To test the safety of tattoos in MRI machines, researchers started with small ones where the risk of burns was least. ©Albina_Glisic/Shutterstock.com/MPI CBS

Two things that have become a lot more common in recent years are MRI scans and tattoos, but do they go together? Medical professionals have been concerned that putting tattooed skin into the powerful magnetic field of an MRI machine could have serious consequences, leading many to avoid the scans to be on the safe side. However, a new study has shown that, provided certain conditions are replicated, having ink is seldom a reason not to get scanned.

A lot of different chemicals go into the various ink colors used in tattooing. Those that contain iron or nickel respond to magnetic fields. Most fields are too weak to have a noticeable effect, but MRIs are a different matter. Skin isn't going to come flying off like an errant lump of metal, but people have described feeling as if their skin was being pulled, even making it into an episode of House M.D.

Electrically conductive pigments are far more common than those that can be magnetized. In the presence of a rapidly changing magnetic field, electric currents are induced in conductive materials. "High-frequency fields usually have a frequency of a few hundred megahertz. That happens to correspond to the resonance lengths of conductive structures similarly sized as tattoos,” said Professor Nikolaus Weiskopf of the Max Plank Institute in a statement. “In this case, the tattoo may absorb much of the energy of the high-frequency field, which would normally be spread out more widely. It can then happen that the tattoo heats up. In the worst case, this can lead to burns.”

Most MRI research is directed at the brain, but the fields affect the whole room, including frequently tattooed areas like the upper arms. Weiskopf reports in the New England Journal of Medicine these fears should seldom prevent getting scanned. After studying 330 people with 932 tattoos, Weiskopf found that any conductivity effects were usually too small to be noticed, let alone cause damage.

"There was one specific case where the study doctor found that side effects – a tingling sensation on the skin – were related to scanning,” he said. “However, this unpleasant feeling disappeared within 24 hours without the affected person having required medical treatment."

Naturally, Weiskopf and co-authors were keen to avoid doing anything dangerous, so they limited each tattoo to 20 centimeters (8 inches) in size and would not allow people with more than 5 percent of their body inked to participate. The lack of detectable effects in these cases, however, suggests that somewhat larger tattoos are unlikely to represent a serious risk either. The study used three Tesla scanners, at the stronger end of those in widespread use, although some research institutions use fields 20 times as strong.

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