Multiple-gated acquisition (MUGA) scan
The multiple-gated acquisition (MUGA) scan, also called a cardiac blood pool study, is a non-invasive nuclear medicine test that enables clinicians to obtain information about heart muscle activity. The scan displays the distribution of a radioactive tracer in the heart. The images of the heart are obtained at intervals throughout the cardiac cycle, and are used to calculate ejection fraction (an important measure of heart performance) and evaluate regional myocardial wall motion.
A MUGA scan may be done while the patient is at rest and again with stress. The resting study is usually performed to obtain the ejection fraction of the right and left ventricles, evaluate the left ventricular regional wall motion, assess the effects of cardiotoxic drugs (i.e., chemotherapy), and differentiate the cause of shortness of breath (pulmonary vs. cardiac). Ejection fraction and wall motion are also important measurements made during a stress study, but the stress study is performed primarily to detect coronary artery disease and evaluate angina.
The MUGA scan is a series of images that demonstrate the flow of blood through the heart, providing information about heart muscle activity. Before images are taken, a radionuclide is injected into the bloodstream, a process that requires two injections in most health care facilities. The first injection contains a chemical that adheres to red blood cells, and the second contains a radioactive tracer (Tc99m) that attaches to that chemical. Alternatively, the two chemicals can be mixed together first and then injected, but the material tends to accumulate in bone and may obscure the heart.
The pictures are taken via gamma camera driven by a computer program that times the images, processes the information, and performs the mathematical calculations to provide ejection fraction and demonstrate wall motion. Images are obtained at various intervals during the cardiac cycle. Electrodes are placed on the patient so that a time frame can be established, for example, the time period between each "wave" (a part of the cardiac cycle seen on an EKG). The time frame is divided into several intervals, or "multiple gates." The result is a series of pictures showing the left and right ventricles at end-diastole (when the heart is dilated and filled with blood) and end-systole (when the heart is contracted and blood is being pumped out), and a number of stages in between.
A MUGA scan is performed in a hospital nuclear medicine department or in an outpatient facility. It takes approximately 30 minutes to one hour. The patient lies down on a bed alongside the gamma camera, receives the radionuclide injections, and multiple images are taken. If a stress study is indicated, the rest study is performed first. In a stress study, the patient usually lies on a special bed fitted with a bicycle apparatus. While an image is being recorded, the patient is asked to cycle for about two minutes, then the resistance of the wheels is increased. After two more minutes of exercise , another image is obtained and the resistance is increased again. Blood pressure and ECG are monitored during the procedure. After the stress portion is finished, one more resting, or recovery, study is obtained.
Standard preparation for an ECG is required. Special handling of nuclear materials by a nuclear medicine technologist may be required for the injections.
The patient may resume normal activities immediately following the test.
A normal MUGA scan should not demonstrate areas of akinesis (lack of movement), or hypokinesis (decreased movement) of the heart muscle walls. Abnormal motion, especially in the left ventricle, is suggestive of an infarct or other myocardial defect. The ejection fraction is a measure of heart function, and should be within the normal limits established by the testing facility.
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Christine Miner Minderovic, B.S., R.T., R.D.M.S.
Lee A. Shratter, M.D.