Rhythmical Index of Ictal High Frequency Oscillations in Stereo-Electroencephalograph from Epileptic Patients

High-frequency oscillations (HFOs) are considered reliable markers of epileptic tissues. Digital filter is widely used to extract the HFOs, but it also introduces fake oscillations because of Gibbs effects. In this paper we propose a pipeline for HFOs extraction using ensemble empirical mode decomposition (EEMD) method. Stereo-Electroencephalograph (SEEG) is decomposed into intrinsic mode functions (IMFs). Rhythmical index (RI) of detected HFOs is calculated, which corresponds to the normalized angular acceleration of oscillation. The ictal SEEG is processed with nine seizures recorded from three patients, who underwent surgical intervention and got seizure free. Results show that proposed pipeline can extract HFOs from ictal SEEG automatically. RI values of HFOs in resected area are higher than non-resected area. The proposed pipeline with RI measure may serve as an effective way for extracting pathological HFOs.