8 Encoding of Coded Entry Data
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# 8 Encoding of Coded Entry Data

The primary method of incorporating coded entry data in DICOM IODs is the Code Sequence Attribute. Code Sequence Attributes are encoded as a Sequence of Items using a macro that is described in this section. These Attributes typically include the string "Code Sequence" in the Attribute Name. Their purpose is to encode terms by using codes from coding schemes.

### Note

In this Standard, Code Sequence Attributes are defined for a variety of concepts, for example: Primary Anatomic Structure Sequence (0008,2228) and other Attributes to describe anatomy; and Intervention Drug Code Sequence (0018,0029), to document administration of drugs that have special significance in Imaging Procedures.

Each Item of a Code Sequence Attribute contains the triplet of Coding Scheme Designator (0008,0102), the Code Value (0008,0100) (or Long Code Value (0008,0119) or URN Code Value (0008,0120)), and Code Meaning (0008,0104). Other optional and conditional attributes may also be present.

For any particular Code Sequence Attributes, the range of codes that may be used for that attribute (the Value Set) may be suggested or constrained by specification of a Context Group. The Module or Template in which the attribute is used will specify whether or not the context group is baseline or defined. A Baseline Context Group lists codes for terms that are suggested and may be used, but are not required to be used. A Defined Context Group lists codes for terms that shall be used if the term is used.

Context Groups are defined in a Mapping Resource, such as the DICOM Content Mapping Resource (DCMR) specified in PS3.16. Context Groups consist of lists of contextually related coded concepts, including Code Value (0008,0100) (or Long Code Value (0008,0119) or URN Code Value (0008,0120)) and Coding Scheme Designator (0008,0102). Each concept is unique within the Context Group and identified by its Code Value (0008,0100) (or Long Code Value (0008,0119) or URN Code Value (0008,0120)) and Coding Scheme Designator (0008,0102). The Context Group specification identifies whether it is extensible, i.e., whether it may be modified in an Application to use additional terms (see PS3.16). Whether a Context Group is used as a Baseline or Defined Context Group is defined not in the mapping resource, but rather in the Template or Module in which the Code Sequence Attribute is used.

Context Groups are identified by labels referred to as Context Identifiers (CID). Formally, the Context Identifier specifies the context of use, not the specific list of coded values selected for that context of use in the Context Group. The set of values specified in the Standard for a particular context may change over time, and set of values used by an Application Entity for a particular context may include a local or private extension beyond the Standard value set.

### Note

1. A specific set of coded values used by an Application Entity is therefore identified by the Mapping Resource Identifier, plus the Context Identifier, plus the Context Group Version, plus the identifiers for any private extension.

2. The use by an Application Entity of coded terms not in the Standard specified Context Group does not require the explicit identification of a private extension. The Application Entity is then the implicit source of the extension.

3. For the purpose of harmonization with HL7 vocabulary concepts, Context Groups are equivalent to HL7 Value Sets.

## 8.1 Code Value

Code Value (0008,0100) is an identifier that is unambiguous within the Coding Scheme denoted by Coding Scheme Designator (0008,0102) and Coding Scheme Version (0008,0103).

The Long Code Value (0008,0119) or URN Code Value (0008,0120) is only used for codes that exceed the 16 character size limit of Code Value (0008,0100). If the code value length exceeds 16, the Code Value (0008,0100) shall not be present. If the code value length is 16 characters or less, the Code Value (0008,0100) shall contain the code and neither Long Code Value (0008,0119) nor URN Code Value (0008,0120) shall be present. The URN Code Value (0008,0120) shall be used for codes that are represented using URN or URL notation. The Long Code Value (0008,0119) shall be used for codes that are represented using other notations and that exceed 16 characters in length.

### Note

The Code Value is typically not a natural language string, e.g., "T-04000".

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