Correlation between CT Number shift and tissue temperature change during radiofrequency ablation: an ex-vivo study using bovine liver

Current post-RFA (radiofrequency ablation) evaluation of unresectable liver tumours relies on visual inspection of non-enhancing tissues on the contrasted CT (computed tomography) images. This research investigated the correlation between CT number shift (dHU) and tissue temperature change (dT) during real-time CT-guided RFA of ex-vivo bovine livers. The study aimed to develop a non-invasive CT thermometry method to guide clinicians in assessing ablation outcome. 10 liver samples were individually ablated for 12 minutes using a RFA electrode, powered by an impedance-controlled RF generator (Cool-tipTM, Metronic, USA) and subsequently cooled for 15 minutes. An optical fiber inscribed with 4 equally spaced Fiber Bragg Gratings (FBG) was inserted sideward through the liver to measure 4 temperature points at the grating positions. CT scans were performed at interval of 3 minutes from 0 to 27 minute. CT numbers at the grating positions were manually extracted, and dHU and dT were computed and plotted to investigate the relationship. From the results, CT number decreased as temperature increased during RFA, and vice versa. A negative linear relationship (y = -0.66x + 1.23, R² = 0.925) between dHU and dT was observed. The thermal sensitivity was determined as -0.66 ± 0.03 HU/˚C. The strong correlation between dHU and dT during RFA could be used to estimate tissue temperature based on the CT number measured during real time CT-guided RFA. This approach would help the interventionalists in determining the ablation outcome hence improving treatment efficacy.