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Mammography exam: How is it performed?

During mammography, the technologist will position the patient and image each breast separately. One at a time, each breast is carefully positioned on a special film cassette and then gently compressed with a paddle (often made of clear Plexiglas or other plastic). This compression flattens the breast so that the maximum amount of tissue can be imaged and examined.

At some facilities, mammography technologists may place adhesive markers to the breast skin prior to taking images of the breast. The purpose of the adhesive markers is twofold: first, to identify areas with moles, blemishes or scars so that they are not mistaken for abnormalities, and secondly, to identify areas that may be of concern (e.g. a lump was felt during physical examination). Some centers routinely mark the nipple with a small dot to provide a clear "landmark" for the radiologist on the mammogram images.

To "take" a mammogram, the x-ray source is turned on and x-rays are radiated through the compressed breast and onto a film cassette positioned under the breast. The x-rays hit a special phosphor coating inside the cassette. This phosphor glows in proportion to the intensity of the x-ray beams hitting it, thus exposing the film with an image of the internal structures of the breast. Highly sensitive film and special x-rays are used for mammography to create the highest quality images at the lowest exposure.

The resulting "exposed film" inside the cassette is then developed in a dark room much like a regular photograph is developed. It is the special energy and wavelength of the x-rays that allow them to pass through the breast and create the image of the internal structures of the breast. As the x-rays pass through the breast, they are attenuated (weakened) by the different tissue densities they encounter. Fat is very dense and absorbs or attenuates a great deal of the x-rays. The connective tissue around the breast ducts and fat is less dense and attenuates or absorbs far less x-ray energy. It is these differences in absorption and the corresponding varying exposure level of the film that create the images which can clearly show normal structures such as fat, fibroglandular tissue, breast ducts, and nipples. Further, abnormalities such as microcalcifications (tiny calcium deposits), masses, and cysts are also visible.

The developed mammography films are then interpreted by a radiologist, who compares the new images of a woman's breast to each other and to previous mammograms a woman has had. The radiologist will look for shadows and patterns of tissue density to detect any abnormalities.

A mammogram is like a fingerprint; the appearance of the breast on a mammogram varies tremendously from woman to woman, and no two mammograms are alike. It is extremely helpful for the radiologist to have films (not just the report) available from previous examinations for comparison purposes. This will help the doctor to recognize small changes that occur gradually over time and detect a cancer as early as possible.

The breast is made of fat, fibrous tissue and glands. Breast masses (these include benign and cancerous lesions) appear as white regions on mammogram film. Fat appears as black regions on a mammogram film. Everything else (glands, connective tissue, tumors and other significant abnormalities such as microcalcifications) appear as levels of white on a mammogram.

Last updated on 21 July 2009