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The purpose of this study was to compare a large-area direct read-out flat-panel detector system with a speed class 200 screen-film system, a storage-phosphor system and a mammography screen-film system with regard to the detection of simulated rheumatoid erosions and to assess its diagnostic performance with decreasing exposure dose. The performance of a flat-panel system in such small lesions was considered especially interesting, as the spatial resolution of this system, limited by its pixel size, is considerably lower than that of conventional screen-film systems. An animal model with 160 joint specimens from 20 monkey paws was used. 640 regions were defined in these 160 meta- carpophalangeal and proximal interphalangeal joint specimens. Simulated rheumatoid erosions were created in 320 of these 640 regions. Specimens were enclosed in containers filed with water to obtain absorption and scatter radiation conditions similar to a human hand. Imaging was performed using a flat-panel system, a sped class 200 screen-film system, a mammography screen-film system and a storage- phosphor system under exactly matched conditions. Different exposure doses equivalent to speed classes of S equals 100, 200, 400, 800, 1600 and 3200 were used. Presence or absence of a lesion was assessed by three radiologists using a five level confidence scale. Receiver operating characteristic analysis was performed for a total of 21,120 observations and diagnostic performance estimated by the area under the ROC curve. The significance of differences between Az values was tested with analysis of variance. ROC-analysis showed Az values of 0.809, 0.768, 0.737, 0.710 and 0.685 for the flat-panel system, 0.770 for the screen-film system, 0.781, 0.739, 0.724 and 0.680 for the storage-phosphor system, and 0.798 for the mammography screen-film system. Analysis of variance showed significant differences for certain combinations of imaging modalities and exposure doses. The diagnostic performance of the flat-panel detector system is superior to that of a screen-film system and a storage-phosphor system for the detection of erosive lesions at clinical exposure settings. Using the flat-panel system the exposure does can be reduced by 50 percent to obtain a diagnostic performance comparable to a speed class 200 screen-film system.
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