Medical Image and Signal Processing Group, Department of Electronics and Information Systems, Ghent University - iMinds, Ghent, Belgium.
Epilepsia. 2013 Aug;54(8):1409-18. doi: 10.1111/epi.12206. Epub 2013 May 3.
Fifteen percent to 25% of patients with refractory epilepsy require invasive video-electroencephalography (EEG) monitoring (IVEM) to precisely delineate the ictal-onset zone. This delineation based on the recorded intracranial EEG (iEEG) signals occurs visually by the epileptologist and is therefore prone to human mistakes. The purpose of this study is to investigate whether effective connectivity analysis of intracranially recorded EEG during seizures provides an objective method to localize the ictal-onset zone.
In this study data were analyzed from eight patients who underwent IVEM at Ghent University Hospital in Belgium. All patients had a focal ictal onset and were seizure-free following resective surgery. The effective connectivity pattern was calculated during the first 20 s of ictal rhythmic iEEG activity. The out-degree, which is reflective of the number of outgoing connections, was calculated for each electrode contact for every single seizure during these 20 s. The seizure specific out-degrees were summed per patient to obtain the total out-degree. The electrode contact with the highest total out-degree was considered indicative of localization of the ictal-onset zone. This result was compared to the conclusion of the visual analysis of the epileptologist and the resected brain region segmented from postoperative magnetic resonance imaging (MRI).
In all eight patients the electrode contact with the highest total out-degree was among the contacts identified by the epileptologist as the ictal onset. This contact, that we named "the driver," always laid within the resected brain region. Furthermore, the patient-specific connectivity patterns were consistent over the majority of seizures.
In this study we demonstrated the feasibility of correctly localizing the ictal-onset zone from iEEG recordings by using effective connectivity analysis during the first 20 s of ictal rhythmic iEEG activity.
15%至 25%的耐药性癫痫患者需要进行侵入性视频脑电图（EEG）监测（IVEM），以精确划定发作起始区。这种基于记录的颅内 EEG（iEEG）信号的划定是由癫痫专家通过视觉进行的，因此容易出现人为错误。本研究的目的是研究在癫痫发作期间记录的颅内 EEG 的有效连通性分析是否提供了一种定位发作起始区的客观方法。
本研究分析了 8 名在比利时根特大学医院接受 IVEM 的患者的数据。所有患者均有局灶性发作起始，并在切除性手术后无癫痫发作。在 ictal 节律性 iEEG 活动的前 20 秒计算有效连通模式。在这 20 秒内，计算每个电极接触点在每个单个癫痫发作期间的出度，出度反映了传出连接的数量。对每个患者的特定癫痫发作的出度进行求和，以获得总出度。总出度最高的电极接触点被认为是定位发作起始区的指标。将这一结果与视觉分析结果和术后磁共振成像（MRI）分割的切除脑区进行比较。
在所有 8 名患者中，总出度最高的电极接触点都在癫痫专家确定为发作起始的接触点中。该接触点，我们称之为“驱动点”，始终位于切除的脑区中。此外，患者特定的连通模式在大多数癫痫发作中是一致的。
在这项研究中，我们通过使用癫痫发作期间前 20 秒的有效连通性分析，证明了从 iEEG 记录中正确定位发作起始区的可行性。
