MRI for Cancer

An MRI can be used to find cancer or plan further cancer treatment.

What is MRI?

MRI is an imaging test that creates cross-sectional pictures of the inside of your body. MRI is short for magnetic resonance imaging. Unlike x-rays and CT scans, which use radiation, MRI uses strong magnets to make images.

An MRI scan shows your body from many angles, as if someone were looking at a slice (cross section) of it from the front, the side, or above your head. This type of scan creates pictures of soft tissue that are sometimes hard to see on other imaging tests.

Can MRI detect and diagnose cancer?

MRI helps doctors find problems, including cancer. It can give them important information about the size and spread of a tumor, but it is usually combined with other tests, such as a biopsy, to confirm a cancer diagnosis.

An MRI can:

• Show a tumor’s shape, size, location, and nearby blood vessels
• Find and pinpoint certain types of cancer, such as breast cancer
• Show if cancer has come back (recurred) or spread (metastasized) from its original location

It can also help doctors:

• Plan cancer treatment, such as surgery or radiation
• Evaluate liver, heart, bowel, and reproductive system problems

How does MRI work?

An MRI scanner is a long cylinder or tube that holds a large, very strong magnet. As you lie on a table in the center of the tube, the MRI scanner surrounds you with a powerful magnetic field.

The scanner uses this 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 made during the test.

MRI with contrast dye

An MRI with contrast dye is the best way to see certain types of tumors, such as brain, spinal cord, and liver tumors. Oral contrast might also be used for exams that look at the bowels.

This dye is injected into a vein (IV) and absorbed into your body tissue. It is absorbed into many, but not all, tumors.

Contrast dye within the tissue creates stronger signals to make the MRI images of the tissues clearer, especially tumors. How a tumor absorbs contrast over time can also tell doctors whether that tumor is more likely to be benign (not cancer) or malignant (cancer).

How do I get ready for an MRI?

MRI scans are usually done on an outpatient basis. You don’t have to be in a hospital to get one.

An MRI is painless and you usually don’t have to do anything special to get ready for it. For certain MRI scans, you might be told not to eat or drink for a few hours before the test. Ask your health care team if you are unsure about the instructions for your scan.

If being in a small, enclosed space is a problem for you, you might need medication to help you relax. Not eating or drinking 4 to 6 hours prior to the MRI is especially important in this case.

Sometimes, it can help to talk with the technologist (tech) who does the MRI. Seeing the machine before the test can also help. In some cases, you can arrange to have an open MRI, which allows more space around your body. See below for more about open MRI.

Contrast dye

If you need contrast dye for your MRI, you will either swallow a liquid or have an 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. It isn’t the same as the contrast dye used in CT scans. Let your doctor and the tech know if you have any kind of allergies, kidney problems, or have had problems with any contrast used in imaging tests in the past.

Metal and other devices

It is very important to tell your doctor and the tech if you have any metal in your body, including, but not limited to:

• Surgical clips
• Staples, screws, plates, or stents
• Artificial joints
• Metal fragments (shrapnel)
• Tattoos or permanent makeup
• Artificial heart valves
• Implanted infusion ports, nerve stimulators, or breast expanders

If you have any of the following, do not even enter the MRI scanning area unless you are told to do so by a radiologist or tech who is aware of it:

• An implanted defibrillator or pacemaker
• Clips used on a brain aneurysm
• A cochlear implant
• Metal coils put inside blood vessels

You may need an x-ray to check for metal objects if there’s any doubt.

What is it like having an MRI?

For your safety, and to get the best images, you may be asked to:

• Undress and put on a gown or other clothes without zippers or metal.
• Remove any metal objects like hair clips, jewelry, braces or other removable dental objects, and body piercings.
• Let the tech know if you have any metal in your body.

For most MRIs, you will lie down on a narrow, flat table. For a breast MRI, you will lie on your stomach with your breasts placed through openings in the table. The tech might use straps or pillows to make you comfortable and help keep you from moving.

If you get contrast dye, you might experience flushing, a feeling of being cold or warm, or a metallic taste in your mouth. The dye used in scans to determine if liver lesions are benign or malignant might cause trouble breathing. All of these are usually brief and go away quickly.

During the scan

During the scan, the table slides into a long, narrow cylinder. The part of your body being scanned will be in the center of the cylinder. This area might feel a little warm during the test. This is normal and nothing to worry about.

You’ll be alone in the exam room, but the tech will be able to see, hear, and talk to you at all times.

An MRI is painless, but you might find it uncomfortable to lie very still inside the cylinder with its surface a few inches from your face. Some newer MRI machines have a larger opening, which can be more comfortable.

It’s important to stay very still while the images are being made. Each image can take a few minutes at a time. You might be asked to hold your breath during certain parts of the test. Tell the tech if you need to move or take a break.

As the magnet switches on and off, the machine makes loud banging, thumping, clicking, and whirring noises, much like the sound of a washing machine. You may be given earplugs or headphones with music to block out some of the noise during the scan.

What is an open MRI?

An open MRI machine is less restrictive and open on the sides, which may be easier for some people.

This design lessens the banging sound and the feeling of lying in an enclosed space. But the machine doesn’t create as strong of a magnetic field, and the pictures might not be as clear or detailed as they are with standard MRI. If this happens, you may need to get rescanned on a standard MRI machine.

How long does an MRI take?

MRI scans usually take between 30 to 60 minutes, but they can sometimes take up to 2 hours. After the test, you might be asked to wait while the pictures are reviewed, to make sure they are clear and show everything. If they aren’t clear, you might need more pictures.

What are the possible risks and side effects of an MRI?

People can be hurt in MRI machines if they take metal items into the room or if metal items are left behind by others.

Some people become very uneasy and even panic when lying inside the MRI scanner.

Reactions to contrast material: Rarely, some people react to the contrast material. Reactions can include:

• Nausea
• Pain at the needle site
• A headache that develops a few hours after the test is over
• Low blood pressure, leading to a feeling of lightheadedness or faintness (this is rare)
• Itchiness or hives
• Wheezing or difficulty breathing, in very rare cases

Tell your health care team if you have any of these symptoms or notice any other changes after you get the contrast material.

If you have severe kidney problems: Gadolinium, the contrast material used for MRI, can cause a serious problem in people who are on dialysis or who have severe kidney problems, so it is rarely used in this case. If you need an MRI with contrast, your health care team will discuss this with you.

Gadolinium in the body: Small amounts of gadolinium can stay in your brain, bones, skin, and other parts of your body for several months to years after the test. It isn’t known if this has any health effects, but studies so far haven’t found any harmful effects in people with normal kidneys.

Can MRI cause cancer?

Studies have not shown that MRI causes cancer. MRI does not expose you to radiation. You are not at risk for radiation exposure from the test. This is true for both closed and open MRI. You can learn more in Understanding Radiation Risk from Imaging Tests.

Getting an MRI during pregnancy

Getting an MRI during pregnancy has not been proven to show risk to the pregnant person or unborn baby. Some facilities or doctors may delay MRI until after the baby’s birth, unless there is a strong medical reason to use it. If you are pregnant and need an MRI, talk to your health care team to determine the best plan for you.  

What else should I know about an MRI?

• An MRI can cost a lot. Before you have this test, make sure your health insurance will cover it.
• People with excess body weight may have trouble fitting into the MRI machine. If this applies to you, your health care team will talk with you about your options.
• Don’t bring credit cards or other items with magnetic scanning strips into the exam room. The magnet could wipe out the information stored on them.
• An MRI doesn’t expose you to radiation.