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Safety of Hybrid Electrodes for Single-Neuron Recordings in Humans

Hefft, Stefan MD, PhD*; Brandt, Armin Dipl Biol; Zwick, Stefan PhD§; von Elverfeldt, Dominik PhD§; Mader, Irina MD; Cordeiro, Joacir PhD; Trippel, Michael MD; Blumberg, Julie Dipl Physicist; Schulze-Bonhage, Andreas MD, PhD

doi: 10.1227/01.neu.0000429840.76460.8c
Research-Human-Clinical Studies

BACKGROUND: Intracranial 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.

OBJECTIVE: The aim of this study was to assess neurosurgical safety of implantations, recordings, and imaging using hybrid electrodes in humans.

METHODS: Perioperative 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.

RESULTS: There 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.

CONCLUSION: Given 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.

ABBREVIATIONS: EEG, electroencephalography

MPRAGE, magnetization preparing rapid acquired gradient echo

*Cellular Neurophysiology II, Department of Neurosurgery,

Epilepsy Center,

§Division of Medical Physics, Department of Radiology,

Department of Neuroradiology,

Division of Functional and Stereotactic Neurosurgery, Department of Neurosurgery, University Hospital Freiburg, Freiburg, Germany

Correspondence: Stefan Hefft, MD, PhD, Neurocenter, University Hospital Freiburg, Breisacher Str. 64, 79106 Freiburg, Germany. E-mail:

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Received September 18, 2012

Accepted March 12, 2013

Copyright © by the Congress of Neurological Surgeons