fMRI Functional Connectivity Analysis for Localizing Epileptic Focus

Localization of epileptic foci in patients with focal epilepsy is one of the main steps in presurgical evaluation. Knowing the precise location of the epileptic focus, the surgical procedure will be most efficient. Among all non-invasive interictal neuroimaging modalities, the combination of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) has been attractive for localizing the epileptic focus. However, the fMRI data alone is more available than simultaneous EEG-fMRI and can be used in many cases to achieve the correct location of the epileptic foci. In this study, we developed a new method using fMRI data alone for the localization of epileptic foci based on spatial independent component analysis (sICA) and functional connectivity (FC) analysis. The method is sufficiently accurate to be used in many cases. We applied it to a dataset of eighteen patients with focal epilepsy and measured the concordance based on the anatomical distance between the foci found by the presented method and the actual location of the epileptic focus. The results showed 56% fully concordant localized foci with an average distance of 16.31 mm from the actual epileptic focus. The presented method does not use the simultaneously recorded EEG signal, and thus, is independent of epileptic foci depth and occurrence of spikes during data recording sessions. It also provides simplicity in terms of data acquisition and artifact removal.