MRI Scans Pose Small Risk for Patients with Tattoos

A new study suggests that tattoo-related adverse reactions from magnetic resonance imaging (MRI) are possible, but come at low risk.

Researchers at the Max Planck Institute for Human Cognitive and Brain Sciences (MPI-CBS; Leipzig, Germany) and University College London (UCL; United Kingdom) examined 330 people sporting tattoos before and after an MRI scan, for a total of 932 tattoos. Information regarding the tattoos was systematically collected, including size, location, country of origin (with most arising in Europe, but also from America, Asia, Africa and Australia), and what colors were used. The majority of the ink used was black, but various colors were also registered.

The 3T MRI scanners used in the study were used under a set of specific conditions. For example, in order to ensure participants safety, exclusion criteria concerned the size and number of tattoos. A single tattoo was not allowed to exceed 20 centimeters, no more than 5% of the body could be covered by tattoos, and the maximum number of tattoos allowed was seven. Only one mild tattoo-related adverse reaction was observed, which led the researchers to estimate the probability of an adverse reaction at 17% overall, and 30% for repeated sessions. The study was published on January 31, 2019, in the New England Journal of Medicine (NEJM).

“In MR imaging, high-frequency magnetic fields are used to generate the images by effectively labeling protons. 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 senior author Nikolaus Weiskopf, PhD, director of the MP-CBS. “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.”

“The most important questions for us were: Can we conduct our studies with tattooed subjects without hesitation? What restrictions may exist?” concluded Dr. Weiskopf. “We found that the majority of the participants did not notice any side effects with tattoos. There was one specific case where the study doctor found that side effects - a tingling sensation on the skin - were related to scanning. However, this unpleasant feeling disappeared within 24 hours without the affected person having required medical treatment.”

Tattoo ink can contain pigments that are ferrous, and therefore magnetic. The strong magnetic fields involved in the MRI scanning procedure can interact with these small particles, which in turn can lead to an interaction with the tattooed skin.

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