Epileptic seizure propagation analysis

This proposal is the revision of the FWF project nr. P 21619-N13 "Epileptic seizure propagation analysis". We did some changes and Prof. Christoph Baumgartner, a renowned physician and researcher in the fields of epilepsy, joined our team. A resective neurosurgical intervention can allow a successful treatment of therapy refractory patients. For the exact localization of the epileptic focus, EEG data are presurgically recorded and visually analyzed by neurologists. The analysis of these data is extremely difficult and time-intensive. The planned research project proposes an automated focus detection and seizure propagation analysis for epileptic seizures for the aforementioned presurgical monitoring by means of time series analysis methodology. Based on invasive and scalp EEG data, spatial and temporal dependencies of brain areas shall be determined and analyzed during epileptic seizures. We want to aid physicians in the difficult interpretation of these EEG signals. The planned research project comprises the following parts: 1. In a first step the temporal structure of the EEG recordings, which are highly instationary bio signals, shall be studied. Hereby, dynamic segmentation and methods for the detection of local stationarity are employed. 2. Based on these results, algorithms for reduction of the used input channels shall be developed. Methods like the An algorithm, which perform a dynamic channel selection, could be appropriate. Furthermore, by means of dynamic factor models we intend to model the fact that electrical signals originating from one source are recorded by several electrodes. 3. By means of graphical modeling and appropriate dependency measures coupling effects between the different electrodes shall be analyzed. The evolution of the obtained dependencies shall give a hint for the localization of the focus and the propagation of the seizure. Neurophysical informations shall be involved in the modeling. 4. We want to investigate the circumstances where scalp EEG data is sufficient for our analysis, and when invasive EEG data really yields relevant new information. Furthermore we want to compare the results of the EEG analysis with other investigation methods.

This project dealt with quantitative approaches in the presurgical evaluation of epilepsy patients. It led to the development of four automatic methods for epileptic seizure propagation analysis in invasive EEG (electrocorticography, ECoG), which allow to determine the seizure onset zone (SOZ) and the initial seizure spread.Epilepsies, defined as disorders with recurrent unprovoked seizures, are among the most common neurological diseases. In case of focal epilepsy, seizures are characterized by abnormal synchronized neuronal discharge in circumscribed networks in one hemisphere. About one third of focal epilepsy patients suffer from drug resistance, and epilepsy surgery has become a valuable treatment option for them. Presurgical evaluation relies on long-term video-EEG monitoring, but surface electroencephalography (EEG) is often limited by movement artifacts, suppression of high frequencies and low spatial resolution. In contrast, invasive subdural strip electrodes (ECoG) allow for a better identification of the SOZ. As the visual inspection of the ECoG recordings is a time-demanding and highly subjective task, computational approaches to epileptic seizure propagation analysis are clinically desired.For this purpose, three quantitative approaches for epileptic seizure propagation analysis were developed, successfully applied to one patient and compared with clinical findings:First, the detection of ictal high-frequency oscillations (HFOs) allows to determine the HFO-generating zone which is highly correlated with the SOZ.Second, the application of causality measures in the context of autoregressive modeling (AR) allows to determine the SOZ. The initial spread of hyper-synchronous epileptic activity is indicated by arrows, which point away from the SOZ.Third, segmentation of the individual channels and classification of the segments regarding their epileptic character yields the SOZ and the initial seizure spread. The temporal delay of the start of epileptic activity on different channels is an indicator for seizure propagation. The channels showing epileptic activity first mark the SOZ.