Thallium and Cardiolite Scans

The thallium and Cardiolite scans (Cardiolite is the trade name for sestamibi) are tests that show how well blood is flowing to various portions of the heart muscle. These tests, which are varieties of nuclear perfusion studies, are generally used in conjunction with stress tests to non-invasively diagnose the presence of coronary artery disease.

What are thallium and Cardiolite?

Thallium and Cardiolite are radioactive substances. When injected into the bloodstream, these substances collect in the portions of heart muscle that have good blood flow. If one of the coronary arteries (the arteries that supply blood to the heart muscle) is blocked or partially blocked, not as much thallium (or Cardiolite) accumulates in the muscle supplied by that blocked artery.

How are nuclear perfusion studies performed?

During a stress test, either thallium or Cardiolite is injected into the patient's vein when the maximum level of exercise is reached. The radioactive substance distributes itself throughout the cardiac muscle in proportion to the blood flow received by that muscle. Cardiac muscle receiving normal blood flow accumulates a larger amount of thallium/Cardiolite than cardiac muscle that is supplied by diseased coronary arteries.

An image of the heart is then made by a special camera that can "see" the thallium/Cardiolite. From these pictures, portions of the heart that are not receiving normal blood flow (because of blockage in the coronary arteries) can be identified.

What are nuclear perfusion studies good for?

Using thallium or Cardiolite perfusion imaging greatly increases the accuracy of the stress test in diagnosing coronary artery disease. A normal thallium/Cardiolite test is an excellent indication that the patient has no significant coronary artery disease. Patients with abnormal perfusion scans are highly likely to have significant coronary artery disease.

What are the risks of nuclear perfusion scans?

These noninvasive studies are very safe. Their only drawback is that radiation is used. The level of radiation the patient receives is felt to produce only a very small risk of harm, and for appropriately selected patients the potential for benefit far outweighs this small risk.