By National Council on Radiation Protection and Measurements
This file bargains present perspectives on publicity standards for scientific diagnostic ultrasound. subject matters coated contain: nonthermal mechanisms for bioeffects, noninertial cavitation, nonlinear bubble responses and inertial cavitation, versions for publicity estimation in humans, and epidemiology of ultrasound publicity.
desk of Contents
1. govt precis
three. Nonthermal Mechanisms for Bioeffects within the Absence of Cavitation
four. Noninertial Cavitation; Gas-Body Activation
five. Nonlinear Bubble reaction; Inertial Cavitation
6. Bioeffects of Noninertial Cavitation regarding unfastened and Stabilized fuel our bodies in Non-Mammalian structures
7. Bioeffects of Inertial Cavitation in vitro
eight. Bioeffects of Acoustic Cavitation in Mammalian Tissues
nine. versions for publicity Estimation in humans
10. hired and wanted Sound strain Waveforms
eleven. Temperature Elevation and Its organic results
12. Epidemiology of Ultrasound publicity
thirteen. precis and Conclusions
Appendix A: Mechanical Equilibrium of loose Bubbles
Appendix B: Output demonstrate regular
Appendix C: Nepers and Decibels
Appendix D: Nonlinear Propagation: An replace
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Additional resources for Exposure Criteria for Medical Diagnostic Ultrasound: II. Criteria Based on All Known Mechanisms
When ultrasound is focused on the surface of adult bone or lung, most of the energy is absorbed or diffusely scattered, and the radiation force on the surface of incidence is of the order of W cמ1. However, the radiation force on an individual soft-tissue layer is much less, since only a relatively small fraction of the acoustic energy is reflected or absorbed by the layer. Nevertheless, it can sometimes be biologically significant, if the beam is focused and its acoustic power concentrated in a small area.
1 10 1 Exposure Duration (s) 100 Fig. 2. , 1981). 26 / 3. NONTHERMAL MECHANISMS FOR BIOEFFECTS associated with the high intensities that exist during the bursts at the lower values of PRF (NCRP, 1992). , 1993a). Threshold levels for these effects occurred at acoustic pressure amplitudes of the order of 10 MPa. Two qualitatively different effects were observed. Their occurrence depended upon the phase of the heart cycle when the pulse arrived. , 1993b). If the pulse of ultrasound arrives when the heart is relaxed (late diastole), it may cause premature ventricular contraction.
1997a). The reflector transmits radiation force to the heart tissue, but eliminates any direct interaction of the sound with the heart and therefore excludes heating or cavitation as contributing mechanisms. 4). There are marked similarities in the response of neural and cardiac tissues. Threshold levels are comparable; relatively long pulses, compared to those used in diagnostic ultrasound, are required to produce these responses. With cardiac tissues, there is rapid increase in the effectiveness of the ultrasound with an increase in pulse length in the range from 1 to 10 ms.