Laser Fiber Displacement Velocity during Tm-Fiber and Ho:YAG Laser Lithotripsy: Introducing the Concept of Optimal Displacement Velocity

Background: Endocorporeal laser lithotripsy (EL) during flexible ureteroscopy (URS-f) often uses “dusting” settings with “painting” technique. The displacement velocity of the laser fiber (LF) at the stone surface remains unknown and could improve EL’s ablation rates. This in vitro study aimed to define the optimal displacement velocity (ODV) for both holmium:yttrium-aluminium-garnet (Ho:YAG) and thulium fiber laser (Tm-Fiber). Methods: A 50W-TFL (IRE Polus®, Russia) and a 30W-MH1-Ho:YAG laser (Rocamed®), were used with 272µm-Core-Diameter LF (Sureflex, Boston Scientific©), comparing three TFL modes, “fine dusting” (FD:0.05–0.15 J/100–600 Hz); “dusting” (D:0.5 J/30–60 Hz); “fragmentation” (Fr:1 J/15–30 Hz) and two Ho:YAG modes (D:0.5 J/20 Hz, Fr:1 J/15 Hz). An experimental setup consisting of immerged cubes of calcium oxalate monohydrate (COM) stone phantoms (Begostone Plus, Begoã) was used with a 2 seconds’ laser operation time. LF were in contact with the stones, static or with a displacement of 5, 10 or 20 mm. Experiments were repeated four times. Stones were dried and µ-scanned. Ablation volumes (mm3) were measured by 3D-segmentation. Results: ODV was higher in dusting compared to fragmentation mode during Ho:YAG lithotripsy (10 mm/sec vs. 5 mm/sec, respectively). With Tm-Fiber, dusting and fragmentation OVDs were similar (5 mm/sec). Tm-Fiber ODV was lower than Ho:YAGs in dusting settings (5 mm/s vs. 10 mm/sec, respectively). Without LF displacement, ablation volumes were at least two-fold higher with Tm-Fiber compared to Ho:YAG. Despite the LF-DV, we report a 1.5 to 5-fold higher ablation volume with Tm-Fiber compared to Ho:YAG. Conclusions: In dusting mode, the ODVTm-Fiber is lower compared to ODVHo:YAG, translating to a potential easier Tm-Fiber utilization for “painting” dusting technique. The ODV determinants remain unknown. Dynamic ablation volumes are higher to static ones, regardless of the laser source, settings or LF displacement velocity.

Experimental ex-vivo performance study comparing a novel, pulsed thulium solid-state laser, chopped thulium fibre laser, low and high-power holmium:YAG laser for endoscopic enucleation of the prostate

Purpose The aim of this study was to compare the enucleation performances of four different types of laser devices in an ex-vivo experiment: a novel, pulsed Tm:YAG solid-state laser evaluation model (p-Tm:YAG), chopped thulium fibre laser (TFL), low-power Ho:YAG laser (LP-Ho:YAG), and a high-power Ho:YAG laser (HP-Ho:YAG). Methods Our primary aim was to endoscopically separate the fascial layers of a porcine belly using laser fibres within a time period of 60 s. The size of a “tissue pocket” was assessed numerically. The enucleation characteristics reflecting the surgeon’s experience were evaluated via the NASA Task Load Index (TLX) questionnaire and a questionnaire based on Likert scale. Results HP-Ho:YAG achieved with the available laser settings the largest overall “tissue pocket” (31.5 cm2) followed by p-Tm:YAG (15 cm2), TFL (12 cm2), and LP-Ho:YAG (6 cm2). The coagulation performances of p-Tm:YAG and TFL were rated the best. In the performance evaluation by the Likert questionnaire, HP-Ho:YAG (average score of 4.06) was rated highest, followed by p-Tm:YAG (3.94), TFL (3.38), and LP-Ho:YAG (3.25). The evaluation of the NASA-TLX performance questionnaire revealed average scores for HP-Ho:YAG, LP-Ho:YAG, TFL and p-Tm:YAG of 4.38, 4.09, 3.92 and 3.90, respectively. Conclusion We are the first to compare different laser devices and settings in an ex-vivo study. We found that the surgeons were most satisfied with the HP-Ho:YAG laser device, followed by the p-Tm:YAG. These findings could be highly relevant for future research and for the practical utilisation of laser systems in endourology.

Laser epilation of luminal hair following skin graft urethroplasty for hypospadias: the hair snare

A 66-year-old man, who underwent urethral reconstruction using skin grafts for hypospadias five decades earlier as a 13-year-old child, presented with burning micturition and recurrent UTI. A retrograde urethrogram along with micturating cystourethrogram revealed a bulbar urethral stricture and broad neck distal penile urethral diverticulum. On a cystourethroscopic examination, a urethral diverticulum was seen just proximal to the hypospadiac external urethral meatus with 12–15 hair follicles inside the diverticulum and a 1 cm long mid-bulbar stricture. Visual internal urethrotomy for the bulbar stricture, a diverticular neck incision, laser epilation and hair follicle photocoagulation was performed using a 30 W Ho:YAG laser. The depilated hair tufts were extracted. The process was repeated again in 6 months due to recurrent symptoms. A patent urethra with a wide open diverticulum without any residual hair follicles was confirmed. No perioperative complications noted and the patient is doing well on 1 month of follow-up.

Comparison of Holmium:YAG and Thulium Fiber Lasers on the Risk of Laser Fiber Fracture

Objectives: To compare the risk of laser fiber fracture between Ho:YAG laser and Thulium Fiber Laser (TFL) with different laser fiber diameters, laser settings, and fiber bending radii. METHODS: Lengths of 200, 272, and 365 μm single use fibers were used with a 30 W Ho:YAG laser and a 50 W Super Pulsed TFL. Laser fibers of 150 µm length were also tested with the TFL only. Five different increasingly smaller bend radii were tested: 1, 0.9, 0.75, 0.6, and 0.45 cm. A total of 13 different laser settings were tested for the Ho:YAG laser: six fragmentation settings with a short pulse duration, and seven dusting settings with a long pulse duration. A total of 33 different laser settings were tested for the TFL. Three laser settings were common two both lasers: 0.5 J × 12 Hz, 0.8 J × 8 Hz, 2 J × 3 Hz. The laser was activated for 5 min or until fiber fracture. Each measurement was performed ten times. Results: While fiber failures occurred with all fiber diameters with Ho:YAG laser, none were reported with TFL. Identified risk factors of fiber fracture with the Ho:YAG laser were short pulse and high energy for the 365 µm fibers (p = 0.041), but not for the 200 and 272 µm fibers (p = 1 and p = 0.43, respectively). High frequency was not a risk factor of fiber fracture. Fiber diameter also seemed to be a risk factor of fracture. The 200 µm fibers broke more frequently than the 272 and 365 µm ones (p = 0.039). There was a trend for a higher number of fractures with the 365 µm fibers compared to the 272 µm ones, these occurring at a larger bend radius, but this difference was not significant. Conclusion: TFL appears to be a safer laser regarding the risk of fiber fracture than Ho:YAG when used with fibers in a deflected position.