What to Expect With Molecular Breast Imaging

Molecular breast imaging (MBI) uses a small amount of a radioactive substance called a tracer, which is injected into your vein, and a special camera, called a gamma camera, to look for cancer in the breast. Cells that are growing quickly, like cancer cells, take up more of the tracer and then look brighter in the pictures taken by the camera.

Your doctor may recommend molecular breast imaging for several reasons.

If you received abnormal results on a mammogram or other breast imaging test, you may have MBI. MBI images are more detailed than mammogram and breast ultrasound images.

If you have dense breasts, you may have supplemental screening with MBI. Dense breasts make it hard for radiologists to see cancer on a mammogram. That’s because cancer looks white on a mammogram and so does dense breast tissue. Breast density doesn’t affect MBI pictures.

If you’ve been diagnosed with breast cancer, you may have MBI to look for other spots of cancer. If you’re receiving chemotherapy or other treatment, you may have MBI to see how well it’s working.

Molecular breast imaging and breast MRI are both better than a mammogram at finding cancer in dense breasts, but there are differences in how the tests are done and who can have them. Studies suggest that both MBI and breast MRI find the same number of cancers, so either is a good supplemental screening test for dense breasts.

Some people can’t have an MRI, so MBI is the safer option. For example, if you have an implanted medical device or other metal objects in your body (including some breast tissue expanders), MBI is the better choice. This is because breast MRI uses magnets and radio waves to make 3D images of the breast. If you have metal in your body, the magnets can pull it out or make it change position. Similarly, if you have liver or kidney disease, the contrast solution used in a breast MRI can cause complications.

In most cases, breast MRI requires you to be very still inside a metal tube for up to 40 minutes. People with claustrophobia often can’t have MRIs, so MBI is a better option for them.

MBI exposes your body to a small amount of radiation, while MRI uses no radiation.

MBI is generally less expensive than breast MRI, but breast MRI is available at many more centers and much more likely to be covered by insurance.

A small amount of a radioactive tracer is put into a vein in your arm. The tracer travels through your bloodstream to your breast tissue. Because they grow faster than healthy breast cells, breast cancer cells absorb more of the tracer. The gamma camera detects radioactive gamma rays released by the tracer. Cells that take up more of the tracer show up brighter than the cells around them on the camera image. The MBI image only shows cells that take up more of the tracer, it doesn’t show the structure of the breast tissue.

Most people are told to avoid food and drink only clear liquids, like water or sports drinks, for at least three hours before MBI. Not eating helps your breast tissue absorb more of the tracer. But if you have diabetes or another health condition, ask your doctor about how you should prepare.

If you menstruate (have periods), try to schedule the MBI at the beginning of your cycle. To do this, count the first day of your last period as day one and then schedule the appointment between day seven and day 14. Although this is the best time to have an MBI, you can have the test at any time during your cycle.

Tell your doctor if you’re pregnant or nursing. MBI isn’t recommended if you’re pregnant. If you’re nursing, your doctor usually recommends that you stop nursing for a short while to give the tracer time to leave your body. You can use a pump to collect milk before the MBI and use it to feed the baby after the test.

At the imaging center, you take off your clothes above the waist and change into a gown, much like you would for a mammogram. The technician may give you a blanket to keep your chest area warm. If the area is warm and relaxed, it can improve how well the cells take up the tracer.

You then receive the tracer infusion through an IV. It takes about five minutes for the tracer to travel to the breasts. You sit in a chair facing the gamma camera system. The technician may put pillows behind your back so you’re more comfortable. The pillows also help hold you still while the cameras are working. One at a time, each breast is very lightly compressed between two camera plates. (Some people may have MBI on only one breast.) It’s similar to getting a mammogram, but with much less compression. The pressure is just enough to hold the breast in place and shouldn’t be painful. The cameras take two views of each breast. Each view takes about seven to 10 minutes to complete. So the whole MBI imaging process takes between 28 to 40 minutes.

After the test is done, the technician takes out the IV and you get dressed and go home.

Like most tests that screen for breast cancer, molecular breast imaging is considered safe. But it does have some risks and limitations.

MBI exposes you to a small amount of radiation, about four times the amount you’re exposed to during a mammogram. It’s considered safe for routine screening and for most people, the benefits of finding cancer outweigh any risk.

The tracer, 99mTc-sestamibi, may cause an allergic reaction in some people. It’s been used for more than 30 years and the rate of allergic reactions is very low. In most cases, any allergic reaction is mild, such as a minor rash or pin-prick feeling where the IV is located. More serious allergic reactions happen in only 0.01% to 0.04% of people who have MBI. If you have allergies or are concerned about reacting to the tracer, talk to your doctor before you schedule the test.

MBI doesn’t find all breast cancers, and it might find something that turns out to not be cancer. Like any screening test, MBI isn’t 100% sensitive, so there is a small risk that it won’t find a breast cancer. At the same time. MBI might return what’s called a false-positive result. This means the results show something that looks like cancer, but turns out to be nothing when more testing is done.

A radiologist (a doctor who specializes in interpreting medical images) will analyze the images from your MBI test. Areas that take up more of the tracer look like bright spots on the images. If there are bright spots, your doctor may recommend more tests, including more imaging tests or a biopsy.

If there are no bright spots on the images, then the result is considered normal.

Molecular breast imaging is available at a limited number of medical centers that offer nuclear medical testing. A March 2026 study reported that in the United States, MBI was available at only 32 centers in 19 states. These centers are usually larger, regional medical facilities rather than smaller cancer clinics. The doctor who recommends you have MBI usually can suggest a center where you can have the test done.

Insurance coverage for molecular breast imaging varies depending on your carrier. If you have Medicare or Medicaid, coverage for MBI is limited and often depends on whether it is deemed medically necessary. MBI is more likely to be covered by insurance if your doctor recommends it to further analyze a suspicious finding on a mammogram, rather than for supplemental screening for dense breasts.

It’s a good idea to contact your health insurance company before you have MBI and ask if the test is covered and if you’ll have any out-of-pocket costs (such as a deductible, co-pay, or co-insurance). Also, ask if the insurance company needs to authorize the test beforehand for it to be covered. If your insurance company initially says it won’t cover MBI, you and your doctor may want to make the case for them to cover it.