Chest Radiography: Digital Imaging Updates
Screening workers for pneumoconioses has employed chest x-rays acquired using film-based technology for more than 70 years. However, the use of film is rapidly being replaced by digital imaging. This alone demands that the use of digital chest images be researched and that reliable guidelines for their acquisition and use be developed. In addition, it may be that digital chest imaging has the potential for more accurate and reliable evaluation of the pneumoconioses and related diseases than previous technology. Towards these ends, NIOSH has embarked upon a program of research and evaluation of digital imaging methods, focused to date on chest x-rays, but not excluding other chest imaging modalities (e.g., computerized tomography).
NIOSH proposed federal regulations in January 2012 to enable use of digital chest imaging in the CWHSP. NIOSH then drafted final regulations that were responsive to public comments. On September 13, 2012, NIOSH achieved the major milestone of publishing the final regulationsexternal icon enabling use of modern, digital chest images in the CWHSP. The new regulations became effective on October 15, 2012.
Recent studies conducted by NIOSH and others have demonstrated that the digital radiography systems widely used in clinical practice perform similarly to traditional film-screen radiography when used to categorize chest images according to the International Labor Organization (ILO) classification system for the presence and severity of changes found in pneumoconiosis. Accordingly, classifications of digital images displayed on diagnostic quality monitors were similar to those obtained using film, while inter- and intra-reader variability was not affected. An important consideration is that these studies used no more than standardized methods and equipment to achieve positive results. This information has greatly assisted NIOSH in its development of guidance for use of digital chest images for classification of pneumoconiotic changes.
NIOSH has provided detailed guidance on appropriate methods for digital chest image acquisition and viewing for the purposes of classification using revised (2011) edition of the Guidelines for the use of the ILO International Classification of Radiographs of Pneumoconiosesexternal icon, which was announced on 11/17/2011. NIOSH has also posted the NIOSH BViewer, free software, on its website to enable standardized viewing of digital reference and examinee images.
The ILO Standard Digital Images (ILO 2011-D) in DICOMexternal icon format are now available on DVD for purchase from U.S. distributors.
These images are digitized versions of the 2000 ILO standard radiographs that were adapted to allow pneumoconiosis classification of digital (digitally acquired) radiographs using diagnostic monitors. Examinee digital chest images should always be classified based on side by side comparison with the new ILO 2011-D standard reference images. NIOSH does not recommend use in the U.S. of film-based ILO reference radiographs for comparison with examinee digital chest images or printed hard copies of the images.
For the immediate future we plan to retain support for film-based classification in the NIOSH B Reader program and worker health monitoring activities (e.g., Coal Workers’ Health Surveillance Program).
NIOSH B Reader Program
The NIOSH B Reader program currently consists of training materials and examinations intended to demonstrate new and continuing proficiency in classifying film images using the ILO system. With respect to digital application, we have already digitized the film images used in the teaching syllabus, and made them them available for download, in the DICOM format. Eventually, we plan to develop a syllabus based on digitally acquired images that will parallel the film-based course. We have also digitized the film images used in the certification and re-certification examinations, and plan to start offering this optional version of the examinations as soon as possible. In addition, we plan to develop new examinations based on digitally acquired images for intial and continuing B Reader candidates. We will also be evaluating the current examinations for efficiency and validity in discriminating between readers with varying skills, and modifications may be made to the format of the examinations based on these findings. Images acquired gathered as part of the Repository activity may be used for these purposes.
Though the comparative studies of film-screen radiographs and digital chest images have been consistent, they have highlighted additional opportunities to improve the practice of chest image classification. For example, quality assurance measures such as inserting images of known profusion into readers’ assignments as a way to monitor readers’ performance and provide feedback for improvement can be applied more easily with digital images. Additional research as to the most effective ways to assure high quality classifications is needed. This could include considerations of optimal approaches to deriving final determinations using digital images.
NIOSH is also interested in pursuing research that could lead to better methods for detecting and evaluating occupational lung disease using imaging. These include image enhancement and computerized recognition and classification of abnormalities. Rather than the current practice of controlling the appearance of digital images to be as close as possible to conventional film images, image enhancement is intended to accentuate abnormalities associated with occupational lung disease through specialized image enhancement. By this means, background noise is de-emphasized and the aspects of interest highlighted, leading to better recognition and classification. The next step along this pathway is to program the assessment of the abnormalities so revealed, leading to objective assessment of the profusion of abnormalities, where profusion can be assessed in various ways. Theoretically, image enhancement and computerized recognition removes the subjectivity that arises not only in assessing the level of abnormality but in deciding the implications of the observed radiographic features that arises from the use of human readers.
In addition, and for various reasons, NIOSH research and other efforts in digital methodology have focused almost exclusively on projection radiography. However, there is increasing interest in other imaging modalities (e.g., computerized tomography). As part of its worker protection agenda, NIOSH will be continuing to assess the benefits of these newer techniques, particularly with respect to improving recognition and evaluation of occupational lung disease, bearing in mind negative ramifications such as radiation risk and cost.
Partnering and information gathering/sharing
NIOSH is very interested in learning from and sharing information with partners, stakeholders, and researchers concerning the theoretical and practical utility of digital imaging for the identification and evaluation of occupational lung disease. NIOSH will continue to partner with ILO and others to further modernize and improve the practice of digital chest image classification. As part of this effort, NIOSH has setup an image repository that could, at least in part, supply candidates for new reference images based on digital images and not scanned films, allowing images submitted for classification to be processed for display as is usual in modern clinical settings. As the field evolves, NIOSH will be presenting findings at conferences and in peer-reviewed journals. NIOSH also expects to coordinate meetings of interested parties at which to share information.
NIOSH intends to update this web page as further knowledge becomes available, as events are planned, or as developments occur. Interested parties are invited to revisit this page periodically for updates.