Thulium fiber laser stone dusting using an automated, vibrating optical fiber

This preliminary study investigates an automated, vibrating fiber tip for dusting of kidney stones during Thulium fiber laser (TFL) lithotripsy. A (0.75-mm-diameter, 5-mm-length) magnetic bead was attached to the fiber jacket 2 cm from distal fiber tip, and a solenoid made of ferrite material was used to create a magnetic force on the bead, inducing fiber vibration. Calibration tests for fiber motion in both air and water were performed. Uric acid (UA) stones were ablated using 50-, 100-, and 150-μm-core fibers, and ablation crater characteristics (surface area, volume, depth, and major/minor axis) were measured using optical coherence tomography after delivery of 1500 TFL pulses at 1908 nm, 33 mJ, 500 μs, and 300 Hz. The resonant frequency was dependent on fiber diameter and rigidity, with a cutoff pivot point for optimum motion of 3 to 4 cm. Maximum fiber displacement was about 1 mm in water and 3.5 mm in air. For all fiber diameters tested, ablated surface area was two times greater with vibrating fiber. Similar ablation volume was removed with vibrating and fixed fibers, consistent with previous literature reporting similar ablation rates independent of fiber diameter, given a fixed energy per pulse. This preliminary study demonstrated functionality of an automated, vibrating fiber system for stone “dusting”, with two times larger surface area but equivalent ablation volumes as a fixed fiber. Continued development of this method is warranted, with emphasis on optimization of fiber parameters (especially displacement) and miniaturization of components for future integration into ureteroscopes.