SURFACE-TEMPERATURE DISTRIBUTIONS IN CARBON-DIOXIDE, ARGON, AND KTP (ND-YAG) LASER-ABLATED OTIC CAPSULE AND CALVARIAL BONE

Hypothesis: The spatial and temporal surface temperature distribution was measured after laser irradiation in fresh porcine otic capsule and calvarial bone tissue using an HgCdTe (mercury-cadmium-tellurium) inf rared camera. Background: Carbon dioxide (CO2) (lambda = 10.6 mm), arg on (lambda = 514 nm), and Potassium-Titanyl-Phosphate Neodynium: Yttri um-Aluminum-Garnet (KTP[Nd:YAG]) (lambda = 532 nm) lasers are used for stapes surgery and in the treatment of chronic ear disease. Despite e xtensive clinical use, little is known about the thermal perturbations in otic capsule calcified tissues and what are safe energy parameters for laser use. Methods: A microspot manipulator, lens, and microfiber were used for continuous wave (CW) and super-pulse (SP) CO2, argon, a nd KTP(Nd:YAG) lasers, respectively. Peak tempera tuns after ablation were measured simultaneously along with the full-width-half-maximum of the thermal disturbance and fitted to a Gaussian distribution. The co oling time for the hot spot to return to ambient temperature also was recorded. Results: Temperature changes with CW CO, irradiation were ma rkedly elevated relative to SP mode and also required longer to cool. The KTP and argon-treated bone were irradiated in the presence and abs ence of an initiator (black ink); minimal surface temperature elevatio n was recorded in the absence of an initiator. Further, no surface mod ification was observed. Ln contrast, the addition of an initiator resu lted in marked temperature elevations and significant surface carboniz ation with these two visible wavelength lasers. Cooling times varied f rom 10-40 seconds. No consistent relation to the measured thermal valu es and tissue microarchitecture was observed. Conclusions: The measure d cooling times and Gaussian distribution of surface temperatures serv e as empiric guidelines for minimizing thermal injury to critical stru ctures during laser surgery in the middle ear.