Active protection in pulse cavitational ultrasound therapy (histotripsy)

The overall goal of active protection is to preserve a selected zone (e.g., critical structures) during pulsed cavitational ultrasound therapy (histotripsy) using local suppression of cavitation. A specific application of active protection, focal sharpening, was investigated where a ring area immediately surrounding the focus was selected to be preserved. We have developed a pulse-by-pulse spatial-temporal pulsing strategy for focal sharpening. Treatments in cell-gel phantoms showed that the peripheral damage was substantially suppressed by 77 ± 13 % while desired treatment outcome in the center (i.e., complete fractionation) was maintained. High speed imaging of the bubble clouds showed a significant decrease in the maximum width of bubble clouds by 48 ± 23 % using focal sharpening. Preliminary experiments in ex vivo tissues demonstrated that active focal sharpening produced more confined lesions in real tissues.