Continuing with my series on deciphering Vendor Neutral Archives (VNA), this blog is focused on clarifying the confusion over what VNA’s actually can store, and how they differ in terms of storage. All VNA’s are not created equal! Prospective buyers need to understand their objectives for a VNA up front to insure that they are getting a solution that will meet all of their needs.
Let’s begin by addressing the apparent confusion around the use of industry standards and how they relate to a VNA’s objectives. Many vendors will speak to support of DICOM and XDS as if this is all one needs to know for a VNA to handle any object. From my perspective, this is a case of comparing apples and oranges.
According to the DICOM brochure (http://medical.nema.org/dicom/geninfo/Brochure.pdf) DICOM is “designed to ensure the interoperability of systems used to Produce, Store, Display, Process, Send, Retrieve, Query or Print medical images and derived structured documents as well as to manage related workflow.” It is largely a format for managing digital images, just as JPEG is a format for photographic images, and PDF is a format for cross-platform documents. In other words, DICOM is one of many potential image/document formats that might be encountered in healthcare.
In addition to DICOM, there is an initiative on the part of a joint committee of the Radiological Society of North America (RSNA) and the Health Information Management and Systems Society (HIMSS) organized to “improve the way computer systems share information.” This initiative has become known as Integrating the Healthcare Enterprise, or IHE (http://www.ihe.net/). In the words of the IHE committee, “IHE promotes the coordinated use of established standards such as DICOM and HL7 to address specific clinical need in support of optimal patient care. Systems developed in accordance with IHE communicate with one another better, are easier to implement, and enable care providers to use information more effectively.”
The distinction between the DICOM and IHE initiatives is not inherently clear from these definitions! In the case of DICOM, it is a format for information sharing. Whereas the IHE initiative is protocols for how information should be shared. IHE makes use of format standards such as DICOM and HL7, but in itself, it is not a data format.
One of the IHE profiles is known as XDS, or Cross-Enterprise Document Sharing. In the words of the IHE, XDS “is focused on providing a standards-based specification for managing the sharing of documents between any healthcare enterprise, ranging from a private physician office to a clinic to an acute care in-patient facility and personal health record systems. This is managed through federated document repositories and a document registry to create a longitudinal record of information about a patient within a given clinical affinity domain.” Again, XDS is a protocol for the communication of information, not a specific format.
As an extension of XDS, the IHE initiative created the XDS-I profile for handling images. XDS-I represents a means for handling medical images within the interoperability of the XDS profile for managing documents across an enterprise. It allows for the handling of non-DICOM objects, but it does so within the structure of DICOM by “wrapping” an object within the DICOM format.
Figure 1 is a functional diagram explaining the structure of XDS. Two key elements of the XDS profile are the Document Registry and the Document Repository. The registry keeps track of every object added into the repository, and the repository keeps track of where each object is stored. This is important when there are multiple sources of input, such as in an HIE (Health Information Enterprise). However, if there is only one entity with a common source of patient identification, such as in a large IDN (Integrated Delivery Network), a document registry may not be necessary.
What can one surmise from all of this relative to a VNA?