Radiofrequency ablation lesion detection using MR-based electrical conductivity imaging: A feasibility study of ex vivo liver experiments

Purpose: The aim of this study was to show the potential of magnetic resonance electrical impedance tomography (MREIT) conductivity imaging in terms of its capability to detect ablated lesions and differentiate tissue conditions in liver radiofrequency (RF) ablation. Materials and methods: RF ablation procedures were performed in bovine livers using a LeVeen RF needle electrode. Ablation lesions were created using a power-controlled mode at 30, 50, and 70 W for 1, 3, and 5 min of exposure time, respectively. After the ablation, the liver was cut into several blocks including the ablated lesion, and positioned inside a phantom filled with agarose gel. Electrodes were attached on the side of the phantom and it was placed inside the MRI bore. For MREIT imaging, multi-spin-echo pulse sequence was used to obtain the magnetic flux density data according to the injection currents. Results: The conductivity of ablation lesions was significantly changed with the increase of exposure time (pKW < 0.01, Kruskal-Wallis test). With RF powers of 30 and 50 W, significant differences between the coagulation necrosis and hyperaemic rim were observed for more than 5 min and 3 min, respectively (pMW < 0.01, Mann-Whitney test). At 70 W, all cases showed significant differences except 3 min (pMW < 0.01). The positive correlation between the exposure time and tissue conductivity was observed in both two ablation areas (pSC < 0.01, Spearman correlation). Conclusions: This ex vivo feasibility study demonstrates that current MREIT conductivity imaging can detect liver RF ablation lesions without using any contrast media or additional MR scan.