Cluster linking: Key concepts

Multiple IMPAX cluster configurations use cluster linking to connect more than one system at a site or multiple systems between sites. In multiple IMPAX cluster configurations, users can query and retrieve studies from all the clusters as though they were one, regardless of the physical location of the system. Queried locations can include studies in cache, archived studies, and offline studies.

While the terms cluster linking and database linking are often used interchangeably, they are different. Database linking (or linked databases) is an attribute of database systems, while cluster linking is accomplished with standard and private DICOM messages that flow between each cluster. If the PACS system conforms to the linking specification, then data can be synchronized between the PACS systems.

Types of information communicated

Linked queries allow more information to be communicated between systems than a strictly DICOM query. This information includes:

Interpretation (report) status (New, Dictated, Transcribed, and Approved)
Best study location (cache, non-cache)
Number of images in the study (also available via DICOM in some instances)
Specialty (as computed by remote system using mapping tables)
Body part (as computed by remote system using mapping tables)
Verified status of study
Study comments added from a Client workstation

Advantages of multiple IMPAX cluster configurations

Enabling cluster linking in Network Management provides the following benefits:

Extends the types of constraints used to find studies.
Allows the physician to query all clusters for a particular patient without keeping track of where a patient might have had a prior exam.
Allows physicians to retrieve and display studies from remote clusters, update the studies, and save them to the home cluster.
Provides status, markup, and annotation information between clusters automatically.
Updates at the object level (triggered by markup, annotations, or similar action) contain all series and objects associated with that study; a remote cluster then issues a C-MOVE request to obtain any missing objects so that all clusters have the complete study.
Prefetches relevant priors from other clusters.

Configuring the stations correctly in the Source Manager ensures that studies retrieved from the linked cluster:

Are verified against the appropriate RIS Gateway and that, if required, Study Instance UIDs from a third-party PACS are preserved and synchronized
Do not have routing presets applied
Have the correct Demographic Layouts applied
Have the correct field mappings applied
Are not archived

When queries are performed, standard DICOM queries used in the IMPAX Client to query remote clusters are replaced by linked queries.

Limitations of cluster linking

Cluster update linking handles study, series and object level changes; however, updates are triggered from a limited set of workflows for certain patient and study level changes. (These updates are included in any linked updates that subsequently occur.)
Only unidirectional linking is available between IMPAX systems and third-party PACS systems. Fewer data columns and search criteria are available in the IMPAX Client, and study changes cannot be saved in either direction; however, you can configure HIS stations to receive Study Observed Notifications, preserving and synchronizing Study Instance UIDs from a third-party PACS.
Cluster linking is restricted to information about database queries, study and image updates, and prefetching. It does not include the linking of any type of configuration information such as DICOM network configuration tables, routing tables, mapping tables, or user profiles. All this information must be maintained independently in each system.
Sharing caches between linked clusters is not supported.
Image deletions and additions made in the Client Image area are not saved back to the home cluster.
Bidirectional cluster linking can link a number of IMPAX clusters together. With each site added to the system, data flow traffic increases on each Database Server.