DICOM is a standard for handling, storing, printing, and transmitting information in medical imaging. It was developed by NEMA and ACR to enable sharing of digital medical images between devices. DICOM defines formats for medical images and communication protocols for transferring those images and associated reports between devices. It allows for images from different manufacturers and facilities to be shared through the use of unique identifiers and a standardized data format.

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.