In many ultrasound-based therapies, cavitation (the collapse of bubbles) can play a major role in treatment: inertial cavitation greatly enhances heating during HIFU cavitation acts in various ways to aid localised drug delivery inertial cavitation is a key factor in tissue fractionation (or histotripsy) and also important in shock wave lithotripsy Mapping the spatial and temporal extent of cavitation is therefore an important concern when monitoring ultrasound treatments.