Potential of UWB Radar Systems in Monitoring Liver Ablation: A Phantom Model Study

Ultrawideband (UWB) radar differential imaging has the potential to be one of the noninvasive, real-time, and nonionizing methods for radio frequency ablation (RFA) monitoring. In this study, we developed a novel 3-D UWB radar system for monitoring of the ablation zone (AZ) sizes and shapes. The system was first numerically tested on both homogeneous and heterogeneous patient models, followed by corresponding experiments. We applied a 3-D delay-and-sum (DAS) algorithm to reconstruct and locate AZs, supported by an original method to determine average permittivity for heterogeneous DAS reconstructions. In addition, an algorithm estimating the AZ size and shape was developed. The system demonstrated high precision with a monitoring error of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.2~\pm ~0.9$ </tex-math></inline-formula> mm in simulations and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.3~\pm ~0.8$ </tex-math></inline-formula> mm in ex vivo experiments. AZ volume and shape were approximated with relative errors of 14.8% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm ~9.5$ </tex-math></inline-formula>% in numerical models and 29.6% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm ~24.3$ </tex-math></inline-formula>% in experiments. These results indicate that the developed UWB radar system is a promising method for accurate RFA monitoring.