Assessment of temperature measurement error and its correction during Nd:YAG laser ablation in porcine pancreas

PURPOSE: The aim of this study was to experimentally assess temperature measurement error, or artefact, in ex vivo healthy porcine pancreases undergoing laser ablation due to direct light absorption by thermocouples, investigate this artefact at different relative positions between thermocouples and laser applicator, and correct the artefact by a three-variables model. MATERIALS AND METHODS: Temperature in ex vivo healthy porcine pancreases undergoing laser ablation, using a Nd:YAG laser at two low powers (i.e., 1.6 W and 2 W) and a single applicator, was monitored by thermocouples. Artefact caused by laser light absorption of thermocouple metallic wires was assessed at 12 relative positions by changing the relative distance (d) and the angle (θ) forming between applicator and thermocouples. Reference temperature was measured by fibre Bragg grating sensors. Trials were performed using a three-variables model (i.e., power, d and θ) based on Pennes' equation to correct the artefact. RESULTS: The higher d and θ, the lower the artefact (e.g., at θ = 0° and power = 2 W, the artefact is 14.0 °C at d = 3 mm and 4.0 °C at d = 7 mm). Artefact increases with power. The three-variables model allows the minimising of the artefact: the maximum artefact decreases from 14 °C to 2.8 °C applying the proposed correction. CONCLUSIONS: Artefact is strongly influenced by the relative position between applicator and thermocouples. The correction based on the model minimises the artefact at the two low powers employed during the experiments. Further trials are required to investigate the feasibility of the model at higher powers.