A new strategy to enhance cavitational tissue erosion using a high-intensity, initiating sequence

Our previous studies have shown that pulsed ultrasound can physically remove soft tissue through cavitation. A new strategy to enhance the cavitation-induced erosion is proposed wherein tissue erosion is initiated by a short, high-intensity sequence of pulses and sustained by lower intensity pulses. We investigated effects of the initiating sequence on erosion and cavitation sustained by lower intensity pulses. Multiple three-cycle pulses at a pulse repetition frequency of 20 kHz delivered by a 788-kHz focused transducer were used for tissue erosion. Fixing the initiating sequence at I(SPPA) of 9000 W/cm2, 16 combinations of different numbers of pulses within the initiating sequence and different sustaining pulse intensities were tested. Results showed: the initiating sequence increases the probability of erosion occurrence and the erosion rate with only slight overall increases in propagated energy; the initiating sequence containing more pulses does not increase the sustained cavitation period; and if extinguished and reinitiated, the sustained cavitation period becomes shorter after each initiation, although the waiting time between adjacent cavitation periods is random. The high-intensity, initiating sequence enhances cavitational tissue erosion and enables erosion at intensities significantly lower than what is required to initiate erosion.