Numerical analysis for laser endoluminal treatment of stress urinary incontinence

Stress urinary incontinence (SUI) is a sudden urine-leaking condition during physical activities due to weakened pelvic floor muscles or sphincter malfunction. Recently, a balloon-integrated diffusing applicator (DA) with 980 nm laser wavelength at 20W showed promising results for SUI treatment in light of urethral sphincter tightening and regeneration [1]. However, a large divergence beam emitted from DA can surpass a short treatment length of the sphincter (~16 mm) causing injury to the surrounding healthy tissue. A radial fiber (RF) emits a narrow beam width circumferentially around the fiber tip [2]. The current study aims to numerically compare the laser emission profiles from various angle fiber tips (β) in the balloon-integrated RF for SUI treatment. ZEMAX software was utilized for the numerical simulation. 0.22 NA 400-μm core diameter fibers with three β values were chosen for the simulation (i.e., β = 74°, 58°, and 42°) [2]. 980 nm laser at 20W was delivered by RFs. No significant difference was found among the output beam widths from RFs at the balloon surface (approximately 2 mm). The divergence angles (α) of the output beam from the tips decreased (α = 88°, 59°, and 33°) as β values decreased (β = 74°, 58°, and 42°), respectively. The starting position of the laser beam relative to the fiber tip (d) at the balloon surface was affected by the α values (i.e., d = 0, 1, and 2 mm for α = 88°, 59°, and 33°, respectively). According to the longitudinal emission, the normalized intensity peak for β = 74° was higher than those for β = 58° and 42° (i.e., 10% and 17%, respectively). Therefore, RF with β = 74° can control the position of the laser output beam more accurately and provide more effective energy than the other β values for the laser endoluminal treatment of SUI. Further studies will investigate the performance of RF with β = 74° in both ex vivo and in vivo models in terms of temperature distribution and wound healing.