Visual analysis of high density EEG: as good as electrical source imaging?

Abstract Objective In this study, we sought to determine whether visual analysis of High Density EEG (HD-EEG) would provide similar localizing information comparable to Electrical Source Imaging (ESI). Methods HD-EEG (256 electrodes) recordings from 20 patients suffering from unifocal, drug-resistant epilepsy (13 women, mean age 29.1±2.62 years, 11 temporal lobe epilepsy) were examined. In the visual analysis condition, we identified the 5 contacts with maximal spike amplitude and determined their localization with respect to the underlying cortex. ESI was computed using LAURA algorithm of the averaged spikes in the patient’s individual MRI. We considered the localization “correct” if all 5 contacts were concordant with the resection volume underneath, or if ESI was located within the resection as determined by the post-operative MRI. Results Twelve patients were postoperatively seizure-free (Engel Class IA), eight in class IB to IV. Visual analysis and ESI provided sensitivity of 58% and 75%, specificity of 75% and 87% and accuracy of 65% and 80%, respectively. In 70% of cases, Visual Analysis and ESI provided concordant results. Conclusions Localization of the electrodes with maximal spike amplitude provides very good estimation of the localization of the underlying source. However, ESI has a higher accuracy and adds 3D information, therefore it should remain the tool of choice for presurgical evaluation. Significance The present study proposes the possibility to analyse HD-EEG visually, in tandem with ESI or alone, if ESI is not accessible.