Contrast evaluations in a digital mammographic system

It is worldwide accepted that the enhancement of the dynamic range is probably the most important improvement of digital mammography based on solid state detectors with respect to its screen-film version. In turn, this means a better contrast resolution of the image and then an improved detectability of low-contrast features. Moreover the acquisition of intrinsically digital mammographic images allows to perform specific numerical processing for further a posteriori enhancement of contrast in regions where suspect pathologic details appear. On these bases, a new system for digital mammography has been set up at the Department of Physics of the University of Bologna. Some conventional mammographic screens are alternatively coupled to a fiber optic taper which drives the light onto a CCD camera through a MCP image intensifier. This paper describes the detailed characterization of the system in terms of the achievable spatial resolution and image contrast.