Shock waves generated by toroidal bubble collapse are imperative for kidney stone dusting during Holmium:YAG laser lithotripsy

• Published in: Ultrasonics sonochemistry 2023-12, Vol.101, p.106649-106649, Article 106649
• Main Authors: Xiang, Gaoming, Chen, Junqin, Ho, Derek, Sankin, Georgy, Zhao, Xuning, Liu, Yangyuanchen, Wang, Kevin, Dolbow, John, Yao, Junjie, Zhong, Pei
• Format: Article
• Language: English
• Subjects: Holmium; Humans; Kidney Calculi - therapy; Lasers, Solid-State - therapeutic use; Lithotripsy, Laser - methods; Original
• ISSN: 1350-4177; 1873-2828
• DOI: 10.1016/j.ultsonch.2023.106649

•Shock waves from toroidal bubble collapse is imperative for kidney stone dusting.•Progressively intensified collapse of toroidal bubbles boosts shock wave emission.•The shock waves, not jet impact, are vital for cavitation damage in laser lithotripsy.•The leaky Rayleigh waves may contribute to superficial material removal. Holmium:yttrium–aluminum-garnet (Ho:YAG) laser lithotripsy (LL) has been the treatment of choice for kidney stone disease for more than two decades, yet the mechanisms of action are not completely clear. Besides photothermal ablation, recent evidence suggests that cavitation bubble collapse is pivotal in kidney stone dusting when the Ho:YAG laser operates at low pulse energy (Ep) and high frequency (F). In this work, we perform a comprehensive series of experiments and model-based simulations to dissect the complex physical processes in LL. Under clinically relevant dusting settings (Ep = 0.2 J, F = 20 Hz), our results suggest that majority of the irradiated laser energy (>90 %) is dissipated by heat generation in the fluid surrounding the fiber tip and the irradiated stone surface, while only about 1 % may be consumed for photothermal ablation, and less than 0.7 % is converted into the potential energy at the maximum bubble expansion. We reveal that photothermal ablation is confined locally to the laser irradiation spot, whereas cavitation erosion is most pronounced at a fiber tip-stone surface distance about 0.5 mm where multi foci ring-like damage outside the thermal ablation zone is observed. The cavitation erosion is caused by the progressively intensified collapse of jet-induced toroidal bubble near the stone surface (