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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 16 out of 330
| Title |
A review of physical phenomena associated with ultrasonic contrast agents and illustrative clinical applications. |
| Author |
Deng CX, Lizzi FL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2002 |
| Abstract |
Successful clinical applications of contrast agents involve an understanding of the physical interaction of ultrasound (US) with contrast agents. This paper reviews the physical phenomena involved in these interactions and discusses the relevant theoretical background for modeling US-contrast agent interactions. Measurement techniques using US to obtain information regarding contrast agents are summarized. Illustrative clinical applications are given in the second part of the paper. Recent developments in nonlinear imaging techniques and transient techniques are reviewed. New methods, such as depletion perfusion measurement, and high-frequency applications are included.
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| Title |
A review of some basic limitations in ultrasonic diagnosis. |
| Author |
Reid J. |
| Journal |
Diagn Ultrasound |
| Volume |
|
| Year |
1966 |
| Abstract |
No abstract available. |
| Title |
A review of the physical properties and.biological effects of the high amplitude acoustic fields used in extracorporeal lithotripsy. |
| Author |
Coleman AJ, Whitlock M, Leighton T, Saunders JE. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1993 |
| Abstract |
Extracorporeal shockwave lithotripsy (ESWL) has now been used for more than a decade in the treatment of urinary stone disease. During this period there has been a wide range of studies on the physical properties of the high-amplitude focussed fields used in ESWL and the biological effects of exposure to such fields, including their ability to fragment hard concretions. These studies form a distinct body of knowledge whose relevance to the broader literature on biological effects from lower amplitude exposures has yet to be fully evaluated. This review attempts to present the main results of biological-effects studies in ESWL along with what is known of the physical properties of lithotripsy fields with the aim of assisting this evaluation. In general, the reported biological effects of lithotripsy fields are compatible with those that have been observed at those lower amplitudes of focussed pulsed ultrasound in which transient cavitation is the dominant mechanism of interaction. The relatively large amplitudes and low frequencies in ESWL, however, make it a more potent generator of transient cavitation than most other forms of medical ultrasound. Biological-effects studies with lithotripsy fields may, therefore, be expected to extend our understanding of the nature of transient cavitation and, in particular, its effects in mammalian tissue. |
| Title |
A review of the ultrasonic bioeffects of microsonation, gas-body activation, and related cavitation-like phenomena. |
| Author |
Miller DL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1987 |
| Abstract |
Ultrasonic exposures localized to regions smaller than a wavelength minimize the thermal mechanism, but promote nonthermal mechanisms of ultrasonic bioeffects. Microsonation experiments with vibrating needles or wires exploit this situation for the study of nonthermal mechanisms such as acoustic microstreaming flow. Shear stress in microstreaming flow, which is in excess of critical values for biomembranes, leads to cell lysis. Plane wave exposure of small bodies of gas also yields localized exposure, with further amplification of nonthermal mechanisms by resonance activation of oscillation. Gas body activation in vitro causes gathering of suspended cells by radiation forces, aggregation, cellular effects and lysis by microstreaming. When suitable gas bodies are present, these effects may occur at levels below the threshold for ultrasonic cavitation. In vivo, gas body activation generates intracellular microstreaming in Elodea leaves and disrupts the cells for super-critical shear stress levels. Similar phenomena seem to account for cell death, growth and mitotic index reductions in other plant tissues, and developmental abnormalities and delayed death in fruit flies. Only fragmentary and equivocal evidence presently exists on the medically relevant question of whether such subthreshold cavitation-like activity and bioeffects occur in vertebrates. |
| Title |
A robust and computationally efficient algorithm for mean scatterer spacing estimation. |
| Author |
Simon C, Shen J, Seip R, Ebbini ES. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1997 |
| Abstract |
Mean scatterer spacing (MSS) has been recognized to be a useful tool for tissue characterization. Most of the work in this area either uses the amplitude or the phase information of the spectrum of the backscattered ultrasound echo to. estimate the MSS. Simulations have shown that the latter approach is more robust in the presence of irregularities in the scatterer distribution. However, most of the algorithms based on the phase information of the spectrum are. computationally demanding and cannot be used in real-time. We present a computationally efficient and robust algorithm which uses the magnitude and phase information of the spectrum to estimate the MSS. This algorithm exploits the. spectral redundancy present in the backscattered echo signal by generating spectral lines through a nonlinear (quadratic) transformation of the RF echo signal. Results of simulations comparing the performance of the proposed algorithm. and previous approaches from the literature are presented to demonstrate the robustness of the proposed algorithm. Experiments involving phantoms and in vitro tissue samples are also presented. The feasibility of implementing a. real-time MSS imaging system based on the proposed method is discussed. (19 References). |
| Title |
A robust numerical solution to reconstruct a globally relative shear modulus distribution from strain measurements. |
| Author |
Sumi C, Nakayama K. |
| Journal |
IEEE Trans Med Imaging |
| Volume |
|
| Year |
1998 |
| Abstract |
To noninvasively quantify tissue elasticity for differentiating malignancy of soft tissue, we previously proposed a two-dimensional (2-D) mechanical inverse problem in which simultaneous partial differential equations (PDE's) represented the target distribution globally of relative shear moduli with respect to reference shear moduli such that the relative values could be determined from strain distributions obtained by conventional ultrasound (US) or nuclear magnetic resonance (NMR) imaging-based analysis. Here, we further consider the analytic solution in the region of interest, subsequently demonstrating that the problem is inevitably ill-conditioned in real-world applications, i.e., noise in measurement data and improper configurations of mechanical sources/reference regions make it impossible to guarantee the existence of a stable and unique target global distribution. Next, based on clarification of the inherent problematic conditions, we describe a newly developed numerical-based implicit-integration approach that novelly incorporates a computationally efficient regularization method designed to solve this differential inverse problem using just low-pass filtered spectra derived from strain measurements. To evaluate method effectiveness, reconstructions of the global distribution are carried out using intentionally created ill-conditioned models. The resultant reconstructions indicate the robust solution is highly suitable, while also showing it has high potential to be applied in the development of an effective yet versatile diagnostic tool for quantifying the distribution of elasticity in various soft tissues. |
| Title |
A scan conversion algorithm for displaying ultrasound images. |
| Author |
Leavitt SC, Hunt BF, Larsen HG. |
| Journal |
Hewlett-Packard Journal |
| Volume |
|
| Year |
1983 |
| Abstract |
NO abstract available. |
| Title |
A search for chromosome damage following exposure of Chinese hamster cells to high intensity, pulsed ultrasound. |
| Author |
Hill CR, Joshi GP, Revell SH. |
| Journal |
Br J Radiol |
| Volume |
|
| Year |
1972 |
| Abstract |
A search has been made for evidence of chromosome damage in V79-379A Chinese hamster cells following exposure for one to two hours to 1 MHz ultrasound at peak intensity 150 W cm(^-2) in pulses of 50 ms duration at a repetition frequency of 1 kHz. In a total of 926 cells examined, chromosome aberration rate was found to be not significantly different from control values. |
| Title |
A search for sonoluminescence in vivo in the human cheek. |
| Author |
Leighton TG, Pickworth MJW, Tudor J, Dendy PP. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1990 |
| Abstract |
In a previous experiment, sonoluminescence was observed in aerated water, especially at the pressure antinodes in the standing-wave field of a physiotherapeutic ultrasound device (Therasonic 1030). Mammalian cells in vitro showed growth inhibition when placed at the pressure antinodes but not at adjacent pressure nodes. In the light of these results, we looked for sonoluminescence in vivo when a similar standing-wave field was set up. To detect luminescence, a light guide was held against the inner surface of the human cheek. This would channel any luminescence photons to a cooled, red-sensitive photomultiplier which would quantify the light. Direct insonation of the cheek produced no detectable luminescence. Similarly when a water bag was placed against the outer surface of the cheek, and the latter was insonated through the bag, no luminescence was detected. Sonoluminescence from the water bag was, however, detected when the bag was placed against the inner surface of the cheek, showing that absorption of sound by the cheek tissue was not preventing cavitation. Further analysis showed that if cavitation had been occurring in the cheek without detection using the system employed, then the resulting sonoluminescence would have to be at most 0.025 times as intense as that produced by an equivalent volume of aerated water. |
| Title |
A search for ultrasonic cavitation within the canine cardiovascular system. |
| Author |
Gross DR, Miller DL, Williams AR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1985 |
| Abstract |
Resonant bubble detectors (RBD) were used to search for both pre-existing bubbles and bubbles created by cavitation within the cardiovascular system of 22 dogs. No pre-existing bubbles of 3.8 micron diam or larger were found, nor were any.created by exposing the left ventricle to 0.51-1.61 MHz ultrasound of up to 16 W/cm2 spatial-peak intensity. Bubbles introduced into the arterial system by high speed injection were readily detected and could be held in the heart by 1 MHz.ultrasound at 1-2 W/cm2 or above. A surprising observation was that gas bubbles of resonant size injected into the left ventricle and held by ultrasound did not multiply continuously as happens in saline or water in vitro. This in vivo system was.designed to assess the potential for cavitation bioeffects and the essentially negative results obtained may limit the expected or potential risk of this mechanism in regard to medical applications of ultrasound. |
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