I have a metal rod in my leg from previous surgery. I believe it is titanium. Would this significantly affect/be affected by an nmr machine? I noticed that a sign by it said not to bring metal objects in the room and I wanted to be sure.

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    $\begingroup$ You should speak to the people who run the NMR facility at your department. Very old machines were poorly shielded, making it impossible to go near them with metal implants/pacemakers. Modern machines are highly shielded to the point where you can get very close or even touching without risk of harm. In most NMR suites there are lines drawn on the floor/ropes tied around to show where the magnetic field of the machine extends to. But in any case. Ask the NMR guys at your institution... modifications are often made to NMR spectrometers so they might not be as the manufacturer intended. $\endgroup$
    – NotEvans.
    Commented Aug 30, 2016 at 17:12

2 Answers 2


A little bit about me - I manage a busy research NMR Facility at a leading international tertiary institution. I deal with questions like this not infrequently, and there are some very important things you need to understand about implants and magnetic fields. I have all users of our Facility sign a waiver prior to access to indicate whether they have medical or surgical implants, and for those that do - there is probably 3-4 a year - we make a specific case assessment to determine whether it is safe for them to use the instruments. For some people, we simply arrange an alternative pathway to have samples run. This may be having others run them altogether, or load up samples into an autosampler for them.

A bit about you - that you 'think' it is a titanium implant is not sufficient to allow a proper assessment in your case. Unless you can get this is writing from your doctor, then I would have to assume a surgical grade of stainless steel. And it needs to be made perfectly clear that most surgeons don't know this information. There is no such thing as completely non-magnetic stainless steels - even the highest grade austenitic steels contain minute amounts of ferrite materials. I have had many examples over the years of people believing one thing about their implant and then discovering the truth later. In the most interesting case, I had a user who had surgery and believed they had a titanium plate in their skull. Their doctor put this in writing. Only after a follow-up MRI scan some years later did they discover that they did NOT have any implant. Nothing at all. The doctor checked his records.....ah yes - they didn't need to use one after all! Some implants have additional attachments and electronics that meed to be considered above and beyond the basic 'rod' and these can both be affected by, and affect magnetic fields.

Typically, implants will rarely affect the magnet of the spectrometer to the point of creating problems. In any case, problems only arise through moving through the field - a static object is generally no problem. With MRI, this 'movement' comes from the application of field gradients. Just as passing a current through a coil generates a magnetic field, moving a metal conductor through a magnetic field creates an electric current.

Even surgical grade metals are affected by the stray fields of magnets, and depending on the age, design and size of magnet, this may be of concern to you as a spectrometer operator. Movement of metals through the field will create local eddy currents which can result in localised heating. In MRIs, a common incident is serious burns from the embedded metal in bra straps. For biomedical implants, this risk is still considerable, and consideration should be given to:

  • how long ago the surgery was done. Recent surgery may not have allowed adequate time for bone growth to sufficiently embed the implant, and heating can create swelling and cause problems that may need to rectified. I am aware of one such case with an implant in the wrist that required follow-up surgery to rectify intense swelling that resulted from exposure to a strong magnetic field.
  • where the implant is. Some areas will be more susceptible to problems, or least symptoms. Not everyone that has an implant can detect any changes. Some people do. I'd say that most people who say they experience a symptom have implants associated with joints - elbows and wrists are the most common that come to mind. Symptoms have ranged from tingling in the joint to feeling warm. How much of this is genuine, and how much psychosomatic, I can't say. I once had an older tradesman working within the stray field for a day who commented that the tattoos on his forearm were itchy by the end of the day.
  • what the implant is. Some implants are just not worth taking a risk with. Aneurysm clips, for instance, are simply not worth taking a risk with. Finding an alternative way for a user to access the spectrometer is much easier than cleaning up an exploding head (yes, an exaggeration, I know) and doing the paperwork. Some pacemakers are MRI approved, and most are actually perfectly ok within the small stray fields of a spectrometer. But some aren't ok, so I wouldn't take this risk without plenty of written evidence from doctors and medical suppliers.
  • the extent of stray field form the magnet. All magnets are different through age, design and magnitude. An older unshielded 600 poses a very high dose of exposure; a newer shielded 300 has the 5G line contained within the magnet case, and has an almost neglible exposure. However, magnetic fields are invisible, and unless you know the details about the specific magnet you are using, it is best to assume the worst case. We base all of our stray field limits on our unshielded 400, which has a much greater stray field than our 500 for instance.

Regardless of the final assessment of your condition, I would still advise against undertaking high field procedures, such as changing probes, or doing low temperature connections etc.

Ferromagnetic materials can obviously be a problem because of the large attractive forces created. Most incidents with these arise from large external metal objects being brought within the stray field; gas cylinders and trolleys etc. MRIs are usually more problematic with stray fields due to the bore size, but small objects can also pose a serious concern in strong fields. These include handheld tools, but for NMR spectrometers the biggest problems actually come from things like staples and paperclips and even iron filings that migrate across the floor over time and can cause serious problems if they get near the magnet bore.

The take-home message for you is not to take advice from a bunch of stackexchange users beyond understanding that you need to discuss your individual case with your NMR Facility Manager, your doctor, and quite possibly your supervisor if alternative arrangements need to be considered for your access. A great resource for you to be aware of is Frank Shellock's MRI Safety site.


The only way to know this is to ask your physician. You need to know exactly what the implant is made of to assess the danger. You shouldn't rely on your own potentially unreliable understanding of the material of your implant nor on the advice some random people on the internet give you. The following is for your curiousity, but you shouldn't rely on this for your own safety.

Titanium implants can be safe for MRI, see this study as an example. They do interfere with the measurement, but they typically aren't attracted strong enough by the magnet to be dangerous. Though there is also the additional danger of induced currents by magnetic fields with implanted metal objects, which leads to heating.

The magnets inside an NMR spectrometer are very strong, potentially much stronger than a typical MRI. The amount of shielding of the magnet can also vary a lot, so some spectrometers have a much wider area around them with a strong magnetic field.

The warning are really about your own safety, the presence of metal near the spectrometer is much more dangerous to you than the potential of messing up a measurement. Though a large enough metal object can damage or destroy an NMR spectrometer if it gets near enough.

Incidents with MRIs happen pretty regularly, see this post for some examples, e.g. a patient getting hit by a flat screen or a technician with scissors in they head. The danger is mostly from getting hit by flying metal objects that are brought near the magnet.


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