Comment by logifail | Hacker News Reader

Comment by logifail | Hacker News Reader

I had a "brain MRI with contrast" scan last year, I wasn't offered earplugs. It wasn't that loud, I certainly wasn't in any discomfort.

With hindsight I'm not convinced about the informed consent re: the gadolinium infusion, but when you're lying prone in your underwear and the nurse is about to stick a line in your arm you don't feel particularly empowered...

[Apologies for the anecdote but] one (with hindsight) comedy moment was that they asked me/reminded me multiple times that no metal was allowed to be present but somehow neither they nor I clocked I was still wearing my wedding band ...

So I was lying there in the scanner and suddently I could feel the changes in the magnetic field via the ring on the ring finger of my left hand. A second or two of sheer panic as I wondered if I was about to see my finger get amputated and then I realised it was fine.

I should have known better, gold is diamagnetic.

[Decades ago] I spent my PhD years running my samples in various high-field NMRs. Nearly lost a set of house keys by taking them too close to a magnet, felt it trying to snatch them from me and managed to step away at the last minute....

There was an accident in a small Swedish hospital a few years ago, the patient scheduled for the MRI arrived with a 13 kg / 28 lbs weighted vest that he for some reason persuaded the MRI nurse to put on (I believe they were friends at the gym). The nurse did, but during the MRI session he left the monitoring room and went in to talk to the patient – and got pulled in by the magnetic field. Almost got strangled to death.

Alarm went off, security guards came running – and were also pulled in… In the end it took hours to get everybody out, the nurse and one or two of the security guards were injured, and the MRI machine was damaged.

Every MRI machine has an emergency button labeled "Quench" that releases its liquid helium. After so doing, the MRI loses its superconductivity and anyone pinned to the machine should be released.

Everyone I know who's worked with MRIs has been tempted to press the button!

https://mrimaster.com/mri-quench/

Isn’t that like on the order of tens of thousands of helium?

Interesting, I did not know that. However, the info also says:

> If a ferromagnetic object becomes stuck to the magnet, do not initiate a quench. Quenching will not necessarily release the object and can be extremely costly due to helium loss and potential system damage.

Wait so the people were pulled into the magnetic field? Were they wearing ferromagnetic metal items that were pulled in? And what does that have to do with the vest that the patient is wearing? If that is ferromagnetic, would that not just simply be stuck inside the MRI?

The nurse was wearing a weighted vest. Presumably the weights were metal of some sort. I can only imagine the sort of metal gear the security guards were wearing. Those guys love dangling stuff from their belt.

More info, for anyone interested:

https://www.auntminnieeurope.com/medical-legal-and-practice/...

> The nurse had tucked a total of 13 metal weights into the pockets of the vest, and it was these weights that pulled him into the scanner.

> I should have known better, gold is diamagnetic.

A gold ring is commonly 14k or 58.5% gold. You're lucky none of the other metals were magnetic. Sometimes nickel is included.

I had an MRI in February and specifically asked about my wedding ring, the tech said it wasn't an issue. We didn't discuss composition or any other details.

That's not good at all. There are absolutely rings that would cause a problem.

I've had multiple MRIs and I always ask about my two rings. They have always said they're fine. It feels like they know something I don't, and also feels sketchy.

I'm told that back on the day, a guy working at JEOL, on a small-bore research NMI, was wearing a metal-banded wristwatch. And when it started to heat up, he reflexively pulled his arm out of the bore very quickly.

That is a bad day at work.

What actually happened? I imagine he received a burn on his hand?

IIRC the story (I heard it second hand) he got a very nasty burn around his wrist.

He was quickly moving a conductive loop through a very strong magnetic field with a crazy large gradient.

(I'm not a physicist, but I assume that's the explanation for the burn.)

Makes sense. Thank you!

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