DICOM PS3.5 2019a - Data Structures and Encoding

3 Definitions

For the purposes of this Standard, the following definitions apply.

3.1 Reference Model Definitions

This Part of the Standard makes use of the following terms defined in [ISO 7498]:

Application Entity

See [ISO 7498].

OSI Presentation Protocol

See [ISO 7498].

3.2 ACSE Service Definitions

This Part of the Standard makes use of the following terms defined in [ISO 8649]:

Association

See [ISO 8649].

3.3 Presentation Service Definitions

This Part of the Standard makes use of the following terms defined in [ISO 8822]:

Presentation Context

See [ISO 8822].

Presentation Data Value (PDV)

See [ISO 8822].

Transfer Syntax

See [ISO 8822].

Transfer Syntax Name

See [ISO 8822].

3.4 Object Identification Definitions

This Part of the Standard makes use of the following terms defined in [ISO/IEC 8824]:

OSI Object Identification

See [ISO/IEC 8824].

3.5 DICOM Introduction and Overview Definitions

This Part of the Standard makes use of the following terms defined in PS3.1:

Attribute

Attribute.

Command Element

Command Element.

Data Dictionary

Data Dictionary.

Service-Object Pair Class (SOP Class)

Service-Object Pair Class (SOP Class)

3.6 DICOM Conformance Definitions

This Part of the Standard makes use of the following terms defined in PS3.2:

Conformance Statement

Conformance Statement.

3.7 DICOM Information Object Definitions

This Part of the Standard makes use of the following terms defined in PS3.3:

Attribute Tag

AttributeTag.

Information Entity

Information Entity.

Information Object Definition (IOD)

Information Object Definition.

Multi-frame Image

Multi-frame Image.

3.8 DICOM Service Class Specifications Definitions

This Part of the Standard makes use of the following terms defined in PS3.4:

Service-Object Pair Instance (SOP Instance)

Service-Object Pair Instance (SOP Instance)

3.9 DICOM Network Communication Support For Message Exchange Definitions

This Part of the Standard makes use of the following terms defined in PS3.8:

DICOM Upper Layer Service

DICOM Upper Layer Service.

3.10 DICOM Data Structures and Encoding Definitions

The following definitions are commonly used in this Standard:

Basic Offset Table (BOT)

A table of 32-bit pointers to individual frames of an encapsulated Multi-frame Image.

Big Endian

A form of byte ordering where multiple byte binary values are encoded with the most significant byte encoded first, and the remaining bytes encoded in decreasing order of significance.

Character Repertoire

A finite set of different characters that is considered to be complete for a given purpose and is specified independently of their encoding (also referred to as a character set).

Code String

A string of characters identifying a controlled concept, including Defined Terms and Enumerated Values when represented as character strings. The scope of the controlled concept is limited to the attribute for which the string provides the value; i.e., the attribute defines the allowed set of values for the Code String, and a particular string may have different meanings in different attributes. A Code String is formally an arbitrary code representing a semantic concept; however, English language words (using the constrained character set of the CS Value Representation) are often used as codes for the semantics of those words.

Data Element

A unit of information as defined by a single entry in the data dictionary. An encoded Information Object Definition (IOD) Attribute that is composed of, at a minimum, three fields: a Data Element Tag, a Value Length, and a Value Field. For some specific Transfer Syntaxes, a Data Element also contains a VR Field where the Value Representation of that Data Element is specified explicitly.

Data Element Tag

A unique identifier for a Data Element composed of an ordered pair of numbers (a Group Number followed by an Element Number).

Data Element Type

Used to specify whether an Attribute of an Information Object Definition or an Attribute of a SOP Class Definition is mandatory, mandatory only under certain conditions, or optional. This translates to whether a Data Element of a Data Set is mandatory, mandatory only under certain conditions, or optional.

Data Set

Exchanged information consisting of a structured set of Attribute values directly or indirectly related to Information Objects. The value of each Attribute in a Data Set is expressed as a Data Element. A collection of Data Elements ordered by increasing Data Element Tag number that is an encoding of the values of Attributes of a real world object.

Defined Term

The Value of a Data Element is a Defined Term when the Value of the element may be one of an explicitly specified set of standard values, and these values may be extended by implementers.

Element Number

The second number in the ordered pair of numbers that makes up a Data Element Tag.

Enumerated Value

The Value of a Data Element is an Enumerated Value when the value of the element must be one of an explicitly specified set of standard values, and these values shall not be extended by implementers.

Extended Offset Table (EOT)

A table of 64-bit pointers to individual frames of an encapsulated Multi-frame Image.

Group Number

The first number in the ordered pair of numbers that makes up a Data Element Tag.

Item

A component of the Value of a Data Element that is of Value Representation Sequence of Items. An Item contains a Data Set.

Item Delimitation Data Element

Used to mark the end of an Item of Undefined Length in a Sequence of Items. This is the last Data Element in an Item of Undefined Length.

Little Endian

A form of byte ordering where multiple byte binary values are encoded with the least significant byte encoded first; and the remaining bytes encoded in increasing order of significance.

Nested Data Set

A Data Set contained within a Data Element of another Data Set. Data Sets can be nested recursively. Only Data Elements with Value Representation Sequence of Items may, themselves, contain Data Sets.

Pixel Cell

The container for a single Pixel Sample Value that may include unused bits. The size of a Pixel Cell shall be specified by the Bits Allocated (0028, 0100) Data Element.

Pixel Data

Graphical data (e.g., images) of variable pixel-depth encoded in the Pixel Data, Float Pixel Data or Double Float Pixel Data Element.

Pixel Sample Value

A value associated with an individual pixel. An individual pixel consists of one or more Pixel Sample Values (e.g., color images).

Private Data Element

Additional Data Element, defined by an implementer, to communicate information that is not contained in Standard Data Elements. Private Data elements have odd Group Numbers.

Repeating Group

Standard Data Elements within a particular range of Group Numbers where elements that have identical Element Numbers have the same meaning within each Group (and the same VR, VM, and Data Element Type). Repeating Groups shall only exist for Curves and Overlay Planes (Group Numbers (50xx,eeee) and (60xx,eeee), respectively) and are a remnant of versions of this Standard prior to V3.0.

Retired Data Element

A Data Element that is unsupported beginning with Version 3.0 of this Standard. Implementations may continue to support Retired Data Elements for the purpose of backward compatibility with versions prior to V3.0, but this is not a requirement of this version of the Standard.

Sequence Delimitation Item

Item used to mark the end of a Sequence of Items of Undefined Length. This Item is the last Item in a Sequence of Items of Undefined Length.

Sequence of Items

A Value Representation for Data Elements that contain a sequence of Data Sets. Sequence of Items allows for Nested Data Sets.

Standard Data Element

A Data Element defined in the DICOM Standard, and therefore listed in the DICOM Data Element Dictionary in PS3.6.

DICOM Transfer Syntax

A set of encoding rules that allow DICOM Application Entities to unambiguously negotiate the encoding techniques (e.g., Data Element structure, byte ordering, compression) they are able to support, thereby allowing these Application Entities to communicate. See also Transfer Syntax.

Undefined Length

The ability to specify an unknown length for a Data Element Value (of Value Representation SQ, UN, OW, or OB) or Item. Data Elements and Items of Undefined Length are delimited with Sequence Delimitation Items and Item Delimiter Data Elements, respectively.

Unique Identifier (UID)

A string of characters used to provide global unique identification of a wide variety of items, guaranteeing uniqueness across multiple countries, sites, vendors and equipment. It uses the structure defined by [ISO/IEC 8824] for OSI Object Identifiers.

Value

A component of a Value Field. A Value Field may consist of one or more of these components.

Value Field

The field within a Data Element that contains the Value(s) of that Data Element.

Value Length

The field within a Data Element that contains the length of the Value Field of the Data Element.

Value Multiplicity (VM)

Specifies the number of Values contained in the Value Field of a Data Element.

Value Representation (VR)

Specifies the data type and format of the Value(s) contained in the Value Field of a Data Element.

Value Representation Field

The field where the Value Representation of a Data Element is stored in the encoding of a Data Element structure with explicit VR.

3.11 Character Handling Definitions

This Part of the Standard makes use of the following terms defined in [ISO/IEC 2022]

Coded Character Set

See [ISO/IEC 2022].

Code Extension

See [ISO/IEC 2022].

Control Character

See [ISO/IEC 2022].

To Designate

See [ISO/IEC 2022].

Escape Sequence

See [ISO/IEC 2022].

Graphic Character

See [ISO/IEC 2022].

To Invoke

See [ISO/IEC 2022].

DICOM PS3.5 2019a - Data Structures and Encoding