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Session: Neurophysiology: Clinical Neurophysiology
Session starts: Thursday 24 January, 13:30
Presentation starts: 13:30
Room: Lamoraalzaal

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Jan de Munck (VU University Medical Center)
Petra van Houdt (Kempenhaeghe/VU University Medical Center)
Albert Albert Colon (Kempenhaeghe)
Frans Leijten (University Medical Center Utrecht)
Geertjan Huiskamp ( University Medical Center Utrecht)
Paul Boon (Kempenhaeghe)
Pauly Ossenblok (Kempenhaeghe)

Abstract:
Co-registration of EEG and functional MRI (EEG-fMRI) enables the detection of the brain regions involved with interictal epileptiform discharges (IEDs). Therefore, EEG-fMRI is a potential tool in the pre-operative work-up of epilepsy surgery. The goal of this study was to obtain more insight in the clinical value of EEG-fMRI. For those purposes, the EEG-fMRI results were systematically compared to the interictal invasive EEG recordings, to the seizure onset zone, and to the resection area. The EEG-fMRI data of 16 patients were included who were implanted with subdural grids. An IED-density function was extracted from the EEG indicating the number of IEDs occurring during each fMRI scan. This density function was correlated to the fMRI signals through a general linear model framework (GLM), yielding a correlation pattern of brain regions activated during IEDs, as well as an estimate of the associated hemodynamic response function (HRF). For the validation of these results, a quantitative approach was developed [1,2] revealing the spatiotemporal patterns of the IEDs present in the invasive EEG data. These spatial and temporal patterns were visualized at the same anatomical MRI as the EEG-fMRI data. Finally, the interictal EEG-fMRI results were related to the clinically more relevant seizure onset zone and resection area. In all patients, EEG-fMRI analysis yielded multiple activated BOLD regions of which at least one overlapped with the active electrodes in the invasive EEG data. In 11 of the 16 data sets, multiple EEG-fMRI areas were concordant with active ECoG electrodes. Interestingly, one of those concordant areas appeared to be related to the early onset of the IEDs, suggesting that the other concordant EEG-fMRI areas were related to propagation of the activity. No indications were found that the shape of the HRF was predictive for the role of the EEG-fMRI cluster within the interictal network. Finally, EEG-fMRI clusters included the complete seizure onset zone in 83% and the resection area in 90% of the data sets. This study shows that EEG-fMRI has substantial predictive value regarding both the onset zone and resection area and, therefore, it could play an important role during the planning of implantation strategy of the surgical candidates. REFERENCES [1] Van Houdt PJ, Ossenblok PPW, Colon AJ, Boon PAJM and De Munck JC, A framework to integrate EEG-correlated fMRI and intracerebral recordings, NeuroImage, 60:2042–2053, (2012). [2] Van Houdt PJ, De Munck JC, Leijten FSS, Huiskamp GJM, Colon AJ, Boon PAJM, Ossenblok PPW, EEG-correlated fMRI evaluated with electro-corticographical and clinical outcome measures as gold standards, NeuroImage, submitted, (2012).