Highly dense FBG arrays for millimeter-scale thermal monitoring during nanocomposite-enhanced laser ablation

In this study, we assess the feasibility of highly dense fiber Bragg grating (FBG) arrays for real-time temperature measurement during Nanocomposites (NCs)-enhanced laser ablation (LA) of pancreas tissue. FBG arrays were fabricated with the femtosecond point-by-point writing technology. Each highly dense array contains 25 FBGs with a grating length of 0.9 mm and an edge-to-edge distance of 0.1 mm. As alternative fiber sensors, we used commercially available acrylatecoated FBG arrays containing 5 FBGs. Temperature measurements by the highly dense FBG array were compared to thermal camera readings during laser irradiation of water samples. The augmented thermal effect produced by special NC comprising of a polydopamine matrix embedded with gold and copper was evaluated during the irradiation of an ex vivo phantom. The phantom consisted of a blended porcine pancreas tissue mixed with the NC; tissue mixed with water was used for control. The results clearly demonstrate that the highly dense arrays better detect the peak temperature and temperature distribution. The NC presence increased the maximum temperature reached during LA from 48°C (control) to 90°C (NC) at 2 mm, and from 33 °C to 36°C at 4 mm distance from the laser tip. The low spatial resolution of the commercial arrays produced an underestimation of the peak temperature by 2°C (control), and by 1°C (NC) at 4 mm. These results highlight the importance of the proper selection of the measurement system characteristics, especially when high temperature gradient should be measured in biological tissues undergoing thermal ablation for cancer treatment.