Application of the ILO International Classification of Radiographs of Pneumoconioses to Digital Chest Radiographic Images

The International Labor Organization (ILO) system for classifying chest radiographic changes related to inhalation of pathogenic dusts is predicated on film-screen radiography (FSR). Digital radiography (DR) has replaced FSR in many centers, but there are few data to indicate whether DR is equivalent to FSR in identifying and quantifying interstitial and pleural abnormalities. Furthermore, DR images can be printed and viewed on film, so-called ‘hard copy’ (HC) DR, or can be viewed on a monitor at a computer workstation, so-called ‘soft copy’ (SC) DR. The goal of this investigation is to assess the equivalency of DR in comparison to FSR for diagnosis and quantification of parenchymal and pleural abnormalities due to pneumoconiosis and other forms of fibrotic lung disease, using the ILO classification system. This report is based on analyses of readings of FSR, HC and SC images from 107 subjects by 6 NIOSH certified B-readers. Overall, there were few differences in the reliability of image classifications across image formats (i.e., most inter-rater kappa values of classifications for FSR, HC and SC images did not differ significantly from each other). Readings of HC images demonstrated a significantly greater prevalence of classifications of small parenchymal opacities compared to FSR and SC (e.g., in adjusted logistic models of the prevalence of small parenchymal abnormalities: the odds ratio of FSR versus HC = 0.72, 95% CI = 0.60-0.86; and, the odds ratio of HC versus SC = 1.26, 95% CI = 1.09-1.46); FSR and SC did not differ significantly. The prevalence of classifications for large opacities differed significantly among all three image formats, with HC>FSR>SC, however, the difference between FSR and SC disappeared when images with ‘ax’ were included as large opacities. The prevalence of pleural abnormalities differed significantly among all three image formats, with FSR>HC>SC (e.g., in adjusted logistic models of the prevalence of pleural abnormalities: the odds ratio of FSR versus HC = 1.28, 95% CI = 1.08-1.53; the odds ratio of FSR versus SC = 1.59, 95% CI = 1.35-1.88; and, the odds ratio of HC versus SC = 1.24, 95% CI = 1.08-1.42). These results suggest that while the inter-rater reliability of classifications using HC and SC appears to be largely equivalent to FSR, there are some significant differences among FSR, HC and SC with respect to the prevalence of specific outcomes. Based on our results, interpretation of soft copy digital images for small