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MRI is short for magnetic resonance imaging. You may also hear it referred to as magnetic resonance, MR, and nuclear magnetic resonance [NMR] imaging. MRI creates cross-section pictures of your insides. But unlike x-rays, MRI uses strong magnets to make the images – not radiation. An MRI scan takes cross-sectional slices (views) from many angles, as if someone were looking at a slice of your body from the front, from the side, or from above your head. MRI creates pictures of soft tissue parts of the body that are sometimes hard to see using other imaging tests.
MRI helps doctors find problems, including cancer. It can find tumors that may or may not be cancer and is very good at finding and pinpointing certain types of cancer. Doctors can sometimes tell from the MRI images if a tumor is or isn’t cancer. But, other tests (such as a biopsy) might be needed to confirm if a tumor is cancer or not.
MRI can also look for signs that a cancer has spread from its original area in the body. Looking at MRI results also helps doctors know how to plan cancer treatment, like surgery or radiation.
An MRI scanner is a long cylinder or tube that holds a large, very strong magnet. As you are lying on a table that slides into the tube, and the machine surrounds you with a powerful magnetic field. The machine uses a powerful magnetic force and a burst of radiofrequency waves to pick up signals from the nuclei (centers) of hydrogen atoms in your body. A computer converts these signals into a black and white picture. Many pictures are created during the test.
A specific kind of MRI can be used to look inside the breast. Learn more about breast MRI.
An MRI with contrast dye is the best way to see certain types of tumors, such as brain and spinal cord tumors. Contrast is a dye that is put into the body through a vein to make the MRI images clearer. Once absorbed by the body, the contrast speeds up the rate at which tissues in the body respond to the magnetic and radio waves of the MRI. These stronger signals give clearer pictures.
MRI is painless and you don’t have to do anything special to get ready for this test. MRI scans are most often done on an outpatient basis, so you don’t have to be in a hospital to get one.
If being in a small, enclosed space is a problem for you (you have claustrophobia), you might need to take medicine to help you relax while in the scanner. Sometimes talking with the technologist or a patient counselor, or seeing the MRI machine before the test can help. In some cases, you can arrange to have an open MRI which allows more space around your body (see the next section).
Sometimes a contrast dye material is used for MRI imaging. You may have to swallow the contrast, or you may have an intravenous (IV) catheter put in a vein in your arm so the contrast can be given into your bloodstream. The contrast material used for an MRI exam is called gadolinium. (This is not the same as the contrast dye used in CT scans.) Let your doctor and the technologist know if you have any kind of allergies or have had problems with any contrast used in imaging tests in the past.
It’s very important to tell your doctor and the technologist (the person who does the test) if you have any metal in your body. If you have any of these implants, you should not even enter the MRI scanning area unless told to do so by a radiologist or technologist who knows you have:
Also be sure the technologist knows if you have other permanent metal objects, such as surgical clips, staples, screws, plates, or stents; artificial joints; metal fragments (shrapnel); tattoos or permanent makeup; artificial heart valves; implanted infusion ports; implanted nerve stimulators; and so on.
You may need to have an x-ray to check for metal objects if there’s any doubt.
You may be asked to undress and put on a gown or other clothes without zippers or metal. Be sure to remove any metal objects you can, like hair clips, jewelry, dental work, and body piercings. Before the scan, the technologist will ask you if you have any metal in your body.
You will lie down on a narrow, flat table. The technologist may use straps or pillows to make you comfortable and help keep you from moving. The table slides into a long, narrow cylinder. The part of your body that’s being scanned will be in the center of the cylinder. The scanned part of your body may feel a little warm during the test, this is normal and nothing to worry about.
You’ll be in the exam room alone, but you can talk to the technologist, who can see and hear you at all times.
The test is painless, but you have to lie inside the cylinder with its surface a few inches from your face. It’s important to stay very still while the images are being made, which can take a few minutes at a time. You may be asked to hold your breath during certain parts of the test. Tell the technologist if you need to move or take a break.
The machine makes loud, thumping, clicking, and whirring noises, much like the sound of a washing machine, as the magnet switches on and off. You may be given earplugs or headphones with music to block noise out during the scan.
Special, open MRI machines that are less restrictive may be easier for some people. These machines replace the narrow cylinder with a larger ring. This design lessens the banging sound and the feeling of lying in an enclosed space. But the machine doesn’t create as strong a magnetic field, and the pictures may not be as clear or detailed as they are with standard MRI. Sometimes, this can lead to getting rescanned on a standard MRI machine.
MRI scans usually take between 45 and 60 minutes, but can sometimes take up to 2 hours. After the test, you may be asked to wait while the pictures are checked to make sure that they are clear and show all of the body part. If not, more pictures may be needed.
People can be hurt in MRI machines if they take metal items into the room or if other people leave metal items in the room.
Some people become very uneasy and even panic when lying inside the MRI scanner.
Some people react to the contrast material. Such reactions can include:
Be sure to let your health care team know if you have any of these symptoms or notice any other changes after you get the contrast material.
Gadolinium, the contrast material used for MRI, can cause a special complication when it’s given to patients on dialysis or who have severe kidney problems, so it’s rarely given to these people. Your doctor will discuss this with you if you have severe kidney problems and need an MRI with contrast.
Small amounts of gadolinium can stay in the brain, bones, skin and other parts of your body for a long time (several months to years) after the test. It’s not known if this might have any health effects, but so far, studies haven’t found any harmful effects in patients with normal kidneys.
Studies have not shown that MRI causes cancer. This is becaues MRI does not expose you to radiation. Whether you have a closed or an open MRI, you are not at risk for radiation exposure from the test. You can learn more in Understanding Radiation Risk from Imaging Tests.
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American College of Radiology/Radiological Society of North America. RadiologyInfo. Magnetic Resonance Imaging (MRI) – Body. Accessed at https://www.radiologyinfo.org/en/info/bodymr on February 16, 2024.
Hricak H, Akin O, Bradbury MS, et al. Advanced imaging methods: Functional and metabolic imaging. In: DeVita VT, Hellman S, Rosenberg SA, eds. Cancer: Principles & Practice of Oncology. 7th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2005:589-720.
Little JB, Grdina DJ. Ionizing radiation. In: Kufe DW, Bast RC, Hait WN, et al, eds. Cancer Medicine. 7th ed. Hamilton, Ontario: BC Decker; 2006:270-282.
Last Revised: February 16, 2024