Overview: Value Representations

The Value Representation (VR) of a Data Element describes the data type and format of that Data Element's Value(s). PS 3.6 of the DICOM Standard lists the VR of each Data Element by Data Element Tag.

Values with VRs constructed of character strings, except in the case of the VR UI, shall be padded with SPACE characters (20H, in the Default Character Repertoire) when necessary to achieve even length. Values with a VR of UI shall be padded with a single trailing NULL (00H) character when necessary to achieve even length. Values with a VR of OB shall be padded with a single trailing NULL byte value (00H) when necessary to achieve even length.

All new VRs defined in future versions of DICOM shall be of the same Data Element Structure as defined in Section 7.1.2 of the DICOM Standard (i.e. following the format for VRs such as OB, OW, SQ and UN).

Note: Since all new VRs will be defined as specified in section 7.1.2, an implementation may choose to ignore VRs not recognized by applying the rules stated in Section 7.1.2 of the DICOM Standard.

An individual Value, including padding, shall not exceed the Length of Value. For multi-valued fields see Section 6.4 – PS 3.5 of the DICOM Standard.

Note: The length of Value Representations for which the Character Repertoire can be extended or replaced are expressly specified in characters rather than bytes in Table 6.2-1 of the DICOM Standard. This is because the mapping from a character to the number of bytes used for that character’s encoding may be dependent on the character set used.

Escape Sequences used for Code Extension shall not be included in the count of characters.

Note: For a listing of default information about Values Representations, refer to the Default Value Representation Table.