Cavitation memory effects occur when remnants of cavitation bubbles (nuclei) persist in the host medium and act as seeds for subsequent events. In pulsed cavitational ultrasound therapy, or histotripsy, this effect may cause cavitation to repeatedly occur at these seeded locations within a target volume, producing inhomogeneous tissue fractionation or requiring an excess number of pulses to completely homogenize the target volume. Cavitation memory can be removed with a dithering technique. The spatial-temporal memory effect of micro-bubbles can be defeated by (1) passive temporal dithering, (2) active dithering, or (3) use of therapy pulses above the de novo threshold.
