title: Combining EEG and MEG for the reconstruction of epileptic activity using a calibrated realistic volume conductor model.
abstract: To increase the reliability for the non-invasive determination of the irritative zone in presurgical epilepsy diagnosis, we introduce here a new experimental and methodological source analysis pipeline that combines the complementary information in EEG and MEG, and apply it to data from a patient, suffering from refractory focal epilepsy. Skull conductivity parameters in a six compartment finite element head model with brain anisotropy, constructed from individual MRI data, are estimated in a calibration procedure using somatosensory evoked potential (SEP) and field (SEF) data. These data are measured in a single run before acquisition of further runs of spontaneous epileptic activity. Our results show that even for single interictal spikes, volume conduction effects dominate over noise and need to be taken into account for accurate source analysis. While cerebrospinal fluid and brain anisotropy influence both modalities, only EEG is sensitive to skull conductivity and conductivity calibration significantly reduces the difference in especially depth localization of both modalities, emphasizing its importance for combining EEG and MEG source analysis. On the other hand, localization differences which are due to the distinct sensitivity profiles of EEG and MEG persist. In case of a moderate error in skull conductivity, combined source analysis results can still profit from the different sensitivity profiles of EEG and MEG to accurately determine location, orientation and strength of the underlying sources. On the other side, significant errors in skull modeling are reflected in EEG reconstruction errors and could reduce the goodness of fit to combined datasets. For combined EEG and MEG source analysis, we therefore recommend calibrating skull conductivity using additionally acquired SEP/SEF data.
authors.affiliation: Institute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster, Münster, Germany.
authors.forename: Ümit
authors.initials: Ü
authors.lastname: Aydin
authors.affiliation: Institute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster, Münster, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Vorwerk
authors.affiliation: Institute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster, Münster, Germany; Department of Neurology, Klinikum Osnabrück, Osnabrück, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Küpper
authors.affiliation: Ruhr-Epileptology Department of Neurology, Universitätsklinikum Knappschaftskrankenhaus Bochum, Bochum, Germany.
authors.forename: Marcel
authors.initials: M
authors.lastname: Heers
authors.affiliation: Department of Clinical Radiology, Universitätsklinikum Münster, Münster, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Kugel
authors.affiliation: Department of Neuropediatrics, Universitätsklinikum Schleswig-Holstein, Kiel, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Galka
authors.affiliation: Department of Neuropediatrics, Universitätsklinikum Schleswig-Holstein, Kiel, Germany.
authors.forename: Laith
authors.initials: L
authors.lastname: Hamid
authors.affiliation: Ruhr-Epileptology Department of Neurology, Universitätsklinikum Knappschaftskrankenhaus Bochum, Bochum, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Wellmer
authors.affiliation: Department of Neurology, Klinikum Osnabrück, Osnabrück, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Kellinghaus
authors.affiliation: Epilepsy Center, Department of Neurology, Universitätsklinikum Erlangen, Erlangen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Rampp
authors.affiliation: Institute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster, Münster, Germany.
authors.forename: Carsten Hermann
authors.initials: CH
authors.lastname: Wolters
mesh_terms: D000200:Action Potentials; D000293:Adolescent; D004553:Electric Conductivity; D004569:Electroencephalography; D004827:Epilepsy / Q000175:diagnosis / Q000503:physiopathology*; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D059629:Signal-To-Noise Ratio; D012886:Skull / Q000503:physiopathology