Three-Dimensional Temperature Map During Microwave Ablation of Ex Vivo Porcine Liver: Theoretical Prediction and Experimental Validation

Abstract

The aim of the present study was to experimentally assess the three-dimensional temperature map while applying a microwave (MW) ablation (MWA) system in ex vivo porcine liver. The principle of MWA is based on inducing the water molecule of the tissue to flip about 5 billions of time per second, depending on the frequency of the microwave. The interaction among the molecules is responsible of the increment of tissue temperature, thus of cellular death. A fresh porcine liver was treated by means of a 2.45 GHz antenna (100 W, 4 min). Tissue temperature was measured during the whole procedures by fiber optic-based probes located at eight fixed distances from the antenna. A three-dimensional temperature map was obtained by simulating the interaction between MW and liver; such map was then experimentally validated. Both theoretical and experimental temperature distribution around the antenna can be modelled by a Gaussian trend. There is a good agreement between experimental and theoretical temperature distributions. The validated model provides lethal isotherms, hence allowing extracting the volume of coagulated tissue. Simulations showed that shape of the coagulated tissue is an ellipse with long and short axes of 4.5 cm and 2.3 cm, respectively. Finally, it was verified that the Gaussian trend obtained by simulated data fit well experimental temperatures; this was also confirmed by the high value of the correlation coefficient $(\mathbf{R}^{2} > \pmb{0.97})$ , and by the low value of the root mean squared error (RMSE $\approx \pmb{2.9} ^{\circ}\mathbf{C})$ . Distributed temperature measurements allow validation of a Gaussian model, which accurately predicts the three-dimensional temperature distribution around a 2.45GHz MW antenna.