Dielectric properties of RF heatedex vivoporcine liver tissue at 480 kHz: measurements and simulations

The outcome of radio frequency thermal ablation (RFTA) is significantly affected by the tissue electrical conductivity: understanding the dielectric properties changes during heating is fundamental to suitably model the medical procedure. Dielectric measurements at 480 kHz were performed on saline, porcine 'native' liver tissue (NL) and 'homogenised' liver tissue (HL) during uniform RF heating (up to 100 °C) using a two-electrode setup that allowed proper control of the rate of heating. HL was obtained by homogenising the tissue using a blender. The accuracy of the dielectric measurement setup was preliminary assessed using numerical simulations and then validated through experimental measurements on saline solution. The electrical conductivity of liver tissue at 37 °C was 0.2851 ± 0.0215 S m −1 for NL and 0.4135 ± 0.0399 S m −1 for HL. The conductivity increased with increasing temperature: above 60 °C different trends were observed for high and low heating rate experiments (fast and slow heating). While saline and HL were purely resistive, NL showed a capacitive behaviour, progressively lost above 60 °C; the relative permittivity of NL tissue at 37 °C was 2,523 ± 423. This behaviour is connected to the irreversible structural changes of the tissue: an Arrhenius-based model was able to suitably reproduce the different trends observed for NL with a single set of parameters. Finally, the effects of different electrical conductivity models are outlined through RFTA numerical simulations. While the Arrhenius-based models are the most physically based, the performed simulations show that all tested models are suitable for the simulation of RFTA, as long as the electrical conductivity changes with temperature are taken into account.