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Miniature ureteroscopes (< 2-mm-outer-diameter) may potentially enable less expensive, office-based, laser lithotripsy in the lower urinary tract with patients only requiring local anesthesia. This preliminary study describes a flexible miniature ureteroscope design combining illumination and irrigation channels using a saline liquid light guide (LLG). Teflon AF 2400 is a novel, flexible, biocompatible material with lower refractive index (n = 1.29) than saline (n = 1.33), thus enabling total internal reflection (TIR) of light through an LLG. Irrigation rates were measured through an annulus-shaped LLG, sandwiched between concentric inner (OD = 0.74mm / ID = 0.61mm) and outer (OD = 1.60mm / ID = 1.02mm) Teflon AF 2400 tubing. A flexible plastic fiber optic imaging bundle (7.4k pixels / OD = 0.5mm / NA = 0.5) was placed within the inner Teflon tubing core. Two optical fibers of 0.100-mm / 0.140-mm / 0.170-mm (core/cladding/buffer) were placed between the Teflon layers, as spacers, steering cables, and for energy delivery. Computational fluid mechanics models (ANSYS) and optical simulation software (Zemax) were used to predict irrigation rates and illumination, respectively, over a wide range of Teflon dimensions. Computational models calculated gravitational flow rates up to 12.8 ml/min for a larger annulus with concentric inner and outer Teflon AF tubing dimensions of 0.74-mm-OD and 1.80-mm-ID, with two fiber spacers decreasing annular flow by an additional 10%. Optical simulations predicted optimal illumination out of the annulus-shaped saline light guide of 72-77% of initial input. The LLG flexible ureteroscope design utilized concentric Teflon AF tubing for TIR of light through an annulus-shaped irrigation channel, minimizing cross-sectional area, for a miniature ureteroscope (< 2-mm-OD). With further development, miniature ureteroscopes may enable an office-based approach to laser lithotripsy.
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