Localization of Epileptogenic Zone: A Graph Theoretical Approach

For a class of focal epileptic patients having drug-resistant epilepsy, resective surgery seems to be a valid option for treatment. In case of surgery, a minimum amount of cerebral cortex known as Epileptogenic Zone (EZ) will be removed to achieve seizure freedom. Presurgical assessment is an important task since the outcome of surgery depends on how precisely EZ is localized. Analysis of electrical activities of the brain will help in localizing EZ. Stereo-Electroencephalogram (SEEG) is an invasive methodology to explore the bioelectrical activities of deep brain structures. Graph theory can be used for the analysis of SEEG, where each channel of SEEG is taken as a node and cross power transmission in beta and gamma frequency subbands are taken as an edge connecting them. Laplacian centrality measure is used to find the relative importance of a node in this graph and it represents the drop in Laplacian energy when that particular node is removed from the graph. In focal channels (channels in the EZ), at the seizure onset, there is a sharp increase in Laplacian centrality, which shows the extent of the contribution of these channel regions in seizure genesis. Finally, we have marked this extent of increase in centrality value to rank all the channels in the order of their epileptogenicity.