Our preliminary study investigates an automated, vibrating fiber optic tip for dusting of kidney stones during thulium fiber laser (TFL) lithotripsy. A (0.75-mm diameter and 5-mm length) magnetic bead was attached to the fiber jacket, centered 2 cm from distal fiber tip. A solenoid was placed parallel to the fiber with a 0.5-mm gap between solenoid and magnetic bead on fiber. The solenoid 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. The ablation crater characteristics (surface area, volume, depth, and major/minor axis) of uric acid stones were measured using optical coherence tomography, after delivery of 1500 TFL pulses at 1908 nm, 33 mJ, 500 μs, and up to 300 Hz, through 50-, 100-, and 150-μm-core fibers. The resonant frequency was dependent on fiber diameter and rigidity, with a cutoff pivot point for optimum vibration amplitude at 4 cm. Maximum fiber displacement is about 1 mm in water and 4 mm in air. For 50-, 100-, and 150-μm-core fibers, ablated surface area averaged 1.7, 1.7, and 2.8 times greater with vibrating fiber than fixed fiber, respectively. For these fibers, ablation volume averaged 1.1, 1.5, and 1.1 times greater with vibrating fiber than fixed fiber, given a fixed energy per pulse, respectively. Our preliminary study demonstrates the functionality of an automated, vibrating fiber system for stone “dusting,” with significantly larger surface area but similar ablation volumes as a fixed fiber. Future studies will focus on optimization of fiber parameters (especially displacement) and miniaturization of system components to facilitate integration into ureteroscopes.
Laser lithotripsy depends in part on fragmenting stones to sufficiently small size for spontaneous passage or extracting all large residual stone fragments to provide high stone free success rates, so a second repeat procedure is unnecessary. This preliminary study describes initial development of an optical system and software capable of tracking and labeling kidney stones. Machine learning and image processing techniques were implemented to track, label, and size, on a relative scale, stone fragments. Thresholds were placed on minimum stone fragment size (based on pixel sizes). For system validation, a series of still images from the laboratory setup and previously recorded clinical lithotripsy procedures were analyzed. A laboratory test was also conducted with homogenous background and video to determine number of true positives, false positives, and false negatives. In still images, 8/8 (100%) stones in the laboratory setup and 4/4 (100%) stones in clinical lithotripsy videos were correctly identified. A separate laboratory study correctly identified all five stones in each frame across a total of 110 video frames (550/550) (100%) with a total of 49/550 false positives (9%) and 0/550 (0%) false negatives, at a maximum frame rate of 50 Hz. This preliminary stone tracking study correctly identified stone fragments in laboratory frames for still and motion video and during still images from clinical lithotripsy procedures and experimental settings. Further development of software and optical tracking system is planned.
Dual pulse mode has recently been integrated into Holmium:YAG laser systems to reduce stone retropulsion. This study explores similar pulse shaping approaches with Thulium fiber laser (TFL). A TFL at 1940 nm wavelength produced three temporal pulse profiles: (1) square pulse, (2) dual pulse, with low energy initial pulse followed by higher energy second pulse, and (3) ascending staircase pulse shape. Energies of 0.1 - 2.0 J, pulse rates of 5 - 200 Hz, average power of 10 and 20 W, and laser irradiation time of 5 s were used (n=5 per group). Stone phantoms (6-mmdiameter, 200-mg-mass) were placed on a horizontal, v-shaped trough, submerged in water, and then irradiated with TFL using a 200-μm-core optical fiber. Dual pulse stone displacements using pulse energies of 0.1, 0.2, 0.5, 1.0, and 2.0 J, measured 65%, 75%, 100%, 100%, and 110% of square pulse displacement at 10 W, and 65%, 60%, 60%, 90%, and 105% of square pulse displacement at 20 W. Staircase pulse stone displacements measured ~ 85% of square pulse stone displacement at 1.0 and 2.0 J for both 10 and 20 W. At lower energies (0.1 - 0.5 J), staircase profile produced a suction effect, resulting in the stone being pulled back to the fiber. Dual pulse mode only reduced stone retropulsion at lower energy settings, possibly due to excessive energy in initial pulse at higher settings. Low power (10 W) square, dual, and staircase pulse shapes ablated uric acid stones at rates of 1.7 ± 0.4, 1.9 ± 0.5, and 1.7 ± 0.5 mg/s, respectively. High power (20 W) square, dual, and staircase pulse shapes ablated stones at a rate of 2.6 ± 0.6, 3.0 ± 0.4, and 2.7 ± 0.7 mg/s, respectively. Future studies will utilize optical imaging of vapor bubble formation as a function of temporal pulse profile to optimize laser parameters for reducing stone retropulsion and enhancing TFL stone ablation rates.
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.