What Does It Show?

Cardiac perfusion imaging helps doctors diagnose coronary heart disease, which is caused by narrowed or blocked coronary arteries (the vessels that supply blood to the heart muscle).

Figure 1.     Cardiac Perfusion Scan The images show the heart from two different "angles" during stress and at rest. The stress images show a "defect," which disappears at rest. This suggests a narrowing in the artery which supplies blood to that area of the heart muscle.

During the test, adenosine or dipyridamole is injected into a vein. The drug causes the coronary arteries to dilate (widen), which increases blood flow to the heart muscle. Arteries that are diseased cannot dilate as much as healthy arteries. As a result, blood flows mostly to areas supplied by healthy arteries.

Once the dilating drug has been given, a small amount of the tracer is injected into the vein. The tracer collects in those parts of the heart muscle that have good blood flow.

The tracer gives off a small amount of radiation that is detected with a scanning camera. A computer processes the information and produces images that show how radioactivity is distributed in the heart.

If an area of the heart receives less blood than the rest of the heart (because of a narrowed or blocked artery), it will pick up less radioactivity and will show up as a lighter area, called a “defect.”

Additional tracer is injected while you are at rest, and another set of images is taken. By comparing the stress and rest images, doctors can identify areas of the heart muscle with reduced blood flow as well as areas that may be scarred from a previous heart attack.

Preparing for the Test