Hamandi, K.; (2008) Functional MRI of focal and generalised interictal epileptiform discharges. Doctoral thesis , University of London.

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Abstract

Localizing the source of epileptic discharges is important in gaining a greater understanding of the disease, classifying epilepsy, and identifying areas suitable for potentially curable surgical resection. Functional imaging measures haemodynamic, metabolic or neurochemical correlates to localise neural activity. Combining EEG with functional MRI (EEG-fMRI) allows the localisation of haemodynamic correlates of neuronal events recorded on surface EEG. The work in this thesis aims to identify the spatial haemodynamic correlates of interictal epileptiform discharges (IED) in patients with epilepsy using EEG-fMRI. Five studies form the main body of this thesis. In the first study, 46 patients with frequent generalised spike wave activity (GSW) were studied with EEG-fMRI on a 1.5 Tesla scanner. The main finding was of a characteristic pattern of fMRI signal decrease in frontal, parietal and posterior cingulate cortex, areas of association cortex, during GSW. In the second study, 4 patients from this first series were re-studied with a 3 Tesla scanner. A high degree of reproducibility was seen in the spatial distribution of fMRI changes. Perfusion MRI with an arterial spin label sequence was used that showed a decrease in blood flow to these areas during GSW. In the third study, a novel method for the analysis of fMRI data in epilepsy, temporal clustering analysis (TCA) was assessed. The technique was confounded by subject motion, and we were unable to reliably detect correlates of IED. The fourth study moves away from correlating visually identified IEDs on the EEG, and correlates power fluctuations in the delta frequency band with simultaneously acquired fMRI. Finally a combination of EEG-fMRI and MR tractography were used to study a patient with temporal lobe epilepsy. The issues surrounding potential use of EEG-fMRI as a clinical tool are discussed.

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