Evidence for ultrasonically induced cavitation in vivo.

The possibility of stable bubbles being produced during ultrasonic irradiation of a guinea-pig hind limb, has been examined using a pulse echo ultrasonic imaging technique, that can visualise, within a cross-section of the limb, both moving and stationary bubbles of diameters down to 10 mu m (Beck et al. 1978). The observations reported clearly show that acoustic cavitation, leading to stable bubble production, occurs in vivo in mammalian tissue as a result of irradiation with ultrasound above 80 mW cm-2 intensity. However, before the biological consequences of such bubble formation can be assessed, further studies must be carried out to define more fully the intensity threshold as a function of the time or irradiation, and to establish the time course for re-absorption of these stable bubbles in the absence of a sound field.