What is DICOM? The standard for Digital Imaging and Communications in Medicine. Developed by the National Electrical Manufacturers Association (NEMA) in.

What is DICOM?

The standard for Digital Imaging and Communications in Medicine. Developed by the National Electrical Manufacturers Association (NEMA) in conjunction with the American College of Radiology (ACR). Covers most image formats for all of medicine. Specification for messaging and communication between imaging machines.

A little history

The first version was ACR-NEMA, released in 1985. Its goal in developing a standard was

• To enable users to retrieve images and associated information from digital imaging equipment in a standard format using point-to-point connection.

• To hide differences same across multiple image equipment manufacturers.

To handle developing network and image standarts, a new standart, DICOM, was proposed in 1981.

DICOM Application Domain

MAGN

ETOM

Information Management System

Storage, Query/Retrieve, Storage, Query/Retrieve, Study ComponentStudy Component

Query/RetrieveQuery/RetrieveResults ManagementResults Management

Print ManagementPrint Management

Media ExchangeMedia Exchange

LiteBox

Summary of DICOM Features

NETWORK PROTOCOL● DICOM incorporates negotiation to permit peers to

agree on the functions to be performed MESSAGE ENCODING

● DICOM defines 24 data types (V2.0 had 4)● DICOM message encoding includes JPEG

compression (17 varients)● DICOM supports multiple character repertoires

Summary of DICOM Features

OBJECT DATA MODEL● DICOM is based on a completely specified data model ● DICOM includes a robust UID mechanism

DATA DICTIONARY● DICOM includes a large number of new data elements

SERVICE CLASSES● DICOM defines classes of service for specific

applications (e.g. image management, printing) and conformance levels

DICOM Objects

Things such as images, reports, and patients are all objects and are called information objects.

Two kinds of objects in DICOM:

• Composite objects (Old objects inherited from NEMA).

• Normalized objects (New objects defined in DICOM). All objects and their format constitutes Data Dictionary. DICOM uses UIDs to identify information objects, such as the

images, reports, or transfer syntaxes. The form of the UID conforms to an international standard.

• 1.2.840.10008 is the root and the same for every DICOM UID.

• Example: UID for the DICOM explicit VR little endian transfer syntax is 1.2.840.10008.1.2.1

DICOM Service Classes

Composite● Verification● Storage● Query/Retrieve● Study Content Notification

Normalized● Patient Management● Study Management● Results Management● Basic Print Management

DICOM Service Elements

Complex services are built using service elements, called DICOM message service elements, or DIMSEs.

There are both composite and normalized services for composite and normalized information objects.

There are 5 DIMSEs that are used for composite information objects (called DIMSE-C) and 6 that are used for normalized information objects (called DIMSE-N).

Two categories of DIMSEs:

• operations (such as "store")

• notifications (such as "event report”)

DIMSE-C Services

DIMSE-C services:

• Operations:

• C-Store

• C-Get

• C-Move

• C-Find

• C-Echo

• No notification services

DIMSE-C Services

The C-STORE service is invoked by a DIMSE-service-user to request the storage of Composite SOP Instance information by a DIMSE-service-user.The C-FIND service is invoked by a DIMSE-service-user to match a series of Attribute strings against the Attributes of the set of SOP Instances managed by a DIMSE-service-user. The C-FIND service returns for each match a list of requested Attributes and their values.The C-GET service is invoked by a DIMSE-service-user to fetch the information for one or more information objects from a DIMSE-service-user, based upon the Attributes supplied by the invoking DIMSE-service-user.

DIMSE-C Services

The C-MOVE service is invoked by a DIMSE-service-user to move the information for one or more Composite SOP Instances from a DIMSE-service-user, to a third party DIMSE-service-user, based upon the Attributes supplied by the invoking DIMSE-service-user.The C-ECHO service is invoked by a DIMSE-service-user to verify end-to-end communications with a DIMSE-service-user.

DIMSE-N Services

DIMSE-N services:

• Operations:

• N-Get

• N-Set

• N-Action

• N-Create

• N-Delete

• Notifications:

• N-Event-Report

DIMSE-N Services

N-EVENT-REPORT service is invoked by a DIMSE-service-user to report an event about a SOP Instance to a DIMSE-service-user.N-GET service is invoked by a DIMSE-service-user to request the retrieval of information from a DIMSE-service-user.N-SET service is invoked by a DIMSE-service-user to request the modification of information by a DIMSE-service-user.

DIMSE-N Services

N-ACTION service is invoked by a DIMSE-service-user to request a DIMSE-service-user to perform an action.N-CREATE service is invoked by a DIMSE-service-user to request a DIMSE-service-user to create an instance of a information object.N-DELETE service is invoked by a DIMSE-service-user to request a DIMSE-service-user to delete an instance of a information object.

DICOM Service-Object Pair (SOP)

The service classes and information objects are combined to form SOP.

The SOP class is the elemental unit of DICOM. Everything that DICOM does is based on the use of SOP

classes.

DICOM Service-Object Pair (SOP)

SOPSOP

Data DictionaryData Dictionary

Information Object Information Object DIMSE Service ElementDIMSE Service Element

DICOM File Format (Overview)

A single DICOM file contains:

• A header (which stores information about the patient's name, the type of scan, image dimensions, etc)

• Image data (in compressed (bitmap) or uncompressed form (jpeg, gif...))

DICOM File Header

DICOM requires a 128-byte preamble (usually set to zero).

'D', 'I', 'C', 'M' letters comes next. The rest is the real header information in

groups.• For example: group 0002hex is the file meta

information group.

DICOM File Header

DICOM File Header

The meaning of some fields:• 0002:0010 --> Reports the structure of the

image data

• 0028:0002 --> Samples Per Pixel

• 0028:0004 --> Photometric Interpretation

• 0028:0100 --> Bits Allocated

• ...

Association Services

Before everything, Association establishment must be done. During Association establishment, A DIMSE-service-user exchanges initialization information.The initialization information includes:

• Application context

• DIMSE-specific user information

• DIMSE service information

• Presentation and session requirements

Association Services

A-ASSOCIATE Service is invoked by a DIMSE-service-user with related parameters to establish an Association with another DIMSE-service-user. Association release is done using A-RELEASE and A-ABORT services.