gms | German Medical Science

Objective: The combined utilization of neurophysiological methods and intraoperative MR-imaging might improve the surgeons’ anatomical and functional orientation. Nevertheless, an MRI environment requires a specific technical approach for intraoperative monitoring. Heating of electrodes resulting in thermal lesions and interference with imaging quality are of concern. This study provides technical details with respect to the employed electrode and the incidence of artefacts.

Methods: A 0.5 T low field open MRI (Polestar, Medtronic, USA) was utilized for the study. MRI was performed before and after the electrodes were positioned with the following axial/coronal sequences: esteady (8mm; 0.45 min), T1 (4mm, 7 min) and Flair (8mm, 3.5 min). The images were analyzed for artefacts. Single use Pt/Ir-electrodes (Viasys Healthcare, USA) have a low magnetic susceptibility and were used for transcranial electric stimulation to elicit motor evoked potentials (MEPs; 6 electrodes) as well as for recording somatosensory evoked potentials (SEPs, 6 electrodes). The electrode were positioned according to the international 10-20-EEG-system at C4, C2, C3, C1, Cz and Cz+6cm and C4', C3', Cz', Fz and Fpz (serving as reference electrode). Other parts of the monitoring equipment (ISIS, Inomed, Germany) were positioned at least 1 m away from the magnet or outside the 5-Gauss line, looping of cables was avoided and the cables were disconnected from the headbox while scanning. Position sides were inspected for adverse events and the monitoring quality compared to non-MRI environment.

Results: 22 patients (11f, 11m; 40.2±14.2 years) underwent supratentorial tumor surgery in the vicinity of the central region. At the electrode positions no adverse events such as burns were noticed. In all patients, MEPs and SEPs were obtainable without influencing the monitoring quality. The imaging quality was adequate in all patients, but in 5/22 patients a stripe-like signal void was noticed which did not interfere with image interpretation.

Conclusions: With the utilization of Pt/Ir electrodes and unhooking the electrodes during MRI data acquisition, the combined use of intraoperative monitoring and open MRI is safe. Thus, the combination of neurophysiological methods and intraoperative imaging provides a powerful and safe tool for intraoperative anatomical and functional orientation.