A parametric study of bubble dynamics and lesion formation in liver tissue phantom during pressure-modulated shockwave histotripsy

Pressure-modulated shockwave histotripsy (PSH) is a new type of histotripsy that has recently been proposed for precise mechanical tissue fractionation without inducing the shock scattering effect. Though a previous initial proof-of-concept study clearly demonstrated the feasibility of PSH through introducing the pressure modulation time point (t_m) to minimise the shock scattering effect, this study was limited to the examination of the effect of a single PSH pulse at a constant t_m on bubble dynamics. Here, we investigated the effects of varying PSH exposure conditions, particularly changes of t_m and the number of pulses, on bubble dynamics and lesion formation in liver tissue phantoms. Our experimental results reveal that a gradual increase in t_m beyond the time-to-boil can start to initiate shock scattering effect, thereby forming a larger PSH lesion with the transformation of the lesion shape of an ellipsoid to an elongated tadpole. Furthermore, the PSH lesion size gradually increased with PSH pulses. Under the 2 MHz PSH exposure, the smallest oval-shaped lesion area was measured to be 0.18 mm² with t_m of 4 ms and a single PSH pulse, whereas the largest tadpole-shaped lesion area of 5.39 mm² was produced with t_m of 9 ms and 50 PSH pulses. Taken together, these suggest that PSH could be a promising approach for effectively controlling bubble dynamics and lesion formation.