Like many problems, there are more than one valid solution. For the challenge of getting images to both diagnostic consumers (e.g. Radiologists) and clinical consumers (e.g. ordering physicians, EMR users), there are many ways to define a solution architecture, but two are most obvious: PACS-centric and VNA-centric.
In this model, the PACS is the primary system, interfacing with modalities, providing a client to diagnostic users, as well as access to clinical users though an enterprise client embedded in the EMR. Mobile access may be direct or via a mobile EMR user interface, but it is getting images from the PACS. Enterprise images are captured and stored in the PACS (though storing to VNA and routing to PACS is also possible). The VNA’s role is primarily as an archive to (one or more) PACS.
In this approach, the VNA is the primary image management system. The PACS likely still interfaces with modalities (though not always), but captured enterprise images are stored to the VNA, and sent to the PACS when needed/supported. Clinical viewing in the EMR is done by an Enterprise Viewer, which may or may not be provided by the VNA vendor. Mobile access is also through the Enterprise viewer, getting images from the VNA.
Pros and Cons
As stated, both are valid approaches, but each has some inherent strengths and challenges.
The PACS-centric solution has a high likelihood of having all parts of the medical imaging record being available in both diagnostic and enterprise viewers. Proprietary data (e.g. markups and key images) not provided through standard data objects (e.g. DICOM GSPS and KOS) are more likely to be visible in all clients. There may also be some common application configuration settings across clients, which would reduce administration complexity and cost. Getting the image management and image viewing (diagnostic and enterprise client) all working together is the burden of the vendor (i.e. it is an engineered solution designed to function as a single system).
The VNA-centric solution is better suited to support a multi-PACS environment, providing a common management and viewing platform for enterprise users—only the single Enterprise Viewer is embedded in the EMR (vs. the multiple ones provided by each PACS). Environments with multiple PACS and Mini-PACS benefit as the VNA is the common sharing (and data quality validation) point among them—this allows for a more “pluggable” solution where systems that address niche needs can be used until the primary PACS is able to replace them. In this model, the integration among the components is more complex and places a higher burden on the institution to get it all working (i.e. the informatics and IT staff need to be willing and able to put this together), even with purchased professional services from all the vendors involved.
Both a well-designed PACS and VNA (and Enterprise Viewer) can provide effective multiple patient ID management methods (e.g. MPI or IHE Patient Identifier Cross-Referencing), to allow integration/exchange of patient imaging records across patient ID domains, though the VNA and Enterprise Viewer are traditionally more likely than PACS to support flexible models.
In both models, storage for the long term archive is expanded at the VNA.