EEG source connectivity to localize the seizure onset zone in patients with drug resistant epilepsy

Abstract

Electrical source imaging (ESI) from interictal scalp EEG is increasingly validated and used as a valuable tool in the presurgical evaluation of epilepsy as a reflection of the irritative zone. ESI of ictal scalp EEG to localize the seizure onset zone (SOZ) remains challenging. We investigated the value of an approach for ictal imaging using ESI and functional connectivity analysis (FC). Ictal scalp EEG from 111 seizures in 27 patients who had Engel class I outcome at least 1 year following resective surgery was analyzed. For every seizure, an artifact-free epoch close to the seizure onset was selected and ESI using LORETA was applied. In addition, the reconstructed sources underwent FC using the spectrum-weighted Adaptive Directed Transfer Function. This resulted in the estimation of the SOZ in two ways: (i) the source with maximal power after ESI, (ii) the source with the strongest outgoing connections after combined ESI and FC. Next, we calculated the distance between the estimated SOZ and the border of the resected zone (RZ) for both approaches and called this the localization error ((i) LEpow and (ii) LEconn respectively). By comparing LEpow and LEconn, we assessed the added value of FC. The source with maximal power after ESI was inside the RZ (LEpow = 0 mm) in 31% of the seizures and estimated within 10 mm from the border of the RZ (LEpow ≤ 10 mm) in 42%. Using ESI and FC, these numbers increased to 72% for LEconn = 0 mm and 94% for LEconn ≤ 10 mm. FC provided a significant added value to ESI alone (p < 0.001). ESI combined with subsequent FC is able to localize the SOZ in a non-invasive way with high accuracy. Therefore it could be a valuable tool in the presurgical evaluation of epilepsy.

Interictal epileptogenic zone localization in patients with focal epilepsy using electric source imaging and directed functional connectivity from low‐densityEEG

“…This is the first study using low‐density scalp EEG during interictal periods with the aim of validating DFC measures. A recent study using the ESI methodology, and a similar Granger‐causality approach, demonstrated the feasibility of this procedure for EZ localization during ictal periods . We demonstrate that both ESI and whole‐brain directed‐connectivity measures using low‐density EEG during interictal spikes are able to localize the EZ with a relatively high sensitivity.…”

“…A recent study using the ESI methodology, and a similar Granger-causality approach, demonstrated the feasibility of this procedure for EZ localization during ictal periods. 14 We demonstrate that both ESI and whole-brain directedconnectivity measures using low-density EEG during interictal spikes are able to localize the EZ with a relatively high sensitivity. We show that the regions with the highest summed outflow, clustering coefficient, betweenness centrality, and efficiency were concordant with the EZ in patients with TLE and ETLE during interictal spikes.…”

“…We showed that left temporal lobe epilepsy (LTLE) and right TLE (RTLE) involve very different network alterations in terms of the main drivers of information flow during interictal spikes and also in the absence of visible epileptic activity . Recent evidence from ictal recording suggests a high localization value for functional connectivity applied to low‐density ictal recordings …”

“…13 Recent evidence from ictal recording suggests a high localization value for functional connectivity applied to low-density ictal recordings. 14 In this study, we investigate whether ESI and DFC can correctly localize the EZ in patients with focal epilepsy (TLE and extra-TLE, ETLE) during interictal spikes, based on clinical recordings (21-38 electrodes). We investigated whether the identified regions with highest source activity and connectivity (summed outflow, clustering coefficient, betweenness centrality, and efficiency) were inside the presumed EZ, defined as the resection area in patients who were seizurefree after surgery, or the epileptogenic lesion in patients who did not undergo surgery.…”

Ictal and interictal electric source imaging in pre‐surgical evaluation: a prospective study

“…In a recently published study, using a high‐density array for LTM, only 14 of 34 (41%) patients had IC activity, in addition to the II discharges . A recent study suggested that combining ESI with functional connectivity analysis increases its accuracy . Although the ESI accuracy reported here (51–62%) was lower than in some previous studies (Table S6), it was similar to the accuracy of the conventional neuroimaging methods.…”