Fast conductivity imaging in magnetic resonance electrical impedance tomography (MREIT) for RF ablation monitoring

Purpose: This study shows the potential of magnetic resonance electrical impedance tomography (MREIT) as a non-invasive RF ablation monitoring technique.

Materials and methods: We prepared bovine muscle tissue with a pair of needle electrodes for RF ablation, a temperature sensor, and two pairs of surface electrodes for conductivity image reconstructions. We used the injected current non-linear encoding with multi-echo gradient recalled echo (ICNE-MGRE) pulse sequence in a series of MREIT scans for conductivity imaging. We acquired magnetic flux density data induced by externally injected currents, while suppressing other phase artefacts. We used an 8-channel RF head coil and 8 echoes to improve the signal-to-noise ratio (SNR) in measured magnetic flux density data. Using the measured data, we reconstructed a time series of 180 conductivity images at every 10.24 s during and after RF ablation.

Results: Tissue conductivity values in the lesion increased with temperature during RF ablation. After reaching 60 °C, a steep increase in tissue conductivity values occurred with relatively little temperature increase. After RF ablation, tissue conductivity values in the lesion decreased with temperature, but to values different from those before ablation due to permanent structural changes of tissue by RF ablation. Conclusion: We could monitor temperature and also structural changes in tissue during RF ablation by producing spatio-temporal maps of tissue conductivity values using a fast MREIT conductivity imaging method. We expect that the new monitoring method could be used to estimate lesions during RF ablation and improve the efficacy of the treatment.