Simplifying DICOM Study Imports: Busting the Myth of XDS Complexity
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Demystifying DICOM Import Reconciliation

In my previous "Mythbuster" blog I addressed a question related to how you can use the IHE XDS-I and XCA-I profiles to retrieve DICOM Studies from a remote PACS and import them into a "destination" PACS. This "import pattern" refers to use cases referenced as "image sharing" or "radiology referral".

The myth to bust in this article is that importing external studies from an XDS-based network is difficult to do.

There is more to image sharing than pushing DICOM studies around. From a pure technical perspective, it involves applications in the image exchange chain, to properly implement the XDS-I/XCA-I actors and transactions. From a more functional perspective, there is much more that needs to be considered given that image sharing intersects, or perhaps interferes, with existing workflows and processes in the radiology department. 

A key characteristic of such workflows is a radiology department “runs” on locally requested procedures. When a procedure request is made through the EMR or RIS, modalities are informed of "scheduled procedures" through (DICOM) modality worklists, such that the local PACS understands what studies are acquired for what procedure, when they arrive through DICOM transactions from the modalities.

However, when external studies are received it is unlikely that they are known as "requested procedures" in the same ways locally acquired studies are. To make external studies land in a PACS in a way the radiology workflow is not disturbed, "import reconciliation processes" are typically designed. 

During "reconciliation" external study and procedure information is modified in ways to make it look as if the external study was acquired locally. IHE defined an integration profile for this a long time ago in the days when most external studies arrived through CD/DVD media. Even though the CD/DVD media has been replaced by other exchange technologies, the functional part of the import reconciliation process and its complexities still remains. 

This means that you'll need to find ways to create new patient records for patients who are referred, but who are not (yet) known at the receiving location. It furthermore involves mapping external procedure information to local procedure information, such that the receiving systems (EMR, RIS, and PACS) understand what it is they are receiving and, for example, hanging protocols work for external studies as they do for local ones.

There are multiple strategies to consider to achieve import reconciliation. Most include manual user intervention to make sure no mistakes are made such that external studies do not accidentally end up with the wrong patient record.

The Founda platform offers four approaches to exporting and reconciling external studies (three are shown in the picture below). Which one to use depends on the capabilities of your local EMR, RIS, and PACS. 

Founda Health - Export Dialog

Founda Health - Export Dialog 

No manual modification

The first approach assumes the availability of a master patient index that maintains a link between an external patient MRN, and the corresponding local patient MRN. If an MPI is available the DICOM Patient ID attribute (0010,0020) is automatically updated during import. This makes it more likely that a PACS will not refuse the external study because of an "unknown patient error". Note that in case no MPI is available, or no link is found, the DICOM header is left unmodified during export.

Overwrite values

The second approach assumes that a local (radiology) procedure request has been created as a "placeholder" for an external study. As a result, a locally generated accession number is available. Before an import of an external study is started, both the local Patient MRN and the Accession Number are entered by a user, such that the DICOM header of the external study is updated with both before exporting the study to a destination PACS. This prevents an "unknown patient", and/or an "unverified procedure" error. 

Select from worklist

The third approach is a variation on the second and assumes that a locally created requested procedure is available through a DICOM Modality Worklist service. Once an external study is selected for import a user can select the corresponding entry from the modality worklist. As the study is sent to the destination PACS its DICOM header is updated with information from the worklist items. In case the DICOM Modality Worklist item also includes attributes like "Body Part Examined", "Study Description", the DICOM header of the imported study is updated accordingly.

Customized export flow

The fourth and most advanced approach is that the user is presented with a list of suggested local requested procedure codes based on the meta-data of the selected external study. The picture below shows a (Dutch) example of a customized form. After confirming a requested procedure code (Dutch: 'verrichtingscode') the study is imported. However, prior to sending it to the destination PACS a request for a new procedure is sent to the EMR/RIS (as an HL7v2 ORM message) such that a new request is automatically created. Once created successfully the DICOM header of the external study is updated, and it is sent to PACS.

Founda Health - Customized Export Flow

Founda Health - Customized Export Flow 


DICOM Study Import Reconciliation workflows can be used to reduce the workload that is required to update external study (meta) data such that they are recognized by your RIS/PACS. 

However, in the absence of a shared patient identifier, and as long as there are different requested procedure codes used for external studies, import reconciliation workflows and their associated manual interventions are hard to avoid. 

The most ideal solution consists of your local EMR, RIS, and PACS to properly implement the IHE XDS-I and/or XCA-I transactions allowing their users to discover external studies from their PACS workstation and import or review external studies as easily as locally acquired studies. 

The good news is that quite a few PACS systems offer support for XDS(-I) based reconciliation workflows. Some PACS import external studies to a "dedicated" first-in-first-out cache such that imported studies do not "pollute" your image archive. Others are capable of on-demand retrieving of external studies, or linking it to existing prefetch rules. For a fully PACS integrated reconciliation workflow I recommend you talk to your PACS supplier. 



Andries Hamster

Andries' expertise lies in the domain of "standards-based interoperability" to realize health information exchanges. Throughout his career he has been exposed to many interoperability standards such as DICOM, HL7 and he has been involved with IHE from the start.

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