Biological effects of ultrasound—A review

The history of ultrasound related to bioeffects studies begins in the 1920's and continues to the present. Because of the type of effects exhibited between high-frequency mechanical waves and biological systems, there emerged a low-intensity medical therapeutic regime using ultrasound in the 1930's. In the late 1940's and early 1950's, research began on the use of ultrasound in the pulse-echo mode to visualize soft tissues of the human body. The interaction of ultrasound and tissue in this mode underlies the present expanding capability of its medical diagnostic use. During the same time period, the use of intense, sometimes highly focused ultrasound was explored for its interactive effects on tissue. Out of these bioeffects studies emerge possibilities for therapy and some preliminary clinical trials have been conducted. Bioeffects studies involve assessment of thermal, cavitational, and other mechanical entities in their contribution to the interaction with ultrasound. Considerable progress has been made so that in some modes, it is possible to predict the magnitude of a given effect by computational means. In other modes the reliably, predictable effects have not yet become tractable by computational means alone.