By National Council on Radiation Protection and Measurements
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Extra info for Biological effects of ultrasound : mechanisms and clinical implications
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.
An A-scan image is formed by emitting a short pulse of ultrasound from the transducer, which passes into the tissue being examined, and simultaneously starting the bright spot of an oscilloscope to sweep along the x-axis of the screen. During the sweep, acoustic echoes returning to the transducer, which acts both as transmitter and receiver, are applied to the oscilloscope to deflect the bright spot along the y-axis. These echoes come from reflecting surfaces, such as tissue interfaces, in the patient's body.
We now consider the general situation presented by a sound field in a liquid near a rigid boundary in which the particle velocity (or a component of it) is parallel to the boundary. , that a "nonslip" condition applies. An abrupt transition in velocity then occurs in a thin layer, called the "acoustic boundary layer," whose characteristic thickness is I where q is the coefficient of shear viscosity and p the density for the fluid, while f is the frequency. 56 pm. , the velocity which would be obtained in the sound field if the boundary were absent.
Biological effects of ultrasound : mechanisms and clinical implications by National Council on Radiation Protection and Measurements