Automated interictal source localisation based on high-density EEG

Abstract

To study the accuracy of automated interictal EEG source localisation based on high-density EEG, and to compare it to low-density EEG. Methods: Thirty patients operated for pharmacoresistant focal epilepsy were retrospectively examined. Twelve months after resective brain surgery, 18 were seizure-free or had 'auras' only, while 12 had persistence of disabling seizures. Presurgical 257-channel EEG lasting 3-20 h was down-sampled to 25, 40, and 204 channels for separate analyses. For each electrode setup, interictal spikes were detected, clustered, and averaged automatically before validation by an expert reviewer. An individual 6-layer finite difference head model and the standardised low-resolution electromagnetic tomography were used to localise the maximum source activity of the most prevalent spike. Sublobar concordance with the resected brain area was visually assessed and related to favourable vs. unfavourable postsurgical outcome. Results: Depending on the EEG setup, epileptic spikes were detected in 21-24 patients (70-80%). The median number of single spikes per average was 470 (range 17-15,066). Diagnostic sensitivity of EEG source localisation was 58-75%, specificity was 50-67%, and overall accuracy was 55-71%. There were no significant differences between low-and high-density EEG setups with 25 to 257 electrodes. Conclusion: Automated high-density EEG source localisation provides meaningful information in the majority of cases. With hundreds of single spikes averaged, diagnostic accuracy is similar in high-and low-density EEG. Therefore, low-density EEG may be sufficient for interictal EEG source localisation if high numbers of spikes are available.

Comparative analysis of background EEG activity in juvenile myoclonic epilepsy during valproic acid treatment: a standardized, low-resolution, brain electromagnetic tomography (sLORETA) study

“…EEG source localization based on recordings with a limited number of electrodes can be better integrated into the clinical setting and broaden the practical applications. sLORETA localization properties have been independently validated [ 45 ] and the accuracy has been demonstrated to be similar in high- and low-density EEG [ 46 , 47 ]. Therefore, we believe that there is a justification for reporting our results.…”

Comparative analysis of background EEG activity based on MRI findings in neonatal hypoxic-ischemic encephalopathy: a standardized, low-resolution, brain electromagnetic tomography (sLORETA) study

“…Also, the high-density EEG with additional electrodes can improve the results of source reconstruction. However, the properties of sLORETA localization have been independently validated [ 25 ] with accuracy similar in high- and low-density EEG [ 40 , 41 ]. Therefore, we believe that our results are justified.…”

Electric Source Imaging in Presurgical Evaluation of Epilepsy: An Inter-Analyser Agreement Study

“…All patients underwent long term video-EEG (LTM) recording in the epilepsy monitoring unit, where at least one seizure was detected. LTM EEG was recorded using 40 scalp electrodes, in accordance with the 10-10 setting, by adding to the standard IFCN 25-channel electrodes [ 20 ] eight intermediate electrodes (FC1, FC2, FC5, FC6, CP1, CP2, CP5, CP6) and seven inferior electrodes (AF1, AF2, PO1, PO2, IO1, IO2, Iz) [ 16 ]. Subsequently, high density EEG (HD) was performed in 15 patients (median age: 29 years, range 12–61; 7 females).…”

“…The inverse solution method, the number of electrodes (low density, extended scalp array, high density or very high density), the signal (ictal or interictal) and the software used to perform ESI are all factors that have to be considered when performing ESI [ 7 , 13 , 14 , 15 , 16 , 17 , 18 ]. Therefore, several studies were conducted to explore differences between various inverse solutions [ 14 , 15 ], interictal and ictal source imaging [ 13 ], low and high density EEG [ 16 , 17 , 18 ] and different software [ 10 ]. However, in clinical practice, in spite of a standardized analysis protocol, ESI includes steps with subjective decisions about the individual patient by the analyser, i.e., the expert doing the ESI.…”