DICOM MWL, differences and confusion about StudyID, StudyInstanceUID, ProcedureId, AccessionNumber, etc.

When working with DICOM MWL (modality worklist) there are multiple DICOM tags that are important and some if them can be confused with less important ones. Let’s take a look first at the list of DICOM MWL important terms:

  • Requested Procedure, is a container holding the study information (StudyInstanceUID, AccessionNumber) and the patient
  • Study, maps one-to-one to Requested Procedure
  • ScheduledProcedureStep holds the details for a single modality. One RequestedProcedure might contain multiple steps (CT, SPECT) which are treated as different procedure steps. Or there might be two different examinations done on the single modality
  • Series – response to the one of the steps consist of a series, which is a set of images from a single modality (and the procedure step)
  • SOP Instance – is effectively an image

This is quite simple once you find the information, however you have to be careful while working with the ID’s of these items:

  • RequestedProcedureID identifies the RequestedProcedure
  • StudyInstanceUID – identifies the study
  • StudyID – not to be confused with the StudyInstanceUID. StudyID  is supposed to be a human readable ID of the study, but it is not used in the PACS and MWL broker for study identification
  • PatientID – DICOM ID of the patient
  • AccessionNumber ID generated usually in HIS which identifies the study for the administrative purposes (billing, etc.)

What is important is that ALL the ID’s above provided by the MWL broker needs to be sent back to PACS, otherwise in most cases PACS will refuse accepting the C-STORE request. See my other post on the dataset serialization.

I also recommend these articles for some extra explanations:

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