not at all practical. a big ol buzzer would have prevented this maybe, but really it's the relaxed culture around the MRI that let it happen. people need to be told either you don't go past the big heavy door with the NO METALS sign, or you get all the metal off you now, or both.

A - standard metal detectors probably won't work well right at the MRI room door. Some facilities may have a longer hallway for access and putting one there, far from the actual MRI suite, would make a lot of sense (I think I visited one location that had that layout), but not all facilities are laid out in a way that that could work.

B - the nature of how a metal detector works would probably have negative impacts on MRI image quality if it is too close to the imager - even outside the shield room door.

I did a sort of tour of a couple dozen MRI facilities for a couple of years, the stronger ones all have radio-frequency shield rooms complete with metal / gasketed doors that are supposed to be closed during imaging. Actual practice regarding keeping those doors closed was pretty loose in the places / times I was visiting. And, in the article's case it sounds like imaging wasn't in progress so the door was probably standing open...