(Study type: Nuclear scan; related body system: Circulatory system.)

Two main types of cardiac blood pool scans are performed on adults and children. They are used to evaluate the direction of blood flow in the major blood vessels, to provide information regarding patency of vessels after vascular surgery, and to evaluate the ejection fraction of the right and left ventricles. First-pass or shunt imaging scans are commonly performed on pediatric patients to measure left-to-right shunts and assess for congenital heart defects. MUGA blood pool imaging, also known as radionuclide ventriculogram (RVG), provides information about cardiac function such as ejection fraction, ventricular wall motion, ventricular dilation, stroke volume, and cardiac output. Heart shunt imaging is sometimes done in conjunction with a resting MUGA scan to obtain ejection fraction and assess regional wall motion.

The radionuclide is prepared by one of several in vitro or in vivo methods. One commonly used in vitro method of preparation is performed by adding a radioactive tracer, technetium-99m (Tc-99m) (pertechnetate), to a sample of the patient’s blood and reinjecting the labeled blood. The in vivo method involves two steps: first an injection of stannous pyrophosphate (PyP), a “sticky” substance that adheres to the circulating RBCs, followed 20 min later by an injection of Tc-99m (pertechnetate) that adheres to the PyP. The radionuclide is injected into a jugular or antecubital vein. The ventricular blood pool can be imaged during the initial transit of a peripherally injected, IV bolus of radionuclide (first-pass technique) or when the radionuclide has reached equilibrium concentration. For multigated studies, the patient’s heartbeat, as measured with an electrocardiogram (ECG), is synchronized to the gamma camera imager and computer and therefore termed gated.

MUGA scans can be performed with the heart at rest or additionally as part of a stress test. The MUGA procedure, performed with the heart in motion, is used to obtain multiple images of the heart in contraction and relaxation during an R-to-R cardiac cycle. The resulting images can be displayed in a cinematic mode to visualize cardiac function. They can also be compared to MUGA scans performed at rest. Repetitive data acquisitions are possible during graded levels of exercise, usually a bicycle ergometer or handgrip, to assess ventricular functional response to exercise. The MUGA scan can also be used to evaluate the effectiveness of sublingual nitroglycerin on ventricular function; nitroglycerin is a strong vasodilator used to treat angina.

A related cardiac nuclear study is the myocardial perfusion scan (MPS). The MPS evaluates myocardial tissue perfusion, as demonstrated by presence of the Tc-99m (sestamibi) or Tc-99m (tetrofosmin), which localizes near mitochondria in the myocardial tissue cells, whereas the MUGA scan evaluates blood flow and the pumping action of the heart by following the movement of a radionuclide in the circulating blood. Combined technologies are now being used to offer higher quality, three-dimensional imaging in color. The single-photon emission computed tomography (SPECT) scan is an example of combining conventional nuclear medicine imaging provided by a gamma camera with CT. Stress testing is frequently performed following the MPS. Stress on the heart is induced, either by exercise or with drugs. Scanning may then be performed with a conventional gamma camera or with SPECT/CT. For additional information regarding the myocardial perfusion scan, refer to the study titled “Myocardial Perfusion Heart Scan.”