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BRL Abstracts Database |
Your search for ultrasound produced 3296 results. Page 55 out of 330
Title |
Biological effects of ultrasound: development of safety guidelines. Part I: personal histories. |
Author |
Nyborg WL. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
2000 |
Abstract |
After the end of World War II, advances in ultrasound (US) technology brought improved possibilities for medical applications. The first major efforts in this direction were in the use of US to treat diseases. Medical studies were accompanied by experiments with laboratory animals and other model systems to investigate basic biological questions and to obtain better understanding of mechanisms. Also, improvements were made in methods for measuring and controlling acoustical quantities such as power, intensity and pressure. When diagnostic US became widely used, the scope of biological and physical studies was expanded to include conditions for addressing relevant safety matters. In this historical review, a major part of the story is told by 21 investigators who took part in it. Each was invited to prepare a brief personal account of his/her area(s) of research, emphasizing the "early days," but including later work, showing how late and early work are related, if possible, and including anecdotal material about mentors, colleagues, etc. |
Title |
Biological effects of ultrasound: development of safety guidelines. Part II: general review. |
Author |
Nyborg WL. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
2000 |
Abstract |
In the 1920s, the availability of piezoelectric materials and electronic devices made it possible to produce ultrasound (US) in water at high amplitudes, so that it could be detected after propagation through large distances. Laboratory experiments with this new mechanical form of radiation showed that it was capable of producing an astonishing variety of physical, chemical and biologic effects. In this review, the early findings on bioeffects are discussed, especially those from experiments done in the first few decades, as well as the concepts employed in explaining them. Some recent findings are discussed also, noting how the old and the new are related. In the first few decades, bioeffects research was motivated partly by curiosity, and partly by the wish to increase the effectiveness and ensure the safety of therapeutic US. Beginning in the 1970s, the motivation has come also from the need for safety guidelines relevant to diagnostic US. Instrumentation was developed for measuring acoustic pressure in the fields of pulsed and focused US employed, and standards were established for specifying the fields of commercial equipment. Critical levels of US quantities were determined from laboratory experiments, together with biophysical analysis, for bioeffects produced by thermal and nonthermal mechanisms. These are the basis for safety advice and guidelines recommended or being considered by national, international, professional and governmental organizations. |
Title |
Biological effects of ultrasound: Rationale for the measurement of selected ultrasonic output quantities. |
Author |
O'Brien WD Jr. |
Journal |
Echocardiography |
Volume |
|
Year |
1986 |
Abstract |
Research into the biological effects of ultrasound is a two-edged sword. On the one hand, there is the potential to show that some of the current clinical practices with diagnostic ultrasound may be more risky than previously thought. If so, clinical practice with ultrasound may have to be modified based upon a reassessment of its risk. On the other hand, such research could identify potential benefits in terms of therapeutic applications of ultrasound. In either case, the care provided to patients with ultrasound would have been improved, although the short-term impact of a newly identified ultrasonically induced biological effect might tend to affect adversely the diagnostic side.
There has been a considerable amount of research into how ultrasound affects developmental tissue because a large fraction of all pregnant women have their fetuses examined with ultrasound. In fact, virtually all of the biological effect literature has been carefully evaluated in terms of assessing the risk from ultrasound on the fetus. It is encouraging that the risk to the fetus is viewed as a "potential risk." LIttle, if any, examination of this literature has been brought to bear on assessing the potential risk of ultrasonic energy on nondevelopmental tissue.
In the past six years, there have been so many reviews of ultrasonically induced biological effects that it is not possible to duplicate this effort in this article. Further, these extensive reviews provide a comprehensive bibliography for anyone who desires to study this topic in greater depth than will be provided here.
This review will examine the relationship between the ultrasonic output quantities of current diagnostic ultrasound imaging equipment and the biological basis for such measurements. Specifically, the basis for measuring specific exposure quantities lies in the fundamental mechanisms responsible for causing biological alterations to living systems. |
Title |
Biomedical photoacoustics beyond thermal expansion using triggered nanodroplet vaporization for contrast-enhanced imaging. |
Author |
Wilson K, Homan K, Emelianov S. |
Journal |
Nat Commun |
Volume |
|
Year |
2012 |
Abstract |
Since being discovered by Alexander Bell, photoacoustics may again be seeing major resurgence in biomedical imaging. Photoacoustics is a non-ionizing, functional imaging modality capable of high contrast images of optical absorption at depths significantly greater than traditional optical imaging techniques. Optical contrast agents have been used to extend photoacoustics to molecular imaging. Here we introduce an exogenous contrast agent that utilizes vaporization for photoacoustic signal generation, providing significantly higher signal amplitude than that from the traditionally used mechanism, thermal expansion. Our agent consists of liquid perfluorocarbon nanodroplets with encapsulated plasmonic nanoparticles, entitled photoacoustic nanodroplets. Upon pulsed laser irradiation, liquid perfluorocarbon undergoes a liquid-to-gas phase transition generating giant photoacoustic transients from these dwarf nanoparticles. Once triggered, the gaseous phase provides ultrasound contrast enhancement. We demonstrate in phantom and animal studies that photoacoustic nanodroplets act as dual-contrast agents for both photoacoustic and ultrasound imaging through optically triggered vaporization. |
Title |
Biomedical ultrasound beam forming. |
Author |
Lu JY, Zou H, Greenleaf JF. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1994 |
Abstract |
The principles of biomedical ultrasound beam forming control the quality of diagnostic imaging. Beam parameters associated with imaging quality are: (1) lateral and axial resolutions; (2) depth of field; (3) contrast and (4) frame rate. In this paper, we review some of the current beam forming techniques and their principles. We focus on trade-offs among the above four aspects of beam forming and relate them to system parameters such as aperture size, f-number (the ratio between focal length and aperture diameter), central frequency (wavelength), system bandwidth and sidelobes. Methods for steering conventional and limited diffraction beams with array transducers are also reviewed. |
Title |
Biomolecular absorption of ultrasound. I: Molecular.weight. |
Author |
Kremkau FW, Cowgill RW. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
1984 |
Abstract |
Amino acid solutions have absorptions which are generally small compared to those for proteins. Proteolytic enzyme treatment of proteins in solution reduces their absorption. These observations suggest that absorption increases with molecular weight. However, measurements of sugars, polysaccharides, amino acids, and proteins yield no correlations of absorption with molecular weight within these groups. Therefore, it is concluded that absorption increases in these molecules with.increasing molecular weight only in a threshold sense, with absorption increasing significantly only in a restricted molecular weight range. This range may approximate that observed for polyethylene glycol and dextran, viz., 1 to 100 monomer units. However, there is some indication that the transition range may.be narrower than a factor of 100 in molecular weight. |
Title |
Biomolecular absorption of ultrasound. III. Solvent.interactions. |
Author |
Kremkau FW. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
1988 |
Abstract |
Absorption coefficients for several biomolecules have been measured to determine the role of solvent interactions in the absorption characteristics of biomolecules at neutral pH. The presence of phosphate buffer ions in aqueous solvent dramatically increases the absorption of small biomolecules (sugars and amino acids). These increases suggest the importance of solvent interactions in absorption. For large molecules (proteins and polysaccharides), buffer ion effects are lessened and the role of solvent interactions is not as clear. Absorptions of hemoglobin are.essentially the same in each of five aqueous solvents and are greater in nonaqueous solvents. Solvation interactions may be inhibited by the tertiary structure of globular proteins. Solvation apparently does contribute to absorption in biomolecules along with other physicochemical processes. . |
Title |
Biomolecular absorption of ultrasound: II. Molecular.structure. |
Author |
Kremkau FW, Cowgill RW. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
1985 |
Abstract |
Measurements of absorption coefficients in several globular and linear proteins yield no correlations of absorption with alpha-helix content or with the number of polypeptide chains in the protein. Removal of all but the primary structure with denaturing agents that convert proteins to random chains causes only small changes in the absorption of globular proteins. Complete denaturing of linear muscle proteins results in large reductions in absorption. Therefore, it is concluded that absorption in globular proteins is insensitive to structural characteristics while in linear proteins it is dependent upon the amount of alpha-helix content. An alternative explanation of the results is that alpha-helix contributes to absorption.in both globular and linear proteins but tertiary structure in globular proteins reduces absorption because of inhibited solvent interactions. |
Title |
Biophysical effects of ultrasound at therapeutic intensities. |
Author |
Coakley WT. |
Journal |
Physiotherapy |
Volume |
|
Year |
1978 |
Abstract |
No abstract available |
Title |
Biophysical implications of bubble dynamics. |
Author |
Nyborg WL, Miller DL. |
Journal |
Appl Sci Res |
Volume |
|
Year |
1982 |
Abstract |
Evidence is reviewed, from theory and experiment, that biological systems can be affected by ultrasound at low levels, if resonant gas bodies are present. In a suspension of cells or other particles a pulsating gas bubble causes the particles to migrate toward its surface via radiation force. This motion, in addition to acoustic microstreaming, transports particles into the bubble near-field where they are subjected to highly localized stress fields. In plant leaves containing gas-filled channels, the ultrasonic intensity required to produce cell death varies with frequency, showing minima in ranges corresponding roughly to calculated frequencies for resonance of the channels. |
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