gms | German Medical Science

Objective: The combination of Intraoperative neurophysiological monitoring (IONM) and high-field intraoperative MRI (ioMRI) with the use of conductive cables in the MR scanner may lead to unexpected problems. We investigated the prevalence of complications and tested MR-heating experimentally.

Method: We documented all subcutaneous needle electrodes since 2013 that remained on the patient during intraoperative 3 Tesla ioMRI scans in our clinic. We also simulated an ioMRI session with gel and measured the temperature increase with optical fibers.

Results: We placed 1093 subcutaneous needles in 52 surgical procedures, patients aged 18 months to 65 years, with concurrent IONM and ioMRI. One patient suffered from a skin irritation at his shoulder. In one of seven patients with needles placed in the orbital cavity, an electrode with a 0.4 m cable was used and may have caused tissue heating. A corneal erosion with a resulting corneal scar and necessity of amblyopia treatment was diagnosed postoperatively. In the simulated ioMRI session we achieved a heating of more than 7°C for the electrode with the 0.4 m cable but not for the 1.5 m cable. Heating was due to the electric effect of the conductive cable and can occur with both ferromagnetic and diamagnetic materials. All other needles had no side effects.

Conclusions: We have corroborated the history of safe use for 1091 electrodes with 1.5 m cable. Needles with 0.4 m electrode cable should not be used in MRI. Heating can occur in poorly perfused tissue like the cornea. Placement of electrodes in the orbital cavity should be evaluated carefully.