Magnetic Resonance Imaging (MRI)

Aprobado por la Junta Editorial de Cancer.Net, 10/2020

Magnetic resonance imaging (MRI) is a test that can be used to find a tumor in the body and to help find out whether a tumor is cancerous. Doctors also use it to learn more about cancer after they find it, including:

  • The size and location of the tumor

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

  • To see how well treatment is working

How does an MRI work?

An MRI is an imaging test. It uses powerful magnets and radio waves to make detailed, computer-generated pictures of the body. A standard MRI machine has a narrow, tunnel-like opening. It looks like a large donut. Some imaging centers have "open" MRI machines that are more spacious. This can be an option if you are worried about the small space or if you have a larger body.

An MRI does not use x-rays or other forms of radiation. That is why doctors often use it to look for problems in the reproductive system. An MRI is generally safe, even for pregnant women. Doctors also use it to take pictures of the brain, spinal column, abdomen, and chest, including the breast. Learn more about a breast MRI in a separate article on this website.

What kind of health care provider will I see for an MRI? Where will my MRI be done?

You can have an MRI at a hospital's radiology department or at an outpatient imaging center. A radiologist or a radiology technologist will do your MRI. A radiologist is a medical doctor who performs and interprets imaging tests to diagnose diseases. A radiology technologist is a health care professional who is specially trained and certified to do an MRI.

How can I prepare for my MRI?

When you schedule your MRI, the hospital or imaging center staff will tell you how to prepare. Talk with your health care team about anything that is unclear. Here are some things that you can expect:

What to eat. You may not be able to eat for 2 or more hours before the MRI.

What to wear. Wear loose fitting clothing without metal zippers or buttons. You will need to remove any clothing that includes metal and could affect the scan. This includes belts, earrings, shirts with snaps or zippers, and glasses. You may be required to remove all of your clothing, as some undergarments may not be compatible with the MRI. You will also need to remove any jewelry you are wearing before the exam, so you may choose to leave that at home. If your clothing cannot be worn during the scan, you can wear a hospital gown.

Personal medical history or concerns. Be ready to talk about these topics with your health care team:

  • All medications you take, including herbs, supplements, and over the counter medications

  • Any drug allergies or other medical problems you have

  • If there is any chance you could be pregnant

  • Any metal implants or metal fragments in your body. These can cause serious and even life-threatening problems if exposed to the strong magnetic pull of the MRI. For example, people with a pacemaker cannot have an MRI.

Insurance, costs, and consent. If you are concerned about the cost of your MRI, find out beforehand what your insurance provider will cover. Ask how much of the cost you will have to pay. Once you get to the doctor's office or hospital, the staff will ask you to sign a consent form. This form states that you understand the benefits and risks of the scan and agree to have it. A health care team member will explain the test before you sign the form, and you can ask any questions that you might have.

What to bring. Consider asking if you can bring music to your appointment. Some imaging centers let you listen to music through headphones during the MRI. It may help distract you from the loud noises the MRI machine makes.

What happens during an MRI?

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

You may need to receive a special dye called a contrast medium before the test. This dye travels through your bloodstream and creates clearer pictures of specific body parts. The contrast dye is given through an intravenous (IV) line. When the dye is injected into the line, you may feel a cold sensation spreading through your body. You may also get a metallic taste in your mouth, a mild headache, or an upset stomach. These effects typically only last a few moments.

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. Your head will be on a headrest. The technologist may then place small devices, called coils, over or around part of your body. The coils help send and receive radio waves to create a clearer picture.

Before the scan begins, the technologist will leave the exam room. They will be in a nearby control room and they will be able to see you through a window or by video. You will also be able to talk with them through an intercom system.

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

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

When the MRI is done, the technologist may ask you to stay on the exam table for a few minutes. During this time, a radiologist will look at the pictures to see if the technologist needs to take more.

After the MRI, you can go back to your normal activities right away.

Is an MRI painful?

An MRI is not painful. You may become uncomfortable lying still. Some people are nervous about the loud sounds the machine makes. You can block some of the noise by wearing earplugs or listening to music.

If you are afraid of small spaces, tell your health care provider before the MRI starts. A radiologist may be able to give you a medication to help you relax. This medication is called a sedative. If you receive a sedative, you will need someone else to drive you to and from the MRI appointment.

Questions to ask your health care team

Before having an MRI, you may want to ask your health care team these questions:

  • Who will do my MRI?

  • Where will I go to get my MRI?

  • Does the recommended imaging center usually perform MRIs?

  • What happens during an MRI?

  • How long will my MRI take?

  • If I'm afraid of small spaces, who should I tell before the MRI?

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

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

  • When and how will I get my test results? Who will explain them to me?

  • What will the results of the MRI tell you?

  • 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

Medline Plus: MRI Scans Magnetic Resonance Imaging