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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 27 out of 330
| Title |
Acoustic cavitation generated by microsecond pulses of ultrasound. |
| Author |
Crum LA, Fowlkes JB. |
| Journal |
Nature |
| Volume |
|
| Year |
1986 |
| Abstract |
Under extreme acoustic stress liquids can be caused to rupture, with the transient generation of a vapour cavity. The subsequent collapse of these cavities is normally violent enough to be observed with the unaided eye or ear, and often generates free radicals due to the high temperatures and pressures associated with the collapse. Flynn (1982) has calculated that microsecond pulses of ultrasound with peak intensities in the range 10-30 W cm/sup -2/ can generate transient cavitation in water. Because some diagnostic ultrasound systems now in clinical use generate microsecond length pulses with temporal peak intensities >100 W cm/sup -2/, there is reason to believe that this mechanism could operate in diagnostic conditions in aqueous media. It is shown that ultrasonic pulses as short as one cycle at a frequency of 1.0 MHz give rise to luminescence flashes characteristic of violent cavitation. This provides the first experimental confirmation of Flynn's theoretical calculations. |
| Title |
Acoustic cavitation in phacoemulsification: Chemical effects, modes of action and cavitation index. |
| Author |
Topaz M, Motiel M, Assia E, Meyerstein D, Meyerstein N, Gedanken A. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2002 |
| Abstract |
High-intensity ultrasound (US) energy (HIUE) has been extensively used in the last 3 decades in a wide range of surgical procedures, including phacoemulsification. The generation of radicals and sonoluminescence (SL) by application of continuous-wave (CW) HIUE to an aqueous medium under conditions simulating cataract phacoemulsification surgery is demonstrated by electron paramagnetic resonance (EPR) spectroscopy and a sensitive photon-detecting system. The findings provide direct evidence for the generation of acoustic cavitation in the simulated intraocular environment, pointing out that generation of acoustic cavitation in clinical phacoemulsification and other surgical applications of US is possible. The findings imply that the effects of acoustic cavitation in aqueous medium may contribute to the endothelial damage observed clinically following phacoemulsification cataract surgery. Saturation of the irrigating solution with various gases modifies the acoustic cavitation. Saturation of the irrigating solution with CO2 practically eliminates acoustic cavitation, with the concomitant elimination of radicals and SonL. CO2 may be utilized clinically to suppress acoustic cavitation in phacoemulsification and other medical applications. A cavitation index (CI) is introduced for the purpose of standardizing phacoemulsification instrumentation and other medical US devices that employ HIUE.
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| Title |
Acoustic cavitation produced by microsecond pulses of ultrasound: A discussion of some selected results. |
| Author |
Crum LA, Roy RA, Dinno MA, Church CC, Apfel RE, Holland CK, Madanshetty SI. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1992 |
| Abstract |
Because of its extensive utilization in clinical practice, and because the subjects examined are often fragile and sensitive to trauma, the safety of diagnostic ultrasound has always been of concern. Of the various mechanisms through which ultrasound could act in a manner deleterious to a patient, acoustic cavitation, should it occur, appears to possess significant potential for biological damage. This paper reviews several recent reports of progress by our two groups and.demonstrates the conditions under which cavitation has been observed by microsecond pulses of ultrasound. Although these results give no indications that diagnostic ultrasound may pose a true.risk to a patient, they do indicate that in vivo cavitation may occur under certain conditions. .. |
| Title |
Acoustic cavitation series: Part six, Gas body activation. |
| Author |
Miller DL. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1984 |
| Abstract |
A small body of gas which is stabilized against dissolution in a liquid by a supportive structure may oscillate in response to an ultrasonic field and this form of cavitation is termed gas body activation. Linear theory describes the response of gas-filled intercellular channels in plant tissue and of gas-filled micropores in thin sheets of plastic. Calculations from this theory yield good agreement with indirect observations of resonance frequencies and rough agreement with direct.measures of aggregate response (transmission and reflection coefficients). Studies of gas body activation in biological systems should allow quantitative analysis of cavitation bioeffects for relatively low-intensity ultrasound applications. |
| Title |
Acoustic cavitation thresholds and cyclic processes. |
| Author |
Neppiras EA. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1980 |
| Abstract |
There is currently renewed interest in previous termcavitation thresholdsnext term in connection with industrial and medical applications of ultrasound. This paper is a review of the theory relating to previous termthresholds.next term In particular, it shows how these previous termthresholdsnext term can be located using simple approximate formulae. The paper also examines a number of interesting previous termcyclic processesnext term that take place around the previous termthresholds.next term The paper is an expanded form of recent seminars. |
| Title |
Acoustic cavitation: a possible consequence of biomedical uses of ultrasound. |
| Author |
Apfel RE. |
| Journal |
Br J Cancer Suppl |
| Volume |
|
| Year |
1982 |
| Abstract |
Those concerned with acoustic cavitation often use different measures and nomenclature to those who employ ultrasound for medical purposes. After illustrating the connections between the two, acoustic cavitation phenomena are divided into two classes: (1) relatively moderate amplitude changes in the bubble size that occur during each acoustic cycle, as with rectified diffusion and resonant bubble motion, and (2) rather dramatic changes in the bubble radius that occur in one cycle. It is seen that pulse-echo diagnostic equipment can excite the dramatic changes whereas continuous wave therapeutic equipment will excite the slower, but no less important, changes. The ranges of the acoustic variables and material states for which these phenomena are possible are quantified. It is shown that whereas the concept of an ultrasonic (energy) dose may be appropriate for the effects of acoustically induced heating or resonant bubble motion. It is inappropriate when discussing the effects of the transient type of cavitation that can occur from short, high amplitude acoustic pulses. |
| Title |
Acoustic dispersion and the propagation of hypersound in liquids. |
| Author |
Pesin MS, Fabelinskii IL. |
| Journal |
Sov Phys Dokl |
| Volume |
|
| Year |
1958 |
| Abstract |
I. Acoustic dispersion in liquids has been the subject of many investigations [1] both because of the great physical interest of the problem and also because with the exception of acetic and propionic acids [2-4] and more recently carbon bisulfide [5] low-viscosity liquids do not exhibit acoustic dispersion in the ultrasonic region (10(^6)-10(^8)cps). The quadratic dependence of the sound absorption coefficient a on sound frequency f in such low-viscosity liquids as benzene, carbon tetrachloride and many others, which is maintained up to the highest frequencies at which experiments were performed (f~ 200 Mc), suggests that acoustic dispersion would appear in these liquids at still higher frequencies (10(^9)-10(^10)cps). The artificial generation and transmission of such sound waves to liquids is still too difficult. We therefore determine the velocity of hypersound (10(^10) cps) from the fine structure of a Rayleigh line, for comparison with the velocity of ultrasound in these liquids under the same conditions, as a basis for quantitative conclusions concerning acoustic dispersion. Such investigations were attempted a long time ago [6-8] but the first encouraging results were obtained only recently [9-11]. II. The velocity of hypersound as determined from measurements of the distances between fine structure components of scattered light in liquids still does not exceed 2-5% in accuracy, which is much below the accuracy of modern methods of determining sound velocities. Therefore such experiments make it possible to detect acoustic dispersion only when it is of very appreciable magnitude. |
| Title |
Acoustic dispersion in liquid triethylamine. |
| Author |
Aliev SS, Parpiev K, Khabibullaev PK. |
| Journal |
Sov Phys Acoust |
| Volume |
|
| Year |
1970 [1969] |
| Abstract |
The results are presented from a measurement of the attenuation and velocity of ultrasound in liquid triethylamine. The coefficient of sound attenuation was measured by pulse techniques in the frequency range from ~10(^7) to 10(^9) cps in the temperature interval from 10 to 50?C. The velocity of sound was measured by the phase method. Acoustic dispersion is produced in liquid triethylamine by rotational-isomer relaxation and is characterized in the indicated frequency range by a single relaxation time. |
| Title |
Acoustic droplet vaporization for therapeutic and diagnostic applications. |
| Author |
Kripfgans OD, Fowlkes JB, Miller DL, Eldevik OP, Carson PL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2000 |
| Abstract |
A phase shift droplet emulsion is introduced as an aid to unusual ultrasound (US) applications. The transpulmonary droplet emulsion (90% < 6 microm diameter) is made by mixing saline, bovine albumin and dodecafluoropentane. It has been observed that an acoustic pressure threshold exists, above which the droplets vaporize into bubbles approximately 25 times the original diameter. For frequencies between 1.5 and 8 MHz, the threshold decreases from 4.5 to 0.75 MPa peak rarefactional pressure. This paper presents preliminary results for droplet preparation and their evaporation as a function of applied acoustic pressure and frequency, as well as simulations of the lifetime of these gas bubbles based on gas diffusion. In vivo experiments were simulated by the evaporation of droplets in blood flowing under attenuating material. We propose that this agent might be useful for tissue occlusion in cancer treatment, as well as for phase aberration corrections in acoustic imaging. |
| Title |
Acoustic emission as a measure of exposure of suspended cells in vitro. |
| Author |
Edmonds PD, Ross P. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1985 |
| Abstract |
Cell viability, survival, and growth of C1300 mouse neuroblastoma cells were assayed by trypan blue dye exclusion, clonogenesis, and culturing, respectively, after exposure in suspension to therapeutic levels of ultrasound (1 MHz; continuous wave; spatial peak intensity 0.9, 1.7, and 2.6 W/cm2; 5 min at 37°C). Acoustic emission from the cavitating cell suspensions was recorded as the rms value of the half-harmonic and noise components combined. Cell viability and survival appeared better correlated with acoustic emission than with spatial peak intensity, implying that acoustic emission may provide a more direct measure of insult to the cells in a cavitating field than the incident intensity. Biological assay results of growth were well correlated with spatial peak intensity but not with acoustic emission levels, which seems to imply that for this end point incident intensity is a more directly interacting parameter than cavitational activity, provided however that the latter is present. Further refinement of the technique for measuring acoustic emission from cell suspensions should permit separate measurements of the half-harmonic and noise components. When thus refined, it may provide the means to demonstrate cavitational action without resorting to additional experiments to suppress cavitation. |
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