3.1 Introduction

Digital Radiography (DR) is the science of devising X-ray digital imaging detectors that may substitute the conventional radiographic screen-film combination for use in diagnostic radiology. In projection radiography, a digital imaging detector maps the two-dimensional distribution of X-ray photons transmitted by the irradiated body in discrete spatial units (pixels) and discrete signal units (bits), as opposed to the X-ray film (plus the radiographic intensifying screen, when used in a screen-film combination) which directly provides only an analogue recording of the two-dimensional detected photon distribution. In principle, the digital approach has several significant benefits over the analogue film. First, it gives directly a digital image, able to be processed with computer methods as soon as it is acquired, for image storage, manipulation, archiving and network circulation within the hospital(s). This would avoid the necessity of film digitization with X-ray film scanners. This is an additional processing step after film exposure and development which would equally provide a digital X-ray image from X-ray film, but would add the cost of the film scanner which might represent a significant fraction of the cost of the entire X-ray unit. But the very true advantage of the direct X-ray digital image is related to the linearity and dynamic range of the imaging acquisition process. A digital radiographic detector is expected to provide a linear response...