Comment by poulpy123 | Hacker News Reader

Comment by poulpy123 | Hacker News Reader

Most people don't understand the danger of MRI, myself included. I trust the people and follow their directions but I can't really visualize what it would be like to get caught with metal in a MRI magnetic field.

For quoting the article : « According to the US Food and Drug Administration, MRI machines have magnetic fields that will attract magnetic objects of all sizes - keys, mobile phones and even oxygen tanks - which "may cause damage to the scanner or injury to the patient or medical professionals if those objects become projectiles". » the choice of words from both the bbc and the FDA don't really convey the risks.

Anyway there are very surprising issues in what is described : why did the wife needed her husband's help to get help although it is the role of the technicians ? Why was the husband in a place where he was able to hear his wife and not being prepped for MRI ? Why was it possible for him to enter ? And why wasn't the technician able to stop him entering ?

I got to take apart an MRI-safe(ish¹) video projector recently. Turns out it was just a regular DLP projector in an RF shielding box, but all the screws and components on the outside (anything that could be removed) were either plastic, non-magnetic stainless steel, or aluminum. They even converted the stock remote control to be powered with a cable instead of a AA battery (most batteries have steel cases).

They replaced the lens with a very long throw one so the projector could be located far away and bolted to the wall. It still had some steel components inside, but the manual made it very clear you were not supposed to open the case while in the same room with the magnet. No other manual I've read has warnings that trying to change a light bulb could kill you.

¹it was designed to be used within the same room as the MRI, but not to go into the magnet bore itself. You were supposed to securely mount it at a distance where the field strength was less than 100 gauss. Since it still contained steel, there were still warnings all over that "this device may become a projectile" if you got too close to the magnet. Installation must have been a bit nerve wracking!

>Installation must have been a bit nerve wracking!

They almost certainly just selected a drywall anchor based on the rating advertised on the package and sent it without any more thought, their ass was covered.

Big picture people who take a step back think about what they're doing don't tend to find themselves installing projectors in hospitals, or if they do they aren't there very long.

Likely true. For all the warnings the thing had about "securing" it, it did not have very many mount points or threaded holes to do so, just some rubber feet. Probably was just sat on a shelf and tied off with a nylon strap. I suppose you aren't going to casually walk past the magnet with a bulky projector like this as you would do with a screwdriver you forgot in your pocket.

> Big picture people who take a step back think about what they're doing don't tend to find themselves installing projectors in hospitals, or if they do they aren't there very long.

They're installed for fMRI research, to show stimuli to study participants.

My point was that a maintenance guy who without prompting thinks to himself "hmm, drywall anchors are rated for vertical loading, not horizontal, let's find a (invariably metal, because office) stud and toggle bolt that bitch" is shortly onto bigger better things.

https://www.youtube.com/watch?v=EJJ9oqmkItI

I love this old GE training video around the time of MRI's introduction to the medical market. Even the oldest machines could show some significant power back then.

Watching the scale attached to a pipe wrench pulling some significant weight on a wrench will help show the forces that a 20 pound chain would have made...

(Oh, and stay for the 'old custodian' tale in the intro of this one...)

When that dude got to throw the wrench at the MRI, you know he was having his best day at work ever. I wouldn't be able to be on camera because of giggling.

The flying wrenches remind me of the Gravity gun i Half-Life 2 :D

> Why was it possible for him to enter?

This is probably the main one. I could completely understand wanting the assistance of a loved one for mundane things like standing up.

Although to your “not prepped for MRI” point, it is kind of wild that someone with a 20 lbs chain around their neck would be allowed even on the same floor as a MRI machine. Although last time I saw one in person, the door to the room did have some pretty blunt warning text in large print.

You would think a simple metal detector to go through before the lock on the MRI room door unlocks would be a requirement.

I guess maybe the MRI machine might interfere with metal detecting?

Nope, metal detectors are fairly typical for MRI access. They just generally aren’t set up as an engineering control like you suggest.

I'm not sure what "engineering control" means. Just put it in front of the door to the MRI room. Alarm goes off, you do not get to enter, it should be as simple as that.

An engineering control is how your microwave works—if the door isn’t physically closed, it can’t run. The way many (most?) hospitals currently operate is called an administrative control—analogous to a sign on the microwave door telling people not to run the microwave with the door open or open the door when the microwave is on.

But MRI machines can't be turned on and shut off that easily. As someone here explained, it takes up to 15 minutes for the magnet in an MRI to "shut down", and costs $50,000 each time.

Why not just control access to the room behind a metal detector? It would be really simple, but effective. I don't think any MRI should be allowed to operate without this basic level of protection.

Sure, an engineering control for MRI room access would be implemented differently--that's just the canonical example that people are familiar with. One possible implementation for MRI access is the airlock method, where the inner access door would only be allowed to unlock with the outer door locked and no metal detected in the space between (also the outer door would be prohibited from unlocking when the inner door is unlocked, except for some kind of inner emergency override that might also be tied to the emergency quench).

Literally no one disagrees with you on this, and most (if not all) hospital administrators will say they already do it the way you suggest. I'm pointing out that the actual implementations I'm aware of are often ineffective because they use administrative rather than engineering controls, and this is a critical distinction people need to be more aware of when interacting with dangerous systems. Managers, at least in my experience, tend to wildly overestimate compliance rates with administrative controls, even ignoring any possibility of deliberate noncompliance.

Last time I went to an MRI, there was a prep room before the MRI machine. There was a stern and visible warning to remove anything metallic from your body before going through the second door. I am fully aware if the pins on my leg were affected, the machine would gladly remove them from my, most likely along with the bone and the leg they are attached to.

A lot of fatal accidents are like that - a series of small mistakes nobody notices, each individually harmless, followed by THAT ONE BIG MISTAKE that ends up killing someone (or a lot of people).

That huge chain though.

People with 10kg chains around their neck might not be the kind of people that you can tell no to.

Mr. T seems like he'd be quite reasonable if you were discussing medical safety procedures.

His chain is gold though and not magnetic =)

That's because Mr. T respects MRI safety.

Mr. T pities the fool who would walk around with an iron chain.

"you need to take off the chain"

"nah man, gotta hit my 5k steps wearing 20lb for my fitness goal"

"ok, well just don't go in the room"

"sure"

The kind of interaction that many people will pretty much forget having within the hour.

People should try a magnet fishing magnet.

A fist-sized powerful magnet that's next to impossible to straight-up pull out of ANYTHING. You need to slide it carefully and NOT let your fingers get in between it and anything else.

Now imagine a magnet that's infinitely more powerful than that.

A good N52 neodymium magnet can be 1.5 tesla- MRIs are usually 1.5 tesla. The pull force is around the same too- a steel object will experience say 20g, and 100 lb fishing magnets are not hard to find.

The difference is the size. Even a large magnet only hits that 20g force over an inch or two. An MRI pulls at that force over a full foot or more; equivalent to dropping the object from 20'+. Worse, the MRI starts pulling at 5 or 10 feet away. Objects can experience a tremendous amount of uncontrolled acceleration in fractions of a second.

It's not like a black hole- unless you are trapped under something very large, the crushing force is substantial but not incredible. In fact inside the tube the gradient is actually smaller than the entrance of the tube- you are pulled in strongly, but once inside the tube you are pressed against the wall somewhat less forcefully. Instead it's like an invisible waterfall, and any metal will be swept away in it, fast enough to put holes in you.

Not sure about medicine, but at least in research, most MRI fields are 3T and up.

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