Purpose: While cavitation during laser lithotripsy contributes to the Moses effect, the impact of cavitation on stone damage is less clear. Using different laser settings, we investigate the role of cavitation bubbles in energy delivery and stone damage. Materials and Methods: The role of cavitation in laser energy delivery was characterized using photodetector measurements synced with high-speed imaging for laser pulses of varying durations. BegoStone samples were treated with the laser fiber oriented perpendicularly in contact with the stone in water or in air to assess the impact of cavitation on crater formation. Crater volume and geometry were quantified using optical coherence tomography. Furthermore, the role of cavitation in stone damage was elucidated by treatment in water with the fiber oriented parallel to the stone surface and by photoelastic imaging. Results: Longer pulse durations resulted in higher energy delivery but smaller craters. Stones treated in water resulted in greater volume, wider yet shallower craters compared to those treated in air. Stones treated with the parallel fiber showed crater formation after 15 pulses, confirmed by high-speed imaging of the bubble collapse with the resultant stress field captured by photoelastic imaging. Conclusions: Despite improved energy delivery, the longer pulse mode produced smaller crater volume, suggesting additional processes secondary to photothermal ablation are involved in stone damage. Our critical observations of the difference in stone damage treated in water vs. in air, combined with the crater formation by parallel fiber suggest that cavitation is a contributor to stone damage during laser lithotripsy.

Objective: Low energy and high frequency settings are used in stone dusting for holmium lasers. Such settings may not be optimal for thulium fiber laser (TFL). With the seemingly endless combination of settings, we aim to provide guidance to the practicing urologists and assess the efficiency of the TFL platform in an automated in vitro “dusting model.” Materials/Methods: Three experimental setups were designed to investigate stone dusting produced by an IPG Photonics TLR-50 W TFL system using 200 μm fiber and soft BegoStone phantoms. The most popular 10 and 20 W dusting settings among endourologist familiar with TFL were evaluated. We directly compared short pulse (SP) vs long pulse (LP) mode using various combinations of pulse energy (E _p ) and pulse frequency (F). Thereafter, we tested the 10 and 20 W settings and compared them among each other to elucidate the most efficient settings at each power. Treatments were performed under the same total laser energy delivered to the stone at four different standoff distances (SDs) with a clinically relevant scanning speed of either 1 or 2 mm/sec. Ablation volumes were quantified by optical coherence tomography to assess stone dusting efficiency. Fragment size after ablation at different pulse energies was evaluated by sieving and evaluating under a microscope after treatment. Results: Overall, SP provided greater ablation volume when compared with LP. Our dusting efficiency model demonstrated that the maximum stone ablation was achieved at the combination of high energy/low frequency settings ( p < 0.005) and at a SD of 0.2 mm. At all tested pulse energies, no stone phantoms were broken into fragments >1 mm. Conclusions: During stone dusting with TFL, SP offers superior ablation to LP settings. Optimal dusting at clinically relevant scanning speeds of 1 and 2 mm/sec occurs at high energy/low frequency settings. Thulium lithotripsy with high E _p does not result in increased fragment size.

To investigate the effects of fiber lateral scanning speed across the stone surface (v_fiber) and fiber standoff distance (SD) on dusting efficiency during short pulse holmium (Ho): YAG laser lithotripsy (LL), pre-soaked BegoStone samples were treated in water using 0.2 J/20 Hz at SD of 0.10~0.50 mm with v_fiber in the range of 0~10 mm/s. Bubble dynamics, pressure transients, and stone damage were analyzed. To differentiate photothermal ablation vs. cavitation damage, experiments were repeated in air, or in water with the fiber tip at 0.25 mm proximity from the ureteroscope end to mitigate cavitation damage. At SD = 0.10 mm, the maximum dusting efficiency was produced at v_fiber = 3.5 mm/s, resulting in long (17.5 mm), shallow (0.15 mm), and narrow (0.4 mm) troughs. In contrast, at SD = 0.50 mm, the maximum efficiency was produced at v_fiber = 0.5 mm/s, with much shorter (2.5 mm), yet deeper (0.35 mm) and wider (1.4 mm), troughs. With the ureteroscope end near the fiber tip, stone damage was significantly reduced in water compared to those produced without the ureteroscope. Under clinically relevant v_fiber (1~3 mm/s), dusting at SD = 0.5 mm that promotes cavitation damage may leverage the higher frequency of the laser (e.g., 40 to 120 Hz) and, thus, significantly reduces the procedure time, compared to at SD = 0.1 mm that promotes photothermal ablation. Dusting efficiency during short pulse Ho: YAG LL may be substantially improved by utilizing an optimal combination of v_fiber, SD, and frequency.