this post was submitted on 21 Jul 2025
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[–] UnspecificGravity@lemmy.world 32 points 15 hours ago (2 children)

Couple things:

The magnet is ALWAYS on.

The "kill switch" takes about five minutes to actually deactivate the magnet and it costs about thirty grand in helium every time you push it.

[–] Lemminary@lemmy.world 4 points 7 hours ago

Not to mention it's not renewable. Once it his the upper atmosphere, you can't get it back.

[–] 0x0@lemmy.zip 1 points 15 hours ago (6 children)

Isn't it an electomagnet?

it costs about thirty grand in helium every time you push it.

Oh, right, i forgot human lives have a price in the US.

[–] MangoCats@feddit.it 5 points 4 hours ago

It's a super conducting electromagnet, and if you quench it instantly pieces would be flying all over the room

[–] exasperation@lemmy.dbzer0.com 12 points 11 hours ago (2 children)

The US is an outlier in how it charges prices for healthcare services.

But every country in the world has prices charged for cold liquid helium. It's very expensive to gather, process, store, and ship, regardless of what kind of health care economics apply in your country.

[–] MangoCats@feddit.it 3 points 4 hours ago (1 children)

Not just the helium, there's a considerable time spent "recharging" the magnet with electricity - many patients will lose access to MRI scan service during the multiple days it is down for recharge.

[–] MrFinnbean@lemmy.world 1 points 6 minutes ago

Dont they loose the access to the machine anyway for few day? Im under impression metal slamming to the machine usually breaks it pretty good.

And in fact, doesn't the US have most of the world's supply of helium?

[–] UnspecificGravity@lemmy.world 21 points 13 hours ago

Its a superconducting magnet that cannot be instantly shut off. I am sorry that the physics of this makes you so angry.

[–] chiliedogg@lemmy.world 12 points 14 hours ago (1 children)

Depends on the machine type. Closed bore machines (the vast majority) use supercunducting electromagnets that are surrounded by liquid helium that creates a very strong magnetic field. To demagnetize them requires dumping the helium.

Some open bore machines use electromagnets, but they're much less common and not as powerful.

[–] 0x0@lemmy.zip 1 points 12 hours ago (2 children)

So the helium itself becomes magnetized, is that it?

[–] mavu@discuss.tchncs.de 13 points 11 hours ago

the helium is liquid, which it only is when it is very very cold.
The superconductor will keep it's magnetic field forever, as long as it's superconducting, and it will stay superconducting while it is very very cold.

There is physically no way (as in, it is simply impossible, due to how our world works, not money, not people, not technology) to instantly "switch off" the magnet.

it needs to go above a certain temperature, to lose it's superconducting nature, and it needs to do it at a pace that doesn't dump a GINORMOUS amount of energy in this magnetic field instantly, because that would be even worse.

the fault here is in allowing anyone with any magnetic metal anywhere near an MRI. And whoever let that happen is going to have a very bad week.

[–] chiliedogg@lemmy.world 8 points 12 hours ago

No, the liquid helium cools the magnets to the point where they become superconductive. As to how that works exactly, I do not know. I don't think I have the math for it.

[–] AlexLost@lemmy.world 8 points 15 hours ago

I'm sure he was barely trained and had specific instructions to "never push that button!" When you whole life in the country is tied to your employment, it's every moron for themselves.

[–] Chrobin@discuss.tchncs.de 2 points 15 hours ago (1 children)

It's not an electromagnet, it's a superconducting magnet. And turning it immediately off makes it melt.

[–] brendansimms@lemmy.world 14 points 14 hours ago (1 children)

It's both! MRI magnets are electromagnets that are cooled down to 4 Kelvin using liquid helium. Once they reach those low temperatures, they become superconducting. This way, the magnet isn't gobbling up tons of electricity to stay at the desired field strength. Instead, the liquid helium needs to be replenished occasionally to keep it at superconducting temperature. Source: I work with MRI scanners.

[–] 0x0@lemmy.zip 2 points 12 hours ago