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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 169 out of 330
| Title |
Measurement and simulation of the scattering of ultrasound by penetrable cylinders. |
| Author |
Robinson BS, Greenleaf JF. |
| Journal |
Acoust Imaging |
| Volume |
|
| Year |
1984 |
| Abstract |
This paper presents some results of a study on the direct scattering problem. however, due to the intimate relationship between direct and inverse scattering, the results also have relevance for inverse scattering. for the results to have relevance for diffraction tomography, the complex amplitude, both magnitude and phase, of forward scattering in the near field was investigated. the results indicate that quite small changes in acoustic speed cause significant scattering, particularly in the forward direction. |
| Title |
Measurement and use of acoustic nonlinearity and sound speed to estimate composition of excised livers. |
| Author |
Sehgal CM, Brown GM, Bahn RC, Greenleaf JF. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1986 |
| Abstract |
The acoustic nonlinearity parameter B/A and sound speed c have been determined for excised normal and abnormal human livers at 20-37 ?C. These values are compared with analytic measurements of fat and water content of tissues. The results show that normal liver containing 71.0% water and 2.9% fat by weight has a B/A value of 6.75 and sound speed of 1592 m/s at 37 ?C. Both these parameters increase at an average rate of 0.026 ?C and 1.5 m/s/?C, respectively, as the temperature is raised from 20 to 37 ?C. Fatty liver (24% fat by weight) exhibits highest B/A (9.12) and lowest c (1522 m/s) of all the livers studied. In contrast to normal livers sound speed in such a liver was found to decrease with temperature. Based on the acoustic and composition measurements, quantitative correlations of B/A and c with fat-water composition have been developed. Inversion of these relationships provide a simple method to determine composition of a tissue sample from B/A and c measurements. |
| Title |
Measurement of acoustic dispersion using both transmitted and reflected pulses. |
| Author |
He P. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
|
| Abstract |
Traditional broadband transmission method for measuring acoustic dispersion requires the measurements of the sound speed in water, the thickness of the specimen, and the phase spectra of two transmitted ultrasound pulses. When the sound speed in the specimen is significantly different from that in water, the overall uncertainty of the dispersion measurement is generally dominated by the uncertainty of the thickness measurement. In this paper, a new water immersion method for measuring dispersion is proposed which eliminates the need for thickness measurement and the associated uncertainty. In addition to recording the two transmitted pulses, the new method requires recording two reflected pulses, one from the front surface and one from the back surface of the specimen. The phase velocity as well as the thickness of the specimen can be determined from the phase spectra of the four pulses. Theoretical analysis and experimental results from three specimens demonstrate the advantages of this new method. |
| Title |
Measurement of blood flow by ultrasound: accuracy and sources of error. |
| Author |
Gill RW. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1985 |
| Abstract |
Doppler ultrasound has now developed to the point where the rate of flow of blood in a given vessel can be measured with appropriate instrumentation. The theoretical basis of Doppler flow measurement is reviewed in this paper, with particular emphasis on the potential and actual sources of error. Three distinct approaches are identified, and the strengths and weaknesses of each discussed. The separate errors involved in estimating the vessel cross-sectional area, the angle of approach, and the Doppler shift are analyzed, together with the question of the uniformity of scattering from the blood. In vivo and in vitro tests of the accuracy obtained using a number of Doppler flow measuring instruments are then reviewed. It is concluded that the Doppler methods are capable of good absolute accuracy when suitably designed equipment is used in appropriate situations, with systematic errors of 6% of less. There are, however, considerable random errors, attributable primarily to errors in measuring the cross-sectional area and the angle of approach. Repeating the measurement of flow several times and averaging the results can reduce these random errors to an acceptable level. |
| Title |
Measurement of bone properties by ultrasound to develop diagnostic equipment. |
| Author |
Chubachi N, Sannomyia T, Asai H. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1990 |
| Abstract |
In this paper, a new extracorporeal measurement system by means of excitation and detection of leaky surface waves has been proposed in order to develop diagnostic equipment for bones. Bovine femoral bone has been taken as a bone sample for in vitro experiments, and velocities and attenuations for the longitudinal bulk waves have been measured in the range of 2-10 MHz. Based on the measured results as well as the published data for bone properties, an ultrasonic measurement system has been designed to be operated at a frequency of 1 MHz. With the measurement system, leaky surface skimming compressional waves (LSSCWs) have been successfully excited on a polished flat surface of bones with water coupling, and phase velocities of LSSCWs have been measured by the V(z) curve method developed in acoustic microscopy. |
| Title |
Measurement of fluid flow using the ultrasound time domain correlation technique in a flow phantom and in guinea pigs. |
| Author |
Safvi AA. |
| Journal |
Thesis(MS): Univ of Illinois |
| Volume |
|
| Year |
1996 |
| Abstract |
Measurement of blood flow is an important consideration in diseases that involve the circulatory system. Ultrasound has been used extensively to measure blood flow in the past. There are two techniques that can be used to measure flow, Doppler and time domain correlation. In this thesis the time domain correlation technique is used. A computer implementation of the technique is developed. It is first verified by using it to calculate velocity from a known set of data. A fluid flow phantom is developed in which a known rate of flow can be established. The phantom is utilized in the measurement of flow using the correlation technique. It is further tested in a live guinea pig to measure blood flow in various organs. The results verify the correct implementation of the time domain correlation technique. The phantom measurements confirm its ability to measure fluid flow. The guinea pig results do not confirm or deny the ability of the technique to measure flow in the live animal. It requires further examination and evaluation in the live animal model to determine its true capability to measure flow in complex flow patterns such as the micro- vasculature. |
| Title |
Measurement of fluid turbulence based on pulsed ultrasound techniques. Part 1. Analysis. |
| Author |
Garbini JL, Forster FK, Jorgensen JE. |
| Journal |
J Fluid Mech |
| Volume |
|
| Year |
1982 |
| Abstract |
No abstract available. |
| Title |
Measurement of fluid turbulence based on pulsed ultrasound techniques. Part 2. Experimental investigation. |
| Author |
Garbini JL, Forster FK, Jorgensen JE. |
| Journal |
J Fluid Mech |
| Volume |
|
| Year |
1982 |
| Abstract |
An extensive experimental program in both laminar and turbulent flow was undertaken to examine the validity of all of the major implications of the model of the pulsed ultrasonic Doppler velocimeter for turbulent flow developed in part 1 of this investigation. The turbulence measurements were made in fully developed flow at the center of a 6-28 cm diameter pipe. The Reynolds number of the flow ranged from 6000 to 40 000. The carrier frequency of the ultrasonic velocimeter was 4-7 MHz. Measurements of the turbulence intensity and of the one-dimensional velocity spectra made with the ultrasonic velocimeter are compared with the analysis and with the actual quantities as measured by a hot-film anemometer. The experimental results are in agreement with theoretical predictions. Measurements of one-dimensional turbulence spectra with reduced ambiguity spectra made by the two sample volume methods described in part 1 are presented. The results verify the analysis and indicate that an improvement in the useful dynamic range of the velocity power spectrum of nearly three orders of magnitude can realistically be achieved. |
| Title |
Measurement of high frequency ultrasound in liquids using high-resolution Bragg reflection technique. |
| Author |
Takagi K, Negishi K. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1978 |
| Abstract |
A new light scattering technique has been established for simultaneous measurement of ultrasonic velocity and absorption in liquids over a frequency range from 100 to 1000 MHz. The technique is applied to studies of vibrational relaxation in the uhf range, and the velocity-dispersion and absorption curves in several organic liquids are presented. |
| Title |
Measurement of human fetal blood flow. |
| Author |
Eik-Nes SH, Brubakk AO, Ulstein MK. |
| Journal |
Br Med J |
| Volume |
|
| Year |
1980 |
| Abstract |
Real-time B-mode ultrasonography was combined with a pulsed Doppler ultrasound technique for transcutaneous measurement of human fetal blood flow in the aorta and intra-abdominal part of the umbilical vein. The target vessel was located and its diameter measured in the two-dimensional real-time image. The pulsed Doppler transducer was attached to the real-time transducer at a fixed angle. By processing the Doppler shift signals the instrument estimated the mean and maximum blood velocities and the integral under the velocity curves. This permitted calculation of the blood flow. The method was applied to 26 fetuses in normal late pregnancies. Mean blood flow in the descending part of the fetal aorta based on maximum velocity was 191 ml/kg/min. Mean flow in the intra-abdominal part of the umbilical vein was 110 ml/kg/min. This method of measurement is non-invasive and opens new perspectives in studying fetal haemodynamics. |
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