Mammography machines use low doses of X-rays to produce a black and white image of the breast and breast tissues, which is then processed wither by using a film screen or digital techniques. The image is then examined by a radiologist, who can change the brightness or contrast levels and zoom in or magnify suspicious areas. Radiologists look for changes or inconsistencies in the breast tissue. Dense and hard areas appear as white areas on the film, while fattier areas seem grayish-black. Tumors, ducts, glands, tiny calcium deposits and benign lumps show up as thick, white images on a mammogram.
The tiny particles of light (called photons) in X-rays have more energy than the photons in visible light. So the X-rays can pass through matter made of small atoms, while large atoms tend to absorb X-rays. The soft tissue in the breast is made of smaller atoms that do not absorb X-ray photons very well, while the harder areas, such as tumors and calcium deposits, are made of much larger atoms, and do absorb X-ray photons, causing the grayish-black areas on a mammogram.