Several Specific Character Set attributes in a single DICOM object

Question

I came across DICOM objects that contain sequences in private tags; each item in that sequence contains its own Specific Character Set (0008,0005). All Specific Character Set elements have the same value. I also found that these extra Specific Character Sets create problems in some applications. Is it allowed by DICOM standard to have multiple Specific Character Sets in a single object? If it is, what are the scope rules?

I could not find the answer in Nema documents. I also check several DICOM Conformance Statements, with the same result.

Answer 1

Including Specific Character Set is explicitly allowed in DICOM. The reference is here:

DICOM PS3.5

Specifically, the standard says:

An encapsulated Data Set shall only include the Specific Character Set (0008,0005) data element if the Attribute Specific Character Set is defined in the IOD for that sequence of items.

Note: An encapsulated Data Set does not include the Specific Character Set data element unless the Specific Character Set Attribute is defined as part of the IOD for that sequence.

If an encapsulated Data Set includes the Specific Character Set Attribute, it shall apply only to the encapsulated Data Set. If the Attribute Specific Character Set is not explicitly included in an encapsulated Data Set, then the Specific Character Set value of the encapsulating Data Set applies.

In this case an "encapsulated Data Set" is a DICOM sequence. Technically since you are seeing the attributes in a private sequence, this is not legal, although this could occur when an IOD defines it (specifically for DICOMDIRs).