DICOM PS3.5 2024c - Data Structures and Encoding

7.4.3 Type 2 Required Data Elements

IODs and SOP Classes define Type 2 Data Elements that shall be included and are mandatory Data Elements. However, it is permissible that if a Value for a Type 2 Data Element is unknown it can be encoded with zero Value Length and no Value. If the Value is known the Value Field shall contain that Value as defined by the Data Element's VR and VM as specified in PS3.6. These Data Elements shall be included in the Data Set and their absence is a protocol violation.


  1. The intent of Type 2 Data Elements is to allow a zero length to be conveyed when the operator or application does not know its Value or has a specific reason for not specifying its Value. It is the intent that the device should support these Data Elements.

  2. A Type 2 Sequence Data Element will contain zero or more Items, as defined by the IOD (irrespective of the VM of the Sequence, which is always one (Section 7.5)). An empty Type 2 Sequence is one with no Items, as opposed to an Item that is present but empty. Whether or not Items may be empty (contain no Data Elements) depends on the IOD definition of the Data Set for each Item, rather than the Type of the enclosing Sequence Data Element.

DICOM PS3.5 2024c - Data Structures and Encoding