COMPARISON OF TWO PHASE SYNCHRONIZATION ANALYSES TECHNIQUES FOR INTERICTAL FOCUS LATERALIZATION IN MESIAL TEMPORAL LOBE EPILEPSY
Abstract number :
1.130
Submission category :
Year :
2002
Submission ID :
3461
Source :
www.aesnet.org
Presentation date :
12/7/2002 12:00:00 AM
Published date :
Dec 1, 2002, 06:00 AM
Authors :
Alexander Kraskov, Thomas Kreuz, Rodrigo Quian Quiroga, Peter Grassberger, Florian Mormann, Ralph G. Andrzejak, Christian E. Elger, Klaus Lehnertz. John von Neumann Institute for Computing, Research Center Juelich, Juelcih, Germany; Department of Epilepto
RATIONALE: In a number of recent studies, the concept of phase synchronization has been applied to EEGs for description of spatiotemporal dynamics of the epileptic brain. We compare two different phase synchronization analyzes techniques on a theoretical basis. Subsequently the ability of both measures to lateralize the focal hemisphere in patients with mesial temporal lobe epilepsy (MTLE) is investigated.
METHODS: Fifty five interictal artifact-free EEG recordings were selected from 23 MTLE patients. Data were recorded using chronically implanted intrahippocampal depth electrodes each equipped with 10 contacts. We applied two phase synchronization analyzes techniques that are based on two different approaches for extraction of the instantaneous phase, namely the Hilbert and the wavelet transform. We calculate the wavelet transform using complex demeaned Morlet wavelet. For each time and scale the instantaneous phase of the EEG was defined as the argument of the corresponding complex wavelet coefficient. Lateralization of the focal hemisphere was done by comparing the degree of synchronization for ipsi- and contralateral hemispheres after averaging over time and over all combinations of channels for the respective side.
RESULTS: Based on theoretical considerations we show the close relation of the phases defined from Hilbert and wavelet transforms. These phases are identical if prefiltering of the EEG signal is applied before the calculation of the Hilbert transform. The filter characteristics should correspond to the wavelet mother function. Using the Hilbert phase synchronization, we could correctly lateralize the focal hemisphere in 18 of the 23 patients. A better discrimination was achieved by means of wavelet phase synchronization for the scales of the wavelet corresponding to the beta frequency range (20 correct cases).
CONCLUSIONS: The comparison shows good performance of both phase synchronization analyzes techniques for focus lateralization in MTLE. The better discrimination achieved by the wavelet phase synchronization analyzes technique can be explained by its ability to extract more specific information for different frequency ranges. The techniques described in this study might render additional information helpful for an improvement of the presurgical evaluation of MTLE patients.
[Supported by: Deutsche Forschungsgemeinschaft]