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PLoS One. 2015 Mar 11;10(3):e0118753. doi: 10.1371/journal.pone.0118753. eCollection 2015.

Combined EEG/MEG can outperform single modality EEG or MEG source reconstruction in presurgical epilepsy diagnosis.

Author information

1
Institute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster, Münster, Germany; Institute for Biomedical Engineering and Informatics, Technische Universität Ilmenau, Ilmenau, Germany.
2
Institute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster, Münster, Germany.
3
Epilepsy Center, Universitätsklinikum Freiburg, Freiburg im Breisgau, Germany.
4
Institute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster, Münster, Germany; Department of Neurology, Klinikum Osnabrück, Osnabrück, Germany.
5
Department of Clinical Radiology, Universitätsklinikum Münster, Münster, Germany.
6
Epilepsy Center, Universitätsklinikum Freiburg, Freiburg im Breisgau, Germany; Ruhr-Epileptology Department of Neurology, Universitätsklinikum Knappschaftskrankenhaus Bochum, Bochum, Germany.
7
Ruhr-Epileptology Department of Neurology, Universitätsklinikum Knappschaftskrankenhaus Bochum, Bochum, Germany.
8
Department of Neurology, Klinikum Osnabrück, Osnabrück, Germany.
9
Institute for Biomedical Engineering and Informatics, Technische Universität Ilmenau, Ilmenau, Germany.
10
Ruhr-Epileptology Department of Neurology, Universitätsklinikum Knappschaftskrankenhaus Bochum, Bochum, Germany; Epilepsy Center, Department of Neurology, Universitätsklinikum Erlangen, Erlangen, Germany.
11
Epilepsy Center, Department of Neurology, Universitätsklinikum Erlangen, Erlangen, Germany.

Abstract

We investigated two important means for improving source reconstruction in presurgical epilepsy diagnosis. The first investigation is about the optimal choice of the number of epileptic spikes in averaging to (1) sufficiently reduce the noise bias for an accurate determination of the center of gravity of the epileptic activity and (2) still get an estimation of the extent of the irritative zone. The second study focuses on the differences in single modality EEG (80-electrodes) or MEG (275-gradiometers) and especially on the benefits of combined EEG/MEG (EMEG) source analysis. Both investigations were validated with simultaneous stereo-EEG (sEEG) (167-contacts) and low-density EEG (ldEEG) (21-electrodes). To account for the different sensitivity profiles of EEG and MEG, we constructed a six-compartment finite element head model with anisotropic white matter conductivity, and calibrated the skull conductivity via somatosensory evoked responses. Our results show that, unlike single modality EEG or MEG, combined EMEG uses the complementary information of both modalities and thereby allows accurate source reconstructions also at early instants in time (epileptic spike onset), i.e., time points with low SNR, which are not yet subject to propagation and thus supposed to be closer to the origin of the epileptic activity. EMEG is furthermore able to reveal the propagation pathway at later time points in agreement with sEEG, while EEG or MEG alone reconstructed only parts of it. Subaveraging provides important and accurate information about both the center of gravity and the extent of the epileptogenic tissue that neither single nor grand-averaged spike localizations can supply.

PMID:
25761059
PMCID:
PMC4356563
DOI:
10.1371/journal.pone.0118753
[Indexed for MEDLINE]
Free PMC Article

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