Feasibility assessment of an FBG-based probe for distributed temperature measurements during laser ablation

During thermal procedures, the monitoring of tissue temperature is useful to improve therapy success. The aim of this study is the feasibility assessment of a Fiber Bragg Grating (FBG)-based probe, which contains six FBGs, to obtain distributed temperature measurement in tissue undergoing laser ablation (LA). Among different thermometric techniques, FBG sensors show valuable characteristics, even though their sensitivity to strain entails measurement error for patient respiratory movement. We performed: i) the static calibration of the FBG-based probe to estimate the thermal sensitivity of the six FBGs; ii) the estimation of the response time of the FBGs. All FBGs have a thermal sensitivity of 10 pm·°C-1 and a time constant in the order of <; 250 ms. Additionally, we performed a preliminary estimation of the error due to the strain and caused by respiratory movements. Experiments were carried out by simulating a typical respiratory movement on ex vivo swine liver. The measurement error was <;0.6 °C for all FBGs. Eventually, experiments were performed on ex vivo porcine liver undergoing LA to assess the measurement error, called artifact, caused by the direct absorption of the laser light by the metallic needle. The artifact was firstly investigated at 12 relative positions between the needle and the laser applicator, then corrected by a two-variables model. After adjustment, the artifact decreases from about 2.1 °C to about 0.1 °C. The solutions proposed in this study foster confirming the feasibility of the FBG-based probe for temperature monitoring in organ undergoing LA.