Magnetic resonance imaging, otherwise known as MRI, uses a combination of magnetic fields and radio waves to take images of the internal structures of your body. Your doctor, with the help of a radiologist, can then examine these images to determine whether there is anything wrong with your foot or ankle.
MRI can provide more detailed images than x-rays, CT scans, or other imaging methods, and the way the images are obtained enables the radiologist to view cross-sections of your body as though you had been sliced like a loaf of bread.
How MRI Works
An MRI machine is a large, cylinder-shaped device, inside which is a hollow, tube-shaped space surrounded by a ring-shaped magnet. The patient lies on an examination bed that slides in and out of this device
Unlike x-rays and other imaging scans, MRI does not use ionizing radiation, which makes it somewhat safer to use (although x-rays nowadays are not dangerous for most patients).
For this reason, MRI is often preferred over CT scanning, even in cases in which either method would be able to provide the same information.
What Are the Advantages of MRI Over X-Rays and Other Methods?
The complex, three-dimensional anatomy of the foot and ankle makes this one of the most difficult regions of the body from which to obtain medically useful images.
MRI addresses this problem well because it provides your medical team with a way to view three-dimensional images of your foot and ankle—if necessary from multiple angles. Additionally, it provides a high degree of contrast between soft tissues, denser tissue, and bone; it can even show bone marrow.
Another advantage of MRI is that unlike CT scanning, it does not usually require the injection of “contrast material” to improve the contrast in the images produced. When such material does need to be employed, it is less likely to cause an allergic reaction than the iodine-based materials used for CT.
MRI is not always the most appropriate choice of imaging method—it is far more expensive than x-rays, and in some cases the enormous amount of detail it provides may be too much for the doctor to sift through; one doctor at the American Academy of Podiatric Sports Medicine likens it to traveling across the country with a map that shows every single road and side street, rather than one that only shows the major highways you need to take.
It is, however, extremely useful for diagnosing a wide variety of injuries and conditions, including Morton’s neuroma, plantar fasciitis, Tarsal tunnel syndrome, stress fracture, and others. MRI is particularly helpful for evaluating soft tissue injuries.
What You Should Expect During Your Foot/Ankle MRI
Unlike some other medical tests, an MRI does not require you to fast the night before. You may eat normally and take whatever medications you would normally take. When you arrive for your appointment, the technician may ask you to change into a medical gown.
You will also be asked to remove all jewelry (including wedding ring), as well as eyeglasses, hairpins, dentures, or a hearing aid. Make sure not to wear an underwire bra that day, if it can be avoided.
When it is time for the MRI to begin, you will lie down on the examination table, which will then slide into the open end of the tube in the machine. The technician conducting the scan will monitor you from another room, and you will have an intercom through which you can communicate if necessary.
The procedure usually takes 30–60 minutes, and it is completely painless. You will not be able to feel the magnetic field or the radio waves. It will be necessary for you to remain as still as possible, however, and some people find this stillness difficult to maintain for the duration of the scan.
Throughout the procedure, the machine will make a variety of very loud, unpleasant noises—clanking, banging, and buzzing that resembles a car alarm—which most patients find disconcerting, to say the least. The technician conducting the scan will probably provide you with earplugs, and sedation may be an option.
Is MRI Dangerous?
When magnetic resonance imaging is done properly and all appropriate safety guidelines are observed, the procedure presents no danger whatsoever. However, if you suffer from claustrophobia, you may need to be sedated.
Also, if you have any kind of metal implant or electronic device inside your body or on your person, it may interfere with the imaging process, and there is even a chance that it can create a safety hazard. Examples of such objects and devices include:
- Prosthetic joints with metal parts
- Cochlear implant
- Shrapnel, bullets, etc.
Before getting a foot or ankle MRI, it is advisable to inform your doctor if you are pregnant or think you may be.