The thallium and Cardiolite scans (Cardiolite is the trade name for sestamibi) are tests that help to show how well blood is flowing to various portions of the heart muscle. These tests, so-called "nuclear perfusion studies," are generally used in conjunction with stress tests to non-invasively detect the presence of coronary artery disease (CAD) that is producing partial obstructions in the coronary arteries.
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 is blocked or partially blocked, relatively little thallium (or Cardiolite) accumulates in the muscle supplied by that blocked artery.
How are nuclear perfusion studies performed?During your stress test, either thallium or Cardiolite will be injected into your vein when you have attained your maximum level of exercise. The radioactive substance will distribute itself throughout your heart 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 your heart will then be made by a special camera that can "see" the thallium/Cardiolite. From these pictures, any 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 obstructive CAD. A normal thallium/Cardiolite test is an excellent indication that you have no significant blockages in your coronary arteries. On the other hand, patients with abnormal perfusion scans are highly likely to have significant blockages.
What are the risks of nuclear perfusion scans?These noninvasive studies are very safe. Their only drawback is that a small amount of 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.
Gibbons, RJ, Abrams, J, Chatterjee, K, et al. ACC/AHA 2002 guideline update for the management of patients with chronic stable angina. Available at: www.acc.org/qualityandscience/clinical/statements.htm (accessed August 24, 2006)