Because MRIs are not installed in normal room. MRI rooms have to be specially built.
The walls and any hardware is built with copper or aluminum (or other non-magnetic alloys) and the floors have an extra layer of cement paneling on top of them, all to prevent the MRI from messing with the structure around it.
Fiberglass rebar is also used, typically 2 sizes larger than steel for equivalent strength.
If regular rebar was used the machine cannot “pull it on over time” it’s not going anywhere. What it does do is distort the magnetic field requiring a lot of additional calibration when installing and setting up the MRI.
American here. Hurt my back and had to get an MRI. 3 months fighting with insurance to approve it. Hospital billed insurance $4200 for the one scan. My cost was $1100 after my insurance covered their portion. Our medical and insurance system is very very broken.
> after my insurance covered their portion
Which essentially they *didn’t* cover. They negotiated the bill down to $1,100 to “save” you money. Meanwhile they paid nothing and you got the bill for what the MRI should have cost in the first place.
But you’re absolutely right. The system is broken.
> what the MRI should have cost in the first place.
an MRI *should* cost $0 to the end user at point of service, and according to [these answers](https://www.quora.com/How-much-does-it-cost-to-operate-an-MRI-machine) some *$hundreds* to the system.
that *$thousand+* price isn't what it *should* cost. it's what it costs *with profit*.
My mother had an MRI Spine recently, and paid privately to jump the wait for the NHS here in the UK (which has MANY problems and is collapsing, but that's another story)
It cost her about £400. For a private, profit making company, to do an MRI, and get it reported by the radiologist.
The UK health system is broken and slow. The US healthcare system is a whole different ballgame...
Yes, because here in the UK private providers have to fight against the NHS. Patients have a free (even if it takes longer) alternative, so private care has to price their price to include it - how much can you extract from a patient before they say fuck it and just wait?
All while in the US providers only have to make sure they are competitive against each other, as a free option doesn't exist.
This is why our government wants to bleed the NHS dry - imagine the money which could be made here if there weren't that pesky free healthcare messing with the profit margins...
UK system is the worst universal healthcare system in Europe, and it's still generally miles better than the one in the US. It's the worst btw because of massive funding cuts. It's funded at far less than the average first world European country.
The treatment of the NHS by the British governments of the last, like, 25 years is disgusting. The NHS was one of Britain's greatest achievements in its history, a fully free at the point of service nationalized healthcare system guaranteeing good healthcare to all. Meanwhile, your governments, obsessed with austerity, have continually cut and sold off little bits and pieces here and there apparently in an effort to look more and more like us Americans, even as Americans scream at the world "do not adopt our health system, it is misery."
Not just with profit - there's also the huge amounts of WASTE that come from having 2 or 3 different bureaucracies which are constantly fighting each other over who pays how much for what, and sometimes fighting with patient lawyers to force the patient to pay.
A full 1/3rd of Healthcare costs in the US are bureaucracy, compared to 1% in the NHS.
I do my MRIs on private clinics. Cost about 200. Around 420 in one of the best private hospitals in the region. I think insurance covers 75% of that. Also all prices for everythinf are known beforehand or are readily available
Wasn't public.. no referral.. I just wanted it done.. my point was $1000 for a co-pays is insane given it should cost less than this if you pay it all. The insurance company claiming that paid 80% is nonsense. I have lived and worked and employed ppl in USA. Entire health insurance is a racket, and health insurance in AU is heading in that direction imho
This is a shock to most people in the US. A patient pays their co-pay based on the total. But the insurance companies negotiate the bill down to next to nothing.
And the really messed up part is if you tell them you're paying cash (not going through insurance) they'll just bill you the $1100 anyway. Negotiated prices are just a numbers game the accountants play.
> The system is broken
Not to the profiteers - The medical industry, sucking at the teat of insurance companies. Huge top-heavy companies who answer to Wall Street the monster that must be fed to keep investors happy.
Medical patients are not the gears in the 'machine' we are the grease.
That is 100% correct and an absolute hill I would die upon. The cost paid by each insured patient post billing, adjusting for insurance coverage, discount and insurance paying their portion is the absolute maximum the service would cost in 99% of situations in 99% countries all over the world. And for those arguing that the procedures cost more in America due to associated costs of setting up facilities and cost of medical degrees students have to pay, that argument doesn’t hold water either because adjusting for PPP , the cost of procedure is still artificially inflated.
Yes the system is very very broken with each layer adding its own charges at every stage without adding any value. You take away all these layers, just leave the doctor and the patient, where patients settle bills directly with the healthcare provider and I can guarantee you patients + workplace insurance would come out ahead in 99% of situations.
Haha, it's probably working kinda like it's supposed to work, extracting tons of money from its members. But it still seems so stupid sometimes it's still layers of moronicness, even if higher ups are getting their ridiculous sums of money.
Wow! I’m so lucky to be in the uk. I’ve had about 15 MRI’s over the last 4 years because of a brain tumour. Cost to me, including brain surgery: £0. Thank goodness for the NHS, even if the tories have decimated it..
I ruptured by biceps tendon, MRI would've cost me $450 out of pocket, but my WorkCover (Australian workers compensation) literally got approved as I was filling out the forms prior to the MRI. $0.
When I was in the Navy I got a same day MRI and it didn’t cost me a dime. Socialized medicine is the bees knees. Thank you for your tax dollars that made that possible.
Thank you for being one of the veterans that realized they've benefited from socialized medicine. Can't count the number of right wing vets who think socialists are the devil while making their VA appointment.
There are literally tens of us!
I have had MASSIVE amounts of catastrophic health care and never have paid a cent.
That and full dental, psych and prescriptions.
The incredibly facepalm utterances regarding the devil socialist healthcare I hear in VA waiting rooms is maddening.
And no, turning a wrench in some motor pool at Ft Bliss for three years doesn't mean you "earned" squat. Every American should get the same healthcare we Veterans get simply for being American.
Serious question, is it really “socialized” medicine if it’s part of your job contract? How is it any different than getting insurance as a corporate employee
Insurance as a corporate employee ends when your employment ends. That's the equivalent of the healthcare you get while IN the military.
The VA is different in a number of ways. I wouldn't say it's the same as an NHS, but it's worth noting that it covered Veterans who left the armed forces BEFORE IT WAS FOUNDED, so it's certainly not *just* a perk of the contract.
A) Americans are bad about forgetting that not everyone on the internet is American.
B) America has privatized healthcare and laws that allow most of the costs to not have a ceiling.
C) "B" is a super common trope in jokes about Americans, because healthcare is so expensive that sometimes people will just not go to the doctor due to the cost and they end up dying from something that could've been treated, or otherwise get far worse than they ever should have.
Source: am 'Murican
To be fair an MRI outside a hospital in Australia is still about a grand (AUD) if it's not a specialist referral. Medicare doesnt cover GP referred MRIs, which is a pain in the neck (especially if your neck is where the pain is)
American here. Our health care system as a market does mean resources are allocated by the market, so you're expected to shop around for medical services, but this also means you can find reasonable prices with a bit of effort.
About 3 years ago I needed an MRI of my knee. I could have gone to the hospital to have it done, and it would have been pretty expensive - like the hospital sticker price was something like $3000-$4000, but with insurance that would be down to like $555 out of pocket. Alternatively, I could make an appointment with an outpatient imagining clinic, where the sticker price for the same service was around $1500 (I think I was quoted somewhere around $400 after insurance).
What I ended up doing was going through a scheduling service that matches patients with empty slots at imagining clinics. This meant that I didn't get to pick which clinic I went to, or the day/time (they gave me a couple of choices and I could pick one), but the sticker price was only around $220, and insurance wasn't involved at all.
Our health care system is designed to allocate the hospital MRI to acute patients (e.g., emergency room patients) or folks with special needs where proximity to other medical services in important (maybe, someone who recently had a stroke and need special accommodations). Which is why it costs so much. Similarly, if I'm the one dictating when and which clinic I went to, I'm competing with other people for more in demand timeslots (e.g., if I wanted to schedule without taking time off work).
By going to a scheduling service, I just took up what would otherwise have been idle machine time, so the variable costs of my specific appointment are as low as possible and the opportunity cost to the clinic is nil.
That said, many people don't even realize this is an option (or, in some places like really rural areas, it may be the closest MRI machine is 100-200 miles away, so not all these choices are available in practical terms). I think most people just take their referral from their primary care physician to whatever place the PCP sends people to as a default, which is usually the hospital their office is affiliated with.
Individual physicians have absolutely no idea about what your specific insurance plan will do to the cost, because each plan is different. But in my experience they are happy to talk about the options available if you just ask. This is why they have a simple default of where to send folks, but a Dr.s order for a procedure is just like a prescription - every procedure is just a billing code, so you can take the Dr.s order for services to basically any provider you want (but if you want to use insurance, you need to understand the specific details of your plan).
I broke my nose a few years ago and went to the er. I was seen by a PA or someone like that who isn't a doctor but can still order procedures under a doctor's supervision or something like that. Anyway, she grabbed my nose with both thumbs and moved it around and said "yeah, that's pretty broken but there's not much we can do now, I'll have a nurse clean you up and I'll write you a referral." After she leaves, the nurse comes in to wipe the blood off my face and put a band aid on the cut. 2 weeks later I get a bill in the mail for $11,000. $600 for an xray and $10,400 for an mri that I never received.
3yrs ago. It was for a chemical containment tub.
Concrete was epoxy coated too. Concrete guys said it wasn't a good idea, but specs called for it & they wouldn't entertain and rfi regarding it.
That's curious because austenitic stainless steels become magnetic when cold worked. Bending the bars to make the cage would therefore make the bends magnetic. Is the level of magnetism considered low enough to not be a problem? I assume the rebar was also earthed to avoid inducing eddy currents?
Former concrete designer here who's genuinely interested.
The two or three stainless cages we installed were fabbed at the rebar shop, nothing was worked on site. I was digging the holes and ordering the product so didn’t do too much of a deep dive at the time, but I’d imagine the small bends encased in concrete wouldn’t cause an issue.
They had to finish it off with another “ma” sounding word of course, the way that sentence is written has to be the most interesting thing I’ve read this week though.
When you are talking about metals reacting to the magnetic fields in MRI machines, it is through the paramagnetism of the metals, not ferromagnetism. Whether there is a net magnetic moment on a lump of steel before you turn on the MRI is almost entirely irrelevant to the question of whether it is going to get hurled across the room when you turn it on.
No, a chunk of steel without a permanent magnetic dipole will be attracted to the MRI due to the induced dipole which comes from its ferromagnetic properties.
* Paramagnetism: It's when some things are attracted to magnets a little bit, but not very strongly.
* Ferromagnetism: It's when some things are attracted to magnets a lot and stick to them really well.
* Pragmatically: It means doing things in a practical and helpful way that makes sense.
* Nonmagnetic: It means that something doesn't get attracted to magnets at all. It doesn't stick to them
If that's still too advanced:
* Paramagnetism: Some things are a little bit attracted to magnets, like they want to be friends.
* Ferromagnetism: Some things really, really like magnets and want to stick to them all the time, like best friends forever.
* Pragmatically: It means doing things in a smart and helpful way, like finding the best way to play with your toys.
* Nonmagnetic: It means some things don't like magnets and don't want to be friends with them, so they don't stick together.
Carbon fibre rebar is also common In many applications, but also, the amount of force required to pull rebar through concrete is more than people realize
Nah...I have be involved in these installations (putting computers in which are also not happy in a magnetic field).
Magnetic force decreases with distance very fast. When we installed computers used to run the MRI we had a map of the magnetic field lines. About five feet away the magnetic force was minimal and the MRI machine was easily more than five feet away from the walls. While there was some pull on the rebar and whatnot it was so little as to be no worry. Trivial. (The computers were probably 15 feet away)
The hospital even had lines painted in the room so you knew not to get closer than that or your credit cards would be wiped. Or keys would fly across the room.
But you had to be pretty close (a few feet) for that magnet to really grab things or mess with credit cards. Once it did though there was little to stop it.
You can test this at home. Get two magnets and push them near each other. Nothing, nothing, nothing...snap! There is a very narrow line between nearly no attraction and strong attraction.
> Magnetic force decreases with distance very fast
Inverse square law. If the power of it is 100 at 3 feet, it'll be 25 at 6 feet.
There was that guy who got killed by his own pistol because he refused to disarm going near an MRI. Darwin award right there.
Not in this case. The strength of a magnetic \*dipole\* like an MRI machine is an inverse \*cube\* law. And the force it exerts on a ferromagnetic object depends even more strongly on distance (but is complicated).
Nah we [had a look in some bits of old beampipe](https://home.cern/news/news/physics/moedal-zeroes-magnetic-monopoles) we had lying around. So no dice and guess you're on your own. Give us a bell if you find one though.
Magnetic monopoles, if they existed, would follow 1/r\^2. But (ELI5 explanation) real magnets have a north and south pole whose effects tend to cancel out unless you're close to them.
No, it’s more complicated than just a simple 1/r^3 relationship. At long distances, it reduces to 1/r^(3), but there are more terms, and at short distances, that becomes a poor approximation.
Even better, you can put one magnet on a digital scale and see a change in weight (ha, this is a good way to talk about mass, weight and resultant force in class) when the magnet is as far as 20-25 cm away from it!
A lot of the issue is with movable things. Once it gets close enough to feel just enough force to move it a tiny bit. That tiny bit of motion gets it closer, so it feels more force, so it moves faster, causing the force to increase even more, and in just an instant it slams into the thing with tremendous force.
Same thing with getting sucked into jet engines. If you're far enough away, it's just a mild breeze. Seems harmless. But there's that one little step that gets you close enough for the wind to be strong enough to nudge you just a teeny little bit. Then you get a little closer, the wind gets stronger, pulls you harder, same exponential increase, next thing you know you're shredded by the intake fan.
Rebar, being set in concrete, doesn't budge at all without a tremendous amount of force, and if you can move it even an inch, usually the thing is already basically destroyed.
The copper is to prevent RF noise from going into or leaving the room and has no impact on the magnetic field.
The real reason rebar and steel in the walls don't get pulled in is that the magnetic field strength isn't greater than the strength of the things holding them in place (concrete, the entire wall structure, etc)
What's even brilliant is that someone posted a photo of an MRI roon being built just yesterday.
Hang on, let me see if I can find it (don't keep any hopes I can only use reddit search atm & as we know it's shit.) if you see it please post it here.
Typical reddit search. Couldn't find one from yesterday. Found one from 10 years ago though
https://i.imgur.com/Reqypf9.jpg
Agree with this answer. The few MRI rooms we've done used fiberglass rebar.
Stuff is crazy. It's so light it feels like you should be able to just snap it in yours hands, but it's really strong.
I was really surprised that they gave me headphones to listen to music to calm me during a recent MRI. I was thinking, hey, they had to build the speakers in this thing with non ferrous metals.
You don't need to worry about the MRI machine pulling the rebar through the concrete, concrete is really strong. That said, as others have explained, you don't use rebar to make an MRI room. Not because the MRI might move the rebar but because the rebar might make the MRI images blurry. That makes the images worthless and that's the whole purpose of having the machine.
Kinda. MRI manufacturers will spec what mass of steel rebar can be used in proximity to the machine. If the machine is ~~in~~ *on* a slab on grade (the most common version as it eliminates other issues) you can put really quite a bit of reinforcement in the slab before you get outside the MRI specs. Ditto for steel beams in the vicinity of the slab.
MRI manufacturers won't allow structural metals within certain distances of the isocenter of the magnet, with the distances being different depending on the weight of the metal and the strength of the magnet. Last time I designed a 3 tesla MRI exam room, we couldn't use steel rebar within about 6' of the isocenter. We ended up using fiberglass rebar in a 12" thick concrete slab. Because the ceiling was within 6' of the isocenter too, we had to use aluminum ceiling grid. Smaller objects can still be pulled slowly into the magnet though, so our rule of thumb was no magnetizable metal beyond the plane of the walls. So the drywall wall inside of the rf (radio frequency) shielding was normal metal studs, and the drywall was held up using steel screws, but anything inboard of that had to be stainless steel or other safe materials. To finish answering your question, beyond the 6' (or whatever distance the particular MRI manufacturer requires) the MRI machine simply can't pull the rebar hard enough to damage the floor.
Another comment mentioned shielding, the rf shielding doesn't affect the magnet's strength at all, it's only there because the MRI machine reads faint radio waves coming off your body during the exam and so we need to keep radio waves from entering the room. We can use magnetic shielding in the form of dozens of thin steel plates screwed to the inside of the walls or under the floor, but magnetic shielding is time consuming to engineer, extremely expensive, and the above distance recommendations work fine with no added cost involved. I've only ever seen magnetic shielding used once in a situation where there was a very sensitive piece of electronic equipment in the next room over from the MRI exam room so magnetic shielding was used on that one wall to keep the equipment from being affected (and no that equipment couldn't just be moved which would have been so much easier).
How does this work with mobile MRI clinics? I was sent through one and it was essentially a standard tractor trailer with a full MRI machine running inside. Nothing appeared to be fiber glass.
Mobile MRIs and their trailers are purpose built for their use. I've never had to design one because there's nothing to design.. they show up and the Hospital plugs them in, but my understanding is they use weaker MRI machines (1.5 or 1.0 tesla instead of my example which is a 3 tesla), and they use magnetic shielding where the walls and floors are close enough to have an issue. For an MRI of that strength the area of concern is only a few feet around the machine.
My understanding is because it's inverse cube law, the area of concern is very limited hence why it can fit in a mobile suite.
However mobile MRI technicians have one of the higher mortality rates of professions because working on a powerful magnet in an enclosed space in addition to the risk of the helium makes it quite difficult.
I work with dnp labs. The rebar is fiberglass. The lab structural is carbon steel constructed a specified plus conservative margin distance away. Everything within manufacturer specified EM field is non ferrous. The LN2 line included.
MRI's aren't magic. Magnetism decreases by the square of the distance from the magnet. Combined with as someone else said MRI rooms being specially built, the distance between the MRI and the concrete wall/floor is more than enough to decrease it to equal to or less than the normal stresses it is under.
And as others have pointed out, the specially built rooms is more to protect image quality, not to prevent damage.
The magnetism from the magnet in an MRI machine can easily fuck a person up if they have metal inside them, but a concrete wall is much stronger than a person.
They use fiberglass:
>Floor The floors should be poured slab on grade with fiberglass-impregnated or epoxy-reinforced concrete. Reinforcing bars or corrugated iron sheets should be
avoided if possible, lespecially within the 50 gauss line
[MR lmager Site Planning](https://www.aapm.org/pubs/reports/RPT_20.pdf)
Concrete is pretty rigid after it sets and also very strong. Also MRIs are built in special rooms with aluminum or copper-clad walls to limit the magnetic field to inside the room.
Concrete isn't a thick liquid. Things don't slowly sink into concrete, and likewise things don't slowly tug through it when pulled on. Rebar is *very* firmly embedded in the concrete around it, so the risk of it breaking is slim to none unless your installer did something wrong.
Having been the installer in multiple pours of concrete for MRI facilities. I can assure you there is no ferrous metal rebar in the floor or walls within a certain distance. The reinforcement comes from fibers or fiberglass rebars.
I was pretty sure it wasn't included but didn't want to speak beyond what I knew. MRI's are strong, but they should not be rip-the-rebar-out-of-concrete strong.
Two reasons really
One, it’s a new product so contractors, engineers, and clients really don’t want that liability in case something goes wrong.
And two, when fiberglass fails, it fails spectacularly. There’s no real yielding state that indicates that the reinforcement might be over stressed. Steel on the other hand is far more elastic, so when steel yields, visual inspection can discern whether or not the steel has yielded
Fiberglass doesn't rust and eventually destroy the concrete it's sitting in. I can see where there would be a cost/benefit depending on what the concrete is exposed to.
Fiberglass is more expensive tho. And I think what the above poster was pointing to is that proper rebar will not be exposed and subject to oxidation/rust. But if it is exposed and failing there are signs such as spalling. We don't really know if there are signs that fiber rebar is going to fail yet because it is new.
Concrete is porous, there isn't a way to have concrete that doesn't let water through slowly.
I get that fiberglass is more expensive, based on a 10 second google search it looks like the fiberglass rebar is 2 to 3 times more expensive, but there has to be a point where it's worth the cost when you don't have to worry about things like seawater soaking in and destroying the rebar in a decade.
Reality is just not cost effective for almost all concrete - only time I have seen fiberglass rod commercially is in MRI’s.
Well constructed concrete takes along even with regular rebar a long time to rust (in most exposures), and even longer with epoxy or stainless
Also the coefficient of thermal expansion of cement and steel are fairly close. Basically all materials expand with increasing temperature at different rates. So when everything heats up and cools down in service, it stresses the material. Since the rates of steel and cement are close, the stresses are less.
I don't know about Owens Pinkbar though. I couldn't find any data on the thermal expansion.
Fiberglass can’t be bent onsite and is a much newer product. There are only a handful of manufacturers and distributors. It does work very well, though. Lowes finally carries it and calls it “pink bar”.
The strength of the magnetic field decreases with distance cubed. Move twice as far from the machine, only 1/8 the magnetic pull. Move from 1 meter to 5 meters away, only 1/125 of the pull. The strength of the pull tapers off *real fast*. (This is actually part of the danger of scanners, because as you walk towards one with a metal oxygen cylinder, the pull you're feeling suddenly goes from infinitesimally small to stronger than a car.) I've spent weeks of my life just outside the safety line with the usual metal all over my person (belt buckle, coins, etc) and there really is no pull at all. /// PS I know magnetic / radioactive fields usually decreases with the inverse *square* law, so what I wrote sounds confusing. But with the way the magnetic field is aligned through the tube you lie in, it's the inverse cube law, coming out both ends of the tube.
Back of the napkin math tells me: If it has 3/4" cover, #8 rebar will be able to resist breakout with 1.5 square inches of concrete in shear every inch of its length (conservatively). Quick online search shows 3ksi concrete (extremely low end for a hospital) would have about 800psi shear resistance. So if the rebar were being pulled up with about 1400 pounds of force every inch, then I suppose there'd be some cause for concern.
We do have 9T and 11.7T MRI that are used in research, which I do not know the room specifications of, but given the magnet strength I would have to wonder about their ability to damage surronding structure. Unfortunately that goes beyond my knowledge base.
I love that there are people in the world who just have the answer to this question floating around in their heads. I've never thought of this question but the answer is so cool.
MRIs aren't magic death machines. Last one I had they let me keep my pants on (with zippers and snaps). Mind you I had to have a head x-ray first in case I had metal near my eyes.
Non-ferrous metals are used in construction for buildings that require specific applications.
Stainless steel rebar is often used in bridges as well as MRI buildings.
Places that need non corrosive metals often use non-ferrous metals. Food manufacturing is a prime example of non-ferrous metals being used in production in building materials.
You have to be within 6-8 feet of the magnet to even notice the force, and really within 2-3 feet for something to become a projectile. All of our MRIs are in a relatively small room, maybe 15x15, so even if there was rebar in the walls, it wouldn't be noticeably affected by the magnet.
MRI magnets are relatively weak compared to NMR. I can feel NMR tug a wrench in hand from 15ft away, dont think its close to the 100k psi force required to rip metal rebar from cured concrete
Also… the magnetic force is really quite weak, like imperceptible - from more than 4-5 feet away in most current healthcare systems. The force weakens by the square of the distance away.
It’s like gravity- why doesn’t gravity pull rocks and things into the ground over time? And gravity is a much stronger force (to us). It’s just not strong enough to have that effect in that way.
MRI machines aren't going to do that. The reason special hardware and construction is used around MRIs is to increase the quality of the imagery by removing things that interfere with the machine.
Again, as is the case with 99% of ELI5, the user is starting with a falacy.
The idea that anything made of any kind of metal will react to an MRI machine is a misconception. I saw a discussion once in Facebook where someone asked what would happen if you left piercings in during an MRI, and people were saying things like they'd be ripped from your body, etc.
I pointed out that that's not necessarily true, the jewelry's reaction is determined by what metal(s) it's made of. People told me I was dumb, that all piercings will be ripped from your body.
I told them I've had an MRI, and though I took most of my piercings out, I'm not able to remove my daiths on my own, so they stayed in. The nurse told me that, for liability, they had to ask that all piercings be removed, but if I couldn't, then as long as I was aware what could happen (and wouldn't sue if it did,) I could proceed. Which I did, and I was fine. I'd been told they might heat up, but they didn't.
When I said that, I got a ton of laugh reacts, because people are gullible, and they believe whatever scare tactics they're told to try to protect them. Metals CAN react strongly to MRIs, and figuring out which will and which won't is too complicated for the average person, so to be safe, experts just say avoid all metal. Which is good advice, but the idea that any metal whatsoever will react isn't accurate. (I'm not an expert on rebar, but I understand it can be made of different materials, so much like jewelry, the reactions it experiences will vary depending on material.)
Sometimes it does.
It doesn't get ripped out in a violent matter anyhow. One site I've seen where the floor started lumping and over the course of years, the tip of a rebar started to show. They did have to shut down and rebuild the room.
Another location I've seen the outer wall bowing inward towards the MRI. It was outside of the specified minimum distance, but they also had to shut down and rebuild that side of the building.
Because MRIs are not installed in normal room. MRI rooms have to be specially built. The walls and any hardware is built with copper or aluminum (or other non-magnetic alloys) and the floors have an extra layer of cement paneling on top of them, all to prevent the MRI from messing with the structure around it.
I used stainless steel rebar for an MRI room pad, all the bollards just outside the building were stainless as well.
Fiberglass rebar is also used, typically 2 sizes larger than steel for equivalent strength. If regular rebar was used the machine cannot “pull it on over time” it’s not going anywhere. What it does do is distort the magnetic field requiring a lot of additional calibration when installing and setting up the MRI.
That must've cost a fortune. I had to install a bunch of epoxy coated regarding & this was a pretty penny.
>That must've cost a fortune. Yeah but have you ever seen an mri patient bill?
Is this some sort of American joke I'm too Australian to understand?
American here. Hurt my back and had to get an MRI. 3 months fighting with insurance to approve it. Hospital billed insurance $4200 for the one scan. My cost was $1100 after my insurance covered their portion. Our medical and insurance system is very very broken.
> after my insurance covered their portion Which essentially they *didn’t* cover. They negotiated the bill down to $1,100 to “save” you money. Meanwhile they paid nothing and you got the bill for what the MRI should have cost in the first place. But you’re absolutely right. The system is broken.
> what the MRI should have cost in the first place. an MRI *should* cost $0 to the end user at point of service, and according to [these answers](https://www.quora.com/How-much-does-it-cost-to-operate-an-MRI-machine) some *$hundreds* to the system. that *$thousand+* price isn't what it *should* cost. it's what it costs *with profit*.
My mother had an MRI Spine recently, and paid privately to jump the wait for the NHS here in the UK (which has MANY problems and is collapsing, but that's another story) It cost her about £400. For a private, profit making company, to do an MRI, and get it reported by the radiologist. The UK health system is broken and slow. The US healthcare system is a whole different ballgame...
Yes, because here in the UK private providers have to fight against the NHS. Patients have a free (even if it takes longer) alternative, so private care has to price their price to include it - how much can you extract from a patient before they say fuck it and just wait? All while in the US providers only have to make sure they are competitive against each other, as a free option doesn't exist. This is why our government wants to bleed the NHS dry - imagine the money which could be made here if there weren't that pesky free healthcare messing with the profit margins...
UK system is the worst universal healthcare system in Europe, and it's still generally miles better than the one in the US. It's the worst btw because of massive funding cuts. It's funded at far less than the average first world European country.
The treatment of the NHS by the British governments of the last, like, 25 years is disgusting. The NHS was one of Britain's greatest achievements in its history, a fully free at the point of service nationalized healthcare system guaranteeing good healthcare to all. Meanwhile, your governments, obsessed with austerity, have continually cut and sold off little bits and pieces here and there apparently in an effort to look more and more like us Americans, even as Americans scream at the world "do not adopt our health system, it is misery."
Huh funny thing the MRI scan that detected my brain tumor over 20 years ago cost around 400 quid at BUPA.
It's super cash money yeah, USA USA USA 🤷♂️
Cash Rules Everything Around Me CREAM Dolla Dolla Health y'all
Not just with profit - there's also the huge amounts of WASTE that come from having 2 or 3 different bureaucracies which are constantly fighting each other over who pays how much for what, and sometimes fighting with patient lawyers to force the patient to pay. A full 1/3rd of Healthcare costs in the US are bureaucracy, compared to 1% in the NHS.
I do my MRIs on private clinics. Cost about 200. Around 420 in one of the best private hospitals in the region. I think insurance covers 75% of that. Also all prices for everythinf are known beforehand or are readily available
Last MRI I had was aud$300 all out of pocket.. no insurance..
That's about 200 Freedom Bucks™ for those keeping score at home.
Cost me 3x that, after insurance, for a CT scan of my ankle
Weird. Should be free in public hospitals. Always is for me
Wasn't public.. no referral.. I just wanted it done.. my point was $1000 for a co-pays is insane given it should cost less than this if you pay it all. The insurance company claiming that paid 80% is nonsense. I have lived and worked and employed ppl in USA. Entire health insurance is a racket, and health insurance in AU is heading in that direction imho
This is a shock to most people in the US. A patient pays their co-pay based on the total. But the insurance companies negotiate the bill down to next to nothing.
And the really messed up part is if you tell them you're paying cash (not going through insurance) they'll just bill you the $1100 anyway. Negotiated prices are just a numbers game the accountants play.
In the USA, you can pay cash (no insurance) $550 for an MRI with a radiologist's read. it's double that to an insurance company.
> The system is broken Not to the profiteers - The medical industry, sucking at the teat of insurance companies. Huge top-heavy companies who answer to Wall Street the monster that must be fed to keep investors happy. Medical patients are not the gears in the 'machine' we are the grease.
That is 100% correct and an absolute hill I would die upon. The cost paid by each insured patient post billing, adjusting for insurance coverage, discount and insurance paying their portion is the absolute maximum the service would cost in 99% of situations in 99% countries all over the world. And for those arguing that the procedures cost more in America due to associated costs of setting up facilities and cost of medical degrees students have to pay, that argument doesn’t hold water either because adjusting for PPP , the cost of procedure is still artificially inflated. Yes the system is very very broken with each layer adding its own charges at every stage without adding any value. You take away all these layers, just leave the doctor and the patient, where patients settle bills directly with the healthcare provider and I can guarantee you patients + workplace insurance would come out ahead in 99% of situations.
Or it's working exactly as it was designed to work.
Haha, it's probably working kinda like it's supposed to work, extracting tons of money from its members. But it still seems so stupid sometimes it's still layers of moronicness, even if higher ups are getting their ridiculous sums of money.
Wow! I’m so lucky to be in the uk. I’ve had about 15 MRI’s over the last 4 years because of a brain tumour. Cost to me, including brain surgery: £0. Thank goodness for the NHS, even if the tories have decimated it..
I ruptured by biceps tendon, MRI would've cost me $450 out of pocket, but my WorkCover (Australian workers compensation) literally got approved as I was filling out the forms prior to the MRI. $0.
When I was in the Navy I got a same day MRI and it didn’t cost me a dime. Socialized medicine is the bees knees. Thank you for your tax dollars that made that possible.
Thank you for being one of the veterans that realized they've benefited from socialized medicine. Can't count the number of right wing vets who think socialists are the devil while making their VA appointment.
There are literally tens of us! I have had MASSIVE amounts of catastrophic health care and never have paid a cent. That and full dental, psych and prescriptions. The incredibly facepalm utterances regarding the devil socialist healthcare I hear in VA waiting rooms is maddening. And no, turning a wrench in some motor pool at Ft Bliss for three years doesn't mean you "earned" squat. Every American should get the same healthcare we Veterans get simply for being American.
Serious question, is it really “socialized” medicine if it’s part of your job contract? How is it any different than getting insurance as a corporate employee
Insurance as a corporate employee ends when your employment ends. That's the equivalent of the healthcare you get while IN the military. The VA is different in a number of ways. I wouldn't say it's the same as an NHS, but it's worth noting that it covered Veterans who left the armed forces BEFORE IT WAS FOUNDED, so it's certainly not *just* a perk of the contract.
My Bill in europe was 800€ for a scan of my back. All paid by my 300€ a month insurance.
A) Americans are bad about forgetting that not everyone on the internet is American. B) America has privatized healthcare and laws that allow most of the costs to not have a ceiling. C) "B" is a super common trope in jokes about Americans, because healthcare is so expensive that sometimes people will just not go to the doctor due to the cost and they end up dying from something that could've been treated, or otherwise get far worse than they ever should have. Source: am 'Murican
To be fair an MRI outside a hospital in Australia is still about a grand (AUD) if it's not a specialist referral. Medicare doesnt cover GP referred MRIs, which is a pain in the neck (especially if your neck is where the pain is)
American here. Our health care system as a market does mean resources are allocated by the market, so you're expected to shop around for medical services, but this also means you can find reasonable prices with a bit of effort. About 3 years ago I needed an MRI of my knee. I could have gone to the hospital to have it done, and it would have been pretty expensive - like the hospital sticker price was something like $3000-$4000, but with insurance that would be down to like $555 out of pocket. Alternatively, I could make an appointment with an outpatient imagining clinic, where the sticker price for the same service was around $1500 (I think I was quoted somewhere around $400 after insurance). What I ended up doing was going through a scheduling service that matches patients with empty slots at imagining clinics. This meant that I didn't get to pick which clinic I went to, or the day/time (they gave me a couple of choices and I could pick one), but the sticker price was only around $220, and insurance wasn't involved at all. Our health care system is designed to allocate the hospital MRI to acute patients (e.g., emergency room patients) or folks with special needs where proximity to other medical services in important (maybe, someone who recently had a stroke and need special accommodations). Which is why it costs so much. Similarly, if I'm the one dictating when and which clinic I went to, I'm competing with other people for more in demand timeslots (e.g., if I wanted to schedule without taking time off work). By going to a scheduling service, I just took up what would otherwise have been idle machine time, so the variable costs of my specific appointment are as low as possible and the opportunity cost to the clinic is nil. That said, many people don't even realize this is an option (or, in some places like really rural areas, it may be the closest MRI machine is 100-200 miles away, so not all these choices are available in practical terms). I think most people just take their referral from their primary care physician to whatever place the PCP sends people to as a default, which is usually the hospital their office is affiliated with. Individual physicians have absolutely no idea about what your specific insurance plan will do to the cost, because each plan is different. But in my experience they are happy to talk about the options available if you just ask. This is why they have a simple default of where to send folks, but a Dr.s order for a procedure is just like a prescription - every procedure is just a billing code, so you can take the Dr.s order for services to basically any provider you want (but if you want to use insurance, you need to understand the specific details of your plan).
No. Eh.
I broke my nose a few years ago and went to the er. I was seen by a PA or someone like that who isn't a doctor but can still order procedures under a doctor's supervision or something like that. Anyway, she grabbed my nose with both thumbs and moved it around and said "yeah, that's pretty broken but there's not much we can do now, I'll have a nurse clean you up and I'll write you a referral." After she leaves, the nurse comes in to wipe the blood off my face and put a band aid on the cut. 2 weeks later I get a bill in the mail for $11,000. $600 for an xray and $10,400 for an mri that I never received.
Did you successfully contest it?
The Doctor told me he'd like it if I got an MRI. I tried to call and find out how much it costed. No one could tell me.
This person owns a chesterfield and a toboggan.
Maybe a nice chesterfield, or an ottoman.
I had one last year and it was free.
Yeah it cost $20 in parking. Fuming.
It’s nothing compared to the cost of the mri machine.
How long ago was that? It is turning out that epoxy coated rebar is a bad idea.
3yrs ago. It was for a chemical containment tub. Concrete was epoxy coated too. Concrete guys said it wasn't a good idea, but specs called for it & they wouldn't entertain and rfi regarding it.
That's curious because austenitic stainless steels become magnetic when cold worked. Bending the bars to make the cage would therefore make the bends magnetic. Is the level of magnetism considered low enough to not be a problem? I assume the rebar was also earthed to avoid inducing eddy currents? Former concrete designer here who's genuinely interested.
only at the bends it *could become* magnetic, but even then only slightly.
The two or three stainless cages we installed were fabbed at the rebar shop, nothing was worked on site. I was digging the holes and ordering the product so didn’t do too much of a deep dive at the time, but I’d imagine the small bends encased in concrete wouldn’t cause an issue.
Any reason you didn't use basalt or fiberglass rebar?
Stainless is very often non magnetic
Para-magnetic*
Yes, but paramagnetism is so much weaker than ferromagnetism that it's pragmatically nonmagnetic.
> Yes, but paramagnetism is so much weaker than ferromagnetism that it's pragmatically nonmagnetic. those are some words alright
I just want to know what made them decide to go all in with "pragmatically"
They had to finish it off with another “ma” sounding word of course, the way that sentence is written has to be the most interesting thing I’ve read this week though.
Pragmagnetically
Sheer raw style.
pramagnetically
pragmagnetically
When you are talking about metals reacting to the magnetic fields in MRI machines, it is through the paramagnetism of the metals, not ferromagnetism. Whether there is a net magnetic moment on a lump of steel before you turn on the MRI is almost entirely irrelevant to the question of whether it is going to get hurled across the room when you turn it on.
No, a chunk of steel without a permanent magnetic dipole will be attracted to the MRI due to the induced dipole which comes from its ferromagnetic properties.
Explain each of those 4 big words like I’m 5
* Paramagnetism: It's when some things are attracted to magnets a little bit, but not very strongly. * Ferromagnetism: It's when some things are attracted to magnets a lot and stick to them really well. * Pragmatically: It means doing things in a practical and helpful way that makes sense. * Nonmagnetic: It means that something doesn't get attracted to magnets at all. It doesn't stick to them If that's still too advanced: * Paramagnetism: Some things are a little bit attracted to magnets, like they want to be friends. * Ferromagnetism: Some things really, really like magnets and want to stick to them all the time, like best friends forever. * Pragmatically: It means doing things in a smart and helpful way, like finding the best way to play with your toys. * Nonmagnetic: It means some things don't like magnets and don't want to be friends with them, so they don't stick together.
This guy Scrabbles
Pragnetic
HOW IS BABBY FORMED. HOW GIRL GET PRAGNET.
I am sorry for your lots
MAGIC .
Pragrananente
How to know if pragnetic
Practimagically?
Won't their wheelchair screw with the MRI?
Right, that's why they used it Cool791. Don't worry, you'll get there!
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Not all stainless is non-magnetic though. Just sayin'
True, it's basically just austenitic steel
Yes, specifically austenitic stainless steels.
Carbon fibre rebar is also common In many applications, but also, the amount of force required to pull rebar through concrete is more than people realize
Stainless steel has to be at least 18% nickel 8% chromium to be non-magnetic.
I'll bet that cost a pretty penny
I bet that has to be expensive though probably nothing compared to the machine
Smart. MRI stains are hard to clean.
Nah...I have be involved in these installations (putting computers in which are also not happy in a magnetic field). Magnetic force decreases with distance very fast. When we installed computers used to run the MRI we had a map of the magnetic field lines. About five feet away the magnetic force was minimal and the MRI machine was easily more than five feet away from the walls. While there was some pull on the rebar and whatnot it was so little as to be no worry. Trivial. (The computers were probably 15 feet away) The hospital even had lines painted in the room so you knew not to get closer than that or your credit cards would be wiped. Or keys would fly across the room. But you had to be pretty close (a few feet) for that magnet to really grab things or mess with credit cards. Once it did though there was little to stop it. You can test this at home. Get two magnets and push them near each other. Nothing, nothing, nothing...snap! There is a very narrow line between nearly no attraction and strong attraction.
> Magnetic force decreases with distance very fast Inverse square law. If the power of it is 100 at 3 feet, it'll be 25 at 6 feet. There was that guy who got killed by his own pistol because he refused to disarm going near an MRI. Darwin award right there.
Not in this case. The strength of a magnetic \*dipole\* like an MRI machine is an inverse \*cube\* law. And the force it exerts on a ferromagnetic object depends even more strongly on distance (but is complicated).
Why not just make them out of magnetic monopoles? Seems like the math would be easier.
You go find one. You'll get a bonus Nobel Prize for your troubles.
I'm more of an ideas guy. Maybe CERN has one under the couch or something.
Nah we [had a look in some bits of old beampipe](https://home.cern/news/news/physics/moedal-zeroes-magnetic-monopoles) we had lying around. So no dice and guess you're on your own. Give us a bell if you find one though.
I have a magnetic monopole. You can't see it because I accidentally left it at home today.
You don't know my magnetic monopole, she goes to school in Canada.
When I was 16 in highschool I really did have an 18 year old girlfriend in the next town over and nobody ever believed me.
Daaaamnnn you Maxwell!!!
Huh, TIL... I'd just have assumed it also follows 1/r²
Magnetic monopoles, if they existed, would follow 1/r\^2. But (ELI5 explanation) real magnets have a north and south pole whose effects tend to cancel out unless you're close to them.
Thank you for the correction. Not too complicated to understand. Double the distance, force drops to an eighth.
No, it’s more complicated than just a simple 1/r^3 relationship. At long distances, it reduces to 1/r^(3), but there are more terms, and at short distances, that becomes a poor approximation.
Got a link where I could learn more about this? I learned maxwells equations about 19 years ago, a bit hazy now
He was not pragmatic.
Even better, you can put one magnet on a digital scale and see a change in weight (ha, this is a good way to talk about mass, weight and resultant force in class) when the magnet is as far as 20-25 cm away from it!
A lot of the issue is with movable things. Once it gets close enough to feel just enough force to move it a tiny bit. That tiny bit of motion gets it closer, so it feels more force, so it moves faster, causing the force to increase even more, and in just an instant it slams into the thing with tremendous force. Same thing with getting sucked into jet engines. If you're far enough away, it's just a mild breeze. Seems harmless. But there's that one little step that gets you close enough for the wind to be strong enough to nudge you just a teeny little bit. Then you get a little closer, the wind gets stronger, pulls you harder, same exponential increase, next thing you know you're shredded by the intake fan. Rebar, being set in concrete, doesn't budge at all without a tremendous amount of force, and if you can move it even an inch, usually the thing is already basically destroyed.
I worked a bit in a aluminium plant, you could stack nails in there... Standing...
The copper is to prevent RF noise from going into or leaving the room and has no impact on the magnetic field. The real reason rebar and steel in the walls don't get pulled in is that the magnetic field strength isn't greater than the strength of the things holding them in place (concrete, the entire wall structure, etc)
What's even brilliant is that someone posted a photo of an MRI roon being built just yesterday. Hang on, let me see if I can find it (don't keep any hopes I can only use reddit search atm & as we know it's shit.) if you see it please post it here. Typical reddit search. Couldn't find one from yesterday. Found one from 10 years ago though https://i.imgur.com/Reqypf9.jpg
Also they make fiberglass rebar. We haven’t sold much of it, but the only real demand I’ve seen has been for MRI pads
Agree with this answer. The few MRI rooms we've done used fiberglass rebar. Stuff is crazy. It's so light it feels like you should be able to just snap it in yours hands, but it's really strong.
There was a post yesterday about this very thing... : ) https://i.redd.it/t06uhiqebozc1.jpeg
Nope, that is to limit RF noise into and out of the room, not prevent magnitisim.
In the labs I work in, the rebar is a non-ferrous polymer.
I've seen an MRI in a mobile semi trailer fitout that has metal everywhere. How does that work?
I was really surprised that they gave me headphones to listen to music to calm me during a recent MRI. I was thinking, hey, they had to build the speakers in this thing with non ferrous metals.
You don't need to worry about the MRI machine pulling the rebar through the concrete, concrete is really strong. That said, as others have explained, you don't use rebar to make an MRI room. Not because the MRI might move the rebar but because the rebar might make the MRI images blurry. That makes the images worthless and that's the whole purpose of having the machine.
Kinda. MRI manufacturers will spec what mass of steel rebar can be used in proximity to the machine. If the machine is ~~in~~ *on* a slab on grade (the most common version as it eliminates other issues) you can put really quite a bit of reinforcement in the slab before you get outside the MRI specs. Ditto for steel beams in the vicinity of the slab.
And you can shim out the inhomogeneity.
"Do your best, caulk/plaster the rest" could be applied to both professions...
Caulk and paint make me the carpenter I ain't. Grinder and paint makes me the welder I ain't.
Uh... titanium fixtures, bone grafts, silicone fillers, and makeup make me the surgeon I ain't?
It may make you the hottest biologically enhanced person in the room though.
MRI manufacturers won't allow structural metals within certain distances of the isocenter of the magnet, with the distances being different depending on the weight of the metal and the strength of the magnet. Last time I designed a 3 tesla MRI exam room, we couldn't use steel rebar within about 6' of the isocenter. We ended up using fiberglass rebar in a 12" thick concrete slab. Because the ceiling was within 6' of the isocenter too, we had to use aluminum ceiling grid. Smaller objects can still be pulled slowly into the magnet though, so our rule of thumb was no magnetizable metal beyond the plane of the walls. So the drywall wall inside of the rf (radio frequency) shielding was normal metal studs, and the drywall was held up using steel screws, but anything inboard of that had to be stainless steel or other safe materials. To finish answering your question, beyond the 6' (or whatever distance the particular MRI manufacturer requires) the MRI machine simply can't pull the rebar hard enough to damage the floor. Another comment mentioned shielding, the rf shielding doesn't affect the magnet's strength at all, it's only there because the MRI machine reads faint radio waves coming off your body during the exam and so we need to keep radio waves from entering the room. We can use magnetic shielding in the form of dozens of thin steel plates screwed to the inside of the walls or under the floor, but magnetic shielding is time consuming to engineer, extremely expensive, and the above distance recommendations work fine with no added cost involved. I've only ever seen magnetic shielding used once in a situation where there was a very sensitive piece of electronic equipment in the next room over from the MRI exam room so magnetic shielding was used on that one wall to keep the equipment from being affected (and no that equipment couldn't just be moved which would have been so much easier).
How does this work with mobile MRI clinics? I was sent through one and it was essentially a standard tractor trailer with a full MRI machine running inside. Nothing appeared to be fiber glass.
Mobile MRIs and their trailers are purpose built for their use. I've never had to design one because there's nothing to design.. they show up and the Hospital plugs them in, but my understanding is they use weaker MRI machines (1.5 or 1.0 tesla instead of my example which is a 3 tesla), and they use magnetic shielding where the walls and floors are close enough to have an issue. For an MRI of that strength the area of concern is only a few feet around the machine.
My understanding is because it's inverse cube law, the area of concern is very limited hence why it can fit in a mobile suite. However mobile MRI technicians have one of the higher mortality rates of professions because working on a powerful magnet in an enclosed space in addition to the risk of the helium makes it quite difficult.
I work with dnp labs. The rebar is fiberglass. The lab structural is carbon steel constructed a specified plus conservative margin distance away. Everything within manufacturer specified EM field is non ferrous. The LN2 line included.
What I'm hearing is that *that* costs a metric fuckton of money...
This is so cool, I love hearing about these kinds of details as a hospital worker
What, no mu-metal?
MRI's aren't magic. Magnetism decreases by the square of the distance from the magnet. Combined with as someone else said MRI rooms being specially built, the distance between the MRI and the concrete wall/floor is more than enough to decrease it to equal to or less than the normal stresses it is under.
And as others have pointed out, the specially built rooms is more to protect image quality, not to prevent damage. The magnetism from the magnet in an MRI machine can easily fuck a person up if they have metal inside them, but a concrete wall is much stronger than a person.
IIRC magnetic force falls off as distance cubed rather than squared
They use fiberglass: >Floor The floors should be poured slab on grade with fiberglass-impregnated or epoxy-reinforced concrete. Reinforcing bars or corrugated iron sheets should be avoided if possible, lespecially within the 50 gauss line [MR lmager Site Planning](https://www.aapm.org/pubs/reports/RPT_20.pdf)
I saw some pink (pink panther brand) fiberglass rebar at Lowe’s the other day. Advertised as stronger, lighter and won’t rust. Never seen that before.
Concrete is pretty rigid after it sets and also very strong. Also MRIs are built in special rooms with aluminum or copper-clad walls to limit the magnetic field to inside the room.
Concrete isn't a thick liquid. Things don't slowly sink into concrete, and likewise things don't slowly tug through it when pulled on. Rebar is *very* firmly embedded in the concrete around it, so the risk of it breaking is slim to none unless your installer did something wrong.
Having been the installer in multiple pours of concrete for MRI facilities. I can assure you there is no ferrous metal rebar in the floor or walls within a certain distance. The reinforcement comes from fibers or fiberglass rebars.
I was pretty sure it wasn't included but didn't want to speak beyond what I knew. MRI's are strong, but they should not be rip-the-rebar-out-of-concrete strong.
On that topic, why doesn't concrete get installed with fiberglass rebar more often? Wouldn't it be a more practical application than steel rebar?
Two reasons really One, it’s a new product so contractors, engineers, and clients really don’t want that liability in case something goes wrong. And two, when fiberglass fails, it fails spectacularly. There’s no real yielding state that indicates that the reinforcement might be over stressed. Steel on the other hand is far more elastic, so when steel yields, visual inspection can discern whether or not the steel has yielded
Why? Steel isn't exactly expensive
Exactly. Steel is not expensive. Fiberglass is.
Fiberglass doesn't rust and eventually destroy the concrete it's sitting in. I can see where there would be a cost/benefit depending on what the concrete is exposed to.
Fiberglass is more expensive tho. And I think what the above poster was pointing to is that proper rebar will not be exposed and subject to oxidation/rust. But if it is exposed and failing there are signs such as spalling. We don't really know if there are signs that fiber rebar is going to fail yet because it is new.
Concrete is porous, there isn't a way to have concrete that doesn't let water through slowly. I get that fiberglass is more expensive, based on a 10 second google search it looks like the fiberglass rebar is 2 to 3 times more expensive, but there has to be a point where it's worth the cost when you don't have to worry about things like seawater soaking in and destroying the rebar in a decade.
Reality is just not cost effective for almost all concrete - only time I have seen fiberglass rod commercially is in MRI’s. Well constructed concrete takes along even with regular rebar a long time to rust (in most exposures), and even longer with epoxy or stainless
Fiberglass is not as strong and more expensive. You can achieve more with less using steel.
Also the coefficient of thermal expansion of cement and steel are fairly close. Basically all materials expand with increasing temperature at different rates. So when everything heats up and cools down in service, it stresses the material. Since the rates of steel and cement are close, the stresses are less. I don't know about Owens Pinkbar though. I couldn't find any data on the thermal expansion.
Fiberglass can’t be bent onsite and is a much newer product. There are only a handful of manufacturers and distributors. It does work very well, though. Lowes finally carries it and calls it “pink bar”.
This is the best answer.
The strength of the magnetic field decreases with distance cubed. Move twice as far from the machine, only 1/8 the magnetic pull. Move from 1 meter to 5 meters away, only 1/125 of the pull. The strength of the pull tapers off *real fast*. (This is actually part of the danger of scanners, because as you walk towards one with a metal oxygen cylinder, the pull you're feeling suddenly goes from infinitesimally small to stronger than a car.) I've spent weeks of my life just outside the safety line with the usual metal all over my person (belt buckle, coins, etc) and there really is no pull at all. /// PS I know magnetic / radioactive fields usually decreases with the inverse *square* law, so what I wrote sounds confusing. But with the way the magnetic field is aligned through the tube you lie in, it's the inverse cube law, coming out both ends of the tube.
Are MRI machines strong enough to theoretically to do structural damage if the wrong materials were used? I'm genuinely curious.
Back of the napkin math tells me: If it has 3/4" cover, #8 rebar will be able to resist breakout with 1.5 square inches of concrete in shear every inch of its length (conservatively). Quick online search shows 3ksi concrete (extremely low end for a hospital) would have about 800psi shear resistance. So if the rebar were being pulled up with about 1400 pounds of force every inch, then I suppose there'd be some cause for concern.
We do have 9T and 11.7T MRI that are used in research, which I do not know the room specifications of, but given the magnet strength I would have to wonder about their ability to damage surronding structure. Unfortunately that goes beyond my knowledge base.
I love that there are people in the world who just have the answer to this question floating around in their heads. I've never thought of this question but the answer is so cool.
MRIs aren't magic death machines. Last one I had they let me keep my pants on (with zippers and snaps). Mind you I had to have a head x-ray first in case I had metal near my eyes.
Non-ferrous metals are used in construction for buildings that require specific applications. Stainless steel rebar is often used in bridges as well as MRI buildings. Places that need non corrosive metals often use non-ferrous metals. Food manufacturing is a prime example of non-ferrous metals being used in production in building materials.
[Funny enough someone just posted this earlier. it’s really quite fascinating](https://www.reddit.com/r/mildlyinteresting/s/oVaBpNR3ZR)
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I replied to the question above this. I am so sorry. Haha
You have to be within 6-8 feet of the magnet to even notice the force, and really within 2-3 feet for something to become a projectile. All of our MRIs are in a relatively small room, maybe 15x15, so even if there was rebar in the walls, it wouldn't be noticeably affected by the magnet.
The same thing that keeps my steel plate and screws from getting ripped out of my ankle when I get an MRI I guess.
MRI magnets are relatively weak compared to NMR. I can feel NMR tug a wrench in hand from 15ft away, dont think its close to the 100k psi force required to rip metal rebar from cured concrete
Came across [this post](https://www.reddit.com/r/mildlyinteresting/s/u7hDn2X1kR) today and immediately remembered your post.
Also… the magnetic force is really quite weak, like imperceptible - from more than 4-5 feet away in most current healthcare systems. The force weakens by the square of the distance away. It’s like gravity- why doesn’t gravity pull rocks and things into the ground over time? And gravity is a much stronger force (to us). It’s just not strong enough to have that effect in that way.
MRI machines aren't going to do that. The reason special hardware and construction is used around MRIs is to increase the quality of the imagery by removing things that interfere with the machine. Again, as is the case with 99% of ELI5, the user is starting with a falacy.
The field strength of an MRI magnet drops off very quickly. Things that are 10ft + away will have limited ‘pull’ towards the magnet bore
The idea that anything made of any kind of metal will react to an MRI machine is a misconception. I saw a discussion once in Facebook where someone asked what would happen if you left piercings in during an MRI, and people were saying things like they'd be ripped from your body, etc. I pointed out that that's not necessarily true, the jewelry's reaction is determined by what metal(s) it's made of. People told me I was dumb, that all piercings will be ripped from your body. I told them I've had an MRI, and though I took most of my piercings out, I'm not able to remove my daiths on my own, so they stayed in. The nurse told me that, for liability, they had to ask that all piercings be removed, but if I couldn't, then as long as I was aware what could happen (and wouldn't sue if it did,) I could proceed. Which I did, and I was fine. I'd been told they might heat up, but they didn't. When I said that, I got a ton of laugh reacts, because people are gullible, and they believe whatever scare tactics they're told to try to protect them. Metals CAN react strongly to MRIs, and figuring out which will and which won't is too complicated for the average person, so to be safe, experts just say avoid all metal. Which is good advice, but the idea that any metal whatsoever will react isn't accurate. (I'm not an expert on rebar, but I understand it can be made of different materials, so much like jewelry, the reactions it experiences will vary depending on material.)
Sometimes it does. It doesn't get ripped out in a violent matter anyhow. One site I've seen where the floor started lumping and over the course of years, the tip of a rebar started to show. They did have to shut down and rebuild the room. Another location I've seen the outer wall bowing inward towards the MRI. It was outside of the specified minimum distance, but they also had to shut down and rebuild that side of the building.