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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 294 out of 330
| Title |
Ultrasonic propagation through fixed and unfixed tissues. |
| Author |
Bamber JC, Hill CR, King JA, Dunn F. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1979 |
| Abstract |
Ultrasound attenuation and backscattering coefficients and speed of sound were determined experimentally, as functions of frequency, in samples of fresh mammalian brain, liver, and spleen, and in the same specimens fixed histochemically. It is observed that 4% formalin and 5% potassium dichromate are greatly superior to ethyl alcohol for consistently preserving the ultrasonic propagation properties to within only a few percent of those of the original fresh, unfixed material. |
| Title |
Ultrasonic properties of biological media. |
| Author |
Dunn F. |
| Journal |
Ultrasound Interact Biol Med |
| Volume |
|
| Year |
1983 |
| Abstract |
No abstract available. |
| Title |
Ultrasonic pulse-echo beam width and axial response approximations for clinical broadband focused transducers. |
| Author |
Banjavic RA Zagzebski JA. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1981 |
| Abstract |
A means of estimating the pulse-echo response beam width and the position of the peak: in the pulse-echo axial response for clinical ultrasonic transducers is presented. Using a simple model based on continuous wave propagation, equations describing the width of a transmitted beam and the axial pressure amplitude as a function of distance from the transducer have been adapted to describe broadband transducers. The efficacy of these adaptations is verified by comparison to actual measurements performed on both focused and non-focused transducers for attenuating paths as well as "lossless" water paths. By using either the center frequency or a computed mean frequency to represent a broadband pulse, both the −20 dB pulse-echo response beam width and the divergence of the beam as it propagates through tissue-like material can be well approximated. Also, for nonattenuating paths, the position of the peak in the axial pressure profile, and, hence, the focal plane position, can be estimated from the phys ical dimensions of the focused transducer and the center or mean frequency. |
| Title |
Ultrasonic pulse-echo techniques in ophthalmic examination and diagnosis. |
| Author |
Freeman MH. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1963 |
| Abstract |
The use of ultrasonic techniques in medicine has been a research field for some years and they are now acde3pted as having a place, albeit in the future, alongside the X-ray techniques of radiotherapy and diagnosis. The therapeutic use of ultrasound has already promoted the inclusion of a paper in this journal. Its use in ophthalmology for diagnosis of abnormal ocular conditions has been developed over the past eight years; more recently it has been applied to the measurement of the more important optical dimensions of the healthy eye in the investigation of refractive error and its cause. This paper traces the development of these diagnostic and biometric applications of ultrasound to ophthalmology. |
| Title |
Ultrasonic quantification of the tissue microstructure of spontaneous mammary tumors in rats. |
| Author |
Oelze ML, Zachary JF, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2002 |
| Abstract |
The quantification of tissue microstructure using ultrasound can aid in the detection and classification of disease. Eight retired breeder were acquired that had developed spontaneous mammary tumors. Two-dimensional B-mode images of the rat tumors were constructed from backscattered echoes. After scanning, tumors were dissected free from each rat, trimmed in the plane of ultrasound exposure, fixed in 10 % neutral-buffered formalin, embedded in paraffin, sectioned at 5 /spl mu/m, and stained with hematoxylin and eosin. Tumors were diagnosed microscopically as mammary gland fibroadenomas. Regions-of-interest (ROIs) were selected in the tumors and surrounding tissues and scatterer properties (average scatterer size and acoustic concentration) were estimated from the backscattered RF signal. Scatterer estimates were made by using least squares to fit a line to the measured form factor that was calculated from the backscattered power spectrum. Noise reduces the ability to make estimates of scatterer properties. A weighting scheme was used to reduce the effects of noise and increase the ability to make accurate estimates. Comparison of scatterer estimates made between normal tissues and tissues inside the tumors were made. On average, the estimated scatterer diameters inside the tumors were 30 % larger at 107 micrometers than estimates of scatterer diameters outside the tumors averaging 82 micrometers. Similarly, the average acoustic concentration estimated inside the tumor was 3.16/spl times/10/sup -2/ mm/sup -3/ as opposed to 0.746 mm/sup -3/ for outside the tumor. In all but one of the rats, there was a statistically significant difference (P<0.05) between estimates of scatterer properties made inside the tumors and in surrounding healthy tissues. Enhanced B-mode images were constructed by superimposing colored pixels that corresponding to the estimated scatterer properties on the gray-scale B-mode images. The enhanced B-mode images also showed differences between tissues inside and outside the tumors. |
| Title |
Ultrasonic reflection mode imaging of the acoustic nonlinearity parameter. |
| Author |
Hooman H. |
| Journal |
Thesis(PHD): Univ of Illinois |
| Volume |
|
| Year |
1992 |
| Abstract |
The problem of mathematically modeling the nonlinear interaction of ultrasound beams is addressed. The counterpropagation model is studied and a new model, called the copropagation reflection model, is proposed. The new model shows that the copropagation of the probe and the reflected pump leads to nonlinear interaction. Simulation of the nonlinear interaction of the pump and the probe shows that the sensitivity of the copropagation reflection is higher than the counterpropagation nonlinear interaction. The theoretical curves representing the different models are compared with experimental data obtained under different experimental conditions, and the experimental study of the nonlinear interaction shows that the copropagation reflection model is confirmed by experimental data. This model offers the possibility of achieving greater accuracy in nonlinear imaging. |
| Title |
Ultrasonic reflectivity:Role of proteins and fat. |
| Author |
Ahuja AS. |
| Journal |
Reflections |
| Volume |
|
| Year |
1979 |
| Abstract |
Reflection and scattering characteristics of interfaces in a tissue depend upon the differences in acoustic impedances or bulk moduli and mass densities. For ultrasonic imaging purposes,soft tissue is modeled as a composite of three components, namely water, proteins,such as hemoglobin and collagen, and of fat have been estimated and reflection coefficients at collagen interfaces have been computed.
Velocity of ultrasound in blood and hemoglobin solutions has been known for decades, however, the bulk modulus of hemoglobin has not been estimated. By applying a mixture law based on volume averages to the velocity data, the bulk modules of hemoglobin has been computed to be 4.4x1010dynes/cm2.
Published attenuation data in normal and infarcted myocardial tissues have been correlated with the viscoelastic model proposed earlier. Infarction is known to enhance the level of collage in myocardium. From the knowledge of the correlation parameters, by assuming the infarcted myocardium as a composite of collagen and normal myocardium, and by applying the appropriate mixture laws, bulk modulus of collagen is determined to be approximately 3.9x1010dynes/cm2.
The mass densities of fat, hemoglobin and collagen are 0.95,1.34 and 1.35g/cm3, respectively. Heretofore, based on the small differences in average densities of tissues (about 5%), the role of density has been ignored. As is seen, large density differences on the order of 30-40% exist in soft tissues. Since scattering occurs at interfacial discontinuities in densities contribute significantly to the ultrasonic scattering.
The bulk moduli of fat,isotonic saline and myocardium are , 2x1010, 2.31x1010, 2.515x1010dynes/cm2, respectively. By using the values of densities and bulk moduli, reflection coefficients at collagen interfaces with saline, myocardium and fat have been seen to be 6to 8 times greater than that at saline-myocardium interface. These results qualitatively support the observed enhanced reflectivity in abnormal livers and infarcted hearts.
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| Title |
Ultrasonic Schlieren system using a pulsed gas laser. |
| Author |
Newman DR. |
| Journal |
IEEE Trans Sonics Ultrason |
| Volume |
|
| Year |
1973 |
| Abstract |
A pulsed gas laser emitting an extremely short duration and high power pulse at fast repetition rates has been used in an ultrasonic schlieren system. The system allows visualization of individual wavefronts within tone bursts of ultrasound at frequencies up to 20 MHz. Highly damped, high resolution pulses can also be imaged. The effect of variations of the light pulse duration, jitter, and focal plane aperture on the resulting image is discussed. The experimental ultrasonic and optical systems are described, and examples of ultrasonic propagation are shown. |
| Title |
Ultrasonic spectral investigations for tissue characterization. |
| Author |
Lizzi FL, Laviloa MA. |
| Journal |
Ultrasound Med |
| Volume |
|
| Year |
1976 |
| Abstract |
No abstract available. |
| Title |
Ultrasonic spectral parameter characterization of apoptosis. |
| Author |
Kolios MC, Czarnota GJ, Lee M, Hunt JW, Sherar MD. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2002 |
| Abstract |
Ultrasound (US) spectral analysis methods are used to analyze the radiofrequency (RF) data collected from cell pellets exposed to chemotherapeutics that induce apoptosis and other chemicals that induce nuclear transformations. Calibrated backscatter spectra from regions-of-interest (ROI) were analyzed using linear regression techniques to calculate the spectral slope and midband fit. Two f/2 transducers, with operating frequencies of 30 and 34 MHz (relative bandwidths of 93% and 78%, respectively) were used with a custom-made imaging system that enabled the collection of the raw RF data. For apoptotic cells, the spectral slope increased from 0.37 dB/MHz before drug exposure to 0.57 dB/MHz 24 h after, corresponding to a change in effective scatterer radius from 8.7 to 3.2 microm. The midband fit increased in a time-dependent fashion, peaking at 13dB 24 h after exposure. The statistical deviation of the spectral parameters was in close agreement with theoretical predictions. The results provide a framework for using spectral parameter methods to monitor apoptosis in in vitro and in in vivo systems and are being used to guide the design of system and signal analysis parameters. |
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