The reason is in the name - MRI machines use exceptionally strong magnets that can turn any magnetic objects, like hairpins, jewellery and watches, into hazardous missiles.
Strict precautions are therefore necessary to keep everybody safe, but as new products continue to hit the market, these boundaries are constantly moving. Today, there's a new cosmetic craze that might be slipping through the cracks.
A pair of radiologists is now warning that magnetic eyelashes - in which false lashes are secured to the eyelid with magnets instead of glue - should not go anywhere near an MRI machine.
"We strongly recommend inserting a line about magnetic eyelashes on the MRI safety questionnaire and adding stops in the screening system to prevent the entry of anyone with these lashes, including staff, into the MRI scanner room," the team writes.
The recommendation is based on their new research, which suggests that if magnetic eyelashes are not removed prior to scanning, they can not only degrade the resulting images, but potentially even place the patient in danger.
Attaching two sets of magnetic eyelashes from the same manufacturer to a specially designed test device called a phantom, the researchers measured how these products cope in an MRI setting compared to aneurysm clips, a known medical item that can distort the scans, and is not allowed in scanners due to patient safety.
Compared to the clips, magnetic eyelashes were found to create a much larger disturbance in the image, obscuring the entire phantom. And while all the eyelashes stayed on the device during scanning, on removal of the phantom, one set of eyelashes actually became detached and started moving towards the other.
Given how cheap and popular these new cosmetic products have become, the researchers are warning that all radiologists should be on the lookout for patients and staff members with potentially false lashes of the magnetic sort.
"Although our staff had little to no awareness of the existence of magnetic eyelashes, The Wall Street Journal reported that instruction on their use and application was the top trending beauty-related search on Google in 2018," the authors write.
There's currently no evidence that anyone has been harmed from magnetic eyelashes during an MRI scan. Still, the researchers point out that unless there is a death, these accidents are likely underreported.
"Although we tested only one kind of magnetic eyelashes, it is reasonable to assume that all such lashes will behave in this manner, producing either somewhat less or somewhat more magnetic field distortion, and that all will be attracted to the static magnet," they conclude.
The article, currently available ahead of print, will be published in the American Journal of Roentgenology in November.