Cardiac Magnetic Resonance Imaging (MRI Scan)

The MRI scanner was originally known as a nuclear magnetic resonance scanner. The word "nuclear" was dropped because it suggested that nuclear radiation was used in the procedure although, in fact, no nuclear radiation is involved.

The patient lies inside a huge, hollow, cylindrical magnet in which the body is exposed to a magnetic field 30,000 times more powerful than the earth’s magnetic field. The nuclei of the body’s atoms normally point randomly in different directions. In a magnetic field, however, they line up parallel to each other, like rows of tiny magnets. If the nuclei are knocked out of alignment by a strong pulse of radio waves, they produce detectable radio signals as they realign themselves. Radio receiver coils in the machine detect these signals and a computer converts them into an image based on the strength and location of the signals.

Today's MRI scanners operate on the nuclei of hydrogen atoms. Because hydrogen is present in water and in a variety of other substances that make up a large proportion of the body, almost the entire structure of the body can be imaged. Tissues that contain a great deal of hydrogen, such as fat, produce a bright image; those that contain less hydrogen, such as bone, appear darker.

MRI can also provide precise images of the heart and major blood vessels and gives a detailed picture of blood flow. It reveals blood in arteries and veins and contrasts it well with surrounding tissue. It can detect changes in the thickness of the heart muscle following a heart attack and can image congenital heart disease abnormalities.

The images produced by MRI are similar to those produced by CT scanning but MRI generally provides a much greater contrast between normal and abnormal tissue. Also, MRI provides flexibility by virtue of its ability to scan the patient in any plane (e.g., vertically or crosswise).

What happens during the MRI?

The MRI machine is a tube that is about 3 feet wide and 6 feet long. Your whole body will be inside this tube with your head about one foot from the end of the tube. You may be given medicine to help you relax during the test. You must lie very still during the examination.  There is nothing to be apprehensive about if your doctor recommends MRI. You will not feel pain and the examination should be over in 45 to 60 minutes or less. All you will hear is the clicking sound of the machinery. About 10 percent of patients suffer feelings of claustrophobia (fear of closed places) during a scan.

Because your body will be placed in a strong magnetic field, it is extremely important that you not carry any metallic. Do not use hair spray or wear makeup. Remove jewelry, eyeglasses, hearing aides, contact lenses and any removable dental work.

Unlike CT scan, MRI can depict blood vessels and heart chambers without the need for injecting a contrast agent (x-ray “dye”) and can picture them in three dimensions

or from any angle. Images can also be obtained in movie format to show heart motion and blood flow. MRI is superior to CT scan when differentiating abnormalities next to the heart from abnormalities of the heart itself.

Unlike echocardiography, which shares some of these advantages, MRI is not limited by the distance of the organ from the skin or by intervening bone structures and air.  MRI is very helpful in assessing tumors or blood clots in the heart, pericardial disease, and diseases of the aorta such as aneurysms and dissection. MRI can determine cardiac anatomy, how well the heart pumps, and perfusion (blood actually getting to the heart muscle) but cannot adequately picture the coronary arteries.

Magnetic Resonance Angiography (MRA Scan)

MRA scan gives a view of specific blood vessels (arteries and veins). MRA may be included with an MRI exam.