Response to Wollin re: "Strike Rate: Analysis of Laser Fiber to Stone Distance During Different Modes of Laser Lithotripsy"

Introduction: Different techniques of laser lithotripsy (fragmentation, dusting, and popcorning) are commonly used during ureteroscopy. The efficiency of a single laser pulse is dependent on minimizing laser fiber-stone distance, yet it has not been reported how often the laser fiber is in contact with the stone during laser lithotripsy. In this study, we sought to measure laser fiber to stone distance using light reflectance for each technique of laser lithotripsy. Methods: Continuous light from a 660 nm (red) light-emitting diode (LED) was coupled into a 200 μm fiber using a fiber X-coupler. The LED fiber was positioned immediately next to a 242 μm holmium fiber, and both were passed through the working channel of an ureteroscope. One fiber was used to deliver laser energy to the stone, and the other fiber was used to measure distance based on light reflected from the stone back into the fiber. For fragmentation and dusting experiments, a 5 mm BegoStone was placed into a 20 mm three-dimensional printed caliceal model. For popcorn experiments, 10 BegoStones (3 × 3 × 1.5 mm) were placed in an 11 mm caliceal model and the laser fiber positioned 2 mm away from the stone surface. Data were analyzed using a MATLAB software to report fiber to stone distance at each laser pulse. Results: With fragmentation, 52% of laser pulses were delivered when the fiber was within 0.5 mm of the stone compared to 23% and 4% for dusting and popcorning, respectively. Laser pulses delivered when fiber to stone distance was >1 mm (least effective) accounted for 34%, 48%, and >80% of total pulses during fragmentation, dusting, and popcorning, respectively. Conclusion: Current methods of laser lithotripsy that rely on fixed firing rates are inefficient, especially for the popcorn technique. These data highlight areas for improvement by appropriately gating pulse delivery to maximize lithotripsy effect for each pulse fired. © Copyright 2021, Mary Ann Liebert, Inc., publishers 2021.