Reversible anonymization of DICOM images using automatically generated policies

Many real-world applications in the area of medical imaging like case study databases require separation of identifying (IDATA) and non-identifying (MDATA) data, specifically those offering Internet-based data access. These kinds of projects also must provide a role-based access system, controlling, how patient data must be organized and how it can be accessed. On DICOM image level, different image types support different kind of information, intermixing IDATA and MDATA in a single object. To separate them, it is possible to reversibly anonymize DICOM objects by substituting IDATA by a unique anonymous token. In case that later an authenticated user needs full access to an image, this token can be used for re-linking formerly separated IDATA and MDATA, thus resulting in a dynamically generated, exact copy of the original image. The approach described in this paper is based on the automatic generation of anonymization policies from the DICOM standard text, providing specific support for all kinds of DICOM images. The policies are executed by a newly developed framework based on the DICOM toolkit DCMTK and offer a reliable approach to reversible anonymization. The implementation is evaluated in a German BMBF-supported expert network in the area of skeletal dysplasias, SKELNET, but may generally be applicable to related projects, enormously improving quality and integrity of diagnostics in a field focused on images. It performs effectively and efficiently on real-world test images from the project and other kind of DICOM images.