Cardiac MRI

Medically Reviewed By William C. Lloyd III, MD, FACS
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What is a cardiac MRI?

Cardiac MRI (magnetic resonance imaging) is a painless but advanced cardiac imaging test to visualize the structure of the heart in detail. Unlike X-rays and CT (computed tomography) scans, MRIs do not use ionizing radiation to provide images. Instead, MRIs use powerful magnets and radio waves. An MRI is extremely sensitive and can distinguish between healthy and diseased tissue with better accuracy than other imaging tests like X-ray and ultrasound.

During the imaging test, the MRI scanner generates a strong magnetic field around the patient. It then sends a series of harmless radio wave pulses. The scanner receives radio wave signals back from the area being imaged. A computer converts the signals into images, each representing a very thin slice of your heart. The computer program joins the slices together to form a more detailed image.

Sometimes, doctors use a contrast agent to make it easier to see blood vessels and blood flow in the images. This is magnetic resonance angiography (MRA).

Why is a cardiac MRI performed?

A chest X-ray is commonly the first test to do if someone complains of possible cardiac-related symptoms, but an X-ray of the heart does not show enough detail to confirm a diagnosis. An MRI of your heart, sometimes called a MRI heart scan, can show your heart’s structure and function—how well blood can flow through the heart and major blood vessels.

Doctors use MRIs to diagnose a heart problem, monitor the progress of heart disease, or evaluate how well treatment is working. Your cardiologist may request a cardiac MRI if there are signs of:

  • Cardiac tumors

  • Congenital heart defects

  • Coronary heart disease

  • Heart failure

  • Heart valve problems

  • Muscle damage to the heart caused by a heart attack

  • Pericarditis

Who performs a cardiac MRI?

A specially trained radiologic technologist performs the cardiac MRI, but a radiologist interprets the test results. A radiologist is a medical doctor who specializes in supervising and interpreting (reading) X-rays and other imaging tests. The radiologist sends the results to your cardiologist or primary care physician.

How is a cardiac MRI performed?

Cardiac MRIs are performed in a specialized radiology clinic or in a hospital. MRI is a painless imaging procedure. The MRI scanner itself can be an enclosed “tube” or open-ended. If you have any metal implants, particularly a pacemaker or defibrillator, or if you are pregnant, it’s vital that you tell your doctor and the technologist before the test. Your doctor may suggest an alternative test. Tell your doctor if you are claustrophobic, which could make it difficult to lie still in the MRI machine for extended periods. Your doctor can prescribe a sedative before the test if you are claustrophobic. The test lasts 30 to 90 minutes.

An intravenous (IV) will be necessary if you are having a heart scan with contrast agent. An IV is a thin catheter inserted in your vein to administer of the contrast agent, as well as fluids and medications.

What to expect the day of your cardiac MRI

In general, this is what happens for the procedure: 

  • You dress in a hospital gown and lie on a narrow table.

  • The technologist may place pillows or straps around and you to keep your body in position during the procedure.

  • If the test involves a contrast agent, a nurse or technologist will start an IV line in your arm or the top of your hand.

  • Once you are ready, the table will slowly slide into the MRI machine.

  • MRI machines are noisy, so you may be given ear plugs, ear buds or headphones so you can listen to music.

  • You will need to take a deep breath from time to time and hold it for a few seconds. This helps produce clearer images.

There is an intercom in the machine that the operator uses to communicate with you throughout the test. You may go home after the procedure. If you had a sedative, it is best if someone accompanies you home. If you received a contrast agent, your doctor will ask you to drink extra fluids to flush the dye out of your body.

What are the risks and potential complications of a cardiac MRI?

There are no risks or complications to a cardiac MRI without contrast agent. If you do have contrast, risks are related to possible allergic reaction to the contrast or kidney damage as your body tries to excrete it. The risk of kidney problems is greater for people who have decreased kidney function or kidney transplant.

The magnetic field when the MRI scanner is on can cause serious problems if you have metal implants or objects in or on your body. The magnetic field could cause the metal parts to move inside your body or they may heat up from the energy. You may need to a have a different type of heart scan if you have a pacemaker, defibrillator, or neurostimulation device. Speak with your doctor about your options.

How do I prepare for a cardiac MRI?

Wear clothes that are easy to remove. If you are going to receive a sedative, ask someone to be with you when the test is over, to accompany you home. If you are concerned about being inside the machine or for lying still for the procedure, speak to your doctor about these concerns. You may have access to an open-ended MRI machine.

The technologist will ask you to remove anything containing metal, including hearing aids and even makeup. Metal objects like orthopedic hardware (pins, plates and screws) and dental implants are acceptable, but they may interfere with image quality if they are in or near the area being scanned.

What can I expect after my cardiac MRI?

The radiologist will send the results of your cardiac MRI directly to your doctor. Ask your doctor if you should schedule a follow-up appointment to discuss the results and next steps in your care.

When should I call my doctor?

Although you will likely have a follow-up appointment with your doctor, you may need to call your doctor if you experience any of these issues after a cardiac MRI with contrast:

  • Difficulty urinating, which may signal a kidney problem related to the contrast material

  • Itching, swelling or rash, which may be signs of a serious allergic reaction

  • Redness or warmth at the IV infusion site, which may be signs of infection

How might a cardiac MRI affect my everyday life?

Unless there is a specific situation unique to you, there are generally no restrictions following a cardiac MRI. The test may help your cardiologist diagnose and treat heart disease or conditions revealed by the images. Your doctor may ask you to have other cardiac diagnostic and imaging tests, such as a stress test or cardiac catheterization.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Jan 23
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