A Vendor Neutral Archive (VNA) is a medical imaging technology in which images and documents (and potentially any file of clinical relevance) are stored (archived) in a standard format with a standard interface, such that they can be accessed in a vendor-neutral manner by other systems.
This terminology is used as distinct from a traditional Picture Archiving and Communications Systems (PACS), although there is debate about where the boundary between a VNA and a PACS lies along the continuum of their common features.
Definition The simplest definition is "a medical device that stores medical images in a standard format with a standard interface, such that they can be accessed in a vendor-neutral manner by other systems".
So-called "vendor neutrality" is implied by the standard format and interface, and the neutrality is with respect to vendor-specific devices that produce or consume those images (e.g., for display, distribution or analysis, with or without specific workflows, such as for radiology reporting, i.e., a PACS).
The exact definition and feature set is contentious though, and evolves as different vendors of VNAs attempt to distinguish themselves from their competitors and avoid being excluded, and customers express desires ranging from pragmatic to fantastic.
There is general agreement on the following key features:
Storage of DICOM images and related composite objects (presentation states, key objects, structured reports) DICOM network standard interface for storage, query and retrieval Administrative updates and corrections (patient ID changes and study merges) Scalability
Each of the following features remain contentious, in the sense that some customers and vendors claim that some or all are fundamental to the concept, but others disagree:
Storage of objects not directly related to images (such as human-generated requests and reports) Storage of non-DICOM content (such as HL7 CDA documents) Non-DICOM access protocols (such as IHE Cross-Enterprise Document Sharing (XDS and XDS-I) Cross-domain identity and code resolution (patient ID, accession #, procedure codes) Dynamic DICOM tag morphing Information lifecycle management Exclusion of workflow management database content Independence from choice of database engine Audit trail of access
History
Evolution Traditionally, the need to store medical images has been most common in the radiology and nuclear medicine departments, and has been implemented in the form of sub-specialty and departmental (PACS), which have combined the functions of image management and image archiving into a single solution. Whilst such systems all have standard interfaces (DICOM and IHE) for ingestion and distribution of images over the network and on physical media (like CD), typically the workflow and optimal performance for display are achieved using proprietary software and protocols. Further, the persistent storage "inside" a proprietary PACS may not be in a standard form, the PACS may not update the stored files with the latest study and demographic updates and annotations stored in the database, and it may extend, abuse or depend on specific standard and non-standard (private) DICOM attributes in the stored files.
Over time, in many implementations, the underlying storage infrastructure has been "factored" out of the traditional (PACS) at the hardware and file system (DAS, NAS, SAN) level, and are supplied instead by non-domain-specific computer data storage vendors.
As more medical specialties incorporate images in their practice, the need to extend image storage and distribution capability to other departments, enterprise wide. Increasingly there is a desire to inter-operate at a higher application level, separating departmental-specific workflows, display and analysis solutions from image storage infrastructure, using standard protocols that are image and metadata aware, without sacrificing display performance.
A complicating factor is that the (PACS) offerings are in a constant state of flux with respect to features and quality of service, and traditionally users will abandon one vendor and replace their product with another's every 3–5 years. This triggers the need to "migrate" the images and associated information to the new architecture without data loss, a non-trivial task despite the use of standard formats for image encoding. The concept of a VNA theoretically allows for greater stability (re-usability and less frequent migration) at the archive level, despite rapid evolution and change at the higher application-level (display and workflow). Of course, migrating from one vendor's VNA to another isn't trivial either, just hopefully less frequent.
An alternative term for a VNA is a "PACS Neutral Archive", which perhaps better conveys the original intent, but this term is rarely used, and for better or for worse, VNA has become the buzzword of choice amongst customers and salesmen.
Literature As noted above, the archive of images is naturally mostly static—that is, most of the content of an archive is unchanged, with only a (relatively) small number of studies added each day, with few changes and corrections required.
From the early days of PACS, it was expected that standard interoperability boundaries would need to be defined. The ACR-NEMA, and later DICOM, standards arose to address not only the need for a standard file format but also protocols for storage of images from acquisition modalities to archives, and to query and retrieve images from the archive. Even the first ACR-NEMA standard from 1985 defined FIND and GET transactions. I.e., the separation of workstations and workflow management from archives was envisaged from the beginning. The first DICOM demonstrations at RSNA beginning in 1992 made use of a so-called "central test node", which arguably was one of the first DICOM-based vendor neutral archives, though that label was not in use at the time. Homegrown PACS or mini-PACS typically described the archive and workstation as separate entities. Many, but not all, monolithic commercial PACS continued to make use of proprietary protocols between their integrated workstations and archives, but the need to support separate third-party workstations for specialized work, such as 3D processing and radiotherapy planning, was always recognized, and implemented using the DICOM protocol.
In 1998, Erickson and Hangiandreou discussed the advantages of once again separating the archive functionality from the conventional monolithic PACS and making use of pre-fetching to populate the "interpretation storage device". They also describe query and retrieval from multiple archives (in a manner that would now be called a federated query) to provide inter-enterprise image sharing. The article noted some of the practical challenges at the time, such as the relative inefficiency of doing DICOM queries against such multiple archives and separating out those responses relevant for pre-fetching, as well as challenges of patient identifiers. Nevertheless, the ability to have images in a separate system from the workstation was felt to be an important capability. Ultimately, Erickson and colleagues developed this into a startup company, TeraMedica in 2000, which was purchased by Fuji Medical Systems in 2015.
In one of many blog entries on the subject, Michael Gray makes a reference to an early description of the concept of separating the front-end clinical applications from the back-end storage function, in an article by Nadim Daher, a Medical Imaging Market Analyst at Frost & Sullivan.
A long running Aunt Minnie PACS Forum thread digressed to discuss the issue of neutral archives amongst a broader audience after a response from Michael Gray.
A white paper from 2009 by Wayne DeJarnette is an early attempt to establish a definition based on a required feature set, and his company has also provided a more recent interpretation.
Michael Gray offers his essential ingredients of a VNA in his 2009 blog entry, making reference to Acuo's checklist of attributes, the most recent form of which can be found in Shannon Werb's white paper on attributes of a "true" VNA.
In 1997 Larry Sitka left 3M/Imation having assisted Cemax/Icon in construction of Archive Manager and a decentralized archive called IMAS which was never released to the market and started a company called Acuo Technologies. It took 2 years and 3 months to raise capital to hire 3 other founding Acuo engineers. Funded by a private investor named Jim Jundt, Acuo officially opened an office on Jan 1, 2000 with 4 employees. The company focused on separating viewing applications (PACS) from data management and storage devices.
Acuo provided a service giving vendor agnostic viewing over a single normalized central repository for all imaging content. Content was stored/linked inside Acuo using messaging and protocols by routing, mapping of DICOM messaging. To PACS the Acuo solution looked like a single repository when content came from locally stored, or protocol connected locations. It was Michael Gray who in 2004 coined the phrase "Vendor Neutral Archive" directly referencing the Acuo platform’s ability to separate Viewing, Content Management and Message Orchestration, and Storage. Acuo’s ROI was built around pulling the archive out of PACS, never again paying for migrations (application or storage) and enabling best of breed access to viewing applications sitting on top. Vendor Neutrality from PACS viewing applications and Storage providers sitting underneath.
Many Healthcare delivery organizations are still reaping the savings from those installations, some as old as 23 years.
Herman Oosterwijk provides a more recent description on behalf of Teramedica, in his white paper, in which he offers a more detailed definition: "A Vendor Neutral Archive (VNA) is a medical device that provides scalable image and information and life cycle management so that images and related information can be queried, stored, and retrieved in a manner that is defined by open standards at multiple department, enterprise, and regional level while maintaining patient privacy and security. Characteristic for a VNA is that it provides a patient-centric approach that transcends upgrades and changes of the different viewing, acquisition, and workflow management components as they should be interchangeable without having to migrate, convert, or change the data formats or interface of the VNA."
The relationship of VNA to storage of medical images in the cloud is also nebulous, though offers high potential for buzzword compliance, and Michael Gray provides some clarity in his paper commissioned by EMC.
Various alternative deployment models and frameworks have been described, which address matters of cost, value and barriers to entry.
Since the term "VNA" has been so abused as a marketing term, it has already achieved mythical status.
Features
Administrative updates and corrections A passive archive will simply store what it receives, and potentially overwrite the same thing when it is received again with changes but the same (unique) identifiers. This is insufficient in a production operation, where mistakes are made, and it is necessary to correct patient demographics, or correct mistakes (wrong patient or request or side was selected during an exam and incorrect information present in the image headers).
Standards exist that cover some use cases, such as IHE Patient Information Reconciliation (PIR) and Imaging Object Change Management (IOCM).
Cross-domain identity and code resolution For an archive to span departments, institutions, regions or even national boundaries, the question of identification of entities and concepts must be addressed.