FUNDAMENTAL STUDY FOR DETECTION OF LOW CONTRAST OBJECT : COMPARISON OF COMPUTED RADIOGRAPHY (CR) AND SCREEN-FILM SYSTEM

Abstract

We compared the detectability of low-contrast objects made by 2mm beads in diameter using screen-film and computed radiography (CR) systems, respectively. A Medium-speed screen-film system (BH III A) was used as a conventional system, and three sizes of ST imaging plates (IP) were used as the CR system. Effects of incident dose to the IP (ie, ST and HR) and image processing (ie, contrast enhancement, unsharp masking) on the detectability of low-contrast objects were also measured. Observer performance tests were carried out using receiver operating characteristic (ROC) analysis. The results indicated that the detectability of low-contrast objects in the CR system radiographed under isoexposure with the screen-film system was comparable to that of the medium-speed screen-film system. The detectability of low-contrast objects in the CR system depends on the size of IP used and the incident dose; however, the detectability of low-contrast objects decreases with a decrease in the incident dose to the IP, and increases with use of contrast enhancement or unsharp masking techniques.