An introduction to DICOM

Digital Imaging Communications in Medicine (DICOM), a set of comprehensive communication standards, was developed to promote interoperability of digital imaging devices in human medicine.1-3 Before DICOM, digital image formats in human medicine were not standardized, and digital images created on one manufacturer's equipment could not be viewed on a competing manufacturer's workstation. This lack of standardization not only hampered the exchange of information among physicians but also exerted undue pressure on hospitals to purchase equipment from the same manufacturer.3 The American College of Radiology and the National Electrical Manufacturers Association recognized the need to develop imaging and data standards and addressed it by jointly developing DICOM,4 which is now the accepted imaging standard in human medicine.

Although digital imaging is relatively new to veterinary medicine, it is becoming increasingly important that the profession standardize its digital format so we do not suffer the same difficulties human medicine faced. Consequently, the American College of Veterinary Radiology (ACVR) supports the use of DICOM as the digital imaging standard for veterinary medicine and sponsors a committee (DICOM workgroup 25) to incorporate veterinary terminology and nomenclature into the DICOM standard.

Jonathan T. Shiroma, DVM, MS, DACVR

DICOM BASICS

Making up the most basic level of dicom, which is also the most relevant to veterinary medicine, are standards for image exchange between senders and receivers. Several different types of images (e.g. JPEG, RLE, JPEG-LS, JPEG 200) can be used in DICOM files.4 While DICOM is commonly referred to as a type of image, it is not—it's an image format. DICOM files consist of image pixel data and precise attributes (identification, management, and acquisition information) combined with services (e.g. commands for transmitting data), resulting in service-object pair (SOP) classes. SOP classes represent the basic unit of DICOM conformance: Devices can be a service class user, which sends images, or a service class provider, which receives images and stores them for the user.1,2,5

Implementing digital imaging typically involves adopting some format for archiving images and for distributing images (and associated data) to workstations and, possibly, outside the hospital (e.g. to other veterinarians or veterinary radiologists). DICOM is the tool that permits standardized communication among various devices (e.g. acquisition device, archive device, display device).3

CONFORMANCE

As discussed earlier, DICOM is well-accepted in human medicine and has been adopted by manufacturers of imaging devices. However, there are many facets (or layers) involved in exchanging DICOM files among different devices. Because of the multitude of functions and transfer syntaxes involved, not all DICOM devices can communicate with each other.1

To determine whether exchanges can be performed between different devices, manufacturers of human imaging devices (as well as some veterinary vendors) voluntarily create DICOM conformance statements to unambiguously define what the devices can exchange and in what specific manner.2 These statements permit users to determine in advance whether devices can communicate with each other.

Not all digital imaging devices currently being sold in veterinary medicine are DICOM-compatible. DICOM capability is sometimes considered an additional option with an associated fee.

IMAGE DISPLAY

Although digital imaging makes it possible for images to be exchanged and displayed at multiple locations, the grayscale depiction of these images can differ on various workstations. To promote identical grayscale image display on different monitors and consistent hard-copy images from various printers, the DICOM committee developed a lookup table to display digitally assigned pixel values. To use the DICOM grayscale standard display function (GSDF), images must be viewed (or printed) on devices that have this lookup curve or on devices that have been calibrated to the GSDF curve.6

SUMMARY

DICOM is the accepted standard in human medicine for exchanging medical images and is supported by the ACVR as the digital imaging standard in veterinary medicine. DICOM is also useful in interfacing image data with medical information systems (e.g. practice management software), although, to date, this interface is of limited availability in veterinary medicine. DICOM is a proven technology that is continuing to develop and is rapidly being adopted by medical disciplines outside diagnostic imaging. As a result, the list of objects supported by DICOM is expanding to include nonimaging data such as electrocardiograms, hemodynamic and audio waveforms, and procedure logs.5

Jonathan T. Shiroma, DVM, MS, DACVR

MedVet Medical Center for Pets

300 E. Wilson Bridge Road

Worthington, OH 43085

REFERENCES

1. Bidgood WD Jr, Horii SC. Introduction to the ACR-NEMA DICOM standard. Radiographics 1992;12:345-355.

2. Horii SC. Primer on computers and information technology. Part four: a nontechnical introduction to DICOM. Radiographics 1997;17:1297-1309.

3. Clunie DA. DICOM, PACS, and veterinary radiology, in Proceedings. Am Coll Vet Radiol Annu Sci Mtg 2005.

4. National Electrical Manufacturers Association. Digital imaging and communications in medicine (DICOM) standard. Rosslyn, VA: NEMA, 2006 PS 3.1, PS 3.2, PS 3.14.

5. Clunie DA. DICOM implementations for digital radiography. In: Samei E, Flynn MJ, eds. Advances in digital radiography: RSNA categorical course in diagnostic radiology physics. Oak Brook, Ill: RSNA, 2003;163–172.

6. Krupinski EA, Roehrig H. The influence of a perceptually linearized display on observer performance and visual search. Acad Radiol 2000;7:8-13.