The evolution of digital radiography: from storage phosphors to flat-panel detectors

At present, conventional radiology is being slowly but inexorably replaced by digital radiology. While storage phosphors introduced approximately twenty years ago are now routinely used, flat panel systems are increasingly popular. There are two types of flat panels: those with direct X-ray conversion to electric charge and those where there is initial X photon conversion to visible light from optical amorphous silicon photodiode coupling for conversion to electric charge. The charge is therefore amplified and digital signal conversion is obtained with an analog-to-digital converter. One of the main advantages of Computed Radiography is the separation of image acquisition processing and display. Acquisition systems of digital images with image processing techniques allow the operator to adapt the image characteristics to the clinical requirements. Contrast value and image brightness can be changed soon after acquisition to optimize visualization before printing or transfer to the workstation for postprocessing. Image processing can be interactive, directly on the system consolle. To digital data various processing algorithms can be applied as high spatial frequency enhancement through the construction of the shadow mask. The new digital systems have improved the quality of conventional radiological images as compared to the screen-film and storage phosphor systems with shorter times of procedures and lower exposure dose to patients, while the diagnostic potentialities of the acquired image are enhanced.