Pulse duration and peak intensity during focused ultrasound surgery: theoretical and experimental effects in rabbit brain in vivo.

The goal of this study was to establish the exposure parameters that will generate predictable thermally induced lesions in brain. In addition, the accuracy of a theoretical model for prediction of the lesion size was tested. To do this, 160 adult rabbits were sonicated (frequency 0.936 and 1.72 MHz) and then sacrificed at various intervals after the sonications. The results showed that predictable thermal lesions could be induced if the exposure durations were between 0.5 and 2 s. Dimensions of the necrosed tissue volume were roughly predictable by the theoretical calculations based on purely thermal effects. Shorter sonications required higher intensities (above 3700 W cm-2 at 1.72 MHz) resulting in mechanical effects with extensive vascular damage. Lesion size varied more at longer exposures (5 and 10 s), perhaps due to the increased effect of tissue perfusion. As a conclusion, focused ultrasound can be used for destruction of tissues deep in brain without causing undesirable mechanical effects, if the exposure parameters are selected properly.