Performance of various X-ray film/screen systems in demonstrating small simulated low-density lung nodules

A high-quality, conventional chest radiograph should be obtained in lung cancer screening programs to efficiently detect the faint, small nodular shadows due to early lung cancer in the lung fields, although, it is difficult to image the entire lung field within the linear part of the characteristic curve of the screen/film system owing to the wide variation in tissue density in the thorax, which ranges from the well aerated lung superimposed on the intercostal spaces to the lung area superimposed on the heart or diaphragm. In the detection of early cancer in the lung fields, it is important to consider the very low density (CT values of nearly -600 HU to -300 HU) commonly exhibited by early adenocarcinomas in the lung. The detectability of such nodules would be greatly influenced by the contrast and noise characteristics of the photographic system, the complexity of anatomical structures around the nodule, the characteristics of the observation system for x-ray films, the interpreter, and so on. The choice of x-ray film/screen system basically determines the efficacy of screening; specifically, the contrast characteristics of x-ray films together with noise level, which varies at different optical densities, affect the detectability of nodular shadows. The present study was carried out to determine the most suitable sensitometric characteristics and to assess the effects of the noise level of the x-ray film/screen system on the detectability of nodular shadows within the lung fields, particularly in low-density areas.