DICOM PS3.16 2018e - Content Mapping Resource

7.2.2 Units of Measurement

Context Group 82 is defined to include all units of measurement relevant to DICOM IODs. In the past it was envisaged that an extensible list of pre-coordinated codes would be included in the mapping resource.

DICOM has now adopted the Unified Codes for Units of Measurement (UCUM) standard for all units of measurement. This coding scheme allows for the "construction" of pre-coordinated codes from atomic components.

The specialization of the UCUM standard as it is used in DICOM involves the following rules:

The UCUM standard states that the preferred display values for codes deg (degrees of plane angle) and Cel (degrees Celsius) are "°" and "°C". However, the character ° does not have a representation in the DICOM default character set (ASCII, ISO-IR 6). The Code Meaning specified in this Part therefore uses "deg" and "C". SOP Instances that specify a Specific Character Set that allows the character ° may use Code Meanings "°" and "°C".


  1. Code Meaning "C" formally conflicts with the Code Meaning for Coulomb. In the context of DICOM use, the possibility of confusion to a user based on the display of the Code Meaning is considered remote, as there is little use of Coulomb in imaging, and the context of the displayed item Concept Name would resolve between temperature and electric charge. Automated processing based on the Code Values should not face an issue as the Code Values differ.

  2. The character ° has Unicode code point U+00B0, and is represented as 0xB0 in ISO-IR 100 (Latin-1), ISO-IR 101 (Latin-2), ISO-IR 109 (Latin-3), ISO-IR 110 (Latin-4), ISO-IR 126 (Greek), ISO-IR 138 (Hebrew), and ISO-IR 148 (Latin-5). It is not encodable in ISO-IR 13 (Katakana), ISO-IR 144 (Cyrillic), ISO-IR 127 (Arabic), or ISO-IR 166 (Thai).

DICOM PS3.16 2018e - Content Mapping Resource