Multimodality approach in presurgical evaluation of epilepsy

Introduction: Both Electroencephalography-functional Magnetic Resonance Imaging (EEG-fMRI) coregistration and high density EEG (hdEEG) map abnormal brain activation elicited by epileptic processes. EEG-fMRI is an imaging technique which provides localizing Blood Oxygenation Level Dependent (BOLD) information of irritative regions. Conversely, the source analysis estimates the current density of the source that generates a measured electric potential. Objectives: Clinical assessment of these techniques is done in patients with focal epilepsy who subsequently underwent epilepsy surgery. Methods: The standard EEG (32 electrodes) and the fMRI data were acquired during a scanning session (1.5T). The hdEEG recording was performed using 256 channels. Each patient underwent to a 3T scan to create a constraint for the source localization. The analysis of EEG-fMRI data was performed by using both the conventional (General Linear Model, GLM) and a novel method, which integrates in the conventional one two new modules: individual-based hemodynamic response function, and EEG protocol. Source localization of interictal epileptiform discharges (IEDs) using 32 (EEG acquired inside the magnet) and 256 EEG channels was calculated. Results: Changes in BOLD signal were observed in 22 out of 30 patients in whom IEDs are recorded. In 82%, these are concordant with expected epileptic activity defined by EEG and clinical outcome. The remaining 8 patients had no significant BOLD activity because of either technical prob- lems or no interictal epileptiform EEG activity inside the scanner. Three patients with activation were selected to underwent a hdEEG and showed significant source localization correlating with the EEG-fMRI activation. Conclusions: The combination of multimodality techniques such as EEG- fMRI coregistration and hdEEG is a useful tool of a presurgical workup of epilepsy providing two different methods of localization of the same epileptic foci.