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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 30 out of 330
| Title |
Acoustic scattering theory applied to soft biological tissues. |
| Author |
Shung KK, Thieme GA. |
| Journal |
Book Chapter |
| Volume |
|
| Year |
1993 |
| Abstract |
Interest in quantitative ultrasound scattering measurements in biological tissues stems from the belief that only a fraction of the total information available in the echo signal is visible in the gray-scale ultrasound image. Much information of potential diagnostic significance concerning tissue characteristics can be made available only through sophisticated signal processing. A more fundamental understanding of the basic acoustic interactions in tissue is a prelude to this processing, which holds the promise for improvement in imaging technology and enhancement in the diagnostic utility of the modality. |
| Title |
Acoustic sizing of an ultrasound contrast agent. |
| Author |
Maresca D,Emmer M,van Neer PLMJ,Vos HJ,Versluis M,Muller M,de Jong N,van der Steen AFW. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2010 |
| Abstract |
Because the properties of ultrasound contrast agent populations after administration to patients are largely unknown, methods able to study them noninvasively are required. In this study, we acoustically performed a size distribution measurement of the ultrasound contrast agent Definity®. Single lipid-shelled microbubbles were insonified at 25 MHz, which is considerably higher than their resonance frequency, so that their acoustic responses depended on their geometrical cross sections only. We calculated the size of each microbubble from their measured backscattered pressures. The acoustic size measurements were compared with optical reference size measurements to test their accuracy. Our acoustic sizing method was applied to 88 individual Definity® bubbles to derive a size distribution of this agent. The size distribution obtained acoustically showed a mean diameter (2.5 μm) and a standard deviation (0.9 μm) in agreement within 8% with the optical reference measurement. At 25 MHz, this method can be applied to bubble sizes larger than 1.2 μm in diameter. It was observed that similar sized bubbles can give different responses (up to a factor 1.5), probably because of shell differences. These limitations should be taken into account when implementing the method in vivo. This acoustic sizing method has potential for estimating the size distribution of an ultrasound contrast agent noninvasively. |
| Title |
Acoustic streaming generated by a focused gaussian beam and finite amplitude tonebursts. |
| Author |
Wu J, Du G. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1993 |
| Abstract |
Theoretical models for calculating the on-axis acoustic streaming velocity generated by a continuous-wave (CW) and pulsed finite.amplitude ultrasonic beams have been developed. Using these models, the on-axis streaming velocity is calculated for unfocused.linear plane wave ultrasonic beams, focused linear Gaussian beams, and unfocused ultrasonic tonebursts of finite amplitude. The.numerical results show that the on-axis streaming velocity is significantly enhanced by the nonlinear harmonic generation of.finite-amplitude ultrasonic tonebursts. . |
| Title |
Acoustic velocity and attenuation of eye tissues at 20 MHz. |
| Author |
de Korte CL, van der Steen AF, Thijssen JM. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1994 |
| Abstract |
The ultrasound velocity and frequency-dependent attenuation of human and porcine eye tissues.(cornea, lens, retina, choroid, sclera, vitreous body) were measured in the frequency range from.17 to 23 MHz. The results for the ultrasound velocity were compared to values taken from the.literature and appeared to be in the same range. A comparison made between the acoustic.parameters of human and porcine eyes showed that the porcine eye can serve as an animal model.for the human eye. A mathematical operation is proposed to extrapolate the attenuation to the.lower frequencies that are commonly used in clinical equipment. Finally, a first attempt was.made to investigate the age dependence of the acoustic parameters of human tissues: some tissues.showed a significant age effect. |
| Title |
Acoustic visualization of transient inhomogeneities induced by intense focused ultrasound in lucite. |
| Author |
Okuyama D, Fry W, Fry FJ, Leichner GH, Kelly-Fry E. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1966 |
| Abstract |
On the basis of analytical considerations, it was first indicated by one of the authors (W.J.F.) that transient inhomogeneities in sound speed induced in media by pulsed acoustic energy of appropriate level would be detectable by standard ultrasonic reflection techniques. [Ultrasonic Energy, Biological Investigations and Medical Applications, Elizabeth Kelly, Ed. (University of Illinois Press, Urbana, 1965)]. This presentation is concerned with describing conditions appropriate for demonstrating such effects in Lucite by employing 3‐Me/sec ultrasound for durations over the range 0.3–1.6 sec. The results obtained indicate that the total energy applied for heating is the significant parameter (for the range of pulse durations employed) whose values can be used to characterize the observed effects. [Investigation supported in part by the National Cancer Institute, National Institutes of Health. Public Health Service, U. S. Department of Health, Education, and Welfare.] |
| Title |
Acoustical evaluation of a prototype sector-vortex phased-array applicator. |
| Author |
Umemura SI, Cain CA. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1992 |
| Abstract |
A prototype sector-vortex phased-array applicator for ultrasound hyperthermia was constructed and acoustically evaluated. The array transducer consists of special lead-titanate ceramic elements of 16 sectors and two tracks attached on a disk-shaped aluminum shell with spherical curvature. Each array element is driven by a complimentary pair of power MOSFET's at 750 kHz. An annular focal field approximated by the Mth order Bessel function is theoretically predicted to be formed when the array elements are driven with a phase distribution that rotates M (
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| Title |
Acoustical study of erythrocyte membranes. |
| Author |
Braginskaya FI, Gendel LY, Zorina OM, Kruglyakova KE, Sadykhova SK, Serysheva OA. |
| Journal |
Sov Phys Acoust |
| Volume |
|
| Year |
1979 |
| Abstract |
The absorption of ultrasound in suspension of erythrocyte membranes (erythrocyte "ghosts") is investigated by a pulse technique in the frequency range from 12 to 68 MHz as a function of the concentration, pH, ultrasonic irradiation, and other modifying factors of the medium. The results indicate that the absorption of ultrasonic energy is attributable to the occurrence of structural relaxation in the applied frequency range. It is hypothesized on the basis of an analysis that the most probable mechanisms of the observed structural relaxation are intramembranous conformational interactions. The minimum relaxation times of the indicated equilibrium structural rearrangements are 10(-7) to 10(-4) sec. The treatment of erythrocyte ghosts with cavitating ultrasound (intensity, 4 W/cm2 at the radiating surface; frequency, 750 kHz) produces a structural modification in the membrane, which is detectable by the spin-probe method. Ultrasonic fragmentation of the ghosts takes place up to a certain critical limit and is attended by a partial loss of membrane protein. The disruption of conformational interactions in insonified erythrocyte membranes causes a reduction in the ultrasonic absorption coefficient in the applied frequency range. |
| Title |
Acoustically-active microbubbles conjugated to liposomes: Characterization of a proposed drug delivery vehicle. |
| Author |
Kheirolomoom A, Dayton PA, Lum AFH, Little E, Paoli EE, Zheng H, Ferrara KW. |
| Journal |
J Cont Rel |
| Volume |
|
| Year |
2007 |
| Abstract |
A new acoustically-active delivery vehicle was developed by conjugating liposomes and microbubbles, using the high affinity interaction between avidin and biotin. Binding between microbubbles and liposomes, each containing 5% DSPE-PEG2kBiotin, was highly dependent on avidin concentration and observed above an avidin concentration of 10 nM. With an optimized avidin and liposome concentration, we measured and calculated as high as 1000 to 10,000 liposomes with average diameters of 200 and 100 nm, respectively, attached to each microbubble. Replacing avidin with neutravidin resulted in 3-fold higher binding, approaching the calculated saturation level. High-speed photography of this new drug delivery vehicle demonstrated that the liposome-bearing microbubbles oscillate in response to an acoustic pulse in a manner similar to microbubble contrast agents. Additionally, microbubbles carrying liposomes could be spatially concentrated on a monolayer of PC-3 cells at the focal point of ultrasound beam. As a result of cell–vehicle contact, the liposomes fused with the cells and internalization of NBD-cholesterol occurred shortly after incubation at 37 °C, with internalization of NBD-cholesterol substantially enhanced in the acoustic focus. |
| Title |
Action of ultrasonic irradiation on the DNA.of cultivated bovine epithelial lens cell. |
| Author |
Treton JA, Courtois Y, Lang J. |
| Journal |
Biomedicine |
| Volume |
|
| Year |
1977 |
| Abstract |
Cultivated epithelial lens cells have been submitted to a 20 kHz continuous.ultrasonic irradiation. At relativity high intensity, destruction of the cells was.observed. At lower intensities, where no cell destruction appeared, the.molecular weight of the single strand DNA of these cells was monitored to.determine whether breakage of DNA molecules was induced by the.ultrasound. No breakage of the single strand DNA was observed for.intensities below 0.1 and 0.4 W cm-2 with irradiation times of less than 20.minutes and 15 seconds, respectively. These intensities and their.corresponding irradiation time are higher than those used in current diagnostic.practice. |
| Title |
Action of ultrasound on a viscoelastic solid. |
| Author |
Frost HM, Nyborg WL. |
| Journal |
Proc Ultrason Int Conf |
| Volume |
|
| Year |
1973 |
| Abstract |
An ultrasonic horn with tip in the form of a wedge with rounded apex was vibrated at 85 kHz while pressed against the edge of a strain-birefringent plastic sample; resulting time-dependent isochromatics characterizing the strain fields in the material were observed through a polarizing microscope. The isochromatics observed in a soft epoxy are often nearly circular in shape, and thus are like those from a static line force; they can be "recorded" or "erased" at will. Dependence of the diameter D of the circular isochromatics on static force, acoustic amplitude, and irradiation time has been studied. Response of the test material to the applied acoustic stress exhibits viscoelastic retardation and non-linearity. Evidence for a phase transition is seen. Near the vibrating tip plastic flow may occur in an acoustic streaming pattern. |
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