Abstract
We investigated proposed mechanisms of laser lithotripsy, specifically for the novel, experimental Thulium fiber laser
(TFL). Previous lithotripsy studies with the conventional Holmium:YAG laser noted a primary photothermal
mechanism (vaporization). Our hypothesis is that an additional mechanical effect (fragmentation) occurs due to
vaporization of water in stone material from high absorption of energy, called micro-explosions. The TFL irradiated
calcium oxalate monohydrate (COM) and uric acid (UA) stones, as well as artificial stones (Ultracal30 and
BegoStone), in air and water environments. TFL energy was varied to determine the relative effect on the ablation
mechanism. Scanning electron microscopy (SEM) was used to study qualitative and characteristic changes in surface
topography with correlation to presumed ablation mechanisms. Laser irradiation of stones in air produced charring
and melting of the stone surface consistent with a photothermal effect and minimal fragmentation, suggesting no
mechanical effect from micro-explosions. For COM stones ablated in water, there was prominent fragmentation in
addition to recognized photothermal effects, supporting dual mechanisms during TFL lithotripsy. For UA stones,
there were minimal photothermal effects, and dominant effects were mechanical. By increasing TFL pulse energy, a
greater mechanical effect was demonstrated for both stone types. For artificial stones, there was no significant
evidence of mechanical effects. TFL laser lithotripsy relies on two prominent mechanisms for stone ablation,
photothermal and mechanical. Water is necessary for the mechanical effect which can be augmented by increasing
pulse energy. Artificial stones may not provide a predictive model for mechanical effects during laser lithotripsy.
