Abstract
BACKGROUND AND PURPOSE: Simultaneous EEG/fMRI is an effective noninvasive tool for identifying and localizing the SOZ in patients with focal epilepsy. In this study, we evaluated different thresholding strategies in EEG/fMRI for the assessment of hemodynamic responses to IEDs in the SOZ of drug-resistant epilepsy.
MATERIALS AND METHODS: Sixteen patients with focal epilepsy were examined by using simultaneous 92-channel EEG and BOLD fMRI. The temporal fluctuation of epileptiform signals on the EEG was extracted by independent component analysis to predict the hemodynamic responses to the IEDs. We applied 3 different threshold criteria to detect hemodynamic responses within the SOZ: 1) PA, 2) a fixed threshold at P < .05 corrected for multiple comparison (FWE), and 3) FAV (4000 ± 200 activated voxels within the brain).
RESULTS: PA identified the SOZ in 9 of 16 patients; FWE resulted in concordant BOLD signal correlates in 11 of 16, and FAV in 13 of 16 patients. Hemodynamic responses were detected within the resected areas in 5 (PA), 6 (FWE), and 8 (FAV) of 10 patients who remained seizure-free after surgery.
CONCLUSIONS: EEG/fMRI is a noninvasive tool for the presurgical work-up of patients with epilepsy, which can be performed during seizure-free periods and is complementary to the ictal electroclinical assessment. Our findings suggest that the effectiveness of EEG/fMRI in delineating the SOZ may be further improved by the additional use of alternative analysis strategies such as FAV.
Abbreviations
- BOLD
- blood oxygen level–dependent
- EEG
- electroencephalography
- FAV
- fixed numbers of activated voxels
- FWE
- family-wise error
- FWHM
- full width at half maximum
- IC
- independent component
- IED
- interictal epileptic discharge
- LTLE
- lateral temporal lobe epilepsy
- MTLE
- mesial temporal lobe epilepsy
- PA
- peak activation
- SOZ
- seizure-onset zone
- © 2012 American Society of Neuroradiology
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