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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 199 out of 330
| Title |
Physical mechanisms of the action of intense ultrasound on tissue. |
| Author |
Dunn F. |
| Journal |
J Phys Med |
| Volume |
|
| Year |
1958 |
| Abstract |
No abstract available. |
| Title |
Physical principles of ultrasound. |
| Author |
Kremkau FW. |
| Journal |
Semin Roentgenol |
| Volume |
|
| Year |
1975 |
| Abstract |
Ultrasound has characteristics that enable it to yield information concerning internal body structures. Let us first describe what ultrasound is and then consider those characteristics that make it useful in sonography. Then we will discuss the means by which ultrasound is generated and received. A list of definitions is presented in the Glossary for ready reference. Greater detail may be found in the References. |
| Title |
Pitfalls in quantitative contrast echocardiography: the steps to quantitation of perfusion. |
| Author |
Wiencek JG, Feinstein SB, Walker R, Aronson S. |
| Journal |
J Am Soc Echocardiogr |
| Volume |
|
| Year |
1993 |
| Abstract |
Current methods used clinically to assess myocardial perfusion are invasive and expensive. As.the technology of ultrasound imaging improves, CE may provide a relatively inexpensive,.noninvasive means of quantitating myocardial perfusion. Issues regarding stability of.microbubble contrast agents must be studied more closely under physiologic conditions. As.such, encapsulated microbubbles may provide more stability under physiologic pressures than.free gas microbubbles. Introducing high concentrations of contrast, either by hyperconcentrating.the contrast agent or by increasing the injection rate, may provide greater stability under.physiologic conditions. Further, before quantitative statement of tissue perfusion can be made,.the relationship between tracer concentration and system response must be established. Further, a."linear" postprocessing ultrasound setting does not eliminate this requirement as data must still.undergo nonlinear transformation during log compression and time-gain compensation..Additionally, issues regarding "electronic thresholding" must be explored more extensively in.vivo. Commercial ultrasound scanners, in their present form, may not offer adequate sensitivity.for absolute quantitative studies. Further development of modified ultrasound systems may provide sufficient sensitivity for quantitative perfusion imaging. CE offers a potentially powerful tool in the clinical management of patients with ischemic heart disease. Conventional coronary angiography provides information on the size of a lesion, but accompanying tissue perfusion distal to the lesion cannot be determined. Doppler ultrasonography determines velocity of blood flow in large vessels but does not offer the potential to quantitate tissue perfusion. Clearly, CE has a place in the future of diagnostic imaging. The recent work of Ito et al. demonstrated the qualitative potential of CE in the identification of "areas at risk" in patients who had undergone thrombolysis or percutaneous transluminal coronary angioplasty after an acute myocardial infarction. With further improvement in the ultrasound imaging techniques and microbubble stability, CE may offer an inexpensive, noninvasive means of assessing myocardial perfusion. |
| Title |
Plasma membrane poration induced by ultrasound exposure: Implication for drug delivery. |
| Author |
Mehier-Humbert S, Bettinger T, Yan F, Guy RH. |
| Journal |
J Cont Rel |
| Volume |
|
| Year |
2005 |
| Abstract |
Sonoporation, in the presence of ultrasound contrast agents (UCA), is a technique that permits the transfer of drugs, including genes, into cells. In this study, the size of the pores created by ultrasound application, and the duration of the pore opening, have been characterized via indirect molecular probing and microscopic observation. Internalization of molecules with diameters up to 37 nm was efficient and generally well-tolerated; on the other hand, confocal microscopy revealed that 75 nm particles entered only a few cells when sonoporation was applied. In general, the larger the species to internalize, the poorer the transfer. Direct visualization of pores following insonification, using scanning electron microscopy, was hampered by the presence of numerous villi on the surface of the cells employed (MAT B III), and by the short duration of pore opening. Clearer observations of porated regions were possible using red blood cells. T his research (i) confirms that sonoporation is a means with which to achieve macromolecule delivery into cells, and (ii) characterizes in some detail the phenomenon of ultrasound induction of transient pores in the cell membrane. |
| Title |
Platelet aggregation in vivo by therapeutic ultrasound. |
| Author |
Zarod AP, Williams AR. |
| Journal |
Lancet |
| Volume |
|
| Year |
1977 |
| Abstract |
No abstract available. |
| Title |
Platelet aggregation induced by ultrasound under specialized conditions in vitro. |
| Author |
Miller DL, Nyborg WL, Whitcomb CC. |
| Journal |
Science |
| Volume |
|
| Year |
1979 |
| Abstract |
Human platelets were induced by 2.1-megahertz ultrasound to form aggregates around gas-filled pores in membranes immersed in platelet-rich plasma. The spatial peak intensities required were only about 16 to 32 milliwatts per square centimeter. Ultrasound generated by a medical Doppler device, whose intensity exceeded this, induced aggregate formation under the same conditions. |
| Title |
Poroelastography: imaging the poroelastic properties of tissues. |
| Author |
Konofagou EE, Harrigan TP, Ophir J, Krouskop TA. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2001 |
| Abstract |
In the field of elastography, biological tissues are conveniently assumed to be purely elastic solids. However, several tissues, including brain, cartilage and edematous soft tissues, have long been known to be poroelastic. The objective of this study is to show the feasibility of imaging the poroelastic properties of tissue-like materials. A poroelastic material is a material saturated with fluid that flows relative to a deforming solid matrix. In this paper, we describe a method for estimating the poroelastic attributes of tissues. It has been analytically shown that during stress relaxation of a poroelastic material (i.e., sustained application of a constant applied strain over time), the lateral-to-axial strain ratio decreases exponentially with time toward the Poisson?s ratio of the solid matrix. The time constant of this variation depends on the elastic modulus of the solid matrix, its permeability and its dimension along the direction of fluid flow. Recently, we described an elastographic method that can be used to map axial and lateral tissue strains. In this study, we use the same method in a stress relaxation case to measure the time-dependent lateral-to-axial strain ratio in poroelastic materials. The resulting time-sequenced images (poroelastograms) depict the spatial distribution of the fluid within the solid at each time instant, and help to differentiate poroelastic materials of distinct Poisson?s ratios and permeabilities of the solid matrix. Results are shown from finite-element simulations. |
| Title |
Portable ultrasound device for battlefield trauma. |
| Author |
Hwang J-J, Quistgaard J, Souquet J, Crum LA. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1998 |
| Abstract |
A handheld device is developed for imaging soft tissue as well as blood flow with high quality in real time. Four component ASICs for digital beamforming, signal processing and scan conversion are designed and integrated with a convex array scanhead in this device. The device can be either battery driven or AC powered with image storage and cineloop playback capability. It weighs less than five pounds. In addition to diagnosing trauma in the combat battlefield, this device can also be used in a variety of mobile diagnostic applications, bringing quality medical imaging to the bedside, areas of natural disaster, or remote areas that do not have access to medical imaging. |
| Title |
Positive and negative effects of diagnostic intensities of ultrasound on erythrocyte blood group markers. |
| Author |
Rosenfeld E, Romanowski U, Williams AR. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1990 |
| Abstract |
Human erythrocytes were exposed in vitro to diagnostic intensities of ultrasound.Various antigenic tests were conducted to see if the different blood group markers had been changed. No change was observed following sonication for Ss, M, K1, ABO, and the rhesus factors. However a marked reduction was found for the N antigen when assayed using the lectin isolated from Vicia graminea. Several experiments were performed to ensure that this effect was not an artefact. If the cells were not resuspended in fresh medium immediately following sonicating then the magnitude of the effect rapidly decreased. We were unable to detect free N antigen in the supernatants from the sonicated cell suspensions. We were also unable to demonstrate changes in the level of the N antigen following sonication if we used anti-N sera from rabbits. A surprising observation was that different batches of the lectin preparation from the same manufacturer could eliminate the effect. |
| Title |
Possibility of microcavitation from diagnostic ultrasound. |
| Author |
Apfel RE. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1986 |
| Abstract |
There is little or no definitive data in the literature that addresses the question of the possibility of adverse bioeffects in a single biological cell due to diagnostic ultrasound. A formula is derived that predicts the conditions that will produce transient acoustic cavitation on the scale of a single biological cell in one acoustic cycle. It is found that if the viscosity of the cellular medium or its surroundings is sufficiently low (within a factor of two or three of water, as with plasma) and if the frequency is sufficiently low (below 2-3 MHz), then some current diagnostic units may produce microcavitation when a small cavitation nuclei exits in or near a cell. |
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