Evaluations of laser ablation for treatment of multifocal urethral strictures

Urethral stricture (US) is a prevalent urological condition where the urethra becomes narrowed due to scarring, injury, or inflammation. The US causes weak urine flow and painful urination. Recently, laser ablation (LA) becomes a promising method to control ablation depths and areas for urology treatment. Laser is delivered by a diffusing fiber or a radial fiber to yield a circumferential ablation of fibrotic tissue. However, due to the heterogeneous urethral strictures, the incomplete LA and the early recurrence can be occurred. This study is to evaluate the efficacy of the lateral near-infrared laser of side-firing fiber for the multifocal ablation of urethral strictures. 1908nm laser wavelength was selected due to the high absorption of urinary tissue. The 600-μm core diameter fibers with 38° mechanical polishing angle were applied to fabricate side-firing fibers (SFFs) (i.e., 38° angled-ball and -flat tips). ZEMAX software was utilized for the SFF simulations. Ex vivo porcine liver experiments with various diameters of glass tubes (d=6, 12, and 18mm) were conducted to compare fabricated SFFs. A 5-mm customized basket-integrated side-firing fiber (BISF) was used to validate in ex vivo rabbit esophagus experiments. The BISF can undergo both rotational and translational motions. The applications of 1908nm at 4 W – 3 s and 1 W – 3 s were used for ex vivo porcine liver and ex vivo rabbit esophagus experiments, respectively (N=10). A significant difference in beam shapes was observed in the fabricated SFFs at all d values (i.e., 38° angled-ball tip: elliptical shape, and 38° angled-flat tip: kite shape). The elliptical shape offers more predictable ablation area and prevents thermal damage to adjacent tissue, while the kite shape causes sharp points. According to ex vivo rabbit esophagus experiments, the 5-mm BISF with 38° angled-ball tip generated an ablation depth=0.38±0.06mm comparable to 0.4mm in [3] for minimizing the peripheral damage and bleeding. Therefore, the BISF with 38° angled-ball tip with 1908nm can control the laser beam position and ablation depth on treatment of the heterogeneous USs. Further vivo animal studies with various laser conditions will be performed to validate the performance and safety of the proposed BISF.