Hazards of the MEG Environment
There are no known risks associated with MEG/EEG recordings. The MEG procedure consists of sitting in a chair or lying on a bed while your head is slid into the helmet-shaped bottom of the MEG device that contains magnetic field sensors. These superconducting sensors passively detect weak magnetic fields outside the head produced by brain activity. It is thus a non-invasive technique and uses neither strong magnetic fields nor radioactivity and injected contrast agents.
If subjects are recommended to not have an MEG/EEG recording, it is due to the possibility of acquiring poor data, and not due to the possibility of personal harm (thus a completely different hazard than with the magnets).