Can an MRI really rip metal through flesh?

Factual Questions
1

Magnetic Resonance Imaging or “MRI” uses a super-powerful magnet. So they always tell you to remove all metal, and apparently cannot be used on anyone who has metal inside his or her body.

I’ve heard joking remarks on TV about MRIs ripping people open if used on someone with metal in their body. Would that really happen?

I was watching 20/20 about a woman who has shotgun pellets in her brain and I thought - man, an MRI would scramble her brains!

So what’s the truth? I’m sure shotgun pellets probably could be pulled through brain tissue, which is notoriously soft, and the pellets are unanchored. But what about pins and plates bound in bones?

2

Not only will it yank metal through your body, it will throw an oxygen canister at you from across the room.

Of course, magnets only attract some metals (Iron and most ferrous alloys, etc.) I think shotgun pellets are usually made out of lead. I’m not sure if they’re magnetic or not.

3

Actually being ripped out of the body? Probably not…but cause intense pain and damage to the body? Yes. The magnet in an MRI is crazy powerful. However, the vast, vast, majority of medical implants are made from non-ferrous metals (mostly titanium and non-ferrous stainless steel alloys.)

Here’s a video about MRI safety. It’s long, but just go to about the one minute mark to see a metal wrench fly through the air and obliterate bricks that are between it and an MRI magnet.

However, like I said, the odds of it happening to a patient are slim…for one, they would not only have to have one of the few implants that are ferrous, but they’d also have to somehow avoid having it be noticed by the doctors/MRI techs. It’s pretty common to get an X-ray or two or three before an MRI if anyone is unsure if you have metal in you. Most of the implants that are ferrous are electronic, like a pacemaker, cochlear implant, etc, and therefore even more likely to be known about by the patient and be on their chart…most plain metal things (pins, screws, joint replacements) are ok to be in an MRI, however, the metal will still cause distortion and artifacts in the image itself (there’s also a small risk of the metal getting heated through induction.)

As for shotgun pellets…I have no idea if those are ferrous or not. But yes, if they are, she would be fucked in an MRI. Hell, she’d probably be fucked just entering the room it’s in, without it even being on. But again, if the doctors, nurses, and techs are doing their job, she’d never get to that point. IIRC, most injuries and deaths from MRIs aren’t from something internal to the patient, they are from someone bringing something external into the room that then flies into the bore of the MRI, where the patient is, at very high speed. The most common culprit is an oxygen tank…how the fuck this happens I have no idea. There are aluminum O2 cylinders that are clearly marked that they are the ONLY kind to be used near an MRI, yet someone the steel ones work their way in there…

4

Shotgun pellets are often made of steel, particularly for waterfowl shooting. (It’s often mandated, as lead can be ingested by fowl and result in lead poisoning). Steel, being largely composed of iron, is magnetic and steel pellets within the body would be problematic within an MRI. Lead, all by itself, is not magnetic. From this cite (Ctrl-F for “lead shot”), shotgun pellets are 99.8% lead, and 0.2% antimony; neither would be attracted to a magnet.

5

I have had a few MRIs. Once, as I was being slid into the machine, I heard a massively loud bang. It was my keys, which we had all forgotten about, smacking into the side of the tunnel.

That could have gone horribly wrong…
pdts

6

I have a platinum clip on a blood vessel in my brain. I’m told it will be safe…

7

Wow; even though you ended up alright, that’s actually rather horrifying. I mean, I would think they’d be ultra-zealous about checking for any and all potentially magnetically problematic material, but in particular, I would think keys would be just about the most common metal objects to account for…

8

Yeah, I’ve only done an MRI twice but it seemed like emptying your pockets is a pretty standard procedure. I can’t imagine them just forgetting to implement that step when they are supposedly doing it every single time they use the machine - so if it happened once, it means they probably weren’t doing their jobs on a regular basis.

9

I have my MRI outfit - a knit sports bra that pulls on over my head, no underwires or clasps, a big oversized tshirt and light sweat pants … and I know I have alloy B bronze shrapnel in my face and neck, but it is not magnetic so we don’t worry about it =) All I do is remove my medicalert tag and earrings and I am good to go!

I can not imagine being in the bore and having a cylinder come clanging in and braining me :eek:

10

Just how many teslas are used in a standard MRI magnet and how does that compare to a reasonably high-field (say 500 MHz) NMR magnet? Personally, what would scare me even more would be the (extremely unlikely) chance of a quench while in the tube. I’ve seen an NMR quench and I’d prefer not to see another one. (The Varian tech was bringing a brand-new one online and it quenched.)

11

quench ??

12

Now, now, wait a minute…

Doesn’t anybody here have metal fillings in their teeth? Did THOSE go ripping out? Clearly, little nonferrous things aren’t going to move perceptibly.

I went for an MRI a few years ago and noticed a funny vibrating feeling on my hand, and realized I still had my wedding band on. I thought I was ruining things and pushed the little button, and asked, and they said it didn’t matter and they didn’t ask people to remove them anymore, which they had been doing for my previous MRIs. So, standards are relaxing.

Most recently I got a titanium “plate”, a two inch boxy figure “8” with 8 screws of titanium, in my neck. I asked, and they said I could still have MRIs, I just needed to tell people about this, and it would somewhat distort and scramble the images of the immediately surrounding area.

Now, IIRC, MRI machines use a magnetic field intensity of a tesla or two or three, with the number gradually increasing over the years, and the machines cost a million dollars per tesla as a rule of thumb. You can feel a one tesla field at the surface of a good neodymium iron boron magnet. These are the pricy little chrome plated ones they sell now in hardware stores, the ones that snap together so hard they can shatter. In the right circumstances these can pull an iron splinter out of the eye, I hear, but in general the fact that you can grab something iron with your fingers and pull it off the face of the magnet means that it’s not going to drag such things through your flesh unless you’re talking very soft flesh.

A steel nail precariously embedded right between various delicate structures in the brain sounds like something to worry about. A forgotten earring doesn’t sound very dangerous, though.

The steel oxygen tanks are another story, but they aren’t a good analogy for implanted metal. The oxygen tank is dangerous because it starts out a few feet away and accelerates through the field before meeting the patient. It gets a running start. If you dropped the tank on the patient from a height of 20 feet, that could also be a real problem, but we don’t say that gravity makes implanted metal dangerous, do we?

13

Gas cylinders should always be chained down. Standard safety procedure anywhere.

14

Just what it sounds like. Any NMR these days uses a supercooled superconducting electromagnet. The magnet is, basically, a loop of wire cooled to about 5 K by liquid helium. (The liquid helium is kept cold by a much larger dewer of liquid nitrogen at 77 K.) At that temperature, the metal becomes superconductive and the magnet is created by sending electricity through the loop. Once it’s fully energized, the magnet can keep running indefinitely without needing to add any more electricity to the system as long as it’s kept cold. For an NMR, the liquid nitrogen fill schedule is about once a week and the liquid nitrogen fill is about once a month. If for some reason some part of the magnet is no longer cooled and can start to heat up, that starts vaporizing the liquid helium. As that starts to expand near-explosively, all of a sudden you’ve got a big plume of inert gas coming out of the magnet and it won’t stop until the phase change is complete. In the meantime, everybody needs to get out of the room as there can be enough gas generated to dangerously lower the oxygen level. An NMR quench means lots of downtime and money lost as the magnet has to be brought back online.

15

I wondered about your posting, too. Near as I understand, a quench is just emptying the cryogen from the coil assembly through an exhaust pipe. From the point of an MRI center, I can see why buying and installing a bunch of liquid helium, and canceling a bunch of patient procedures, would be a big negative. But it doesn’t sound like the event of quenching itself would be bothersome. Why would you prefer to never see another one? Was there something upsetting about it?

16

Depending on the setup it can be really loud and you may not be able to see anything because of all the condensing water vapor from the cold gas coming out of the instrument. I wouldn’t call it traumatic, but it could be kind of scary if you don’t understand what’s happening.

And it’s not just bothersome; it may ruin the instrument. No guarantee that you’ll be able to reenergize the magnet.

17

http://video.google.com/videoplay?docid=-7139941690708614565

18

That’s… interesting :eek:.

I had an MRI a couple of months ago and they gave me scrubs to wear for the process. I guess they didn’t want to risk anything. The other MRI that I had, many years earlier, I was able to wear street clothes after assuring them there was nothing metallic in them.

I had surgery (gallbladder) a month or so after this most recent MRI and the surgeon assured me that the metallic clips used were titanium and would not pose problems with future MRIs.

19

More of an issue than being ‘ripped out of the body’ is the torquing/twisting of tiny bits of metal (ferrous or not). As the fields are changed/pulsed in the acquisition of images (the bangings heard during a scan, per se), things metallic can be twisted back and forth to align with the ‘pulsing’ mag field (which is stationary when not scanning). This, and the heating of loops of catheters or such, are big issues with medical magnets and little pieces of stuff within persons. I’ve had plenty of patients tell me that they could ‘feel’ the labeled-safe clip while the scanner was doing its buzzing, and many of them I actually believe.

20

Don’t forget, that as the coolant evaporates, the coil with a whole pile of stored magnetic and electrical energy is no longer superconductive - all that magnetic and electrical energy has to go somewhere as well, usually with a jolt and maybe a bang. When the LHC quenched a few days after startup (link), massive magnets had to be realigned along with the electrical repairs. I can imagine for an MRI system, that sort of repair is expensive.

Si