Steven C. Horii, MD
The initial goal in developing a standard for the transmission of digital images was to enable users to retrieve images and associated information from digital imaging equipment in a standard format that would be the same across multiple manufacturers. The first result was the American College of Radiology (ACR)-National Electrical Manufacturers' Association (NEMA) standard, which specified a point-to-point connection. However, the rapid evolution of computer networking and of picture archiving and communication systems meant that this point-to-point standard would be of limited use. Consequently, a major effort was undertaken to redesign the ACR-NEMA standard by taking into account existing standards for networks and current concepts in the handling of information on such networks. The Digital Imaging and Communications in Medicine (DICOM) standard was the result of this effort. Its popularity has made discussion, if not implementation, of the standard common whenever digital imaging systems are specified or purchased.
The DICOM standard is extremely adaptable, a planned feature that has led to the adoption of DICOM by other specialties that generate images (eg, pathology, endoscopy, dentistry). The fact that many of the medical imaging equipment manufacturers are global corporations has sparked considerable international interest in DICOM. The European standards organization, the Comitâ Europâen de Normalisation, uses DICOM as the basis for the fully compatible MEDICOM standard. In Japan, the Japanese Industry Association of Radiation Apparatus and the Medical Information Systems Development Center have adopted the portions of DICOM that pertain to exchange of images on removable media and are considering DICOM for future versions of the Medical Image Processing Standard. The DICOM standard is now being maintained and extended by an international, multispecialty committee.
The DICOM standard has become the predominant standard for the communication of medical images. However, even though the standard is widely available from manufacturers and is rapidly expanding to include nonradiologic imaging, most radiologists' understanding of it is limited. In part, this is because DICOM has a "steep learning curve" and most introductory material has been written either for the engineer and is highly technical, or for the administrator and is rather superficial.
Why all the interest in what would seem to be a simple task? The answer is that it is not as simple as it first appears. Most radiologists are familiar primarily with film images, and film can be viewed anywhere there is a light source. It is the transition from film images to digital images and the need to communicate, display, and store these images that has made DICOM necessary. With film, slight differences in exposure, processing, and viewing will have little effect in these areas. In digital imaging, however, the difference of a few bytes can make it impossible to transfer an image from one system to another.
The DICOM standard consists of multiple documents (1); as of this writing, there are 13 published parts. Each DICOM document is identified by title and standard number, which takes the form "PS 3.X-YYYY," where "X" is commonly called the part number and "YYYY" is the year of publication. For example, DICOM Part 2 has a title of "Conformance" and document number PS 3.2-1996. In informal usage, the year is often dropped.
In this article, a basic, nontechnical introduction to DICOM is presented that will enable the reader to understand the basic concepts and principles used in the standard. A number of key terms and their definitions are listed in the Appendix at the end of this article.
1. National Electrical Manufacturers' Association. Digital Imaging and Communications in Medicine (DICOM). Rosslyn, Va: NEMA, 1996; PS 3.1-1996-3.13-1996.
From the Department of Radiology, University of Pennsylvania Medical Center, 3400 Spruce St, Philadelphia, PA 19104. Received July 10, 1997; accepted July 16. Address reprint requests to the author.
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