Watch your distance: a study of laser fiber working distance on fragmentation when altering pulse width or modulation (Conference Presentation)

Abstract

Introduction: The Moses technology for the Ho:YAG laser introduces a pulse-shape modulation that optimizes energy delivery through water. The aim of this study was to assess fiber tip to stone working distance on fragmentation incorporating a variety of pulse modes. Methods: Experiments were conducted with a 3D positioner, a 30 mm flat BegoStone, and a 230 µm fiber utilizing short pulse (SP), long pulse (LP), Moses Contact (MC), and Moses Distance (MD) modes. Ablation crater volume was measured by 3D confocal microscopy, after a single pulse (1.0J) with the fiber tip positioned at 0, 0.5, 1, 2, and 3 mm from the stone. Fragmentation efficiency (1Jx10Hz) was assessed with the fiber tip at 0 and 1 mm distance, programmed to fragment the stone over 3 minutes. Fragmentation was defined as difference in stone mass before and after each experiment. Results: For all tested pulse modes, ablation crater volume and fragmentation were greatest when the fiber tip was in contact with the stone. Ablation declined as the working distance increased with no ablation occurring at 3 mm. At 1 mm distance, ablation volume using MD mode was significantly higher when compared to SP, LP and MC (p<0.05). Compared to all modes tested, MD resulted in 28% and 39% greater fragmentation at both 0 and 1 mm working distance, respectively (p<0.05). Conclusion: Holmium laser lithotripsy is significantly affected by fiber working distance. At 0 and 1 mm distance, MD had the greatest fragmentation efficiency suggesting this mode may have advantages during ureteroscopy.