A MUGA scan (multigated acquisition scan) is a nuclear imaging test that measures how well your heart pumps blood with each beat. It produces a precise number called your ejection fraction, which tells doctors what percentage of blood your heart pushes out each time it contracts. MUGA scans are most commonly ordered for people undergoing chemotherapy, since certain cancer drugs can weaken the heart muscle over time.
How the Scan Works
The test uses a small amount of a radioactive tracer called technetium-99m, which is injected into a vein in your arm. This tracer attaches to your red blood cells, essentially lighting them up so a special camera can track blood as it moves through your heart. Sticky electrodes are placed on your chest to monitor your heart’s electrical activity at the same time.
Here’s where the “gated” part of the name comes in. The camera syncs its snapshots to your heartbeat using signals from those electrodes. It captures images at multiple points during each cardiac cycle, hundreds of heartbeats’ worth, then combines them into a short, looping video of your heart filling and squeezing. This gating technique is what gives the scan its high level of consistency from one test to the next. You lie still on an exam table while the camera is positioned over your chest, and the technician takes images from several angles. The entire process typically takes about an hour.
Why Doctors Order a MUGA Scan
The most common reason is chemotherapy monitoring. Several widely used cancer drugs, including doxorubicin, daunorubicin, idarubicin, and trastuzumab, carry a known risk of damaging the heart muscle. Doctors need a reliable way to check your heart’s pumping strength before, during, and sometimes after treatment. If your ejection fraction drops below a certain threshold, your oncologist may pause or adjust your treatment plan.
How often you’ll need the scan depends on your level of risk. Patients on trastuzumab, commonly used for breast cancer, often require more frequent imaging over a longer follow-up period than those on shorter chemotherapy regimens. Beyond oncology, MUGA scans can also be used to evaluate heart function after a heart attack, assess heart failure, or check how well the heart is working before major surgery.
MUGA Scan vs. Echocardiogram
An echocardiogram uses ultrasound waves to image the heart and can also estimate ejection fraction. So why would a doctor choose a MUGA scan instead? The key advantage is reproducibility. MUGA scans tend to give very consistent results each time, which matters when you’re tracking small changes in heart function over months of chemotherapy. If your ejection fraction drops from 60% to 50%, your doctor needs to trust that the change is real and not just measurement variability.
That said, recent international cardio-oncology guidelines now recommend echocardiography as the first choice for monitoring, with cardiac MRI as a second option and MUGA scans as a third-line option when neither is available. The shift is partly because echocardiograms don’t involve radiation exposure, and imaging technology has improved their accuracy. Still, many cancer centers around the world continue to use MUGA scans as their primary monitoring tool because of accessibility, cost, and the consistency of results.
What Your Results Mean
The main number you’ll get from a MUGA scan is your left ventricular ejection fraction, or LVEF. This is the percentage of blood your heart’s main pumping chamber pushes out with each beat. The ranges differ slightly between men and women:
- Normal: 52% to 72% for men, 54% to 74% for women
- Mildly abnormal: 41% to 51% for men, 41% to 53% for women
- Moderately abnormal: 30% to 40% for both
- Severely abnormal: below 30% for both
A general rule of thumb is that a normal ejection fraction falls between 50% and 70%. An ejection fraction of 40% to 49% means your heart’s pumping ability is slightly below normal. At 39% or below, you’re in the range associated with heart failure with reduced ejection fraction. For chemotherapy patients, even a drop of 10 percentage points from your baseline, or a reading that falls below 50%, can be enough to trigger a change in your cancer treatment.
What to Expect During the Procedure
The MUGA scan is noninvasive and painless apart from the needle stick for the tracer injection. You’ll lie on an exam table, and a technician will attach EKG electrodes to your chest with adhesive pads. After the tracer is injected into your vein, you’ll wait a short time for it to circulate and bind to your red blood cells. Then the gamma camera is positioned close to your chest, and imaging begins.
You’ll need to stay as still as possible while the camera captures images from different angles. Some facilities ask you to avoid caffeine before the scan, and your care team will give you specific prep instructions based on your situation. The scan itself is quiet compared to an MRI, with no loud banging or enclosed tube. Most people find it straightforward, if a bit boring.
Safety and Radiation Exposure
The radioactive tracer used in a MUGA scan delivers a relatively small dose of radiation. Your body clears the tracer naturally through your urine over the following day or two. Drinking extra fluids after the scan helps speed up this process.
For a single scan, the radiation exposure is generally considered low risk. The concern becomes more relevant for patients who need repeated scans over months or years of cancer treatment. Patients on longer treatment regimens, particularly those receiving trastuzumab for breast cancer, tend to accumulate more imaging studies and therefore more cumulative radiation. This is one reason the field has been shifting toward echocardiography as a first-line option when image quality is adequate.
The scan is not appropriate during pregnancy because of the radiation exposure to the fetus. If you’re pregnant, might be pregnant, or are breastfeeding, let your care team know before the test is scheduled.