Abstracts

SAM COMPARED WITH ECOG IN CHILDREN WITH FOCAL CORTICAL DYSPLASIA

Abstract number : 3.188
Submission category :
Year : 2002
Submission ID : 891
Source : www.aesnet.org
Presentation date : 12/7/2002 12:00:00 AM
Published date : Dec 1, 2002, 06:00 AM

Authors :
Ryouhei Ishii, Hiroshi Otsubo, Ayako Ochi, Masaomi Kitayama, Jing Xiang, Sylvester H. Chuang, Nathaniel A. Chuang, O. Carter Snead III, Christo Pantev. The Rotman Research Institute for Neuroscience, Baycrest Centre for Geriatric Care, University of Toron

RATIONALE: Accurate localization of the epileptic zone is important for a successful outcome from epilepsy surgery. Patients with focal cortical dysplasia (FCD) had clusters of magnetoencephalography (MEG) spike sources within and extending from the lesion on magnetic source imaging (MSI). Synthetic Aperture Magnetometry (SAM) is a spatially constrained minimum-variance beamformer for MEG and provides three-dimensional images of cortical power changes within specific frequency bands. The purpose of this study was to compare the localization of certain frequencies in the interictal discharges detected by SAM with the location of ictal rhythmic discharges identified by electrocorticography (ECoG) in children with intractable partial seizures secondary to FCD.
METHODS: MEG data were obtained using a whole head helmet-shaped 151-channel SQUID sensor array (Omega 151, CTF Systems Inc.) in a magnetically shielded room. We recorded MEG for 30 minutes in 3 children with intractable partial seizures secondary to FCD and analyzed interictal discharges by using SAM. The first step was to compute the covariance of the data, with band pass filter of delta (1-4Hz), theta (4-8Hz), alpha (8-15Hz), beta (15-30Hz) and gamma (30-60Hz) bands. At each bands SAM weights were computed at 5 mm intervals throughout the entire MR images. We recorded subdural EEG with split screen video monitoring to localize the seizure onset zone. We analyzed ictal subdural EEG data at same frequency bands using Gaussian Wavelet frequency analysis at the most active subdural electrodes in the FCD.
RESULTS: The Wavelet frequency analysis revealed various frequencies in ictal stages, but accumulated beta band in 2 patients, gamma band in one at the time of seizure onset. The interictal SAM analysis demonstrated high z value in alpha (2 patients), beta (3 patients) and gamma (1 patient) frequency bands. SAM delineated the anatomical location of those frequencies corresponding to the seizure onset zone defined by subdural EEG.
CONCLUSIONS: SAM analysis of interictal MEG discharges and ictal recordings on subdural EEG in patients with FCD agree in frequency and extent of epileptogenesis. SAM data from interictal MEG discharges may delineate the intrinsically epileptogenic FCD at the specific frequency band.