Abstracts

Rationale: Simultaneous recording of EEG and fMRI provide a feasible means of localizing interictal epileptic foci within the brain [1]. This technique may be used to assess target regions identified for surgical resection in medically incurable epilepsies [2]. Currently, a significant percentage of all surgical interventions in epilepsy fail to completely cure the disease. This may be because the target for surgery was only a part of the epileptic network. In neurosurgical decision making, therefore, it is not only important to identify a focal target for resection but also to investigate possible networks of epileptogenic activity. We use functional connectivity analysis with epileptic focus as seed to investigate brain networks associated with that focal region. Methods: Twenty one subjects with intractable epilepsy who were candidates for epileptogenic resection were scanned using a simultaneous EEG-fMRI protocol. Resting state fMRI data were collected on a Siemens MRI scanner using 10 min. runs with 64x64 matrix, alpha=80, TE/TR=30/1550ms. Nineteen channel EEG was recorded at 500 Hz using an MRI compatible EEG system (a modified version of Maglink, NeuroScan, Charlotte, NC). Interictal spike activity timings in their EEGs were visually identified and used in an event-related fMRI analysis to generate functional images of epileptic focal points. These focal points were then used as seed region in the functional connectivity analysis covering the entire brain. The 3D connectivity map was obtained by first averaging the fMRI time activities in the focal region and correlating it with time activities from every voxel in the brain. Networks of epileptogenic activity were visually identified. These networks were evaluated in the context of whether the subject had a successful surgical intervention or not. Results: The results of the analysis show that the functional connectivity map with the epileptic focus as seed region can reveal associated networks. Figures 1a and 1b show the seed region from fMRI data and the corresponding connectivity map of three subjects who had successful surgical intervention. In these cases the surgical target and the fMRI focal points matched. Figures 2a and 2b show the focal seeds and connectivity maps for three subjects for whom surgical intervention failed and the epileptic symptoms persisted even after the surgery. In these cases the focal point obtained from fMRI did not match with the target for surgery determined by standard procedures. The connectivity maps revealed other focal activations that need to be examined as potential targets for intervention. Conclusions: It is clearly shown that simultaneous EEG-fMRI and functional connectivity analysis can be a powerful tool in evaluating targets for surgical intervention in epilepsy. References 1. Jean Gotman et.al. Combining EEG and fMRI: A multimodal tool for epilepsy research. J Magnetic Resonance Imaging. 2006:23:906-920. 2. Frederique Liegeois, et.al. Role of fMRI in the decision-making process: Eplilepsy surgery for children. J. Magnetic Resonance Imaging, 2006:23:933-940.