Objective

The irritative zone - the area generating epileptic spikes - can be studied non-invasively during the interictal period using Electrical Source Imaging (ESI) and simultaneous electroencephalography-functional magnetic resonance imaging (EEG-fMRI). Although the techniques yield results which may overlap spatially, differences in spatial localization of the irritative zone within the same patient are consistently observed. To investigate this discrepancy, we used Blood Oxygenation Level Dependent (BOLD) functional connectivity measures to examine the underlying relationship between ESI and EEG-fMRI findings.

Methods

Fifteen patients (age 20–54), who underwent presurgical epilepsy investigation, were scanned using a single-session resting-state EEG-fMRI protocol. Structural MRI was used to obtain the electrode localisation of a high-density 64-channel EEG cap. Electrical generators of interictal epileptiform discharges were obtained using a distributed local autoregressive average (LAURA) algorithm as implemented in Cartool EEG software. BOLD activations were obtained using both spike-related and voltage-map EEG-fMRI analysis. The global maxima of each method were used to investigate the temporal relationship of BOLD time courses and to assess the spatial similarity using the Dice similarity index between functional connectivity maps.

Results

ESI, voltage-map and spike-related EEG-fMRI methods identified peaks in 15 (100%), 13 (67%) and 8 (53%) of the 15 patients, respectively. For all methods, maxima were localised within the same lobe, but differed in sub-lobar localisation, with a median distance of 22.8 mm between the highest peak for each method. The functional connectivity analysis showed that the temporal correlation between maxima only explained 38% of the variance between the time course of the BOLD response at the maxima. The mean Dice similarity index between seed-voxel functional connectivity maps showed poor spatial agreement.

Significance

Non-invasive methods for the localisation of the irritative zone have distinct spatial and temporal sensitivity to different aspects of the local cortical network involved in the generation of interictal epileptiform discharges.

中文翻译：

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通过电源成像和与脑电图相关的功能磁共振成像分析确定的刺激性区域的功能连通性

目的

可以在发作期使用电源成像（ESI）和同步脑电图功能磁共振成像（EEG-fMRI）进行无创研究刺激性区域-产生癫痫高峰的区域。尽管该技术产生的结果可能在空间上重叠，但始终观察到同一患者内刺激性区域的空间定位差异。为了调查这种差异，我们使用了血氧依赖水平（BOLD）功能连通性度量来检查ESI和EEG-fMRI结果之间的潜在关系。

方法

使用单次静息状态EEG-fMRI方案对15例（20-54岁）进行了术前癫痫检查的患者进行了扫描。结构MRI用于获得高密度64通道EEG帽的电极定位。使用在Cartool EEG软件中实现的分布式局部自回归平均值（LAURA）算法，可以获取发作期癫痫样放电的发电机。使用与尖峰相关和电压图EEG-fMRI分析获得大胆激活。每种方法的全局最大值用于调查BOLD时间进程的时间关系，并使用功能连接图之间的Dice相似性指数评估空间相似性。

结果

ESI，电压图和与峰值相关的EEG-fMRI方法分别确定了15例患者中的15例（100％），13例（67％）和8例（53％）的峰值。对于所有方法，最大值均位于同一瓣内，但在亚瓣下定位不同，每种方法的最高峰之间的中位距离为22.8 mm。功能连通性分析表明，最大值之间的时间相关性仅解释了最大值处BOLD响应的时间过程之间38％的方差。种子体素功能连接图之间的平均Dice相似性指数显示差的空间一致性。

意义

用于定位刺激性区域的非侵入性方法对参与发作间期癫痫样放电的局部皮质网络的不同方面具有明显的时空敏感性。