MP35-10 MECHANISMS OF FIBER-TIP DEGRADATION DURING LASER LITHOTRIPSY

Abstract

You have accessJournal of UrologyCME1 Apr 2023MP35-10 MECHANISMS OF FIBER-TIP DEGRADATION DURING LASER LITHOTRIPSY Yuri Pishchalnikov, William Behnke-Parks, and Marshall Stoller Yuri PishchalnikovYuri Pishchalnikov More articles by this author , William Behnke-ParksWilliam Behnke-Parks More articles by this author , and Marshall StollerMarshall Stoller More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003269.10AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Ureteroscopic lithotripsy breaks urinary stones using laser pulses delivered to the stone via optical fibers. Degradation of fibers reduces the efficacy of lithotripsy and varies with fiber diameter, stone composition, laser pulse energy and duration. The goal of this work was to reveal the physical mechanisms of fiber-tip damage (burnback) in water and air. METHODS: The dynamics of fiber-tip damage was studied using a high-speed camera Shimadzu HPV-X2 at a frame rate up to two million frames per second. The camera was mounted to a microscope focused on the 242-µm glass-core-diameter fiber positioned in direct contact with a target—typically, a glass slide coated with a 25±5 µm layer of hydroxyapatite (Himed, NY). Selected experiments were conducted with BegoStones and whole surgically retrieved urinary stones. Damaged fibers were cleaved to start each series of 20 pulses with flat fiber tips. Laser pulses were produced using a Lumenis VersaPulse holmium:YAG laser. Temporal profiles of infrared laser pulses and flashes of visible light were resolved using photodetectors. Cross-sectional profiles of laser-beam energy were assessed using Zap-It paper. Microscope images were used to measure the burnback length of the fiber. RESULTS: Burnback of optical fibers was associated with flashes of light (sparks) observed both in water and in air. Sparks in air could crack and fragment the fiber during single laser pulse. Twenty pulses in air produced the burnback length of 0.37 mm at 1.0 J (95% CI: 0.11–0.64 mm) and 0.14 mm at 0.6 J (95% CI: 0.10–0.18 mm), smaller than that at 1.0 J (p=0.010). In water, the fibers were damaged by sparks during the laser pulse and after the pulse during the collapse of laser-induced cavitation bubbles. Contribution of cavitation varied from insignificant to most dramatic, breaking a 1.1-mm length of the fiber in a single laser pulse. Cavitation without sparks showed no burnback with only minor damage of cladding (500 pulses, 1.0 J). Sparks were associated with an increased absorption of laser energy and were observed at laser energies typically >0.5 J and only with certain target materials near the fiber tip. Cross-sections of laser beams were larger with fibers damaged in air than that in water (p=0.007) and both were larger than that with undamaged fibers (p<0.005). CONCLUSIONS: These results suggest that the burnback degradation of optical fibers is associated mainly with laser-induced heating, ionization, and optical breakdown of target material. A better understanding of the mechanisms of fiber-tip damage will aid in development of future improvements to minimize degradation of optical fibers. Source of Funding: Research reported in this publication was supported by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health under Award Number R43DK129104. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e473 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Yuri Pishchalnikov More articles by this author William Behnke-Parks More articles by this author Marshall Stoller More articles by this author Expand All Advertisement PDF downloadLoading ...