Teleradiology: DICOM & RADIOLOGY


ACR Bulletin
October 1996

The Importance and Use of the Standard

by Steven C. Horii, M.D., Chair
Committee on ACR-NEMA Standards

Members of the ACR, in conjunction with medical imagingequipment manufacturers represented by the National Electrical Manufacturers Association (NEMA), have been active for 14 years in establishing standards for the electronic connection of medical imaging equipment. These connections, or interfaces, were first developed in response to College member requests for a manner in which digital imaging modalities (at the time only CT, nuclear imaging, and some ultrasonography) could output images and associated information in a nonproprietary format. The result was the ACR-NEMA Digital Imaging and Communications Standard, first published in 1985.

The objectives of the DICOM (Digital Imaging and COmmunications in Medicine) standard are (i) to promote communication of digital image information, regardless of manufacturer, (ii) to facilitate the development and expansion of PACS that can interface with other systems of hospital information, and (iii) to allow the creation of diagnostic information databases that can be accessed by a wide variety of devices distributed geographically.

The rapid growth of digital imaging in radiology and the increasing use of computer communications systems prompted the ACR-NEMA Committee to re-engineer the ACR-NEMA standard to accommodate these recent advances. The result, DICOM, has been very successful. Its widespread adoption is evident from the number of vendors
demonstrating their hardware at the annual RSNA meetings since 1992. The success of the standard is such that other specialties using digital imaging, such as cardiology, gastrointestinal endoscopy, dentistry, pathology, dermatology, and others have turned to the ACR-NEMA Committee for assistance in applying DICOM to their imaging needs. The DICOM standard was specifically developed to be general enough to encompass the wide variety of medical images used throughout healthcare. The long-term objective is to avoid different standards for different medical images so that electronic patient records that include images can be both stored and transmitted. The leadership evidenced by radiology through the ACR has been well recognized, as other specialties and international standards efforts begin to adopt DICOM.

The maturity of DICOM is such that its specification by radiologists and radiology administrators for new equipment purchases should be routine. Though no standard with the flexibility of DICOM can guarantee that devices meeting
the specification will communicate, interfacing equipment that conforms to DICOM is much simpler than developing customized solutions. If a vendor claims to be "DICOM conformant," the purchaser may insist on reviewing that vendor''s DICOM Conformance Statement, a formal part of the Standard. A purchaser may not be sufficiently experienced with DICOM to fully understand the implications of conformance statements. In that case, the purchaser should request that the vendors involved review their respective conformance statements and either warrant that their
devices will communicate properly and meet the user''s needs or provide a plan for achieving proper operation.

There is little in the way of current imaging equipment that does not have digital input and output. This includes imaging devices, as well as film digitizers, workstations, and film printers. All of the major radiology equipment vendors and a majority of the smaller ones support DICOM in at least some of their products. Even if a facility does not have
a PACS, the use of DICOM can simplify connecting equipment to a printer or workstation, setting up a teleradiology system, or distributing images to nonradiology clinical areas.

For many years, the ACR has supported its members working on DICOM. Their effort has resulted in a standard that is showing its benefits in radiology as well as for other users of medical imaging. Radiologists are encouraged to become familiar with the standard and to seek conformance with the standard in equipment purchases. The College intends to develop informational material to assist radiologists in using the standard in these purchase decisions.


For those with World Wide Web access, additional information on DICOM is available on the ACR-NEMA DICOM home page at http://www.acr.org/standards.html or at http://www.nema.org/medical/ (the NEMA home page).

OVERVIEW OF THE DICOM STANDARD

The standard consists of 13 parts. This modular design was done to facilitate expansion and updating without the need to republish the entire standard.

Part 1 of DICOM provides an overview of the standard. It presents a description of the design principles, defines many of the terms used, and gives a brief description of all of the parts.

Part 2 covers conformance to DICOM. It specifies the general requirements which must be met to claim conformance and specifies the information which must be present in a conformance statement.

Part 3 describes how information objects, abstractions of real information entities (e.g., CT image, results information), are defined.

Part 4 contains service class specifications. A service class associates one or more information objects with one or more commands to be performed on these objects. For example, the query/retrieve service class supports basic operations to access and move images based on simple search criteria (e.g., get all of the images of a particular patient).

Part 5 addresses the encoding rules necessary to construct a data stream to be conveyed in a DICOM message. The main function of this part can be thought of as defining the language that two devices will use to speak to one another.

Part 6 is the complete listing of all data elements along with their numeric names, their text names, their representation (text, floating-point number, etc.), whether they contain one or more items, and what the allowed values are for those elements that can only take on certain values.

Part 7 specifies the operations and protocol used to exchange messages.

Part 8 defines the services and protocols used to exchange messages in a networked environment.

Part 9 defines the services and protocols used to exchange messages in point-to-point communications.

Part 10 specifies a general model for the storage of medical imaging information on removable media. It provides a framework allowing the interchange of various types of medical images and related information on a broad range of physical storage media.

Part11 specifies standard subsets of elements from the various other parts of the DICOM standard used to build media interchange applications to a specific clinical need.

Part 12 defines specific media and file systems used by the application profiles.

Part 13 defines a point-to-point connection environment that supports the DICOM print service class for direct connection of imaging equipment to printers (where no network is used).