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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 223 out of 330
| Title |
Safety standard for diagnostic ultrasound equipment. |
| Author |
O'Brien WD Jr. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1983 |
| Abstract |
Diagnostic ultrasound has been used for over 40 years with no reported harmful effects in humans. Despite the excellent safety of diagnostic ultrasound to date, new applications of ultrasound including pulsed Doppler and the use of intracavitary transducers may result in exposure conditions that have not been extensively encountered in the past. Although several possible mechanisms for the experimental production of bioeffects with ultrasound are recognized, thermal mechanisms are believed to be those most relevant to diagnostic ultrasound applications. In recent years a significant body of information has accumulated related to the production of thermal bioeffects with ultrasound, the biological consequences of thermal effects particularly in the fetus, and in procedures for estimating the heating likely to occur under specified exposure conditions. Although many questions remain, current knowledge permits a number of important conclusions to be drawn regarding thermal mechanisms for the production of biological effects with ultrasound. During the course of discussions at the WFUMB Workshop the participants formulated statements to sumarise the current state of knowledge on thermal effects of B-mode imaging and Doppler ultrasound as used in clinical practice. |
| Title |
Sampled-cw study of "inhomogeneous" ultrasonic responses in solids. |
| Author |
Miller JG, Bolef DI. |
| Journal |
J Appl Phys |
| Volume |
|
| Year |
1970 |
| Abstract |
The "propagating wave" analysis of an ultrasonic resonator is extended to include some effects of nonparallelism, guided wave phenomena, and electrical loading. Each of these effects contributes an "inhomogeneous" broadening to the continuous wave frequency domain response and an "inhomogeneous" damping tot he time domain decay. Experimental verification for ultrasound propagating in both thin and bulk solid specimens is obtained by utilizing the sampled-continuous wave ultrasonic spectrometer. Quantitative evaluation of interference effects among harmonic and inharmonic responses is achieved using the spectrometer in the time domain mode of observation. |
| Title |
Scanning acoustic microscopy of polymeric materials and biological substances. |
| Author |
Mayev RG. |
| Journal |
Arch Acoust |
| Volume |
|
| Year |
1988 |
| Abstract |
For the last few years a new method of visualization and quantitative analysis of physico-mechanical properties and microstructure of heterogenetic media - the acoustic microscopy - has been intensively elaborated in the world. In this method waves of ultrasound and hypersound range are used as an analysis factor. It allows to use this method for investigating a wide variety of opaque materials and goods and obtaining information about their inner structures as well as for optically transparent materials in which the contrast between different structures is practically absent. In both cases an investigator receives information that is quite different from that obtained with the help of other methods, namely, the distribution of local physico-mechanical properties for example, bulk compression, shift, etc in the material of the sample. We give a review of the results of the work on methods and means of acoustic microscopy, worked out in the Centre for Acoustic Microscopy of the USSR Academy of Sciences for investigation of polymeric composites and biological objects as well as the results of analogical investigations of the leading scientific centres in the world. We set forth common physical basis and principles of getting acoustic images as well as the methods of studying microstructures and mechanical properties of heterogenetic objects with the help of acoustic microscope. |
| Title |
Scatterer size estimation in pulse-echo ultrasound using focused sources: Calibration measurements and phantom experiments. |
| Author |
Bigelow TA, O'Brien WD Jr. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2004 |
| Abstract |
In a companion paper [T. A. Bigelow and W. D. O'Brien Jr., J. Acoust. Soc. Am. 116, 578 (2004)], theory, supported by simulations, showed that accurate scatterer size estimates could be obtained using highly focused sources provided that the derived generalized attenuation-compensation function was used and the velocity potential field near the focus could be approximated as a three-dimensional Gaussian. Herein, the theory is further evaluated via experimental studies. A calibration technique is developed to find the necessary equivalent Gaussian dimensions for a focused source using reflections obtained from a rigid plane scanned through the focus. Then, the theoretical analysis of focused sources is validated experimentally using three spherically focused ultrasound transducers to estimate the radius of glass beads imbedded in tissue mimicking phantoms. Both the impact of focusing (f/1, f/2, and f/4) and the effect of scatterer type (comparing glass bead results to simulation results that used scatterers with Gaussian impedance distributions) were tested. The simulated differences agree with the measured differences to within 2.5% provided that the comparison is made between the same scatterer type and sources with the same equivalent Gaussian dimensions. The improvement provided by the generalized attenuation-compensation function is greatly influenced by the type of scatterer whose size is being estimated and decreases as the wavelength dependence of the Gaussian depth of focus is reduced. |
| Title |
Scatterer size estimation in pulse-echo ultrasound using focused sources: Theoretical approximations and simulation analysis. |
| Author |
Bigelow TA, O'Brien WD Jr. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2004 |
| Abstract |
The speckle in ultrasound images has long been thought to contain information related to the tissue microstructure. Many different investigators have analyzed the frequency characteristics of the backscattered signals to estimate the scatterer acoustic concentration and size. Previous work has been mostly restricted to unfocused or weakly focused ultrasound sources, thus limiting its implementation with diagnostically relevant fields. Herein, we derive equations capable of estimating the size of a scatterer for any reasonably focused source provided that the velocity potential field in the focal region can be approximated as a three-dimensional Gaussian beam, scatterers are a sufficient distance from the source, and the field is approximately constant across the scatterer. The calculations show that, when estimating the scatterer size, correcting for focusing requires a generalized attenuation-compensation function that includes both attenuation and focusing along the beam axis. The Gaussian approximation is validated by comparing the ideal velocity potential field for three spherically focused sources with f-numbers of 1, 2, and 4 to the Gaussian approximation for frequencies from 2 to 14 MHz. The theoretical derivations are evaluated by simulating the backscatter by using spherically focused sources (f-numbers of 1, 2, and 4) adjacent to attenuating media (0.05 to 1 dB/cm/MHz) that contain scatterers with Gaussian impedance distributions. The generalized attenuation-compensation function yielded results accurate to 7.2% while the traditional attenuation-compensation functions that neglected focusing had errors as high as 103%. |
| Title |
Scatterer size estimation using a generalized ultrasound attenuation-compensation function to correct for focusing. |
| Author |
Bigelow TA, O'Brien WD Jr. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
2003 |
| Abstract |
The frequency statistics of the backscattered waveform observed between tissue boundaries can be matched to a model to estimate the characteristic size of the scatterer in the tissue region of interest. In the past, the models have all assumed plane wave propagation requiring the use of unfocused or weakly focused sources in the experiment. In our work, we challenged this assumption by re-deriving the scattering equations assuming that the focused field can be accurately modeled as a 3D Gaussian distribution in addition to the traditional assumptions that the scatterers are a sufficient distance from the source and that the field is approximately constant across the scatterer. We showed that correcting for focusing when estimating the scatterer size only requires a generalized attenuation-compensation function that includes the impact of focusing along the beam axis. We then generated computer simulations to aid in the understanding of the impact of diffraction along the beam axis and compared the performance of our attenuation-compensation function to the performance of previously proposed attenuation-compensation functions for various levels of focusing (f/1, f/2, f/4), attenuation (0.05 to 1 dB/cm/MHz), and rectangular window length used to gate the time domain signal (1 to 13 mm). The generalized attenuation-compensation function yielded results accurate between 2% and 7.2% while the traditional attenuation-compensation functions that neglected focusing had errors greater than 50% for moderate attenuation and window lengths. |
| Title |
Scattering by single physically large and weak scatterers in the beam of a single-element transducer |
| Author |
Kemmerer JP, Oelze ML |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2015 |
| Abstract |
Quantitative ultrasound techniques are generally applied to characterize media whose scattering sites are considered to be small compared to a wavelength. In this study, the backscattered response of single weakly scattering spheres and cylinders with diameters comparable to the beam width of a 2.25 MHz single-element transducer were simulated and measured in the transducer focal plane to
investigate the impact of physically large scatterers. The responses from large single spherical scatterers at the focus were found to closely match the plane-wave response. The responses from large cylindrical scatterers at the focus were found to differ from the plane-wave response by a factor of f(^-1). Normalized spectra from simulations and measurements were in close agreement: the fall-off of the responses as a function of lateral position agreed to within 2 dB for spherical scatterers and to within 3.5 dB for cylindrical scatterers. In both measurement and simulation, single scatterer diameter estimates were biased by less than 3% for a more highly focused transducer compared to estimates for a more weakly focused transducer. The results suggest that quantitative ultrasound
techniques may produce physically meaningful size estimates for media whose response is dominated by scatterers comparable in size to the transducer beam. |
| Title |
Scattering of ultrasound by blood. |
| Author |
Shung KK, Sigelmann RA, Reid JM. |
| Journal |
IEEE Trans Biomed Eng |
| Volume |
|
| Year |
1976 |
| Abstract |
The ultrasonic volumetric scattering cross section of the erythrocyte has been measured over a range of frequencies by comparing the rms value of the gated backscattered signal from the blood with that of a wave reflected from a flat reflector with known reflection coefficient. It is found to be proportional to the fourth power of the frequency predicted by the wave scattering theory for small particles in the frequency range from 5 MHz to 15 MHz. The relation between the scattering coefficient and the hematocrit is also examined up to a hematocrit of 45 percent. This coefficient is found to increase along with the hematocrit until it reaches a maximum around hematocrit = 26 percent and then decreases as the hematocrit increases. Twersky?s wave scattering theory is applied to describe this result. |
| Title |
Scattering of ultrasound by emulsions. |
| Author |
McClements DJ, Povey MJ. |
| Journal |
J Phys D |
| Volume |
|
| Year |
1989 |
| Abstract |
Ultrasonic scattering theory is used to relate the ultrasonic velocity and attenuation of emulsions to their physical properties (e.g. droplet size and volume fraction). This theory includes visco-inertial and thermal scattering mechanisms and corrections due to multiple scattering. The physical significance of the scattering mechanisms is discussed so as to highlight the factors which influence ultrasonic measurements in these systems. Theoretical predictions were compared with experimental measurements of velocity and attenuation in sunflower oil in water emulsions with varying droplet radii (0.14-0.74 micrometers), mass fraction (0-0.5) and frequency (1.25-10.0 MHz) at 293.1 K. Appreciable excess attenuation and velocity dispersion were observed which could be attributed to thermal scattering. The relationship between the measurable ultrasonic parameters and the physical properties of emulsions means ultrasonic scattering should prove a useful means of investigating these systems. |
| Title |
Scattering of ultrasound by tissues. |
| Author |
Sehgal CM, Greenleaf JF. |
| Journal |
Ultrason Imaging |
| Volume |
|
| Year |
1984 |
| Abstract |
Scattering of ultrasound by biological tissues (continuous-inhomogeneous media) is discussed. An analytical expression for the attenuation due to scattering (alpha Tsc) and backscatter coefficients (sigma T) of tissues are obtained. The results explain the variation of alpha Tsc and sigma T with frequency for a number of tissues. The study also provides two statistical parameters, velocity fluctuation coefficient and correlation length, in terms of which the scattering of tissues can be defined quantitatively. |
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