DICOM spec introduction

1. 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.

2. 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.

3. DICOM Application Domain
MAGN
ETOM
Information Management System
Storage, Query/Retrieve,
Study Component
Query/Retrieve
Results Management
Print Management
Media Exchange
LiteBox

4. 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

5. 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

6. 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

7. DICOM Service Classes
 Composite
● Verification
● Storage
● Query/Retrieve
● Study Content Notification
 Normalized
● Patient Management
● Study Management
● Results Management
● Basic Print Management

8. 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”)

9. DIMSE-C Services
 DIMSE-C services:
• Operations:
• C-Store
• C-Get
• C-Move
• C-Find
• C-Echo
• No notification services

10. 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.

11. 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.

12. DIMSE-N Services
 DIMSE-N services:
• Operations:
• N-Get
• N-Set
• N-Action
• N-Create
• N-Delete
• Notifications:
• N-Event-Report

13. 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.

14. 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.

15. 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.

16. DICOM Service-Object Pair (SOP)
SOP
Data Dictionary
Information Object DIMSE Service Element

17. 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...))

18. 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.

19. DICOM File Header

20. 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
• ...

21. 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

22. 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.