Fig. 1.

Half-section view of the experimental setup used to study effects of sonication frequency on the bubble removal process. Primary cavitation was initiated by an array of eight 2 MHz histotripsy modules arranged in a spherical pattern, while bubble removal pulses were delivered from a separate bubble removal module (0.5, 1, or 2 MHz) aligned at a predetermined offset relative to the histotripsy focus (see text). All transducer modules were held within an Accura 60 plastic scaffold that also served as the water tank for the experiments. Optical windows in the front and rear of the scaffold permitted the use of backlit high speed photography to monitor the bubble removal process. A needle hydrophone positioned adjacent to the histotripsy focus, at an offset 2 mm distal relative to the bubble removal module, was used to measure the transmission of interrogation pulses propagating through the field.