Use of Neurophysiological Monitoring during MRI-Guided Ablation Procedures at 1.5 Tesla: Workflow and Safety Considerations.

PURPOSE: To evaluate the feasibility of intraoperative neurophysiological monitoring (IONM) during MRI-guided ablations and identify strategies to reduce IONM electrode radiofrequency (RF)-heating during MRI.

MATERIALS AND METHODS: Ex vivo experiments with a porcine tissue phantom simulating a typical high RF-heating risk IONM setup during an MRI-guided ablation procedure on the shoulder were performed on a 1.5 T scanner. Mutual interference between MRI and IONM was evaluated. To assess RF-heating risks, four pairs of IONM electrodes were inserted into the phantom at regions corresponding to the shoulders, mid-arm, and wrist. MRI of the "shoulder" was performed at three different specific absorption rate (SAR) levels with electrode wires positioned in various geometrical configurations. Different combinations of electrode connections to the IONM system were investigated. Temperatures of each electrode were recorded using fiber-optic sensors.

RESULTS: Simultaneous IONM readout and MRI resulted in distortion of the IONM signal, but interleaving MRI and IONM without moving electrodes was feasible. During MRI, temperature elevations greater than 60 °C at the electrode insertion sites were observed. Temperature reductions were achieved by routing electrode wires along the scanner central axis, reducing the wire length within the scanner bore, or lowering the SAR of the imaging sequence. Altering the electrode connection with the IONM system did not result in consistent changes in RF-heating.

CONCLUSIONS: With electrodes in the scanner bore, interleaving IONM and MRI is desired to avoid signal interference, and several strategies identified herein can reduce risk of electrode RF-heating during MRI-guided ablation.