What is DICOM

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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.

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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.

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DICOM Application Domain
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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

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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

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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

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DICOM Service Classes

• Composite
• Verification
• Storage
• Query/Retrieve
• Study Content Notification
• Normalized
• Patient Management
• Study Management
• Results Management
• Basic Print Management

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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)

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DIMSE-C Services

• DIMSE-C services
• Operations
• C-Store
• C-Get
• C-Move
• C-Find
• C-Echo
• No notification services

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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.

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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.

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DIMSE-N Services

• DIMSE-N services
• Operations
• N-Get
• N-Set
• N-Action
• N-Create
• N-Delete
• Notifications
• N-Event-Report

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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.

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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.

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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.

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DICOM Service-Object Pair (SOP)
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DICOM Messages

• DICOM communication involves the exchange of SOP
  instances with use of DICOM messages.
• The DICOM message is the communication version of
  the SOP class.
• It contains the commands that use or provide the
  specified service and the data objects.
• To be learnt further..)

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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...))

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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.

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DICOM File Header
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DICOM File Header

• The meaning of some fields
• 00020010 --gt Reports the structure of the image
  data
• 00280002 --gt Samples Per Pixel
• 00280004 --gt Photometric Interpretation
• 00280100 --gt Bits Allocated
• ...

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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

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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.