Intraoperative neurophysiological monitoring in an open low-field magnetic resonance imaging system: clinical experience and technical considerations.
OBJECTIVE
The intraoperative combination of an open magnetic resonance imaging (MRI) system with neurophysiological localization and continuous monitoring techniques allows for the best available anatomic and physiological orientation as well as real-time functional monitoring. Methodological aspects and technical adaptations for this combination of methods and the experience in 29 patients with tumors in the central region are reported.


METHODS
MRI-compatible platinum/iridium electrodes for intraoperative neuromonitoring were attached to the patient's head. All other electrodes located outside the magnet were stainless steel needle-electrodes for recording of motor evoked potentials and for stimulating somatosensory evoked potentials. Intraoperative MRI was performed using a 0.15-T intraoperative magnetic resonance scanner (PoleStar N20; Medtronic Surgical Navigation Technologies, Louisville, KY).


RESULTS
The calculated and measured values of the maximum induced magnetic field (2 x 10(-6) T), induced voltage (0.1 V), and force (0.01 N) by the static or changing magnetic field within all attached electrodes were negligible and proved the method's safety. In 29 patients, platinum/iridium electrodes with low susceptibility showed no interference with the imaging quality. Furthermore, neurophysiological monitoring could be performed with unaffected recording quality. Side effects (e.g., thermal induction) were not observed.


CONCLUSIONS
Neurophysiological monitoring for evoked potentials and direct cortical stimulation can be performed with standard quality within a low-field intraoperative MRI system. Electrodes fixed to the head should be of low magnetic susceptibility to guarantee optimal imaging quality. The combined use of an open ultra low-field MRI system and intraoperative monitoring allows for resection control and continuous functional monitoring.
Szelényi
Andrea
A
Department of Neurosurgery, Johann Wolfgang Goethe University Hospital, Frankfurt, Germany. A.Szelenyi@em.uni-frankfurt.de
Gasser
Thomas
T
Seifert
Volker
V
D000293:Adolescent; D000328:Adult; D000368:Aged; D016477:Artifacts; D001932:Brain Neoplasms / Q000175:diagnosis* / Q000601:surgery*; D002648:Child; D003287:Contrast Media; D004558:Electric Stimulation; D004567:Electrodes, Implanted / Q000592:standards; D004574:Electromagnetic Fields; D004594:Electrophysiology; D004867:Equipment Design / Q000592:standards; D005071:Evoked Potentials / Q000528:radiation effects; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000295:instrumentation* / Q000379:methods; D038361:Neuronavigation / Q000295:instrumentation*; D019635:Neurosurgical Procedures / Q000295:instrumentation*; D019047:Phantoms, Imaging; D025321:Surgery, Computer-Assisted / Q000295:instrumentation*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
D003287:Contrast Media