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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 287 out of 330
| Title |
Ultrasonic backscattering from porcine whole blood of varying hematocrit and.shear rate under pulsatile flow. |
| Author |
Lin Y-H, Shung KK. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1999 |
| Abstract |
It was shown previously that ultrasonic scattering from whole blood varies during a flow cycle under pulsatile flow both in vitro and in vivo. It has been postulated that this cyclic variation may be associated with the dynamics of red cell aggregation because the shearing force acting on the red cell aggregates across the lumen is a function of time during a flow cycle. In all studies, the local shear rate variation as a function of time is unknown. The effect of shear rate on the red cell aggregation and, thus, on ultrasonic scattering from blood can only be merely speculated. One solution to this problem is to estimate the shear rate in a flow conduit by finite element analysis (FEA). An FEA computational fluid dynamics (CFD) tool was used to calculate local shear rate in a series of experiments in which ultrasonic backscattering from porcine whole blood under pulsatile flow was measured as a function of hematocrit and shear rate intravascularly with a 10-MHz catheter-mounted transducer in a mock flow loop. The results show that, at 20 beats per min (BPM), the magnitudes of the cyclic variation for hematocrits at 30, 40, and 50% were approximately 4 dB. However, at 60 BPM, the magnitude of cyclic variation was found to be minimal. The results also confirm previous findings that the amplitude and the timing of the peak of ultrasonic backscattering from porcine whole blood under pulsatile flow during a flow cycle are dependent upon the shear rate and hematocrit in a complicated way. |
| Title |
Ultrasonic bioeffects:A view of experimental studies. |
| Author |
O'Brien WD Jr. |
| Journal |
Birth |
| Volume |
|
| Year |
1984 |
| Abstract |
Diagnostic ultrasound of the pulse-echo imaging type is used in at least 25 per cent of pregnancies, and Doppler continuous wave ultrasound, as employed in external electronic fetal monitors, is used in nearly all pregnancies. Diagnostic ultrasound energy levels are from 0.1 to 40 mW/cm2. These intensity levels depend on the characteristics of the ultrasonic beam and temporal exposure. The American Institute of Ultrasound in Medicine states that…“there have been as of October, 1982 no independently confirmed significant biological effects in mammalian tissues exposed to intensities below 100 mW/cm2.” Some of the animal studies reviewed by the AIUM to reach this conclusion are discussed.
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| Title |
Ultrasonic biomicroscopy of viable, dead and apoptotic cells. |
| Author |
Czarnota GJ, Kolios MC, Vaziri H, Benchimol S, Ottensmeyer FP, Sherar MD, Hunt JW. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1997 |
| Abstract |
Ultrasonic imaging is frequently used in medical diagnosis to differentiate normal and tumour tissues. Here we investigate if distinct types of cell death can be discriminated through the use of ultrasound biomicroscopy. By using a well-controlled system in vitro, we demonstrate that this imaging modality can be used to differentiate living cells, dead cells and cells that have died by programmed cell death or apoptosis. The results indicate a greater than twofold ultrasound backscatter signal from apoptotic cells in comparison to viable cells, whereas heat-killed cells exhibit an intermediate level of ultrasound backscatter. The results have potential implications in the study of disease-related biological processes involving apoptosis. |
| Title |
Ultrasonic biophysics. |
| Author |
Frizzell LA. |
| Journal |
Book Chapter |
| Volume |
|
| Year |
1998 |
| Abstract |
The field of ultrasonic biophysics is very broad, encompassing a large range of frequencies and many different biological systems. The modern use of ultrasound started several decades ago in the form of sonar for military applications. Since then it has developed to the point where it is used very extensively in industry, bioengineering, and medicine. Its original applications in medicine were for therapy, where the energy absorbed from ultrasound waves was used to heat a variety of tissues and structures lying below the body surface. Ultrasound could penetrate and deposit heat within these tissues, whereas insufficient heat could be conducted from surface sources. Improved instrumentation and techniques available after World War II led to the development of ultrasound systems for medical imaging. Over the past 35 years ultrasound has developed into an indispensable clinical diagnostic tool. Currently, ultrasound is used to image most parts of the body, and more than half of all pregnant women in the United States are examined with ultrasound. This widespread utilization has resulted from ultrasound?s proven clinical utility for imaging soft tissues compared to more expensive imaging techniques. The development of ultrasound, particularly for fetal examinations, as also been fostered by its safety record; no case of an adverse biological effect induced by diagnostic ultrasound has ever been reported in humans (AIUM, 1993.)
Ultrasound has been used for many years to characterize biological materials. This results in large part from a desire to understand better the interaction of ultrasound with biological tissues so that clinical ultrasonic systems might be made more efficacious. However, ultrasound has also found application to the determination of rate constants in chemical reactions and in recent years has been used, via ultrasonic cavitation, to enhance desired chemical reactions that normally occur very slowly or not at all. The latter application has spawned the area of sonochemistry (Suslick, 1988) which has the potential for significantly increasing industrial production of many important chemical products, but which is beyond the scope of this article and will not be discussed further.
Section 1 discusses some of the basic principles underlying the use of ultrasound in medical imaging, therapy, and other applications. This is followed by discussions of the acoustical characteristics of biological media and the techniques for measuring them. The article ends with a brief discussion of recent developments in medical imaging and therapy.
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| Title |
Ultrasonic bubbles in medicine: Influence of the shell. |
| Author |
Postema M, Schmitz G. |
| Journal |
Ultrason Sonochem |
| Volume |
|
| Year |
2007 |
| Abstract |
Ultrasound contrast agents consist of microscopically small bubbles encapsulated by an elastic shell. These microbubbles oscillate upon ultrasound insonification, and demonstrate highly nonlinear behavior, ameliorating their detectability. (Potential) medical applications involving the ultrasonic disruption of contrast agent microbubble shells include release-burst imaging, localized drug delivery, and noninvasive blood pressure measurement. To develop and enhance these techniques, predicting the cracking behavior of ultrasound-insonified encapsulated microbubbles has been of importance. In this paper, we explore microbubble behavior in an ultrasound field, with special attention to the influence of the bubble shell.
A bubble in a sound field can be considered a forced damped harmonic oscillator. For encapsulated microbubbles, the presence of a shell has to be taken into account. In models, an extra damping parameter and a shell stiffness parameter have been included, assuming that Hooke’s Law holds for the bubble shell. At high acoustic amplitudes, disruptive phenomena have been observed, such as microbubble fragmentation and ultrasonic cracking. We analyzed the occurrence of ultrasound contrast agent fragmentation, by simulating the oscillating behavior of encapsulated microbubbles with various sizes in a harmonic acoustic field. Fragmentation occurs exclusively during the collapse phase and occurs if the kinetic energy of the collapsing microbubble is greater than the instantaneous bubble surface energy, provided that surface instabilities have grown big enough to allow for break-up. From our simulations it follows that the Blake critical radius is not a good approximation for a fragmentation threshold.
We demonstrated how the phase angle differences between a damped radially oscillating bubble and an incident sound field depend on shell parameters. |
| Title |
Ultrasonic cardiac pacing in the porcine model. |
| Author |
Towe BC, Rho R. |
| Journal |
IEEE Trans Biomed Eng |
| Volume |
|
| Year |
2010 |
| Abstract |
Periodic pulses of intense ultrasound energy at 70 kHz with 5-ms duration at 3 MPa SPL applied to the exposed pig myocardium at physiologic rhythms were observed to produce cardiac pacing. Ten animals were successfully paced at pulse width and energy conditions above a certain threshold. Sigmoid strength-duration curves characterizing ultrasound's effectiveness in pacing were observed to resemble those of electrical stimulation. We suggest that bioelectrical stimulatory effects of ultrasound on the heart are a radiation pressure effect and a manifestation of the known myocyte sensitivity to stretch. |
| Title |
Ultrasonic cavitation indirectly induces single strand breaks in DNA of viable cells in vitro by the action of residual hydrogen peroxide. |
| Author |
Miller DL, Thomas RM, Frazier ME. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1991 |
| Abstract |
Direct exposure of cells to vigorous ultrasonic cavitation results predominantly in mechanical cell lysis, but latent effects due to production of toxic sonochemicals can also be present. Phosphate buffered saline (PBS) was exposed to 1.61 MHz ultrasonic cavitation at 20 degrees C in a rotating tube exposure system to build up sonochemical products. Single strand DNA breaks (SSBs) were then induced by treating Chinese hamster ovary (CHO) cells with the cavitated PBS for 30 min on ice. The SSBs resided in viable cells, as evidenced by their ability to repair the breaks when warmed. This indirect effect could be explained by the action of cavitation-generated hydrogen peroxide that had built up (e.g., to 16 microM after 30 min exposure) in the PBS. Dissolution of argon gas in the PBS before exposure enhanced the SSB effect and the H2O2 production. Addition of catalase to the cavitated PBS before cell treatment eliminated the H2O2 and the SSB gamma effect. Tests with hydrogen peroxide showed that 16 microM H2O2 treatment for 30 on ice was as effective as 1 Gy dose of 60Co gamma rays in producing single strand breaks. The SSB effect of H2O2 and gamma rays was reduced by addition of the radical scavenger cysteamine to the cells before treatment, but cysteamine did not reduce the SSB effect of direct exposure to ultrasonic cavitation. These results help to clarify the potential for genetic effects from ultrasonic cavitation. These effects help to clarify the potential for genetic effects from ultrasonic cavitation. |
| Title |
Ultrasonic characterization of aging in skin tissue. |
| Author |
Bhagat PK, Kerrick W, Ware RW. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1980 |
| Abstract |
The propagation velocity (c) and attenuation coefficient (a) of ultrasound were measured at room temperature in skin tissues excised from twenty aged (27 months) and eight young (2 months) Bar Harbor strain female mice. Frequencies used were 2.25, 5.0, 7.5 and 10.0 MHz. Both velocity and attenuation data were obtained using a pulse-echo technique. Transit times were measured with a universal counter timer to 10 nsec resolution, and corrected for the "dead time" due to the transducer matching layer. Aged skin had significantly lower values of c and a at all frequencies than did the corresponding young tissues. This preliminary study suggests that the tissue changes which collectively constitute aging may, in some instances, be predictably associated with measurable changes in the acoustic properties of those tissues. |
| Title |
Ultrasonic characterization of AlbunexR, a new contrast agent. |
| Author |
Bleeker HJ, Shung KK, Barnhart JL. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1990 |
| Abstract |
A new, promising ultrasound contrast agent, Albunex? (Molecular Biosystems, Inc., San Diego, California), is increasingly being used in experimental myocardial contrast echocardiography. Albunex? is a suspension of stable microencapsulated air bubbles prepared from 5% albumin. Contrast agents like Albunex? have been used to estimate regional myocardial perfusion. Current methods that use contrast media to assess myocardial perfusion in vivo from ultrasonic images are neither reliable nor absolute. The primary reason is that the fundamental relationship between ultrasonic properties and physical properties of the contrast media is unknown. Ultrasonic backscatter, acoustic velocity, and attenuation of Albunex? as a function of its concentration, size, and temperature at 7.5 and 5 MHz were measured. The backscatter coefficient, which is an absolute measure of ultrasonic backscatter, was found to be approximately linearly proportional to the number of microspheres in Albunex? (r=0.86) at low concentrations. The attenuation coefficient was found to be linearly proportional to the number of microspheres (r=0.96). An understanding of the relationship between the physical and ultrasonic properties of Albunex? is essential if it is to be used to quantify myocardial perfusion. |
| Title |
Ultrasonic characterization of blood during coagulation. |
| Author |
Shung KK, Fei DY, Yuan YW, Reeves WC. |
| Journal |
J Clin Ultrasound |
| Volume |
|
| Year |
1984 |
| Abstract |
Recently ultrasound has been found to be extremely useful in detecting intracardiac thrombi as well as intracranial hemorrhages in neonates. The principal criterion used for clinical diagnosis of thrombus has been an increase in the echogenicity of clotted blood. However, echogenicity is a rather nonspecific and qualitative description of tissue ultrasonic properties. A rise in echogenicity could be the result of an increase in ultrasonic backscatter, or a decrease in attenuation, or a combination of both. In order to ascertain the mechanism responsible for the.clinically observed increase in echogenicity and thus put the technique on a firm foundation, we have measured serially the ultrasonic velocity, attenuation and backscatter in human blood up to 24 hours following the onset of coagulation. Preliminary results show that all three ultrasonic properties increase during this time period. At 24 hours following clotting, the mean rises in velocity, attenuation and backscatter are 3.36 +/- 0.35 X 10(3) cm/sec, 2.3 +/- 0.22 db/cm and 18.5 +/- 1.2 dB per unit volume of blood (at 7.5 MHz and a temperature of 23 degrees C), respectively. These results indicate that the increase in echogenicity of a thrombus is due to a substantial increase in ultrasonic backscatter, which is moderated to a certain extent by the accompanied increase in attenuation. |
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