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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 28 out of 330
| Title |
Acoustic emissions during 3.1 MHz ultrasound bulk ablation in vitro. |
| Author |
Mast TD, Salgaonkar VA, Karunakaran C, Besse JA, Datta S, Holland CK. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2008 |
| Abstract |
Acoustic emissions associated with cavitation and other bubble activity have previously been observed during ultrasound (US) ablation experiments. Because detectable bubble activity may be related to temperature, tissue state and sonication characteristics, these acoustic emissions are potentially useful for monitoring and control of US ablation. To investigate these relationships, US ablation experiments were performed with simultaneous measurements of acoustic emissions, tissue echogenicity and tissue temperature on fresh bovine liver. Ex vivo tissue was exposed to 0.9-3.3-s bursts of unfocused, continuous-wave, 3.10-MHz US from a miniaturized 32-element array, which performed B-scan imaging with the same piezoelectric elements during brief quiescent periods. Exposures used pressure amplitudes of 0.8-1.4 MPa for exposure times of 6-20 min, sufficient to achieve significant thermal coagulation in all cases. Acoustic emissions received by a 1-MHz, unfocused passive cavitation detector, beamformed A-line signals acquired by the array, and tissue temperature detected by a needle thermocouple were sampled 0.3-1.1 times per second. Tissue echogenicity was quantified by the backscattered echo energy from a fixed region-of-interest within the treated zone. Acoustic emission levels were quantified from the spectra of signals measured by the passive cavitation detector, including subharmonic signal components at 1.55 MHz, broadband signal components within the band 0.3-1.1 MHz and low-frequency components within the band 10-30 kHz. Tissue ablation rates, defined as the thermally ablated volumes per unit time, were assessed by quantitative analysis of digitally imaged, macroscopic tissue sections. Correlation analysis was performed among the averaged and time-dependent acoustic emissions in each band considered, B-mode tissue echogenicity, tissue temperature and ablation rate. Ablation rate correlated significantly with broadband and low-frequency emissions, but was uncorrelated with subharmonic emissions. Subharmonic emissions were found to depend strongly on temperature in a nonlinear manner, with significant emissions occurring within different temperature ranges for each sonication amplitude. These results suggest potential roles for passive detection of acoustic emissions in guidance and control of bulk US ablation treatments. |
| Title |
Acoustic evaluation of american acoustics labs ultrasonic device. |
| Author |
Homans BL, Hedeen RA. |
| Journal |
Rep IIT Res Inst |
| Volume |
|
| Year |
1981 |
| Abstract |
This report presents information relating to the measurement of the American Acoustics Labs Ultrasonic Device presented for test by IIT Research Institute. A description of human hazards, pest control, and vermin control dealing with ultrasonic devices as obtained form a detailed literature search is presented. Following these reviews, the acoustic evaluation as performed in the IITRI Anechoic chamber is described. Conclusions follow at the end of the report. Sound and ultrasound, which are forms of radiant energy other than electromagnetic and particle radiations, have received much attention for pest-control possibilities. Sonic and ultrasonic energy is propagated through air or other materials by means of a mechanical vibratory wave phenomenon associated with pressure differentials in the medium. As with electromagnetic radiation, the frequency and wavelength determine the characteristics of the radiation. The range of audibility for humans falls within the 20 to 20,000 Hz (cps) frequency range. Vibrations above the human auditory response limit are termed ultrasonic. |
| Title |
Acoustic generation of bubbles in excised canine urinary bladders. |
| Author |
Fowlkes JB, Carson PL, Chiang EH, Rubin JM. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1991 |
| Abstract |
A high-intensity, 555-kHz acoustic field was used to generate bubbles within urinary bladders excised from dogs. Following the exposure, bubbles were visualized on a diagnostic ultrasound scanner with a 5-MHz in-line mechanical sector scanhead. Scattering of the high-intensity ultrasound by the bubbles was also observed during the exposure as high-amplitude scan lines. The bladders used had been surgically removed after tying off the ureters and urethra to prevent urine loss and exposure to external contaminants. Each bladder was sealed in a plastic bag filled with a degassed saline solution. The bladder was centered in a sealed degassed water path at the common focus of a 7-cm-diam transducer and a 10-cm-diam brass reflector. The 555-kHz transducer and reflector were both focused at 10 cm and were aligned coaxially. Using various acoustic pressure amplitudes, two, 10-s low-frequency exposures, separated by approximately 30 s, occurred at approximately 2-min intervals. Experiments on a single bladder lasted as long as 45 min. The sizes of the largest bubbles, which were easily imaged, were estimated from rise velocity measurements as 50-70 microns in radius, and pressure amplitudes used to generate those large bubbles were estimated as 10-20 bars. The detection of smaller bubbles was limited by the inability to clearly distinguish bubble echoes from artifacts caused by the reverberant field within the bladder. Visual inspection of the exterior and interior bladder wall showed no significant discoloration within the high intensity beam path. results of this study indicate that bubbles might be generated in vivo from external sources for possible use as echo contrast agents and for studying the bioeffects of acoustic cavitation. |
| Title |
Acoustic generation of intra-arterial contrast boluses. |
| Author |
Ivey JA, Gardner EA, Fowlkes JB, Rubin JM, Carson PL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1995 |
| Abstract |
Microbubbles generated by ultrasonic cavitation in vivo might be useable as flow indicators in some situations instead of injectable contrast agents. Knowledge of those vascular microbubble-generating ultrasonic fields which produce from negligible up to significant damage will help improve guidelines for more effective, safer diagnostic and therapeutic ultrasound. Microbubble boluses have been generated by a 1.8-MHz, focused sound field in the in vivo canine abdominal aorta. Spatial peak acoustic intensities of 19000 W cm/sup -2/ generated microbubble boluses when exposure was longer than 12 ms, whereas intensities greater than 4300 W cm/sup -2/ generated a bolus when exposure was for 250 ms. The onset time of these boluses (less than one cardiac cycle) is unachievable with intravenous contrast injection. With optimized waveforms and focusing, acoustic bolus generation may prove to be an effective, minimally invasive method for fast performance of certain selective angiography. |
| Title |
Acoustic imaging using impulsive sound. |
| Author |
Okujima M, Endoh N. |
| Journal |
Proc Second Meet World Fed Ultrasound Med Biol - Miyazaki |
| Volume |
|
| Year |
1979 |
| Abstract |
No abstract available. |
| Title |
Acoustic interaction of spherical and cylindrical bubbles on plane sheets and ribbons. |
| Author |
Miller DL. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1980 |
| Abstract |
Theory is developed to describe the acoustical interaction of a plane wave with a ribbon of material containing resonant scatterers. Infinitely wide, finite and very narrow ribbons are considered which contain free spherical bubbles, plant-tissue gas bodies (cylindrical bubbles) or bubbles trapped in pores. The interaction leads to a reduction of the pressure amplitude at the bubbles below that of the normally-incident plane wave, and this reduces the resulting pulsation amplitude of the bubbles, especially at resonance. The results are applicable to quantitative studies of physical, chemical, and biological effects of ultrasound when stable cavitation is important. |
| Title |
Acoustic microscopy of mammalian kidney. |
| Author |
Kessler LW, Fields SI, Dunn F. |
| Journal |
J Clin Ultrasound |
| Volume |
|
| Year |
1974 |
| Abstract |
Acoustic micrographs of unstained specimens of mouse kidney were produced at frequencies of 100 MHz and 220 MHz with resolutions of 20?m and 9 ?m, respectively. The acoustically revealed structure has been examined in relation to established microanatomy. High contrast details corresponding to connective tissue boundaries of supporting elements of the nephron are exhibited. In addition, various regions of the kidney such as the cortex and the three medullary regions can be differentiated. At these frequencies, the acoustically exhibited structures are considered to result from scattering at connective tissue interfaces, resulting from local acoustic impedance discontinuities, rather than from intrinsic acoustic absorption with in the microstructures of the tissue. |
| Title |
Acoustic microstreaming around an isolated encapsulated microbubble. |
| Author |
Liu X, Wu J. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2009 |
| Abstract |
An analytical theory has been developed to calculate microstreaming velocity inside and outside an encapsulated microbubble (EMB) in a viscous liquid produced by its oscillations driven by an ultrasound field, taking account of two predominant modes of the EMB's motion: a monopole (pulsation) and a dipole (translational harmonic vibrations). Analytical expressions of radial as well as tangential stresses are derived near the shell of the EMB. Numerical calculations in parameter regimes applicable to sonoporation are presented. For the calculation the following parameters unless specified otherwise are used: f=1 MHz, r(0)=2 microm, kappa=1.4, rho(L)=1000 kg/m(3), rho(s)=1100 kg/m(3), P(0)=100 kPa, micro(s)=0.05 Pa s, micro(L)=0.001 Pa s, sigma(1)=0.04 N/m, sigma(2)=0.005 N/m, and G(s)=15 MPa. The calculated results show that the streaming velocity and stresses near an EMB are functions of the mechanical properties of shell and gas. Overall, the streaming velocity and stresses for an EMB are found to be greater than those for a similar size free bubble under the same ultrasound excitation. This finding is consistent with the existing theory of acoustic streaming of an oscillating bubble near a boundary given by Nyborg (1958). |
| Title |
Acoustic modeling of shell-encapsulated gas bubbles. |
| Author |
Frinking PJA, Jong ND. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1998 |
| Abstract |
Existing theoretical models do not adequately describe the scatter and attenuation properties of the ultrasound contrast agents Quantison and Myomap. An adapted version of the Rayleigh-Plesset equation, in which the shell is described by a viscoelastic solid, is proposed and validated for these agents and Albunex®. The acoustic transmission and scattering are measured in the frequency band from 1-10 MHz. The measured transmission is used to estimate two parameters, the effective bulk modulus, Keff, describing the elasticity, and the friction parameter, SF, describing the viscosity of the shell. For the scattering, the difference between measurements and calculations is < 3 dB. For Quantison, the effective bulk modulus is independent of the bubble diameter. For Albunex®, it increases for decreasing bubble diameter. The nonlinear response of Quantison is minimal for acoustic pressures up to 200 kPa. For acoustic pressures above 200 kPa, the measured scattering abruptly increases. This increase reaches a level of 20 dB for an acoustic pressure of 1.8 MPa. This response cannot be predicted by the theoretical model developed in this article. |
| Title |
acoustic output measurement and labeling standard for diagnostic ultrasound equipment. |
| Author |
Unknown. |
| Journal |
Rep AIUM |
| Volume |
|
| Year |
1992 |
| Abstract |
No abstract available. |
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