Thermal characteristics of CO 2 , Argon, and KTP (Nd:YAG) ablated bone

Abstract

C02 (10.6 j.tm), Argon (5 14 nm), and KTP(Nd:YAG) (532 nm) are the lasers of choice for the stapedotomy operation. While each of these lasers is effective in surgically treating otoscierosis, few studies exist which compare the relative deleterious effects of these lasers in a model that is relevant to clinical practice and also based on the physics of laser-tissue interactions. This study focuses on surface temperature changes that occur in otic capsule, cortical, and lamellar bone when treated with clinical laser energy densities.Fresh porcine otic capsule, cortical, and lamellar bone were micromachined to a uniform thickness of 0.8 mm. A microspot manipulator was used for CO2, testing both continuous wave (CW) and super-pulse (SP) modes. A focused lens based system was used for argon, and a micro fiber was used for KTP. A Hg-Cd-Te infrared imaging system was used to measure temperature. Hot spot temperatures were recorded, as well as the full width-half maximum (FWHM) of the thermal disturbance at that time. The time for the hot spot to return to ambient temperature was also recorded. With visible wavelengths, the experiments were performed in the presence and absence of an initiator (black ink). Temperature elevations with CW CO2 were markedly elevated relative to SP mode. The CW irradiated tissue also required longer to cool. In both KTP and argon treated bone, minimal surface temperature elevation was recorded in the absence of an initiator. No surface modification was observed by light microscopy. In contrast, the addition of an initiator resulted in marked temperature elevations and significant surface carbonization with these visible wavelengths. The mechanisms of ablation and thermal conduction are discussed along with the clinical relevance of these findings.