Radionuclide Angiography - Procedure

Procedure

The MUGA scan is performed by labeling the patient's red blood pool with a radioactive tracer, technetium-99m-pertechnetate (Tc-99m), and measuring radioactivity over the anterior chest as the radioactive blood flows through the large vessels and the heart chambers.

The introduction of the radioactive marker can either take place in vivo or in vitro. In the in vivo method, stannous (tin) ions are injected into the patient's bloodstream. A subsequent intravenous injection of the radioactive substance, technetium-99m-pertechnetate, labels the red blood cells in vivo. With an administered activity of about 800 MBq, the effective radiation dose is about 8 mSv to 12 mSv. In the in vitro method, some of the patient's blood is drawn and the stannous ions (in the form of stannous chloride) are injected into the drawn blood. The technetium is subsequently added to the mixture as in the in vivo method. In both cases, the stannous chloride reduces the technetium ion and prevents it from leaking out of the red blood cells during the procedure. The in vivo technique is more convenient for the majority of patients since it is less time-consuming and less costly and more than 80 percent of the injected radionuclide usually binds to red blood cells with this approach. Red blood cell binding of the radioactive tracer is generally more efficient with the in vitro labeling, and it is preferred in patients with indwelling intravenous catheters to decrease the adherence of Tc-99m to the catheter wall and increase the efficiency of blood pool labeling.

The patient is placed under a gamma camera, which detects the low-level 140keV gamma radiation being given off by technetium-99m. As the gamma camera images are acquired, the patient's heart beat is used to 'gate' the acquisition. The final result is a series of images of the heart (usually sixteen), one at each stage of the cardiac cycle.

Depending on the objectives of the test, the doctor may decide to perform either a resting or a stress MUGA. During the resting MUGA, the patient lies stationary, whereas during a stress MUGA, the patient is asked to exercise during the scan. The stress MUGA measures the heart performance during exercise and is usually performed to assess the impact of a suspected coronary artery disease. In some rare cases, a nitroglycerin MUGA may be performed, where nitroglycerin (a vasodilator) is administered prior to the scan.

The resulting images show that the volumetrically derived blood pools in the chambers of the heart and timed images may be computationally interpreted to calculate the ejection fraction and injection fraction of the heart. This nuclear medicine scan yields an accurate, inexpensive and easily reproducible means of measuring and monitoring the ejection and injection fractions of the ventricles, which are one of many of the important clinical metrics in assessing global heart performance.