Development and characterization of a Fibre Bragg Grating temperature probe for medical Laser Ablation therapy

Temperature monitoring in tissue undergoing Laser Ablation (LA) is particularly beneficial to optimize therapy outcomes. During last decades several approaches have been proposed to perform thermometry during thermal ablation. Among others, Fiber Bragg Grating (FBG) sensors show valuable characteristics for such measurement, but their sensitivity to strain entails measurement error for patient respiratory movements. In this work two needle-like probes were developed using two different procedures to encapsulate an FBG into a surgical needle, aiming to allow safe insertion into the patient tissue and to neglect mechanical disturbance due to tissue movements occurring during breathing. The static calibration of the two probes has been carried out in a wide range of temperature (i.e., from 18 °C up to 100 °C), and their response time has been estimated. The calibration curves of the two probes show good linearity and a different sensitivity, and their response time is fast enough to meet the criteria set for temperature monitoring during LA. Since the metallic needle entails a measurement error, called artifact, due to the direct absorption of the laser radiation, the two abovementioned probes have been employed during LA on ex vivo liver. Then, their measurements have been compared to the measurement provided by an FBG without needle, which does not experience artifacts. The good results in terms of both static and dynamic properties of the two probes encourage to perform further analysis regarding the amplitude of the artifacts due to the direct absorption of the metallic needle and regarding the capability of the probes to neglect mechanical disturbance.