DICOM PS3.17 2022c - Explanatory Information

YYYY.5 Use Cases

YYYY.5.1 Migration and Consolidation

A use case of increasing significance is wholesale transfer of large DICOM repositories from one image management system to another, denoted migration. As a regular part of managing IT obsolescence, users may replace their image management system after about 12-15 years, often with change of vendor and underlying hardware. Replacement requires migrating historical data to the new system. Similar transfer needs arise when healthcare institutions merge previously disparate systems into an enterprise image management system; the repositories from the old systems need to be migrated.

The process of migration involves multiple phases or steps, of which an early task is obtaining an inventory of the source repository. This step is directly addressed by the Repository Query and the Inventory IOD and its related Services. Additional steps may include data reconciliation between the source repository and the databases of the radiology information system (RIS), electronic medical record system (EMR), hospital information system (HIS), and/or master patient index (MPI).

A subsequent step in migration is extracting the DICOM data from the source system and transferring it to the destination system. There are two significant challenges with this data movement. First is the volume of data to be migrated, which as noted above may be a petabyte or more. Second, migration often occurs when either the source system or the destination, or both, are in clinical operation. Systems designed and configured to handle the throughput of regular operations might not have capacity in their DICOM protocol implementation for the additional massive input/output requirements of migration.

The Inventory, whether obtained through the Repository Query responses or through Inventory SOP Instances, indirectly supports this data movement. Many repositories store their DICOM data in the DICOM File Format (as defined in Section 7 “DICOM File Format” in PS3.10), and can provide a non-DICOM direct file access protocol. By bypassing the DICOM protocol processing to access these files, significantly higher transfer rates can often be achieved, and there may be less impact on the resources required to support ongoing clinical operations. The Inventory includes optional access Attributes identifying available non-DICOM file access protocols for each SOP Instance in the repository.

Non-DICOM file movement may be further streamlined if the SOP Instances of a Study or Series are combined into a single container file (ZIP or TAR). The access Attributes may identify such container files.

At the destination repository, the process of building the local database for the incoming data may be facilitated by processing the Inventory, rather than parsing the migrating data one SOP Instance at a time. Image management systems commonly also require order (or imaging service request) information to be received prior to imaging data for the most efficient integration of new data into the database; the Inventory may be processed to provide that data up front before the bulk data transfer is started.

A final step of verification of the migration, ensuring that all data has been transferred, may also use the Inventory. In particular, as an initial check, the count of the number of Series and Instances in a Study could be compared between the Inventories of the source and destination systems.

DICOM PS3.17 2022c - Explanatory Information