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

癫痫患者发作间期的脑电棘波与癫痫的发生有关。尖峰是由皮层的刺激区产生的。脑电功能磁共振成像（EEG-fMRI）是一种非侵入性的刺激区定位方法。脑血管中氧合血红蛋白和脱氧血红蛋白浓度比率的变化反映了神经元活动的变化。这种变化被称为血氧水平依赖效应（BOLD）。在fMRI中，BOLD效应是基于模型（HRF）计算的。发作间期发放导致位于发放区的显著BOLD变化。然而，EEG-fMRI在癫痫患者中提出了两个问题：首先，该方法的灵敏度较低，为40 - 60%，其次，观察到正和负BOLD效应。本研究旨在通过精确表征HRF来提高EEG-fMRI的灵敏度，并确定局灶性癫痫中BOLD负效应和正效应的潜在病理生理学。使用的方法是不同的HRF，例如患者区域特定的HRF和HRF的形状分析。45例有症状，隐源性或特发性局灶性癫痫，在我们的研究所进行脑电图功能磁共振成像研究的儿科患者的数据将重新分析。这将在蒙特利尔神经研究所完成，该研究所在分析癫痫的HRF方面获得了丰富的经验。不同类型癫痫的特异性HRF将增加EEG-fMRI的灵敏度，并且是更好地了解癫痫发生器的一步。

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.