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Spatial correlation of hemodynamic changes related to interictal epileptic discharges with electric and magnetic source imaging

Authors

  • Marcel Heers,

    Corresponding author
    1. Montreal Neurological Institute, Department of Neurology and Neurosurgery, McGill University, Montreal, Canada
    • Correspondence to: Marcel Heers, MD, Montreal Neurological Institute, Department of Neurology and Neurosurgery, McGill University, 3801 University Street, room 786, Montreal, QC, Canada, H3A 2B4. E-mail: marcel.heers@gmail.com

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  • Tanguy Hedrich,

    1. Multimodal Functional Imaging Laboratory, Biomedical Engineering Department, McGill University, Montreal, Canada
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  • Dongmei An,

    1. Montreal Neurological Institute, Department of Neurology and Neurosurgery, McGill University, Montreal, Canada
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  • François Dubeau,

    1. Montreal Neurological Institute, Department of Neurology and Neurosurgery, McGill University, Montreal, Canada
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  • Jean Gotman,

    1. Montreal Neurological Institute, Department of Neurology and Neurosurgery, McGill University, Montreal, Canada
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  • Christophe Grova,

    1. Montreal Neurological Institute, Department of Neurology and Neurosurgery, McGill University, Montreal, Canada
    2. Multimodal Functional Imaging Laboratory, Biomedical Engineering Department, McGill University, Montreal, Canada
    3. Physnum team, Centre de Recherches Mathématiques, Montreal, Canada
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  • Eliane Kobayashi

    1. Montreal Neurological Institute, Department of Neurology and Neurosurgery, McGill University, Montreal, Canada
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Abstract

Introduction

Blood oxygenation level-dependent (BOLD) signal changes at the time of interictal epileptic discharges (IEDs) identify their associated vascular/hemodynamic responses. BOLD activations and deactivations can be found within the epileptogenic zone but also at a distance. Source imaging identifies electric (ESI) and magnetic (MSI) sources of IEDs, with the advantage of a higher temporal resolution. Therefore, the objective of our study was to evaluate the spatial concordance between ESI/MSI and BOLD responses for similar IEDs.

Methods

Twenty-one patients with similar IEDs in simultaneous electroencephalogram/functional magnetic resonance imaging (EEG/fMRI) and in simultaneous EEG/magnetoencephalogram (MEG) recordings were studied. IEDs in EEG/fMRI acquisition were analyzed in an event-related paradigm within a general linear model (GLM). ESI/MSI of averaged IEDs was performed using the Maximum Entropy on the Mean. We assessed the spatial concordance between ESI/MSI and clusters of BOLD activations/deactivations with surface-based metrics.

Results

ESI/MSI were concordant with one BOLD cluster for 20/21 patients (concordance with activation: 14/21 patients, deactivation: 6/21 patients, no concordance: 1/21 patients; concordance with MSI only: 3/21, ESI only: 2/21). These BOLD clusters exhibited in 19/20 cases the most significant voxel. BOLD clusters that were spatially concordant with ESI/MSI were concordant with IEDs from invasive recordings in 8/11 patients (activations: 5/8, deactivations: 3/8).

Conclusion

As the results of BOLD, ESI and MSI are often concordant, they reinforce our confidence in all of them. ESI and MSI confirm the most significant BOLD cluster within BOLD maps, emphasizing the importance of these clusters for the definition of the epileptic focus. Hum Brain Mapp 35:4396–4414, 2014. © 2014 Wiley Periodicals, Inc.

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