I'm really a big defender of science and technology not being intrinsically evil, but this comes under "things to be aware of department":

When workers dismantled an MRI machine recently at the University of Texas, they discovered dozens of pens, paper clips, keys and other metal objects clustered inside. Each had sailed through the air from a pocket or a folder, drawn to the huge magnet that powers the MRI's medical scanner. And deaths have been reported when an MRI machine's magnetic power disrupted metal aneurysm clips or cardiac pacemakers inside patients' bodies. At least once, a patient was blinded when a piece of metal, long embedded in his eye, moved in response to the machine.

But last week was what experts believe is the first death caused by an outside ogject in an MRI room, although a recent study suggests that similar accidents may be on the rise. An oxygen tank the size of a fire extinguisher became a magnet-seeking missile, killing Michael Colombini last weekend at Westchester Medical Center in Valhalla, N.Y.

(MRI's are safe machines, as long as you follow certain rules and don't bring metal into the room, and are used across the country for more than one million scans each year.)