MRI tech here. No, it won’t be ripped put. But it could move and cause issues (but probably won’t, especially without your torso in the tube and the bb being deeper in you). Some issues arise from metal heating up, but that also should not be an issue in your case. You’re going to be asked about it on your consent form, cover your ass and make sure you write that down.
See the following:
MRI Ripped My Flesh. Wasn’t that an album by the Mothers of Invention?
I knew someone worked at Bell Labs until they basically liquidated the concept and went to for-profit research. During retirement they could buy some of the surplus lab equipment they were working with, so I got to play with a giant electromagnet. Not superconducting, gap was only about an inch across the magnet on each side a cylinder about a foot diameter and six inches thick.
When this was turned on, it grabbed a standard yellow pencil with the eraser on the end. I could not pull the eraser holder (steel?) off the magnet until the power was turned off. If I yanked any harder, the pencil likely would have broken. And, that’s just a small lab magnet. Don’t mess with physics in the wild.
Another question - would they really vent liquid helium? As I understand, that stuff is seriously expensive.
I recall a suggestion during the initial excitement about high temperature superconducting one suggestion was that instead of a battery a house could have a superconducting unit the size of a small fridge to store solar or wind power. Someone else pointed out the interesting effect that would result in a house fire or some such when the liquid nitrogen fails and the unit releases a few dozen kilowatt-hours of stored power when resistance kicks in. How do you “Drain” a superconducting coil in a hurry?
It depends a bit on what the MRI is looking for in your knee, but if you really are scared (and x-ray vision’s post didn’t reassure you) you can ask your doctor for a CT scan instead.