- Magnetoencephalogram (MEG) : Magnetoencephalogram (MEG is the magnetic equivalent of the Electroencephalogram in which a three-dimensional magnetic field of the brain can then be calculated. Superconducting quantum interference device (SQUID) detects the small magnetic fields in the brain that are a marker of neural activity. A disadvantage of MEG is related to that it is expensive and not readily available for clinical applications.