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Is it true that the DICOM "UID of the storage medium instance SID" = "SID of the instance UID"? What for?

I have two questions when I read the DICOM Standard:

In the DICOM file (0002 0003) "SOP media instance ID" and (0008 0018) "SOP Instance UID", are they the same? What about (0002 0002) and (0008 0016)? and why?

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Chris is right, they are the same. From the standard dicom C.12.1.1.1 section :

SID and SOP instance UID UID attributes are defined for all DICOM IODs. However, they are only encoded in composite IODs with a type of 1. See Section C.1.2.3. When encoding, they must be equal to their respective attributes in the DIMSE and File Meta services. Information header (see PS3.10 Media Storage).

Due to the fact that these elements are duplicated, I can only speculate, but the file metadata header exists only in dicom files (it is not transmitted to SCP / SCU). When SCP writes a file from the DICOM data it receives, it must retrieve the SOP ID and UID of the instance from the data set, so this is the mechanical reason why they are the same. As for why these tags, and not some others, I’m sure there are many reasons, but note that the metadata file is always read by any dicom object, since it is always “Small Endian Explicit” even if the next data set is what Some kind of weird transfer syntax. Thus, these two fields are always guaranteed to be read and used in any valid dicom file (even if the versions of group 8 have unreadable transfer syntax).

I also tried to find the condition:

However, they are only encoded in composite IODs.

Almost every IOD is a composite IOD when I look at the standard:

Normalized IODs

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Yes, they are the same. Tags with group 0002 are part of the DICOM P10 header, I assume that they are duplicated, so they can be quickly read without having to parse the entire file.

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Source: https://habr.com/ru/post/1231924/

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