And those, i think, are just from the fixed magnets (which may be a type of superconducmting electromagnet thats just normally on.). During a scan, dont mangetic fields go way way up? The fixed ones are just there for stability and whatnot.
They are superconducting magnets kept that way through cryogenic helium. They can lose their magnetism through a process called quenching. If you search on youtube for "MRI quench" there are several videos of people messing around with MRI's before they get decommissioned. Not exactly safe.
