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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 1 out of 330
| Title |
Experimental evaluation of some possible nonlinearity indicators. |
| Author |
Bigelow TA, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2002 |
| Abstract |
Due to regulatory reasons, the output levels of ultrasound sources for use in medical applications must be known. Currently, this is done by making focal pressure measurements for a very large number of drive voltage amplitudes and then linearly derating the measured pressure levels. In order to reduce calibration times, some have proposed to linearly extrapolate pressures rather than perform direct measurements. However, nonlinear propagation effects corrupt the linear extrapolation and derating procedure. Thus, a reliable indicator of nonlinearity is needed to identify when linear extrapolation/derating would be valid. In this study, eight different nonlinearity indicators were evaluated experimentally in terms of their correspondence to the linear extrapolation error. Spherically focused ultrasound transducers were selected and excited to test the indicators sensitivity to frequency (3 - 8 MHz), f/# (1 and 2), transducer diameter (1.905 and 5.08 cm), pulse duration (1 and 3 cycles), and pulse phase (0/spl deg/ and 180/spl deg/). None of the eight nonlinearity indicators yielded consistent results. The lack of consistency resulted from the competing effects of nonlinear absorption and asymmetric distortion, which have yet to be combined into a unified theory. |
| Title |
Time-domain solution of the temperature increase induced by diagnostic ultrasound. |
| Author |
Goueygou M, Harris JG, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1999 |
| Abstract |
Presents a complete time-domain solution to estimate the temperature increase induced by pulsed ultrasonic fields, such as those used in diagnostic applications. The authors' computational model includes 3 steps: (1) calculation of the acoustic field, (2) of the rate of heat generation and (3) of the temperature distribution. For step 1 and 3, the acoustic and thermal fields are computed by integrating the known acoustic and thermal Green functions of the homogenous medium, respectively, over the surface of the transducer and over the volume of interest. For step 2, the authors derive a new expression for the instantaneous rate of heat generation. Previous expressions gave only the average rate of heat for a single frequency excitation. The authors finally present computational results of the temperature increase induced by a point source and by a circular focused transducer. |
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| Abstract |
In ultrasonic hyperthermia, hot spots are usually generated by focusing the ultrasonic beams. However, it is difficult to heat regions other than gas and bones owing to the attenuation and scattering of the ultrasonic beams. The authors propose an ultrasonic heating method in which low-frequency ultrasound is used to heat the depths of the body, and heat generation is localized by synthesizing an acoustic field from several incident waves. The heat generation and temperature distribution are analyzed using models with properties similar to tissue.<> |
| Title |
On the validity of the linear approximation in the parametric measurement of attenuation in tissues. |
| Author |
Narayana PA, Ophir J. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1983 |
| Abstract |
A known method for the determination of the attenuation coefficient of tissues involves the measurement of the center frequency downshift of Gaussian spectra. The tissue is generally assumed to have linear frequency dependent attenuation. This assumption results in a simple relationship between the spectral downshift and the attenuation coefficient. However, recent studies have shown that many tissues exhibit nonlinear frequency dependent attenuation. In this paper we investigate the consequences of applying the linear assumption to non-linear cases. These studies shown that even a small deviation from linearity results in significant errors in the determination of the attenuation parameters. |
| Title |
Accurate and precise measurement of blood flow using ultrasound time domain correlation. |
| Author |
Hein IA, Suorsa V, Zachary J, Fish R, Chen J, Jenkins WK, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1989 |
| Abstract |
The goal of this research is to produce an ultrasonic device to assist in the diagnosis of venous thrombosis in humans. The ultrasound time-domain correlation technique can accurately and precisely estimate the volumetric fluid flow through a circular vessel without prior knowledge of the vessel diameter, flow velocity profile, or transducer measurement angle. This technique estimates the change in arrival time (instead of frequency) of ultrasound reflected from scatterers. A system based on this technique has been constructed and the technique has been verified in a blood-flow phantom system with both a blood-mimicking substance and porcine blood. Under in vitro conditions, the measurement angle has been determined within 5%, and continuous and pulsatile volumetric flow has been measured to 150 beats/min with an accuracy better than 18%. |
| Title |
Evaluation of the soft tissue thermal index and the maximum temperature increase for homogeneous and layered tissues. |
| Author |
Ellis DS, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1992 |
| Abstract |
Theoretical tissue temperature increases due to focused diagnostic ultrasound fields are evaluated for both homogeneous and three-layer tissue models. Applying the monopole-source solution, the general acoustic pressure field distribution is obtained for a specific source temporal average power. The axial steady-state temperature increase is calculated by applying the point-source solution of the bio-heat transfer equation to the pressure field distribution. Homogeneous and three-layer fetal tissue model examples for 3 MHz for circular source apertures are presented and compared to the thermal index of the recently approved Standard for Real-Time Display of Thermal and Mechanical Acoustic Output Indices on Diagnostic Ultrasound Equipment. |
| Title |
High-frequency, nonlinear flow imaging of microbubble contrast agents. |
| Author |
Goertz DE, Needles A, Burns PN, Foster FS. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2005 |
| Abstract |
It has been shown that nonlinear scattering can be stimulated from microbubble contrast agents at high-transmit frequencies (14-32 MHz). This work was extended to demonstrate the feasibility of nonlinear contrast imaging through modifications of existing ultrasound biomicroscopy linear B-scan imaging instrumentation. In this study, we describe the development and evaluation of prototype coherent flow imaging instrumentation for nonlinear microbubble imaging using transmit frequencies from 10 to 50 MHz. Phantom validation experiments were conducted to demonstrate color and power flow imaging using nonlinear 10 MHz (subharmonic) scattering induced by a 20-MHz transmit frequency. In vivo flow imaging of a rabbit ear microvessel was successfully performed. This work indicates the feasibility of performing flow imaging at high frequencies using nonlinear scattering from microbubbles. |
| Title |
Single-element focused transducer method for harmonic motion imaging. |
| Author |
Maleke C, Pernot M, Konofagou EE. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2005 |
| Abstract |
The harmonic motion imaging (HMI) technique for simultaneous monitoring and generation of ultrasound therapy using two separate focused ultrasound transducer elements was previously demonstrated. In this study, a new HMI technique is described that images tissue displacement induced by a harmonic radiation force using a single focused-ultrasound element. A wave propagation simulation model first indicated that, unlike in the two-beam configuration, the amplitude-modulated beam produced a stable focal zone for the applied harmonic radiation force. The AM beam thus offered the unique advantage of sustaining the application of the spatially-invariant radiation force. Experiments were performed on gelatin phantoms and ex vivo tissues. The radiation force was generated by a 4.68 MHz focused ultrasound (FUS) transducer using a 50 Hz amplitude-modulated wave. A 7.5 MHz pulse-echo transducer was used to acquire rfechoes during the application of the harmonic radiation force. Consecutive rf echoes were acquired with a pulse repetition frequency (PRF) of 6.5 kHz and ID cross-correlation was performed to estimate the resulting axial tissue displacement. The HMI technique was shown capable of estimating stiffness-dependent displacement amplitudes. Finally, taking advantage of the real-time capability of the HMI technique, temperature-dependent measurements enabled monitoring of HIFU sonication in ex vivo tissues. The new HMI method may thus enable a highly-localized force and stiffness-dependent measurements as well as real-time and low-cost HIFU monitoring. |
| Title |
"Seeing" - Your ailments with sound. |
| Author |
Hamilton A. |
| Journal |
Today's Health |
| Volume |
|
| Year |
1968 |
| Abstract |
Ultrasound-pitched beyond human hearing - has been used widely as a treatment for certain ailments. Now many doctors employ it as a diagnostic tool. |
| Title |
"Sonoelasticity" images derived from ultrasound signals in mechanically vibrated tissues. |
| Author |
Lerner RM, Huang SR, Parker KJ. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1990 |
| Abstract |
A method has been developed for detecting and imaging the relative "stiffness," or elasticity of tissues. Externally applied vibration at low frequencies (10-1000 Hz) is used to induce oscillations within soft tissues, and the motion is detected by Doppler ultrasound. The results are displayed in a format resembling conventional Doppler color flow mapping, and are termed "sonoelasticity images." Preliminary experiments indicate that these novel images may be useful for detecting hard tumors in the prostate, liver, breast, and other organs. |
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