I wrote something about this sort of thing happening in Star's "nye knot nye nung neersed" thread.
In that thread we talking about piercings and other extreme 'decorations'. They will have to divest themselves of all their piercings if they ever get a MRI done. The "M" stands for magnetic and the magnet involved generates SERIOUSLY strong fields.
At these strengths metal inclusions can be literally pulled out of the body in a straight line. That is why you see those warnings about pacemakers, metallic prosthtetics, key and other metal things outside MRI units. Remember the cartoons where Tweety-pie or the Roadrunner hold up a magnet and Sylvester gets 'attacked' by a drawer full of kitchen knives? This can literally happen around a big MRI magnet. If the metals are not large enough, severe burns can result. Even metallic inks used in some tattoos can cause trouble. So I was not too surprised when I read that it was the foil backing often used in patches causing problems.
'Non-magnetic' doesn't mean anything either. To magnets with that much power everything is magnetic. (Anyone wanting a lesson in atomic structure and diamagnetic fields explaining this statement can PM me. I'm not going into it here unless demand justifies it.)
Marg's Man