Abstracts

3D source localization of an epileptic seizure using non-invasive EEG recordings often suffers from inaccuracies resulting from other activity generators not related to the epileptic zone. These generators may be active for only short time intervals in parallel to the source activity, shielding epileptic-relevant information. Localizing the epileptic zone using methods as BESA is based on extracting features related to the spatial form of the wave in a given very short time interval. In contrast, our new method, TDSL, is based on identifying ictal epileptic-relevant information on a much longer time scale, reducing the influence of other sources. In cases of a single epileptic focus we aim at isolating the activity resulting from that source, and then by applying a dipole source localization algorithm, identify the exact location. We analysed three scalp ictal EEG recordings from patients with temporal lobe epilepsy. These patients were known to have a single temporal epileptic focus confirmed by MRI scan and a subsequent surgical procedure. Scalp EEG was digitally recorded with electrodes placed according to 10/20 system, using 23 channels. An interval of 4-6 seconds from the onset of each ictal scalp recording was sliced as an input data to the TDSL algorithm for identifying source-related typical rhythmic waveform in each electrode during the time interval. The result of this process, namely, the epileptic activity in each electrode, was used as an input to the localization process based on solving the EEG inverse problem. In these three patients our algorithm has accurately identified the ictal onset zone in accordance with raw EEG analysis and the subsequent surgical outcome. The results of this preliminary study illustrate the possible contribution of a time domain source localization analysis of ictal EEG epileptic activity. TDSL methods may also be used to evaluate the propagation of the epileptic activity to cortical areas distant from the source.