The combination of EEG Source Imaging and EEG‐correlated functional MRI to map epileptic networks

Abstract

SUMMARYFunctional electrophysiologic techniques such as electroencephalography (EEG) and magnetoencephalography (MEG) give insights into the dynamics of the networks involved in the generation of interictal and ictal epileptic activity and their interaction with physiologic brain activity. With recent advances in methodology and clinical validation, EEG source imaging (ESI) may now be used to map epileptic activity as well as evoked responses to external stimuli. By its ability to show hemodynamic changes time locked to epileptic activity in the whole brain, EEG-correlated functional magnetic resonance imaging (fMRI) (EEG-fMRI) is the natural counterpart of ESI, circumventing some of its limitations, the former adding data from the depths of the brain, and the latter temporal resolution. To better understand the potential and limitations of both techniques, this review starts with a description of the neurophysiologic mechanisms that give rise to the measured signals, followed by validation studies based on comparison with intracranial EEG and surgical outcome. We then discuss analysis strategies to combine both techniques by reviewing studies in epilepsy, current methodologic development, and future directions of this fast-developing field.

Pulse Artifact Detection in Simultaneous EEG–fMRI Recording Based on EEG Map Topography

“…• Importantly, our study showed that the EEG-based PA correction did not alter the identification of spikes and preserved their scalp topography compared to the spikes observed in the recording performed outside the magnetic environment. The acquisition and analysis of the EEG-based method should therefore be compatible with fMRI analysis guided by EEG topography (Grouiller et al 2011), source activity (Vulliemoz et al 2010) or simultaneous analysis of EEG-fMRI and Electric source Imaging (Vulliemoz et al 2009). In clinical practice, current topographic EEG analyses with the 256-channel EEG-system used here are often computed by not considering the electrodes on the cheek (Brodbeck et al 2009).…”

Epileptic network of hypothalamic hamartoma: An EEG-fMRI study

“…EEG-fMRI can detect blood-oxygen-level dependent (BOLD) changes that are related to interictal discharges identified from scalp EEG (Lemieux et al, 2001;Warach et al, 1996). It was reported to be clinically useful for localizing the epileptic focus and investigating epileptic network even in the deep brain structures Vulliemoz et al, 2010). In addition, it possibly predicts postsurgical outcome non-invasively although its clinical utility in comparison with other techniques, e.g.…”

Clinical Applications of fMRI

“…In patients with epilepsies, electroencephalography (EEG) and magnetoencephalography (MEG) can uniquely define the temporal dynamics of the networks involved in the generation of abnormal interictal and ictal activity. By showing hemodynamic changes as they are related to epileptiform events across the whole brain, EEG-correlated fMRI (EEG-fMRI) allows a theoretically less confounded approach to source imaging than either EEG or MEG used alone (Vulliemoz et al 2009).…”