How is the MUGA scan performed?A MUGA scan is performed by attaching a radioactive substance, Technetium 99, to red blood cells, then injecting the red blood cells into the patients bloodstream. The patient is then placed under a special camera (a gamma camera), which is able to detect the low-level radiation being given off by the Technetium-labelled red cells. Since the red blood cells (including those that are radio-labelled) fill the cardiac chambers, the image produced by the gamma camera is essentially an outline of those chambers. With some fancy computer manipulation, the the final product is a movie of the heart beating.
What can be learned from the MUGA scan?Several important features of cardiac function can be measured from the MUGA scan. If a patient has had a heart attack, or any other disease that affects the heart muscle, the MUGA scan can localize the portion of the heart muscle that has sustained damage, and can assess the degree of damage. But more importantly, the MUGA scan gives an accurate and reproducible means of measuring and monitoring the ejection fraction of the cardiac ventricles.
The left ventricular ejection fraction (LVEF) is an excellent, and the most commonly used, measure of overall cardiac function. The ejection fraction is simply the proportion of blood that is expelled from the ventricle with each heart beat. So, for instance, if the left ventricle ejects 60% of its blood volume with each beat, the LVEF is 0.6. (A normal LVEF is 0.5 or greater.)
When is the MUGA scan more useful than other heart tests?The advantages of the MUGA scan over other techniques (such as the echocardiogram) for measuring the LVEF are twofold. First, the MUGA ejection fraction is highly accurate, probably more accurate than that obtained by any other technique. Second, The MUGA ejection fraction is highly reproducible. That is, if the LVEF measurement is repeated several times, nearly the same answer is always obtained. (With other tests, variations in the measured LVEF are much greater.) These advantages - along with its noninvasive nature - make the MUGA scan ideal for detecting subtle changes in a patient's cardiac function over time.
A common clinical situation in which repeated MUGA scans are useful is in following a patient's cardiac function during the delivery of chemotherapy for cancer. Some chemotherapeutic agents (adriamycin being the most notable) can be quite toxic to the heart muscle. By measuring the MUGA ejection fraction periodically during chemotherapy, oncologists can determine, on an ongoing basis, whether it is safe to continue with the therapy, or whether certain medications need to be stopped. The MUGA scan is accurate and reproducible enough to detect subtle, early changes in cardiac function that might easily be missed by other techniques. It is a highly effective, noninvasive means of monitoring one of the worst side effects of chemotherapy, and allowing that therapy to be delivered more safely and effectively than would otherwise be possible.