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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 188 out of 330
| Title |
Nonviral transfection of suspension cells in ultrasound standing wave fields. |
| Author |
Lee Y,Peng C. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2007 |
| Abstract |
Ultrasound-induced cavitation has been widely used for delivering DNA vectors into cells. However, this approach may seriously disrupt cell membranes and cause lethal damage when cells are exposed to the inertial cavitation field. In this study, instead of using sonoporation, ultrasound standing wave fields (USWF) were explored for nonviral transfection of suspension cells. Acoustic resonance in a tubular chamber was generated from the interference of waves emitted from a piezoelectric transducer and consequently reflected from a borosilicate glass coverslip. The suspended K562 erythroleukemia cells were transfected by polyethyleneimine (PEI)/DNA complexes with and without exposure to 1-MHz USWF for 5 min. During USWF exposure, K562 cells moved to the pressure nodal planes first and formed cell bands by the primary radiation force. Nanometer-sized PEI/DNA complexes, circulated between nodal planes by acoustic microstreaming, then used the cell agglomerates as the nucleating sites on which to attach. After incubation at 37 degrees C for 48 h, the efficiency of nonviral transfection based on EGFP transgene expression was determined by fluorescent microscopy and fluorometry. Both studies showed that USWF brought suspended K562 cells and PEI/DNA complexes into close contact at the pressure nodal planes, yielding an approximately 10-fold increment of EGFP transgene expression compared with the group without ultrasonic treatment. |
| Title |
North Shields. |
| Author |
Unknown. |
| Journal |
Med World News |
| Volume |
|
| Year |
1973 |
| Abstract |
A simple and reliable method for early diagnosis of multiple pregnancy is reported by two British physicians. Drs. Peter Barker and Denis Cashman employ two ultrasonic devices simultaneously while attempting to find separate sites where fetal heart sounds are clearly audible. If there is more than one heart, the sounds on the machines will not be synchronous. They suggest that 24 weeks of pregnancy is a good time to obtain an accurate diagnosis using the ultrasound machines. |
| Title |
Novel approach to evaluate the interaction of pulsed ultrasound with embryonic development. |
| Author |
Barnett SB Walsh DA Angles JA. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1990 |
| Abstract |
An in vitro whole-embryo culture system was used which allowed ultrasound to interact directly with rat embryos, at 9.5 days of gestation, under conditions of controlled temperature. Neural plate damage, expressed during a critical period of forebrain development, was evaluated 48 h post-insonation. Ultrasound-induced effects were thus identified in the absence of significant temperature changes or complications from the influence of maternal physiology. Exposures to 3.2 microseconds pulses of 3.14 MHz ultrasound at a PRF of 2 kHz and 1.2 W cm-2 intensity (ISPTA) for durations of 5, 15 or 30 min produced no major morphological abnormalities at a temperature of 38.5 degrees C. Embryonic response to stress was evidenced by changes in protein synthesis, and delayed development was indicated by a reduction in somite number. These effects were enhanced when the insonation temperature was elevated by 1.5 degrees C. |
| Title |
Nuclear medicine and ultrasound: Correlation in diagnosis of disease of liver and biliary tract. |
| Author |
Lomonaco A, Kline P, Halpern S, Leopold G. |
| Journal |
Semin Nucl Med |
| Volume |
|
| Year |
1975 |
| Abstract |
Even though the radiocolloid scan is nonspecific it will be approximately 70%-80% accurate in predicting the presence or absence of liver disease and somewhat less accurate than that in making statements as to the specific type of disease. This compares well with other modalities. The ability of nuclear medicine techniques to provide a correct diagnosis is improved when additional isotopic techniques such as hepatic blood flow studies and 131I-rose bengal and 67Ga scanning are performed. Ultrasound scanning is also non specific. To date, the major application of ultrasound in the study of the liver has been in deciphering puzzling contour abnormalities seen on nuclear medicine scans and in demonstrating fluid-filled abnormalities. Its usefulness in diffuse and solid focal lesions has been less dramatic. More recently, however, the development of gray scale has necessitated a reevaluation of the technique. Gray scale demonstrates a large number of intrahepatic interfaces that were previously invisible, and it has already been shown to demonstrate focal disorders such as metastasis more easily than the nongray-scale method. It can also demonstrate dilated biliary radicals, the gallbladder, and gallstones. In addition, while routinely studying the liver one can evaluate diaphragmatic motion and various retroperitoneal structures such as the pancreas, lymph nodes, and abdominal vascular structures. |
| Title |
Nucleation and evolution of ultrasonic cavitation in a rotating exposure chamber. |
| Author |
Miller DL, Williams AR. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1992 |
| Abstract |
The nucleation and progression of ultrasonic cavitation in a rotating exposure chamber were investigated by observing hemolysis of a 0.5% suspension of erythrocytes. Bursts of 1.6 MHz ultrasound beams of 11 W/cm2 spatial peak intensity were synchronized with the rotation to aim the bursts down the axis of a cylindrical chamber. Cavitational hemolysis always occurred in fresh phosphate buffered saline (PBS) solution, but cavitation incidence declined to 38% in 4 day old PBS. The amount of hemolysis for 11 ms or 44 ms bursts with 60 rpm rotation increased in proportion to the number of bursts. Hemolysis was found above a minimum burst duration of 5.5 to 8.3 ms in the normal 2 cm chamber. This did not appear to change for 1 cm or 4 cm chamber lengths, but it did change to about 2.2 ms and about 44 ms for over- and undersaturated gas conditions, respectively. Off-times associated with rotation speeds of 15 to 30 rpm reduced the effectiveness of the cavitation, and addition of fixed cells at only 0.01% to 0.02% greatly reduced the hemolysis. For this ultrasonic exposure system, several thousand bubbles, possibly generated from as few as one cavitation nucleus, move across the chamber at up to 10 m/s, each lysing a few hundred cells, and then are cycled back to the front of the chamber by the rotation to reinitiate the cavitation on the next burst.
|
| Title |
Nucleation and stabilization of microbubbles in liquids. |
| Author |
Crum LA. |
| Journal |
Appl Sci Res |
| Volume |
|
| Year |
1982 |
| Abstract |
An important aspect of the processes of cavitation and boiling is the concept of a nucleus that acts as a preferential site for the inception of these events. It is commonly thought that except for rare instances or specially controlled experiments, all cavitation and bioling istes originate at the location of such a nucleus. In order to study these important phenomena, then, it is imperative that as much as possible be known about nucleation in cavitation and boiling. It is generally accepted that free air bubbles normally do not act as nucleation sites because they are inherently unstable to dissolution due to surface tension. Thus, the study of nucleation is necessarily associated with mechanisms for stabilizing microbubbles or pockets of gas within the liquid. In this paper, various stabilization models that have been proposed are reviewed as well as the experimental evidence that supports the specific models. One particular model, the crevice model, is examined in some detail, and its predictions are used to explain several different measurements of boiling and cavitation inception. Finally, some evidence that has recently become available concerning the damaging aspects of high intensity ultrasound is examined. Many aspects of this evidence point to the existence of cavitation as the damage mechanism. Also given in this paper are preliminary explanations of these effects due to the growth of microbubbles or cavitation nuclei by rectified diffusion. |
| Title |
Numerical analysis of ultrasonic transmission and absorption of oblique plane waves through the human skull. |
| Author |
Hayner M, Hynynen K. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2001 |
| Abstract |
Ultrasonic transmission and absorption of oblique plane waves through the human skull are analyzed numerically for frequencies ranging from 1/2 to 1 MHz. These frequencies are optimum for noninvasive ultrasound therapy of brain disorders where numerical predictions of skull transmission are used to set the phase and amplitude of source elements in the phased array focusing system. The idealized model of the skull is a three-layer solid with ivory outer and inner layers and a middle marrow layer. Each layer is modeled as a flat, homogeneous, isotropic, linear solid with effective complex wave speeds to account for focused energy losses due to material damping and scattering. The model is used to predict the amplitude and phase of the transmitted wave and volumetric absorption. Results are reported for three different skull thicknesses: 3 mm, 6 mm, and 9 mm. Thickness resonances are observed in the transmitted wave for 3 mm skulls at all frequencies and for the 6 mm skulls below 0.75 MHz. Otherwise, the transmission is dominated by the direct wave. Skull phase errors due to shear waves are shown to minimally degrade the power at the focus for angles of incidence up to 20 degrees from normal even for low material damping. The location of the peak volumetric absorption occurs either in the outer ivory or middle marrow layer and shown to vary due to wave interference. |
| Title |
Numerical evaluation of ultrasonic pulse-echo subwavelength defect detection. |
| Author |
Yin X, Morris SA, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2002 |
| Abstract |
The ultrasonic pulse-echo Backscattered Amplitude Integral (BAI)-mode imaging technique [UFFC Trans, 45:30, 1998] has been developed to detect small channel defects in flexible food package seals. This technique detects 38-/spl mu/m-diameter channels reliably and 6-/spl mu/m-diameter channels occasionally using a 17.3-MHz focused transducer in water (20/spl deg/C, /spl lambda/ /spl ap/ 86 /spl mu/m, total sample thickness 22 /spl mu/m). However, interaction between ultrasound and sample microstructure - the underlying detection mechanism is poorly understood. Experimental evidence showed at the subwavelength channel was fused inside the two binding trilaminate plastic package films. Each trilaminate film a three sublayers. Package sample impedance profiles along the ultrasound beam axis were examined. Although identical in nominal impedance properties before sealing, the two binding films showed an asymmetric impedance profile after sealing. A generalized impedance profile model was proposed. The defect detection behavior of the echo signal was investigated by solving the 2D linear acoustic wave equations in fluid with finite-difference time-domain method and the perfectly matched layer absorbing boundary. The normalized correlation coefficients between the simulated and the measured RF echo waveforms were greater than 95% for this generalized model. |
| Title |
Numerical simulation of the acoustic field of a phased-array medical ultrasound scanner. |
| Author |
Cahill MD, Baker AC. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1998 |
| Abstract |
In order to evaluate the possible side effects of diagnostic medical ultrasound, and in particular the effects of nonlinear propagation of sound, it is necessary to characterize the scanners used. Ts end, the acoustic field emitted by a phased-array Hitachi EUB-26 ultrasound scanner operating in a strongly focused mode was measured a small distance from the scanner head, and the velocity field at the surface of the head deduced. A finite difference model was then used to propagate the pressure field beyond the focus, taking into account nonlinear effects, attenuation and diffraction, and the result compared with observations in water, giving reasonable agreement out of the scan plane focus. The extrapolated field was then examined in detail, revealing those regions in which most power is lost to the medium, some of which are off-axis, and so might not be detected by normal calibration procedures. |
| Title |
Numerical simulation of ultrasound-thermotherapy combining nonlinear wave propagation with broadband soft-tissue absorption. |
| Author |
Ginter S. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
2000 |
| Abstract |
Ultrasound (US) thermotherapy is used to treat tumours, located deep in human tissue, by heat. It features by the application of high intensity focused ultrasound (HIFU), high local temperatures of about 90 degree C and short treating time of a few seconds. Dosage of the therapy remains a problem. To get it under control, one has to know the heat source, i.e. the amount of absorbed US power, which shows nonlinear influences. Therefore, accurate simulations are essential. In this paper, an improved simulation model is introduced which enables accurate investigations of US thermotherapy. It combines nonlinear US propagation effects, which lead to generation of higher harmonics, with a broadband frequency-power law absorption typical for soft tissue. Only the combination of both provides a reliable calculation of the generated heat. Simulations show the influence of nonlinearities and broadband damping for different source signals on the absorbed US power density distribution. |
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