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DICOM specefic glossary

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Glossary and Relevant Terms

MIND utilizes a proprietary transfer and storage protocol, DICOM . Because of this, it is appropriate to include explanations to terms and concepts relevant to DICOM

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A
ACR American College of Radiology.
Access Control traffic rules to establish an Association and avoid collision.
ACSE Association Control Service Element used to establish an Association.
AE VR of type Application Entity.
Angiography an x-ray made of blood vessels after the introduction of a radioopaque substance called a Contrast Medium.
ANSI American National Standards Institute.
Application Context identifies the overall communications context.
Application Entity (AE) A DICOM conformant Application on the network.
Application Entity (AE) Title the name of an Application Entity. The name consists of printable ASCII characters and is limited to a length of 16. The AE Title is not the same as the host name.
Application Model see DICOM Application Model.
Application Profile a Media Storage Application Profile defines a selection of choices at the various layers of the DICOM Media Storage Model which are applicable to a specific need of context in which the media interchange is intended to be performed.
ARTIM Association Request / Reject / Release Timer.
AS an Age String type of VR.
Association a network connection between two DICOM Applications.
Attribute a property of an Information Object (IO). An Attribute has a name and a value which are independent of any encoding scheme.
Attribute Tag see Tag.

 

 

B

Basic Offset Table a table of pointers to individual frames of an encapsulated multi-frame image.
Big Endian one of 2 methods of representing multi-byte values in memory. In Big Endian format, the least significant byte is sent last in a network data stream. See also Little Endian.
Bits Allocated (0028, 0100) specifies the total number of bits allocated for the storage of a pixel sample.

See also Image Attributes

Bits Stored (0028, 0101) specifies the total number of Bits Allocated that will be said to represent a pixel sample value. Bits Stored shall never be larger than Bits Allocated.

See also Image Attributes

Blue Palette Color Lookup Table Descriptor (0028, 1103) specifies the format of the Blue Palette Color LookupTable Data (0028, 1202). Required if Photometric Interpretation (0028, 0004) has a value of PALETTECOLOR or ARGB. See Section C.7.6.3.1.5 of PS 3.3 Information Object Definition.
Blue Palette Color Table Data (0028, 1203) Blue Palette Color Lookup Color Table Data. Required if Photometric Interpretation (0028, 0004) has a value of PALETTECOLOR or ARGB.
Byte Ordering see Endian
Byte Swapping see Endian

 

C

Called AE Title the AE Title of the SCP with which a SCU attempts to start an association. This is the name of the DICOM Application that is being called.
Calling AE Title the AE Title of the SCU that is attempting to start an Association with a SCP. This is the name of the DICOM Application that does the calling.
CAT Computed Axial Tomography. Now called simply Computed Tomography. See Computed Tomography.
CEN TC 251 Comite Europeen de normalisation Technical Committee 251
Center see Window
Cine a series of image frames that can be displayed one after the other to produce a movie loop.
Client the Application which initiates the initial DICOM Association with a "server". In DICOM a client is known as an Service Class User (SCU).
Client/Server network terms for specific roles, equivalent to SCU and SCP
Columns (0028, 0011) number of columns of pixels in the image. This is the same as the image width.
Command Element

 

Command Set

Data Element that belongs to the Command Set. Group numbers of Command Elements are zeros.

Part of the DICOM message that specifies the operation to be performed on the Data Set.

Complex Object Composite or normalized object
Composite Information Object Definition (C-IOD) an Information Object Definition which represents parts of several entities in the DICOM Aplication Model. Such an IOD includes attributes which are not inherent in the Real World object that the IOD represents but rather are inherent in the related Real World objects.
Command Element an encoding of a parameter of a Command which conveys this parameter’s value.
Command Stream the result of encoding a set of DICOM Command Elements using the DICOM encoding scheme.
Composite Object representing more than one real world object.
Computed Axial Tomography (CAT) now called simply Computed Tomagraphy (see below)
Computed Radiology (CR) the digital generation of x-ray images using storage phoshors instead of going directly to film.
Computed Tomagraphy (CT) the generation of a computed image from the collection of hundreds of x-rays made of a single object. The x-ray source and x-ray detector pair is rotated about the object. A computer then analyzes the series of images to create a single very detailed image that shows differences in soft tissue as well as the bony material.
Conformance Statement a formal statement associated with a specific implementation of the DICOM Standard. It specifies the Service Classes, Information Objects, and Communication Protocols supported by the implementation. The requirements of a Conformance Statement can be found in PS 3.2.
CS a Code String type of VR

 

 

D

DA a Date type of VR
Data Dictionary Part 6 of the DICOM Standard. A registry of DICOM Data Elements which assigns a unique Tag, a name, value characteristics, and semantics to each Data Element. Also included in this part is a Registry of DICOM Unique Identifiers (UID).
Data Element The Data Element is a sub-unit of information defined by a single entry in the DICOM Data Dictionary. (PS 3.6). An encoded Information Object Definition (IOD) Attribute is composed of, at minimum, 3 fields: a Data Element Tag, a Value Length, and a Value Field. For Explicit Transfer Syntaxes, a Data Element also contains a Value Representation (VR) field. The description of the Data Element is found in PS 3.5. Each Data Element holds an Attribute of a real world object.

Private Data Elements - A Data Element that is defined by an Application and is not in the Standard DICOM Data Dictionary (PS 3.6) Private Data Elements all have a Group Number that is odd.

Retired Data Element - A Data Element that is not supported beginning with current version of DICOM. Implementation may continue to support Retired Data Element for the purpose of backwards compatibility with versions 1.0, 2.0 and 3.0.

Data Element Tag the first part of any Data Element. This is a 32-bit value that identifies the Data Element. It is made up of two 16-bit values. The first is the Group Number and the second is the Element Number. The DICOM specification uses the following notation for a Data Element Tag: (0010,0030). This example is for the Patient's Birthday.
Data Element Type used to specify whether an Attribute of an Information Object Definition or an Attribute of a SOP Class Definition is mandatory, is mandatory only under certain condition, or is optional. The DICOM specification defines several levels of these types.

1 - required; must have non-zero Value Length (VL)

1c - conditional required. Depends on IOD and SOP Class

2 - must be listed, but can have zero value and zero length

2c - conditional

3 - user defined

 

Data Set a structured set of Attributes directly or indirectly related to Information Objects. That is an organized collection of Data Elements that contain data about a specific Real World Object. The Data Elements are sorted in a Data Set by increasing Tag values.

See also Nested Data Set.

Data Stream a series of data items that is placed one after another. The result of encoding a Data Set using the DICOM encoding scheme.
Defined Term the value of a Data Element is a Defined Term when it is selected from a finite set of possibilities. A Defined Term is different from an Enumerated Value in that a Defined Term’s range can be expanded by an Application
Derived Image an image that contains pixel data that was constructed from the pixel values of one or more other source images. An example would be a 3-D rendering of a series of CT slices.
DICOM Digital Imaging and Communications in Medicine – a public standard jointly developed by the American College of Radiology (ACR) and the National Electronics Manufacturers Association (NEMA). The intent of this standard is to allow interoperation of different imaging modalities, Picture Archiving and Communications Systems (PACS), and workstation displays via a common, public standard of communication.
DICOM Application Model an entity-relationship diagram used to model the relationships between real-world objects which are within the area of interest of the DICOM specification
DICOMDIR see DICOMDIR File
DICOMDIR File a unique and mandatory DICOM File within a File Set which contains the Media Storage Directory SOP Class. This File is given a single component File ID, DICOMDIR
DICOM File formally a DICOM file is one that is formatted according to PS 3.10 of the DICOM Specification. It contains a File Meta Information Header followed by a properly formatted DICOM Data Set. Informally, a DICOM file may be a Data Set missing the File Meta Information Header
DICOM File Format the DICOM File Format provides a means to encapsulate in a File the Data Set representing a SOP Instance related to a DICOM Information Object.
DICOM Information Model an entity-relationship diagram which is used to model the relationships between the information object definitions representing classes of real-world objects defined by the DICOM Application Model.
DICOM Methods DIMSE-C Services
DIMSE Message An aggregate of Data Elements that contains the Command and Data components. Command specifies the method and Data is the information on which the method is executed.
Domain an Internet zone of authority, part of the address structure.
DS a Decimal String type of VR
DT a Date Time type of VR

 

 

E

Element Number the second 16-bit piece of the Data Element Tag. The Element Number identifies which Data Element the Tag represents in the Data Element Group.
Encapsulated Format pixel data is conveyed in compressed format that is not part of the DICOM standard. See Native Format.
Endian defines the byte ordering. There are two methods of ordering multi-byte data values in a computer - Little Endian and Big Endian. In order for DICOM Application Entities to communicate with one another they must either use the same Byte Ordering or be able to Negotiate which byte ordering to use and then have one communication partner Byte Swap to match the other

Note: Little Endian orders the byte sequence with the least significant byte first and the most significant last. Big Endian orders bytes in the reverse sequence. Endian ordering applies only to numbers. Text strings are represented by ASCII bytes in the sequence of letters or symbols.

Enumerated Value the value of a Data Element is an Enumerated Value when it is selected from a finite set of possibilities. An Enumerated Value is different from a Defined Term in that an Enumerated Values range can not be expanded by an Application from the standard defined in the DICOM specification.
ES an Endoscopy type of modality
Explicit VR see Value Representation

 

 

F

FD VR of type Floating Point Double (IEEE 754:11985) 8 bytes
FDDI Fiber-distributed data interface, high-speed network
File an ordered string of zero or more bytes. Files are identified by a unique File ID that can be written, read and deleted.
File ID a unique identifier that references a file in a File Set. A set of ordered File ID Components (up to 8) forms a File ID.
File ID Components a string of one to 8 characters of a defined character set.
File Meta Information Header see Part 10 Image
File Service see DICOM File Service
File Set a collection of DICOM Files (and possibly non-DICOM Files) that share a common naming space within which File IDs are unique.
File Set Creator an Application Entity that creates the DICOMDIR File and zero or more DICOM Files.
File Set Reader an Application Entity that accesses Files, creates additional Files or deletes an existing File in a File Set.
File Set Updater an Application Entity that makes appropriate alterations to the DICOMDIR file, reflecting the additions or deletions.
File Set User an Application Entity that accesses one or more Files in a File Set.
Film Session a group of films
FL a Floating Point Single (IEEE 754:1985) 4 bytes type of VR.
flatten takes every structure’s individual data member and puts them into an ordered list
FSM Finite State Machine
Frame a data packet

 

 

G

Gateway device and conversion method between heterogeneous networks or systems.
General Series Module DICOM object sub-structure
General Study Module DICOM object sub-structure
Green Palette Color Lookup Table Descriptor (0028, 1102) specifies the format of the Green Palette Color Lookup Table Data (0028, 1202).; Required if Photometric Interpretation (0028, 0004) has a value of PALETTECOLOR or ARGB. See Section C.7.6.3.1.5 of PS 3.3 Information Object Definition.
Group Number the first part of a Data Element Tag. It is a 16-bit value that identifies the Group that the Data Element falls in to. All Standard DICOM PS 3.6 Group Numbers are even. Odd Group Numbers are reserved for Private Data Elements and are defined by a specific Application. Starting with DICOM 3.0 Group Number has no significance and should not be considered to Group any Tags even though similar Tags continue to share the same Group Numbers.

See also Repeating Group

 

 

H

High Bit see Image Attributes
HIS Hospital Information Systems
HISPP Health Care Informatics Standards Planning Panel
HL7 High Level 7, an ANSI member, dealing with HIS development

 

 

I

IE see Information Entity
Image Attributes descriptions of the format of an image. Items like width, height, and bits per pixel are all attributes.

Bits Allocated: the size of the Pixel Cell that contains a single Pixel Sample Value Bits Stored: the total number of these allocated bits that will be used to represent a Pixel Sample Value

High Bit: specifies where the high order bit of the Bits Stored is to be placed with respect to the Bits Allocated.

Photometric Interpretation: defines how the image pixels should be interpreted. Some examples are: MONCHROME1, MONOCHROME2, RGB.

See also Part 10 Image.

Information Entity (IE) that portion of information defined by a composite IOD which is related to one specific class of real-world object. There is a one-to-one correspondence between information entities and the entities in the DICOM Application Model.
Information Entity (IE) Module a number of logically related Elements that are grouped together. Patient Module is an example. It contains Data Elements like Patient Name (0010,0010), Patient ID (0010,0020), Referenced Patient Sequence (0008,1120) etc. In DICOM 3.0 the Group Number has no particular significance. An IE may consist of Data Elements from different Groups. Various IE Modules can then be grouped in to IOD Modules.
IO See Information Object
Information Objects (IO) an abstraction of a Real World Information Entity (e.g. CT Image, Study, etc) which is acted upon by one or more DICOM Commands.

See also Composite Information Objects and Normalized Information Objects.

IOD see Information Object Definition Module
Information Object Definition (IOD) Module a number of logically related IE Modules are grouped together to form a IOD Module. For instance a CT Image IOD Module consists of a Patient Module, Study Module, Image Module, etc.
Information Object Instance a representation of an occurrence of a Real World entity, which includes values for the Attributes of the Information Object Class to which the entity belongs
Information Model See DICOM Information Model
Internet A collection of networks and gateways, including ARPnet, NSFnet, MILnet, and others.
Instance a representation of Class.
IS an Integer String type of VR.
ISO International Standards Organization
Item Sequences of Items are used to represent nested data sets. Each item contains a set of data elements.

a component of the Value of a Data Element that is of Value Representation (VR) Sequence of Items (SQ).

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

J

JIRA Japanese Industry of Radiology Apparatus

 

 

L

LO a Long String type of VR.
Listening Port a TCP/IP device that is listening for other devices wishing to establish a connection of Association.
LT a Long Text type of VR.

 

 

M

Media Format Data structures and associated policies which organize the bit streams defined by the Physical Media in to Data File structures and associated file directories.
Media Storage the storage of DICOM Files on a Physical Medium
Meta Service Object Pair Class (Meta SOP Class) a predefined set of SOP classes that may be associated under a single SOP for the purpose of negotiating the use of the set with a single item.
MI-MEDICOM Media Interchange for Medical Image Communication
Message A structured data unit for communication, divided into PDUs according to part 8 of the DICOM standard (for network communication). A data unit of the Message Exchange Protocol exchanged between two cooperating DICOM Application Entities. A Message is composed of a Command Stream followed by an optional Data Stream
Modality A device that uses a specific type of physics to create a non-invasive image of an object’s internal structure
Modality LUT A LUT that gives unitless pixel values real-world meaning.
Module A set of Attributes within an Information Entity or Normalized IOD which is logically related to another.
MONOCHROME1 see Image Attributes
MONOCHROME2 see Image Attributes
MR Modality of type Magnetic Resonance
Multi-Frame Image an image than contains multiple 2-dimentional images. See also Basic Offset Table

 

N

NEMA National Electrical Manufacturers Association. Along with the American Collage of Radiology (ACR) is the standards organization that developed and controls the DICOM Specification.
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 (VR) of Sequence of Items (SQ) may contain Nested Data Sets.
Normalized Information Object Definition (N-IOD) an Information Object Definition which represents a single entity in the DICOM Application Model. Such an IOD includes Attributes which are only inherent in the Real World Object that the IOD represents
Nuclear Medicine a modality that uses radioactive material placed in the body to create images that show the metabolism of the body.

 

 

O

OB an Other Byte type of VR.
OW an Other Word type of VR.
OSI Open System Interconnection (Model developed by the ISO). An international standard that comprises of a layered model of the communication protocols. DICOM allows for communications over Point to Point, TCP/IP and OSI protocols.
Overlay an image, usually graphics, that can be placed over another image.

 

 

P

Packet The size of a block of binary data handled by TCP/IP protocol, usually between 1 and 1,500 characters in length.
PAD Packet assembler/disassembler, an X.25 term
Part 10 Image File a DICOM image that has been saved to disk using the Part 10 section of the DICOM Standard. These files contain a File Meta Information Header at its beginning. In particular, this header contains information on how the Data Set included in this file was encoded.
Patient Attributes attributes or characteristics of a given patient.
PDU Protocol Data Unit, the transported structure of information
Photometric Interpretation see Image Attributes
Physical Media material with recording capabilities for storing streams of computer data.
Pixel Data the part of a DICOM Data Set that contains the actual image intensity values. This is encoded using the OW or OB Value Representations (VR).
PN a Patient Name type of VR.
Point to Point a communication channel that consists of a short physical cable. Mostly used for connecting peripherals like printers. DICOM allows for communications over Point to Point, TCP/IP and OSI protocols.
Port gate number in a Berkeley socket library.
Presentation Context the combination of abstract syntax and Transfer Syntax
Private Data Element see Data Element
Protocol a set of rules that allow Applications of various levels to communicate with one another.
PS 3.x each part of the DICOM 3.0 specification is numbered. When referring to part 2 you will see PS 3.2

 

 

R

Radiology the branch of medicine that deals with radiant energy in the diagnosis and treatment of disease.
Repeating Group standard Data Elements that differ from each other within a range of Group Numbers and have the same Element Number, e.g., (5000,0000), (5002,0000), (5004,0000), etc. It is a carry over from ACR-NEMA 2.0. Newer IODs in DICOM use Sequences instead of Repeating Groups.
Retired Data Element see Data Element
Routers path switches of computer networks

 

 

S

Secondary Capture a general catch-all Modality that is used for images that did not originate as a DICOM image. Images that were stored as TIFF or BMP that are converted to DICOM are given this Modality.
SCP see Service Class Provider.
SCU see Service Class User.
Series Attributes Descriptive Elements of a series of images
Service Class a structured description of an activity performed, e.g., Storage, Printing, etc
Service Class Provider (SCP) a role of an AE that corresponds to a Server in a Client / Server Pair.
Service Class User (SCU) a role of an AE that corresponds to a Client in a Client / Server Pair.
SH a Short String type of VR.
Stack a set of lower OSI layer protocols (i.e., TCP/IP or OSI)
SMTP Simple mail transfer protocol, usually part of TCP/IP
SOP see Service Object Pair
Service Object Pair (SOP) the combination of a specific set of DICOM Message Service Element (DIMSE) and one related Information Object Definition (IOD). A collection of SOP Classes and / or Meta SOP Classes which are related in that they are described together to accomplish a single Application.
Service Object Pair (SOP) Class the union of a specific set of DIMSE Services and one related Information Object Definition (as specified by a Service Class Definition) which completely defines a precise context of communication.
Service Object Pair (SOP) Instance a concrete occurrence of an Information Object and a communication context.
Sequence Delimitation Item A special Data Element that is used to mark the end of a Sequence of Items that are of undefined length.
SQ a Sequence of Items type of VR.
SQL Structured Query Language
SS a Signed Short type of VR.
ST VR of type Short Text

 

 

T

Tag A unique identifier for an Attribute or Data Element. A DICOM Tag is made up of 2 parts, Group Number and Element Number. The DICOM specification uses the notation of (0010,0030). The first 2 byte hexadecimal value is the Group Number and the second is the Element Number. These can be looked up in the Data Dictionary (PS 3.6).
TCP/IP Transmission Control Protocol divides the PDUs into sequences of packets and, at the receiving end, reassembles these packets into PDUs. This set of Protocols allows various networks to connect to other networks. TCP/IP is implemented through the concept of Sockets. DICOM allows for communications over Point to Point, TCP/IP and OSI protocols.
Teleradiology the electronic transmission of radiological images from one location to another for interpretation and/or consultation
Telnet A terminal emulation program of TCP for manipulating a remote computer
Tomography a method of producing a 3-D image of internal objects by comparing the energy (usually x rays) that is absorbed at various angles about the outside of the object. See also Computed Tomography.
TM a Time type of VR.
TPSQ Top Parent Sequence Data Element
Transfer Syntax the description of the encoding method used by a DICOM Data Set. Data Element Structure, Byte Ordering, and Image Compression are defined in the Transfer Syntax. The Transfer Syntax must be known or discovered before a Data Set can be decoded.

 

 

U

UI a Unique Identifier type of VR.
Unique Identifier (UID) a string of up to 64 characters comprising decimal digits and decimal points. These strings provide a method to encode unique codes for a wide variety of items. The coding is based on the OSI Object Identification (numeric form) as defined by the ISO 8824 Standard. A UID is made up of 2 parts: a root and a suffix. The root is registered by an organization with NEMA. No one else will be authorized to use this root. The usage of the suffix is then the responsibility of that organization. The root "1.2.840.10008" is reserved for DICOM and may UIDs using this root can be found in the DICOM Data Dictionary. A UID should not be coded as to contain data in it self but should be treated as a whole and reference a single interpretation.
UL an Unsigned Long type of VR.
Ultra Sound (US) A modality that uses high frequency sound waves to create images.
US an Unsigned Short type of VR.
Undefined Length the ability to specify an unknown length for a Data Element Value (of Value Representation SQ, OW, or OB) or Item. Data Elements of Undefined Length are delimited with a Sequence Delimitation Items and Item Delimiter Data Elements

 

V

Value A component of a Value Field. A Value Field many consist of one or more Values.
Value Field The last component of a Data Element. The Value Field is always made up of an even number of bytes. The data held in this field is padded if needed to make it have even length. The data held in this field must conform to the rules given by the VR for the Data Element.
Value Length (VL) A mandatory component of a Data Element that specifies the length of the Value Field.
Value Multiplicity (VM) Specifies the number of Values contained in the Value Field of a Data Element.
Value Representation (VR) an optional component of a Data Element. The VR is the data type of the information in the Value Field of the Data Element. DICOM defines many of these data types and defines them in PS 3.5 of the DICOM standard. Each VR is enumerated by a 2 character code. The codes are: AE, AS, AT, CS, DA, DS, DT, FL, FD, IS, LO, LT, OB, OW, PN, SH, SQ, SS, ST, TM, UI, UL, US. Each of these is defined else where in this glossary. The use of the VR in the Data Elements depends on the negotiated Transfer Syntax for the Data Set. The VR can be either Explicit or Implicit.

Specifies how to interpret the Data Element Value. All VRs are defined in the PS 3.5. Some examples of VR are: AE (Application Entity), DA (Date), US (unsigned Short). The negotiated transfer syntax determines whether the VR field needs to be included in the Data Element. See Value Representation Explicit, Value Representation Explicit.

Value Representation, Explicit Indicates that the VR is to be included in each Data Element in the Data Set
Value Representation, Implicit Indicates that the VR is not to be included in each Data Element in the Data Set. The VR of each Data Element must be looked up in the Data Dictionary.
VL see Value Length.
VM see Value Multiplicity.
VOI see Value Of Interest.
VOI LUT see Value Of Interest.
VR see Value Representation

 

W

Width see Window
Window the continuous range of pixel values that are to be displayed on a computer monitor as distinct intensity values. Pixel values above the Window range are displayed as all white and those below the Window are displayed as all black.
Window Center the pixel value that falls in the center of the Window range. Changing the Window Center changes the brightness of image.
Window Width the number of pixel values within the contrast Window. Half of the Width is above the Center and half are below it. Changing the Window Width changes the contrast of the image.