Localisation of Epileptic Foci in Children with Focal Epilepsies using 3-Tesla Simultaneous EEG-fMRI Recordings

Objective: EEG-related fMRI (EEG-fMRI) allows to detect focal epileptic brain activity by measuring spike related BOLD responses. Several studies focussed on the localization of the irritative network in adult epilepsy patients [1], but fMRI knowledge on the developing brain is lacking. This study applied the EEG-fMRI technique to the pediatric age group and evaluated possible clinical implications.

Fig. 1A

Fig. 1B

Methods: Nine children (age: 11.6±3.6 years, with idiopathic (3), symptomatic (3) and cryptogenic (3) epilepsy) were investigated under sedation using simultaneous recordings of EEG (Brain Vision, MR-compatible EEG amplifier, 32 channels according to 10–10 system, impedance <5 kOhm, 5000Hz sampling rate, 250Hz lowpass) and fMRI (3-T Philips Achieva scanner, EPI-T2* sequences, TR=2250 ms, TE=64 ms, 64×64 matrix, FOV=210mm, flip angle=90°, 240 scans in 20min.). EEGs were processed offline using BrainVision-Analyser and BESA software. After spike detection, an event-related design was used to analyse the BOLD responses (SPM-2). Resulting (de)activation patterns were co-registered to T1-weighted anatomical images.

Results: In all subjects the BOLD responses corresponded with the bioelectrial (EEG) localization of interictal discharges. Most children showed a negative BOLD response („deactivation“) corresponding with the area of interictal spikes and few additional (de)activation patterns were observed. The negative BOLD on Fig. 1a corresponds to the right central spikes (n=609), and the one on Fig. 1b correlates with the right temporal spike localization (n=74), in a patient with right-sited polymicrogyria in the area of the Sylvian fissure. Negative BOLD responses may differentiate pediatric from adult epilepsy patients [2,3]. Developmental aspects as well as influence of vigilance on the BOLD signal may explain a specific hemodynamic response in young subjects. Difficulties applying EEG-fMRI technique in children will be discussed and methodological suggestions will be provided.

Conclusion: Simultaneous EEG-fMRI recordings in a 3-T scanner may be successfully used to localize the irritative zones in children suffering from focal epilepsies, and revealed negative BOLD responses in this area. Nature and origin of the negative BOLD in many young subjects will be investigated in future studies.

References:

[1] Gotman et al., Journal of Clinical Neurophysiology 2004; 21: 229–240

[2] Kobayashi et al., Neurology 2005; 64: 1263–1266

[3] Federico et al., Neurology 2005; 64: 1125–1130