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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 189 out of 330
| Title |
NxN square-element ultrasound phased-array applicator: simulated temperature distributions associated with directly synthesized heating patterns. |
| Author |
Ibbini MS, Ebbini ES, Cain CA. |
| Journal |
IEEE Trans Ultrason Ferroelectr Freq Control |
| Volume |
|
| Year |
1990 |
| Abstract |
Computer simulations to demonstrate the possibility of heating small tumors by appropriately driving the electronic control circuitry of an nxn square-element ultrasonic phased array are conducted. The synthesis method consists of simultaneously focusing the ultrasonic beam at different points uniformly distributed along the tumor periphery and, hence, involves no scanning. It is demonstrated that by combining the multiple focusing feature with a new field phasing concept, typical undesired hot spots can be eliminated. The tissue thermal response to this heating modality is investigated by iteratively solving the three-dimensional steady-state bioheat equation. Temperature distributions associated with different directly synthesized power deposition patterns are simulated and discussed. |
| Title |
Observation of pulsed medical ultrasound gratings in the optical farfield. |
| Author |
Riley WA, Barnes RW. |
| Journal |
Proc Ninety-Fourth Meet Acoust Soc Am - Miami Beach |
| Volume |
|
| Year |
1977 |
| Abstract |
No abstract available. |
| Title |
Observations on the combined effect of ultrasound and x-rays on the growth of the roots of Zea mays. |
| Author |
Hering ER, Shepstone BJ. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
1976 |
| Abstract |
The roots of Zea mays seedlings were exposed to ultrasonic radiations (1 MHz) of intensities in the range of 0-1-0-8 W cm-2 (pulsed or continuous modes) for times between 2 and 60 min, together with an X-ray dose of 775 rad which was given before, after or simultaneously with the ultrasound. These experiments have shown that ultrasound and X-rays seem to act independently of each other, suggesting that the mechanism of damage due to X-rays is different from that due to ultrasound. An increase in the X-ray effectiveness under the action of ultrasound, as reported.by various authors who worked with different tissues, has not been found. |
| Title |
Observed cellular effects of ultrasound: Applicability to the issue of safety. |
| Author |
Miller MW. |
| Journal |
Appl Radiol |
| Volume |
|
| Year |
1983 |
| Abstract |
The application of data from experiments with nonhuman, nonthermal exposures of ultrasound to the question of human health and safety can be made only if information on physical mechanisms of action is available. For many such reported in vitro biologic effects of ultrasound, a commonality is the involvement of bubbles stabilized against diffusion. |
| Title |
Observer efficiency in boundary discrimination tasks related to assessment of breast lesions with ultrasound. |
| Author |
Abbey CK, Zemp RJ, Liu J, Lindfors KK, Insana MF. |
| Journal |
Proc SPIE |
| Volume |
|
| Year |
2006 |
| Abstract |
The statistical efficiency of human observers in diagnostic tasks is an important measure of how effectively task relevant information in the image is being utilized. Most efficiency studies have investigated efficiency in terms of contrast or size effects. In many cases, malignant lesions will have similar contrast to normal or benign objects, but can be distinguished by properties of their boundary. We investigate this issue in the framework of malignant/benign discrimination tasks for the breast with ultrasound. In order to identify effects in terms of specific features and to control for other effects such as aberration or specular reflections, we simulate the formation of beam-formed radio-frequency (RF) data. We consider three tasks related to lesion boundaries including boundary eccentricity, boundary sharpness, and detection of boundary spiculations. We also consider standard detection and contrast discrimination tasks. We find that human observers exhibit surprisingly low efficiency with respect to the Ideal observer acting on RF data in boundary discrimination tasks (0.08%-3.3%), and that efficiency of human observers is substantially increased by Wiener-filtering RF frame data. We also find a limitation in efficiency is the computation of an envelope image from the RF data recorded by the transducer. Approximations to the Ideal observer acting on the envelope images indicate that humans may be substantially more efficient (10%-75%) with respect to the envelope Ideal observers. Our work suggests that significant diagnostic information may be lost in standard envelope processing in the formation of ultrasonic images. |
| Title |
Observer efficiency in discrimination tasks simulating malignant and benign breast lesions imaged with ultrasound. |
| Author |
Abbey CK, Zemp RJ, Liu J, Lindfors KK, Insana MF. |
| Journal |
IEEE Trans Med Imaging |
| Volume |
|
| Year |
2006 |
| Abstract |
We investigate and extend the ideal observer methodology developed by Smith and Wagner to detection and discrimination tasks related to breast sonography. We provide a numerical approach for evaluating the ideal observer acting on radio frequency (RF) frame data, which involves inversion of large nonstationary covariance matrices, and we describe a power-series approach to computing this inverse. Considering a truncated power series suggests that the RF data be Wiener-filtered before forming the final envelope image. We have compared human performance for Wiener-filtered and conventional B-mode envelope images using psychophysical studies for 5 tasks related to breast cancer classification. We find significant improvements in visual detection and discrimination efficiency in four of these five tasks. We also use the Smith-Wagner approach to distinguish between human and processing inefficiencies, and find that generally the principle limitation comes from the information lost in computing the final envelope image. |
| Title |
Obstetric sonography: The output display standard and ultrasound bioeffects. |
| Author |
O'Brien WD Jr, Siddiqi TA. |
| Journal |
Book Chapter |
| Volume |
|
| Year |
2001 |
| Abstract |
No abstract available. |
| Title |
Occurrence of transient cavitation in pulsed sawtooth ultrasonic fields. |
| Author |
Ayme EJ, Carstensen EL. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1988 |
| Abstract |
Thus far, studies conducted to assess the safety of diagnostic ultrasound have employed.sinusoidal sound fields. To evaluate the influence of nonlinearly distorted acoustic fields, this article compares the responses of microbubbles of variable size, exposed to (1) a sinusoidal pulse and (2) a sawtooth pulse. The nonlinear oscillations of a spherical bubble in a viscous compressible liquid stimulated into motion by an ultrasonic pulse are predicted, using a theoretical model for bubble dynamics. The maximum gas pressures inside the bubble when it collapses under the influence of a sinusoid or a sawtooth are deduced. Experimental work on Drosophila larvae exposed to sinusoidal and to sawtooth fields is consistent with the theoretical analysis. |
| Title |
Oil-in-gelatin dispersions for use as ultrasonically tissue-mimicking materials. |
| Author |
Madsen EL, Zagzebski JA, Frank GR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1982 |
| Abstract |
A form of tissue-mimicking material is reported in which oil droplets are dispersed in a water-based gelatin. Broad ranges of ultrasonic parameters, including speed of sound, attenuation coefficient, density and backscatter level, exist for this material. Very important, the attenuation coefficients are nearly proportional to the frequency as in the case of mammalian tissue and the available attenuation coefficient slopes span the range of mammalian tissues. The available range of slopes is 0.1.dB/cm/MHz through at least 2.0 dB/cm/MHz. The available speeds of sound range from a minimum below that of mammalian fat (approximately 1460 m/s) to a maximum above the accepted average for human tissue (1540 m/s). Densities available range from below that of fat (approximately 0.92 gm/cm3) through about 1.00 gm/cm3. Backscatter levels are easily made negligible compared to clinical levels and compared to those exhibited in previously reported tissue-mimicking materials in which the suspended particles are solid (Madsen et al. 1978; Burlew et al., 1980). Addition of solid or hollow glass scatterers allows backscatter levels to be made comparable to those clinically observed. |
| Title |
Oil-in-gelatin dispersions for use as ultrasonically tissue-mimicking materials. |
| Author |
Madsen EL, Zagzebski JA, Frank GR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1982 |
| Abstract |
A form of tissue-mimicking material is reported in which oil droplets are dispersed in a water-based gelatin. Broad ranges of ultrasonic parameters, including speed of sound, attenuation coefficient, density and backscatter level, exist for this material. Very important, the attenuation coefficients are nearly proportional to the frequency as in the case of mammalian tissue and the available attenuation coefficient slopes span the range of mammalian tissues. The available range of slopes is 0.1 dB/cm/MHz through at least 2.0 dB/cm/MHz. The available speeds of sound range from a minimum below that of mammalian fat (~1460 m/s) to a maximum above the accepted average for human tissue (1540 m/s). Densities available range from below that of fat (~0.92 gm/cm3) through about 1.00 gm/cm3. Backscatter levels are easily made negligible compared to clinical levels and compared to those exhibited in previously reported tissue-mimicking materials in which the suspended particles are solid (Madsen, 1978; Burlew, 1980). Addition of solid or hollow glass scatterers allows backscatter levels to be made comparable to those clinically observed.
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