Ho:YAG laser lithotripsy in non-contact mode: optimization of fiber to stone working distance to improve ablation efficiency.

Abstract

To evaluate how variable working distances between the laser fiber and the stone influence ablation volume. A laser fiber was fixed on a robotic arm perpendicular to an artificial stone. A single laser pulse was triggered at different working distances (0-2.0mm in 0.2mm increments) between the distal fiber tip and the stone. To achieve a measurable impact, pulse energy was set to 2 and 3J, with either short or long pulse duration. Ablation volume was calculated with an optical microscope. Experiments were repeated five times for each setting. Highest ablation volume was observed with a long pulse of 3J at a working distance of 0.4mm between the laser fiber and the stone surface (p value<0.05). At 2J, the highest ablation volume was noticed with a short pulse in contact mode. However, ablation volume of the latter was not significantly greater than with a long pulse of 2J at a working distance of 0.4mm (p value>0.05). Compared to lithotripsy in contact mode, triggering a single long pulse at 0.4mm increased ablation volume by 81% (p value=0.016) at 2J and by 89% (p value=0.034) at 3 J. For Ho:YAG laser lithotripsy, ablation volume may be higher in non-contact mode using long pulses, rather than in direct contact to the stone. Findings of the current study support the need of further studies of lithotripsy in non-contact mode.