There is no question that digital mammography is booming. One of the reasons is probably due to the results of the recent National Cancer Institutes multi-center Digital Mammographic Imaging Screening Trial (DMIST) which concluded that for certain age groups of women it might be better to have a digital mammogram performed, rather than conducting conventional film-screen mammography. In addition, the use of computer-assisted diagnosis (CAD) is becoming mainstream in many mammography practices (a recent survey showed about 30 percent regularly use CAD). Of course, it is possible to use CAD by digitizing film, but from a workflow perspective, it is much easier to utilize CAD when it is integrated with a digital system. Lastly, the U.S. market will soon see the introduction of CR-based digital mammography systems from different vendors once they clear the FDA (which is expected soon), offering competitive alternatives to the current DR-based systems.
The FDA approved the initial digital mammography systems as complete, single vendor acquisition and printing or viewing systems. Since than, several third-party workstation and PACS vendors have received FDA clearance for their viewing stations to be used for digital mammography (when used with an approved monitor), which means that users now have a choice. However, this introduced a whole set of new interconnectivity and interoperability issues. As a matter of fact, early adopters of this new technology that were brave enough to use different vendors for digital mammography and diagnostic workstations have truly felt what it meant to be “on the bleeding edge” of technology. It can hurt.
The good news is that there has been a flurry of activity to define a set of requirements in the form of a special profile by the Integrating the Healthcare Enterprise (IHE) organization to address the issues that came to the surface while exchanging images between the acquisition devices and CAD devices and displaying the results on image displays. (See www.ihe.net/mammo for details.) One should be aware that compliance from the vendors with these profiles might take a while, with some estimates forecasting at least a year. One might reasonably expect that facilities jumping into digital mammography today will have to deal with similar workflow issues and challenges, especially if they want to use PACS workstations and digital mammography systems from different vendors during this interim period.
What are some of the issues addressed by this IHE profile? First of all, the profile requires the use of the DICOM Digital Mammography object for all mammography images, whether a digital detector performs the acquisition, computed radiography is used or film is digitized (and not the CR or Secondary Capture objects). The DICOM image definition allows some identification, technique and dose attributes to be left empty by a manufacturer, and where these are considered sufficiently important by users, regulatory authorities and professional associations, the IHE profile raises the bar and requires them to be filled in by the acquisition device and displayed on the workstation as well as printed on film. This includes information required by MQSA for patient and unit identification. A means of identifying and encoding the background air outside the breast skin edge also is required to be present; this allows window width/level adjustments by the user without changing the background air intensity. Different vendors have used various different mechanisms available in DICOM for specifying how the image contrast is to be encoded and adjusted, and the profile requires that the workstation support all of these mechanisms so that images will have the expected appearance regardless of which combination of modality and workstation is used. Of course, all workstations are required to be calibrated to the standard DICOM grayscale function, though it will likely be necessary to use the same technology (LCD or CRT) throughout the organization as well as to choose the same minimum and maximum luminance levels to achieve consistency.
Since CAD also is expected to be an important factor in the widespread use of digital mammography for screening, the IHE profile makes the ability to display CAD marks encoded in standard DICOM mammography CAD SR objects a required capability for the workstation. Mammography images need to be processed into a suitable form (“For Presentation” images) before display to the user or