Implementations may require communication of information that cannot be contained in Standard Data Elements. Private Data Elements are intended to be used to contain such information. Such Private Data Elements shall not change the semantics of the Information Object Definition or SOP Class Definition.
Private Data Elements have the same structure as Standard Data Elements specified earlier in Section 7.1 (i.e., Data Element Tag field, optional VR field, length field, and value field). The Group Number used in the Element Tag of Private Data Elements shall be an odd number. Private Data Elements shall be contained in the Data Set in increasing numeric order of Data Element Tag. The Value Field of a Private data element shall have one of the VRs specified by this standard in Section 6.2.
For each Information Object Definition or SOP Class Definition, certain Data Elements are required (Data Element Type 1, 1C, 2, or 2C) as specified in PS 3.3 and PS 3.4. Private Data Elements shall not be used in place of required Standard Data Elements.
It is possible that multiple implementors may define Private Elements with the same (odd) group number. To avoid conflicts, Private Elements shall be assigned Private Data Element Tags according to the following rules.
Note: The versions of this standard prior to V3.0 described shadow groups. These were groups with a group number one greater than the standard groups. Elimination of conflicts in Private Data Element Tags have made this distinction obsolete and this terminology has been retired.
Note: The versions of this standard prior to V3.0 specified private group element numbers (gggg,10FF- 7FFF) reserved for manufacturers and private group element numbers (gggg, 8100-FFFF) reserved for users. Elimination of conflicts in Private Data Element Tags has made this distinction obsolete and this specification has been retired.
Since each Item within a sequence is a self contained Data Set (see Section 7.5 on the nesting of Data Sets via Sequences of Items), any Item which contains Private Data Elements shall also have Private Creator Data Elements reserving blocks of Elements for those Private Data Elements. The scope of the reservation is just within the Item. Items do not inherit the Private Data Element reservations made by Private Creator Data Elements in the Data Set in which the Item is nested.
Note: If a sequence is itself a Private Data Element and the Items within the sequence also have Private Data Elements, then there will be Private Creator Data Elements both outside the sequence and within the sequence Items.
Note: Different Items may reserve the same block of Private Data Elements for different private creators. This is necessary to allow the nesting of Data Sets collected from multiple sources into folders.
The Value Representations used for Private Data Elements shall be the same as those VRs specified for Standard Data Elements in Section 6.2. The encoding shall conform to the requirements for those VRs and shall be in accordance with the negotiated Transfer Syntax. A Private Data Element with SQ VR (a Private Data Sequence) may include Items with both Standard and Private Data Elements. Standard Data Elements used within a Private Data Sequence shall use the VRs as defined in PS 3.6 for those data elements.
The semantics of Standard Data Elements within a Private Data Sequence, and the definition of Attribute Values, are implementation dependent.
For a Standard Extended SOP Class the Attributes (07FE,0010) Pixel Data, (5400,1010) Waveform Data, and (60xx,3000) Overlay Data shall not be included within a Private Sequence Item, nor within a standard Sequence Item nested directly or indirectly within a Private Sequence Item.