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Summary:Purpose: In this study, we tried to show that EEG and magnetoencephalography (MEG) are clinically complementary to each other and that a combination of both technologies is useful for the precise diagnosis of epileptic focus.Methods: We recorded EEGs and MEGs simultaneously and analyzed dipoles in seven patients with intractable localizationrelated epilepsy. MEG dipoles were analyzed by using a BTI Magnes 148-channel magnetometer. EEG dipoles were analyzed by using a realistically shaped four-layered head model (scalp-skull-fluid-brain) built from 2.0-mm slice magnetic resonance imaging (MRI) images.Results: (a) In two of seven patients, MEG could not detect any epileptiform discharges, whereas EEG showed clear spikes. However, dipoles estimated from the MEG data corresponding to the early phase of EEG spikes clustered at a location close to that of the EEG-detected dipole. (b) In two of seven patients, EEG showed only intermittent high-voltage slow waves (HVSs) without definite spikes. However, MEG showed clear epileptiform discharges preceding these EEGdetected HVSs. Dipoles estimated for these EEG-detected HVSs were located at a location close to that of the MEGdetected dipoles. (c) Based on the agreement of the results of these two techniques, surgical resection was performed in one patient with good results.Conclusions: Dipole modeling of epileptiform activity by MEG and EEG sometimes provides information not obtainable with either modality used alone. Key Words: MEG-EEGLocalization-related epilepsy-Dipole.The dipole localization method has been widely used for noninvasive localization of spike foci (1-3). After the development of magnetoencephalography (MEG), most comparative studies of MEG and EEG have focused on comparing the localization accuracy of MEG and EEG dipoles (4,5). We addressed the way in which dipole localization with a combination of MEG and EEG supplements the information obtainable by either technique alone. We try to show that EEG and MEG are clinically complementary to each other, and that a combination of both technologies is useful for the precise diagnosis of epilepsy patients. PATIENTS AND METHODSSubjects were drawn from all the outpatients and inpatients of Okayama University Hospital who were being considered for antiepileptic surgery between July 2000 and June 2001. We obtained consent from the parents of seven of these patients to perform MEG investigation at the Okayama Ryogo Center. The patients consisted of six boys and one girl (average age, 15 years and 1 month; range, 5 years and 7 months to 19 years and 2 months). All the patients had intractable localizationrelated epilepsy.We recorded EEGs and MEGs simultaneously. MEGs were recorded with a 148-channel whole-head magnetometer (BTI Magnes, San Diego, CA, U.S.A.) with simultaneous 21-channel EEG recording by using the international 10-20 system with additional electrodes at Fpz and Oz referenced to the ears. The MEG and EEG sampling rates were 678.17 and 500 Hz. The MEG signal was filtered in real time with a highp...

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