Optical fibers have frequently been used for photothermal laser therapy due to its efficiency to deliver laser energy directly to tissue. The aim of the current study was to develop a diffusing optical fiber to achieve radially uniform light irradiation for endoscopically treating urethral stricture. The optical diffuser was fabricated by micro-machining helical patterns on the fiber surface using CO2 laser light at 5 W. Visible light emission (632 nm) and spatial emissions (including polar, azimuthal, and longitudinal emissions) of the fiber tip were evaluated to validate the performance of the fabricated diffuser. Prior to tissue tests, numerical simulation on heat distribution was developed to estimate the degree of tissue coagulation depth during interstitial coagulation. Due to a high absorption coefficient by tissue water, 1470 nm laser was used for photothermal therapy treatment of urethral stricture to obtain a more precise depth profile. For in vitro tissue tests, porcine liver tissue was irradiated with three different power levels (3, 6, and 9 W) at various irradiation times. Porcine urethral tissue was also tested with the diffuser for 10 sec at 6 W to validate the feasibility of circumferential photothermal treatment. The treated tissue was stained with hematoxylin and eosin (H and E) and then imaged with an optical transmission microscope. The spatial emission characteristics of the diffusing optical fiber presented an almost uniform power distribution along the diffuser tip (less than 10% deviation) and around its circumference (less than 5% deviation). The peak temperature in simulation model at the tissue interface between the glass-cap and the tissue was 373 K that was higher than that at the distal end. The tissue tests showed that higher power levels resulted in lower coagulation thresholds (e.g., 1 sec at 9 W vs 8 sec at 3 W). Furthermore, the coagulation depth was approximately 20% thinner than the simulation results (p<0.001). The extent of coagulation thickness in urethral tissue was measured to be 1.3±0.2 mm, which was slightly thicker (18%) than the liver testing (1.1±0.1 mm) under the same conditions (p < 0.001). The proposed optical diffuser may be a feasible tool to treat the urethral stricture in a uniform manner.
Laser light has been widely used as a surgical tool to treat benign prostate hyperplasia with high laser power.
The purpose of this study was to validate the feasibility of photoactive dye injection to enhance light absorption
and eventually to facilitate tissue ablation with low laser power. The experiment was implemented on chicken
breast due to minimal optical absorption Amaranth (AR), black dye (BD), hemoglobin powder (HP), and
endoscopic marker (EM), were selected and tested in vitro with a customized 532-nm laser system with radiant
exposure ranging from 0.9 to 3.9 J/cm<sup>2</sup>. Light absorbance and ablation threshold were measured with UV-VIS
spectrometer and Probit analysis, respectively, and compared to feature the function of the injected dyes.
Ablation performance with dye-injection was evaluated in light of radiant exposure, dye concentration, and
number of injection. Higher light absorption by injected dyes led to lower ablation threshold as well as more
efficient tissue removal in the order of AR, BD, HP, and EM. Regardless of the injected dyes, ablation
efficiency principally increased with input parameter. Among the dyes, AR created the highest ablation rate of
44.2±0.2 μm/pulse due to higher absorbance and lower ablation threshold. Preliminary tests on canine prostate
with a hydraulic injection system demonstrated that 80 W with dye injection yielded comparable ablation
efficiency to 120 W with no injection, indicating 33 % reduced laser power with almost equivalent performance.
In-depth comprehension on photoactive dye-enhanced tissue ablation can help accomplish efficient and safe
laser treatment for BPH with low power application.