Abstracts

Simultaneous fMRI and EEG may localize the generators of interictal spikes recorded on scalp EEG. Temporal clustering analysis (TCA) is a method to analyze fMRI images independently of EEG information. TCA seeks to identify resting state activations related to the epileptogenic zone. The objective of this study was to compare the results of these two analyses in a series of patients with temporal lobe epilepsy (TLE). BOLD fMRI images were acquired in 22 TLE patients on a 1.5T MRI scanner with simultaneous continuous EEG in two-hour sessions at the MNI (64x64x25, 5mm x 5mm x 5mm, TR=3sec, 120 volumes per series, 8-10 series per patient). For EEG-BOLD analysis, EEGs were processed offline and spikes were identified in the filtered EEG for event-related analysis. For the TCA-BOLD analysis, only the first three series were used. Data were analyzed by previously published TCA methods in which a histogram is created indicating the number of voxels that reach at least 80% of their maximum at each time point. Activated regions were determined by using a fixed-effects analysis of the three series. The concordance of the temporal lobe activation identified by the two methods and the temporal lobe spikes were assessed. Patients were divided into those with unilateral and those with bilateral independent temporal lobe spikes on EEG. One patient[apos]s fMRI was not analyzed due to excess motion. Fourteen patients had unilateral spikes on EEG: 12/14 had TCA-BOLD temporal activation (6 were ipsilateral to the EEG spikes, and 2 had bilateral activation with predominance ipsilateral to the spikes) and 9/14 showed EEG-BOLD activation (2 were ipsilateral to the EEG spikes, 5 had bilateral activation with predominance ipsilateral to the spikes, one had bilateral activation with no side predominance). Seven patients had bilateral independent temporal spikes on EEG: all patients showed TCA-BOLD activation in the temporal lobes, but it was bilateral (concordant with the EEG) in 3; 4/7 patients showed EEG-BOLD temporal lobe activation, bilateral in 3. Overall, we observed an agreement between both methods in 7/11 patients. Activations in the temporal lobes were detected in 90% of patients using TCA-BOLD and in 68% using EEG-BOLD. TCA, which has the advantage of not using the information from the EEG, was concordant with EEG-BOLD analysis in 64% of those who showed activations, and disclosed responses not present in the former one in 5. TCA-BOLD could lateralize the underlying structural MRI lesion in 52% of the patients, similar to that observed with EEG-BOLD analysis (48%). More development is required for both methods. (Supported by Epilepsy Foundation and the Canadian Institutes of Health Research, Preston Robb MNI fellowship, and Savoy Foundation for Epilepsy.)