Benefit of combined use of EEG and MEG dipole

Purpose: In this study, we tried 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 epileptic focus. Subjects and methods: We recorded EEGs and MEGs simultaneously and analyzed dipoles in five patients suffering from intractable localization-related epilepsy with ages ranging from 13 to 19 years. MEG dipoles were analyzed using a BTI Magnes 148-channel magnetometer. EEG dipoles were analyzed using a realistically shaped four-layered head model (scalp–skull–liquor–brain) built from 2.5-mm-slice MRI images. Results: (1) In two of five patients, MEG could not detect any epileptiform discharges, while EEG showed clear spikes. However, dipoles estimated from the MEG data correspond to the early phase of EEG spikes clustered at a location close to that of the EEG-detected dipole. (2) In two of five patients, EEG showed only intermittent high-voltage slow waves (HVSs) without definite spikes. However, MEG showed clear epileptiform discharges preceding these EEG-detected HVSs. Dipoles estimated for these EEG-detected HVSs were located at a location close to that of the MEG-detected dipoles. Conclusion: Simultaneous recording of MEG and EEG with dipole modeling is more useful for accurate determination of epileptic focus than either technique alone.