Mammogram Basics

A mammogram is a low-dose x-ray that allows specialists to look for changes in breast tissue. Screening mammograms are used to look for breast changes in women who do not appear to have breast problems. A diagnostic mammogram is used to get more information about breast changes in women who have breast symptoms or an abnormal screening mammogram.

Why do I need mammograms?

A mammogram can often find or detect breast cancer early, when it’s small and even before a lump can be felt. This is when it’s easiest to treat.

What are the types of mammograms?

Screening Mammograms

A screening mammogram is used to look for signs of breast cancer in women who don’t have any breast symptoms or problems. X-ray pictures of each breast are taken from 2 different angles.

Diagnostic Mammograms

Mammograms can also be used to look at a woman’s breast if she has a breast problem or a change is seen on a screening mammogram. When used in this way, they are called diagnostic mammograms. They may include extra views (images) of the breast that aren’t part of screening mammograms. Sometimes diagnostic mammograms are used to screen women who were treated for breast cancer in the past.

What do mammograms show?

Mammograms can’t prove that an abnormal area is cancer, but they can help health care providers decide whether more testing is needed. The 2 main types of breast changes found with a mammogram are calcifications and masses. Learn more about these and other breast changes in the section about calcifications and masses.

How do mammograms work?

A mammogram uses a machine designed to look only at breast tissue. The machine takes x-rays at lower doses than usual x-rays. Because these x-rays don’t go through tissue easily, the machine has 2 plates that compress or flatten the breast to spread the tissue apart. This gives a better picture and allows less radiation to be used.

Find more on our page about what you can expect when getting a mammogram.

illustration showing a woman getting a mammogram

digital mammogram (also known as full-field digital mammography or FFDM) is like a standard mammogram in that x-rays are used to make pictures of the breast. The differences are in the way the picture is made, looked at, and stored. Standard mammograms are printed on large sheets of film. Digital images are recorded and saved as files in a computer. Digital mammograms are becoming more widely available. They may be better than standard film mammograms for some women, but they’re not clearly better for everyone. Women should not skip their regular mammogram because a digital one isn’t available.

A newer type of mammogram is known as breast tomosynthesis or 3D mammography. For this, the breast is compressed once and a machine takes many low-dose x-rays as it moves over the breast. A computer then puts the images together into a 3-dimensional picture. This uses more radiation than most standard 2-view mammograms, but it may allow doctors to see the breast tissues more clearly. Some studies have suggested it might lower the chance of being called back for follow-up testing. It may also be able to find more cancers. But not all health insurances cover tomosynthesis.

Are mammograms safe?

The benefits of mammography outweigh any possible harm from the radiation exposure. Modern machines use low radiation doses to get breast x-rays that are high in image quality. On average the total dose for a typical mammogram with 2 views of each breast is about 0.4 mSv. (A mSv is a measure of radiation dose.)

To put dose into perspective, people in the US are normally exposed to an average of about 3 mSv of radiation each year just from their natural surroundings. (This is called background radiation.) The dose of radiation used for a screening mammogram of both breasts is about the same amount of radiation a woman would get from her natural surroundings over about 7 weeks.

If there’s any chance you might be pregnant, let your health care provider and x-ray technologist know. Although the risk to the fetus is likely very small, screening mammograms aren’t routinely done in pregnant women.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Puliti D, Duffey SW, Miccinesi G, et al. Overdiagnosis in mammographic screening for breast cancer in Europe: a literature review. J Med Screen, 2012;19:Suppl 1:42-56.

Rose SL, Tidwell AL, Bujnoch LJ, et al. Implementation of breast tomosynthesis in a routine screening practice: an observational study. AJR Am J Roentgenol. 2013 Jun;200(6):1401-1408.

Skaane P, Bandos AI, Gullien R, et al. Comparison of digital mammography alone and digital mammography plus tomosynthesis in a population-based screening program.  Radiology. 2013 Apr;267(1):47-56. 

Last Medical Review: June 1, 2016 Last Revised: August 18, 2016

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