Norme DICOM introduction

Standard DICOM in Medical imagery

Elementary base:

A directed standard object, a specific language often difficult to include/understand...:

Standard DICOM is directed object, that means that each object DICOM (generally image) contains at the same time the informations(le name of the patient, the pixels of the image...) and the methods (or functions) which must undergo this information.

Example:

information: an image IRM or scanner..., in language DICOM: Object Information . .
methods: to print and/or back up, in DICOM a Service .

Processing DICOM of information consists in pairing an object DICOM(for example an image) with a specific function or Service to be applied to this object (to print, back up, etc.).

Thus the combination of " Object Information " (by ex an image) with " a Service " (for example impression of this image) is called: Even Service/Object or SOP .

Object information + Class Service = Service / Even Object or SOP

or, for example:

An Image + Its Impression = a service DICOM

This Information/Service parity is the element principal of conformity to the standard. A machine in conformity to the standard must manage a class of Service/Objet parity at least and not only to emit or collect files of images to standard DICOM.

To conform to a Class of Parity Objet/Service (SOP Class) a machine (or any applicative entity DICOM, Application Entity AE ) must be able to manage a particular type of image and to carry out a specific type of processing (or service) corresponding to the definition of this Class of Parity, DICOM defines all the classes of possible parities.

In addition the Class of Objet/Service Parity must specify if service DICOM is employed as a user ( Service Class User or SCU ) or as a provider ( Service Class Provider SCP ). Example: A scanner uses the service which provides him the reprographe, the scanner is then equipped with a Class of Service User SCU for reprographe, the reprographe on its side is equipped with a Class of Service Provider, SCP for the scanner.

Another example:

For example, if a machine of IRM implements 3 classes of services DICOM as a user: Then, these three classes allow to be connected to 3 machines DICOM if they implement the following classes:

Class service To use of a workstation, (the IRM can use the workstation)
Class service To use of a station of filing, (the IRM can use a program of filing DICOM)
Class service To use of a reprographe, (the IRM can use a reprographe DICOM)

The workstation must implement a Service Class Provider for the IRM
The station of filing must implement a Service Class Provider for the IRM

The reprographe: must implement a Service Class Provider for the IRM

In terminology DICOM:

The Application Entity AE " IRM " implements:

SCU of Workstation
SCU of Archive
Print Class To use of Printer

AE " IRM " transmits objects DICOM to 3 other AE, applicatives entities (machines or programs) which implement the corresponding classes of service

AE workstation: manage classes SCP for MR.
AE Archive station: manage classes SCP for MR.
AE reprographe: manage Printer Class Provider for MR.

Realization practises connection of 2 machines:

When a applicative entity (a scanner) has an Object DICOM (an image to be reproduced), if it is in conformity DICOM to use class of service of impression (Service Class User of Printer), then it addresses itself to an Entity Applicative (the reprographe) which provides a class of service of corresponding impression (Service Class Provider for CT).

It then results a phase from it from negotiation during which the machines agree on the type of data to be exchanged and the way in which it will exchange them (for example, for a word of two bytes, they agree to transmit the most significant byte in first). **time-out** this phase make it possible to establish the " Presentation Context ", the way in which be exchange the information (the syntax of transfer ) be call Be worth Representation ( VR ), if the byte the more significant be transmit in first, it himself act of a VR Little Endian in the case reverse one speak of VR big endian.

The various syntaxes of transfer suggested by Entitées DICOM are indexed in the Documents of Conformity.

Currently available classes of Service in the standard:

Classes of Service: Type of Service:

Checking (Checking Class Service)
Used for the tests, allows to know if the machines " get along " mutually, this class is not associated with an object DICOM, it returns information in the form of an echo. (C-ECHO)

Storage(Storage Class Service)

Media Storage Class Service

Allows the transfer and the backup of the images between two entities DICOM. (Cr, Ct, Mr. Storage Class Service)

There is an alternative: Media Storage Class Service which specifies the exchanges between 2 machines by the intermediary of a media (CD rom, diskettes etc...)

Query/Retrieve
Implement standard commands: FIND, MOVE, GET. FIND makes it possible to require a list of image, MOVE and GET make it possible to initiate a transfer, which into carried out will be carried out via the class " Storage Service Class "

Study Content Notification
Used to notify the arrival of a new image or series of images, can be used to initiate a transfer or to check if the transfer of a series of image is complete.

Print Management
Allows the connection with a reprographe, specifies the type of image, (Colors, levels of gray etc.)

Patient Management
Allows to interface the machine with hospital network PACS or HIS/RIS ( Hospital Information Service / Radiological Information Service )

Management of the data of the patients, demography, admission and output of the patients

Study Management
Creation, management of appointment, follow-up of the examinations.

Result Management
Allows the management of the results of the examinations.

What means " Full Dicom "?

It is about an expression nondefined in the standard, it seems that " Full Dicom " means that the machine implements the totality of the Classes of Service enumerated above.

Classes of Service:	Type of Service:
Checking (Checking Class Service)	Used for the tests, allows to know if the machines " get along " mutually, this class is not associated with an object DICOM, it returns information in the form of an echo. (C-ECHO)
Storage(Storage Class Service) Media Storage Class Service	Allows the transfer and the backup of the images between two entities DICOM. (Cr, Ct, Mr. Storage Class Service) There is an alternative: Media Storage Class Service which specifies the exchanges between 2 machines by the intermediary of a media (CD rom, diskettes etc...)
Query/Retrieve	Implement standard commands: FIND, MOVE, GET. FIND makes it possible to require a list of image, MOVE and GET make it possible to initiate a transfer, which into carried out will be carried out via the class " Storage Service Class "
Study Content Notification	Used to notify the arrival of a new image or series of images, can be used to initiate a transfer or to check if the transfer of a series of image is complete.
Print Management	Allows the connection with a reprographe, specifies the type of image, (Colors, levels of gray etc.)
Patient Management	Allows to interface the machine with hospital network PACS or HIS/RIS ( Hospital Information Service / Radiological Information Service ) Management of the data of the patients, demography, admission and output of the patients
Study Management	Creation, management of appointment, follow-up of the examinations.
Result Management	Allows the management of the results of the examinations.