[Detection of simulated lung nodules evaluated with various film/screen systems].

The imaging characteristics (contrast and noise) of x-ray film/screen combinations were examined for their suitability in the detection of faint nodules of lung cancer. Two hundred conventional chest radiographs of a human chest phantom were obtained with 5 mm or 10 mm spherically or hemispherically shaped simulated nodules placed on the posterior surface of an anthropomorphic chest phantom. Nodules were placed on several selected lung areas, and were overlain by the intercostal spaces, ribs or mediastinum. Five combinations of film/screen systems that differed in their contrast (characteristic curve) and noise were used to obtain the radiographs. The detectability of simulated nodules shown on the radiographs was evaluated based on the results obtained by an interpretive study by 6 observers utilizing receiver operating characteristic (ROC) analysis and calculating the average area under the ROC curve (Az). The system with standard contrast and improved noise reduction was favorable in detecting nodules of 5 mm in diameter. The system with latitude-type contrast was not suitable for the detection of nodules placed in the intercostal spaces. Systems with degraded noise or low contrast showed poor performance in detecting hemispheric nodules, since ill-defined nodules were overlain by the ribs. For the detection of nodules on the mediastinum or diaphragm, display of these regions with sufficient density and improved contrast appeared mandatory. The combination of a high contrast x-ray film, Iow noise x-ray film/screen combination, high voltage x-ray exposure, and the addition of a compensatory x-ray filter or screen appears suitable for improved recognition of a small, faint, lung nodules.