Technical note: digital mammography--the comparative evaluation of film digitizers.

To study the potential of the computer interpretation of digital mammograms it is necessary to use digitized conventional films because at the present time insufficient resolution may be achieved using computed radiography. For example, the automatic detection of very small subtle calcifications requires digitization at 50 μm or smaller with at least 8 bits of grey level (Chan et al, 1987; Dance, 1993). In this paper we present a simple and practical method to evaluate and compare the technical performance of three film digitizers. These all cost about £20 000 and are being assessed as possible methods for obtaining digital mammograms for a national database (Astley, 1993). The digitizers investigated are a drum scanning microdensitometer, a laser scanning densitometer and a CCD camera. According to manufacturers' specifications, each has a high resolution sampling pixel size (50 μm or less) and is capable of digitizing to a grey level of at least 8 bits over the complete range of diffuse optical densitie...