Heart magnetic resonance imaging (MRI) is a method that uses powerful magnets and radio waves to create pictures of the heart. It does not use radiation (x-rays).

The test may be done as part of a chest MRI.

You will be asked to lie on a narrow table, which slides into a large tunnel-like tube. The health care provider may inject a dye through one of your veins. This helps certain diseases and organs show up better on the images.

Unlike and computed tomographic (CT) scans, MRI does not use radiation. Instead, it uses powerful magnets and radio waves. The magnetic field produced by an MRI forces certain atoms in your body to line up in a certain way. It's similar to how the needle on a compass moves when you hold it near a magnet.

The radio waves are sent toward these atoms and bounce back, and a computer records the signal. Different types of tissues send back different signals. For example, healthy tissue sends back a slightly different signal than cancerous tissue.

A technologist will operate the machine from a room next door and watch you during the entire study.

Several sets of images are usually needed. Each one takes about 2-15 minutes. A complete scan may take up to 1 hour. Newer scanners may complete the process in less time.

There is usually no preparation needed. An MRI can be done immediately after other imaging studies. If contrast (dye) or sedation is used, you may be asked not to eat for 4 to 6 hours prior to the scan.

The strong magnetic fields created during an MRI can interfere with certain implants, particularly cardiac pacemakers. People with cardiac pacemakers can not have an MRI and should not enter the MRI area.

If you have any of the following metallic objects in your body, you should not get an MRI:

• Brain aneurysm clips
• Certain artificial heart valves
• Inner ear (cochlear) implants
• Older vascular stents
• Recently placed artificial joints

You will be asked to sign a consent form that says you do not have any of these items in your body. You may be asked to wear a hospital gown.

Certain metallic objects are not allowed into the room.

• Items such as jewelry, watches, credit cards, and hearing aids can be damaged.
• Pins, hairpins, metal zippers, and similar metallic items can distort the images.
• Removable dental work should be taken out just prior to the scan.

When the MRI magnet is turned on, pens, pocketknives, and eyeglasses may fly across the room. This can be dangerous, so such items are not allowed into the scanner area.

A heart MRI exam causes no pain. Some people may become anxious when inside the scanner. If you have difficulty lying still or are very anxious, you may be given a mild sedative. Excessive movement can blur MRI images and cause errors.

The table may be hard or cold, but you can request a blanket or pillow. The machine produces loud thumping and humming noises when turned on. Ear plugs are usually given to help reduce the noise.

An intercom in the scanner allows you to speak to the person operating the exam at any time. Some MRIs have televisions and special headphones that you can use to help the time pass.

There is no recovery time, unless sedation was necessary. (You will need someone to drive you home if sedation was given.) After an MRI scan, you can resume your normal diet, activity, and medications, unless otherwise instructed by your doctor.