DICOM Specification Overview: Value Multiplicity (VM) and Delimitation

The Value Multiplicity of a Data Element specifies the number of Values that can be encoded in the Value Field of that Data Element. The VM of each Data Element is specified explicitly in PS 3.6 of the DICOM Standard. If the number of Values that may be encoded in an element is variable, it shall be represented by two numbers separated by a dash; e.g., "1-10" means that there may be 1 to 10 Values in the element.

Note: Elements having a multiplicity of "S", which represented "single", in versions of this standard preceding V3.0, will have a multiplicity of "1" in this version of this standard.

When a Data Element has multiple Values, those Values shall be delimited as follows:

For character strings, the character 5CH (BACKSLASH "\" in the case of the repertoire ISO IR-6) shall be used as a delimiter between Values.

Note: BACKSLASH ("\") is used as a delimiter between character string Values that are of fixed length as well as variable length.

Multiple binary Values of fixed length shall be a series of concatenated Values without any delimiter.

Each string Value in a multiple valued character string may be of even or odd length, but the length of the entire Value Field (including "\" delimiters) shall be of even length. If padding is required to make the Value Field of even length, a single padding character shall be applied to the end of the Value Field (to the last Value).

Note: A padding character may need to be appended to a fixed length character string value in the above case.

Only the last UID Value in a multiple valued Data Element with a VR of UI shall be padded with a single trailing NULL (00H) character when necessary to ensure that the entire Value Field (including "\" delimiters) is of even length.

Data Elements with a VR of SQ, OW, OB or UN shall always have a Value Multiplicity of one. For a listing of default information about supported VRs, refer to the Default Value Representation Table.