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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 157 out of 330
| Title |
Interlaboratory comparison of ultrasonic attenuation and speed measurements. |
| Author |
Madsen EL, Frank GR, Carson PL, Edmonds PD, Frizzell LA, Herman BA, Kremkau FW, O'Brien WD, Parker KJ, Robinson RA. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1986 |
| Abstract |
A set of test samples, all containing ultrasonically equivalent tissue-mimicking material, was produced and measurements of ultrasonic speed and ultrasonic attenuation coefficients were made at seven laboratories using various techniques. The ultrasonic speed values agree well with one another, having a spread of about 0.3 per cent; thus, speed values for tissue parenchyma appearing in the literature are likely to be accurate. Values of ultrasonic attenuation coefficients agree fairly well with one another, with differences between individual values and the group mean of generally less than 20 per cent of the group mean. |
| Title |
Interlaboratory comparison of ultrasonic backscatter coefficient measurements from 2 to 9 MHz. |
| Author |
Wear KA, Stiles TA, Frank GR, Madsen EL, Cheng F, Feleppa EJ, Hall CS, Kim BS, Lee P, O'Brien WD Jr, Oelze ML, Raju BI, Shung KK, Wilson TA, Yuan JR. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
2005 |
| Abstract |
Objective. As are the attenuation coefficient and sound speed, the backscatter coefficient is a fundamental ultrasonic property that has been used to characterize many tissues. Unfortunately, there is currently far less standardization for the ultrasonic backscatter measurement than for the other two, as evidenced by a previous American Institute of Ultrasound in Medicine (AIUM)–sponsored interlaboratory comparison of ultrasonic backscatter, attenuation, and speed measurements (J Ultrasound Med 1999; 18:615–631). To explore reasons for these disparities, the AIUM Endowment for Education and Research recently supported this second interlaboratory comparison, which extends the upper limit of the frequency range from 7 to 9 MHz. Methods. Eleven laboratories were provided with standard test objects designed and manufactured at the University of Wisconsin (Madison, WI). Each laboratory was asked to perform ultrasonic measurements of sound speed, attenuation coefficients, and backscatter coefficients. Each laboratory was blinded to the values of the ultrasonic properties of the test objects at the time the measurements were performed. Results. Eight of the 11 laboratories submitted results. The range of variation of absolute magnitude of backscatter coefficient measurements was about 2 orders of magnitude. If the results of 1 outlier laboratory are excluded, then the range is reduced to about 1 order of magnitude. Agreement regarding frequency dependence of backscatter was better than reported in the previous interlaboratory comparison. For example, when scatterers were small compared with the ultrasonic wavelength, experimental frequency-dependent backscatter coefficient data obtained by the participating laboratories were usually consistent with the expected Rayleigh scattering behavior (proportional to frequency to the fourth power). Conclusions. Greater standardization of backscatter measurement methods is needed. Measurements of frequency dependence of backscatter are more consistent than measurements of absolute magnitude. |
| Title |
Interlaboratory comparison of ultrasonic backscatter, attenuation, and speed measurements. |
| Author |
Madsen EL, Dong F, Frank GR, Garra BS, Wear KA, Wilson T, Zagzebski JA, Miller HL, Shung KK, Wang SH, Feleppa EJ, Liu T, O'Brien WD Jr, Topp KA, Sanghvi NT, Zaitsev AV, Hall TJ, Fowlkes JB, Kripfgans OD, Miller JG. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1999 |
| Abstract |
In a study involving 10 different sites, independent results of measurements of ultrasonic properties on equivalent tissue-mimicking samples are reported and compared. The properties measured were propagation speed, attenuation coefficients, and backscatter coefficients. Reasonably good agreement exists for attenuation coefficients, but less satisfactory results were found for propagation speeds. As anticipated, agreement was not impressive in the case of backscatter coefficients. Results for four sites agreed rather well in both absolute values and frequency dependence, and results from other sites were lower by as much as an order of magnitude. The study is valuable for laboratories doing quantitative studies. |
| Title |
Interpolation scan convesion in pulse-echo ultrasound. |
| Author |
Robinson DE, Knight PC. |
| Journal |
Ultrason Imaging |
| Volume |
|
| Year |
1982 |
| Abstract |
Some disadvantages of current digital scan conversion techniques are reviewed. An improved system is described which uses linear interpolation between available sampled data points to provide an estimate of the echo reflectivity at each grid point in the image. This approach avoids the problems of 'missed pixels' inherent in the current approach, and the need to provide some smoothing or blurring function to remove them. The interpolated scan conversion allows data line spacing to be increased, leading to a reduced scan time for static scans and increased frame-rate for real-time, while retaining all the resolution available from the ultrasound system. |
| Title |
Intervening attenuation affects first-order statistical properties of ultrasound echo signals. |
| Author |
Zagzebski JA, Chen JF, Dong F, Wilson T. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1999 |
| Abstract |
Previous studies show that first-order statistical properties of ultrasound echo signals are related to the effective number of scatterers in the `resolution. cell' of a pulse-echo ultrasound system. When the effective number of scatterers is large (approximately 10 or more) this results in echo signals whose. amplitude follows a Rayleigh distribution, with the RF echo signal obeying Gaussian statistics; deviation from Rayleigh or Gaussian statistics yields. information on scatterer number densities. In this paper, the influence of the medium's attenuation on non-Gaussian properties of the echo signal is. considered. Preferential attenuation of higher frequency components of a pulsed ultrasound beam effectively broadens the beam and increases the. resolution cell size. Thus, the resultant non-Gaussian parameter for broad bandwidth excitation of the transducer depends not only on the scatterer. number density but also on the attenuation in the medium. These effects can be reduced or eliminated by using narrow-band experiments. |
| Title |
Intestinal hemorrhage from exposure to pulsed ultrasound. |
| Author |
Dalecki D, Raeman CH, Child SZ, Carstensen EL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1995 |
| Abstract |
Threshold exposures for producing intestinal hemorrhage in mice were determine using focused sources operating at 0.7, 1.1, 2.4 and 3.6 MHz. The choice of pulse length (10 microseconds) and pulse repetition frequency (100 Hz) made the exposures diagnostically relevant, while at the same time, minimized possible thermal contributions to the mechanism of action of the ultrasound. Each animal was irradiated at four to five abdominal sites for 5 min per site. Suprathreshold lesions ranged from small petechiae to hemorrhagic regions extending 4 mm or more along the intestine, depending upon the exposure levels. Higher frequencies were less effective in producing intestinal hemorrhage than lower frequencies. Thermocouple measurements of temperature rise in the intestine during ultrasound exposure revealed temperature increments between 1 degrees and 2 degrees C at the highest exposure levels. The frequency dependence of the production of intestinal hemorrhage together with the observed limited heating is consistent with a cavitation-related mechanism of action of pulsed ultrasound. |
| Title |
Into the eye with ultrasound. |
| Author |
Unknown. |
| Journal |
Time Mag |
| Volume |
|
| Year |
1964 |
| Abstract |
No abstract available. |
| Title |
Intracardiac ultrasound scanner using a micromachine (MEMS) actuator. |
| Author |
Zara JM, Bobbio SM, Goodwin-Johansson S, Smith SW. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2000 |
| Abstract |
Catheter-based intracardiac ultrasound offers the potential for improved guidance of interventional cardiac procedures. The objective of this research is the. development of catheter-based mechanical sector scanners incorporating high frequency ultrasound transducers operating at frequencies up to 20 MHz. The authors'. current transducer assembly consists of a single 1.75 mm by 1.75 mm, 20 MHz, PZT element mounted on a 2 mm by 2 mm square, 75 mu m thick polyimide table that. pivots on 3- mu m thick gold plated polyimide hinges. The hinges also serve as the electrical connections to the transducer. This table-mounted transducer is tilted using a. miniature linear actuator to produce a sector scan. This linear actuator is an integrated force array (IFA), which is an example of a micromachine, i.e., a. microelectromechanical system (MEMS). The IFA is a thin (2.2 mu m) polyimide membrane, which consists of a network of hundreds of thousands of micron scale. deformable capacitors made from pairs of metallized polyimide plates. IFAs contract with an applied voltage of 30-120 V and have been shown to produce strains as large. as 20% and forces of up to 8 dynes. The prototype transducer and actuator assembly was fabricated and interfaced with a GagePCI analog to digital conversion board. digitizing 12 bit samples at a rate of 100 MSamples/second housed in a personal computer to create a single channel ultrasound scanner. The deflection of the table. transducer in a low viscosity insulating fluid (HFE 7100, 3M) is up to +or-10 degrees at scan rates of 10-60 Hz. Software has been developed to produce real-time sector. scans on the PC monitor. |
| Title |
Intracavitary ultrasound phased arrays for noninvasive prostate surgery. |
| Author |
Hutchinson EB, Hynynen K. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1996 |
| Abstract |
The feasibility of using intracavitary ultrasound phased arrays for thermal surgery of the prostate was investigated. A simulation study was performed which demonstrated the ability of phased arrays to generate necrosed tissue volumes over anatomically appropriate ranges (2-6 cm deep and >6 cm axially) and investigated the effects of varying frequency, sonication time, maximum temperature, and blood perfusion on the necrosed tissue volume. An advantage that phased arrays have over geometrically focused transducers is that they are able to electronically scan a single focus over a specified range very quickly. This study demonstrated that the necrosed tissue volume may be increased by more than a factor of 100 by using electronic scanning. Scan parameters that were investigated included foci spacing, scan width, perfusion, maximum temperature, and unequal weighting of the foci. An optimization was performed to select the foci weighting parameters such that a uniform thermal dose was achieved at the focal depth, providing a more uniformly heated target volume. Finally, the ability of linear ultrasound phased arrays to create necrosed tissue lesions was demonstrated experimentally in fresh beef liver using a single stationary focus and single focus scans generated by an aperiodic 0.83-MHz 57-element linear ultrasound phased array. |
| Title |
Intracellular microcurrents caused by ultrasound waves. |
| Author |
El'piner IE, Faikin IM, Basurmanova OK. |
| Journal |
Fed Proc Transl Suppl |
| Volume |
|
| Year |
1966 |
| Abstract |
No abstract available |
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