This is already a common practice. One of the issues with the standard implementation is that it’s set up as an administrative control rather than an engineering control (which would be significantly more difficult/expensive/space-consuming). At least one other comment thread has discussed the airlock implementation that I’m sure a very large number of people have independently thought of.
I recently had an MRI in one of those full-body MRI machines.. and we went through two locked doors and they used a wand on me (like they have at airports) to scan my body, even after I answered that I had no metal anywhere in my body. There were 3 operators/nurses in the inner ring of all this, operating machines.. securing my limbs, etc.
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.
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.
Given the rather spectacular failure mode, isn't this rather a case of "better safe than sorry"? i.e. even if it's technically safe, why not require people to remove everything that triggers the detector just to be sure?
Unlike many facilities, we insist everyone strips down to underpants (no bra) and wears a gown. We push quite hard to remove all jewellery (including piercings), but many places do not.
It removes a whole category of problems, but is also slow, has an extra cost (laundry) and still patients leave things on, covered up by the gown.
But the percentage of people with something in them is very very high.
We are dealing with a population that by definition has health issues, and I’d estimate that 75%+ have something metal in them.
Sternal wires, fillings, clips, biopsy markers, screws, plates, braces, joint replacements (x6), ports, mesh, vascular stent, urinary stents, breast implants.
These are conditionally safe implants from yesterday. If we expanded it to a week we could add heart valves, hearing implants, vsd closure devices and about 20 other implants I’m sure.
We have either memorised or looked up the conditions for each. We pay techs well because we want good staff. Minimum staffing levels include using healthcare assistants and suchlike. There are potential downsides to this approach, particularly around safety.
and still patients leave things on, covered up by the gown
A strong but still relatively weak "test magnet" seems like it might be a good idea to use on patients --- if it has any effect on any metal pieces they're wearing, tell them the MRI is going to pull on it with a thousand times or more force.
What distinguishes fine from not fine? During COVID a tech asked me to get in the MRI machine wearing a face mask with a metal wire across the nose. They seemed exasperated when I refused.
Ferromagnetism. A 24-carat gold necklace would not be sucked into the machine for example, while a 7-carat gold necklace would (that contains steel, which contains iron). However, any kind of metal can be less dangerous for other reasons. For example, (pure, 24 Ct) gold, while not ferromagnetic, is an electrical conductor (like almost all metals), and so will heat up with the eddy currents passing through it. This could cause burn injuries if you are wearing it.
wise - some face masks become projectiles and are a risk to eyes. This was tested during covid. Some masks are ok. Some also have ferrous staples that attach the elastic straps, and these are also a problem.
