Also how they have to get people in. One of my MRIs was hours after surgery - I was wheeled in on a stretcher while attached to IV and other machines. They slid me on and off the machine since I wasn't allowed to move myself (I'm not sure if I could have what with the drugs still in my system. take my story with some salt: because of the drugs I wouldn't trust my own memory of the event). Which is to say they need a lot of space around these machines and the doors/gates would need to be very big to fit all the people involved through.

The emergency personnel still needs to be controlled to make sure they aren't carrying magnetic stuff.

It is.

There are locked doors with badges pretty much everywhere in a hospital in my country though (including the door leading to the ER, and the escalator which goes from the ER to the ICU, in my city's hospital), so I don't really understand what would prevent to put such a door at the entrance of the MRI room.