Magnetic Resonance Imaging (MRI) of the Heart

(MRI Scan of the Heart, Cardiac MRI)

Procedure overview

What is magnetic resonance imaging (MRI) of the heart?

Magnetic resonance imaging (MRI) is a diagnostic procedure that uses a combination of a large magnet, radiofrequencies, and a computer to produce detailed images of organs and structures within the body.

How does MRI work?

The MRI machine is a large, cylindrical (tube-shaped) machine that creates a strong magnetic field around the patient. This magnetic field, along with a radiofrequency, alters the hydrogen atoms' natural alignment in the body. Computers are then used to form two-dimensional (2D) images of the heart's structure based on the activity of the hydrogen atoms. Cross-sectional views can be obtained to reveal further details. MRI does not use ionizing radiation, as do X-rays or computed tomography (CT scans).

A magnetic field is created and pulses of radio waves are sent from a scanner. The magnetic field aligns the hydrogen protons in your body along the same vector. The radio waves then knock the protons out of this aligned position. As the nuclei realign back into proper position, they send out radio signals. These signals are received by a computer that analyzes and converts them into an image of the part of the body being examined. This image appears on a viewing monitor. Some MRI machines look like narrow tunnels, while others are more open.

MRI may be used instead of a CT scan in situations where organs or soft tissue are being studied, because with MRI scanning bones do not obscure the images of organs and soft tissues, as does CT scanning.

Other related procedures that may be used to assess the heart include resting or exercise electrocardiogram (ECG), Holter monitor, signal-averaged ECG, cardiac catheterization, chest x-ray, computed tomography (CT scan) of the chest, electrophysiological studies, myocardial perfusion scans, radionuclide angiography, and ultrafast CT scan. Please see these procedures for additional information.

Reasons for the procedure

MRI of the heart may be performed for further evaluation of signs or symptoms that may suggest:

• Atherosclerosis. A gradual clogging of the arteries over many years by fatty materials and other substances in the blood stream
• Cardiomyopathy. An enlargement of the heart due to thickening or weakening of the heart muscle
• Congenital heart disease. Defects in one or more heart structures that occur during formation of the fetus, such as a ventricular septal defect (hole in the wall between the two lower chambers of the heart)
• Congestive heart failure. A condition in which the heart muscle has become weakened to an extent that blood cannot be pumped efficiently, causing buildup (congestion) in the blood vessels, lungs, feet, ankles, and other parts of the body
• Aneurysm. A dilation of a part of the heart muscle or the aorta (the large artery that carries oxygenated blood out of the heart to the rest of the body), which may cause weakness of the tissue at the site of the aneurysm
• Valvular heart disease. Malfunction of one or more of the heart valves that may cause an obstruction of the blood flow within the heart
• Cardiac tumor. A tumor of the heart that may occur on the outside surface of the heart, within one or more chambers of the heart (intracavitary), or within the muscle tissue of the heart

There may be other reasons for your doctor to recommend an MRI of the heart.

Risks of the procedure

Because radiation is not used, there is no risk of exposure to ionizing radiation during an MRI procedure.

Due to the use of the strong magnet, MRI cannot be performed on patients with implanted pacemakers, some older intracranial aneurysm clips, cochlear implants, certain prosthetic devices, implanted drug infusion pumps, neurostimulators, bone-growth stimulators, certain intrauterine contraceptive devices, or any other type of iron-based metal implants. MRI is also contraindicated in the presence of some internal metallic objects, such as bullets or shrapnel, as well as surgical clips, pins, plates, screws, metal sutures, or wire mesh.

If you are pregnant or suspect that you may be pregnant, you should notify your health care provider. MRI is generally considered safe in pregnancy; however, especially in the first trimester, you and your doctor should discuss the potential risks and benefits of having the procedure done.

If contrast dye is used, there is a risk for allergic reaction to the dye. Patients who are allergic to or sensitive to medications should notify their doctor. If you have severe kidney disease or are on kidney dialysis, there is a risk of a condition called "nephrogenic systemic fibrosis" from the dye. You should discuss this risk with your doctor prior to the test.

MRI contrast may have an effect on other conditions, such as allergies, asthma, anemia, hypotension (low blood pressure), kidney disease, and sickle cell disease.

Nephrogenic Systemic Fibrosis (NSF) is a very rare but serious complication of MRI contrast use in patients with kidney disease or kidney failure. If you have a history of kidney disease, kidney failure, kidney transplant, liver disease or are on dialysis, you must inform the MRI technologist or radiologist prior to receiving contrast.

There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.

Before the procedure

• Your doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
• If your procedure involves the use of contrast dye, you will be asked to sign a consent form that gives permission to do the procedure. Read the form carefully and ask questions if something is not clear.
• Notify the technologist if you have ever had a reaction to any contrast dye, or if you are allergic to iodine.
• Generally, there is no special restriction on diet or activity prior to an MRI procedure.
• Notify the technologist if you are pregnant or suspect you may be pregnant.
• Before the examination, it is extremely important that you inform the technologist if any of the following apply to you:
  • You are claustrophobic and think that you will be unable to lie still while inside the scanning machine, in which case you may be given a sedative
  • You have a pacemaker or have had heart valves replaced
  • You have any type of implanted pump, such as an insulin pump
  • You have metal plates, pins, metal implants, surgical staples, or aneurysm clips
  • You have any metallic fragments anywhere in the body
  • You have permanent eye liner or tattoos
  • You are pregnant or suspect you may be pregnant
  • You ever had a bullet wound
  • You have ever worked with metal (for example, a metal grinder or welder)
  • You have any body piercing
  • You have an intrauterine device (IUD)
• Sedative medication may be given if you have claustrophobia and/or anxiety that would make it difficult for you to remain still during the procedure.
• Based on your medical condition, your doctor may request other specific preparation.

During the procedure

MRI may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor's practices.

Picture of a patient in a scanner

Generally, an MRI follows this process:

1. You will be asked to remove any clothing, jewelry, eyeglasses, hearing aids, hairpins, removable dental work, or other objects that may interfere with the procedure.
2. If you are asked to remove clothing, you will be given a gown to wear.
3. If you are to have a procedure done with contrast, an intravenous (IV) line will be started in the hand or arm for injection of the contrast dye.
4. You will lie on a scan table that slides into a large circular opening of the scanning machine. Pillows and straps may be used to prevent movement during the procedure.
5. The technologist will be in another room where the scanner controls are located. However, you will be in constant sight of the technologist through a window. Speakers inside the scanner will enable the technologist to communicate with and hear you. You will have a call button so that you can let the technologist know if you have any problems during the procedure. The technologist will be watching you at all times and will be in constant communication.
6. A surface coil may be placed over the area to be examined.
7. You will be given earplugs or a headset to wear to help block out the noise from the scanner. Some headsets may provide music for you to listen to.
8. During the scanning process, a clicking noise will sound as the magnetic field is created and pulses of radio waves are sent from the scanner.
9. It will be important for you to remain very still during the examination, as any movement could cause distortion and affect the quality of the scan.
10. At intervals, you may be instructed to hold your breath, or to not breathe, for a few seconds. You will then be told when you can breathe. You should not have to hold your breath for longer than a few seconds.
11. If contrast dye is used for your procedure, you may feel some effects when the dye is injected into the IV line. These effects include coolness or discomfort at the IV site, and should only last for a few moments.
12. You should notify the technologist if you feel any breathing difficulties, sweating, numbness, or heart palpitations.
13. Once the scan has been completed, the table will slide out of the scanner and you will be assisted off the table.
14. If an IV line was inserted for contrast administration, the line will be removed.

While the MRI procedure itself causes no pain, having to lie still for the length of the procedure might cause some discomfort or pain, particularly in the case of a recent injury or invasive procedure, such as surgery. The technologist will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.

On occasion, some patients with metal fillings in their teeth may experience some slight tingling of the teeth during the procedure.

After the procedure

You should move slowly when getting up from the scanner table to avoid any dizziness or lightheadedness from lying flat for the length of the procedure.

If any sedatives were taken for the procedure, you may be required to rest until the sedatives have worn off. You will also need to avoid driving.

If contrast dye is used during your procedure, you may be monitored for a period of time for any side effects or reactions to the contrast dye, such as itching, swelling, rash, or difficulty breathing.

If you notice any pain, redness, and/or swelling at the IV site after you return home following your procedure, you should notify your doctor as this could indicate an infection or other type of reaction.

Otherwise, there is no special type of care required after a MRI scan of the heart. You may resume your usual diet and activities, unless your doctor advises you differently.

Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.