DICOM Digital Imaging Communications in Medicine

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DICOMDigital Imaging Communicationsin Medicine
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Communication Protocols Key to Connectivity

• Layered Model, each layer performs a specific
  function
• Set of Services and Protocols
• Connectivity requires sharing of a complete
  protocol
• Communication requires a shared Semantic Context

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ISO Reference Model
File Transfer, E-mail, HTTP
APPLICATION
Upper Layers (DICOM)
Data Formatting, Compression,Encryption
PRESENTATION
Synchronization,Comm. Management
SESSION
End-to-End communication
TRANSPORT
Internetworking
NETWORK
Lower Layers
LLC
DATA LINK
MAC
Ethernet, FDDI, etc.
PHYSICAL
Fiber, Coax, UTP, µWave
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Communication Standards

• Protocols are defined by standards
• A Standard is an agreement which may be
  voluntary, Government mandated, or International
  Law
• Protocols may also be proprietary

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Who Defines Communication Standards?

• User Consortia (e.g., HL7)
• Organizations (e.g., NEMA, IEEE)
• US Government Agencies (e.g., ANSI, NIST)
• Foreign Government Agencies (e.g., CEN)
• United Nations (e.g., ISO, CCITT)

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ACR-NEMA

• 1982 - ACR and NEMA form a joint committee
• 1985 - Publication of Version 1.0
• 1988 - Compression and Mag Tape Standards
• 1988 - Publication of Version 2.0
• 1989 - Began work on Network Version with HIS/RIS

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DICOM

• The name was changed to separate the standard
  from the originating body
• 1991 - Release of Parts 1 and 8 of DICOM
• 1992 - RSNA demonstration, Part 8
• 1993 - DICOM Parts 1-9 approved,
  RSNA demonstration of ALL parts
• 1994 - Part 10 Media Storage and File Format
• 1995 - Parts 11,12, and 13 plus Supplements

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The Parts of the DICOM Standard

• Part 1 - Introduction and Overview
• Part 2 - Conformance
• Part 3 - Information Object Definitions
• Part 4 - Service Class Definitions
• Part 5 - Data Structures Semantics
• Part 6 - Data Element Listing and Typing
• Part 7 - Message Exchange Protocol
• Part 8 - Network Support for Message Exchange
• Part 9 - Point-to-Point Support

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The Parts of the DICOM Standard

• Part 10 - Media Storage and File Format
• Part 11 - Media Storage Application Profiles
• Part 12 - Media Formats and Physical Media
• Part 13 - Print Management Point-to-Point

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DICOM Application Domain
Storage, Query/Retrieve, Study Component
Print Management
Query/Retrieve Results Management
Media Exchange
Query/Retrieve, Patient Study Management
Information Management System
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Summary of DICOM Features

• NETWORK PROTOCOL
• DICOM incorporates negotiation to permit nodes 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 includes encapsulated image and multi-frame
  syntaxes
• 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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Summary of DICOM Features

• Off-Line Media Support
• DICOM defines a directory structure and media
  profiles
• CONFORMANCE
• DICOM requires conformance statements and
  contains detailed conformance requirements

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DICOM Terminology

• DICOM Message Service Element (DIMSE) - The set
  of DICOM Application Layer communication
  services.
• DIMSE Service Group (DSG) - A subset of the full
  DIMSE services which is applicable to a specific
  IOD.
• Information Object Definition (IOD) - A data
  abstraction of a class of real-world objects. A
  collection of related attributes (data elements).

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DICOM Terminology

• Service Class - A set of functionality relating
  to a single type or real-world activity. Composed
  of a set of SOP Classes plus rules and associated
  semantics.
• Service-Object-Pair Class (SOP) - The atomic unit
  of DICOM functionality. Composed of an IOD and a
  DIMSE Service Group plus restrictions or
  extensions of the IOD. (Equivalent to an Object
  Class)

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Service-Object Pair Class
Data Dictionary
DIMSE Service Group
Information Object
SOP
Real-World Object
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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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Conformance

• DICOM Part 2 specifies the structure of a
  conformance statement
• DICOM does not specify a test suite or a
  compliance verification mechanism
• All DICOM implementations must be supported by a
  properly constructed conformance statement

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DICOM Conformance Statement

• Implementation Model which describes the
  Application Entities in the implementation
• Detailed specification of Application Entities
• SOP Classes supported
• policies for initiation and acceptance of
  associations
• Presentation Contexts
• SOP options
• Supported communications protocols
• Specializations
• Configuration

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Purpose of a Conformance Statement

• Allow a user to determine which optional
  components of the DICOM Standard are supported by
  a particular implementation, and what extensions
  or specializations an implementation adds.
• By comparing the Conformance Statements from two
  implementations, a knowledgeable user should be
  able to determine whether or not interoperability
  is possible.

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DICOM Conformance Testing

• No Formal Mechanism is Defined in the Standard
• Committee for the Advancement of DICOM
• Define initial test plan and cross-connect matrix
• Future RFP for organization to monitor the
  process
• Problem How to Map DICOM Conformance Statements
  into Test Plans

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The DICOM Explosion

• Joint CEN-DICOM development
• Medicom DICOM
• MIPS 95 work is underway with JIRA
• ISC Harmonization is also in progress
• HL7 Harmonization continuing interest
• New DICOM organization
• Companies NEMA and non-NEMA
• ACR, ACC, CAP, ...
• individuals

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Summary

• Networking is a critical component of all medical
  imaging systems
• Support for Open Communication Standards is a
  MUST
• DICOM is here, NOW
• DICOM products exist on the market
• DICOM is emerging as THE common protocol for
  medical image communication - WORLD WIDE!