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BRL Abstracts Database |
Your search for ultrasound produced 3296 results. Page 195 out of 330
Title |
Parametric modeling in food package defect imaging. |
Author |
Tian Q, Sun B, Ozguler A, Morris SA, O'Brien WD Jr. |
Journal |
IEEE Trans UFFC |
Volume |
|
Year |
2000 |
Abstract |
A novel approach in food package defect detection is proposed based on system identification theory, in which the channel defect detection problem can be regarded as the conventional system identification problem, i.e., estimation of the system impulse response based on the input-output sequence using parametric and nonparametric models. The well-known parametric model ARX has been investigated in this paper. The data are collected with a focused ultrasound transducer (17.3 MHz, 6.35-mm diameter, f/2, 173 μm -6 dB pulse-echo lateral beam width at the focus) scanned over a rectangular grid, keeping the packages in the focus. Performance is measured in terms of detection rate, image contrast, and contrast-to-noise ratio. The results using the ARX model are compared with previous image formation techniques and also compared with the non-parametric method, i.e., spectral analysis. The results show that the ARX model has the comparable detection rate as RFCS and higher detection rate than BAI and RFS (except 6-μm air-filled channel in plastic trilaminate film) for channel in plastic trilaminate film. The ARX model has achieved the moderate contrast enhancement and ranks second in contrast-to-noise ratio enhancement among the compared techniques. The ARX model has a low detection rate for channel defects in aluminum trilaminate film, which shows that its performance is material-dependent. Finally, the parametric method, ARX model demonstrates better performance than the non-parametric method, spectral analysis for food package defect detection. |
Title |
Parametric ultrasound imaging from backscatter coefficient measurements: Image formation and interpretation. |
Author |
Insana MF, Hall TJ. |
Journal |
Ultrason Imaging |
Volume |
|
Year |
1990 |
Abstract |
A broadband method for measuring backscatter coefficients sigma b and other acoustic parameters is described. From the sigma b measurements, using a commercially-available imaging system, four high-resolution parametric ultrasound images are formed in a C-scan image plane. Scatterer size images are computed from the frequency dependence of sigma b and a correlation model function that describes the structure and elastic properties of the medium. Scattering strength images are computed from the absolute magnitude of sigma b. Chi-square images are generated to display how well the correlation model represents the interrogated medium. Integrated backscatter coefficient images are formed over the transducer bandwidth. All four images are generated simultaneously and compared with the corresponding B-mode image. Test samples with known physical properties were used to demonstrate experimentally that accurate parametric images are possible if an accurate correlation model is used. Local variations in attenuation, the center frequency and bandwidth of the transducer, and the distribution of scatterer sizes greatly influence the accuracy of estimates and the appearance of the image, thus demonstrating the importance of these factors in parametric image interpretation. |
Title |
Parametric vs nonparametric measurements in tissues with nonlinear frequency dependent attenuation. |
Author |
Ophir J. |
Journal |
Ultrasound Med Biol |
Volume |
|
Year |
1984 |
Abstract |
The relationship between the attenuation parameters of tissue and the linear regression slope derived from nonparametric estimates of tissue attenuation is investigated. It was found that if the attenuation in the tissue possesses a nonlinear frequency dependence, the linear regression slope parameter becomes dependent on center frequency and on the bandwidth of the measurement. Moreover, it was found that the slope estimate is numerically close to the parameter derived from parametric attenuation measurements in such cases. |
Title |
Partially extended and condened human chromosomes from lymphocytes exposed to iododeoxyuridine (IDU). |
Author |
Fischman HK. |
Journal |
Proc Fourteenth Annu Meet Am Soc Cell Biol - San Diego |
Volume |
|
Year |
1974 |
Abstract |
The experimental alteration of the structure and state of chromosomes has yielded valuable information. Examples are: the supercondensation caused by colchicine-like drugs, relation of ionizing radiation applied at different phases of the cell cycle to types of aberrations obtained, chromosome pulverization caused by virus infection, premature chromosome condensation following induced cell fusion. The presence of partially extended and condensed chromosomes (PECC) in ultrasound-treated human lymphocyte cultures led to an attempt to duplicate this phenomenon in a more consistant fashion and in such a way as to produce yields high enough for analysis. |
Title |
Particle gathering and microstreaming near.ultrasonically activated gas-filled micropores. |
Author |
Miller DL. |
Journal |
J Acoust Soc Am |
Volume |
|
Year |
1988 |
Abstract |
Nonthermal bioeffects of ultrasound can be induced by the physical mechanisms of radiation force and acoustic microstreaming. In this study, microscopical observations of the influence of these mechanisms on small particles near ultrasonically activated gas-filled micropores in thin plastic sheets were compared to approximate theoretical treatments of the particle behavior. The microstreaming flow was localized within a toroidal eddy around an active micropore, as indicated by isopycnic 1-micron polystyrene spheres. The size of the flow pattern seemed to decrease slowly with increasing frequency in the range 0.7-3.5 MHz. Flow.was radially inward along the surface, rather than outward as expected from the theory. All the particles tested, which included particles with density less than, equal to, or more than the medium, seemed to accumulate at the micropores. From the theory for the radiation force, the particles less dense than the medium were expected to be repulsed from the micropores. Therefore, the theories for these phenomena, at least to the level of approximation available, may not be completely adequate for the detailed analysis of these phenomena. |
Title |
Particle-size dependence of the additional absorption of ultrasound in emulsions. |
Author |
Kol'stova IS, Mikhailov IG, Saburov B. |
Journal |
Sov Phys Acoust |
Volume |
|
Year |
1975 |
Abstract |
No abstract available. |
Title |
Particle-stabilized bubbles for enhanced organ.ultrasound imaging. |
Author |
Violante MR, Baggs RB, Tuthill T, Dentinger P, Parker KJ. |
Journal |
Invest Radiol |
Volume |
|
Year |
1991 |
Abstract |
No abstract available. |
Title |
Particulate suspensions as ultrasonic contrast.agents for liver and spleen. |
Author |
Violante MR, Parker KJ, Fischer HW. |
Journal |
Invest Radiol |
Volume |
|
Year |
1988 |
Abstract |
Ultrasonic backscatter and attenuation coefficients of a medium can be increased by.the addition of solid, micron-size inhomogeneities. A potentially useful agent for.ultrasonic contrast of liver images has been identified. Iodipamide ethyl ester (IDE).particles can be produced in the form of dense, relatively incompressible solids with.high impedance mismatch to water. The chemical, biochemical, and pharmacologic.properties of the small, uniform diameter IDE particles permit safe intravenous.injection followed by rapid accumulation of reticuloendothelial (RE) cells of the liver.and spleen, and later elimination from these organs. Since the particles are.phagocytized by RE cells, present in normal liver but not in tumors and many lesions,.the selective enhancement of ultrasonic backscatter should improve detectability of.lesions that are hypoechoic or isoechoic compared with surrounding tissue. The.mechanisms of particle-ultrasound interaction may be described by relative motion.attenuation, and scattering from a cloud of dense, incompressible spheres for the case.of IDE particles in agar. Thus, values of attenuation and backscatter can be controlled.by choice of ultrasound frequency and particle concentration and size. When the.particles are accumulated in rat and rabbit livers, additional mechanisms induce.attenuation and backscatter in excess of that predicted by IDE in agar. This.preliminary work demonstrates that solid, biocompatible particles may be useful as an.ultrasonic contrast agent. |
Title |
Passive detection method for synchronizing with resonant oscillations of bubbles. |
Author |
Carson PL, Fowlkes JB, Gardner EA. |
Journal |
Proc Ultrason Symp IEEE |
Volume |
|
Year |
1992 |
Abstract |
Acoustic control of the mean diameter and distribution of sizes in a cloud of microbubbles should result in numerous applications. In medical ultrasound, microbubbles might be grown in a body fluid to create a bolus of high scattering fluid for study of circulatory or urinary tract dynamics. Microbubble creation and growth via rectified diffusion has been investigated for chirps with a temporally-decreasing frequency to drive the growing bubbles at resonance. A method is considered here for control of the ultrasound frequency and amplitude to maintain the bubbles at a desired size or growth rate. IF the frequency of the ultrasound growth or maintenance field can be modulated over a significant portion of a bubble resonance curve, the modulation of the backscattered or transmitted waveform by the resonance can be employed to keep the frequency centered on the resonance and the amplitude can be adjusted to maintain the desired growth rate. |
Title |
Patterns of thermal deposition in the skull during transcranial focused ultrasound surgery. |
Author |
Connor CW, Hynynen K. |
Journal |
IEEE Trans Biomed Eng |
Volume |
|
Year |
2004 |
Abstract |
The induction of temperature elevation by focused ultrasound is a noninvasive surgical technique for destroying tissue. This technique has been used clinically in soft tissues such as liver, prostate and breast. It has long been desired to extend this technique to noninvasive treatment of brain tumors. Although the skull was once thought to be an unsurpassable barrier to focused ultrasound treatment, it has been shown that the distortion caused by the skull can be corrected to produce a useful intracranial focus. However, the attenuation experienced by the ultrasound in passing through cranial bone is large, and consequently the skull is subject to the deposition of acoustic energy as heat. The nature and extent of this heating process has been difficult to characterize empirically. It is practically difficult to implant a sufficient number of thermocouples to obtain detailed temperature data directly, and bone is an unsuitable medium in which to perform noninvasive thermometry using proton chemical shift magnetic resonance imaging. Furthermore, skull specimens used experimentally lack active blood perfusion of the skull and the overlying scalp. This paper describes the use of large-scale acoustic and thermal simulations to calculate the distribution of temperature within the skull and brain that can be expected to occur during therapeutically useful focused ultrasound sonications of the brain. The results demonstrate that standing waves may be formed within the skull during transcranial sonication leading to nonuniform skull heating. However, the results also show that these effects can be sufficiently controlled to allow therapeutic ultrasound to be focused in the cranial base region of the brain without causing thermal damage to the scalp, skull or outer surface of the brain. |
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