Evaluation of a Monitoring Systems for Determining Ablation Zone Sizes Using Phase-Shift Measurements

This work presents a method to determine the extent of the ablation zone which is generated in a microwave liver ablation (MW A). The approach is based on analyzing the phase-shift between the transmitted and the received microwave. A comparison is made between a theoretical model, a simulation model and a phantom experiment. All three models are two-layer models. The first layer represents the ablated liver (relative permittivity here is 12.4) and the second layer represents the non-ablated liver tissue (relative permittivity here is 40). In the simulation model, these permittivity values are set by software and in the phantom experiment, two different polyethylene glycol (PEG) solutions are prepared to feature these values. In addition, the setups include a self-developed transmitter (slot-applicator) that emits the microwave with a power of 10 dBm and at a frequency of 2.45 GHz into the liver tissue and a self-developed receiver (bowtie-dip antenna) that detects changes in the propagated wave. The radial extension of the ablation zone is changed in 5 mm steps from 5 mm up to 20 mm in both the simulation model and the measurement setup of the phantom experiment. The phase-shift measurement in the phantom experiment is carried out using a software defined radio (SDR) system. The results show that the simulation results deviate from theory by a maximum of 6% and the results of phantom experiments deviate from theory by a maximum of 12%.