Each Item of a Data Element of Value Representation SQ shall be encoded as a DICOM Standard Data Element with a specific Data Element Tag of Value (FFFE,E000). The Item Tag is followed by a 4 byte Item Length field encoded in one of the following two ways:
The encoder of a Data Set may choose either one of the two ways of encoding. Both ways of encoding shall be supported by decoders of Data Sets. Data Element Tags (FFFF,eeee) are reserved by the standard and shall not be used.
Each Item Value shall contain a DICOM Data Set composed of Data Elements. Within the context of each Item, these Data Elements shall be ordered by increasing Data Element Tag value and appear only once (as Data Set is defined in Section 7.1 in PS 3.5 of the DICOM Standard). There is no relationship between the ordering of the Data Elements contained within an Item and the ordering of the Data Element Tag of SQ Value Representation that contains that Item. One or more Data Elements in an Item may be of Value Representation SQ, thus allowing for recursion. Section 7.8 in PS 3.5 of the DICOM Standard specifies rules for incorporating Private Data Elements into Sequence Items.
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