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EEG中的发作间期棘波与癫痫的发生有关。棘波是由大脑皮层的刺激区产生的。脑电功能磁共振成像(EEG-fMRI)是一种无创定位刺激区的方法。神经元活动的变化反映在脑血管中氧合和脱氧血红蛋白浓度比的变化上。这种变化被称为血氧水平依赖效应(BOLD)。在fMRI中，BOLD效应是根据血流动力学反应函数(HRF)模型计算的。发作间期的穗形成导致了位于穗产生区域的显著的大胆变化。然而，癫痫患者的EEG-fMRI存在两个问题：一是灵敏度低，仅为40~60%；二是可观察到阳性和阴性BOLD效应。本研究旨在通过HRF的精确表征来提高EEG-FMRI的敏感性，并明确局灶性癫痫负向和正向BOLD效应的潜在病理生理学基础。使用的方法是不同的HRF，例如针对患者地区的HRF和HRF的形状分析。本文将对45例有症状、隐源性或特发性局灶性癫痫的儿科患者进行脑电-功能磁共振检查，并对其进行再分析。这将在蒙特利尔神经学研究所完成，该研究所在分析癫痫的HRF方面获得了丰富的经验。针对不同类型癫痫的特定HRF将提高EEG-fMRI的敏感性，并有助于更好地了解癫痫的发生原因。

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.