J Clin Neurol.  2015 Oct;11(4):319-330. 10.3988/jcn.2015.11.4.319.

EEG Source Imaging in Partial Epilepsy in Comparison with Presurgical Evaluation and Magnetoencephalography

• Park CJ
• Seo JH
• Kim D
• Abibullaev B
• Kwon H
• Lee YH
• Kim MY
• An KM
• Kim K
• Kim JS
• Joo EY
• Hong SB

• KMID: 2179751
• DOI: http://doi.org/10.3988/jcn.2015.11.4.319

Abstract

BACKGROUND AND PURPOSE
The aim of this study was to determine the usefulness of three-dimensional (3D) scalp EEG source imaging (ESI) in partial epilepsy in comparison with the results of presurgical evaluation, magnetoencephalography (MEG), and electrocorticography (ECoG).
METHODS
The epilepsy syndrome of 27 partial epilepsy patients was determined by presurgical evaluations. EEG recordings were made using 70 scalp electrodes, and the 3D coordinates of the electrodes were digitized. ESI images of individual and averaged spikes were analyzed by Curry software with a boundary element method. MEG and ECoG were performed in 23 and 9 patients, respectively.
RESULTS
ESI and MEG source imaging (MSI) results were well concordant with the results of presurgical evaluations (in 96.3% and 100% cases for ESI and MSI, respectively) at the lobar level. However, there were no spikes in the MEG recordings of three patients. The ESI results were well concordant with MSI results in 90.0% of cases. Compared to ECoG, the ESI results tended to be localized deeper than the cortex, whereas the MSI results were generally localized on the cortical surface. ESI was well concordant with ECoG in 8 of 9 (88.9%) cases, and MSI was also well concordant with ECoG in 4 of 5 (80.0%) cases. The EEG single dipoles in one patient with mesial temporal lobe epilepsy were tightly clustered with the averaged dipole when a 3 Hz high-pass filter was used.
CONCLUSIONS
The ESI results were well concordant with the results of the presurgical evaluation, MSI, and ECoG. The ESI analysis was found to be useful for localizing the seizure focus and is recommended for the presurgical evaluation of intractable epilepsy patients.

Keyword

partial epilepsy; EEG source imaging; MEG source imaging; source localization; presurgical evaluation; epilepsy surgery

MeSH Terms

Electrodes
Electroencephalography*
Epilepsies, Partial*
Epilepsy
Epilepsy, Temporal Lobe
Humans
Insulator Elements
Magnetoencephalography*
Scalp
Seizures

Figure

• 

  Fig. 1 EEG and MEG dipole source analysis of patient #14 who had left temporal lobe epilepsy. A: EEG dipoles [high-pass filter (HPF)=3 Hz, goodness of fit (GOF) levels ≥70%] were localized in left basal and anterior temporal regions. B: MEG dipoles (HPF=3 Hz, GOF levels ≥70%) were localized in left anterior to middle temporal regions. C: Ictal SPECT showed left temporal hyperperfusion. D: SISCOM showed left anterior to mid temporal hyperperfusion. (E) T2-weighted MRI and (F) FLAIR MRI showed left hippocampal sclerosis. L: left, R: right.

• 

  Fig. 2 EEG and MEG dipole source analysis of patient #4 who had right frontocentral lobe epilepsy. A: EEG dipoles [high-pass filter (HPF)=3 Hz, goodness of fit (GOF) levels ≥70%] were localized in right frontal lobe. B: MEG dipoles (HPF=3 Hz, GOF levels ≥70%) were localized in right frontal and parietal regions. C: FDG-PET showed hypometabolism in right frontoparietal cortex. D: SISCOM showed ictal hyperperfusion in the right dorsolateral and medial frontal cortices. L: left, R: right.

• 

  Fig. 3 Different high-pass filter (HPF) setting. The 64 individual dipoles of patient #26 who had left mesial temporal lobe epilepsy. EEG dipoles were analyzed in preoperative boundary element method (BEM) head model in different HPF settings and superimposed on the postoperative MRI. HPF settings were as follow: (A) 0.5 Hz, (B) 1Hz, (C) 2 Hz, (D) 3 Hz, (E) 4 Hz, (F) 5 Hz, and (G) 6 Hz. Low pass filter settings were all 100 Hz. The H shows averaged dipoles of A-G with the matched color. Circles surrounding each dipole indicate confidence ellipsoid range. Each color indicates different HPF setting (red: 0.5 Hz, orange: 1 Hz, yellow: 2 Hz, green: 3 Hz, bright blue: 4 Hz, blue: 5 Hz, violet: 6 Hz). L: left, R: right.

• 

  Fig. 4 The comparison between ECoG and EEG dipoles of patient #26. The patient had left mesial temporal lobe epilepsy. A: Intracranial EEG electrode locations were plotted on the patient's three dimensional MRI. Red circle indicates the electrode location of ictal ECoG onset, and bright blue circle indicates the location of interictal spikes frequently recorded on ECoG. B: EEG dipoles of averaged 64 spikes with different high-pass filter settings: red: 0.5 Hz, orange: 1 Hz, yellow: 2 Hz, green: 3 Hz, bright blue: 4 Hz, blue: 5 Hz, violet: 6 Hz. The circle around each dipole indicates confidence ellipsoid range. L: left, R: right.

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