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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 64 out of 330
| Title |
Characterization of cell membrane response to ultrasound activated microbubbles. |
| Author |
Tran TA, Guennec JYL, Bougnoux P, Tranquart F, Bouakaz A. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2008 |
| Abstract |
Contrast Agents for ultrasound imaging, composed f tiny gas microbubbles, have become a reality in clinical routine. They are extensively used in radiology for detection and characterization of various tumors and in cardiology for left ventricular opacification. Recent experimental studies showed that ultrasound waves in combination with contrast agent microbubbles increase transiently cell membrane permeability in a process known as sonoporation. This effect is thought to allow foreign molecules to enter the cell. In that context, we explored the cell membrane’s responses to microbubbles’ oscillations as the mechanism is not completely understood. Breast cancer sell line in combination with contrast microbubbles were used. Ultrasound was applied using a transducer of 1 MHz center frequency transmitting a 10-cycle burst of different acoustic pressures repeated every 10 μs. Patch-clamp technique in whole cell configuration was used to explore transmembrane ion exchange through the variations in membrane potential. To characterize the activated ion channels, the variations of the intracellular calcium (Ca2+) concentration were explored using a fluorescent marker. The results revealed that ultrasound stimulation induces a rapid hyperpolarization of cell membrane potential when the microbubble is in direct contact with the cell, but the potential returned to its initial value when ultrasound stimulation stopped. The change in cell membrane potential indicates the activation of specific ion channels and depends on the quality of microbubble adhesion to the cell membrane. Microbubbles were shown to induce a mechanical stretch activating BKCa channels. Simultaneous Ca2+ measurements indicate a slow and progressive Ca2+ increase that is likely a consequence of BKCa channels opening, not a cause. These results demonstrate that microbubbles’ oscillations under ultrasound activation entail modulation of cellular function and signaling by triggering the modulation of cellular function and signaling by triggering the modulation of ionic transports through the cell membrane. Cells response to the mechanical stretch caused by gentle microbubble oscillations is characterized by the opening of BKCa stretch channels and a Ca2+ flux, which might potentially trigger other cellular responses responsible for membrane sonopermeabilization. |
| Title |
Characterization of lead zirconate titanate ceramics for use in miniature high-frequency (20-80 MHz) tranducers. |
| Author |
Foster FS, Ryan LK, Turnbull DH. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1991 |
| Abstract |
The development of new endoscopic applications of ultrasound imaging is critically dependent on the availability of efficient broadband transducers with areas of 2 1mm*1mm or less. The materials properties of PZT ceramics for operation in the thickness mode at frequencies as high as 80 MHz are reported. Each of the ceramics tested showed a reduction in k/sub t/ with increasing frequency. In a fine grained PZT, values of k/sub t/ as high as 0.44 were measured at 80 MHz. The effects of grain size were also evident in the measurement of frequency dependent mechanical losses. Experimental and theoretical analysis of 1mm*1mm 45-MHz PZT transducers verified the validity of the properties measurements and demonstrated excellent insertion loss and bandwith characteristics. The minimum insertion loss of ?17.5 dB is in good agreement with theory and is a marked improvement over the performance of polymer devices. Details on the fabrication and testing of high frequency ceramic transducers are described. |
| Title |
Characterization of muscle tissue using ultrasound time-domain correlation techniques. |
| Author |
Nostwick LM. |
| Journal |
Thesis(MS): Univ of Illinois |
| Volume |
|
| Year |
1993 |
| Abstract |
No abstract available. |
| Title |
Characterization of normal and osteoarthritic cartilage using 25MHz ultrasound. |
| Author |
Sanghvi NT, Snoddy AM, Myers SL, Brandt KD, Reilly CR, Franklin TD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1990 |
| Abstract |
The authors evaluate normal and degenerate articular cartilage (AC) using ultrasonic imaging. Samples of grossly normal cartilage were obtained at the time of sacrifice from the knees of nine adult mongrel dogs that had been killed by an injection of barbiturate. Four samples of grossly fibrillated osteoarthritic human cartilage, including the underlying subchondral bone, were obtained from tissues removed at the time of joint replacement surgery. Imaging methods and results are described. The results of the study suggest that ultrasonic imaging of AC may allow accurate reproducible determination of cartilage thickness, suitable for longitudinal observation. The data provide evidence that ultrasonic imaging is a highly sensitive technique for measuring both the thickness and surface characteristics of AC |
| Title |
Characterization of porcine muscle tissue using ultrasound time-domain correlation techniques. |
| Author |
Nostwick LM, Hein IA, Novakofski JE, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1991 |
| Abstract |
The ultrasound time-domain correlation (UTDC) technique involves the determination of a similarity factor, the correlation coefficient. For this application, UTDC was used to calculate the maximum correlation coefficient between RF echo signals of porcine muscle tissue obtained at different times and for different echo spacings. The porcine muscle samples were procured from a slaughterhouse and data acquisition began within 1.5 h post mortem. The echo signals were obtained with a customized ultrasound data acquisition system and analyzed using a 486 PC. The results indicated that observed trends in the correlation coefficient could be used to determine muscle activity post mortem and to determine when this activity stopped, which was approximately 10 h post mortem. An explanation of the methods used and results obtained is presented. |
| Title |
Characterization of reperfused infarcted myocardium from high-frequency intracardiac ultrasound imaging using homodyned K distribution. |
| Author |
Hao X,Bruce CJ,Pislaru C,Greenleaf JF. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2002 |
| Abstract |
Myocardial changes caused by infarction/reperfusion (contraction band necrosis, hemorrhage, edema, etc.) may result in an increased scatterer density and a variation in scatterer arrangement. This paper, for the first time, models most of the scattering conditions resulting from the interaction of ultrasound and normal/reperfused infarcted myocardium using the homodyned K distribution. Furthermore, this method is used to characterize the change in scatterer density by calculating the effective scatterer number per resolution cell. The reliability and the effects of attenuation and scan conversion on effective scatterer number estimation are discussed. We used in vivo data acquired using high-frequency intracardiac ultrasound imaging (8.5 MHz) from the left and right ventricles of open-chest pigs in an acute infarction/reperfusion model. The results show that the homodyned K distribution describes the statistical distribution of backscattered signal from both normal and abnormal myocardium. A significant increase in scatterer density occurs in the infarcted region after reperfusion compared with the same region at baseline (normal myocardium prior to occlusion). The scatterer density of the normal region does not change significantly after reperfusion. We conclude that the homodyned K distribution may characterize normal and reperfused infarcted myocardium using high-frequency intracardiac ultrasound images. |
| Title |
Characterization of the power spectrum of scattered ultrasound using a fractal-based analysis. |
| Author |
Kikuchi T, Kiryu S, Sato S, Miura H. |
| Journal |
Proc Second Joint Meet ASA ASJ |
| Volume |
|
| Year |
1988 |
| Abstract |
No abstract available. |
| Title |
Characterization of thyroid cancer in mouse models using high-frequency quantitative ultrasound techniques |
| Author |
Lavarello RJ, Ridgway WR, Sarwate SS, Oelze ML |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2013 |
| Abstract |
Currently, the evaluation of thyroid cancer relies on the use of fine-needle aspiration biopsy, as non-invasive imaging methods do not provide sufficient levels of accuracy for the diagnosis of this disease. In this study,
the potential of quantitative ultrasound methods for characterization of thyroid tissues was studied using a rodent model ex vivo. A high-frequency ultrasonic scanning system (40 MHz) was used to scan thyroids extracted from
mice that had spontaneously developed thyroid lesions (cancerous or benign). Three sets of mice were acquired having different predispositions to developing three thyroid anomalies: C-cell adenoma, papillary thyroid carcinoma (PTC) and follicular variant papillary thyroidcarcinoma (FV-PTC). A fourth set of mice that did not develop thyroid anomalies (normal mice) were used as controls. The backscatter coefficient was estimated from excised thyroid lobes the different mice. From the backscatter coefficient versus frequency (25–45 MHz), the effective scatterer diameter (ESD) and effective acoustic concentration (EAC) were estimated. From the envelope of the back-scattered signal, the homodyned K distribution was used to estimate the k parameter (ratio of coherent to
incoherent signal energy) and the m parameter (number of scatterers per resolution cell). Statistically significant differences were observed between cancerous thyroids and normal thyroids based on the ESD, EAC and
m parameters. The mean ESD values were 18.0 ± 0.92, 15.9 ± 0.81 and 21.5 ± 1.80
mm for the PTC, FV-PTC and normal thyroids, respectively. The mean EAC values were 59.4 ± 1.74, 62.7 ± 1.61 and 52.9 ± 3.42 dB (mm(^-3)) for the PTC, FV-PTC and normal thyroids, respectively. The mean m values were 2.55 ± 0.37, 2.59 ± 0.43 and 1.56 ± 0.99 for the PTC, FV-PTC and normal thyroids, respectively. Statistically significant differences were observed between cancerous thyroids and C-cell adenomas based on the ESD and EAC parameters, with an estimated ESD value of 21.3 ± 1.50 mm and EAC value of 54.7 ± 2.24 dB mm (^-3) for C-cell adenomas. These results suggest that high-frequency quantitative ultrasound may enhance the ability to detect and classify diseased thyroid tissues. |
| Title |
Characterizing pulses reflected from rough surfaces using ultrasound. |
| Author |
Bozma O, Kuc R. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1991 |
| Abstract |
A model for the scattering of wideband signals from three-dimensional rough surfaces is presented. This development is an extension of the scattering based on the Kirchhoff approximation method for a monochromatic wave source. The usual plane-wave approximation is relaxed and the Kirchhoff method is extended to include spherically diverging waves from the scattering surface. The scattered signal is expressed in terms of the Fourier transform of the acoustic channel. The frequency correlation function of the channel is then derived for a rough surface having the Gaussian spectrum. The coherent and incoherent components of the scattered signal intensity are determined from the frequency correlation function. The theory is applied to the signals produced by the Polaroid transducer operating in air and mounted on a mobile vehicle capable of automatic translation and rotation. Theoretical results are compared with experimental observations from two different rough surfaces. The analytic results are verified over the observable range of incidence angles from 0 ? to 60 ?. |
| Title |
Characterizing tissue microstructure using an ultrasound system-independent spatial autocorrelation function. |
| Author |
Dong F. |
| Journal |
Thesis(PhD): Univ of Wisconsin-Madison |
| Volume |
|
| Year |
1999 |
| Abstract |
The research described in this dissertation is related to characterization of tissue microstructure using a system-independent spatial autocorrelation function (SAF). The function was determined using a reference phantom method, which employed a well-defined "point-scatter" reference phantom to account for instrumental factors.
The SAF's were estimated for several tissue-mimicking (TM) phantoms and fresh dog livers. Both phantom tests and in vitro dog liver measurements showed that the reference phantom method is relatively simple and fairly accurate, providing the bandwidth of the measurement system is sufficient for the size of the scatter being involved in the scattering process.
Implementation of this method in clinical scanner requires that distortions from patient's body wall be properly accounted for. The SAF's were estimated for two phantoms with body-wall-like distortions. The experimental results demonstrated that body wall distortions have little effect if echo data are acquired from a large scattering volume.
One interesting application of the SAF is to form a "scatter size image". The scatter size image may help providing diagnostic tools for those diseases in which the tissue microstructure is different from the normal. Another method, the BSC method, utilizes information contained in the frequency dependence of the backscatter coefficient to estimate the scatter size. The SAF technique produced accurate scatter size images of homogeneous TM phantoms and the BSC method was capable of generating accurate size of dog kidneys, the contrast-to-noise-ratio (CNR) between renal cortex and medulla was improved dramatically compared to the gray-scale image.
The effect of nonlinear propagation was investigated by using a custom-designed phantom with overlaying TM fat layer. The results showed that the correlation length decreased when the transmitting power increased. The measurement results support the assumption that nonlinear propagation generates harmonic energies and causes underestimation of scatter diameters. Nonlinear propagation can be further enhanced by those materials with high B/A values using a new measurement technique, the "simplified finite amplitude insertion substitution" (SFAIS) method. |
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