Mammography uses low-energy x-rays to capture images (mammograms) of the internal structures of the breasts. Quality mammography can help detect breast cancer in its earliest, most treatable stages; when it is too small to be felt or detected by any other method.
HOW IT WORKS
It is normal to use lower-energy X-rays, typically Mo (K-shell x-ray energies of 17.5 and 19.6 keV) and Rh (20.2 and 22.7 keV) than those used for radiography of bones.
Ultrasound is typically used for further evaluation of masses found on mammography or palpable masses not seen on mammograms.
Screen-film mammography where x-rays are beamed through the breast to a cassette containing a screen and film that must be developed. The image is commonly referred to as a mammogram.
Full field digital mammography where x-rays are beamed through the breast to an image receptor. A scanner converts the information to a digital picture which is sent to a digital monitor and/or a printer.
WHEN IS IT SUCCESSFUL
Cancers that are so easily treated that a later detection would have produced the same total cure (woman would have lived even without mammography);
Cancers so aggressive that even "early" detection is too late (woman dies despite detection by mammography);
Cancers that would have receded on their own or are so slow-growing that the woman would die of other causes before the cancer produces symptoms (mammography results in overdiagnosis and overtreatment of this class); and
The small number of breast cancers that are detected by screening mammography and whose treatment outcome improves as a result of earlier detection.
HOWEVER: Only between 3% and 13% of breast cancers detected by screening mammography will fall into this last category.
RISKS AND BENEFITS
Repeated mammography starting at age 50 saves about 1.8 lives over 15 years for every 1,000 women screened. This result has to be seen against the negatives of errors in diagnosis, overtreatment, and radiation exposure.
Mammography has a false-negative (missed cancer) rate of at least 10 percent. This is partly due to dense tissues obscuring the cancer and the fact that the appearance of cancer on mammograms has a large overlap with the appearance of normal tissues. A meta-analysis review of programs in countries with organized screening found 52% over-diagnosis.
According to their analysis one in 2,000 women will have her life prolonged by 10 years of screening, however, another 10 healthy women will undergo unnecessary breast cancer treatment. Additionally, 200 women will suffer from significant psychological stress due to false positive results.
THE PROCEDURE ITSELF
During the procedure, the breast is compressed using a dedicated mammography unit. Parallel-plate compression evens out the thickness of breast tissue to increase image quality by reducing the thickness of tissue that x-rays must penetrate, decreasing the amount of scattered radiation (scatter degrades image quality), reducing the required radiation dose, and holding the breast still (preventing motion blur). In screening mammography, both head-to-foot (craniocaudal, CC) view and angled side-view (mediolateral oblique, MLO) images of the breast are taken. Diagnostic mammography may include these and other views, including geometrically magnified and spot-compressed views of the particular area of concern. Deodorant, talcum powder or lotion may show up on the X-ray as calcium spots, and women are discouraged from applying these on the day of their exam.
Screening mammograms are performed yearly on a patient who presents with no symptoms and consists of only four standard X-ray images. Diagnostic mammograms are reserved for patients with breast symptoms, changes, or abnormal findings seen on their screening mammogram. Diagnostic mammograms are also performed on patients with breast implants, breast reductions, and patients with personal and/or family history of breast cancer.