Mechanism of stone suction in thulium laser lithotripsy: Laser-induced cavitation bubble dynamics

In laser lithotripsy (LL), laser-induced cavitation bubble (LICB) dynamics plays a critical role in driving stone movement. However, the mechanisms by which laser parameters influence bubble dynamics and stone displacement are not yet fully understood. This study addresses this gap by using high-speed imaging and a multiphysics numerical model based on the phase field (PF) method to investigate the impact of laser pulse duration on bubble characteristics and stone motion. The results show that pulse duration significantly affects the shape and behavior of LICBs. Specifically, short pulse durations lead to the formation of pear-shaped bubbles, which generate suction forces that draw the stone toward the fiber. In contrast, longer pulse durations produce elongated bubbles, resulting in retropulsion, or the pushing of the stone away from the fiber. To account for these non-spherical bubbles, we revised the calculation formula for evaluating suction force. A strong positive correlation is observed between the acceleration of the bubble area and the stone's acceleration. Additionally, the study reveals that the negative pressure gradient created during bubble collapse is crucial for stone suction. The initial expansion and collapse jets from the bubbles contribute to the retropulsion forces. This study provides insight into the optimal parameters for enhancing stone suction, offering valuable guidance for improving the efficiency of lithotripsy procedures.