Magnetic resonance imaging (MRI) is unique among radiology exams in that it uses magnetic fields and radio waves instead of radiation to create detailed and dynamic images. While this makes MRI safer than an X-ray or CT scan, entering a powerful magnet comes with its own set of safety concerns, which can lead to questions and anxiety.
Magnets attract metal, and everything from the antiperspirant you put on in the morning to a medical device implanted in your body may contain metal. "Before your appointment, we're going to ask you to leave anything metal at home, and that includes jewelry, watches, or clothes with metal hooks," says Benjamin Navot, MD, assistant professor of radiology at Columbia University Vagelos College of Physicians and Surgeons and MRI medical director at NewYork-Presbyterian's Milstein Hospital Building. "Even a small metal object can fly into the scanner or interfere with the image."
When the metal isn't removable, Columbia has a team of MRI safety experts-board-certified radiologists and physicists-who can address each individual question or concern.
"Most of the time, we can do the scan," says Navot, "but depending on where the metal is, it may require an adjustment to the settings." He answered some of the most common questions patients have about what can and cannot go into an MRI machine:
Makeup and jewelry
Makeup is generally safe for an MRI, Navot says, but mascara and some false eyelashes have enough metal that they can distort the image on a scan of the head. For that reason, it's best to avoid makeup on the day of your appointment if your head is being scanned.
Leaving jewelry at home is also the safest way to go, but some jewelry is not easily removable. The good news is that body piercings tend to be titanium, which isn't magnetic. "We have an old-fashioned horseshoe magnet, and if there's any question, we'll test your jewelry before you go into the scanner," says Navot. "Our facilities also have lockers for keeping your things safe in case you forget."
Braces and retainers
Braces and non-removable retainers are safe for an MRI, but if the area that needs imaging is near the mouth, you may be asked to have your orthodontist remove the wire before your appointment.
Tattoos
Older tattoos, which contain iron in their ink, as well as tattoos with long continuous lines and fresh tattoos can heat up during an MRI and potentially burn the skin. Navot compares this phenomenon to an induction stove, which uses electromagnetism to create heat energy inside a pan. Tell your technologist if you have a tattoo. If there's any question, an ice pack can be placed on the tattoo during the scan.
Bullets and shrapnel
Some of the most common MRI safety questions Navot's team receives are about bullets and shrapnel lodged inside the body. "Most of the time, we can go ahead with the MRI, but we may need to look at the size and location of the shrapnel on an X-ray or CT scan," says Navot. "If it's close to certain structures, like the eye, it's a no."
Pacemakers, stimulators, and other devices
There are so many devices inside people's bodies-spine stimulators, drug injectors, heart assist devices, cochlear implants-and companies know they need to make them safe for patients who may need to get an MRI. "We rely primarily on the manufacturer's guidance for each device," Navot says, emphasizing that if you have a device, it is important to have your imaging done at a place that has a process to properly calibrate the MRI to image safely and accurately for people with your device.
You should always tell your care team ahead of time if you have an implanted medical device to make sure they can make any necessary adjustments to their MRI's settings, and it's a good idea to bring along the information cards for any devices implanted in your body as they can help your imaging team determine the proper settings to use.
Pins and orthopedic hardware
These can be imaged safely in an MRI machine. "We can sometimes even image the bone around the pins," says Navot.
References
Benjamin Navot, MD, is an assistant professor of radiology at Columbia University Vagelos College of Physicians and Surgeons and an assistant attending radiologist at NewYork-Presbyterian Hospital.
