Biological effects of ultrasound

Ultrasound has considerable potential as an agent for modifying cells and tissues. This comes partly from its capability to produce temperature elevation in desired spatial and temporal patterns. It also comes partly from its capability to produce cavitation in one or more of its diverse forms and, in addition, partly from the action of radiation forces, radiation torques, and acoustic streaming. In some situations, several mechanisms are involved and may interact with each other; for example, cavitation can produce heat in a medium, and the resulting temperature rise will affect the cavitation activity. Understanding these and other mechanisms has been, and promises to be, helpful in developing applications of ultrasound to therapy, surgery, and biotechnology, as well as in formulation of criteria for safety in medical procedures involving ultrasound. In this review, examples will be given to which the mechanisms are relevant, and recent developments will be discussed.