Source localization in magnetoencephalography to identify epileptogenic foci.

RATIONALE

Magnetoencephalography (MEG) is useful to localize epileptic foci in epilepsy as MEG has higher spatio-temporal resolution than conventional diagnostic imaging studies; positron emission computed tomography, single photon emission computed tomography and magnetic resonance imaging (MRI).

METHODS

We use 204-channel helmet-shaped MEG with a sampling rate of 600 Hz. A single dipole method calculates equivalent current dipoles to localize epileptic sources. The equivalent current dipoles are superimposed onto MRI as magnetic source imaging (MSI). Ictal MEG data are analyzed using time-frequency analysis. The power spectrum density is calculated using short-time Fourier transform and superimposed onto MRI results.

RESULTS

Clustered equivalent current dipoles represent epileptogenic zones in patients with localization-related epilepsy. The surgical plan is reliably developed from source localizations of dipoles and power spectrum of interictal spike discharges, and ictal frequency.

CONCLUSION

MEG is indispensable in diagnosis and surgical resection for epilepsy to accurately localize the epileptogenic zone.