• Stefan Hefft, Armin Brandt, Stefan Zwick, Dominik von Elverfeldt, Irina Mader, Joacir Cordeiro, Michael Trippel, Julie Blumberg, and Andreas Schulze-Bonhage.
• Cellular Neurophysiology II, Department of Neurosurgery, University Hospital Freiburg, Freiburg, Germany. stefan.hefft@uniklinik-freiburg.de
• Neurosurgery. 2013 Jul 1;73(1):78-85; discussion 85.

BackgroundIntracranial in vivo recordings of individual neurons in humans are increasingly performed for a better understanding of the mechanisms of epileptogenesis and of the neurobiological basis of cognition. So far, information about the safety of stereotactic implantations and of magnetic resonance imaging (MRI) with hybrid depth electrodes is scarce.ObjectiveThe aim of this study was to assess neurosurgical safety of implantations, recordings, and imaging using hybrid electrodes in humans.MethodsPerioperative and long-term safety of implantation of a total of 88 hybrid depth electrodes with integrated microwires was assessed retrospectively in 25 consecutive epilepsy patients who underwent implantation of electrodes from 2007 to 2011 based on electronically stored charts. Safety aspects of MRI are reported from both in vitro and in vivo investigations. Precision of electrode implantation is evaluated based on intraoperative computed tomography and pre- and postoperative MRI.ResultsThere was no clinically relevant morbidity associated with the use of hybrid electrodes in any of the patients. Precision of recordings from the targets aimed at was similar to that of standard depth electrodes. In vitro studies demonstrated the absence of relevant heating of hybrid electrodes with newly designed connectors with MRI at 1.5 T, corresponding to well-tolerated clinical MRI in patients.ConclusionGiven the technical approach described here, precise targeting and safe use are possible with hybrid electrodes containing microwires for in vivo recording of human neuronal units.

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