Molecular breast imaging is a test to look for signs of breast cancer. It uses a radioactive tracer and a special camera to make pictures of the breast tissue.

During the molecular breast imaging exam, a small amount of radioactive tracer is injected into a vein in your arm. The tracer travels through your blood to your breast tissue. Cells that are growing quickly take up more of the tracer than do slowly growing cells. Cancer cells often grow quickly, so they take up more of the tracer.

A special camera, called a gamma camera, detects the radiation released by the tracer. In the pictures made by the gamma camera, the cells that take up more of the tracer look brighter than surrounding cells.

Why it's done

Uses for molecular breast imaging include:

• Breast cancer screening. Molecular breast imaging is sometimes done to look for breast cancer in people who don't have any symptoms. When it's used for breast cancer screening, a molecular breast imaging test is done in addition to a mammogram. Your health care provider might recommend this combination of screening tests if you have dense breasts.

  Breast tissue is composed of fatty tissue and dense tissue. Dense tissue is made of milk glands, milk ducts and fibrous tissue. If you have dense breasts, you have more dense tissue than fatty tissue. On a mammogram, dense tissue can sometimes make it hard to see breast cancer. Using molecular breast imaging and mammogram together finds more breast cancers than does a mammogram alone.

• Investigating symptoms. Molecular breast imaging might be used to take a closer look at a lump or something found on a mammogram. Your provider may recommend molecular breast imaging if other tests haven't been clear. It might also be used in place of an MRI if you can't have an MRI.
• After a breast cancer diagnosis. Molecular breast imaging is sometimes used after a breast cancer diagnosis to look for additional areas of cancer. It can also help your provider see whether your chemotherapy is working.

Risks

Molecular breast imaging is safe. Like every test, it carries certain risks and limitations. These might include:

• The tracer gives off a low level of radiation. During molecular breast imaging, you're exposed to a minimal dose of radiation. The level of radiation is considered safe for routine screening. The benefits of the test typically outweigh the risks of radiation exposure.
• The tracer can cause an allergic reaction. Though very rare, allergic reactions to the radioactive tracer can happen. Tell your provider about any allergies you have.
• The test may find something that turns out to not be cancer. If something is found with molecular breast imaging, you might need more tests to find out what it is. Those tests might show that you don't have cancer. This is called a false-positive result. This is a risk that can happen with any screening test.
• The test can't detect all cancers. As with all tests, molecular breast imaging may miss some cancers. Some cancers may be in areas that are hard to see using molecular breast imaging.

How you prepare

To prepare for a molecular breast imaging test, you might need to:

• Check with your insurance company. In the United States, most health insurance companies cover molecular breast imaging. It's a good idea to check with your insurance company to be sure.
• Tell your health care provider if you're pregnant. Molecular breast imaging isn't recommended if you're pregnant.
• Tell your provider if you're nursing. Molecular breast imaging usually isn't recommended if you're using your own milk to feed a baby. But if the test is needed, your provider may recommend that you stop nursing for a short period of time. This gives the radioactive tracer time to leave your body. You may choose to use a pump to collect milk before your test. You can store the milk to feed to the baby after the test.
• If possible, schedule the test for the beginning of your menstrual cycle. If you menstruate, schedule your molecular breast imaging exam around 3 to 14 days after the first day of your period.
• Don't eat anything for 3 to 4 hours before your test. Fasting before your test increases the amount of the tracer that travels to your breast tissue. It's OK to drink liquids before your test so that you're hydrated. Choose clear liquids such as water, diet soft drinks, and coffee or tea without milk and sugar.

What you can expect

During the test

When you arrive for your molecular breast imaging test, you undress above the waist. You receive a gown to wear until the test begins. You may also receive a blanket to keep your chest warm. Being warm and relaxed can improve the uptake of the tracer.

Next, you receive an injection of the radioactive tracer into a vein in your arm. The tracer is taken up by cells that are growing quickly, such as cancer cells. The tracer emits gamma rays. The rays are detected by two small gamma cameras that are part of the molecular breast imaging system.

The imaging part of the test happens soon after the tracer is injected.

You sit in a chair facing the molecular breast imaging system. It looks kind of like a mammogram machine. One breast is placed on the flat surface of a gamma camera in front of you.

The flat surface of a second gamma camera is lowered on top of the breast. The pressure is light and just enough to hold the breast in place. It shouldn't be painful.

You sit still for 10 minutes as the gamma cameras record an image. Pillows may be placed behind your back for comfort. The pillows help hold you in place so that you can relax during the test. You should breathe naturally.

Your breast is positioned for a second image. You sit still again for 10 minutes as the image is created.

Your other breast is positioned in the machine and the process is repeated. In certain situations, you may have imaging on only one breast.

If you have molecular breast imaging done on both breasts, you need to sit still for about 40 minutes.

After the test

After the test, you may dress and return to your usual activity.

Results

A doctor who specializes in imaging tests looks at the images from your molecular breast imaging test. This doctor is called a radiologist. The radiologist shares the findings with your health care provider. Ask your provider when you can expect to know the results.

Molecular breast imaging shows how much of the radioactive tracer is taken up by your breast tissue. Cancer cells take up more of the tracer. Areas that take up more tracer look like bright spots on the pictures. If your pictures show a bright spot, your provider may recommend more tests. For example, you might need other imaging tests or a procedure to remove a sample of tissue for testing.