Space-oriented segmentation and 3-dimensional source reconstruction of ictal EEG patterns

Abstract

Objectives: Characterization of the EEG pattern during the early phase of a seizure is crucial for identifying the epileptic focus. The purpose of the present investigation was to evaluate a method that divides ictal EEG activity into segments of relatively constant surface voltage distribution, and to provide a 3-dimensional localization of the activity during the different segments.Methods: For each timepoint the electrical voltage distribution on the scalp (the voltage map) was determined from the digitized EEG recording. Through a spatial cluster analysis time sequences where the maps did not change much (segments) were identi®ed, and a 3-dimensional source reconstruction of the activity corresponding to the different mean maps was performed using a distributed linear inverse solution algorithm.Results: Segments dominating early in seizure development were identi®ed, and source reconstruction of the EEG activity corresponding to the maps of these segments yielded results which were consistent with the results from invasive recordings. In some cases a sequence of consecutive segments was obtained, which might re¯ect ictal propagation.Conclusions: Segmentation of ictal EEG with subsequent 3-dimensional source reconstruction is a useful method to non-invasively determine the initiation and perhaps also the spread of epileptiform activity in patients with epileptic seizures. q

Seizure source imaging by means of FINE spatio-temporal dipole localization and directed transfer function in partial epilepsy patients

“…Good performance of equivalent current dipole modeling was demonstrated in source analysis of temporal and frontal lobe epilepsy (Gavaret et al, 2004, 2006). Parameterization of ictal data in time domain or frequency domain was also applied to study ictal source analysis (Worrell et al, 2000; Morlet and Gotman, 2001; Lantz et al, 2001; Boon et al, 2002). The approach applied in this study combines spatio-temporal source localization and source connectivity analysis for seizures.…”

Effects of Repetitive Transcranial Magnetic Stimulation on Spike Pattern and Topography in Patients with Focal Epilepsy

“…Specifically, we applied a modified hierarchical cluster analysis as implemented in Cartool (Topographic Atomize & Agglomerate Hierarchical Clustering (T-AAHC)). Cluster analyses have proven to be a powerful tool for identifying differences in dominant maps between conditions and have been used for characterization of seizure and spike propagation (Lantz et al 2001;Lantz et al 2003) and in the analysis of event-related potentials (for reviews see, Michel et al 2001Michel et al , 2009). The method identifies periods of topographic stability within and between different conditions and defines the sequence of map topographies optimally summarizing the average data (Michel et al 2004;Murray et al 2008).…”

Analysis of the dynamics and origin of epileptic activity in patients with tuberous sclerosis evaluated for surgery of epilepsy

“…Previous attempts to do source analysis of ictal events with spatiotemporal dipoles restricted the study to seizures with few artifacts and good signal to noise ratio, such as temporal lobe seizures (Assaf and Ebersole, 1997). Lantz et al (2001) attempted to address more representative neocortical epilepsies using microstate segmentation of the EEG to obtain snapshots of the intracranial generators throughout the event. This method does not correct for the problem of volume conductor mixing of concomitant activation of different sources which might be present (such as in the events of Figs.…”