What Is Cardiac MRI?

Magnetic resonance imaging (MRI) is a safe, noninvasive test that creates detailed pictures of your organs and tissues. "Noninvasive" means that no surgery is done and no instruments are inserted into your body.

MRI uses radio waves, magnets, and a computer to create pictures of your organs and tissues. Unlike computed tomography (to-MOG-ra-fee) scans (also called CT scans) and standard x rays, MRI doesn't use ionizing radiation or carry any risk of causing cancer.

Cardiac MRI creates pictures of your heart as it's beating, producing both still and moving pictures of your heart and major blood vessels. Doctors use cardiac MRI to get pictures of the beating heart and to look at its structure and function. These pictures can help them decide how to treat people who have heart problems.

Cardiac MRI is a common test. It's used to diagnose and evaluate a number of diseases and conditions, including:

• Coronary heart disease, also called coronary artery disease
• Damage caused by a heart attack
• Heart failure
• Heart valve problems
• Congenital heart defects
• Pericarditis (a condition in which the membrane, or sac, around your heart is inflamed)
• Cardiac tumors

Cardiac MRI can help explain results from other tests, such as x rays and CT scans. Sometimes, cardiac MRI is used to avoid the need for invasive procedures or tests that use radiation (such as x rays) or dyes containing iodine (these dyes may be harmful to people who have kidney problems).

Often during cardiac MRI, a contrast agent is injected into a vein to highlight portions of the heart or blood vessels. This contrast agent often is used for people who are allergic to the dyes used in CT scanning.

People who have severe kidney or liver problems may not be able to have the contrast agent. As a result, they may have an MRI that doesn't use the substance (a noncontrast MRI).

Other Names for Cardiac MRI

• Heart MRI
• Cardiovascular MRI
• Cardiac nuclear magnetic resonance (NMR)

What To Expect Before Cardiac MRI

You'll be asked to fill out a screening form before having cardiac MRI. The form may ask whether you have had previous surgeries, have any metal objects in your body, or have any medical devices (like a cardiac pacemaker) surgically implanted in your body.

Most, but not all, implanted medical devices are allowed near the MRI machine. Talk to your doctor or the technician operating the machine if you have concerns about any implanted devices or conditions that may interfere with the MRI.

MRI can seriously affect some types of implanted medical devices.

• Implanted cardiac pacemakers and defibrillators can malfunction.
• Cochlear (inner-ear) implants can be damaged. Cochlear implants are small electronic devices that help people who are deaf or who can’t hear well understand speech and the sounds around them.
• Brain aneurysm (AN-u-rism) clips can move due to MRI's strong magnetic field. This can cause severe injury.

Your doctor will let you know if you shouldn't have a cardiac MRI because of a medical device. If this happens, consider wearing a medical ID bracelet or necklace or carrying a medical alert card that states that you shouldn't have an MRI.

Your doctor or technician will tell you whether you need to change into a hospital gown for the test. Don't bring hearing aids, credit cards, jewelry and watches, eyeglasses, pens, removable dental work, and anything that's magnetic near the MRI machine.

Tell your doctor if being in a fairly tight or confined space causes you anxiety or fear. This fear is called claustrophobia (klaw-stro-FO-be-a). If you have this condition, your doctor might give you medicine to help you relax. Your doctor may ask you to fast (not eat) for 6 hours before you take this medicine on the day of the test.

Some of the newer cardiac MRI machines are open on all sides. Ask your doctor to help you find a facility that has an open MRI machine if you're fearful in tight or confined spaces.

Your doctor will let you know whether you need to arrange for a ride home after the test.

What To Expect During Cardiac MRI

MRI machines usually are located at hospitals or special medical imaging facilities. A radiologist (ra-de-OL-o-jist) or other doctor who has special training in medical imaging oversees MRI testing.

Cardiac MRI usually takes 45 to 90 minutes, depending on how many pictures are needed. The test may take less time with some newer MRI machines.

The MRI machine will be located in a specially constructed room. This will prevent radio waves from disrupting the machine. It also will prevent the MRI machine's strong magnetic fields from interfering with other equipment.

Traditional MRI machines look like a long, narrow tunnel. Newer MRI machines, called short-bore systems, are shorter, wider, and don't completely surround you. Some of the newer machines are open on all sides. Your doctor will help decide which type of machine is best for you.

Cardiac MRI is painless and harmless. You'll lie on your back on a sliding table that goes inside the tunnel-like machine. The technician will control the machine from the next room. He or she will be able to see you through a glass window and talk to you through a speaker. Tell the technician if you have a hearing problem.

A Patient Having Cardiac MRI

The photo shows a patient lying on a sliding table outside of a cardiac MRI machine. The table will slide into the machine, and the patient will lie quietly while pictures of the heart are taken.

The MRI machine makes loud humming, tapping, and buzzing noises. Earplugs may help lessen the noises made by the MRI machine. Some facilities let you listen to music during the test.

You will need to remain very still during the test. Any movement may blur the pictures. If you're unable to lie still, you may be given medicine to help you relax.

You may be asked to hold your breath for 10 to 15 seconds at a time while the technician takes pictures of your heart. Researchers are studying ways that will allow someone having a cardiac MRI to breathe freely during the exam, while achieving the same image quality.

A contrast agent, such as gadolinium (gad-oh-LIN-e-um), may be used to highlight your blood vessels or heart in the pictures. Contrast agent usually is injected into a vein in your arm with a needle.

You may feel a cool sensation during the injection and discomfort where the needle was inserted. Gadolinium doesn't contain iodine, so it won't cause problems for people who are allergic to iodine.

Your cardiac MRI may include a stress test to detect blockages in your coronary arteries. If so, you'll get other medicines to increase the blood flow in your heart or to increase your heart rate.

What To Expect After Cardiac MRI

If you didn't take medicine to help you relax, you'll be able to return to your normal routine once the cardiac MRI is done.

If you did take medicine to help you relax during the test, your doctor will tell you when you can return to your normal routine. You'll need someone to drive you home.

What Does Cardiac MRI Show?

The doctor supervising your scan will provide your doctor with the results of your cardiac MRI. Your doctor will discuss the findings with you.

Cardiac MRI can reveal various heart conditions and disorders, such as:

• Coronary heart disease
• Damage caused by a heart attack
• Heart failure
• Heart valve problems
• Congenital heart defects
• Pericarditis (a condition in which the membrane, or sac, around your heart is inflamed)
• Cardiac tumors

Cardiac MRI is a fast, accurate tool that can help diagnose a heart attack. The test does this by detecting areas of the heart that don’t move normally, have poor blood supply, or are scarred.

Cardiac MRI can show whether any of the coronary arteries are blocked, causing reduced blood flow to your heart muscle.

Currently, coronary angiography (an-jee-OG-ra-fee) is the most common procedure for looking at blockages in the coronary arteries. Coronary angiography is an invasive procedure that uses x rays and iodine-based dyes.

Researchers have found that cardiac MRI can replace coronary angiography in some cases, avoiding the need to use x-ray radiation and iodine-based dyes. This use of MRI is called MRI angiography.

Cardiac MRI

Figure A shows the heart's position in the body and the location and angle of the MRI pictures shown in figure C. Figure B is an MRI angiogram, which is sometimes used instead of a standard angiogram. Figure C shows MRI pictures of a normal left ventricle (left image), a left ventricle damaged from a heart attack (middle image), and a left ventricle that isn't getting enough blood from the coronary arteries (right image).

Researchers are finding new ways to use cardiac MRI. In the future, cardiac MRI may replace x rays as the main way to guide invasive procedures such as cardiac catheterization (KATH-e-ter-i-ZA-shun). Also, improvements in cardiac MRI are likely to lead to better methods for detecting heart disease in the future.

What Are the Risks of Cardiac MRI?

Cardiac MRI produces no side effects from the magnetic fields and radio waves. This method of taking pictures of organs and tissues doesn't carry a risk of causing cancer or birth defects.

Serious reactions to the contrast agent used for MRI are very rare. However, side effects are possible and include the following:

• Headache
• Nausea (feeling sick to your stomach)
• Dizziness
• Changes in taste
• Allergic reactions

Rarely, the contrast agent can be harmful in people who have severe kidney or liver disease.

If your cardiac MRI includes a stress test, more medicines will be used during the test. These medicines may have other side effects that aren't expected during a regular MRI scan, such as:

• Arrhythmias (ah-RITH-me-ahs), or irregular heartbeats
• Chest pain
• Shortness of breath
• Palpitations (feelings that your heart is skipping a beat, fluttering, or beating too hard or fast)

Key Points

• Cardiac magnetic resonance imaging (MRI) is a safe, noninvasive test that uses radio waves, magnets, and a computer to create detailed pictures of the heart.
• Unlike computed tomography (CT) scans and standard x rays, MRI doesn't use ionizing radiation or carry any risk of causing cancer.
• Cardiac MRI is a common test. It can help diagnose and evaluate a number of heart diseases and conditions. The test helps doctors decide how to treat people who have heart problems.
• Often during cardiac MRI, a contrast agent is injected into a vein to highlight portions of the heart or blood vessels.
• People who have certain types of implanted medical devices in their bodies shouldn't have cardiac MRI. For example, a cardiac MRI can cause implanted cardiac pacemakers and defibrillators to malfunction. Your doctor will let you know if you shouldn't have a cardiac MRI because of a medical device.
• Cardiac MRI usually takes 45 to 90 minutes, depending on how many pictures are needed. The test may take less time with some newer MRI machines.
• During the test, you'll be asked to lie still on a sliding table that goes inside a tunnel-like machine. You may be given medicine to help you relax. Cardiac MRI is painless and harmless.
• A doctor who has experience with MRI will provide your doctor with the results of your test. Your doctor will discuss the findings with you.
• Cardiac MRI produces no side effects from the magnetic fields and radio waves. Serious reactions from the contrast agent used for MRI are rare.
• In some cases, cardiac MRI can replace coronary angiography to look at the flow of blood through the coronary arteries. This helps avoid the need to use x-ray radiation and iodine-based dyes.
• Researchers are finding new ways to use cardiac MRI. In the future, cardiac MRI may be used to guide invasive procedures such as cardiac catheterization.

Links to Other Information About Cardiac MRI

NHLBI Resources

• "Your Guide to Living Well With Heart Disease"

Non-NHLBI Resources

• Heart MRI (MedlinePlus)

Clinical Trials

• Current Research (ClinicalTrials.gov)