Temperature measurement artefacts of thermocouples and fluoroptic probes during laser irradiation at 810 nm

This study examined the artefact induced in temperature measurements made w ith thermocouples and Luxtron fluoroptic probes in the presence of infrared radiation. Localized heating was created using a continuous-wave, 810 nm d iode laser system emitting 2.0 W from a cylindrical diffusing optical fibre , in air, water and an agar-albumin phantom. The temperature was measured e very 1.0 s for 10 to 150 s, with both a thermocouple and a Luxtron fluoropt ic probe at distances of 2, 3, 4, 5, 6 and 7 mm from the cylindrical diffus ing tip. In all cases. the fluoroptic probe recorded a higher temperature t han the thermocouple during laser irradiation. The difference in measured t emperatures between the Luxtron probe and the thermocouple ranged from 1.6 degreesC to 18.8 degreesC in air, from 0.3 degreesC to 10.2 degreesC in wat er, and from 1.4 degreesC to 10.1 degreesC in phantom, depending on the dis tance of the probe from the laser source. The results suggest that in the p resence of laser irradiation, self-heating of the Luxtron probe induces a s ignificant artefact in temperature measurements at distances less than 4 mm from the source fibre. As a result, fluoroptic probes may not be suitable for monitoring tissue temperature for treatments when laser irradiation is present if sensors are located close to the fibre tip (<4 mm).