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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 6 out of 330
| Title |
A comparison of the thermal-dose equation and the intensity-time product, Itm, for predicting tissue damage thresholds. |
| Author |
Harris GR, Herman BA, Myers MR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2011 |
| Abstract |
Thermal dose is the most generally accepted concept for estimating temperature-related tissue damage thresholds in high-intensity focused ultrasound (HIFU) procedures. However, another approach based on the intensity-time product I t(m) =D has been used, where D is a tissue-dependent damage threshold, I is the spatial-peak, temporal-average intensity and t is time. In this study, these two approaches were compared analytically by substituting a well-known soft-tissue solution for temperature vs. time into the thermal dose equation. From power law fits of I vs. t, m was found to fall between about 0.3 and 0.8. In terms of the intensity required for cell death for a given exposure time, the standard deviation of the error between the full thermal-dose formulation and the I t(m) =D prediction based upon the power-law fit was less than 5% for focal beam diameters up to 3 mm. Thus, for the practical range of HIFU parameters examined, the intensity-time product relationship is equivalent to the thermal dose formulation. |
| Title |
A comparison of two techniques for measured iodine release as an indicator of acoustic cavitation. |
| Author |
Ciaravino V, Miller MW. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1983 |
| Abstract |
A spectrophotometric and a radioactive-label technique were used to assess for acoustically induced iodine release from sodium iodide. For both techniques there was a dose-dependent relationship between the percentage of iodine released and the ultrasound intensity (1 MHz, I(SP) to 30 W/cm(^2), continuous wave for 1 min). Iodine release decreased with increased atmospheric pressure or increased concentrations of the radical scavenger cysteamine, thus confirming that the release was related to cavitational processes. |
| Title |
A composite high-frame-rate system for clinical cardiovascular imaging. |
| Author |
Wang S, Lee WN, Luo J, Konofagou EE. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2008 |
| Abstract |
High frame-rate ultrasound RF data acquisition has been proved to be critical for novel cardiovascular imaging techniques, such as high-precision myocardial elastography, pulse wave imaging (PWI), and electromechanical wave imaging (EWI). To overcome the frame-rate limitations on standard clinical ultrasound systems, we developed an automated method for multi-sector ultrasound imaging through retrospective electrocardiogram (ECG) gating on a clinically used open architecture system. The method achieved both high spatial (64 beam density) and high temporal resolution (frame rate of 481 Hz) at an imaging depth up to 11 cm and a 100% field of view in a single breath-hold duration. Full-view imaging of the left ventricle and the abdominal aorta of healthy human subjects was performed using the proposed technique in vivo. ECG and ultrasound RF signals were simultaneously acquired on a personal computer (PC). Composite, full-view frames both in RF- and B-mode were reconstructed through retrospective combination of seven small (20%) juxtaposed sectors using an ECG-gating technique. The axial displacement of the left ventricle, in both long-axis and short-axis views, and that of the abdominal aorta, in a long-axis view, were estimated using a RF-based speckle tracking technique. The electromechanical wave and the pulse wave propagation were imaged in a cineloop using the proposed imaging technique. Abnormal patterns of such wave propagation can serve as indicators of early cardiovascular disease. This clinical system could thus expand the range of applications in cardiovascular elasticity imaging for quantitative, noninvasive diagnosis of myocardial ischemia or infarction, arrhythmia, abdominal aortic aneurysms, and early-stage atherosclerosis. |
| Title |
A computer model for simulating reflected ultrasound signals. |
| Author |
Kuc R, Miwa H. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1986 |
| Abstract |
This letter describes a model for simulating an ultrasound signal reflected from a medium composed of randomly distributed scatterers, as typified by soft biological tissue, such as liver. The model is specified in terms of the effective transducer beam radius B and the mean scatterer spacing S. The novel feature of the model is that the transducer field is partitioned by packing cylinders, called microbeams, into concentric annular regions that lie parallel to the transducer axis. The radii of the microbeams and the annuli are related to S. An independent reflector sequence is generated for each microbeam, the microbeam sequences in each annulus are summed and convolved with the impulse response of a point reflector. The reflected waveform sequence is then generated by summing the annular contributions and convolving with a band-limited pulse waveform. Simulated signals were generated for different values of B and S and compared with actual signals reflected from two in vivo livers and a tissue-equivalent phantom. Estimates of the kurtosis for the simulated signals indicate the range of signals that can be generated by varying the values for S and B. |
| Title |
A computerized system for measuring the acoustic output from diagnostic ultrasound equipment. |
| Author |
Schafer ME, Lewin PA. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1988 |
| Abstract |
A computer-controlled system is described that is specifically designed to measure the acoustic output from diagnostic ultrasound equipment as per the requirements of the US Food and Drug Administration. The measurement arrangement consists of a positioning system with a full range of degrees-of-freedom and a digital oscilloscope, both under complete computer control. The acoustic pressure-time waveform is recorded using membrane-type and needle-type polyvinylidene fluoride (PVDF) hydrophone probes. The overall bandwidth of the system depends on the hydrophone probe used and can range up to 100 MHz. A complete description of the system and the measurement procedures is given, along with a brief discussion of the various factors which affect measurement uncertainty. The largest overall uncertainty of the system associated with acoustic intensity measurements was determined to be no greater than 20 percent for I(sub)sppa and 25 percent for I(sub)spta. Other applications of the system include transducer characterization and research work in ultrasound dosimetry and bioeffects. |
| Title |
A Computerized Ultrasound Exposimetry System. |
| Author |
Chu F. |
| Journal |
Thesis(MS): Univ of Illinois |
| Volume |
|
| Year |
1991 |
| Abstract |
No abstract available. |
| Title |
A constant-flow calorimeter for the measurement of acoustic power at megahertz frequencies. |
| Author |
Torr GR, Watmough DJ. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
1977 |
| Abstract |
The calorimeter absorbs, in a flow of castor oil, a fraction of the acoustic power output of an ultrasound transducer. It has been used to measure powere of between 1 mW and 10 W at frequencies from 1-5 to 3 MHz. Examples are given of results obtained for an ultrasound therapy unit and an ultrasonic pulse--echo scanner. Sources of inaccuracy are defined. It appears that constant-flow calorimetry offers a potentially very sensitive method for the absolute measurement of acoustic power. .. |
| Title |
A contrast-detail analysis of diagnostic ultrasound imaging. |
| Author |
Smith SW Lopez H. |
| Journal |
Med Phys |
| Volume |
|
| Year |
1982 |
| Abstract |
For diagnostic ultrasound imaging, as in computed tomography, a feature of prime importance is the detection of focal lesions of varying size and.contrast (echo amplitude) from surrounding tissue. This study describes a new tissue-stimulating phantom which has been used to measure the.threshold detection of varying contrast, simulated lesions. The phantom consists of a block of tissue-mimicking gelatin which contains a row of.conical targets at a depth of 7 cm. Each cone contains a different tissue-mimicking material so that the echo amplitude of the cones relative to the.background material covers a dynamic range of 20 dB. Cross-sectional B-scans, perpendicular to the lengths of the cones, result in images of disks.of constant diameter but varying contrast. Parallel cross-sectional scans yield "lesions" varying in diameter from 20 to 1 mm. Relative contrast of.the cones vs background tissue is obtained by varying scattering particle sizes from 90 to 300 microns. Ultrasound B-scans of the phantom were.examined by medical physicist observers to determine threshold detection of lesions as a function of size and contrast. The results indicate that.detection of high contrast targets is limited by the imaging system's spatial resolution. Detection of low contrast targets is limited by the image.speckle, i.e., coherent noise. |
| Title |
A coupled two-port network transducer model. |
| Author |
Lockwood GR, Foster FS. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1992 |
| Abstract |
Difficulty in accurately modeling miniature or high frequency transducers is an important obstacle limiting the development of new applications of ultrasound imaging such as catheter based intravascular imaging. This paper describes a method of modeling transducers using network theory. The network model for a given transducer is determined from an experimental measurement of the transducer input impedance with a water and an air acoustic load and a measurement of the pulse echo response of the system. Once this model has be determined, the response of the system can be calculated for any given electrical source, load or acoustic load. Two examples are given which illustrate the application of the network model to acoustic matching and electrical matching. In the first example, the model was derived theoretically by calculating the input impedance and pulse echo response for a miniature (.75 mm diameter 45 mm thick) PZT transducer using the KLM model. In the second example the network model was derived from experimental measurements of a 4 mm diameter 50 MHz PVDF transducer. In each case, the effect of matching was accurately predicted. |
| Title |
A cylindrical-bubble model for the response of plant-tissue gas bodies to ultrasound. |
| Author |
Miller DL. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1979 |
| Abstract |
Many plant tissues contain gas in intercellular channels (gas bodies) which pulsate when sonicated at megahertz frequencies, thus causing perturbations in nearby cells. Certain long, narrow gas bodies may be approximated acoustically by cylindrical gas bubbles with added stiffness due to the cell walls bounding the gas. Typical gas bodies in Elodea leaves and Vicia faba roots have four and three walls, respectively, which are about 0.5 ?m thick and 6 ?m wide. The Young?s modulus of the wall material is estimated to be 10(10) dyn/cm(2), and the walls are subject to a tensile stress of about 10(4) dyn/cm. Theoretical expressions for the effective stiffness and mass and the radiation, viscous, and thermal damping constants are obtained for free cylindrical bubbles and gas bodies. A 6-?m diam cylindrical bubble is expected to be resonant at 0.3 MHz with a total damping constant of 0.33. A four-walled gas body with 6 ?m wide sides is expected to be resonant at 3 MHz, with a total damping constant of 0.48. In a typical plant tissue, significant gas-body activation and intracellular perturbation are expected over the range 0.6-12 MHz, making such tissues useful subjects for the study of the biological effects of ultrasound at these medically relevant frequencies. |
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