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[Detectability of pulmonary coin lesions: a comparative assessment of the image quality of a storage phosphor system and a conventional film screen system].

The object of this study was to compare the prototype of a storage phosphor digital radiography system (Siemens) which allows postprocessing image data adjustment with the stored information, with an optimised conventional film system with respect of image quality and diagnostic accuracy. The test objects were pulmonary coin lesions as the search for primary or secondary lung tumours is one of the most frequent clinical requests and the detectability of coin lesions depends very much on their relative contrast against the surrounding area. In order to achieve reproducible results, an anthropomorphic lung phantom was used. Besides the conventional film radiograms the unprocessed digital radiograms and twelve series with variations of the processing parameters were evaluated. To achieve a homogeneous radiation image an anatomically shaped lead-loaded acrylic glass compensation filter was used. With regard to the true-positive demonstration of coin lesions there were no significant differences between the chosen film system and all digital radiograms. Image processing had no recognisable influence on the demonstration of the findings. Coin lesions of 3 mm diameter were detected only by chance; the detectability of lesions of 5 mm and 10 mm in diameter respectively depended mainly on their localisation. Lesions of 15 mm diameter were detected independent of their localisation. The results indicate that the storage phosphorus radiography system is already comparable to an optimised conventional film system concerning the conspicuity of coin lesions. If the image is homogenised by means of an anatomically shaped lead-loaded acrylic glass compensation filter, selective postprocessing adjustment of the digital radiograms for the evaluation of the mediastinum or the lung parenchyma is unnecessary.