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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 178 out of 330
| Title |
Modeling and optimization of high-frequency ultrasound transducers. |
| Author |
Lockwood GR, Foster FS. |
| Journal |
IEEE Trans Ultrason Ferroelectr Freq Control |
| Volume |
|
| Year |
1994 |
| Abstract |
Obtaining an accurate transducer model for a high-frequency transducer can be troublesome using traditional models, such as the KLM model, since it is often difficult to measure precisely the piezoelectric, dielectric, and mechanical properties of the transducer. This paper describes an alternative method of modeling transducers using network theory. The network theory model for a transducer is determined from a measurement of the transducer impedance in water and the pulse-echo response of the system for a given electrical source and load. A discussion of how this model can be used to optimize the design of an electrical matching circuit is given. This method is illustrated by designing a two-element transmission line matching circuit for a miniature 53 MHz transducer. Excellent agreement between the network model prediction and the experimental response is obtained. |
| Title |
Modeling of high-intensity focused ultrasound-induced lesions in the presence of cavitation bubbles. |
| Author |
Chavrier F, Chapelon JY, Gelet A, Cathignol D. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2000 |
| Abstract |
The classical "Bio Heat Transfer Equation (BHTE)" model is adapted to take into account the effects of oscillating microbubbles that occur naturally in the tissue during high-intensity focused ultrasound (HIFU) treatment. First, the Gilmore-Akulichev model is used to quantify the acoustic pressure scattered by microbubbles submitted to HIFU. Because this scattered pressure is not monochromatic, the concept of harmonic attenuation is introduced and a global attenuation coefficient is estimated for bubble-filled tissues. The first results show that this global attenuation coefficient varies significantly with respect to several parameters such as the frequency and the density of microbubbles in the medium, but also with respect to the incident acoustic pressure which thus becomes a transcendental function. Under these conditions, a layer-by-layer modeling, in the direction of propagation, is proposed to calculate the ultrasonic beam. Finally, the BHTE is solved and the HIFU-induced lesions are estimated by the calculation of the thermal dose. Using this model, it can be observed first that, when the firing power increases, the lesion develops clearly in the direction of the transducer, with a shape agreeing with in vivo experimentation. Next, it is observed that the lesion can be significantly modified in size and position, if an interface (skin or inner wall) is simulated as a zone with multiple cavitation nuclei. With a firing power increase, it is also shown how a secondary lesion can appear at the interface and how, beyond a certain threshold, this lesion develops at the main lesion expense. Finally, a better in-depth homogeneity of lesions is observed when the acoustic frequency of HIFU is increased. |
| Title |
Modeling of ultrasonic wave propagation in teeth using PSpice: A comparison with finite element models. |
| Author |
Ghorayeb SR, Maione E, Magna VL. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2001 |
| Abstract |
Ultrasound is used extensively in the medical field for the detection and characterization of a variety of features in the human body. Finite element models used to understand ultrasonic wave propagation in teeth have been developed so that ultrasound techniques could be realized in dentistry. This paper presents a hypothesis that underlies one possible design of an ultrasonic tool that can be used in a clinical environment, as well as several models that describe acoustic field simulation, propagation, and interaction with the layers of several tooth structures. A complete PSpice model of a single-element transducer based on Redwood's version of Mason's equivalent circuit, a focusing lens, and a multi-layer tooth structure is used to illustrate the validity of this hypothesis. Transmission line theory is employed as a basis for the models of the piezoceramic, the lens, and the different tooth layers. Results clearly depict the transmission and reflection of the ultrasonic waves as they travel through the layers within the tooth structure and point out the noticeable similarity to longitudinal L-wave signatures produced by axisymmetric finite element models presented in earlier studies. |
| Title |
Modification by cysteamine of ultrasound.lethality to Chinese hamster V-79 cells. |
| Author |
Fu YK, Kaufman GE, Miller MW, Griffiths TD, Lange CS. |
| Journal |
Radiat Res |
| Volume |
|
| Year |
1979 |
| Abstract |
Exposure of Chinese hamster V-79 cells to 1.1-MHz continuous wave (CW) ultrasound at intensities of 10, 20, and 30 W/cm2 resulted in cell lysis and the loss of reproductive integrity (i.e., a decrease in plating efficiency) in the remaining intact cells. Sonication in the presence of 8 mM cysteamine, a free-radical scavenger, did not alter the amount of cell lysis, but did result in a smaller decrease in plating efficiency at 20 and 30 W/cm2. Hence, while free radicals do not appear responsible for ultrasonically induced cell lysis, free radicals do appear to be at least partially responsible for loss of reproductive integrity in the remaining intact cells. |
| Title |
Modification by focused ultrasound pulses of.electrically evoked responses from an in vitro.hippocampal preparation. |
| Author |
Rinaldi PC, Jones JP, Reines F, Price LR. |
| Journal |
Brain Res |
| Volume |
|
| Year |
1991 |
| Abstract |
The application of short pulses of focused ultrasound was studied as a method of modifying.electrically evoked responses in the mammalian brain. The in vitro hippocampal preparation was.employed to facilitate delivery and dosimetry of ultrasound, and assessment of mechanisms of.ultrasound effects. Cellular and dendritic field potential responses evoked by electrical.stimulation of the Schaffer/Commissural afferents were examined before, during and after.exposure of a portion of the CA1 region to focused ultrasound pulses for periods ranging from 2.to 15 min. Focused ultrasound with a repetition rate of 150 kHz was delivered in pulses.comparable in duration to an electrical pulse that could initiate activity in the nervous system. The.pulses had a center frequency of 750 kHz, durations of about 6 microseconds, and.spatial-peak-temporal-averaged intensities of about 80 W/cm2. These parameters are markedly.different from those employed in conventional diagnostic ultrasound. Temperatures in the bath.and tissue were monitored. Extracellular field potentials reflecting the presynaptic fiber volley,.dendritic response and cellular discharge were significantly reduced by exposure to ultrasound..Recovery occurred to varying degrees, and in one experiment was complete. Average.temperature changes observed were less than 1 degree C. The present study demonstrates that the.electrically evoked response in mammalian brain can be altered by ultrasound in a non-thermal,.non-cavitational mode, and that such effects are potentially reversible. |
| Title |
Molecular absorption of ultrasound in biological materials. |
| Author |
Kremkau FW. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1987 |
| Abstract |
Attenuation of ultrasound in tissues is due primarily to macromolecular absorption. Protein absorptions are large compared to those for the amino acids of which they are made. Protein absorptions are not correlated with alpha-helix content or number of subunits. Conversion of some structured native proteins to random chains reduces absorption significantly. Phosphate buffer ions dramatically increase absorption in saccharides and amino acids but make only small changes in polysaccharides and proteins. Solvation my contribute to absorption in small molecules and linear proteins but in globular proteins may be inhibited by their tertiary structure. Absorption increases non-linearly with concentration for some proteins. Macromolecular cross-linking increases absorption. |
| Title |
Molecular absorption of ultrasound in biological tissues. |
| Author |
Kremkau FW. |
| Journal |
News Physiol Sci |
| Volume |
|
| Year |
1989 |
| Abstract |
Attenuation of ultrasound in tissues is due primarily to macromolecular absorption. Biomacromolecules have higher absorptions than the constituent molecules of which they are made. Absorption dependencies on structure and solvation are probably interrelated. Underlying absorption processes are enhanced or new processes are added under conditions of high concentration. |
| Title |
Molecular absorption of ultrasound in biological tissues. |
| Author |
kremkau FW. |
| Journal |
Int union Physiol Sci |
| Volume |
|
| Year |
1989 |
| Abstract |
Attenuation of ultrasound in tissues is due primarily to macromolecular absorption. Biomacromolecules have higher absorptions than the constituent molecules of which they are made. Absorption dependencies on structure and solvation are probably interrelated. Underlying absorption processes are enhanced or new processes are added under conditions of high concentration, aggregation, or cross-linking. |
| Title |
Molecular imaging of the initial inflammatory response in atherosclerosis: implications for early detection of disease. |
| Author |
Kaufmann BA, Carr CL, Belcik JT, Xie A, Yue Q, Chadderdon S, Caplan ES, Khangura J, Bullens S, Bunting S, Lindner JR. |
| Journal |
Arterioscler Thromb Vasc Biol |
| Volume |
|
| Year |
2010 |
| Abstract |
Background- We hypothesized that molecular imaging of endothelial cell adhesion molecule expression could noninvasively evaluate prelesion atherogenic phenotype. METHODS AND RESULTS: Mice deficient for the LDL-receptor and the Apobec-1 editing peptide (DKO mice) were studied as an age-dependent model of atherosclerosis. At 10, 20, and 40 weeks of age, ultrasound molecular imaging of the proximal thoracic aorta was performed with contrast agents targeted to P-selectin and VCAM-1. Atherosclerotic lesion severity and content were assessed by ultrahigh frequency ultrasound, histology, and immunohistochemistry. In wild-type mice at all ages, there was neither aortic thickening nor targeted tracer signal enhancement. In DKO mice, lesions progressed from sparse mild intimal thickening at 10 weeks to widespread severe lesions with luminal encroachment at 40 weeks. Molecular imaging for P-selectin and VCAM-1 demonstrated selective signal enhancement (P<0.01 versus nontargeted agent) at all ages for DKO mice. P-selectin and VCAM-1 signal in DKO mice were greater by 3-fold at 10 weeks, 4- to 6-fold at 20 weeks, and 9- to 10-fold at 40 weeks compared to wild-type mice. En face microscopy demonstrated preferential attachment of targeted microbubbles to regions of lesion formation. CONCLUSIONS: Noninvasive ultrasound molecular imaging of endothelial activation can detect lesion-prone vascular phenotype before the appearance of obstructive atherosclerotic lesions. |
| Title |
Molecular therapy using ultrasound: Mechanisms involved in drug activation, apoptosis induction, gene transfer, and alterations of gene expression. |
| Author |
Yoshida T, Kondo T, Ogawa R, Zhao Q, Hassan MA, Watanabe A, Takasaki I, Tabuchi Y, Shoji M, Kudo N, Feril LB Jr., Tachibana K, Buldakov MA, Honda T, Tsukada K, Riesz P. |
| Journal |
Jpn Soc Ther Med |
| Volume |
|
| Year |
2007 |
| Abstract |
Interest in molecular imaging and in molecularly-targeted therapy has grown tremendously, and ultrasound may offer new tools for modern cancer therapy. To understand how therapeutic ultrasound works, it is necessary to understand its biological effects at the molecular level. In this review, investigations on the molecular aspects of ultrasound are discussed, with emphasis on apoptosis induction, gene expression, and gene transfection. In these studies, apoptosis induction was assayed with flow cytometry and with other methods targeting indicators of apoptosis. Gene expression was evaluated using western blotting, real-time polymerase chain reaction, and microarray analysis. Gene transfection was investigated using a luciferase assay and other methods. The reported results show that low intensity ultrasound can induce apoptosis in cancer cell lines, and that this effect can be optimized using pulsed ultrasound. Exposure to ultrasound can result in the down-regulation or up-regulation of some genes. Of particular interest is the striking up-regulation of the heme oxygenase-1 gene, a gene usually associated with oxidative stress in human lymphoma U937 cells. Introducing genes using ultrasound with or without microbubbles also exhibited promising results. Membrane damage is pivotal to biological effects, and using ultrasound to modify or affect cell membranes can either promote or inhibit desired effects. In summary, it is concluded that ultrasound has the potential to help develop useful methods which can be utilized in therapies which require apoptosis induction, gene introduction into cells, alterations in gene regulation, and drug-activation. |
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