Techniques for DC magnetoencephalography.

DC shifts are known to occur in association with a number of physiologic phenomena including spreading depression, hypoxia, epilepsy, and hypercapnia and possibly in migraine, closed head injury, and ischemia. Magnetoencephalography (MEG) makes it possible to record these shifts by prolonged DC monitoring of brain activity and offers several advantages over DC EEG and DC electrocorticography. Among the advantages of MEG is its non-invasive nature and the lack of impedance changes at the electrode-tissue interface that produce baseline shifts in DC EEG. In DC MEG measurements, great care must be taken in dealing with a variety of artifactual signals. Environmental noise can be reduced by magnetic shielding and recognized by use of reference magnetometers. Patient-generated artifacts are numerous and can be recognized and limited by a variety of methods.