evidence: Mammograms can be used to check for breast cancer in women who have no signs or symptoms of the disease. This type of mammogram is called a screening mammogram. Screening mammograms usually involve two or more x-ray pictures, or images, of each breast. The x-ray images often make it possible to detect tumors that cannot be felt. Screening mammograms can also find microcalcifications (tiny deposits of calcium) that sometimes indicate the presence of breast cancer. [...] Radiation exposure. Mammograms require very small doses of radiation. The risk of harm from this radiation exposure is low, but repeated x-rays have the potential to cause cancer. Although the potential benefits of mammography nearly always outweigh the potential harm from the radiation exposure, women should talk with their health care providers about the need for each x-ray. In addition, they should always let their health care provider and the x-ray technologist know if there is any possibility that they are pregnant, because radiation can harm a growing fetus.