As of late 2003, the U.S. Food and Drug Administration (FDA) had cleared four digital mammography units for clinical usethe Senographe 2000D Full-Field Digital Mammography systems, approved in January 2000 and manufactured and marketed by GE Health Systems; the SenoScan, approved in Sept 2001 and manufactured and marketed by Fischer Imaging; and the LORAD LDBI, approved in March 2002 and Hologic/Lorad Selenia Full Field Digital Mammography (FFDM) System, approved in October 2002, both manufactured and marketed by Lorad/Hologic. Fuji-Film Medical Systems is also pursuing a digital system.
Like analog mammography, digital mammography is basically an x-ray of the breast used for both screening and diagnosis. Patients notice no difference between the two forms, as the breast is squeezed between two plates and x-rays pass through the breast tissue.
Unlike traditional mammography, however, which uses film as both a receptor and a display for the image to produce static, fixed images, digital mammography uses detectors (similar to those found in digital cameras) that change the x-rays into electrical signals. These signals are then transferred to a digital receptor that converts the x-ray energy to numbers, processes the numbers, and produces an image that can be displayed on a monitor or printed on a high-resolution laser printer.
Digital detectors create an electronic image as pixels, either indirectly or directly. They use either charge-coupled devices (CCDs), flat-panel arrays or computed radiography cassettes. CCDs are self-scanning devices that provide an electronic readout of an image produced by a scintillator. Electrons, whose numbers are related to the image *produ