Abstract
It has been previously shown [E. ter Haar and S. Daniels, Phys. Med. Biol. 26, 1145–1149 (1981)] that guinea pigs that are exposed to therapeutic ultrasound of intensities in the range of 80 mW/cm2 to 680 mW/cm2 (spatial average) develop air bubbles of observable size within the exposed tissue. We present evidence that air bubble growth in guinea pig tissue during ultrasonic irradiation is due to rectified diffusion. Through numerical integration of existing rectified diffusion equations, for the frequency and intensities used by ter Haar and Daniels in their recent work, we have found that small “undetectable” bubbles grow during irradiation to a “detectable” size. The number of bubbles growing and the final sizes predicted closely resembles the results obtained experimentally. [Work supported by the ONR and the NSF.]
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