Influence of fiber Bragg grating length on temperature measurements in laser-irradiated organs

The present study investigates the influence of uniform FBG length on temperature measurement under substantial temperature gradient. This analysis is particularly relevant in the scenario of laser ablation (LA), where the temperature gradient close to the optical applicator is significant (e.g., up to 50 °C/mm). Aiming to assess how the sensor length affects the measurement process in LA, both bench and ex vivo experiments were carried out by applying temperature gradient in the range 5 °C/cm-30 °C/cm on 1 mm-length FBG and 10 mm-length FBG. Results showed that the use of small-sized FBGs is recommended in LA for two main reasons: i) the spectrum reflected by shorter sensors has not shown significant alterations with the gradient. Alterations of the spectrum shape could compromise peak detection algorithms, and, therefore, the estimation of the actual temperature; ii) Arrays of shorter sensors can provide multipoint temperature measurements, with quiet good spatial resolution (e.g., 3 mm), by inserting a single fiber in the tissue.