We devised a method to continuously measure the distance from fiber tip to stone surface based on the reflectance of an aiming beam back into the fiber during a popcorning scenario to determine how often the stone is close to the laser fiber when firing. Continuous light was coupled into a 200 µm fiber taped immediately next to the holmium fiber. Fibers were placed into a test tube with 5 BegoStones. Reflected light back into the fiber passed through the coupler to a biased photodiode. The fraction of time a stone was within 0.5 mm varied from 5%-18%.
KEYWORDS: In vitro testing, Laser lithotripsy, Thermal modeling, Laser safety, Safety, Laser therapeutics, Injuries, High power lasers, In vivo imaging, Tissues
The objective of this study was to map parameter boundaries for thermally safe laser and irrigation settings. The experimental system consisted of models simulating ureter, renal calyx, and renal pelvis placed in a water bath maintained at 37°C. Thermal dose for each trial was calculated based on Dewey and Sapareto t43 methodology. A parameter safety boundary was established by plotting the maximal safe power level for each irrigation rate. The boundary was found to be linear for each scenario with the renal pelvis able to tolerate the highest laser power and renal calyx the least power without injury.
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.
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