Molecular breast imaging is a test that uses a radioactive tracer and special camera to find breast cancer.

Rather than simply taking a picture of a breast, molecular breast imaging is a type of functional imaging. This means that the pictures it creates show differences in the activity of the tissue. Tissue that contains cells that are rapidly growing and dividing, such as cancer cells, appears brighter than less active tissue.

During molecular breast imaging, a small amount of radioactive tracer is injected into a vein in your arm. The tracer attaches to breast cancer cells that can then be detected using a camera that detects the gamma radiation released by the tracer (gamma camera).

Molecular breast imaging is a new technology, so it isn't yet widely available.

Molecular breast imaging may be used to:

• Screen for breast cancer in women with dense breast tissue. Molecular breast imaging, when combined with a breast X-ray (mammogram), detects more breast cancers in women with dense breast tissue than a mammogram alone.

  Typically, if you and your doctor decide you will have molecular breast imaging, it's done every other year along with an annual mammogram. Molecular breast imaging is considered a supplemental test, so it doesn't replace an annual mammogram.

  Breast tissue is composed of milk glands, milk ducts and fibrous tissue (dense breast tissue), and fatty tissue. Women with dense breasts have more dense breast tissue than fatty tissue. Both dense breast tissue and cancers appear white on a mammogram, which may make breast cancer more difficult to detect in women with dense breasts. Studies show that the combination of molecular breast imaging and a mammogram finds more than three times more breast cancers than a mammogram alone.

• Investigate breast abnormalities. Molecular breast imaging may help doctors evaluate a breast lump or an unusual area detected on a mammogram. Your doctor may recommend molecular breast imaging if other imaging tests have been inconclusive. Molecular breast imaging may be used in women for whom an MRI is recommended but can't be performed, such as those with allergies to the MRI contrast material.

Molecular breast imaging is a safe procedure. Like every test, it carries certain risks and limitations, such as:

• Exposure to a low level of radiation. During molecular breast imaging, you're exposed to a minimal dose of radiation that's considered safe for routine screening. The benefits of the test typically outweigh the risks of radiation exposure.

  When molecular breast imaging is used for breast cancer screening, it's done along with a mammogram, so you'll be exposed to more radiation than you would receive if you had a mammogram alone.

• Allergic reaction to tracer. Though extremely rare, allergic reactions to the radioactive tracer can occur. Tell your doctor about any allergies you have.
• The test may find something that, after additional tests, turns out to not be cancer. Molecular breast imaging may identify a suspicious area that, after additional tests, turns out to be noncancerous. This is known as a false-positive result and it can cause unneeded anxiety if you undergo additional imaging and testing, such as a biopsy, to assess the suspicious area. 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 too small to be detected by the gamma camera. Others may be located in areas that are difficult to view using molecular breast imaging, such as those near the chest wall.
• Another imaging procedure might be needed. If a suspicious area is found with molecular breast imaging, this technology can't be used to guide a needle to remove a sample of tissue for testing (breast biopsy). You'll need additional testing with a different imaging test to guide the biopsy, such as ultrasound, mammogram or breast MRI.

To prepare for a molecular breast imaging test, you'll be asked to:

• Check with your insurance company. Molecular breast imaging is a new technology that may not be covered by all health insurance providers. Some insurance companies may cover molecular breast imaging for breast cancer diagnosis, but not for breast cancer screening. Check with your health insurance company to understand the costs you may incur if you choose this test.
• Tell your doctor if you're pregnant. Molecular breast imaging isn't recommended for women who are pregnant.
• Tell your doctor if you're nursing. Molecular breast imaging usually isn't recommended for women who are breast-feeding. But if the test is necessary, your doctor may recommend that you stop nursing for 24 hours after the test, which gives your body time to eliminate the radioactive tracer. You may choose to use a breast pump before your test to express and store milk for feeding your baby after your test.
• Schedule the test for the beginning of your menstrual cycle. If you haven't been through menopause, it may be preferable to schedule your molecular breast imaging exam around seven to 14 days after the first day of your period.
• Don't eat anything for 3 to 4 hours beforehand. Fasting before your test increases the amount of the tracer that travels to your breast tissue and creates better quality pictures. It's OK to drink liquids, including water, diet soft drinks, and coffee or tea without milk and sugar.

During the test

When you arrive for your molecular breast imaging test, you'll be asked to undress above the waist. You'll receive a gown to cover yourself until the test begins. You may also receive a blanket to keep your chest warm, as being warm and relaxed can improve the uptake of the tracer by your breast tissue.

To begin your molecular breast imaging test, you'll receive an injection of the radioactive tracer into a vein in your arm. The tracer contains a substance that's quickly absorbed by fast-growing cells, such as cancer cells. The tracer emits gamma rays that are detected by two small gamma cameras that are part of the molecular breast imaging system.

You'll be seated in a chair facing the molecular breast imaging system, which looks similar to a mammogram machine. You'll be asked to open or remove your gown and place one breast on the flat surface of a gamma camera in front of you. You may need to lean forward a little, and pillows may be placed behind your back to make this more comfortable.

The flat surface of a second gamma camera will be lowered on top of your breast. The compression is light — just enough to hold your breast in place during the test — and shouldn't be painful or uncomfortable.

You will sit still for 10 minutes as the gamma cameras record the activity of the tracer. Your breast will be repositioned for a second image, and you'll be asked to sit still again for 10 minutes as the image is created.

If you're having both breasts imaged, your other breast will be positioned in the imaging machine and the process will be repeated. Two images are created of each breast, and each image takes about 10 minutes. In total, you'll be asked to sit still for 40 minutes, though you can get up and stretch between images — every 10 minutes. Women with larger breasts may need additional images.

After the test

Once the test is complete, you'll be asked to wait while a technologist checks the quality of the images. If there are problems with the images, you may have to repeat part of the test.

Afterward, you may dress and resume normal activity.

A doctor who specializes in imaging techniques (radiologist) reviews the images from your molecular breast imaging test. A member of your health care team will contact you to discuss the results.

Molecular breast imaging records how much of the radioactive tracer is absorbed by your breast tissue. Areas that absorb more tracer appear as bright spots on the images. If a suspicious concentration of tracer is found, your doctor may recommend additional testing and possibly a breast biopsy to determine whether the area is cancer.