The magnetic resonance imaging (MRI) machine is frequently used to help diagnose a wide range of diseases and medical conditions, ranging from cancer and heart disease to disorders of the bones and joints. “An MRI allows you to see internal anatomy in detail, and also to differentiate between normal and abnormal tissues,” says Jeffrey Weinreb, MD, chief of the MRI service at Yale Medicine.
Rather than using radiation, as X-rays do, the MRI machine uses magnetic fields and radio waves to generate images.This makes it safer, overall.
However, the prospect of getting an MRI scan causes anxiety for some patients. Not only is the machine noisy and confining, but it does not interact well with some metals in the body. Patients with medical implants or other metal in or on their bodies are often unable to undergo the exam in most hospitals; Yale Medicine physicians have developed strategies that often solve this problem. In this article, we examine the issues that might exist in a variety of scenarios—and how Yale Medicine physicians deal with them. They include:
- Cardiac pacemaker or defibrillator
- Braces on your teeth, a retainer or dental fillings
- Embedded bullets, BB's, shrapnel, shotgun pellets or metal filings
- Pins or plates in or on your bones, including metallic joint
- Body piercings, jewelry, metal on or in clothing
- Medical devices with magnets, such as a cochlear implant or chest expanders
- Surgical clips, including aneurysm clips
Cardiac pacemaker or defibrillator
Yale Medicine is able to offer MRI scans for many people with these devices implanted in their bodies in situations where most others hospitals can't do them. Patients with some modern versions of cardiac pacemakers and defibrillators can safely undergo an MRI, but most people have older devices, which aren’t FDA-approved for use in an MRI scanner. “We screen these patients very carefully, and have their devices evaluated,” Dr. Weinreb says. “If they unequivocally need the MRI, and there’s no satisfactory alternative for it, we will often do the scans.”
To ensure the patient’s safety, Yale Medicine gathers a multidisciplinary group, including radiologists, cardiologists, electrophysiology nurses and the MRI team. The cardiac device is set so it won’t malfunction in the MRI scanner, and the scanner is set so it won't exceed specific speeds and intensity limits. The patient is carefully monitored during the MRI. After the test, the implanted device is checked and, if necessary, reprogrammed. “We’ve done hundreds of these safely, and we’re still the only ones in New England doing them on a routine basis,” Dr. Weinreb says.
Braces, retainers or dental fillings
Most metal tooth fillings or other permanent dental implants won’t cause a problem. If you have detachable metal braces or a retainer, you should take them out before you get an MRI. Having a lot of metal in your mouth can distort images if you need an MRI of your head or neck, making the scan less useful for diagnosis and treatment. In those situations, if you have braces that aren't easily detachable, our physician may ask you to have your braces removed in advance by an orthodontist.
Bullets, BB's, shrapnel, shotgun pellets or metal filings
A number of factors help determine if an MRI is safe for you if you have pieces of metal in your body. They include where the metal is, its size, its shape, and whether it's near a vital organ or structure. At Yale Medicine, you might get an X-ray first to answer those questions. “The vast majority of the time, there’s no problem and we’ll go right ahead and do the MRI scan,” Dr. Weinreb says. But the scan may not be possible if the metal is lodged near the eye or an artery in the neck. In those situations, the danger is that the metal might heat up and damage sensitive tissues.
Pins, plates and metallic joints
Metal that is well secured to the bone, such as hip and knee joint replacements, will not be affected by an MRI. The metal won't heat up or move in response to the machine. But if the metal is near an organ, such as the prostate, distortion could be a problem. At Yale Medicine, your doctors will determine whether an MRI is the appropriate examination, or “if there is something else that would be satisfactory or might even be better,” Dr. Weinreb says.
Jewelry, piercings, buckles or keys
You shouldn’t go into an MRI scanning room wearing jewelry or clothing with metal parts. At Yale Medicine, patients are required to change into a hospital gown before undergoing an MRI. (That's not true everywhere. But we play it safe.) Our patients are asked to remove body piercings, and, if they can't remove one, they might be asked to place an ice pack (also called a heat sink) over it during the MRI, to keep the metal cool.
Electronic medical devices or magnets
Some medical devices, including cochlear implants for hearing, contain magnets. Other implants, such as tissue expanders used for breast reconstruction, have magnetic components. “We have to check them out and see if they’ve been tested and are safe in an MRI environment," Dr. Weinreb says. Some patients carry a card with information about their devices, or their doctors have it on file. “If we’re not certain, we’re prudent. We don’t want to hurt somebody,” Dr. Weinreb says. Radiologists might postpone the MRI until the safety of the device is determined, or recommend another course of action, such as a different type of scan. Even if MRI is deemed safe, the item may distort the images created by the scan.
It’s possible that your tattoo could heat up during an MRI and burn you. This is a greater concern with older tattoos, some of which were made with metallic ink. Of course, tattoos are very common, and they won’t keep you from getting an MRI. If there's a concern about burning, the MRI technician will provide an ice bag to keep your tattoo from getting hot.
For the most part, surgical clips are not a problem because modern clips aren't ferromagnetic. The exception is surgical clips used to repair a brain aneurysm. These can be dangerous, says Dr. Weinreb. "f the clip moves during an MRI, it could cause bleeding in the brain.” At Yale Medicine, the MRI staff will determine the make and model of your brain aneurysm clip before an MRI is approved.
Coronary artery stents, the most common type, are considered MRI-safe because they are not typically made of ferromagnetic metal. When stents are elsewhere in the body, especially in a precarious location, such as an artery in the neck, Yale Medicine caregivers investigate before they do a scan. The concern is that the stent could migrate, perhaps opening up the blood vessel. Safety information for each type of surgical stent is carefully researched before a scan is performed.