Wearing the wrong face mask in or around an MR scanner can pose serious risks, including mask displacement and face burns, as well as artifacts that make images unusable and result in repeat scans. Despite this, there is no official guidance on what masks are safe to use.

In a new study, researchers at Cardiff University found these outcomes were possible when wearing certain types of masks due to the ferromagnetic materials within them. Testing eight different types, they found that five contained magnetic components that they say are MR unsafe.

To prevent these adverse events, they recommend a color coded system. “We suggest that where possible, surgical masks should be ordered in a separate color to distinguish between an ‘MR safe’ and an ‘MR unsafe’ surgical mask,” said lead study author Dr. Bethany Keenan, from Cardiff University’s school of engineering, in a statement.
The scientists performed three MR scans on a 3D printed model of a head and neck fitted with eight commercially available FFP3 masks. Safety was based on the presence of ferromagnetic and metallic materials, as well as a measurable deflection at the MR bore, and a temperature greater than 40°C during testing.

Two of the masks were deemed MR safe. One was labeled MR conditional because there was a potential risk of local heating under certain conditions within the MR machine. “It is extremely important to not assume that a mask is safe prior to an MR examination, and to conduct a safety evaluation to determine which components are made of ferromagnetic metals and which are non-ferromagnetic metal,” said Keenan.

In 2020, a U.S. patient undergoing a neck scan was left with burn marks from her mask, which had metal components in it. The FDA says many people are not aware of whether their mask has metal in it, and says patients should confirm with doctors performing the MR scan if their own is safe. “Do not wear a face mask containing metal parts, like a bendable nose piece or staples on the headband, nanoparticles, or antimicrobial coating that may contain metal, when having an MR,” said the agency in a statement.

The findings were published in Clinical Radiology.

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