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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 84 out of 330
| Title |
Determination of in situ exposure. |
| Author |
O'Brien WD. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1986 |
| Abstract |
A distinction was made between the measurable in situ ?exposure,? and ?dose? which is not measurable. The difficulty in attempting to calculate the in situ exposure of ultrasound at the location of the developing embryo within the gestational sac was presented. On the basis of tissue properties the calculated total attenuation of a 3.5 MHz ultrasound beam transmitted from the transducer to the gestational sac is 4.1 dB, shown in Table 6. However, this value varies considerably from published in vivo measurements in different patients, and the subject requires further investigation.
At frequencies used in pregnancy diagnosis the presence in the sound field of spheres with dimensions equivalent to the gestational sac can significantly increase pressure within the sphere. Also a small change (5%) in density or velocity can give rise to an increase by a factor of 20 in p2 compared to a situation where there is no sphere. Therefore the potential for a maximum pressure ?hot spot? exists for a position at the posterior part of the sphere which also corresponds to the position in the gestational sac occupied by a 6?7 wk fetus. These factors indicate the difficulty in attempting to determine dose in situ if exposure parameters alone are used.
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| Title |
Determination of lateral pharyngeal wall motion during connected speech by use of pulsed ultrasound. |
| Author |
Kelsey SA, Ewanowski SJ, Hixon TJ, Minifie FD. |
| Journal |
Science |
| Volume |
|
| Year |
1968 |
| Abstract |
Variations in the position of a point on the lateral pharyngeal wall relative to the external neck wall can be monitored by time-motion display of pulsed ultrasound. Such a portrayal is used to evaluate the lateral pharyngeal wall motion in normal and pathologic speakers during connected discourse. |
| Title |
Determination of postexcitation thresholds for single ultrasound contrast agent microbubbles using double passive cavitation detection. |
| Author |
King DA, Malloy MJ , Roberts AC, Haak A, Yoder CC, O'Brien WD, Jr. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2010 |
| Abstract |
This work presents experimental responses of single ultrasound contrast agents to short, large amplitude pulses, characterized using double passive cavitation detection. In this technique, two matched, focused receive transducers were aligned orthogonally to capture the acoustic response of a microbubble from within the overlapping confocal region. The microbubbles were categorized according to a classification scheme based on the presence or absence of postexcitation signals, which are secondary broadband spikes following the principle oscillatory response of the ultrasound contrast agent and are indicative of the transient collapse of the microbubble. Experiments were conducted varying insonifying frequencies (0.9, 2.8, 4.6, and 7.1 MHz) and peak rarefactional pressures (200 kPa to 6.2 MPa) for two types of contrast agents (Definity® and OptisonTM). Results were fit using logistic regression analysis to define pressure thresholds where at least 5% and 50% of the microbubble populations collapsed for each frequency. These thresholds were found to occur at lower pressures for Definity than for Optison over the range of frequencies studied; additionally, the thresholds occurred at lower pressures with lower frequencies for both microbubble types in most cases, though this trend did not follow a mechanical index scaling.
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| Title |
Determination of the nonlinearity parameter B/A of biological media. |
| Author |
Law WK, Frizzell LA, Dunn F. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1985 |
| Abstract |
The nonlinearity parameter B/A has been determined for various biological solutions and oft tissues using the thermodynamic and finite amplitude methods. Agreement between the two methods is better than 10% for tissues and 1% for the solutions. Fat has a B/A value around 11, the highest among soft tissues studied. Other soft tissues including liver, muscle, brain, and heart muscle have B/A values close to 7. Based on the observed linear relation between B/A value and solute concentration in protein solutions, and also the lack of dependence of the B/A value on solute molecular weight in dextran solutions, it is postulated that the nonlinearity in these solutions is due to solute-solvent interactions. The general trend of increasing B/A value with specimen structural hierarchy suggests that the nonlinearity of biological materials is related to this feature. These observations suggest the use of the nonlinearity parameter B/A in tissue characterization, particularly since structural alteration often attends the pathological state. |
| Title |
Determination of topologic human brain representations and modifications of signs and symptoms of some neurologic disorders by the use of high level ultrasound. |
| Author |
Meyers R, Fry FJ, Fry WJ, Eggleton RC, Schultz DF. |
| Journal |
Neurology |
| Volume |
|
| Year |
1960 |
| Abstract |
No abstract available. |
| Title |
Determining thresholds for contrast agent collapse. |
| Author |
Ammi AY, Mamou J, Wang GI, Cleveland RO, Bridal SL, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2004 |
| Abstract |
Determining the threshold of fragmentation of ultrasound contrast agents is important for both imaging and therapeutic ultrasound applications. We detected acoustic emissions from Optison/spl trade/ microbubbles that were insonified by pulses of ultrasound. Our observations suggest that when the microbubbles rupture, daughter bubbles are created which subsequently grow and then collapse on a time-scale of 1-5 /spl mu/s. The emission from the "rebound" collapse occurs after the end of the excitation pulse and we use the presence of this signal to determine the thresholds for the shell rupture. These shell-disruption thresholds were found to increase with frequency and decrease with pulse length. |
| Title |
Determining Thresholds for contrast agents. |
| Author |
Ammi AY, Mamou J, Wang GI, Cleveland RO, Bridal SL, O'Brien WD Jr. |
| Journal |
Proc IEEE Ultrasonic Symposium |
| Volume |
|
| Year |
2004 |
| Abstract |
Determining the threshold of fragmentation of
ultrasound contrast agents is important for both imaging and
therapeutic ultrasound applications. We detected acoustic
emissions from OptisonTM microbubbles that were insonified by
pulses of ultrasound. Our observations suggest that when the
microbubbles rupture, daughter bubbles are created which
subsequently grow and then collapse on a time-scale of 1-5 µs.
The emission from the “rebound” collapse occurs after the end
of the excitation pulse and we used the presence of this signal to
determine the thresholds for the shell rupture. These shelldisruption
thresholds were found to increase with frequency and
decrease with pulse length. |
| Title |
Developing standards for ultrasound. |
| Author |
Cronin MP. |
| Journal |
Appl Radiol |
| Volume |
|
| Year |
1976 |
| Abstract |
No abstract available. |
| Title |
Development of a detector of variation of underground water level using ultrasound. |
| Author |
Okuyama D, Inoue H, Yoshida Y, Imano K, Abe S. |
| Journal |
Jpn J Appl Phys |
| Volume |
|
| Year |
1986 |
| Abstract |
A system which measures the variation of underground water level in bored hole using ultrasound is proposed. The principle of the measurement is the ultrasonic pulse echo method. A transducer is hung in the underground water and sends 1 MHz of ultrasound with a 50 us pulse width upward to the water surface. The equipment has the ability to measure a depth of about 15 m with almost 3 cm resolution. An experiment using a telemeter system was carried out in a landslide area where there was much snow and no commercial power supply; the rising of the water level was observed with the thawing of the snow. |
| Title |
Development of a divided-ring array for three dimensional beam steering in ultrasonic nondestructive testing: Theoretical and experimental results of a prototype. |
| Author |
Schwarz HP. |
| Journal |
Mater Eval |
| Volume |
|
| Year |
1987 |
| Abstract |
This paper focuses on a newly developed device based on a 2 MHz divided-ring array for nondestructive testing (NDT) application with two rings, 48 elements, and an aperture of 30 mm. With this array, it is possible to steer an ultrasound beam three-dimensionally in space within a range of +/- 45 degrees (longitudinal-wave excitation) and +/- 30-70 degrees (shear-wave excitation). Computations of the directivity pattern, the process of the theoretical optimization, experiments, and a defect reconstruction will be described. One example of a defect reconstruction has been performed representatively, illustrating that the image quality of the first prototype is improved when compared to linear array images because of the higher lateral resolution in elevation direction. |
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