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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 34 out of 330
| Title |
An alternative explanation for a postulated non-thermanl, non-cavitational ultrsound mechanism of action on in vitro cells at hyperthemic temperature. |
| Author |
Inoue M, Miller MW, Church CC. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
1990 |
| Abstract |
V-79 cells were suspended in medium with 10 or 20% serum, and exposed to a continuous wave of 1 or 3.4 MHz ultrasound (0.7-1 W/cm2) for 0-90 min in polystyrene test tubes at 37 or 43?C, and subsequently assessed for cell lysis, plating efficiency and surviving fraction. The effectiveness of the ultrasound regimes was enhanced at 43?C. Thermocouple measurements of temperatures in the cell culture medium in the test-tube revealed an increase of about 0.5?C under insonation conditions, using the 1 MHz; 10% serum; 37?C regime. The results were broadly consistent with an ultrasound-induced incremental thermal burden causing an increased effectiveness of the ultrasound exposures at hyperthermic temperatures. |
| Title |
An analysis of lesion development in the brain and in plastics by high-intensity focused ultrasound at low-megahertz frequencies. |
| Author |
Robinson TC, Lele PP. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1972 |
| Abstract |
Thermal factors are believed to play a dominant role in the development of the structural and functional effects of irradiation of the nervous system with focused ultrasound at low megahertz frequencies. Similar mechanisms are postulated to underlie the effects of irradiation in methacrylate, which is frequently used as a test material to evaluate the influence of various factors on the results obtained. This study was undertaken to determine if thermal mechanisms alone can explain the development of trackless focal alterations (lesions) and all of their measurable characteristics in plastic as well as in brain. A purely thermal model is assumed and analytical prediction of lesion development and lesion size and shape for varying values of ultrasonic and thermal constants and controllable variables (frequency, focusing, dosage, target depth, etc.) is attempted. An empirical equation to describe the axial and radial ultrasonic energy distribution at the focus in water is derived. Appropriate heat transfer equations are developed for temperature distributions resulting from ultrasonic irradiation. The computed temperature profiles are plotted against nondimesionalized parameters. Temperatures at the lesion boundary were determined experimentally. Lesion dimensions read off the computed temperature profiles at the measured lesion boundary temperature are compared with experimental data. Agreement of analysis and data shows that, within the range of ultrasonic parameters used in this study, the development of lesions in the brain are explained by thermal mechanisms. |
| Title |
An analysis of the ultrasonic zone lens. |
| Author |
Golis MJ. |
| Journal |
IEEE Trans Sonics Ultrason |
| Volume |
|
| Year |
1968 |
| Abstract |
The zone lens is discussed both from an analytical and empirical viewpoint for potential applications in industrial materials processing and biological radiation studies. Mathematical analysis shows that the zone lens (a special stepped lens) of Tarnoczy falls in the aplanatic surface class of an ellipse. This lens is investigated in detail with regard to 1) the mathematical derivation of the lens contour, 2) maximum apertures allowable for a given index of refraction, and 3) correlation of index of refraction and ellipse eccentricity. The measured response characteristics of the zone are described for both Textolite and aluminum lenses, using 800-kHz ultrasound exclusively. Laboratory results shown were obtained by using 1) point-by-point field plotting, 2) schlieren photography, and 3) fluid-surface agitation techniques, all used in water. All methods of examination showed an improvement of sound output when zone lenses were introduced. Zone lenses, when compared to simple spherical lenses, supplied higher sound densities within the focal region with Textolite lenses but no appreciable improvement was found with the aluminum lenses. Applications for industrial and medical use are discussed as well as potential areas for future investigation. The zone lenses are considered superior to spherical lenses for in-line excitation purposes due to their inherent hole in the center, thus allowing fluids to flow directly through the lens. |
| Title |
An analytical study of Doppler ultrasound systems. |
| Author |
Azimi M, Kak AC. |
| Journal |
Ultrason Imaging |
| Volume |
|
| Year |
1985 |
| Abstract |
The past theoretical contributions in Doppler ultrasonic imaging have borrowed heavily from the electromagnetic case. In these contributions, most points of departure between the ultrasonic and electromagnetic cases were taken care of by heuristic incorporation of factors in the derived formulas. A theory is presented that is more complete in the sense that it specifically accounts for the diffracted fields of the transducer aperture (assumed to be a source of a Gaussian focussed beam), the interaction of these fields with the scattering sites, and the interaction of the transducer aperture with the back scattered fields. The theoretical formulation was used to perform a series of computer simulation studies on Doppler ultrasound. The control afforded by the theory over different parameters of the system has allowed us to study the effect of the different signal bandwidths, tissue attenuation constants, and the role of transducer design in the ultrasound Doppler systems. |
| Title |
An annular focus ultrasonic lens for local hyperthermia treatment of small tumors. |
| Author |
Beard RE, Magin RL, Frizzell LA, Cain CA. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1982 |
| Abstract |
A system for applying local hyperthermia employing ultrasonic transducers with annular focusing lenses gave better temperature uniformity in small fibrosarcomas than conventional unfocused transducers. The lenses were designed for ultrasonic frequencies of 3, 4, 5 and 9 MHz for tumors approximately 6 mm dia. Tests in degassed water indicated that the focusing lenses concentrated approx. 80% of the ultrasonic energy into an annular-shaped focus of 6 mm dia. located at a distance of 3 cm in front of the lens. These transducers were used to heat subcutaneous PARA-7 fibrosarcomas in hamsters. Steady-state temperature measurements indicated temperature gradients within tumors of 0.5-1.0 degree C when transducers employing annular-focused lenses were used, versus gradients of 2.0-2.3 degree C with 10 mm dia. unfocused transducers. |
| Title |
An anthropomorphic ultrasound breast phantom containing intermediate-sized scatterers. |
| Author |
Madsen EL, Zagzebski JA, Frank GR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1982 |
| Abstract |
An anthropomorphic breast phantom, built from materials which mimic tissue parenchymae with respect to attenuation coefficients, speeds of sound, densities and backscatter levels, is described in detail. One of the outstanding features of the.phantom is that 30% of the volume of the glandular region consists of tissue-mimicking fat, the remainder being tissue-mimicking glandular (non-adipose) tissue. The presence of these tissue-mimicking fat globules should cause ultrasound beam distortions similar to those found in clinical scans of the breasts of younger women. Halliwell (1977) has presented direct evidence for such beam distortions in real breasts. Other tissues simulated in the phantom are: skin, subcutaneous and retromammary fat, Cooper's ligaments, ducts and (abnormal) masses. The potential areas of usefulness of the phantom are: aiding in the development of more effective ultrasound imaging machines, discovering-- or verifying the causes of--various artifacts in breast imaging, routine testing of instruments being used clinically for breast imaging, and training of ultrasonographers. Ultrasound images of the phantom, made using three different instruments, are displayed and discussed. |
| Title |
An approach to boundary detection in ultrasound imaging. |
| Author |
Czerwinski RN, Jones DL, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1993 |
| Abstract |
Ultrasound imaging systems pose unique challenges for standard edge detection algorithms, because the boundaries between regions of interest in an ultrasonogram are typically bright streaks between similar intensity regions, rather than demarcations between regions of differing contrast. This paper presents an approach to boundary identification in ultrasound images that sidesteps this problem by the use of operators that work parallel to the edges rather than perpendicular, as most edge detection procedures do. These operators, called “sticks”, are line segments short enough that they can locally approximate the edges in the image, but long enough that their projections onto background noise are insignificant. The algorithm produces a new image by plotting at every point the local projection of the original image onto the stick whose orientation relative to the image maximizes the projected value. The result is an image with reduced speckle noise and enhanced edges in which boundaries between different regions can be more easily detected. This approach has been applied to real-world distance estimation research; processed images indicate distances which correlate highly with physical measurements of the actual tissue. |
| Title |
An approach to the design of sparse array systems. |
| Author |
Erstad JO, Holm S. |
| Journal |
Proc IEEE Ultrason Symp |
| Volume |
|
| Year |
1994 |
| Abstract |
Sparse arrays have been proposed for two-dimensional arrays for three-dimensional ultrasound imaging in order to reduce the number of channels in the system. Such arrays have been designed by picking array elements in a random fashion, either according to a uniform or a Gaussian distribution. A random array can have large variations in the level of the maximum sidelobe. A method for optimization of the sidelobe level of 1-D sparse arrays has been demonstrated. This shows that weighting can give responses that resemble filled DolphChebyshev arrays. The initial thinning pattern is of less importance for the final result, but the less ideal the unweighted pattern is, the more dynamic range is required from the weight function. |
| Title |
An approach to ultrasonic risk assessment and an analysis of selected experimental studies. |
| Author |
O'Brien WD Jr, Withrow TJ.(Saunders RC, James AE Jr eds.) |
| Journal |
Book Chapter |
| Volume |
|
| Year |
1985 |
| Abstract |
Introduction: It has been more than a decade since the first major efforts to assess the risk of ultrasonic energy have been made (1,2). Since then there have been numerous reviews and assessments (3-10). And, even today, there are projects which have as their aim an assessment of the health risks from diagnostic ultrasound (11-13). And yet, the basic status regarding risk assessment has remained unchanged during this time yiz., the studies necessary to support a reliable assessment of the risks associated with human exposure to ultrasound have not been done. So, rather than present another broad discussion of ultrasonic risk assessment, it seemed to be much more reasonable to focus upon one ultrasonically induced biological observation, yiz., fetal weight reduction. But, prior to a discussion of ultrasonically induced fetal weight reduction, let us first consider an approach to risk assessment and then a view of the general trends as they relate to diagnostic level, ultrasonic biological effects. Here, the effect of ultrasound on immunological function and on sister chromatid exchange frequency will be considered as examples. |
| Title |
An assessment of selected medical instrumentation: A 5-year research and development agendum for ultrasonic imaging diagnostic instrumentation. |
| Author |
Busser JH. |
| Journal |
Rep AEMB |
| Volume |
|
| Year |
1975 |
| Abstract |
A priority list of research and development objectives in medical ultrasound has been assembled to indicate needed development of new capabilities in diagnosis over the next 5 years. Detailed rationale and the complex relationships between issues are given. The four previously published, discipline-oriented reports, from which the list was developed, are included in full as appendices. Thus, a complete background of information is provided for decision making in this field. The useful life of the report is expected to extend over a 3-5 year period. |
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