In vitro investigation of wavelength-dependent tissue ablation: Laser prostatectomy between 532 nm and 2.01 μm

Abstract

Background and Objective: Over a decade, laser prostatectomy has been performed to effectively treat benign prostate hyperplasia (BPH) with low post-operative complications. In this study, two laser wavelengths conventionally used for BPH treatment were compared to characterize the outcomes of in vitro tissue ablation. Study Design/Materials and Methods: Two lasers with wavelengths including 532 nm (Q-switched) and 2.01 μm (continuous wave) were employed to ablate porcine kidney tissue in vitro. Ablation performance was evaluated by varying applied power, treatment speed, and fiber working distance. Optical transmission was measured as a function of working distance and compared with the corresponding ablation volume. Coagulation depth was quantified from gross tissue examination, and histology analysis confirmed coagulation features for both wavelengths. Results: Five hundred thirty-two nanometers yielded up to 30% (P<0.005) higher ablation efficiency than 2.01 μm. Regardless of wavelength, ablation rate increased with power and was maximized at treatment speed of 4 mm/seconds. A comparable ablation depth was found between the two wavelengths, but 532 nm generated relatively wider (up to 30%; P<0.005) craters. Both optical transmission and ablation volume revealed that energy loss by strong water absorption compromised ablation efficiency generated by 2.01 μm. Gross tissue and histology examination demonstrated that 532 nm created a thin coagulation zone whereas 2.01 μm induced ∼20% (P<0.005) more thermal injury in association with carbonized tissue surface. Conclusions: Due to more light scattering and effective thermal confinement, 532 nm induced more efficient tissue ablation with a smaller coagulative necrotic zone. Comparable ablation depth may enable a potential tissue incision technique with 532 nm, possibly allowing both tissue removal and biopsy intraoperatively. © 2010 Wiley-Liss, Inc.