Magnetic Resonance Imaging (MRI)

Approved by the Cancer.Net Editorial Board, 03/2019

Doctors use magnetic resonance imaging, also called an MRI, to find cancer. They also use it to learn more about cancer after they find it, including:

  • Whether a tumor is noncancerous or cancerous

  • The size and location of the tumor

  • To plan cancer treatments, such as surgery or radiation therapy

  • To monitor how well treatment is working

How does an MRI work?

An MRI is an imaging test. It uses powerful magnets and radio waves to produce detailed, computer-generated pictures of the body. It can also be used to measure the tumor's size. The standard MRI machine has a narrow, tunnel-like opening. It looks like a large donut. Some centers have less confining or “open” MRI machines.

An MRI does not use x-rays or other forms of radiation. As a result, it is often used to look for problems in the female and male reproductive systems. An MRI is generally safe, even for pregnant women. It is also often used to take images of the brain, spinal column, abdomen, and chest, including the breast. Learn more about a breast MRI.

Who does my MRI?

An MRI is done by a radiologist or a radiology technologist. A radiologist is a medical doctor who performs and interprets imaging tests to diagnose disease. A radiology technologist is a health care professional who is specially trained and certified to perform an MRI.

You may receive an MRI at a hospital’s radiology department or an outpatient imaging center.

How should I prepare for an MRI?

When you schedule your MRI, you will get detailed instructions on how to prepare.

What to eat. You may need to avoid eating for 2 or more hours before the MRI.

Topics to discuss. Tell your doctor about any medications you are taking. Also mention if you have any drug allergies or other medical conditions. Women should tell their doctors if there is any chance that they may be pregnant.

It is important to mention any metal implants or metal fragments you have in your body. These can cause serious, and even fatal, problems when exposed to the MRI’s strong magnetic pull. For example, people with pacemakers cannot have an MRI.

Consider asking if you can bring music to the appointment. Some centers allow people to listen to music through headphones during the MRI. It may help distract you from the loud noise the MRI machine makes.

Insurance, costs, and consent. Before your appointment, ask your health insurance provider what costs will be covered. Find out how much of the cost you will have to pay. Once you arrive at the doctor's office or hospital, you will be asked to sign a consent form. This form states that you understand the benefits and risks of the procedure and that you agree to have it.

During the test

What should I wear?

Before the test, you will remove jewelry and other metal objects. You may also need to change into a hospital gown.

What will happen during the procedure?

Depending on the part of your body that will be scanned, you may be given a contrast medium. This is a special dye. It is given through an intravenous (IV) line or by mouth.

If the dye is given through an IV, a nurse or doctor will insert a small needle into a vein in your arm or hand. A saline solution will flow through the line until the dye is injected. Saline is a mixture of salt and water. Once injected, the dye will travel through the bloodstream and help create a clearer picture of specific parts of your body.

Then, you will lie on a movable exam table outside of the MRI machine. You will lie on your back with your arms at your side and your head on a headrest.

Small devices, called coils, help send and receive radio waves. These may be positioned over or around part of your body to create a clearer picture.

When you are ready, the exam table will slide through the hole in the center of the MRI machine. You will need to lie still while the machine takes a series of pictures. Each series will take up to 15 minutes. You may need to have 2 to 6 series. This means that an MRI usually lasts up to 90 minutes. The technologist can give you a time estimate before you begin.

During the scan, the technologist will be in a nearby computer room, separated by a window. The technologist will be able to see you. You will be able to talk with the technologist through an intercom system.

You will know when the machine is taking pictures because you will hear loud knocking sounds. Also, the part of your body under examination may feel warm during the MRI. This is normal.

An MRI is not painful. But you may become uncomfortable lying still. If you receive an IV, you may feel discomfort when the needle is inserted. The saline solution in the IV may feel cool at the injection site.

Meanwhile, some people find the machine’s loud sounds unnerving. You may reduce this discomfort by wearing earplugs or listening to music.

If you are afraid of small spaces, tell the technologist before beginning the examination. The radiologist may be able to give you a medication to help you relax. This medication is called a sedative.

Once the MRI is complete, you may be asked to stay on the exam table while a radiologist reviews the pictures to see if more are needed.

After the test

After your MRI, you may return to your usual activities. This includes driving, unless you were given a sedative.

Questions to ask your health care team

Before having an MRI, consider asking the following questions:

  • Who will perform the MRI?

  • Is the radiologist certified by the American Board of Radiology?

  • Is the imaging facility accredited by the American College of Radiology to perform MRIs?

  • What will happen during the MRI?

  • How long will the procedure take?

  • May a friend or family member sit in the MRI room during my examination?

  • What are the risks and benefits of having an MRI?

  • How accurately does an MRI find cancer?

  • When will I learn the results? How will they be communicated to me?

  • Who will explain the results to me?

  • What other tests will I need if the MRI finds cancer?

Related Resources

Computed Tomography (CT) Scan

Positron Emission Tomography and Computed Tomography (PET-CT) Scans

More Information

National Library of Medicine: MRI Scans Magnetic Resonance Imaging