Monday, November 3, 2014

DICOM images on your smartphone: DHIR instead of FHIR?

The DICOM protocol and metadata definitions have served the health care imaging community very well. Since its early definition which dates back to 1992, the protocol has not undergone any major changes. However, with the advent of mobile devices and need to use web services to exchange images, that is about to change. Similar to the HL7 FHIR activity, (see related blog post), which intends to leverage web services and resources to provide a fast implementation platform, DICOM is following the same path and has defined a new protocol for use over the web, and it is especially geared towards mobile device connectivity. I coined this new version “DHIR” after “DICOM Healthcare Interoperability Resources.”

The need to provide a web-friendly version of the DICOM protocol was acknowledged more than 10 years ago, when WADO (Web Access to DICOM Objects) was added to the standard. This option did not really gain any traction until it became part of the XDS-I (cross document exchange for imaging) profile definition several years later. WADO compatible viewers are also relatively new, they did not appear on the market until a few years back.

WADO was the first important step towards a more web-friendly protocol, instead of the traditional DICOM negotiation that has to take place before any image communication can happen, it provides a simple http call or uri (uniform resource identifier) request that includes a pointer to a specific DICOM object using a UID while specifying the content type, for example a dicom, jpeg, or could even be a xml or rtf for reports.

In the meantime, a group of healthcare IT professionals came up with a new concept which they named MINT (Medical Imaging Network Transport), which took the web transport mechanism a step further and also changed how the metadata is being packaged while exchanging the images. There have been a few implementations of MINT, but more importantly, since then, the Working Group 27 of the DICOM standard has taken this into account and included the key concepts of MINT into the DICOM standard as “RESTful DICOM” extensions, very similar again to the HL7 FHIR concepts.
What does RESTful DICOM mean? Well it uses the http protocol, including the authorization, and encryption capabilities of the web communication protocol. The major change is that a request can get the complete metadata of a DICOM object in one request. In addition it allows for “bulk” transfer of information with a clearly defined beginning and end. It is referred to as WADO-RS.

By the way, there is also a so-called WADO-WS defined, which basically requires a message “envelope” to be exchanged in the form of a SOAP message (simple object access protocol), another intermediate step to the RESTful WADO-RS.

As part of the RESTful services, in addition to the new capabilities for bulk transport (i.e. multiple images in a single transaction) and the capability to retrieve only the metadata (DICOM headers) for a study, there are also new protocol services defined, i.e. the WADO-RS, and the capability to do a web-services store (STOW-RS) as well as a query (QIDO-RS).

Does this mean that all devices supporting the “traditional” DICOM protocol today are going to be changed? Certainly not, similar to HL7 that has a very large installed base of version 2 implementations, there is also a huge installed base of DICOM enabled devices, so as HL7 is not going to move all of them to FHIR, DICOM is not going to move them to DHIR either. However, for new applications such as small footprint viewers, plug-ins, apps on mobile devices and tablets, these new standards are a great tool. I expect that it won’t take long before we will see implementations being offered.