[Digital radiography: fundamentals and future potentials].

Digital radiography consists of four major steps which include X-ray detection, digitization, image processing and display. Important parameters in digitization process is the pixel size and the number of grey levels which affect the quality of digitized images. A number of digital radiographic systems have been or are being developed which include the point-beam, line-beam, slot-beam and multiple slit-beam systems as well as conventional wide-beam systems such as image intensifier-TV system, storage phosphor system and film-based system. Important physical properties of digital radiographic systems are the sensitivity, resolution, noise, system response, scatter rejection, contrast sensitivity and image acquisition time. The resolution property is affected by the pixel size, sampling distance, display pixel size, image processing, detector response and X-ray beam characteristics. From ROC studies on chest images, the pixel size of approximately 0.2 mm and the corresponding image matrix of about 2,000 x 2,000 is considered optimal choice of these parameters. Future potentials of digital radiography are likely to be in the areas of computer-aided diagnosis (CAD) and PACS. Preliminary results obtained from recent studies on quantitative analysis of digital radiographic images are promising. The rms variation and the first moment of the texture of abnormal lungs with various interstitial diseases were clearly different from those of normal lungs. Automated detection scheme of nodules in chest images indicated approximately 70% true positive rates and a few false positives in each lung.(ABSTRACT TRUNCATED AT 250 WORDS)