Evaluation of the Thermal Response of Liver Tissue Undergoing Microwave Treatment by Means of Fiber Bragg Grating Sensors

Thermal ablation procedures are gaining ever-growing acceptance in the treatment of hepatic tumors. In this context, the use of microwave ablation (MWA) has been firmly consolidated during the last decades. Being able to monitor the temperature increment within tissues undergoing MWA can be beneficial for improving the treatment outcome, especially for liver tissue which is notoriously not homogeneous and reports the presence of large vessels.In this work a multi-point temperature monitoring was performed on ex vivo liver tissue undergoing MWA. The aim was to investigate the transient phase of the tissue temperature in terms of the constant time (τ). The influence on τ of the following two aspects has been assessed: i) the blood perfusion due to the presence of a blood vessel and ii) the distance between the heat source (i.e., antenna) and the site where the temperature was measured. A power of 50 W was delivered for a treatment time of 480 s by means of a MW system. An aluminum duct providing a flowrate of 0.8 L·min^-1 of water at 37 °C was inserted to mimic the presence of a blood vessel. A multi-point temperature measurement was carried out by using three fiber optics, each embedding an array of 10 fiber Bragg Grating (FBGs) sensors. The fibers were placed into the tissue sample at different distances from both the antenna and the blood vessel. The temperature variations (ΔT) recorded by the FBGs were then plotted, and τ values were calculated. The high dependence of the temperature transient dynamics on both the abovementioned distance and the presence of the vessel was found.