Hollow steel tips for reducing distal fiber burn-back during thulium fiber laser lithotripsy

Thomas C Hutchens,Pierce B Irby,Nathaniel M Fried,Richard L Blackmon

doi:10.1117/1.jbo.18.7.078001

Thomas C Hutchens, Pierce B Irby + Show 2 more

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https://doi.org/10.1117/1.jbo.18.7.078001

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Abstract

The use of thulium fiber laser (TFL) as a potential alternative laser lithotripter to the clinical holmium:YAG laser is being studied. The TFL's Gaussian spatial beam profile provides efficient coupling of higher laser power into smaller core fibers without proximal fiber tip degradation. Smaller fiber diameters are more desirable, because they free up space in the single working channel of the ureteroscope for increased saline irrigation rates and allow maximum ureteroscope deflection. However, distal fiber tip degradation and "burn-back" increase as fiber diameter decreases due to both excessive temperatures and mechanical stress experienced during stone ablation. To eliminate fiber tip burn-back, the distal tip of a 150-μm core silica fiber was glued inside 1-cm-long steel tubing with fiber tip recessed 100, 250, 500, 1000, or 2000 μm inside the steel tubing to create the hollow-tip fiber. TFL pulse energy of 34 mJ with 500-μs pulse duration and 150-Hz pulse rate was delivered through the hollow-tip fibers in contact with human calcium oxalate monohydrate urinary stones during ex vivo studies. Significant fiber tip burn-back and degradation was observed for bare 150-μm core-diameter fibers. However, hollow steel tip fibers experienced minimal fiber burn-back without compromising stone ablation rates. A simple, robust, compact, and inexpensive hollow fiber tip design was characterized for minimizing distal fiber burn-back during the TFL lithotripsy. Although an increase in stone retropulsion was observed, potential integration of the hollow fiber tip into a stone basket may provide rapid stone vaporization, while minimizing retropulsion.

Highlights

1.1 Current Laser Lithotripsy TechniquesApproximately 10% of the U.S population will suffer from urinary stone disease during their lifetime.[1]
To treat severe urinary stone disease, an endoscopic approach is commonly used with an optical fiber, coupled to a holmium:YAG laser, inserted into the working channel of an ureteroscope, which stretches from the urethra to the kidney or to the stone’s location
We explore placing a hollow steel tube over a recessed and fixed fiber tip to precisely control the fiber-to-stone distance for thulium fiber laser (TFL) lithotripsy

Summary

Introduction

10% of the U.S population will suffer from urinary stone disease during their lifetime.[1] To treat severe urinary stone disease, an endoscopic approach is commonly used with an optical fiber, coupled to a holmium:YAG (holmium) laser, inserted into the working channel of an ureteroscope, which stretches from the urethra to the kidney or to the stone’s location. One limitation of the holmium laser is its relatively large and multimode beam waist, which limits optimal power coupling into only optical fibers with core diameters greater than ∼200 μm.[2,3] Due to space limitations in the flexible ureteroscope’s ∼1.2-mm inner diameter working channel, smaller fibers are preferred for improved irrigation and higher flexibility in the upper urinary tract.[4,5,6] coupling the holmium laser’s multimode beam with smaller fibers (∼100-μm core diameter) risks overfilling of the input fiber core, launching into the cladding, and damaging the fiber. Damage in the form of fiber tip degradation and “burn-

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