It won’t shear it straight through your body though. The path of least resistance is to spin you around and then fly off. That doesn’t quite work if the thing is around your neck though.

Just a sensitive metal detector around the doorway where you enter the MRI room. It sounds like this guy would have had the metal detector blaring before he even crossed the threshold.

As would staff shoes, bra, jewellery, access card, ring etc etc.

You can have a metal detector that detects a 20 lb chain and not a pair of nurse's shoes

So the patient with the tiny, unsafe aneurysm clip on a cerebral artery gets in.

They are an imperfect solution. They may help, but dependence on good practice remains.

"There's a huge evil magnet that will tear you apart if you have any metal on you" sounds much easier to grasp and less likely to lose the listener's attention. Then, when you have them listening: "It can grab you from outside the room and hurl you into the machine where the evil magnet lives! Any metal, be it coins, necklaces, pins in your bones, belt buckles, bra wiring, dog tags. Anything can be the end of you, be damn sure you don't have any metal on you."

Oh, wait, you still want them willing to go near the machine? That complicates things a bit ;)