There are many modules in DICOM that use the Image SOP Instance Reference Macro (PS 3.4 Table 10-3), which includes the SOP Instance UID and SOP class UID, but not the Series Instance UID and Study Instance UID. Using the Composite Instance Root Retrieval Classes however, retrieval of such instances is simple, as a direct retrieval may be requested, including only the SOP Instance UID in the Identifier of the C-GET request.
Where the frames to be retrieved and viewed are known in advance, - e.g. when they are referenced by an Image Reference Macro in a structured report, then they may be retrieved directly using either of the Composite Instance Root Retrieval Classes.
If the image has been stored in MPEG-2 format, and if the SCU has knowledge independent of DICOM as to which section of a “video” is required for viewing (e.g. perhaps notes from an endoscopy) then the SCU can perform the following steps:
Use known configuration information to identify the available transfer syntaxes
If MPEG-2 or JPEG 2000 Part 2 Multi-component transfer syntaxes are available, then issue a request to retrieve the required section.
The data received may be slightly longer than that requested, depending on the position of key frames in the data.
If only other transfer syntaxes are available, then the SCU may need to retrieve most of the object using Composite Instance Retrieve Without Bulk Data Retrieve Service to find the frame rate or frame time vector, and then calculate a list of frames to retrieve as in the previous sections.