What is the [Referenced SOP Class/Instance UID] in the Referenced Image Sequence in DICOM images?

Question

I am developing a Modality Worklist client using fo-dicom library.

Following thing are not clear to me related to [Referenced SOP Instance UID (0008,1155)].

1. What is Referenced SOP Instance UID?
2. Is Referenced SOP Instance UID same for entire series?
3. I have seen 2 Referenced SOP Class UIDs in some sample images; Why?

Scenario 1:

I'm trying to retrieve Modality work list to create some image series for a requested study. I have to create a captured image sequence to send the "Completed" notification to the MPPS server. The fo-dicom sample for modality work list includes Referenced SOP Class/Instance UID when creating the completed image sequence to send "Competed" notification to MPPS. My question is what is this Referenced SOP Class/Instance UID?

Scenario 2:

In addition to that, I found some sample DICOM file series and each image contents Referenced SOP Class/Instance UID twice and same to a series.

Are these Referenced SOP Class/Instance UID same or different?

Below is a sample DICOM file contents Referenced SOP Class/Instance UID two times:

Trumpet

Answer 1

First of all:

• The Referenced SOP Class/Instance UID are always items of a sequence, and the sequence defines the meaning of the reference.
• The Referenced Image Sequence does not refer to Modality Worklist, it refers to images and other objects only.

The sequence is intended to accommodate other objects which are relevant for the interpretation of a given image. In DICOM: "A Sequence that references other images significantly related to this image."

These may be:

• other images which are related to the current image (e.g. the ID of the other plane in a Bi-Plane acquisition)

• other images on which the calculation of the current image is based

• the second image in case the current image is part of a stereo pair

Any particular meaning of the reference may be constrained or enforced by the particular type of image you are creating. This information can be obtained by following the references in the IOD (Information Object Definition as defined in DICOM Part 3).

For most images, the referenced image sequence is an optional (Type 3) or "may-be empty" (Type 2) attribute which means that if there is no significant relation to other images, it may be omitted.

Cecilycecity

Answer 2

I have done more research about Referenced SOP Class/Instance UID to understand practical relation to DICOM Modality WorkList implementation which I am currently working on.

@kritzel_sw has already answered mainly for my Scenario 2: question and I have found following more information related to my Scenario 1:question.

According to the DICOM Part4 F.7.2.1.1 Modality Performed Procedure Step Subset Specification (Table F.7.2-1), [Performed Series Sequence (0040,0340)] is a required attribute for N-SET protocol which is part of Modality WorkList Management(send the "COMPLETED" notification to the MPPS server). Referenced SOP Class/Instance UID are sub attributes of [Referenced Image Sequence (0008,1140)] under [Performed Series Sequence (0040,0340)]. Practically, SCU Modality should send a list of SOPInstanceUID of captured images to SCP to complete the requested procedure step with N-SET. Referenced SOP Class/Instance UID under [Referenced Image Sequence (0008,1140)] should be used to send these information.

Following is the basic Modality WorkList Management sequence

1. SCP request Modality WorkList from SCU
2. SCU send Modality WorkLists
3. SCU send "IN PROGRESS" notification to SCU
4. SCP create Image sequences
5. SCU store Images to PACS
6. SCU send "COMPLETED" notification to SCU by referring created Images SOPInstanceUIDs

DICOM Part4 F.7

Trumpet