Real-Time Laser Fiber-to-Stone Distance Proximity Indicator Improves Ureteroscopic Stone Ablation: In Vitro Evaluation.

OBJECTIVE: To assess improvement in laser stone ablation during timed in vitro lithotripsy trials when a prototype real-time fiber-to-stone distance proximity indicator (DPI) was visible vs. covered. METHODS: Twelve experiments were conducted with different laser settings, pulse modes, and proximity settings. Within each experiment 8-24 successive trials were performed with the DPI alternately covered and visible. For each trial, a hemispherical brushite crystalline aggregate model stone was lasered for 2 minutes in a 10 mm diameter test tube. Deionized water irrigation was delivered at 40 ml/min. The mass of ablated stone and applied laser energy were recorded. RESULTS: Total mass of stone ablated (fragments < 4 mm) was greater with the DPI visible vs. covered in 12/12 experiments (10/12 statistically significant). Additionally, greater mass of stone fragments < 0.5 mm was produced, greater laser energy was applied, and higher laser ablation efficiency (mg/J) was achieved when the DPI was visible. CONCLUSIONS: Laser stone ablation was enhanced when the DPI was visible vs. covered during in vitro ureteroscopic lithotripsy timed trials. A greater percentage of time was spent lasing (less targeting) and on average each pulse did more work on the stone. These findings are consistent with better control of the fiber tip in proximity to the stone surface when the DPI is visible. Use of the DPI is expected to decrease lithotripsy time and laser energy requirements for clinical ureteroscopic stone treatment.