Материал: part16

Note​

The set of Content Items in either an Extensible or a Non-extensible Template may be changed in subsequent editions of​ the Standard, in accordance with the procedures of the DICOM Standards Committee.​

A Non-Extensible Template may include a Template that is Extensible. In invoking such a Template, the content structure of SOP​ Instances created from the Non-Extensible Template may vary according to the varying content structure allowed by the extension​ of the included Template.​

Note​

Specification of such extensible content in a Non-Extensible Template may be desirable if the Template defines, e.g., a fixed​ top level structure into which a variety of lower level structures may be "plugged".​

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7 DCMR Context Group Specifications​

Context Groups specify Value Set restrictions for Code Value (0008,0100) (or Long Code Value (0008,0119) or URN Code Value​ (0008,0120)) and Code Meaning (0008,0104) of Code Sequence Attributes for given functional or operational contexts. This Section​ specifies the semantics of DCMR Context Group Tables.​

7.1 Context Group Table Field Definition​

Context Groups are described using tables of the following form (optional columns are shown with italic column titles):​

Table CID <#>. <Context Group Name>​

A row of a Context Group table specifies one coded concept. Each Context Group table is named by a title and identified by a CID​ number and version.​

The columns of the tables consist of:​

•​Coding Scheme Designator: the value of Coding Scheme Designator (0008,0102)​

•​Code Value: the value of Code Value (0008,0100) or Long Code Value (0008,0119) or URN Code Value (0008,0120)​

•​Coding Meaning: the value of Code Meaning (0008,0104)​

Inthosecaseswhereitisnecessary,CodingSchemeVersion(thevalueofCodingSchemeVersion(0008,0103))mayalsobespecified.​ This column may be absent if Coding Scheme Version is not required for any of the coded concepts in the Context Group.​

The value specified in the Code Meaning field is an acceptable value for the specified code value, but does not preclude the use of​ other synonymous text in the same or other language.​

Note​

1.​Some coding schemes do not specify the equivalent of a Code Meaning.​

2.​Capitalization in the Code Meaning is generally not significant, except for abbreviations used in units of measurement​ prefixes (e.g., “ml” milliliter vs. “Ml” megaliter, or “pV” picovolt vs. “PV” petavolt).​

If further description of the concept represented by the code is required in the DCMR (rather than referring to an external coding​ scheme), it is included in a separate table.​

Optional columns may provide an informative mapping from the coded concepts of the Context Group to a reference terminology​ specified in the column heading. Typical reference terminologies include SNOMED CT and UMLS.​

An optional column may provide a normative baseline or defined set of units to use for numeric measurements using the concept,​ either as a single term (e.g., DT ({ratio}, UCUM, "ratio")), a list of such terms, or a reference to a Context Group (e.g., DCID 7277​ "Units of Diffusion Rate Area Over Time").​

A Context Group may alternatively be defined by narrative reference to an externally defined coding scheme.​

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Note​

See for instance CID 82 “Units of Measurement”.​

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​ intheinvokingContextGroup,effectivelysubstitutingthespecifiedContextGroupfortherowwherethemacroisinvoked.Ifan'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 7.2.1-1. Include Context Group Macro​

7.2.2 Units of Measurement​

ContextGroup82isdefinedtoincludeallunitsofmeasurementrelevanttoDICOMIODs.Inthepastitwasenvisagedthatanextensible​ 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 Coding Scheme Designator is specified as "UCUM"​

•​the version of UCUM from which a code is constructed is not required, as it is not needed to resolve ambiguity in the Code Value​ or Code Meaning; however, there is no restriction on the version being specified in Coding Scheme Version​

•​the Code Value will be constructed from UCUM and make use of the "case-sensitive" form of UCUM code (e.g., "ml/s")​

•​the Code Meaning for other than UCUM unity may be one of the following:​

•​the "print" value specified in UCUM (e.g., "mmHg" for Code Value mm[Hg])​

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•​the same string as sent in the Code Value (e.g., "ml/s")​

•​constructed from the "names" of individual components using the Americanized form of name (e.g., "milliliters/second")​

•​constructed from the "names" of individual components using the European form of name (e.g., "millilitres/second")​

•​In the case of UCUM unity ("1", or curly braces expression) it is forbidden to use "1" as a Code Meaning. Annex G provides Code​ Meanings for a Code Value (0008,0100) of 1. A Template or Context Group may constrain the Code Meaning according to the fol-​ lowing rules:​

•​UCUM default unit 1 shall use one of the Code Meaning synonyms specified in Annex G​

•​ratios of identically dimensioned values may use ({ratio}, UCUM, "ratio")​

•​unitless numericscores may use ({M:N}, UCUM, "range: M:N") to specify the minimum and maximum value, for example, ({0:10},​ UCUM, "range: 0:10")​

•​counts using UCUM annotation shall always use the text within the curly braces as the Code Meaning, for example, ({masses},​ UCUM, "masses")​

•​compositions of a curly braces expression with other UCUM values may use a conventional clinical representation, for example,​ ({H.B.}/min, UCUM, "BPM")​

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".​

Note​

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​ inimaging,andthecontextofthedisplayeditemConceptNamewouldresolvebetweentemperatureandelectriccharge.​ 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).​

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. Applications may not add a term that means "unspecified" or "missing" or "unknown"​ similar; if such a concept is intended to be permitted then the Standard will include it in the Context Group already. 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.​

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