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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 192 out of 330
| Title |
On-chip generation of microbubbles as a practical technology for manufacturing contrast agents for ultrasonic imaging. |
| Author |
Hettiarachchi K, Talu E, Long ML, Dayton PA, Lee AP. |
| Journal |
Lab Chip |
| Volume |
|
| Year |
2007 |
| Abstract |
This paper presents a new manufacturing method to generate monodisperse microbubble contrast agents with polydispersity index (α) values of <2% through microfluidic flow-focusing. Micron-sized lipid shell-based perfluorocarbon (PFC) gas microbubbles for use as ultrasound contrast agents were produced using this method. The poly(dimethylsiloxane) (PDMS)-based devices feature expanding nozzle geometry with a 7 µm orifice width, and are robust enough for consistent production of microbubbles with runtimes lasting several hours. With high-speed imaging, we characterized relationships between channel geometry, liquid flow rate Q, and gas pressure P in controlling bubble sizes. By a simple optimization of the channel geometry and Q and P, bubbles with a mean diameter of <5 µm can be obtained, ideal for various ultrasonic imaging applications. This method demonstrates the potential of microfluidics as an efficient means for custom-designing ultrasound contrast agents with precise size distributions, different gas compositions and new shell materials for stabilization, and for future targeted imaging and therapeutic applications. |
| Title |
On-line monitoring of ultrasonic.surgery with MR imaging. |
| Author |
Darkazanli A, Hynynen K, Unger EC, Schenck JF. |
| Journal |
J Magn Reson Imaging |
| Volume |
|
| Year |
1993 |
| Abstract |
Ultrasonic surgery was performed in rabbits and dogs under the.guidance of magnetic resonance (MR) imaging. Two different MR.techniques were used to guide the ultrasound beam. T2-weighted.images showed lesion formation within a few minutes after.sonication. T1-weighted GRASS (gradient-recalled acquisition in the.steady state) images were sensitive to temperature elevations,.permitting monitoring of lesion creation with MR imaging. Short TR.T1-weighted GRASS images were not as helpful in detecting.temperature elevation because of a reduction in signal-to-noise ratio..T2-weighted fast spin-echo images were compared with conventional.T2-weighted spin-echo images. The former produced high-quality.images in a fraction of the imaging time. This study shows that it is.possible to monitor and guide ultrasonic surgery with MR imaging. |
| Title |
One-dimensional computer simulation of a wave incident on randomly.distributed inhomogeneities with reference to the scattering of ultrasound by.blood. |
| Author |
Routh HF, Gough W, Williams RP. |
| Journal |
Med Biol Eng Comput |
| Volume |
|
| Year |
1987 |
| Abstract |
To further the understanding of the complex problem of scattering of ultrasound by blood the authors present a computer simulation of a simpler one-dimensional analogue. Blood is modelled as a row of scatterers of constant thickness, separated by random intervals with a sinusoidal wave incident upon the row. The variation of backscattered power with haematocrit follows qualitatively that found experimentally by other workers for a suspension of erythrocytes in plasma. The model also indicates a large standard deviation of backscattered power analogous to that observed in blood. |
| Title |
Ophthalmologic and histologic changes in rabbit eyes induced by ultrasound. |
| Author |
Jankowiak J, Majewska H, Majewska C. |
| Journal |
Am J Phys Med |
| Volume |
|
| Year |
1965 |
| Abstract |
No abstract available. |
| Title |
Opthalmologic effect of ultrasound at diagnostic intensities. |
| Author |
Ziskin MC, Romayananda N, Harris K. |
| Journal |
J Clin Ultrasound |
| Volume |
|
| Year |
1974 |
| Abstract |
This study examined the possible harmful effects on the eye of prolonged exposure to ultrasound at diagnostic intensities. The left eyes of 20 rabbits were exposed to 9.5 mHz continuous wave ultrasound at 33.7 mW/cm2 for one to four hours. The right eyes served as controls. Careful gross and microscopic examination did not reveal any morphological effects caused by ultrasonic irradiation. |
| Title |
Optical and acoustical dynamics of microbubble contrast agents inside neutrophils. |
| Author |
Dayton PA, Chomas JE, Lum AF, Allen JS, Lindner JR, Simon SI, Ferrara KW. |
| Journal |
Biophys J |
| Volume |
|
| Year |
2001 |
| Abstract |
Acoustically active microbubbles are used for contrast-enhanced ultrasound assessment of organ perfusion. In regions of inflammation, contrast agents are captured and phagocytosed by activated neutrophils adherent to the venular wall. Using direct optical observation with a high-speed camera and acoustical interrogation of individual bubbles and cells, we assessed the physical and acoustical responses of both phagocytosed and free microbubbles. Optical analysis of bubble radial oscillations during insonation demonstrated that phagocytosed microbubbles experience viscous damping within the cytoplasm and yet remain acoustically active and capable of large volumetric oscillations during an acoustic pulse. Fitting a modified version of the Rayleigh-Plesset equation that describes mechanical properties of thin shells to optical radius-time data of oscillating bubbles provided estimates of the apparent viscosity of the intracellular medium. Phagocytosed microbubbles experienced a viscous damping approximately sevenfold greater than free microbubbles. Acoustical comparison between free and phagocytosed microbubbles indicated that phagocytosed microbubbles produce an echo with a higher mean frequency than free microbubbles in response to a rarefaction-first single-cycle pulse. Moreover, this frequency increase is predicted using the modified Rayleigh-Plesset equation. We conclude that contrast-enhanced ultrasound can detect distinct acoustic signals from microbubbles inside of neutrophils and may provide a unique tool to identify activated neutrophils at sites of inflammation. |
| Title |
Optical and acoustical interrogation of submicron contrast agents. |
| Author |
Patel D,Dayton P,Gut J,Wisner E,Ferrara KW. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2002 |
| Abstract |
Unlike conventional ultrasound contrast agents with a diameter of several microns, in this paper we explore the use of submicron contrast agents for the detection and localization of lymph nodes. The submicron agents are gas-filled, double-walled microspheres that rupture when exposed to ultrasound energy at megahertz frequencies. In this study, three experimental systems are combined with model predictions to assist in understanding the response of these unique agents to a range of signal transmission parameters. Optical experimental results for each agent delineate the relative expansion as a function of acoustical peak negative pressure, pulse length, and center frequency. The optical images demonstrate an order of magnitude expansion in radius during the pulse rarefaction, in which the expansion magnitude is dependent on the transmitted pressure and frequency. Simulations using a modified Rayleigh-Plesset model predict an increasing relative expansion for the microbubbles (initial bubble radius ranging from 0.3-1.3 μm) with increasing pressure and decreasing initial radius. Acoustically recorded frequency spectra reveal the presence of harmonics for a range of transmitted pulses. In addition, in-vivo results from a normal canine model demonstrate marked contrast enhancement of first order lymph nodes. We hope to offer an alternative to present intra-operative procedures for sentinel node detection. |
| Title |
Optical and acoustical observations of the effects of ultrasound oncontrast agents. |
| Author |
Dayton PA, Morgan KE, Klibanov AL, Brandenburger GH, Ferrara KW. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1999 |
| Abstract |
Optimal use of encapsulated microbubbles for ultrasound contrast agents and drug delivery requires an understanding of the complex set of phenomena that affect the contrast agent echo and persistence. With the use of a video microscopy system coupled to either an ultrasound flow phantom or a chamber for insonifying stationary bubbles, we show that ultrasound has significant effects on encapsulated microbubbles. In vitro studies show that a train of ultrasound pulses can alter the structure of an albumin-shelled bubble, initiate various mechanisms of bubble destruction or produce aggregation that changes the echo spectrum. In this analysis, changes observed optically are compared with those observed acoustically for both albumin and lipid-shelled agents. We show that, when insonified with a narrowband pulse at an acoustic pressure of several hundred kPa, a phospholipid-shelled bubble can undergo net radius fluctuations of at least 15%; and an albumin-shelled bubble initially demonstrates constrained expansion and contraction. If the albumin shell contains air, the shell may not initially experience surface tension; therefore, the echo changes more significantly with repeated pulsing. A set of observations of contrast agent destruction is presented, which includes the slow diffusion of gas through the shell and formation of a shell defect followed by rapid diffusion of gas into the surrounding liquid. These observations demonstrate that the low-solubility gas used in these agents can persist for several hundred milliseconds in solution. With the transmission of a high-pulse repetition rate and a low pressure, the echoes from, contrast agents can be affected by secondary radiation force. Secondary radiation force is an attractive force for these experimental conditions, creating aggregates with distinct echo characteristics and extended persistence. The scattered echo from an aggregate is several times stronger and more narrowband than echoes from individual bubbles. |
| Title |
Optical farfield method for studying the temperature dependence of ultrasound induced optical birefringence in liquids. |
| Author |
Riley WA. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1977 |
| Abstract |
An optical farfield method is described for studying the temperature dependence of ultrasound induced optical birefringence in liquids. It requires fewer experimental measurements and assumptions than the more commonly used optical nearfield method and permits a more direct evaluation of theoretical parameters describing the effect. Experimental results are given for castor oil to illustrate the general nature of the results which can be obtained. The method can be extended to a wide range of acoustic frequencies and applied to various interaction mechanisms with only slight modification. |
| Title |
Optical observation of contrast agent destruction. |
| Author |
Chomas JE, Dayton PA, May D, Allen J, Klibanov A, Ferrara K. |
| Journal |
Appl Phys Lett |
| Volume |
|
| Year |
2000 |
| Abstract |
Fragmentation of an ultrasound contrast agent on the time scale of microseconds provides opportunities for the advancement of microvascular detection, blood flow velocity estimation, and targeted drug delivery. Images captured by high-speed imaging systems show destruction of a microbubble during compression. Peak wall velocity of –700 m/s and peak acceleration of 1.2×1012 m/s2 is observed for insonation with a peak pressure of –1.1 MPa and a center frequency of 2.4 MHz. Theoretical calculations of wall velocity and acceleration using a modified Rayleigh–Plesset model predict a peak negative wall velocity of –680 m/s and peak acceleration of 2×1012 m/s2. |
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