Surface temperature distributions in carbon dioxide, argon, and KTP (Nd:YAG) laser ablated otic capsule and calvarial...

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) infrared camera.

Carbon dioxide (CO2) (lambda = 10.6 mm), argon (lambda = 514 nm), and Potassium-Titanyl-Phosphate Neodynium: Yttrium-Aluminum-Garnet (KTP[Nd:YAG]) (lambda = 532 nm) lasers are used for stapes surgery and in the treatment of chronic ear disease. Despite extensive clinical use, little is known about the thermal perturbations in otic capsule calcified tissues and what are safe energy parameters for laser use.

A microspot manipulator, lens, and microfiber were used for continuous wave (CW) and super-pulse (SP) CO2, argon, and KTP(Nd:YAG) lasers, respectively. Peak temperatures after ablation were measured simultaneously along with the full-width--half-maximum of the thermal disturbance and fitted to a Gaussian distribution. The cooling time for the hot spot to return to ambient temperature also was recorded.

Temperature changes with CW CO2 irradiation were markedly elevated relative to SP mode and also required longer to cool. The KTP and argon-treated bone were irradiated in the presence and absence of an initiator (black ink): minimal surface temperature elevation was recorded in the absence of an initiator. Further, no surface modification was observed. In contrast, the addition of an initiator resulted in marked temperature elevations and significant surface carbonization with these two visible wavelength lasers. Cooling times varied from 10-40 seconds. No consistent relation to the measured thermal values and tissue microarchitecture was observed.

The measured cooling times and Gaussian distribution of surface temperatures serve as empiric guidelines for minimizing thermal injury to critical structures during laser surgery in the middle ear.