral discontinuities (i.e., the smoothing is not performed across regions with different spectral contents). The proposed approach is set in a Bayesian framework and is based on local autoregressive (AR) estimation, constrained by smoothness priors. These smoothness priors are introduced through a Markov random field in which the associated potential functions are nonquadratic, allowing thereby to preserve discontinuity. The method is validated on simulated RF images and tested on echocardiographic images acquired in vivo. The results are compared to the estimates provided by the conventional Burg technique. These results clearly demonstrate the ability of the proposed approach to improve spectral estimation in terms of variance reduction and discontinuity detection. |
| Title |
Production of deep focal lesions by focused ultrasound - current status. |
| Author |
Lele PP. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1967 |
| Abstract |
No abstract available. |
| Title |
Production of focal destructive lesions in the central nervous system with ultrasound. |
| Author |
Fry WJ, Mosberg WH Jr, Barnard JW, Fry FJ. |
| Journal |
J Neurosurg |
| Volume |
|
| Year |
1954 |
| Abstract |
SUMMARY
A technique, employing a focussed beam of ultrasound, has been described
whereby accurately localized, quantitatively reproducible focal destructive
lesions may be made in the central nervous system. The dura mater need not be opened and the nervous tissue need not be incised or perforated. There is no disruption of the the blood-vessel walls - even within the site of the focal destructive lesion. |
| Title |
Production of lesions in the central nervous system with focused ultrasound: A study of dosage factors. |
| Author |
Hueter TF, Ballantine HT Jr, Cotter WC. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1956 |
| Abstract |
Applications of ultrasonics in neurosurgery involve the production of lesions of a specified size at a specified location, and in a reproducible fashion. Control of the dosage required for a given lesion depends on the geometry of the focal region, the exact determination of focal intensity and the relation between irradiation parameters and biological effect. From an analysis of these factors an optimum frequency for each focal depth is determined and an empirical dosage relationship based on ultrasonically produced paralysis in mice is stated. The mechanism of cell destruction by ultrasound is shown to be a temperature-dependent mechanical effect originating at weak points in the tissue. The difficulties in extrapolating results obtained with experimental animals to applications in human neurosurgery are pointed out. |
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