EEG-fMRI in children with focal epilepsies - Use of variable Hemodynamic Response Functions to increase the sensitivity of EEG-fMRI and learn more about the neurophysiological correlate of the irritative zone

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Interictal spikes in the EEG of epileptic patients are related to their epileptogenesis. The spikes are generated by the irritative zone of the cortex. EEG-functional MRI (EEG-fMRI) is a noninvasive method of localizing the irritative zone. Changes of neuronal activity are reflected by changes in the ratio of the oxy- and deoxyhemoglobin concentration in the cerebral vessels. The changes are called blood oxygenation level dependent effect (BOLD). In the fMRI the BOLD effect is calculated on the basis of a model ¿hemodynamic response function¿ (HRF). Interictal spiking results in significant BOLD changes located in the area of spike generation. However, EEG-fMRI in epileptic patients raised two problems: Firstly the sensitivity of the method is low with 40 ¿ 60%, and secondly positive and negative BOLD effects were observed. This study aims to improve the sensitivity of EEG-fMRIs by precise characterization of the HRF and to define the underlying pathophysiology of negative as well as positive BOLD effects in focal epilepsies. Methods to be used are different HRFs, e.g. patient-region-specific HRF and shape analyses of HRF. Data of 45 paediatric patients with symptomatic, cryptogenic or idiopathic focal epilepsies, which underwent EEG-fMRI studies at our institute will be reanalysed. This will be done at the Montreal Neurological Institute, which gained huge experiences in analysing the HRF in epilepsy. A specific HRF for the different types of epilepsies will increase the sensitivity of EEG-fMRI and is one step toward a better understanding of the generators of epilepsy.