Validation of the International Labour Office Digitized Standard Images for Recognition and Classification of Radiographs of Pneumoconiosis

Chest radiographs are recommended for the detection and prevention of pneumoconiosis in workers involved in dusty trades, such as underground mining (1). In clinical practice and public health surveillance, digital chest radiographs (DR) presented on medical-grade monitors have largely replaced the conventional film-screen radiograph (FSR) technology. The International Labour Office (ILO) Guidelines for the Classification of the Pneumoconioses has been an invaluable tool for standardization of interpretations of chest radiographs for epidemiologic studies of the pneumoconioses (2). To enhance accuracy and precision in applying the ILO classification scoring system, readers are required to perform a side-by-side comparison of each individual worker’s radiograph to one or more prototypical chest images, which illustrate a variety of types and severity of radiographic abnormalities induced by dust inhalation. The ILO classification system includes a standard set of chest images for comparison purposes. Until recently, the ILO classification system only provided a set of standard images in the film-screen radiograph (FSR) format. However, in 2011, the ILO revised its guidelines to “extend the applicability of the Classification to digital radiographic images of the chest” (2). In the 2011 revision of the classification, the ILO includes a set of electronic image files (ILO Standard Digital Images [2011-D]) that was digitized from the film-based standards included in the 2000 revision of the classification. Prior to the adoption of the ILO Standard Digital Images (2011-D), a series of research studies was undertaken to assess any potential impact of image modality on the outcomes of ILO classifications of chest radiographs (comparing FSR to DR displayed on medical-grade diagnostic monitors) (1,3–5). These investigations obtained both FSR and DR chest radiographs from study participants on the same day. FSR chest radiographs were interpreted using the ILO 2000 version of the classification system with the traditional film-based standard images. To enable classification of the DR chest radiographs displayed as soft copies on a medical-grade computer monitor, an existing set of the ILO standard films was scanned and digitized (see Franzblau et al. (3) for methods). The resulting image files (“research” digitized standards) were used as the ILO standards for classifying digital images in a number of previous investigations (3–6). These “research” digitized standards appear quite similar to the current set of standard films that are included in the ILO 2000 classification, but were digitized from a prior version of the ILO standard films that had been issued with a black label rather than the current white label. The methods used in these modality studies required that at least two National Institute for Occupational Safety and Health (NIOSH)-certified B Readers1 interpret each participant’s DR chest radiograph presented as a soft copy image side-by-side with the digitized ILO standard radiographs, using two identical medical-grade monitors. In brief, these studies concluded that, with appropriate attention to image acquisition and soft copy display, both of the widely available digital radiography systems2 can be equivalent to FSR in the visualization and classification of small interstitial lung opacities. Despite the subjective similarity between the “research” digitized standards and the new ILO Standard Digital Images (2011-D), to our knowledge, there is no objective evidence that classifications acquired using either set would be equivalent. The objective of this study was to evaluate the equivalence of the “research” digitized standards and the ILO Standard Digital Images (2011-D) using paired digital and film chest radiographic examinations performed on the same day in miners from our previous studies. We searched for systematic differences in both the level of abnormality reported and the intra- and inter-reader variability.