Temperature-Controlled Optical Stimulation of the Rat Prostate Cavernous Nerves

Optical nerve stimulation (ONS) may be useful for intra-operative identification and preservation of the prostate cavernous nerves (CN's), responsible for erectile function, during radical prostatectomy. ONS relies on a photothermal mechanism of laser-tissue interaction in which elevating nerve temperature to within a narrow range (similar to 42 - 47 degrees C) is critical to successful nerve activation without thermal damage. This preliminary study explores a prototype temperature-controlled laser system for maintaining a constant nerve temperature during ONS of the rat prostate CN's. A 150-mW, 1455-nm diode laser was operated in continuous-wave mode during stimulation of the rat CN's for 30 s through a fiber optic probe with 1-mm-diameter spot. The all-single-mode ONS system was controlled by a computer which opened and closed an in-line mechanical shutter in response to an IR sensor, with a temperature set-point of 45 degrees C. Thermal camera temperature measurements and ONS without temperature control were performed for comparison. Strong correlation was observed between IR sensor and camera temperatures. With temperature control, CN temperature was maintained at 45.0 +/- 1.5 degrees C. Without IR sensor feedback, CN temperatures continued to rise during ONS, reaching unsafe levels of similar to 50 degrees C.