DICOM PS3.18 2021b - Web Services

8.6.2 DICOM Representations (Current)
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### 8.6.2 DICOM Representations

All DICOM objects are defined by Information Object Definitions (IODs). See PS3.3. Representations of DICOM Resources are encodings of DICOM Information Objects into octet streams.

Each IOD has an associated set of Attributes, which define semantic concepts. Each Attribute has:

- a Tag, which identifies the Attribute using an integer

- a Keyword, which identifies the Attribute using a token

- a Type, which indicates whether the Attribute is required or optional

- a Value Representation, which defines the data type of the Attribute's value(s)

- a Value Multiplicity, which specifies the number of values that the Attribute may have

A Data Element is a concrete representation of an Attribute See PS3.5. Each Data Element has:

- an identifier, which would typically be its Tag, but could be its Keyword

- a Value Representation, which defines its data type

- a Value Length

- a Value Field, which is a sequence of bytes containing zero or more values

Each Instance contains Data Elements representing the Attributes from the Patient, Study, Series, and Instance levels of the IOD. For example, if a Series resource contains 12 Instances, then a transaction that retrieves that Series will contain a representation of the Series and its 12 Instances, in a specific media type, and each Instance will have Patient, Study, Series, and Instance level Attributes.

This Part of the Standard defines three distinct representations of DICOM Resources that can be encoded into DICOM Media Types: Instances, Metadata, and Bulkdata.

DICOM Media Types and their corresponding representations are defined in Section 8.7.3. Other media types used in this Part of the Standard are defined in Section 8.7.4.

#### 8.6.2.1 Web Service Constraints

DICOM Web Services only support representations with explicit Value Representations. Implicit Value Representations (see Section 7.1.3 “Data Element Structure with Implicit VR” in PS3.5) shall not be used.

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DICOM PS3.18 2021b - Web Services