Data Element Structure

Note: This section makes numerous references to VRs such as OB, OW, SQ, etc. For a listing of default information about these Values Representations, refer to the Default Value Representation Table.

Data Element Structure with Explicit VR

When using the Explicit VR structures, the Data Element shall be constructed of four consecutive fields: Data Element Tag, VR, Value Length, and Value. Depending on the VR of the Data Element, the Data Element will be structured as follows:

Note: VRs of UT may not have an Undefined Length, i.e., a Value Length of FFFFFFFFH.

An example of a Data Element with an Explicit Length and an Explicit VR of OB, OW, OF, SQ, UT or UN is shown below:

An example of a Data Element with an Explicit VR other than OB, OW, OF, SQ, UT and UN is shown below:

Data Element Structure with Implicit VR

When using the Implicit VR structure the Data Element shall be constructed of three consecutive fields: Data Element Tag, Value Length, and Value. If the Value Field has an Explicit Length then the Value Length Field shall contain a value equal to the length (in bytes) of the Value Field. Otherwise, the Value Field has an Undefined Length and a Sequence Delimitation Item marks the end of the Value Field.

An example of a Data Element with an Implicit VR is shown below:

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