Digital X-ray imaging technology has advanced rapidly over the past few years. This review, particularly aimed at those involved in using and purchasing such technology, is an attempt to unravel some of the complexities of this potentially confusing subject. The main groups of X-ray imaging devices that are considered are digitisers of conventional radiographs, image-intensifier-based fluorography systems, photostimulable phosphor computed radiography, amorphous selenium-based technology for thorax imaging and flat-panel systems. As well as describing these different systems, we look at ways of objectively assessing their image quality. Concepts that are used and explained include spatial resolution, grey-scale bit resolution, signal-to-noise ratio and detective quantum efficiency. An understanding of these basic parameters is vital in making a scientific assessment of a system's performance. Image processing and techniques are also briefly discussed, particularly with reference to their potential effects on image quality. This review aims to provide a basic understanding of digital X-ray imaging technology and enables the reader to make an independent and educated assessment of the relative merits of each system.

A physical evaluation of the imaging performance of a unique high-resolution fluorography system is presented. Measurements have been made of contrast performance, unsharpness (modulation transfer function) and noise (Wiener spectrum and threshold contrast detectability), and the results have been compared with those measured from medium-fast calcium tungstate and rare-earth screen--film combinations and a standard fluorography system. The results have proved sufficiently encouraging that a full-scale trial is now underway to evaluate the system's performance in routine clinical application.