Modality work list - Which items are returned for C-FIND request of a sequence?

Question

My question is a really basic question. Consider to query a modality work list to get some work items by a C-FIND query. Consider using a sequence (SQ) as Return Key attribute for the C-FIND query, for example: [0040,0100] (Scheduled Procedure Step) and universal matching.

What should I expect in the SCP's C-FIND response? Or, better say, what should I expect to find with regards of the scheduled procedure step for a specific work item? All the mandatory items that Modality Work List Information Model declare as encapsulated in the sequence? Should I instead explicitly issue a C-FIND request for those keys I want the SCP return in the response?

For example: if I want the SCP return the Scheduled Procedure Step Start Time and Scheduled Procedure Start Date, do I need to issue a specific C-FIND request with those keys or querying for Scheduled Procedure Step key is enough to force the SCP to send all items related to the Scheduled Procedure Step itself?

Answer 1

Yes, you should include the Scheduled Procedure Step Start Time / Date Tags into the 0040,0100 sequence.

See also Service Class Specifications (K6.1.2.2)

This will not ensure you will retrieve this information, because it depends on the Modality Worklist Provider, which information will be returned. You could also request a Dicom Conformance Statement from the Modality Provider to know the necessary tags for request/retrieve.

Answer 2

As for table K.6-1, you can consider it as showing only the requirement of the SCP side or what SCP is required to use for matching key (i.e. query filter) and additional required attribute values to return (i.e. Return Key) with successful match. It is up to SCP’s implementation to support matching against required key but you can always expect SCP to use the values in matching key for query filter.

Also note that, SCP is only required to return values for attributes that are present in the C-FIND Request. One exception is the sequence matching and there you have the universal matching like mechanism where you can pass a zero length ITEM to retrieve entire sequence. So as stated in PS 3.4 section C.2.2.2.6, you can just include an empty ITEM (FFFE, E000) element with VR of SQ under Scheduled Procedure Step Sequence (0040, 0100) for universal matching.