[The physical aspects of traditional radiology and of computed radiology compared]

In the last decade a new radiographic technique has been establishing itself which makes the most of technological progress in the fields of laser optics, of materials and of computer science and integrates conventional techniques introducing the digital image also into radiographic diagnosis. The authors, who have gained a wide experience in both the theory and the applications of Computed Radiography (CR), carefully reviewed Italian literature and found no review article on technical theoretical principles, while many such papers are found in international literature. Therefore, they took the lead for a review paper on this subject. For easier reading, the paper was divided into three parts: the first one is the necessary introduction to the physical parameters to understand radiographic images, i.e., the signal-to-noise ratio, the modulation transfer function, the Wiener spectrum and the detective quantum efficiency. The second part deals with the physical features of the formation of conventional radiographic images: the latest notions about the conversion of X-ray energy into light photons by intensifying screen phosphors are here reported. Finally, radiographic image readability is related to the characteristics of the screen-film system. The third part of the paper deals with CR, in particular with the problems related to image acquisition through the screens called imaging plates, to the laser reading technique and to image reconstruction. Finally, the different physical phenomena leading to radiant image degradation are examined sequentially, bearing in mind that the diagnostic yield of CR images can be improved with image processing, to obtain images which can be compared to conventional ones.