Detecting cryoablation with EIT and the benefit of including ice front imaging data

Imaging has made cryosurgery, the destruction of unwanted tissue through freezing, valuable. Electrical impedance tomography (EIT) has been explored as a method to determine the volume of tissue that is frozen during the procedure. However, studies have shown that tissue near the edge of the frozen zone often survives since in this region it may only be the extra-cellular space that is frozen. This threatens the usefulness of cryosurgery for cancer therapy since inaccurate ablation either allows the cancer to survive or increases the chances of complications. Since low-frequency conductivity of tissue increases due to cell membrane impairment, and ablated tissue implies impaired membranes, EIT has the capability to recover images of tissue viability. Cryosurgery is a technique that can benefit from this: EIT scans before freezing and after thawing can show changes in conductivity and hence viability due to treatment. Assuming unfrozen tissue will survive treatment, we explore the use of differential EIT in combination with intra-operative ice front imaging modes that are currently in clinical practice to recover enhanced-resolution images of cryosurgical treatment efficacy in a set of simulated experiments. We also investigate the sensitivity to violation of this assumption and predict tolerable levels of measurement noise.