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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 114 out of 330
| Title |
Estimating the thermal dose from backscattered RF echoes. |
| Author |
Bigelow TA, O'Brien WD Jr. |
| Journal |
Proc Fourth Int Symp Ther Ultrasound |
| Volume |
|
| Year |
2005 |
| Abstract |
Over the years many different investigators have attempted to estimate the temperature rise resulting from ultrasound exposure in therapy applications. The developed methods typically rely on thermal expansion or temperature related sound speed variations both of which are dependent on tissue type and cannot be known a priori on a patient-specific basis. We have developed a method to estimate the thermal dose (temperature over time) from the backscattered RF echoes. RF echoes from within the same tissue type can be used to estimate the in vivo local attenuation (assumed to be the same as tissue absorption) as has been shown by other investigators. Similarly, the RF echoes can be compared to reference echoes while assuming a model for the scattering structures to estimate the total attenuation along the propagation path (i.e. the in vivo power spectrum). Hence, the temperature over time can be estimated form the measured in vivo power spectrum and the measured tissue absorption by solving the bioheat equation directly. The estimated thermal dose can then be used to monitor or plan ultrasound therapy on a patient-specific basis. |
| Title |
Estimating the total ultrasound attenuation along the propagation path by applying multiple filters to backscattered echoes from a single spherically focused source. |
| Author |
Bigelow TA. |
| Journal |
IEEE Trans Ultrason Ferroelectr Freq Control |
| Volume |
|
| Year |
2010 |
| Abstract |
Quantifying the correlation length of the tissue microstructure has shown potential for differentiating between benign and malignant tumors. To implement these advances in the clinic, the total frequency-dependent attenuation along the propagation path must be determined on a patient specific basis. Previously, an algorithm was developed to estimate this attenuation using echoes from multiple sources. In this study, the developed algorithm was extended to echoes from a single source by filtering the echoed signal into multiple frequency bands. This step was needed because it would be challenging to scan exactly the same tissue region using multiple sources in the clinic. Computer simulations and phantom experiments were conducted to verify the attenuation could be determined by filtering the echoes from a single source. The simulations utilized a spherically focused single-element source (5 cm focal length, f/4, 14 MHz center frequency, 50% bandwidth) exposing a homogeneous tissue region (Gaussian scattering structures with effective radii of 5 to 55 μm at a density of 250/mm3, attenuation of 0.1 to 0.9 dB/cm∙MHz). The phantom experiments utilized a spherically focused single-element source (5.08 cm focal length, f/4, 7.5 MHz center frequency) exposing a 0.5 dB/cm∙MHz homogeneous glass bead phantom. The computer simulations and phantom experiment confirmed that the total attenuation along the propagation path can be determined by appropriately applying multiple filters to the backscattered echoes from a single source. |
| Title |
Estimating the total ultrasound attenuation along the propagation path by using a reference phantom. |
| Author |
Labyed Y, Bigelow TA. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2010 |
| Abstract |
In this study, an algorithm previously developed for estimating the total ultrasonic attenuation along the propagation path from the surface of the transducer to a region of interest (ROI) in tissue, was modified to make it more practical for use in clinical settings. Specifically, the algorithm was re-derived for when a tissue mimicking phantom rather than a planar reflector is used to obtain the reference power spectrum. The reference power spectrum is needed to compensate for the transfer function of the transmitted pulse, the transfer function of transducer, and the diffraction effects that result from focusing/beam forming. The modified algorithm was tested on simulated radio frequency (RF) echo lines obtained from two samples that have different scatterer sizes and different attenuation coefficient slopes, one of which was used as a reference. The mean and standard deviation of the percent errors in the attenuation coefficient estimates (ACEs) were less than 5% and 10%, respectively, for ROIs that contain more than 10 pulse lengths and more than 25 independent echo lines. The proposed algorithm was also tested on two tissue mimicking phantoms that have attenuation coefficient slopes of 0.7 dB/cm-MHz and 0.5 dB/cm-MHz respectively, the latter being the reference phantom. When a single element spherically focused source was used, the mean and standard deviation of the percent errors in the ACEs were less than 5% and 10% respectively for windows that contain more than 10 pulse lengths and more than 17 independent echo lines. When a clinical array transducer was used, the mean and standard deviation of the percent errors in the ACEs were less than 5% and 25%, respectively, for windows that contain more than 12 pulse lengths and more than 45 independent echo lines. |
| Title |
Estimation of blood flow parameters using pulse Doppler ultrasound with corrections for spectral broadening. |
| Author |
Holland SK, Orphanoudakis SC. |
| Journal |
Proc Twelfth Annu Northeast Bioeng Conf, IEEE - Yale Univ |
| Volume |
|
| Year |
1986 |
| Abstract |
Significant errors may occur in quantitative measurement of blood flow using pulse Doppler ultrasound if the frequency-dependent and spectral-broadening effects of attenuation of ultrasound in tissue and scattering of ultrasound in blood are neglected. These effects cause distortion of an ultrasonic pulse as it propagates through tissue and is backscattered by moving blood. Therefore, estimates of blood flow parameters based upon ultrasonic echoes that have been affected by these frequency-dependent, spectral-broadening mechanisms will be in error. Using a theoretical model of the interactions of ultrasound with tissue and blood, the estimation of blood flow parameters by pulse Doppler ultrasound is formulated as a nonrandom parameter estimation problem. The resulting estimator is implemented using a prototype digital pulse Doppler system designed and constructed for this purpose. Experimental results obtained using this system are presented, along with theoretical aspects of the estimation problem.. |
| Title |
Estimation of blood velocity with high frequency ultrasound. |
| Author |
Ferrara KW, Zagar BG, Sokil-Melgar JB, Silverman RH, Aslanidis IM. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1996 |
| Abstract |
In order to map blood velocity in small regions near the transducer, we evaluate the performance of the wideband maximum likelihood (WMLE) strategy and infinite impulse response (IIR) filters for blood velocity estimation with a transducer center frequency of 38 MHz. Using a short transmitted pulse and the narrow lateral beam width obtained using this frequency, we show that velocities smaller than 1 mm/s can be estimated reliably. In addition, using both changes in the location and magnitude of the peak of the RF correlation, vessels as small as 40 ?m can be visualized in the RF signal and distinguished from stationary tissue. The experimental system also provides the opportunity to examine changes in flow and in the vessel wall over a cardiac cycle. |
| Title |
Estimation of body composition using the velocity of utlrasound. |
| Author |
Fisher AV. |
| Journal |
Pig New Inf |
| Volume |
|
| Year |
1992 |
| Abstract |
The use of ultrasound to estimate body composition of farm animals has a history extending back more than 35 years. Some of the earlier work on cattle was in the USA (Temple et al., 1956), whilst in Europe early work was on pigs: in France by Dumont (1957), and in the Federal Republic of Germany by Claus (1957), amongst others. In the United Kingdom, the earliest report was also on pigs and headed by East and Taylor from Unilever Limited (East et al., 1959). As in many applications of technology to the problem of estimating body composition in meat animals, investigations in human medicine were seminal to the animal work using ultrasound. This was true not only of the adoption of ultrasound as a diagnostic tool in the widest sense, but also applied to the evolution of techniques from simple one-dimensional A-scope displays, to two-dimensional scanning and B-scope displays. The development of the latter for animal studies is intimately associated with Professor Jim Stouffer, formerly of Cornell University, who developed the Scanogram, one of the more successful B-scope machines, and one specifically designed for animal work. Most ultrasonic work on livestock has exploited the potential to quantify tissue thicknesses and cross-sectional areas using energy reflected from tissue boundaries. This approach, known as the pulse-echo technique, was first used in human medicine in the 1940s. However, another approach to quantifying composition using ultrasound is different in that it did not enjoy an earlier embryonic period in the hands of medical equipment engineers. This technique, known as the velocity of sound (VOS), was pioneered for use on meat animals by Miles (Miles and Fursey, 1974). Following encouraging results from measurements on livestock, the technique was later applied to the classification of carcasses for leanness. |
| Title |
Estimation of echo correlation and measurement bias in acoustic adiation force impulse imaging. |
| Author |
McAleavey SA,Nightingale KR,Trahey GE. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2003 |
| Abstract |
Acoustic radiation force impulse (ARFI) imaging is a novel imaging modality in which pulses from a diagnostic ultrasound scanner are used to displace tissue and track its motion. The region displaced has lateral and elevational dimensions of similar scale to the ultrasound beams used to track the motion. Therefore, there is a range of tissue displacements present within the tracking beam, leading to decorrelation of the echo signal. Expressions are derived for the expected value of the displacement estimate and the cross-correlation at the expected displacement. Numerical simulations confirm the analytical model. |
| Title |
Estimation of HIFU induced lesions in vitro: numerical simulation and experiment. |
| Author |
Li F, Feng R, Zhang Q, Bai J, Wang Z. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
2006 |
| Abstract |
The heated necrotic element created by a single high intensity focused ultrasound exposure can be considered as the foundation of high intensity focused ultrasound ablation of tumour lesions. In this paper, we studied the effects of exposure dose and focal depth in tissue on heated necrotic elements, using numerical simulation and experiment. The acoustic field of one of the transducers for the Model-JC HAIFU focused ultrasound tumour therapeutic system was modeled using O Neill's equation, and then using this information together with Pennes' bio-heat-transfer-equation and finite difference techniques, the heated necrotic element was simulated numerically. The results showed that the theoretical predictions were basically in agreement with the experimental data for low exposures, but that the experimental values suddenly increased with the increasing exposure and exceeded the theoretical predictions. The element volume from the theoretical prediction and experiment for the heated necrotic element decreased with increasing focal depth in tissue for a given exposure, and the theoretical predictions were a little lower than the experimental ones. Therefore, heated necrotic elements created by high intensity focused ultrasound can be well predicted from a knowledge of ultrasonic biophysics theories. |
| Title |
Estimation of pulses in ultrasound B-scan images. |
| Author |
Jensen JA. |
| Journal |
IEEE Trans Med Imaging |
| Volume |
|
| Year |
1991 |
| Abstract |
It is shown, based on an expression for the received pressure field in pulsed medical ultrasound systems, that a common one-dimensional pulse can be estimated from individual A-lines. An ARMA model is suggested for the pulse, and an estimator based on the prediction error method is derived. The estimator is used on a segment of an A-line assuming that the pulse does not change significantly inside the segment. Several examples of use of the estimator on synthetic data and data from a tissue phantom and in vitro data measured from a calf's liver are given. They show that a pulse can be estimated, even at moderate signal-to-noise ratios. |
| Title |
Estimation of scatterer volume density near a concentration gradient. |
| Author |
Newhouse VL, Amir I. |
| Journal |
Ultrason Imaging |
| Volume |
|
| Year |
1985 |
| Abstract |
A general formulation of the echo received from a random scatterer ensemble illuminated by a short. electromagnetic or sonic signal is developed. It is shown theoretically and confirmed experimentally with. ultrasound, that a gradient in scatterer density will return an echo which is partially spatially coherent (i.e.. specular). The surface of a random ensemble of uniform scatterers is shown to produce an echo from whose. degree of coherence, the scatterer density and cross section can be calculated. |
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