Abstract: A system for locating a region of varying density in biological tissue such as a breast includes a controlled x-ray source for directing x-rays through the breast, a phosphor screen positioned to receive x-rays exiting from the tissue and producing light in response thereto, a cooled, slow scan CCD camera, a variable magnification optical system positioned to receive light emitted by the phosphor screen and directing it to the cooled, slow scan CCD camera, a high resolution monitor, and a control system receiving signals from the cooled, slow scan CCD camera and digitizing the signals to produce digital data representative of the densities of various locations of the tissue.