MRI And Metal

Many people just learning about MRI safety and hazards ask very similar questions. One of most frequent is, “why do I have to remove all metal before an MRI,” or it’s corollary, “can I get an MRI with some metal on (or in) me?” To answer these questions, let’s start at the very beginning…

As far as the MRI machine is concerned, there are two different types of metal, ferromagnetic and non-ferromagnetic. You may remember back to high school chemistry and the periodic table of elements where many of us learned (and then promptly forgot) that Fe is the symbol for iron.

Fe - Iron from the Periodic Table

Fe - Iron from the Periodic Table

“Fe”, the symbol, is derived from ferrum, the Latin word for iron. Ferromagnetic does not mean that a metal contains iron, but rather that the material has magnetic properties as iron can.

Ferromagnetic metals are iron, cobalt and nickel. These raw ingredients are common in many, many things made from metal, including (likely) the steel grommets in your shoes, to the zipper in your pants, to components in your wristwatch. Another common area to find these metals is in batteries, such as those found in your hearing aid, cell phone and iPod. There are a few non-metal ferromagnetic materials, but these are not very common.

Alright, alright, already… enough chemistry. What does this mean?

When exposed to magnetic fields, ferromagnetic materials become magnets themselves. You can prove this yourself with a fridge-door magnet and a few paper clips. You’ll probably find that paper clips right out of the box aren’t capable of magnetically ‘sticking’ to one another. If you stick one to a chunky fridge-door magnet, however, that paper clip is now magnetized and will likely be able to magnetically ‘stick’ to another paper clip. The length of the magnetic chain of paper clips you can create is a function of how strong the fridge-door magnet is and the magnetic properties of the paper clip steel.

Now, the exact same thing happens with ferromagnetic metals approaching the MRI, but a crucial difference is the distance at which the materials get attracted. With your fridge-door magnet test, the paper clip needs to be touching (or very nearly so) the magnet before the attractive effects are felt. MRI’s, by virtue of the fact that they’re both 1,000’s of time stronger and larger than your fridge-door magnet, can exert profound attractive force at a good distance away from the magnet.

The size and strength of MRI magnets is so great that people have been trapped, injured, and even killed by the force of ferromagnetic objects attracted to the MRI. From concealed roller-skate tennis shoes, to steel-reinforced furniture, to conventional hospital wheelchairs and gurneys, to steel oxygen cylinders, all of these normally harmless (outside the MRI suite) items become life-threatening when subjected to the enormous pull of the MRI’s magnet.

Not all metals are ferromagnetic. In fact, in an MRI suite a concerted effort is usually made to rid the area of ferromagnetic materials and use non-ferromagnetic replacements whenever possible. Non-ferromagnetic metals include aluminum, titanium, brass, copper, and many others. These (and other) non-ferromagnetic metals can present other problems and hazards during MRI imaging, but that’s a topic for another day.

It is almost impossible to determine whether a material is ferromagnetic just by looking at it. In fact, even sometimes when you know what an object is made of, it still isn’t enough to know whether it’s ferromagnetic or not. Stainless steel, is one of these examples.

Stainless steel is not a metal, but rather a family of recipes for metal. Some stainless steel ‘recipes’ (alloys) call for ingredients with ferromagnetic properties. Others which include ferromagnetic ingredients are specially formulated to change the structure of magnetic materials into non-magnetic versions of the material. These special ‘de-magnetized’ stainless steels can become ferromagnetic if the steel is manipulated (shaped, bent, heated, or stressed), so even magnetically ‘safe’ stainless steels can become ‘unsafe’ under certain circumstances (a change that isn’t observable to the eye).

It is remarkably difficult to distinguish magnetically ‘safe’ metals from magnetically ‘unsafe’ metals, either by simply looking at them or, sometimes, even if you know what the metal is. As a result, MRI facilities must assume all metals to be magnetically unsafe unless and until they’ve been verified to be non-magnetic.

So, how do MRI facilities distinguish magnet-unsafe metals? They can use magnets, which shouldn’t be used on patients or sensitive equipment, limiting their applicability. The safer option (and arguably more effective, to boot) is to use a ferromagnetic detector, at least on patients and sensitive equipment.

Ferromagnetic detection instruments, such as the Mednovus products, should be used to help identify magnetically-unsafe materials. This is the standard established by the American College of Radiology, the VA’s MRI Design Guide, and even recommended by the Joint Commission in Sentinel Event Alert #38.

As a patient, it is vital to take seriously the admonitions against wearing or carrying metal into the MRI suite. If you have shrapnel, penetrating metal injuries (particularly in the eye), or any surgeries, implants or prosthetics, it’s critical to have the full information on each to share with your MRI provider. Metal inside the body may not fly across the MRI room like a loose oxygen cylinder (don’t believe what you see on House), but the twisting an pulling that the magnet will exert on an internal ferromagnetic object can be just as dangerous. Active implanted devices, such as pacemakers or nerve stimulators, present particular problems because of both the magnetic attraction and potential interference with the normal function of the device.

Patients should also actively seek out MRI providers that conform with the contemporary safety recommendations, including the use of ferromagnetic detection. You can even contact Mednovus when you want to find providers near you who have this technology available.

Providers of MRI services should make sure that the pre-screening and safety services they provide are in accord with the contemporary best practices, including the use of ferromagnetic detection. With available ferromagnetic detection products equal in cost to only a few hours worth of technical revenue, there’s no financial rationale for not providing this valuable safety benefit to patients and staff. Plus, when weighed against the costs of ferromagnetic object accidents, these instruments of safety are clearly effective risk-management investments.

In all cases, metal brought to the MRI suite (either inside or outside the body of the visitor) should be scrutinized by a trained MRI staff person. This investigation should be aided through the use of ferromagnetic detectors, both to help characterize the hazards of any particular object and to help find ferromagnetic materials that weren’t caught in the prior screening process.

Tobias Gilk, President & MRI Safety Director
Mednovus, Inc.
Tobias.Gilk@Mednovus.com
www.MEDNOVUS.com

180 thoughts on “MRI And Metal

  1. Tobias Gilk Post author

    Rohit,

    I’m not aware of any latent / long-term health consequences having been reported for having had an MRI exam with cosmetic jewelry in place. In my opinion, if there was a problem, it likely would have been apparent at the time of the MRI scan (or very shortly thereafter).

    I hope this helps.

    Tobias

  2. Tobias Gilk Post author

    Nancy,

    I’m sorry for your experience. I would encourage you to discuss this with your general physician if you think that the GI doctor may have done something incorrect (and you want an impartial professional medical opinion).

    I hope this helps.

    Tobias

  3. Tobias Gilk Post author

    Joe,

    I’m not familiar with Inconel as a material. The size or quantity of screws, alone, don’t worry me if their materiality is deemed ok for the magnetic fields to which they’d be exposed (and the screws are embedded). The follow-up question (in my mind) would be what are the screws holding? I presume there’s another structure involved, besides the screws.

    Tobias

  4. Tobias Gilk Post author

    NM,

    In sufficient quantities / concentrations, aluminum or titanium could create a very localized distortion to the magnetic field and would potentially result in a signal loss artifact right at the skin surface. But with the relatively modest amount of metals in most antiperspirants, I should think that any artifact (based on conventional usage) would be negligible, if even detectible.

    I hope this helps.

    Tobias

  5. Tobias Gilk Post author

    Douglas,

    Depending on the stent, it’s quite possible that you could safely have an MRI exam. My recommendation is to get all the information you can about your stent (manufacturer, model, date of implantation, etc…). If they gave you an implant card when you got the stent placed, that should have the information I’m talking about.

    If you’re ever proscribed an MRI, share the information about your stent with the radiologist who will be overseeing your MRI exam. She/he will evaluate it and make sure that there’s no safety risk to you to going forward, or will suggest another imaging option.

    I hope this helps.

    Tobias

  6. Tobias Gilk Post author

    Elizabeth,

    If you’re proscribed an MRI, just make sure to tell the hospital or imaging center about the staple. Depending on its size and position, it may be a complete non-issue, but make sure to share the information with the imaging center before your exam.

    I hope this helps.

    Tobias

  7. Robert Szymanski

    I have a medical issue with my penis and a doctor had a titanium “tube” held in place with a piece of brass. When I go through the airport detector or the courthouse detector, nothing happens. How about an MRI? The device is on permanent..

  8. Tobias Gilk Post author

    Unless you have a specific statement from the implant manufacturer (either on the implant card or in the supplemental information that should be available from the manufacturer) about MRI safety conditions, I advise against making any inferences or generalized statements of safety for this type of implant. If you are ever referred for an MRI, please share any and all information about the implant with the MRI provider so that they can make an informed risk:benefit assessment.

    As an aside, ‘airport’ style metal detectors are highly variable in sensitivity, and I wouldn’t rely on the absence of an alarm from one of them to tell us anything clinically useful.

    I hope this helps.

  9. Nidhi

    One of my patients,was operated upon and a Titanium plate with titanium screws implanted in forearm by an Orthopaedic surgeon. He had a very bad experience(the arm with implant was pulled in) while undergoing MRI of the same forearm and was rejected twice by the technician(the scanner kept beeping). But the third Radiologist managed to the MRI with minor artefacts. What went wrong?

  10. J. White

    I had a brain tumor removed 36 years ago. I was left with 4 staples in my skull. I am now hearing that I can have an MRI…that technology has progressed to the point where people can have an MRI. Not sure if I believe what I have heard. Any specific comments from anyone??

  11. Tobias Gilk Post author

    Nidhi,

    The situation you relay on behalf of the orthopedic surgeon makes no sense to me, and I suspect that you’ve been given bad information. If the implants were titanium, then there’s no way that they could have been pulled in to an MRI, as titanium is non-magnetic at the field strengths used for clinical MRI. Now if the implant was made up of mixed metals… some titanium and some other materials… the other materials may have experienced attractive forces. But particularly with orthopedic implants, anchored to bone, the likelihood of anything ‘flying’ is vanishingly small.

    I also don’t understand the ‘beeping’ statement. MRI scanners typically make a ‘chirping’ noise, all the time, as a part of their operation, and then loud and obnoxious noises while they’re scanning. I’m not aware of any MRI system that ‘beeps’ as a warning of metal.

    I hope this helps.

  12. Tobias Gilk Post author

    It may have always been a manageable risk to have an MRI with metal bone-closures, however different MRI providers have different levels of expertise in (and comfort with) defining risk profiles. Often if an implant or device is not specifically tested and approved for a specific set of MRI conditions, many MRI providers feel ill-prepared to independently perform a risk-assessment, and will turn implant patients away.

    Should you ever have a doctor tell you that you’d benefit from the information that an MRI could provide, I would strongly recommend that you talk with a radiologist about what the relative risks of a study might be with the bone closures that you have. My suspicion is that s/he would say that the risks would be quite low.

    I hope this helps.

  13. Pankaj Shukla

    Hi!
    Can you please advise me if SS 316 L and SS 316 LVM used in orthopaedic implants are MRI compatible, i.e. MRI safe alloys?

    Thanks

  14. Tobias Gilk Post author

    Pankaj,

    316 stainless steel alloys are low iron / low magnetism formulations of stainless. However, any material identified as “steel”, even “stainless steel”, must – by definition – include at least some iron in the alloy. From a magnetic attraction / rotation safety standpoint, 316-L series alloys are one of the safer material choices.

    Quite apart from attraction and rotation factors, however, are electrical conductivity considerations of a material, and the potential to conduct or concentrate induced electrical currents that are a natural byproduct of the scanning process. In this respect, *any* metal carries a potential risk, and it comes down to the specific design / engineering of a product to minimize the risks of collection / conduction / concentration of induced currents.

    I hope this helps.

    Tobias

  15. Andrew Staley

    My daughter went into MRI room while her daughter had an MRI. She had acl surgery and has some metals in her knee.S Since that day she has been in terrible pain in her knee. Could sitting in with her daughter caused some type of injury.

  16. Marina

    Hi, thanks in advance for your shared time and knowledge. Though not exactly your expertise, I am wondering about health risks (not in terms of mechanical issues such as attracting the metal from a body or disrupting the imaging or proper activity of a MRI machine) of having metal while taking MRI. Like, is it possible to cause tumors in tissues around the spot where the metal was placed and similar health conditions in long term? May sound like a silly question, but I am currently undertaking chemotheraphy due to colon tumor and yesterday I had my abdominal MRI taken and I was wearing one of those surgical masks which I was advised to wear at all times when in hospitals. Though the technician was meticilous about cheching for metal, she completely dismissed the mask and a wire on the top with a purpose to adjust the mask on the nose. I am so used to wearing it that I didn’t even realised I was wearing it until half way through the scan. Afterwards I asked about it and she said I didn’t matter since the imaging was taken on the abdomen, away from the head, and that only problem with metal is that it messes up the images. Didn’t buy it, as she didn’t seem so convincing. Afterwards I have experienced headache and weakness but did so also after a PEt CT I have few weeks ago. Thanks again for your input!

  17. patchoulip

    Extremely useful info on this site!

    What about wearing sunscreen during an MRI? I’m especially concerned about physical sunscreen – the one containing zinc oxide and/or titanium dioxide. I’m asking because I’ve read on different sites that one shouldn’t be wearing any lotions, make-up, nail polish etc. when getting and MRI, as those products can have metals in them. But I couldn’t find anything specifically on sunscreens.

    I’m gonna be getting my third MRI in a few days. For the last two, I didn’t wear any sunscreen on the way there, just to be safe, and just applied it after. But this time, that isn’t an option, so I’m wondering if I can simply wear it during the procedure or I should go through the hassle of washing my face at the hospital prior to the exam and then reapplying. Would it be safe to wear or would metal particles burn my skin as they fly off through the room? ZnO and TiO2 are not ferromagnetic on their own, right? It’s a knee MRI, if it makes any difference.

    I remember being pretty freaked out when I went for my last one and the nurse told me to keep my jeans on! She said it didn’t matter that they had metal buttons because the MRI was for my head, so it wouldn’t be focused on the leg area. That’s probably stupid, right? Since the magnetic field is all over the room, regardless of the targeted area. Reading your article, I learned that buttons on clothing are fine because of the type of metal they’re made of. Also, when I called to schedule the current MRI, the woman on the phone told me, among other things, that I can’t take it if I’m wearing braces. I’m not wearing braces, so that’s not an issue, but apparently that’s a big problem for braces wearers: they have difficulty finding a clinic or hospital willing to take them in for an MRI, although it shouldn’t be a problem from what you’ve said. So you see why I can’t just call the clinic and ask about my sunscreen dilemma 🙂

    Greeting from Romania and thanks a lot in advance!

  18. Tobias Gilk Post author

    Andrew,

    In the US, most orthopedic implants used today are made from non-ferromagnetic (or very weakly ferromagnetic) materials. It’s unlikely that the magnetic field from an MRI could impart significant force on a non-magnetic orthopedic implant.

    I hope this helps.

  19. Tobias Gilk Post author

    Marina,

    While there (clearly) are physical interactions between metals and magnetic fields, I am not aware of any scientific consensus (or even substantial minority opinion) that would suggest that the interaction between an MRI’s magnetic field and a metal object on or in a patient would produce some persistent bioeffect. Were I in your shoes, I -personally- would not be concerned about long-term effects from any interaction between metal and the magnetic fields.

    I hope this helps.

  20. Peter

    Hi, thanks in advance for your shared time and knoeledge, I had couples metal tooth crowns and dental fillings from 1
    980s. I don’t know what material they are and I have no way to find the dentist. My doctor asked me to do a mrcp on my abdomen. Am I safe to do that, will my crowns be pull out during the test? What I suppose to do? Thanks for answering.

  21. Leanne

    I have an MRI on my lower back & the R) side of my neck booked. I have various facial piercings which can easily be removed, however there’s a surgical stainless steel piercing in my R) ear which hasn’t been removed since it was put in over 15yrs ago. Will it be ok?

  22. Elaine Devonis

    My neurologist would like me to have a brain MRI done. I told him I had jaw surgery done in 1983, and I have wire in my jawbone. He thought it should not be a problem. I have since found out that I have 24 and 26 gauge wire in my jaw as well as some type of splint and K-wires. Do you think it’s okay for me to get an MRI? Thanks.

  23. Natalia

    Hello,

    Im sorry if there was previously the same question (i have checked few comment pages tho). I have scheduled neck MRI this saturday and im concerned whether or not it can be done. I have 3 bridges and few cobalt-chromium crowns in my mouth (Bridged are covered with ceramic on but not crowns on the back). Normally these metals are dangerous in MRI but i have read that new gen machines can be used when patient has dental metals. If its true, which models are safe to use in my case?

    Thank you

  24. Tobias Gilk Post author

    Jonathan,

    Whenever there is a retained metallic body (e.g. a bullet), unless you can specifically test the object for ferromagnetism (either with a magnet or a ferromagnetic detector), it is best to presume that the object is ferromagnetic and may experience pulling and / or twisting forces when brought near / in the MRI scanner.

    With that presumption, I recommend having a conversation with the supervising physician / radiologist who would be overseeing your exam and see if they would anticipate any risk from the retained projectile greater than that of bruising or discomfort from the proposed study.

    I hope this helps.

  25. Tobias Gilk Post author

    This is a very interesting question. I’m not aware of any reports of MR injuries related to the presence of sunscreen. I suspect that this is because, while sunscreens do include metals, the metals are in such low concentrations that they don’t form a particularly effective electrically-conductive pathway.

    I, personally, would not be particularly worried for my own safety if I were to have an MRI exam while wearing sunscreen.

    Very interesting question. I hope my reply was helpful.

  26. Tobias Gilk Post author

    Peter,

    Even if your crowns were pure iron (they’re not), there’s only so much force that a small amount of metal can exert from magnetic attraction. As a thought-illustration, you could stick a paperclip to bigger, and stronger magnets. At some point (pretty quickly in this experiment) you’d find that no matter how much bigger or stronger the magnet was, the attractive force on the paper clip wouldn’t continue growing meaningfully… it effectively ‘maxes out’ at a point. The same would be true of your crowns, if they were ferromagnetic.

    In the USA, most (but not all) dental work is done with materials that are very weakly ferromagnetic. If your crowns are such, then I would expect the force from the magnetic field to be the tiniest fraction of the force that they experience daily through chewing.

    If I were in your position, I -personally- would not have safety concerns about having an MRI study with a couple of metal crowns.

    I hope this helps.

  27. Tobias Gilk Post author

    Leanne,

    “Surgical stainless steel” isn’t a specific alloy of stainless (“stainless’ isn’t a metal, but rather a family of alloys / recipes, different versions of which have very different magnetic properties), so unfortunately that doesn’t tell us anything meaningful about the potential attractive force.

    In general, the smaller and rounder a magnetizable object, the less magnetic force will act on it. So if the piercing is long and / or large, then there’d be greater concern. This would be easy to test, however, with a sufficiently strong hand-held magnet.

    If the piercing is not attracted to a magnet, then there’s no real concern about pulling or twisting. Even without being attracted to a magnet, there is a potential risk that the metal will distort the magnetic field needed to get a clear image. The amount and reach of the distortion will depend on a number of factors, but again, size is not your friend with respect to distortion.

    If the piercing is attracted to a magnet, then -if it can’t be removed, readily- you may want to see about using a compression bandage (such as an elastic ‘Ace’ bandage) to press that piercing against your head to reduce the amount that it could pull or twist. If it’s attracted to a magnet, this also means that the physical volume around it that may be distorted would be greater. At some point the artifact created by the metal could be big enough to interfere with the clinical value of a study meant to be looking close by.

    My recommendation would first be to see about getting the piercing removed for the MRI study. If that’s not what you want to do, then I’d encourage you to have a conversation with the physician / radiologist who would be supervising your MRI exam and get their thoughts on how best to proceed.

    I hope this helps.

  28. Tobias Gilk Post author

    Elaine,

    The specific safety profile of an MRI study should really be resolved with the radiologist who would be overseeing the exam. Depending on the MRI provider’s equipment and capabilities, I think that there’s a good chance that you can have an MR exam safely. However, this will depend on the combination of your particular implants (location, size, materiality) and the parameters of the MR equipment and exam.

    If your neurologist wants you to have this exam, then I would encourage you (and potentially your neurologist, too) to work with the radiologist to define a method for you to safely obtain this exam.

    I hope this helps.

  29. Tobias Gilk Post author

    Natalia,

    Newer machines have software that is better able to combat the image disruptions (artifacts) that metal implants may create, but the effects of magnetic fields on magnetic materials is not mitigated by new MRI equipment features.

    The good news is that most metals used in the West for dental work are not significantly ferromagnetic. Your MRI provider and the supervising radiologist will likely have a few questions for you, but my speculation is that they are unlikely to find anything particular to your dental work that would be a significant safety issue for you to receive an MRI exam.

    I hope this helps.

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