Oops!

When a sign near an MRI scanner tells you not to bring metal anywhere it, pay attention.

An expensive MRI machine at Virginia Mason Medical Center in Seattle suffered hundreds of thousands of dollars in damage when a metal floor buffer was mistakenly placed nearby and was sucked in by the machine's powerful magnets, KIRO 7 Eyewitness News reported. The incident occurred Jan. 3 when a member of the housekeeping staff improperly took the buffer near the machine, despite a warning sign not to use metal objects near it.

MRI units use either very large permanent magnets, or superconducting coils to generate a magnetic field. Permanent magnets are "always on", and it's both expensive and time-consuming to drop the current in a superconducting coil to zero in order to "power it down".

I recall one case where someone brought a gas cylinder too close to a unit, and it flew right through the middle, winding up suspended in the opening where the patient rests during a scan. (Luckily, there was no patient there at the time!) Although no damage was done to the unit, it took heavy machinery to pull the cylinder back out of the opening.