A Multi-Gated Acquisition (MUGA) scan is a non-invasive nuclear medicine test designed to evaluate the heart’s function. This specialized imaging procedure provides a precise, quantitative measurement of how efficiently the heart pumps blood through its main chambers. By creating a moving image of the beating heart, the MUGA scan allows medical professionals to assess the heart’s overall pumping strength and detect abnormalities in the heart muscle’s movement. It is a highly accurate tool used when a precise assessment of cardiac performance is necessary.
The Technology Behind the Scan
The MUGA scan relies on a small amount of a radioactive substance, or radiotracer, typically Technetium-99m (Tc-99m), which is temporarily introduced into the bloodstream. This radiotracer is chemically prepared to attach directly to the patient’s red blood cells. Once bound, it effectively tags the entire blood pool, making the blood inside the heart chambers visible to specialized equipment.
A gamma camera detects the low-level radiation emitted by the tagged blood cells as they circulate through the heart. The technique called “gating” synchronizes the camera’s image acquisition with the patient’s heart rhythm, tracked using an electrocardiogram (ECG). This synchronization uses the R-wave of the ECG, which marks the beginning of the heart’s contraction, to trigger image capture.
By collecting numerous images over many heartbeats and averaging them, a computer generates a clear, high-resolution “movie” of the heart. This process allows physicians to observe the heart’s movement during both its filling phase (diastole) and its pumping phase (systole). The resulting images delineate the inner borders of the heart’s lower chambers, providing the data necessary to calculate the volume of blood pumped with each beat.
Main Reasons for Testing
The primary medical application for the MUGA scan is monitoring cardiotoxicity in patients receiving certain cancer treatments. Specific chemotherapy drugs, such as anthracyclines (doxorubicin) or targeted therapies (trastuzumab/Herceptin), can potentially weaken the heart muscle. Monitoring heart function with a MUGA scan is standard practice for patients receiving these agents.
The scan allows oncologists to establish a baseline heart function before treatment and track changes during therapy. If the heart’s pumping efficiency drops below a set threshold, the treatment plan may be adjusted, paused, or stopped to minimize permanent heart damage. This surveillance is paramount to safely deliver potentially life-saving cancer treatment.
The scan is also used to diagnose and follow patients with heart failure. It provides a reliable metric of the heart’s ability to pump blood, helping determine the severity of heart failure and guiding medication adjustments. Furthermore, the scan helps assess the extent of heart muscle damage following a heart attack by identifying areas of the ventricle wall that are not contracting correctly. It can also be utilized for pre-operative risk assessment for patients with pre-existing heart concerns scheduled for major non-cardiac surgery.
What to Expect During the Procedure
Preparation for a MUGA scan usually involves avoiding substances that can alter the heart rate, such as caffeine and tobacco, for up to 24 hours before the test. Patients are often instructed to fast for several hours prior to the procedure, and they must inform the medical staff of all current medications, as some heart drugs may need to be temporarily paused.
The patient will have small electrode patches attached to their chest, connecting to an ECG machine to monitor heart rhythm. The radiotracer is then administered, typically through an intravenous line placed in the arm. In some cases, the radiotracer is mixed with a small blood sample outside the body and then re-injected.
The patient is positioned on an examination table, lying still under the gamma camera, which is placed close to the chest. The camera moves around the chest to capture images from multiple angles. The imaging process usually takes about an hour, and the patient must remain as still as possible to ensure clear, high-quality images are obtained.
Understanding the Ejection Fraction
The most important measurement derived from a MUGA scan is the Left Ventricular Ejection Fraction (LVEF). The LVEF is a percentage representing the proportion of blood pumped out of the left ventricle—the heart’s main pumping chamber—with each beat. It is the objective measure of the heart’s overall systolic function, or pumping strength.
A healthy heart typically has an LVEF that falls within the range of 50 percent to 75 percent. An LVEF result below 50 percent indicates the heart is not pumping strongly, which can be a sign of heart muscle dysfunction or heart failure.
The precision of the MUGA scan makes it effective for monitoring small changes in the LVEF over time. For patients undergoing cardiotoxic chemotherapy, a slight decline in this percentage may signal the need to modify treatment before significant heart damage occurs. Tracking this percentage provides a clear, numerical metric for managing long-term cardiac health.