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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 120 out of 330
| Title |
Experimental evaluation of human teeth using noninvasive ultrasound: Echodentography. |
| Author |
Ghorayeb SR, Valle T. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2002 |
| Abstract |
Anomalies present in the hard tissue of teeth are manifested in several ways such as cavities, decay, and caries. The most extensively and commonly used diagnostic modality for the assessment of these abnormalities are x-rays. Unfortunately, these rays are harmful to the human body and may be a source of health risk. This work describes the development of a new testing technique that uses ultrasound designed to complement, or even replace, existing tools used in dentistry applications. Previous studies have shown several models of acoustic field simulation, propagation, and interaction of ultrasound with the layers of several tooth structures. In this paper, experimental data is gathered for the purpose of assessing the viability of this technique in an attempt to detect cavities and fractures in extracted human teeth. A low-intensity, high-frequency ultrasonic set-up is used in all in vitro tests. Four cases have been examined: an intact tooth, a tooth containing an amalgam restoration and a natural surface fissure, a tooth containing a machine side-drilled hole that mimics a cavity, and a calcified tooth-a rare naturally occurring condition. Upon analysis of the obtained A-scans and B-scans, it is verified that these experimental measurements confirm predictions reported in earlier finite element and transmission line studies and suggest that ultrasound is a valuable tool which has the potential to be an addition to, or even an improvement upon, current dental imaging systems. |
| Title |
Experimental evaluation of indicators of nonlinearity for use in ultrasound transducer characterizations. |
| Author |
Bigelow TA, O'Brien WD Jr. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2002 |
| Abstract |
Because the number of applications for medical ultrasonic devices continue to increase and, hence, the number of diagnostic ultrasound (US) systems increase, there is a need to reliably characterize the sources in terms of their output pressures. Currently, the transducers are characterized by making pressure measurements in water for every voltage range applied to the source and, then, linearly derate the measured pressure values to estimate the derated acoustic pressure levels. The process is time-consuming and inaccuracies are introduced in the derating process due to nonlinear effects. Therefore, there is a need to find an indicator of nonlinearity that could classify the measured pressure waveform as either linear, where the derating procedure would yield an accurate derated acoustic pressure estimate, or nonlinear, where the derating process would fail. Eight different indicators of nonlinearity were evaluated experimentally using spherically focused US transducers. The transducers were selected to test the indicator sensitivity to frequency (3 to 8 MHz), f-number (1 and 2), and transducer diameter (1.905 and 5.08 cm). Sensitivity to drive voltage conditions was also tested by exciting one of the transducers with pulses of different duration and phase. None of the eight nonlinearity indicators yielded consistent results. The lack of consistency resulted from the competing effects of nonlinear absorption and asymmetrical distortion, which have yet to be combined into a unified theory.
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| Title |
Experimental evaluation of nonlinear indices for ultrasound transducer characterizations. |
| Author |
Bigelow TA. |
| Journal |
Thesis(MS): Univ of Illinois |
| Volume |
|
| Year |
2001 |
| Abstract |
Over the past few decades, the propagation of acoustic signals through the human
body has found application in medical imaging as well as the treatment of various
ailments. Also, many new applications are being continually developed. As the demand for medical ultrasonic devices increases, so does the demand for reliable methods of characterizing the pressure output of the ultrasound transducers. Currently, every focal region is characterized at every transducer voltage setting by directly measuring the acoustic pressure in a water bath. This process is highly time consuming, ultimately increasing the cost and development time for each transducer. |
| Title |
Experimental frequency spectra of ultrasound.transmission through two-dimensional ensembles of.trapped microbubbles. |
| Author |
Wu JR, Nyborg WL..Department of Physics, University of Vermont, Burlington 05405. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1989 |
| Abstract |
The frequency spectra of transmission coefficients for ultrasound passing through a sheet of.gas-filled micropores have been measured using incident waves with amplitudes up to 2.4 x.10(4) Pa. It is found that as the amplitude of the incident wave is increased, the peak frequency.of transmission loss through the two-dimensional trapped-bubble ensemble shifts to lower values.by as much as 47%. The experiments indicate that the shifting is caused by the net displacements.of air-water-membrane triple-phase lines and the air loss of the trapped bubble, which are due to.the radiation force and microbubble production produced by the incident wave. Results of the.experiments and possible theoretical explanations are discussed. |
| Title |
Experimental gallstone dissolution with methyl-tert-butyl ether (MTBE) and. transcutaneous ultrasound energy. |
| Author |
Griffith SL, Burney BT, Fry FJ, Franklin TD. |
| Journal |
Invest Radiol |
| Volume |
|
| Year |
1990 |
| Abstract |
The simultaneous application of ultrasound energy greatly accelerated the rate of cholesterol gallstone dissolution by methyl-tert-butyl ether (MTBE). In vitro experiments using this treatment showed that a 498-mg stone burden could be dissolved in 19.5 minutes, approximately 100% faster than what could be achieved with MTBE alone. Pigs (n = 13) with surgically implanted gallstones were treated with MTBE and transcutaneously applied ultrasound from a prototype system built for clinical studies. The average stone reduction of all pigs was 470.46 mg +/- 60.44 mg; 91.39% of an average implanted burden of 515.08 +/- 18.03 mg. Control group pigs (n = 9), receiving only an MTBE infusion, showed an average stone reduction of 51.77%. Enzymes indicative of hepatocellular injury showed no significant abnormalities after 6 weeks. Gallbladder ablation with a fibrous remnant (ie, no mucosa, no lumen, patent cystic duct) occurred in 10 (70%) of the pigs. |
| Title |
Experimental investigation of the pulse inversion technique for imaging ultrasound contrast agents. |
| Author |
Verbeek XA, Ledoux LA, Willigers JM, Brands PJ, Hoeks AP. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2000 |
| Abstract |
The application of ultrasound contrast agents aims to detect low velocity blood flow in the microcirculation. To enhance discrimination between tissue and blood containing the contrast agent, harmonic imaging is used. Harmonic imaging requires the application of narrow-band signals and is obscured by high levels of native harmonics generated in an intervening medium. To improve discrimination between contrast agent and native harmonics, a pulse inversion technique has been proposed. Pulse inversion allows wide-band signals, thus preserving the axial resolution. The present study examines the interference of native harmonics and discusses the practical difficulties of wide-band pulse inversion measurements of harmonics by a single transducer. Native harmonics are not eliminated by pulse inversion. Furthermore, only even harmonics remain and are amplified by 6 dB, alleviating the requirement for selective filtering. Finally, it is shown that the contaminating third harmonic contained in the square wave activation signal leaks through in the emitted signal. The spectral location of the contaminating third harmonic is governed by the transducer spectral characteristics while the location of the native and contrast agent second harmonics is not. Thus the contaminating third harmonic and the native and contrast agent second harmonics may overlap and interfere. Optimal discrimination requires a balance between maximal sensitivity for the second harmonic at reception and minimal interference from the contaminating third harmonic. |
| Title |
Experimental investigation of the response of gas-filled micropores to ultrasound. |
| Author |
Miller DL. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1982 |
| Abstract |
Hydrophobic membranes with gas-trapping micropores have been used in ultrasonic bioeffects experiments to determine the efficacy of the cavitation mechanism at low intensities. Membranes were tested with circular pores of about 2.5 to 5.4 micrometers in diameter and these pores trapped gas when the membranes were immersed in water such that the resulting bubbles were stable against diffusion. Only a few pores remain completely filled with gas upon immersion, however, and the distribution in partial filling apparently results in a distribution of resonance frequencies for the bubbles in a membrane, even when the pores are essentially all identical in size. |
| Title |
Experimental methods for accurate determination of acoustic backscatter. |
| Author |
Hall TJ. |
| Journal |
Thesis(PhD): Univ of Wisconsin-Madison |
| Volume |
|
| Year |
1988 |
| Abstract |
Current clinical ultrasound images are qualitative and their interpretation is subjective; i.e., current imaging is system and operator dependent. A quantitative measure of the scattering properties intrinsic to tissue, such as the acoustic backscatter coefficient, would remove system and operator dependencies and allow formation of quantitatively correct images.
We have rigorously tested a method of data reduction for determining acoustic backscatter coefficients from time-gated echo signals. Phantoms with well characterized ultrasonic properties, including their scattering properties, were the basis for these tests. Among these phantoms were some that had low acoustic attenuation, and several that have attenuation coefficients similar to that of most soft tissues.
Initial work appears in the thesis of M.F. Insana, in which the method of data reduction was derived and initially tested. In that work, nonfocused transducers and long duration pulses and time-gates were employed to acquire echo signals from a well characterized phantom placed in the far-field of the pressure beam.
To be a potent clinical tool, however, the method must be proven accurate for a broad range of experimental conditions. A broad range of clinically-relevant experimental tests form the basis of this thesis work. Results obtained with focused or nonfocused transducers excited by narrow-band pulses are independent of transducer-to-scattering-volume distance and time-gate duration. These results are also accurate, typically within 10 percent of values determined independently based on the physical properties of the constituent materials.
A technique was developed that allows accurate determination of backscatter coefficients over the -12dB echo signal band width when broad-band pulses and short duration time-gates are employed. This technique was applied to data acquired with three focused transducers with nominal resonant frequencies of 1.6, 2.25 and 5 MHz. Results obtained with this broad-band analysis technique are accurate, typically well within the uncertainty of this measurement.
|
| Title |
Experimental results in ultrasonic tomography using a filtered backpropagation algorithm. |
| Author |
Sponheim N, Johansen I. |
| Journal |
Acoust Imaging |
| Volume |
|
| Year |
1991 |
| Abstract |
This paper describes an experimental study in diffraction tomography whose main goal was to determine experimentally the performance of the filtered backpropagation algorithm in ultrasound tomography. We have built a simple water tank with a plane wave source and a scanning hydrophone. The test objects have been cylindrical and of a relatively simple structure and made of acrylic and silicone rubber. The resulting reconstructions show that the structure and position of the objects are well reproduced. The velocity of the objects can also be well reproduced if the velocity contrast is not too large. In medical imaging, it is most important to see the structure, and since the velocity change in biological tissue is small, the method should be well suited for medical imaging. |
| Title |
Experimental studies in transmission ultrasound computed tomography. |
| Author |
Jago JR, Whittingham TA. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
1991 |
| Abstract |
The reconstruction of the speed-of-sound distribution within a target can be achieved by CT techniques from measurements on transmitted ultrasonic pulses. The mathematical relationship between speed-of-sound imaging and the conventional CT situation is explained. An experimental system, which has been developed to investigate speed-of-imaging and other forms of in-vivo ultrasound CT, is described, along with the techniques used for data acquisition and image reconstruction. These include measurement of pulse time-of-flight by the threshold or cross-correlation methods. Techniques for reducing artifacts in speed-of-sound images are also described, such as median filtering and modified Shepp-Logan filtering. These techniques have been used to obtain high quality speed-of-sound images of various phantoms. Images of tissue in-vitro have been less satisfactory, because of refraction and attenuation effects. Ways of overcoming these difficulties in an improved system are proposed. |
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