Nuclear imaging is a technique used to produce an image of blood flow, or perfusion, to the heart muscle. It is important because the heart's pumping action is responsible not only for supplying blood to the body, but also to itself through a network of vessels called the coronary arteries.

The entire heart muscle must receive adequate blood flow for the heart muscle to remain healthy. A nuclear perfusion scan is performed using a substance called a "tracer," which is a small amount of radioactive material given by injection into a vein in the arm. A special scanning camera can then "trace" this substance as it

travels through the circulatory system to the heart and the coronary arteries. The scan images reveal a picture of the heart muscle and deviations where blood flow may not be adequate. Most often exercise is used as a part of this test so the heart can be visualized, during and after exercise, as well as during rest. If you cannot exercise because of a medical condition, you may be given a medication to simulate the effects of exercise.

The testing sequence:

Pre-test

• If you smoke, your doctor will probably ask you to stop smoking for a day before the test.

• Caffeine also may be restricted for 24 hours before the test. Remember to ask if this includes such foods as chocolate as well as soft drinks containing caffeine.

• No food or drink is allowed for 4 to 6 hours before the test, except sips of water as instructed by the doctor.

• Comfortable shoes should be worn for the exercise portion of the test.

Exercise precautions

• Be sure to tell your doctor if you experience any discomfort or symptoms, especially any chest pain, or unusual sensations in your arm, shoulder, or jaw, severe shortness of breath, dizziness, or leg cramps or pain.

• Exercise will be stopped when your limit is reached. This is based on how you feel, so be sure to tell the technician when you feel you should not, or cannot, continue. At this point the tracer will be injected through a vein in your arm.

Scanning and Post-Scan

• You will be asked to lie very st