Magnetic source imaging.

Epilepsy surgery primarily aims to control seizures in cases of drug-resistant epilepsy; in addition, neurological or neuropsychological deficits need to be avoided, and social integration improved. Determination of the specific site and extent of interictal and ictal epileptic brain regions is the main task of the presurgical evaluation of partial epilepsies. An additional challenge of the preoperative work-up is to delineate the functionally important regions (motor, somatosensory, language). As a new, non-invasive, functional modality, magnetoencephalography (MEG) yields information that is complementary to electroencephalography (EEG) and magnetic resonance imaging (MRI). As magnetic field distortion by the brain, cerebrospinal fluid, skull and skin is negligible, the technique offers a virtually undistorted view of brain activity and, thus, offers excellent spatiotemporal resolution. In general, MEG is used for focus localization as well as functional mapping as part of the clinical routine. This report presents an overview of the technique, as well as its advantages and limitations in the clinical context of epileptology.