Thermocouples for temperature monitoring during pancreatic laser ablation: Analysis of the measurement error

Laser ablation (LA) is a minimally invasive procedure used to remove cancer by inducing hyperthermia. It is based on the interaction between laser light and tissue: the absorbed light is converted into heat causing a tissue temperature increase. The amount of damaged volume depends on temperature and time exposure of the tissue to the hyperthermia. As a consequence, the monitoring of tissue temperature during LA could be particularly beneficial to optimize treatment outcomes. Thermocouples are one of the most employed transducer for temperature measurement. Their main drawback is related to the strong light absorption of the two metallic wires which constitute a thermocouple. The light absorption causes an overestimation of actual temperature, in literature known as artifact. This work aims at assessing this artifact on ex vivo swine pancreases undergoing LA. The artifacts have been estimated at the three laser powers (1.6 W, 2 W and 5 W) and at two distances from the optical applicator. In particular, the artifact decreases with the distance from the optical applicator and depends on P: at 1.6 W and 2 W it is negligible at 12 mm of distance, on the other hand at 5 W it is significant also at 15 mm (1.7 °C). Summing up: the artifact is strongly influenced by the distance between the thermocouple and the optical applicator, and by the laser power; also at high distance from the applicator it can cause error which are not acceptable for the application of interest (e.g., at 5 W and 10 mm the error is about 4 °C). Although the use of thermocouples entails the concern related to the artifact, it must be considered that proper model can be employed to correct the measurement error.