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

164 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

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