National Council on Radiation Protection and Measurements's Biological effects of ultrasound : mechanisms and clinical PDF
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Extra resources for Biological effects of ultrasound : mechanisms and clinical implications
8. 01 for this fraction. 04 dB. 3. 36 x 10' g/s cmZ. F/M: fat/muscle. 5-Reported attenuation between the abdominal surface and the uterine cavity in early pregnancy from Stewart and Stratmeyer (1982) No. 25 Takeuchi et d, 1977 2 Momhashi and Iizuka, 5 Morohashi and Iizuka. 5 MHz ultrasound from transducer to gestational sac. 5 from t h e compilation of Stewart and Stratmeyer (1982). 5 MHz. 5. From the calculation and experiments, a realistic estimate of the minimum expected attenuation in early pregnancy is, in dB, one or two times the frequency in megahertz.
In most of this theory, 46 / 3. MEDICAL ULTRASOUND FIELDS and in much of the discussion here, it is assumed that the source vibrates uniformly and that there is no motion elsewhere in the plane of the source. While these assumptions are probably never strictly true, the theory (sometimes called "piston-in-a-bafflen theory) so developed has proved very successful in accounting for important features of real fields (Harris, 1981a, 1981b). 1) we discuss some of the principal results of the circular-source theory.
5 ACOUSTIC PROPERTIES OF TISSUES / 27 specified equipment a t a particular location in the body. This is important for effective use of medical ultrasound and also for anticipating any undesirable interactions between the ultrasound and the tissue. In order to make calculations, it is necessary to use quantitative information on acoustic properties of tissues. 3 contains a summary of data available, for different organs and tissues, of four basic acoustic parameters. 1, these parameters are: i) The attenuation coefficient a, used for predicting the reduction in the intensity of a beam with increasing distance from the source; ii) The absorption coefficient a,used for predicting the dissipation of acoustic energy in tissue and for calculating temperature elevation produced by ultrasound; iii) The speed of sound c, used for distance calibration of pulseecho displays and for making calculations on refraction and diffraction; and iv) The characteristic acoustic impedance pc, used for analyzing reflections a t interfaces.
Biological effects of ultrasound : mechanisms and clinical implications by National Council on Radiation Protection and Measurements