Photothermal-induced temperature changes in a model inner ear: a comparison of visible, infrared, and ultraviolet lasers

The temperature change in a model cylindrical vestibule (90 mm³) was measured following irradiation by argon (488-514 nm), CO₂ (10.6 μm), KTP (Nd:YAG) (532 nm), Er:YAG (2.9 μm), and XeCl (308 nm) lasers. Otic capsule bone was used to simulate the otosclerotic stapes footplate, and the thickness of each specimen was machined to variable thicknesses (0.20-0.90 mm). Thermocouples were used to measure the temperature below the air-bone surface at depths of 1.0, 3.0, and 5.0 mm. The time-dependent temperature change, thermocouple position, and bone thickness were measured following single pulse application from argon, CO₂, and KTP (Nd-YAG) lasers. The effect of infrared and ultraviolet lasers on vestibule fluid temperature changes were studied with several fluence and pulse sequences. The temperature change in the vestibule following pulsed laser irradiation decreased with increasing bone thickness and thermocouple depth. Laser irradiation from CO₂, argon, KTP-532, XeCl, and Er:YAG lasers produced minimal (less than 5°) vestibule temperature changes. Measured temperatures were in good agreement with an analytic model, based on a solution to the bio-heat equation in semi-infinite media. The results are discussed with relevance to ear surgery