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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 91 out of 330
| Title |
Direct observations of ultrasound microbubble contrast agent interaction with the microvessel wall. |
| Author |
Caskey CF, Stieger SM, Qin S, Dayton PA, Ferrara KW. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2007 |
| Abstract |
Many thousands of contrast ultrasound studies have been conducted in clinics around the world. In addition, the microbubbles employed in these examinations are being widely investigated to deliver drugs and genes. Here, for the first time, the oscillation of these microbubbles in small vessels is directly observed and shown to be substantially different than that predicted by previous models and imaged within large fluid volumes. Using pulsed ultrasound with a center frequency of 1 MHz and peak rarefactional pressure of 0.8 or 2.0 MPa, microbubble expansion was significantly reduced when microbubbles were constrained within small vessels in the rat cecum (p<0.05). A model for microbubble oscillation within compliant vessels is presented that accurately predicts oscillation and vessel displacement within small vessels. As a result of the decreased oscillation in small vessels, a large resting microbubble diameter resulting from agent fusion or a high mechanical index was required to bring the agent shell into contact with the endothelium. Also, contact with the endothelium was observed during asymmetrical collapse, not during expansion. These results will be used to improve the design of drug delivery techniques using microbubbles. |
| Title |
Direct strain estimation in elastography using spectral cross-correlation. |
| Author |
Varghese T, Konofagou EE,Ophir J, Alam SK, Bilgen M. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2000 |
| Abstract |
Spectral estimation of tissue strain has been performed previously by using the centroid shift of the power spectrum or by estimating the variation in the mean scatterer spacing in the spectral domain. The centroid shift method illustrates the robustness of the direct, incoherent strain estimator. In this paper, we present a strain estimator that uses spectral cross-correlation of the pre- and postcompression power spectrum. The centroid shift estimator estimates strain from the mean center frequency shift, while the spectral cross-correlation estimates the shift over the entire spectrum. Spectral cross-correlation is shown to be more sensitive to small shifts in the power spectrum and, thus, provides better estimation for smaller strains when compared to the spectral centroid shift. Spectral cross-correlation shares all the advantages gained using the spectral centroid shift, in addition to providing accurate and precise strain estimation for small strains. The variance and noise properties of the spectral strain estimators quantified by their respective strain filters are also presented.
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| Title |
Direct ultrasonic velocity measurements of mammalian collagen threads. |
| Author |
Goss SA, O'Brien WD Jr. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1979 |
| Abstract |
Direct ultrasonic velocity measurements have been made in fresh collagen threads from mammalian tendon at a frequency of 100 MHz using the scanning laser acoustic microscope. Tendon is of interest since it contains an unusually large amount of collagen, a structural protein thought to be important to the echographic visualizability of normal and pathologic tissues in medical ultrasound. Results indicate that ultrasonic velocity is appreciably higher than in soft tissues, lending support to the view that tendon, as well as collagen, is markedly distinguished ultrasonically from other biological tissues. |
| Title |
Direct ultrasonic velocity measurements of mammalian collagen threads. |
| Author |
Goss SA, O'Brien WD Jr. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1979 |
| Abstract |
Direct ultrasonic velocity measurements have been made in fresh collagen threads from mammalian tendon at a frequency of 100 MHz using the scanning laser acoustic microscope. Tendon is of interest since it contains an unusually large amount of collagen, a structural protein thought to be important to the echographic visualizability of normal and pathologic tissues in medical ultrasound. Results indicate that ultrasonic velocity is appreciably higher than in soft tissues, lending support to the view that tendon, as well as collagen, is markedly distinguished ultrasonically from other biological tissues. |
| Title |
Direct ultrasound application had no effect on cardiac hemodynamic performance in a baseline isolated rat heart model. |
| Author |
Greenberg S, Finkelstein A, Raisman E, Shapira I, Koronowski R, Laniado S, Keren G. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2000 |
| Abstract |
Therapeutic ultrasound (US) has been used for more than 3 decades to promote tissue healing in cases of tissue injury and muscle soreness. It was previously suggested that US may have vasorelaxatory and inotropic properties. However, the direct effect of therapeutic US in a whole heart model has not yet been investigated. Our hypothesis was that application of US might enhance cardiac function. The Langendorf model was modified in a special manner to allow application of US to the heart. Using this model, 20 male rats were equally divided into two groups. Group 1: the hearts were perfused for 15 min, to obtain baseline measurements, and then they were perfused for another 15 min in a special bath full of perfusate. Group 2: after 15 min of baseline measurements, continuous US of 1 MHz 2 W/cm(2) was applied for another 15 min. The parameters that were measured at 5-min intervals were: left ventricular pressure P(max), first derivative of the rise and fall in left ventricular pressure (dP/dt(max), dP/dt(min)), and pressure-time integral. There was no significant difference between the two groups in all parameters at baseline and during US application. P(max) and dP/dt(max) remained constant. After 15 min of US propagation, P(max) was 98% +/- 3 from baseline level vs. 98% +/- 7 in the control group, and dP/dt(max) was 98% +/- 3 vs. 99% +/- 9 in the control. In dP/dt(min), a gradual decline after 15 min of perfusion was measured. In the US- treated group, it declined to 80% +/- 10 vs. 83% +/- 5 in the controls. In conclusion, US radiation at the dose specified does not improve healthy isolated heart hemodynamic performance. We established a model that may be used for further investigation. |
| Title |
Directory of federal programs in medical diagnostic ultrasound. |
| Author |
Busser JH. |
| Journal |
Rep AEMB |
| Volume |
|
| Year |
1976 |
| Abstract |
No abstract available. |
| Title |
Dispersion of the ultrasonic velocities in human cortical bone. |
| Author |
Yoon HS, Katz JL. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1976 |
| Abstract |
Static and low frequency measurements by previous investigators have shown human and bovine bones are viscoelastic. For noninvasive applications of ultrasound such as ultrasonic encephalography, monitoring of fracture healing in bone and other medical and dental diagnoses where broadband transducers and varying frequencies of ultrasound are often employed, it is desirable to know how tissues respond to different frequencies and to delineate well paths of ultrasound in the part of the human body under consideration. Using an ultrasonic pulse transmission technique, we have studied the dependence of the ultrasonic velocities in human compact bone (dried) at room temperature over the frequency range of 1 to 10 MHz, based on hexagonal symmetry. All the eight independent ultrasonic velocities increase with increasing frequency, implying that human bone is viscoelastic even at these high frequencies. |
| Title |
Display techniques in ultrasound pulse echo investigations: A review. |
| Author |
Kossoff G. |
| Journal |
J Clin Ultrasound |
| Volume |
|
| Year |
1974 |
| Abstract |
No abstract available. |
| Title |
Distortion of finite amplitude ultrasound in lossy media. |
| Author |
Haran ME. Cook BD. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1983 |
| Abstract |
A form of Burgers’ equation is used to derive an algorithm for calculating harmonic generation by a continuous plane wave of ultrasound propagating in a nonlinear, lossy, nondispersive medium. The algorithm accounts for attenuation that is not quadratically related to the frequency of the wave. Attenuation strongly affects the rate of harmonic production. The effect of variations of the relationship between attenuation and frequency is shown. Biological tissue is an example of a highly lossy medium where the attenuation does not increase with the square of the frequency. Calculations for several types of tissue and biological fluids are presented that show, for certain conditions, finite amplitude distortion is possible. |
| Title |
Distortion of ultrasound beams in tissue and tissue-equivalent media. |
| Author |
Banjavic RA, Zagzebski JA, Madsen EL, Goodsitt MM. |
| Journal |
Acoust Imaging Hologr |
| Volume |
|
| Year |
1979 |
| Abstract |
A comparison of ultrasonic pulse-echo beam profiles for broad band, clinical transducers between nonattenuating and attenuating paths has revealed significant differences. The profiles taken through attenuating media, such as soft tissue. samples or tissue equivalent gelatin materials, are enlarged and show a greater rate of enlargement as a function of the distance from the transducer beyond the focal plane. A distortion in the form of axial asymmetries and off-axis. displacement was also noted for attenuating media. A simple model using a superposition of continuous wave beams to describe the pulse-echo response of broad band pulses is proposed. A weighting function is used to combine the. various frequency components of the beam. Attenuation effects are also added to the model, and the final predictions are in agreement with the measured pulse-echo beam profiles. It thus seems that frequency-dependent attenuation is one. of the major causes of pulse-echo beam profile enlargement and beam divergence experienced for attenuating paths. |
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