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Comment by LeifCarrotson | Hacker News Reader

> "I'm saying, 'Could you turn off the machine? Call 911. Do something. Turn this damn thing off!'" [pleaded the victim's wife].

The journalist missed a golden opportunity for education here: most MRI scanner magnets cannot be turned off like that. For the few that can, it's going to cost >$50,000 just to refill the liquid helium, not to mention the real and opportunity costs associated with rendering the machine offline for days or weeks.

If people don't know about the magnet, or don't know that it can't be turned off (or perhaps assume it's "off" because the scan was over, as I would guess happened here), accidents happen.

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If anyone is curious what pushing the button to turn off (AKA "quench) the magnet looks like, there's this video of an MRI machine being decommissioned:

https://www.youtube.com/watch?v=9SOUJP5dFEg

You push the button, then 15 seconds later the liquid helium is vented through a pipe on the roof of the hospital (it's quite a spectacular display), and then the superconductor starts to heat up and no longer be a superconductor so the current that's been flowing through the coils (they are energized once, when the machine is first installed, and then continue flowing forever so long as the superconductor is superconducting since there's no resistance) and the magnetic field decays to nothing.

It's not an instantaneous process.

This is only comment in this entire thread that's worth reading.

A video of ejection of vaporized liquid helium out of a smokestack at a hospital performing a quench of their MRI machine.

https://m.youtube.com/watch?v=h-aLlSi4Rv0

I’m pretty sure when some guy gets sucked into the machine, the downtimes/lawsuits/etc and pressing the emergency button and having a ton of down time is a sunk cost at that point and you are basically obligated to do everytyhing you can to avoid catastrophe to reduce your legal peril.

There’s also the basic idea that a human life is worth saving. The money can be figured out later. Sadly though the magnetic fields of an MRI don’t disappear by simply powering the machine down. It can take a while even then. The fact a man with an enormous iron chain is allowed to walk into the room under any circumstance is where the lawsuits will come from, and rightly so.

The cost isn’t the issue.

Quenching the magnet takes up to several minutes. There are also alarms to warn people to get away because the rapidly expanding helium could displace oxygen in the room.

It’s not about the cost. If there’s an emergency that necessitates pressing the button they’ll be pressing it as soon as someone can reach it. It still takes time for the magnetic field to dissipate.

What sort of decay curve can you plot from the magnetic field dissipating over time? Is it linear?

Not a physist, but I remember from school when studying electrical resonators, the stronger the inductor the lower the resonant frequency. i.e. the stronger the magnetic field the longer it takes to turn back into current.

I would guess a strong magnet takes a while, probably minutes to shed its field.

This is a superconductor. It is basically on full strength until it suddenly isn't.

In the idealized resonator, the impedance is assumed zero what matters is the inductor strength and the capacity in the capacitor.

In a real MRI, I presume there is no capacitor to take the charge, I am guessing the limiting factor is the impedance of wherever the charge is going to go.

Saturation/critical current: zero resistance doesn't mean infinite current. all superconductors gain resistance if the current exceeds a value. This value is temperature dependent.(http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/scbc.html).

No. It basically doesn't dissipate at all until the helium is gone and it warms up.

> most MRI scanner magnets cannot be turned off like that. For the few that can, it's going to cost >$50,000 just to refill the liquid helium, not to mention the real and opportunity costs associated with rendering the machine offline for days or weeks.

I thought these days, most MRIs did have an emergency quench button.

Yeah I would say all modern MRIs do. However one misconception is that loss of field strength is instantanous, it's not. The field strength drops off over about 15s or so as the helium boils off and the magnet losses superconducting properties.

So the emergency quench is less useful than it sounds in these situations... it's very likely if an MRI is going to kill you it's going to do it fast enough for it not to be relevant.

Surely you'd hit the quench button straight away? I cannot imagine policy being "check if the victim is dead, and if not hit the button."

I also wonder what the field decay is like. If it takes 15s and it's linear it's much worse than if it's 15s but decays exponentially. You don't need to field to be gone, you need the field to diminish enough to stop strangling the poor guy.

Takes more than 15sec to strangle someone. 30 shouldn't cause any serious damage beyond whatever mechanical damage there is from being tugged around. Heck, 2-3min is probably fine if the MRI is located at a hospital.

Edit: Per the article that I would like to remind everyone is well worth reading, he had time to say goodbye to his wife, that would seem to me to imply he wasn't tossed hard enough to be incapacitated.

strangle? dude's neck was probably crushed. if I had to guess this was a near decapitation, not a strangling.

honestly, probably, yeah, but the guy running the MRI can't know that and should have quenched immediately. You don't just go "oh well he's probably dead, nothing I can do about it now."

my point is even if he had quenched ASAP the damage might've been done already.

Causing severe head trauma or crushing the trachea can be almost instant. A lot of the more serious MRI related injuries are objects flying across the room and hitting someone, especially over the head.

Per the article, his wife claims that he had time to wave goodbye to her.

A man getting dragged by the neck and hitting an MRI machine head-first is going to make all sorts of hand movements that his grieving widow might interpret as waving goodbye in hindsight.

At distance-sqaured law, he literally accelerated beyond 16 G-force (gravity) and slammed against the machine surface.

With 3,200 lb/ft forces inches away from 1.2 tera-gauss magnet, all damages were already done to artery, veins, tendons, muscle, by the 20 lbs necklace, all beyond surgical repair.

In this case, he died after being removed from the machine and taken to a hospital.

The damage was likely done almost immediately; a heavy 20 pound "necklace" is going to apply a lot of crushing force.

And for the other readers: It wouldn’t be applying twenty pounds of force, it would be applying…

My rule of thumb calculation came to 3,000 lbf, which seems like a lot, but perhaps that’s actually accurate.

Seems spot on to me.

Figure half that to start since most of the loop is gonna wind up laying flat and only the half of it is prevented from doing so by one's neck. Then maybe cut it by 2/3 again since the sides aren't gonna do a ton of direct squishing. That still leaves you with hundreds of pounds, which roughly aligns with the timeline of suffocation in the article High hundreds low thousand likely would be neck snapping or otherwise instantly incapacitating.

> The damage was likely done almost immediately;

Not disagreeing, just saying the tech running the machine couldn't have known that and should have quenched the machine in case the damage was survivable.

Right. You - a person who wasn't there, has had no training, has seen no photos and doesn't understand any of the details of the circumstance - are certainly better positioned to know that than the trained staff who were present.

The article says 1hr before it was turned off. That’s long enough to start questioning.

The person I was replying to wasn't asking questions. He specifically said the operator "should have" quenched the machine. He's just another comment section expert.

I was giving my opinion. I've never claimed to be an expert in anything.

You don't have to voice your opinion just because you have one, if you're an expert people might want to hear what you have to say but otherwise you're just padding the comments with slop.

Magnet is ALWAYS ON, 24/7.

Until that big red emergency button gets pressed to the tune of $25,000 to $50,000 each time (couple that with 1-2 weeks downtime and a messed up scheduled for 1,000 of patients.

Apparently he was lucid and speaking for some time before he passed out.

Good for 15 seconds ... after releasing your futile grip to free yourself by the virtue of circulation to the brain.

Damage was mostly done at wall impact after distance-square acceleration, not just the slamming against the wall but 1.2 Tera-gauss force inches away from superconducting magnet coil applied at least 3,200 lbs/ft forces on the 20lb gold chain crushing nearly everything on the poor victim's neck, artery, veins, tendons, muscle ... beyond any possible surgical repair.

You're in luck. Video of an MRI magnet being quenched that I posted above:

https://www.youtube.com/watch?v=9SOUJP5dFEg

Yeah so this video shows exactly what I am talking about, the chair and other objects don't fall immediately, it takes ~15s for them to drop to the ground after the quench starts.

After GE got their shit together, yes. https://www.diagnosticimaging.com/view/everything-you-need-k...

> The journalist missed a golden opportunity for education here: most MRI scanner magnets cannot be turned off like that.

Thanks for that - and it reminded me of the sad state media is today. I read the same story in about 4 papers and nowhere was written _why_ they couldn't turn off the machine.

Miss the days where journalists actually read what they have written.

> For the few that can, it's going to cost >$50,000 just to refill the liquid helium

In this case, they were going to have to do that anyway. Might as well shut it down right away.

Fair, but these are split-second decisions and they likely didn't have a lot of time to react.

An emergency quench of the magnet takes about 1-2 minutes.

There isn’t a way to instantly turn it off.

All the more reason to push the button immediately.

Isn’t 2 minutes enough?

Nope. Because the crushing action literally rendered his neck beyond surgical repair.

Does that energy basically turn into heat because the superconductors start to have electrical resistance?

If so, I'm curious if that heat causes additional damage to the machine, necessitating a refurbishing or at least some parts replacement.

I believe all that heat goes into boiling off the helium keeping it cool.

They can be quenched (as you note), but there was that one time that GE didn’t connect the quench button to prevent accidental/expensive usage and n India, and someone died.

Surprise! It turns out there is a reason it should be connected.

https://www.diagnosticimaging.com/view/everything-you-need-k...

MRI techs do not think about it cost when life is at danger. If someone is in life danger due to the magnet, you quench. This is standard MRI education.

I think the big question here is why they didn’t..

That's a huge deal. I read the article and assumed the machine was mistakenly thought to be turned off or was "winding down". That's especially frustrating as the patient seems to be blaming the hospital staff for the incident.

The patient would be 100% correct to blame the hospital staff for this incident. The only possible explanation is human error by the staff. The only reason this doesn't happen every day in hospitals around the world is MRI staff are not incompetent.

You are going to have to turn it off if there’s a body attached to your machine too, so that’s not much of a lost opportunity.

In the US the federal government uses numbers around $10 million for the statistical value of a human life when doing cost benefit analysis for various programs or interventions. Any sort of lifesaving medical care can easily come in at more than $50,000. The operators shouldn't be hesitating to shut down that machine to save someone's life, and I would be willing to be that they are trained to do so.

Now you are at the Trolley problem: shut down the machine to (maybe) save one person, but preventing all MRIs for the next x weeks, causing y indirect deaths?

It'll need to be shut down anyway to pull the giant metal chain out. You might as well do it right away. Patients can and will be rescheduled to other MRI facilities.

I'm not sure how this is a Trolley problem?

It's a logistics and legislation problem. Hospitals need to be adequately prepared for emergencies and handle backups.

I think a death machine that can't be stopped is an issue.

The Trolley problem is only a problem because there is perfect information in the hypothetical about the consequences of your actions. In real life, you have far less information to go on, which often leads to a more obvious right answer. Shutting down the machine to try to save the one person right in front of you that you know is in immediate danger is the right answer, versus the far less knowable hypothetical future where some number of people may or may not have delayed or relocated scans which may or may not have delayed treatment that may or may not have been immediately necessary as a life-saving matter. As a private MRI operator, you are not morally responsible for keeping your machine functional in order to help keep (figurative) passers-by alive. But you are morally responsible for the health and safety of the patients and visitors on your premises.

You're not exactly going to be running many scans with a human corpse stuck in the MRI machine...

> most MRI scanner magnets cannot be turned off like that. For the few that can, it's going to cost >$50,000 just to refill the liquid helium,

I now nothing about MDI so please tell me: why does it need to refuel the helium? Aren't the magnets “just” superconductive electromagnets? Why can't the current powering the magnet be stopped?

Edit: thanks everyone for your explanations, I appreciate it.

If it's a loop of superconducting material, which seems likely as that's how you prevent losses, then you don't have to supply current so there's no current to stop supplying.

They require extremely low cooling from the helium to achieve superconductivity.

And with superconductivity, by definition, current flows without resistance; it continues even without energy, so turning off the power won't stop it. Nor will it heat up and decay from resistance. Modern MRIs are well-insulated enough to maintain their field without power from days to weeks.

The only thing that collapses the field is to warm it up to where superconductivity stops, which can be done slow and expensively, or in an emergency, fast and even more expensively.

By venting the supercooled gases in what's called a quench, you can turn it off faster, but the time it needs can depend on the model. It could be 20 seconds, or it could be 2 minutes, which, depending on the emergency, may be insufficient.

A quench itself can be dangerous, though usually less so than a patient pinned to the magnet. There's a chance that poor ventilation can flood the room with helium, causing loss of consciousness in seconds. The increase in pressure can also make it impossible to escape if the door's not built for that. You'd have to break a window. On top of which, it's dangerously cold, and the explosive bang can rupture your eardrums.

From Wikipedia:

"Any change to the current through the magnet must be done very slowly, first because electrically the magnet is a large inductor and an abrupt current change will result in a large voltage spike across the windings, and more importantly because fast changes in current can cause eddy currents and mechanical stresses in the windings that can precipitate a quench [...]. So the power supply is usually microprocessor-controlled, programmed to accomplish current changes gradually, in gentle ramps. It usually takes several minutes to energize or de-energize a laboratory-sized magnet."

https://en.wikipedia.org/wiki/Superconducting_magnet

You actually don't need to actively supply current -- it just keeps going round and round, and you can't "short" it out because the path of least resistance will always be the superconducting winding.

You also can't open a switch to stop the current because it's basically a giant inductor, it really wants to keep the magnetic field (and current) constant. Meaning if you suddenly disconnected the winding, it would arc across the gap (continuously, for quite a while until the stored energy was spent).

So what they do is vent/boil off the liquid helium which is keeping the magnet cold, such that it's no longer superconducting and the current will die off. You can't reclaim the helium, hence you need a fresh refill to chill down the magnet again.

For what it’s worth I just learned this from chatgpt. But the magnet is a superconducting electromagnet, and it’s started up by cooling the superconducter to around 4 Kelvin, and then electricity is turned on, and then once it’s going at the desired current, there is some kind of superconducting switch that disconnects the power source. After that no more power is supplied to the magnet—it will run with that same current for years, as long as you keep it cold enough to be super conducting. Apparently the resistance is actually truly zero, not just almost zero.

So there is no current to turn off. The current in the magnet is running on its own from when it was first supplied. The only way to stop it is to heat up the superconductor.

I thought maybe you could draw it off and use it up somewhere else, but then if I’m remembering right electricity will always take the last of least resistance, so none of it would leave a superconductor. Right?

It also makes me wonder, if someone is ever able to build a warm superconductor, how would we ever stop electricity we’ve put into a system like that?

There is some small losses, it does not run 'forever'.

However the superconducting switch is pretty neat. It's a small section of superconductor between the ends of the coil, but is wrapped in a heating element. When the coils is first powered up the element is heated and the material has a resistance. When the coil is ready the heating element is turned off and the shorted conductor cools down and starts superconducting.

> For what it’s worth I just learned this from chatgpt.

Why the hell are people doing that over again? Nobody asked you to copy-paste a plausible AI-generated response you have no idea about its accuracy.

That some people like do it is depressing, but the fact that you are bragging about that is truly beyond words.

I wrote 100% of my post myself. There’s no bragging going on. I’m warning people that I learned it from chatgpt so they know it may not be trustworthy. Still in my experience the vast majority of what I learn from ChatGPT/gemini/claude is correct, and in this kind of case where the knowledge is interesting but not something I’m going to need to rely on for anything, the benefits of quickly learning are so high for me that I thought someone else might appreciate it too. I’m sorry if I offended you.

> the vast majority of what I learn from ChatGPT/gemini/claude is correct

Roughly 90% according to benchmarks. Which means you're learning 10% bullshit.

> the benefits of quickly learning are so high for me that I thought someone else might appreciate it too

ChatGPT has been there for two and a half years already, of course everyone on this forum knows about it, you don't have to tell people how cool it is… Rather you can safely assume that if someone asks a question here, and not as a ChatGPT prompt, it means they doesn't want an answer from ChatGPT!

I don’t think you fully grasped what I wrote.

I didn’t give you an answer from chatgpt. I’m not telling anyone how cool it is. I’ve been here for years and I’m well aware of the level of exposure to LLMs there is for people on HN .

I did give out a warning to people that I had learned something from chatgpt, not from some other source, so they could take it for what it was worth.

I’m so tired of seeing people in other forums try to help someone and having someone give them a shit response. One thing I like about HN is the fact that that doesn’t happen much here. I still think what I wrote in response to your question was helpful and thoughtful. Back up a minute and just think it over, please.

I’d love to see which benchmarks you’re talking about, and if they apply to all three of those specific LLMs, and which version of their models, and if they differentiate topics. My guess is that in the case of LLM output that is a response to a purely factual question, or a response to a question asking a technological question where I present it with something I know occurs but want to know the means by which it occurs, the amount of hallucination is much less than 10%. And if you have some background in the area you are asking about, you can easily filter out some of what is hallucinated, making the learned material well about 90%. But I’m just guessing based on my experience of asking LLMs a lot of questions about both things I already know quite well and others that I don’t. So, which benchmarks are you talking about?

$50,000 seems like a pretty cheap price for saving a life though.

$50,000 only to find that affected areas are beyond surgical repair due to 3,200 lbs/ft crushing at 16 G-force at wall-impact point.

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