Heart magnetic resonance imaging (MRI) is a non-invasive procedure that uses powerful magnets and radio waves to produce pictures of the heart without exposure to ionizing radiation (X-rays). The heart may be scanned by itself, or a heart MRI may be part of a chest MRI.

MRI uses radio waves very close in frequency to those of ordinary FM radio stations, so the scanner must be located within a specially shielded room to avoid outside interference.

The patient is lies on a narrow table which slides into a large tunnel-like tube within the scanner. Small devices may be placed around the head, arm, or leg, or adjacent to other areas to be studied. These are special body coils which send and receive the radio wave pulses, and are designed to improve the quality of the images. An IV may be placed in the patient's hand or forearm if contrast medium will be used.

A technologist will operate the machine and observe the patient from an adjacent room during the entire study.

Several sets of images are usually required, each taking from 2-15 minutes. A complete scan, depending on the sequences performed, and need for contrast enhancement may take 1 hour or more. Newer scanners may complete the process in less time.

No preparatory tests, diets, or medications are usually needed. An MRI can be performed immediately after other imaging studies. Depending on the area of interest, the patient may be asked to fast for 4 to 6 hours prior to the scan.

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. Pens, pocketknives, and eyeglasses can become dangerous projectiles when the stronge MRI magnet is activated and should not accompany the patient into the scanner area.

The MRI's strong magnetic fields can disrupt cardiac pacemakers cannot be scanned and people with them should not be scanned or even enter the MRI area. MRI also should not be used for people with metallic objects in their bodies such as inner ear (cochlear) implants, brain aneurysm clips, some artificial heart valves, older vascular stents, and recently placed artificial joints.

Sheet metal workers, or persons with similar potential exposure to small metal fragments, will first be screened for metal shards within the eyes with X-rays of the skull. The patient will be asked to sign a consent form confirming that none of the above apply before the MRI begins.

A hospital gown may be recommended, or the patient may be allowed to wear clothing without metal fasteners.

There is no pain. The patient cannot feel the magnetic field and radio waves. The primary possible discomfort is the claustrophobic feeling that some experience from being inside the scanner. The table may be hard or cold, but you can request a blanket or pillow.

The machine produces loud thumping and humming noises during normal operation. Ear plugs are usually given to the patient to reduce the noise. A technologist observes the patient during the entire procedure and may be spoken to through an intercom in the scanner. Some MRI scanners are equipped with televisions and special headphones to help the examination time pass.

Excessive movement can blur MRI images and cause certain artifacts. If the patient has difficulty lying still or is very anxious, an oral or intravenous sedative may be given. There is no recovery time, unless sedation was necessary. After an MRI scan, you can resume normal diet, activity, and medications.

MRI provides detailed pictures of the heart and blood vessels and can distinguish tissues from moving blood. It can differentiate between heart muscle and surrounding tissues and can clarify the findings from previous x-rays or CT scans. MRI excels at showing the heart from multiple views. MRI is useful in diagnosing congenital abnormalities, abnormal growths, and tumors.

MRI is sometimes used to avoid the dangers of angiography, repeated exposure to radiation, or exposure to iodinated contrast dye. It may provide additional information when an echocardiogram is unclear, since bone and air do not interfere with imaging. In addition, heart MRI provides a wider view and better detail than an echocardiogram.