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

119 thoughts on “MRI And Metal

  1. Anne

    I had an MRI of my brain a few years back, and accidentally wore metal while in the machine. The staff didn’t tell me to take my sandals off, so I left them on. I assume the metal was ferromagnetic, as the whole time I was getting the test, I could feel my legs being pulled towards the machine. What a creepy sensation! Luckily it didn’t affect the scans.

  2. T Lopez

    I have a vaginal piercing that I can’t remove, & I’m scheduled for an abdominal & pelvic MRI. Could this cause a problem.

  3. Cindy

    I have a knee brace that has copper-zinc-alloy in the side panels. Can I safely wear this when I am with a patient who is having an MRI?

  4. Tobias Gilk Post author

    *Most* commercial piercings are made from stainless steel or titanium. Titanium piercings are typically good in terms of having no meaningful magnetic attraction. Stainless steel, however, is just a ‘family’ of alloys, some of which can be strongly attracted to a magnet, others will exhibit virtually no attraction. Particularly if the piercing is in an area you’d rather not show the technologist who will be running the MRI scanner for your exam, you may want to test the magnetic nature of your piercing yourself, prior to the exam. If you have a strong magnet (not one of those thin ‘business card’ magnets that pizza companies like to give you to stick on your fridge), you can test to see if there’s noticeable attraction. Be aware, however, that the stronger and larger the magnet you’re using, the further away from the magnet’s surface a ferromagnetic object needs to be before it ‘snaps’ to the magnet. Make sure you’re prepared for the piercing to move, or immobilize it, somehow, when you’re testing. Also make sure that there are no fingertips or folds of skin that might get pinched. Be aware, however, that an at-home test like this – while a good indicator – is not a guarantee that the piercing won’t experience some pulling. MRI scanners’ magnetic fields are much stronger than any magnet you might have at home.

    Apart from the pulling concern, metal does distort the MRI image immediately around it’s location. The less magnetic the metal, the closer the distortion is limited to the location of the metal. Titanium alloys frequently only disrupt the image for a few millimeters from the metal. Ferromagnetic alloys, on the other hand, can make several cm of the image unreadable (the size of the distortion is also dependent on the settings for the MRI scanner for each scan).

    It is always very important to let your MRI provider know of any piercings you have in you prior to your MRI. They will discuss with you the safety ramifications (which would be a good time to discuss the home-test you did, if you did it), and you’ll want them to know about the presence of metal so that they can make any needed adjustments to the settings for the scanner, if that’ll be necessary to get the clinical images that the doctor is after.

    I hope this helps.

  5. Tobias Gilk Post author

    While neither copper nor zinc are ferromagnetic (attracted to magnets), the MRI site may have specific criteria / requirements regarding non-patients in the room, and screening procedures to make certain that nothing is brought into the room that could harm someone or damage the scanner. I strongly recommend that you check with the MRI provider, directly, about their policies for this.

    I hope this helps.

  6. Tobias Gilk Post author

    Most civilian munitions (other than bird shot) in the US are lead, which is a non-magnetic material. If this is the case for the projectile in your leg, then exposure to the magnetic fields of an MRI should have virtually no effect on the bullet. Heating is a concern of electrically conductive materials, but both because of a bullet’s small size, and because of lead’s comparatively poor electrical conductivity, heating is not likely to be a clinically-significant concern, in my opinion.

    If there is a concern that the slug is of a ferromagnetic material (and might be twisted / pulled by the magnetic field), then the radiologist should review X-rays to see if the projectile has deformed and has sharp edges, or might otherwise cause meaningful damage if it moved. A small ferromagnetic sphere (or near-spherical shape) might move with the magnetic field, but unless it was close to sensitive structures / vessels / organs, that movement would likely only produce some discomfort, and potentially bruising, in my opinion.

    In either case, you should check with the radiologist at the imaging center where you will get the MRI and have him / her do a risk : benefit assessment about imaging your leg.

    I hope this helps.

  7. Gennel

    I would appreciate some advice please!!
    Today my husband had an MRI of his knee because he’s been having pain bending and turning
    For several weeks. Today during the MRI he was asked if he ever had surgery on his knee because they see a piece of metal in his knee?!!
    He’s NEVER had surgery, never been on an accident.
    The tech clearly saw it and had to stop the test and put something under my husband’s leg in order to proceed with the MRI. So now we wait for the doctor to review his MRI and hopefully explain how and why my husband has a piece of metal in his knee???
    Any thoughts ?

  8. Randy

    I am building set of cabinets for a company, which will be in an MRI room. Should I look for non-ferromagnetic metal for the cabinet hardware?

    Thanks for the help

  9. Lyuda

    I had a brain mri done recently, wore an underwire bra in the machine. The technitian said it was ok. Having chest pains, weakness, spells of dizziness. Wonder if the metal have effected my heart? The metal in the bra was ferromagnetic as I tested it with a magnet later

  10. J. Nunez

    Hi this is a great post. Question : i have Essure coils implanted in my fallopian tubes which is made up of metal alloys, and mainly nickel. They have been inside of me for over 7 years. Would this cause an mri to be unreadable or give unremarkable results? Also would the mri cause then to move or heat up? Thank you

  11. dawn turner

    HI, I had an MRI on my right knee yesterday. I have 2 piercings in my ear (trogan) which help with my chronic migraines. They tested the metal and said i could leave them in. As soon as i went into the scanner i experienced this very weird strong metallic taste in my mouth. I pushed the buzzer straight away and told the lady doing the scan who said she has never heard of this reaction so we continued. It is 24 hours on and the taste is awful and my saliva glands seem to be in overdrive. Can you please advise have you heard of this reaction before?

  12. Tobias Gilk Post author

    It is not uncommon for people to discover that they have metal fragments. Particularly as children, we fall down quite a bit and – as odd as it may seem – sometimes we may not be aware that a splinter or shard of something entered our body when we fell on it. Feet and knees are some of the more common locations to find retained metal. Your husband’s physician can let you know if the presence of the retained metal is clinically significant or not. I hope this helps.

  13. Tobias Gilk Post author

    In general, yes. To the extent that you can use the smallest amount of ferromagnetic hardware possible. This means aluminum, brass, stainless steel (which may still be magnetic, but much less than conventional steels), or titanium hardware. I’m not aware of non-magnetic European style cabinet hinges, but you might look at aluminum continuous hinge systems like the Roton. I hope this helps.

  14. Tobias Gilk Post author

    The risk of having something ferromagnetic with you in the MRI during scanning would be that the ferromagnetic object might move (which, if it was your bra, I imagine you would have noticed immediately). There’s a theoretical risk that the underwire could have heated up. I say ‘theoretical’ because I’m not aware of any cases – either anecdotal or documented – of an underwire heating. I do not see a mechanism by which an MRI scan (with or without a metal underwire) could produce any of the ‘after the fact’ symptoms you describe. If you have concerns about these symptoms, I would recommend that you contact your physician.

  15. Tobias Gilk Post author

    Excellent question. The manufacturer of the device should have specific test information on the MRI safety of getting an MRI exam. Here’s an abstract I found that states that they were identified as conditionally safe at MRI field strengths of up to 1.5 Tesla.

    The abstract identifies the Essure device as being of stainless steel composition. Depending on the variety (alloy), stainless steel may have moderate, to very low, magnetic permeability (how magnetic it can become). All metals produce a distortion of the magnetic field immediately around an implant. For non-magnetic metals, this distortion is typically millimeters. For strongly magnetic materials, the distortion can be several centimeters. This distortion can make MRIs unreadable in that immediate area, and some MRI machines have special tools that can try and correct for some of that distortion. Even if this implant were raw iron (which it’s not), my suspicion is that imaging areas other than your lower abdomen would not present a problem. There are, of course, a huge number of variables, particularly the sensitivity and capabilities of the MRI scanner on which you’re getting your images done.

    From the abstract (linked above), as long as you’re having the MRI done on a scanner that meets the Essure manufacturer’s tested / labeled conditions, the MRI exam should represent no significant risk to you, either for heating or for movement.

  16. Tobias Gilk Post author

    If your knee was at the very center of the MRI (where it needs to be to be imaged), that would probably put your head near the mouth of the bore (tunnel). That region is where the spatial gradient of the magnetic field (the ‘steepness’ of the change in magnetic strength) is greatest. Moving through this area of the magnetic field can trigger some biostimulation effects in people. This can be dizziness, or tingling, or even metallic taste, all depending on the particular sensitivities of the person. The cause is moving through that ‘steep’ part of the magnetic field, and once you’re removed from that, the impetus is gone. Sometimes the feelings may linger for a while, even when the ‘trigger’ has long since passed. I hope this helps.

  17. Duncan McCririck

    Hi, I am part of a university project designing an MRI safe patient trolley. We are struggling with material selection. Is there a certain grade or alloy of aluminium that is deemed MRI safe? Many aluminium alloys have small amounts of iron in the so would this not make them slightly magnetic, or is it generally assumed all aluminium alloys are completely MRI safe? Any information you have on this would be appreciated.

  18. Tobias Gilk Post author

    Duncan,

    There are three criteria for the ISO / ASTM “MR Safe” label:

    1. None of the materials of which it’s made may be magnetic or magnetizeable (paramagnetic / ferromagnetic)
    2. None of the materials of which it’s made may be electrically conductive
    3. None of the materials of which it’s made may be RF reactive (absorb / concentrate thermal energy from RF)

    Setting aside the notion of whether or not you could obtain an alloy of aluminum that would not have iron, nickel, or cobalt (the three most common para- / ferromagnetic metals), aluminum is highly electrically conductive. If your goal is MR safe, quite simply you can not achieve it with aluminum as one of the materials.

    Materials that may work for an MR Safe object could include carbon fiber, PVC (and other polymers), ceramics, wood / bamboo, glass…

    If your goal is MR Conditional, as long as the trolley doesn’t have enough para- / ferromagnetic material to make it grossly deflect (in your case, roll in response to the magnetic attraction of the MRI system), then you can obtain the MR Conditional designation.

    One final wrinkle, you may wish to consider whether you would wish for your trolley to work in conjunction with ferromagnetic detectors (used for screening persons for para- / ferromagnetic materials). This consideration may bring us around full-circle, asking the question about which alloys have a low enough content of iron materials that they wouldn’t set off a sensitive detector. You may want to look at 6063 aluminum, which is a commercially available alloy with a comparatively low iron content (max 0.35%). There may be other alloys with even lower maximum allowable iron content, and that would be worth a look.

    I hope this helps.

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