A Theoretical Model for RF Ablation of Kidney Tissue and Its Experimental Validation

Radio-frequency (RF) ablation is a minimal invasive thermal therapy, currently considered as an alternative to surgery to eradicate small solid kidney tumors. Our aim is to understand the kinetics of thermal lesion growth in kidney tissue exposed to RF energy by taking into account dynamic time-temperature changes in electrical properties of multiple tissues (i.e. kidney, surrounding fat, muscle). We present a computer model designed to calculate the voltage distribution and the temperature rise in kidney. The model further calculates the RF lesion size based on kinetic processes, which correctly describe coagulative necrosis process. The simulated transient temperatures and lesion size were experimentally validated with good agreement in a porcine kidney model, ex vivo. The expected increase in electrical conductivity of kidney (approximately 3 times) during heating resulted in predicted lesion width and depth that were larger (by as much as 20% and 30% respectively) than those predicted for constant properties. Simulation results also show how the lesion size and shape can be affected by the proximity to the RF electrode of a surrounding layer of fat, which acts as an electro-thermal insulator. The results of this pre-clinical investigation may be useful for treatment planning of RF thermal therapy of kidney tumours.