Histotripsy produced by dual frequency of fundamental and harmonic superimposition with protocol of hundred-microsecond-length pulses and two stages

Confocal fundamental and harmonic superimposition can greatly lower the cavitation threshold and enhance cavitation activity via wave interference. In this study, a histotripsy protocol of using dual frequency of fundamental and harmonic superimposition combined with hundred-microsecond-length pulses and two stages is proposed and testified to get good use of the nonlinear regimes of enhanced cavitation and boiling effects. Each hundred-microsecond-long pulse consists of 400-600μs. Much higher 4-6% duty cycles will be used in stage 1 to induce boiling and at the same time partially homogenize tissue, and 1% duty cycles be used in second stage. Each two-element transducer for either 1.1/3.3 MHz or 1.1/2.2 MHz dual frequencies consists of two confocal-annular-element arrays. The experiments were implemented in gel phantom with BSA, ex vivo of bovine eye lens and porcine kidneys, monitored via high speed camera or passive cavitation detect, PCD. The harmonic pressures in focal region appeared shocks. As expected, the experiment of porcine kidney produced successfully a completely tissue homogenate region (sharply demarcated from untreated tissue) with typical dimension of 7.8 mm×2 mm (axial × lateral). The key reasons to enhance treatment efficiency may boiling generate a lot of times in multi positions within focal region.