Thulium fiber laser (TFL) lithotripsy has recently been introduced for clinical use. Previous TFL laboratory studies demonstrated high-power delivery through small (50- to 150-μm core) optical fibers. This preliminary study simulates forces on fibers during insertion into a flexible ureteroscope and determines mechanical feasibility of small fibers for a clinical setting. Simulations were conducted with commercially available fiber (core/cladding) sizes of 50/70, 72/108, 100/140, 150/165, 150/180, and 200 / 240 μm. Solidworks software integrating Euler’s buckling equation was used to calculate fiber buckling thresholds as a function of typical manual forces (0.15 to 2.0 N) applied near the proximal end of a ureteroscope. Forces on fibers were modeled assuming support from saline flow and resistance by the working channel wall. Simulation results were categorized based on force values previously reported in the literature, with smaller forces (<0.4 to 0.8 N) buckling fibers, mid-range forces (0.8 to 1.6 N) optimal for fiber manipulation, and higher forces (>1.6 to 2.0 N) at risk of damaging the ureteroscope working channel. Fiber sizes were simulated with two different types of holdings on each end to find a range of possible values that most closely simulate clinical behavior. Simulation results were confirmed using a force meter and a benchtop experimental setup. Numerical simulations predicted that optical fibers for TFL lithotripsy should be equal to or larger than 150 / 190 μm (core/cladding), for effective manual manipulation within flexible ureteroscopes.
Laser lithotripsy is performed in a hospital operating room at high cost. Many lower ureter stones could potentially be treated in a less expensive, office-based procedure, if smaller ureteroscopes were available. Thulium fiber laser lithotripsy enables use of smaller (50-150-µm-core) optical fibers than Holmium:YAG laser lithotripsy, saving cross-sectional space within the working channel for exploitation in developing smaller ureteroscopes. A prototype, miniature, flexible, 40k digital ureteroscope tip was tested. Calibration, lighting, imaging, saline irrigation rate studies, and saline temperature safety studies were performed using a porcine ureter model, ex vivo.
Thulium fiber laser (TFL) lithotripsy has recently been introduced in the clinic. Previous TFL laboratory studies demonstrated successful high-power delivery through ultra-small (50-150-µm-core) optical fibers. This preliminary study simulates the forces on fibers during insertion into an ureteroscope and determines the mechanical feasibility of ultra-small fibers in a clinical setting. Simulations were conducted for commercially avalaible silica fiber sizes (core/cladding): 50/70, 72/108, 100/140, 150/165, 150/180, and 200/240 μm. Solidworks software intregrating Euler’s buckling equation was used to calculate fiber buckling thresholds as a function of typical manual forces (0.3- 2.0 N) applied near the proximal end of a standard ureteroscope. Forces on fibers being inserted were modeled, assuming support from saline flow and resistance by the working channel wall. Simulation results were categorized based on force values previously reported in the literature, with smaller forces (< 0.4-0.8 N) buckling fibers, midrange forces (0.8-1.6 N) optimal for fiber manipulation, and higher forces (>1.6-2.0 N) at risk of damaging the working channel. Fiber sizes were simulated with two different types of holdings on each end to find a range of possible values that most closely simulate clinical behavior. The smallest usable standard flat tip fiber was found to be 150/190-μm (core/cladding), assuming a cladding thickness of ten times the laser wavelength of 1.94 μm (or extra 40 μm OD) to prevent leakage of evanescent waves through the core/cladding interface. The smallest usable ball tip fiber was found to be 110/150 μm. Numerical simulations predicted that optical fibers for TFL lithotripsy should be larger than 110/150 μm to provide effective manual manipulation within flexible ureteroscopes.
Significance: Water is a primary absorber of infrared (IR) laser energy, and urinary stones are immersed in fluid in the urinary tract and irrigated with saline during IR laser lithotripsy. Laser-induced vapor bubbles, formed during lithotripsy, contribute to the stone ablation mechanism and stone retropulsion effects.
Aim: Introduction of a surfactant may enable manipulation of vapor bubble dimensions and duration, potentially for more efficient laser lithotripsy.
Approach: A surfactant with concentrations of 0%, 5%, and 10% was tested. A single pulse from a thulium fiber laser with wavelength of 1940 nm was delivered to the surfactant through a 200-μm-core optical fiber, using a wide range of laser parameters, including energies of 0.05 to 0.5 J and pulse durations of 250 to 2500 μs.
Results: Bubble length, width, and duration with surfactant increased on average by 29%, 17%, and 120%, compared with water only.
Conclusions: Our study demonstrated successful manipulation of laser-induced vapor bubble dimensions and duration using a biocompatible and commercially available surfactant. With further study, use of a surfactant may potentially improve the “popcorn” technique of laser lithotripsy within the confined space of the kidney, enable non-contact laser lithotripsy at longer working distances, and provide more efficient laser lithotripsy.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.