MEG (magnetoencephalogram)
It is a machine similar to the EEG but instead of detecting electrical fields, it captures magnetic fields of the brain. Usually, the EEG electrodes that rest on the scalp are blocked by many layers (skin, bone, coverings of the brain) from the deep structures of the brain. This has the potential of interfering with the detection of the electrical signals. In contrast, the MEG can capture activity originating in deep structures of the brain directly because it is not affected by those obstacles.
Technically: the MEG is a very expensive machine (worth millions of dollars) that sits in a shielded room. This shield is needed to make sure that the only magnetic field that is being picked up is coming from the brain. All magnetic fields from other outside sources are blocked. It is only available in a few epilepsy centers in the world. It can be of great help in identifying the source of the patients’ seizures.