A mammogram is a picture of your breast taken with a safe, low dose X-ray machine. It's the most effective exam for early detection of breast cancer.

There are two types of mammography exams: screening and diagnostic. A routine screening mammogram is performed when you have no symptoms. Starting at age 40, the American Cancer Society recommends an annual screening mammogram as part of your routine health care.

A diagnostic mammogram is performed if there is concern regarding your breasts or if a screening mammogram requires additional studies. You don't need to prepare for a mammogram. You can eat normally, and if you take medications, continue to do so. However, you may be asked not to wear deodorant on the day of your mammogram because such products may show up on mammogram images. Also, if you are premenopausal, it's best to schedule your screening exam during the week following your menstrual period, when your breasts may be less tender.

Once checked in, you'll undress from the waist up and wear a special robe. A mammography technologist will perform your mammogram. She has specialized training in mammographic positioning and techniques.

If you are asked to complete a breast-health survey prior to your exam, your technologist can assist and review the survey with you.

Once in the exam room, you'll be asked to stand in front of the mammography unit, a special type of X-ray machine. It can move up and down and side to side.

Your technologist will position your breast between two firm surfaces that compress your breast as flat as possible, to ensure good X-ray pictures. For example, here you can see how the machine flattens the technologist's hand.

She may also switch paddles to get a different view.

Compression is necessary to spread the breast tissue and eliminate motion, which may blur the picture. This may be uncomfortable but shouldn't hurt.

Compression usually lasts no more than 20 to 30 seconds. During which time, an X-ray beam comes from above. The X-ray image is created on a film cassette, located below your breast. The X-rays penetrate your breast tissue and are exposed to the film, much like a camera exposes a photographic image onto film. Denser tissue, such as cancer, appears bright and white, whereas less dense tissue, such as fat, appears dark or gray.

The film is then processed and made available for review and interpretation.

Here we see a baseline mammogram of a 40-year-old woman. Five years later, her formerly clear image now shows cancer.

Don't be concerned if you are asked to remove your gown or reposition, even if it means standing on your toes. This ensures that your gown won't interfere with the pictures and that you are standing correctly. If you are uncomfortable, please tell your technologist.

After the pictures are taken, you may be asked to wait while the X-ray films are processed.

During this time, technologists check your films to assure they are acceptable. If they aren't clear, you may be asked to have more X-rays done. Don't be alarmed if this happens, your technologist simply wants the best images.

A physician trained to read X-ray pictures, a radiologist, will examine your mammograms. Under federal regulations, the radiologist must be experienced in reading mammograms.

If no further studies are required, you'll be released and can resume your regular activities.

Based on what your radiologist sees on your mammogram, you may be asked to return for a diagnostic mammogram. It's not unusual to be called back after your first screening mammogram; this is because your radiologist doesn't have any previous comparison. The additional imaging is usually necessary to clarify a finding on your screening mammogram. Most findings are not cancer, but it's important to have the additional imaging done. This may include specialized and tightly focused X-ray pictures or possibly a breast ultrasound.