Imaging Epileptic Activity Using Functional MRI

Abstract

This review concentrates on functional MRI (fMRI) methods to identify the epileptic focus, i.e. ictal and interictal fMRI. First, established clinical applications of fMRI in the field of epilepsy are briefly introduced: fMRI of sensorimotor, language and memory function can already be considered as clinically relevant tools to identify the eloquent cortex and to predict postoperative functional deficits in patients considered for epilepsy surgery. fMRI offers a valid alternative to invasive methods like the Wada test for establishing language dominance, and it is likely that it will also replace the Wada test for assessing presurgical memory function in the nearer future. Ictal fMRI (fMRI studies of epileptic seizures) will remain confined to exceptional cases due to practical limitations. The generators of interictal epileptiform discharges (IED) can be studied with EEG-correlated fMRI. Despite its technical challenges, it has proved useful to provide insights into the generation of IED in patients with focal and generalized epilepsy. In selected patients with focal IED, EEG-correlated fMRI has the potential to reproducibly identify cortical areas involved in generating IED, i.e. the irritative zone. In patients with generalizes IED, suspension of functional networks due to the IED can be demonstrated. The utility of EEG-correlated fMRI in clinical epileptology cannot be definitely determined yet.

Estimating cortical column sensory networks in rodents from micro-electrocorticograph (μECoG) recordings

“…Currently, the most specific clinical method to pinpoint the seizure source consists of using volume conduction to model ECoG potentials recorded over the suspected cortical area [48, 49, 50]. The neurosurgeon first identifies the electrode recording abnormal activity, then proceeds with the removal of the underlying cortical region.…”

A personalized history of EEG–fMRI integration

“…There was the hope of providing useful clinical information particularly in patients undergoing pre-surgical evaluation. A detailed discussion of the literature is beyond the scope of this article and can be found in reviews (Cunningham et al, 2008;Gotman, 2008;Gotman et al, 2006;Gotman and Pittau, 2011;Hamandi et al, 2004;Krakow, 2008;Laufs and Duncan, 2007;Richardson, 2010;Rosenkranz and Lemieux, 2010;Salek-Haddadi et al, 2003;Stern, 2006;Yu et al, 2005). In summary, research advanced from feasibility studies Hamandi et al, 2004;Lemieux, 2004;Salek-Haddadi et al, 2003;Stern, 2006;Yu et al, 2005) to those attempting to identify the irritative zones in individual or cohorts of patients with focal Krakow et al, 1999;Patel et al, 1999;Salek-Haddadi et al, 2006) or generalized epilepsy syndromes (Aghakhani et al, 2004;Hamandi et al, 2006), or patients with a particular type of pathology (Federico et al, 2005b;Kobayashi et al, 2007;Kobayashi et al, 2006b;Kobayashi et al, 2005).…”

Correction for pulse height variability reduces physiological noise in functional MRI when studying spontaneous brain activity

“…Several studies have shown that the coregistration of EEG and fMRI (EEG-fMRI) is applicable for the identification of the epileptic focus [e.g. Benar et al, 2002;Gotman et al, 2004;Krakow 2008;Salek-Haddadi et al, 2006;Zijlmans et al, 2007]. From the EEG a reference function is extracted, representing the occurrence of the interictal epileptiform discharges (IED).…”