HL7-based Instance Availability Notification

HL7 Alternatives for providing Instance Availability Notification

1. Use a standard Observation Results Unsolicited message (ORU^R01).

   Pattern the study UID, series UID and SOP instance UID referencing mechanism after the one used by the Structured Report Export (RAD-28) transaction from the Radiology Technical Framework. This is based on using a group of 4 OBX segments to represent each referenced image. The four OBX segments in each group reference the study UID, series UID, SOP instance UID and SOP class UID respectively.

   Pros:

   1. Much of the specification can be re-used from Radiology.

   Cons:

   1. If there are a large number of instances that need to be included in the notification, the overall size/ length of the HL7 message will get large quickly. (E.g., notification for a 1000 slice CT study would require an HL7 message with 4000 OBX segments.
   2. It's not clear if the receiving actor (PM/EMR) would be able to distinguish this "type" of ORU message from a more typical ORU that carries and actual report.
2. Use a standard ORU message with a reference enabling the receiving system to launch a remote image viewer (e.g., URL to some sort of viewing application with the correct study context)

   Pros:

   1. Simple way to provide the receiving system with access to the available images

   Cons:

   1. Would need to determine if the reference URL is (or could be made) "standard"
3. Use a standard Medical Document Management message (MDM^T01 or MDM^T03 or MDM^T04 or MDM^???)

   The TXA segment (which is part of all the MDM messages) has elements that are more closely aligned with the purpose/ intent of availability notification. For example, this segment include elements for "Unique Document Number", "Parent Document Number" and "Document Availability Status". The problem is that the TXA segment is not allowed to repeat in the MDM message, thus requiring either multiple MDM messages (one per image), or selecting one of the MDM messages that include one or more OBX segments (using one OBX segment per image reference).

4. Use a standard ORI^O24 message

   This was initially suggested because the ORI message contains the IPC segment which was introduced specifically to convey imaging related information. Unfortunately, the IPC segment contains only a study UID which is insufficient as input to a WADO (Web Access to DICOM Objects) request. In its current form, WADO requests must be issued on a per image basis and require the triplet of: study UID, series UID and SOP instance UID as input parameters.