7.2 Special Conventions for context group tables

7.2.1 Include Context Group

The ‘Include Context Group’ macro is a concise mechanism for including (by-reference) all of the rows of a specified Context Group in the invoking Context Group, effectively substituting the specified Context Group for the row where the macro is invoked. If an ‘Include Context Group’ is specified, it shall be specified in the Concept Name column of a Context Group Table. Table 7.2.1-1 specifies the syntax of the ‘Include Context Group macro. Inclusion may be nested, in that included Context Groups may themselves include other Context Groups. This gives rise to the possibility of circular inclusion and multiple inclusion, in which case the Context Group shall consist of the transitive closure of the set of all coded concepts within the included Context Groups.

Note: For example, it is reasonable to have the following definitions for context groups:

Context ID 1, includes Context IDs 2 and 3

Context ID 2, includes Context IDs 4 and 5

Context ID 3, includes Context IDs 5 and 6

Context ID 4 contains a, b, c

Context ID 5 contains e, f, g

Context ID 6 contains a, h, i

The contents of Context ID 1 will be a, b, c, e, f, g, h, i.

Table 7.2.1-1Include Context Group Macro

Coding Scheme Designator (0008,0102) Code Value (0008,0100) Code Meaning (0008,0104)
Include CID nnn

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:

7.2.3 Extension of Context Groups

An Application may extend an Extensible Context Group by adding terms for new concepts. Applications may not substitute other terms of the same concept in the Context Group. Such extension may be made without a change in Context Group Identifier, but with the specification of Context Group Extensions (see PS3.3).

Non-extensible Context Groups shall not be modified in an Application.

Note: The set of concepts in either an Extensible or a Non-extensible Context Group may be changed in subsequent editions of the Standard, in accordance with the procedures of the DICOM Standards Committee.