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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 126 out of 330
| Title |
Fingerprint structure imaging based on an ultrasound camera. |
| Author |
Bicz W, Banasiak D, Bruciak P, Gumienny Z, Gumulinski S, Kosz D, Krysiak A, Kuczynski W, Pluta M, Rabiej, G. |
| Journal |
Instrum Sci Technol |
| Volume |
|
| Year |
1999 |
| Abstract |
This paper describes the design of an ultrasound camera which has a resolution of 0.1 mm. The camera allows the observation of the near surface structures of solid objects and is suitable for the finger ridge pattern imaging (i.e., pattern which is reflected in a fingerprint). The device can be used for a biometric identification of individuals (for access verification). It can also be employed for all other sorts of structures which have ultrasound detectable changes in the near surface structure, both natural and artificial (e.g., created for information recording). The paper describes the current version of the camera and the physical phenomena behind its operation. Presented are also perspectives of further development of the device. |
| Title |
Finite amplitude distortion and its relationship to linear derating formulae for diagnostic ultrasound systems. |
| Author |
Christopher T, Carstensen EL. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1996 |
| Abstract |
Formulation of indices that can be used as predictors of biological effects of ultrasound involves a process called derating, in which measurements of the sound field made in water are extrapolated to estimates of the magnitude of the sound fields in the tissues of the body. All indices that have been formulated up to the present time assume that the propagation of ultrasound is linear. In fact, under most exposure conditions for which biological effects may be a concern, sound propagation is highly nonlinear. A nonlinear propagation model has been used in this study to evaluate the nature of the effects that occur under realistic exposure conditions encountered in diagnostic procedures. Because of the way that the thermal index is defined, it turns out that ignoring nonlinear propagation leads to underestimates of tissue temperature increments that typically are less than 40%. As currently implemented, the mechanical index may be underestimated by more than a factor of two because it ignores the saturation of the sound fields that result from nonlinear propagation. For large propagation distances in soft tissues (e.g., 10 cm at 3 MHz in liver); however, it is physically difficult to exceed tissue pressures corresponding to MI > 2 because of these same saturation phenomena.
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| Title |
Finite amplitude distortion of the pulsed fields used in diagnostic ultrasound. |
| Author |
Bacon DR. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1984 |
| Abstract |
A simple theoretical model of the non-linear propagation of pulsed focused acoustic beams is described. It enables the distortion of the peak cycle of the pulse to be calculated from a few experimentally measured parameters. The model is discussed, and justified for application to the fields from medical ultrasonic diagnostic equipment. It is particularly relevant for specifying the degree of distortion present, as might be required by future written standards for diagnostic equipment performance. Preliminary experimental verification of the model is reported. |
| Title |
Finite amplitude effects on the thresholds for lesion production in tissues by unfocused ultrasound. |
| Author |
Carstensen EL, Becroft SA, Law WK, Barbee DB. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1981 |
| Abstract |
The phenomenon of thermal lesion production in tissues by unfocused ultrasound has been modeled under the assumptions (1) that damage to the tissues is the result of a chemical rate process and (2) that the time-temperature exposure of the tissue results from a competition between the rate of heat generation by absorption of ultrasonic energy and thermal diffusion. The model was tested by observing thresholds for color change in samples of excised bovine liver at 6 cm from a 2.25-MHz, 1.27-cm-diam piston source and 11.5 cm from a 4.4-MHz, 1.27-cm source. The observations disagreed sharply with predictions of the linear model. However, after recognition of the fact that finite amplitude phenomena modify the effective absorption coefficients of the tissues, the model gives excellent predictions of observed thresholds simply by using intensity dependent values of the absorption coefficients in the numerical calculations. Thermoelectric and radiation force methods were used to demonstrate the nonlinear absorption phenomenon in excised liver. In contrast with the case of focused ultrasound, the thresholds for lesion formation by unfocused sources (1) occur at lower intensities, (2) are strongly dependent upon frequency, and (3) because acoustic saturation in the coupling medium imposes lower limits on tissue intensities for unfocused than for focused ultrasound, unfocused lesions are limited to relatively long exposure times. |
| Title |
Finite-amplitude effects on ultrasound beam patterns in.attenuating media. |
| Author |
Reilly CR, Parker KJ. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1989 |
| Abstract |
Some problems relevant to medical ultrasonics are addressed through experimental measurements.of focused, pure-tone beam patterns under quasilinear conditions where significant nonlinearities.are manifested. First, measurements in water provide a comparison of the beam patterns of the.fundamental and nonlinearly generated harmonics against recent theoretical predictions of others..The radial beamwidths, presence and spacing of sidelobes, axial distances to peak pressures,.focal shock parameter, time-domain waveform asymmetry, and post-focal falloff of the.fundamental through fifth harmonics are discussed relative to various models under preshock.conditions (sigma less than 1). Second, the focused sources are placed in a more attenuating fluid.to mimic the behavior of these fields in tissue. The changes in beam characteristics are examined.relative to measurements at the same intensities in water, and relative to theoretical predictions..The results suggest that, given a known linear (low-intensity) focused beam pattern in water,.guidelines can be followed to predict the beam pattern of the fundamental and higher harmonics.at higher intensities in water, and then in attenuating media such as tissue. |
| Title |
First step in estimating the medial ultrasound in vivo power spectrum on a patient specific basis. |
| Author |
BigelowTA. |
| Journal |
Thesis(PhD): Univ of Illinois |
| Volume |
|
| Year |
2004 |
| Abstract |
No abstract available. |
| Title |
Flow cytometric studies on the effect of experimental pulsed ultrasound on cultured cell in vitro. |
| Author |
Maeda K, Kigawa J. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1986 |
| Abstract |
The changes of flow-cytometric pattern was noted after the exposures of cultered HeLa cells to gamma-ray, cytostatic agents and the pulsed ultrasound with the 10 and 5 ?s pulse durations and SATP 58.6 W/cm2 intensity. No comparable change was observed in the flow-cytometric pattern after the exposure to the pulsed ultrasound with the 10 and 5 ?s pulse duration and SATP 20W/cm2 intensity. |
| Title |
Flow dependence of 2-D temperature distributions induced in the perfused canine kidney by ultrasound. |
| Author |
Prionas SD, Raftery KA, Edmonds PD, Constantinou CE. |
| Journal |
Int J Hyperthermia |
| Volume |
|
| Year |
1991 |
| Abstract |
The influence of perfusate flow rate on the two-dimensional (2-D) temperature distributions induced by hyperthermia in the canine kidney was evaluated. Localized hyperthermia was induced by ultrasound (frequency 2.040 MHz, transducer diameter 6.7 cm) in the ex-vivo perfused kidney. Temperatures were mapped using shielded copper/constantan thermocouple sensors. The 2-D temperature distribution of the kidney was obtained by pulling these sensors through a planar array of eight stainless-steel trocars inserted along its longitudinal axis. The perfusion system allowed for the control of internal/external organ temperature and type of perfusate, and it simulated vasodilation and vasoconstriction by changing the arterial volume flow rate. The temperature data obtained at flow rates ranging from 0 to 570 ml/min and power levels from 0 to 150 W showed that acoustic power densities in excess of 1.5 W/cm2 were required to maintain therapeutic temperatures in this system. Contour maps for characterizing the 2-D temperature distributions induced in this system were analysed with the introduction of a quantitative measure based on the area within a given isotherm. They show the effects of tissue heterogeneity, flow rate, and non-uniform power deposition. Time constants computed from the exponentially decaying temperatures measured following power off ranged from 5 to 555 s. These findings provide a basis for comparison with temperature measurements being acquired in the in-vivo kidney system. Information acquired from this system may facilitate the process of developing tissue-equivalent dynamic phantoms for ultrasound-induced hyperthermia. The ex-vivo model presented in this paper might be used to study the performance of alternative heating applicators, the effect of haematocrit, blood viscosity, and the use of vasoactive drugs. |
| Title |
Flow of red blood cells stopped by ultrasound. |
| Author |
Dyson M, Woodward B, Pond JB. |
| Journal |
Nature |
| Volume |
|
| Year |
1971 |
| Abstract |
No abstract available |
| Title |
Fluorescein isothiocynate-dextran uptake by chinese hamster ovary cells in a 1.5 MHz ultrasonic standing wave in the presence of contrast agent. |
| Author |
Khanna S Hudson B Pepper CJ Amso NN Coakley WT. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2006 |
| Abstract |
Uptake of fluorescein isothiocynate-dextran (FITC-dextran) by Chinese hamster ovary cells was studied after exposure to ultrasonic standing wave (USW) in presence of Optison, an ultrasound contrast agent. Confluent Chinese hamster ovary cells were harvested and suspended in phosphate-buffered saline + 0.1% bovine serum albumin containing FITC-dextran (10, 40, and 500 kDa) at 10 microM final concentration. The suspension was seeded with contrast agent (75 microL/mL) and exposed to a 1.5 MHz USW system at acoustic pressures ranging from 0.98 to 4.2 MPa. Macromolecular uptake was assessed by fluorescent microscopy and quantified by flow cytometry 10 min after exposure. FITC-dextran positive cells, as assessed by flow cytometry, were 1 +/- 0.05% and 2.58 +/- 0.27% for acoustic pressures of 1.96 and 4.2 MPa, respectively (p = 0.006). Fluorescent microscopy indicated a degree of macromolecular loading at 0.98 MPa with 46% of peripherally FITC-dextran- and/or propidium iodide-stained cells coincident with the appearance of significant frequency (f0/2 and 2 f0) emission signals. At higher pressures, high macromolecular loading with 6% peripherally stained cells at 1.96 MPa was associated with lower order emission signals and white noise. The study conclusively demonstrates macromolecular loading in an USW, a significantly higher macromolecular loading at higher pressures and indicates potential of emission signals for a feedback loop to control the acoustic power outputs and fine-tune the biologic effects associated with sonoporation. |
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