FIG. 5.

(Color online) PCD signal processing. (a) Two examples of a filtered PCD signals in the time domain. Focus delay is the time of ultrasound wave propagation from the pHIFU transducer surface to its focus and back to the PCD. A cavitation event was considered observed if the signal after the focus delay was larger than the noise preceding the focus delay by a factor of $\surd 5$ (Rose criterion)—the dashed horizontal line. The black and grey curves correspond to the PCD signals collected at the same output level of a HIFU transducer, with and without observed cavitation event. (b) Definition of cavitation probability and persistence. In the current studies 60 HIFU pulses at the same pressure level were applied to each of the 20 spots in the gel. Thus, N = 20 and K = 60.