Prevalence of complications in intraoperative MRI combined with neurophysiological monitoring

Abstract Background High field intraoperative MRI (ioMRI) is becoming increasingly available in neurosurgery centers, where it has to be combined with intraoperative neurophysiological monitoring (IONM). IONM needle electrodes remain on the patient during ioMRI and may cause image distortions and burns. Objective We tested MR-heating experimentally and investigated the prevalence of complications. Methods We studied electrodes that are certified for IONM, but not “MR conditional”. They consist of copper cables (length 1.5 m) and needles made of either stainless steel (ferromagnetic) or Pt/Ir (paramagnetic). We simulated an ioMRI session with gel and measured the temperature increase with optical fibers. We measured the force an electrode experiences in the magnetic field. We prospectively documented subcutaneous needle electrodes between 2013-2016 that remained on the patient during intraoperative 3 Tesla ioMRI scans. Results The in-vitro testing of the electrodes produced a maximum heating ΔT = 3.9°C and force of 0.026 N. We placed 1237 subcutaneous needles in 57 surgical procedures with combined IONM and ioMRI, where needles remained placed during ioMRI. One patient suffered from a skin burn at the shoulder. All other electrodes had no side effects. Conclusions We have corroborated the history of safe use for electrodes with 1.5 m cable in a 3T MR scanner and demonstrate their use. Nevertheless, heating cannot be excluded, as it depends on location and cable placement. When leaving electrodes in place during ioMRI, risks and benefits have to be carefully evaluated for each patient.