Your Practice's Digital Future
Heard of DICOM and XML? Learn how these data exchange standards will link all of your diagnostic instruments and allow them to communicate via the Web.
By John J. Michon, M.D., Stanford, Calif.

Powered by the relentless improvement in the performance-to-cost ratio of computer chips, the use of Information Technology (IT) in ophthalmic practice will continue to increase, and its impact on workflow will be pervasive. However, for you to take full advantage of those changes in your practice, it must become possible to integrate a diversity of clinical devices into systems that can communicate and exchange information with each other.

In this article, I'll review two important electronic communication standards currently in development that will make that happen: Digital Imaging and Communications in Medicine (DICOM) and Extensible Markup Language (XML). Before we delve into these standards and how they will be applied, let's take a broader view of the state of IT today.

From dial tone to "Web tone"

The Internet and its dominant application, the World Wide Web, represent revolutionary technological advances. Information in the form of text, data, graphics, audio and video can be transmitted between any two networked devices that share a common set of technical standards. With advances in related technologies, such as wireless transmission, optical fiber and networking software, the promise of a truly universal system for information exchange now exists.

One way to think about the Internet is as an extension of our familiar wired telephone network. Our houses and offices contain one or more wall outlets into which we can plug any standard telephone and be connected to a dial tone. We can make calls to anywhere in the world and exchange voice messages. Now, consider the future, where a world full of devices will be able to access a "Web tone" to connect to the Internet and World Wide Web. Each house or office will contain hundreds of Web tone connections, and many will be wireless. These will carry every form of data, not just voice. Text, numerical data, graphics, still images, audio, video -- anything that can be digitized -- will be transmitted. Most devices in your practice, including the phoropter, slit lamp, ophthalmoscope and fundus camera will have a Web connection.

Standards and limitations

One of the most important lessons we've learned from the explosive success of the Web is the enormous utility of standards in IT. The first phase of Web development, including the standard for data transmission (TCP/IP), the Hypertext Transfer Protocol (HTTP) and other protocols, has allowed a highly interoperable system to evolve. Any computer system that complies with these standards can communicate and exchange data with any other computer on the Internet. This allows enormous flexibility and adaptability in the network. But these standards operate at low levels of data exchange, and mostly involve machine processes that are invisible to the computer user.

Even standards that are accessible to users, such as Hypertext Markup Language (HTML), have limitations. Web pages are all written in HTML, which is translated by your browser software into the familiar format that you see on any Web site. However, HTML has what's called a "fixed tag set." This means that only predefined ways to describe page elements can be included in a Web page, making it difficult for users to customize them. HTML tags are used primarily in formatting and display of Web contents, such as bold face or indentation for a new paragraph.

The Semantic Web and XML

That's where XML comes in. To get around the limitations of current standards, the Web's governing body, the World Wide Web Consortium (W3C), has identified a second phase of development called the Semantic Web. The purpose of the Semantic Web is to allow Web pages to express their meaning in a way that's logical and accessible to people as well as computers. Data annotated in this way can explicitly describe information, not simply specify its display. Deduction, logical inference, and more effective search strategies are possible when Web documents allow their content and meaning to be known in this structured manner.

A major component of the Semantic Web will be XML, which extends the functionality of HTML. As the name implies, XML extends the limited range of expression possible with HTML. XML intentionally separates the content of a Web page from its format. In this manner, the essential meaning of the document (its semantics) can be manipulated independently of the way it's actually displayed on a device. User-defined attributes and values may be included, allowing specialized representation of domain data.

This has profound implications for health care and ophthalmology in particular. For example, a medical record could be modeled as a series of integrated Web pages. Information in each Web page could then be understood by other computer programs so that data exchange, analysis and intelligent information retrieval are possible. Queries such as "Show me all Type I diabetics over 70 years old with macular edema whose acuity improved after grid photocoagulation" can be modeled in the data structure of XML. This metadata, or data about data, (such as age and diabetic status in this example) may be easily represented using XML and made explicit for complex searches carried out by you. Further advantages are that XML is platform-neutral, open and universal, and has been tailored for use over the Internet. It's compatible with HTML and supported by most modern browsers.

An important part of the function of XML is schemas -- a framework for XML documents that describes their conforming structures and vocabulary. Schemas essentially tell what information is contained in a document and how it is interrelated. Schemas allow software to understand data structure without any prior built-in description. (That is, the description is provided by the schema accompanying an XML-containing Web page.)

XML was published as a W3C recommendation in February 1998, and has enjoyed rapid acceptance. As an adjunct to the basic XML standard, tools to implement XML and extend its function have been created. One of the most important has been extensible style sheets. Once data is expressed in XML format, it can then be displayed in a variety of formats on different devices. For example, a PC screen may display high-resolution graphics, whereas a handheld device would have a much smaller screen and be more suitable for display of simpler text or numerical data.

Using style sheets, it's possible to assemble information from multiple sources and transform it for delivery into any XML-supported format. For example, technician and physician notes, fundus photos, ultrasound, and other studies can be combined as needed to generate medical reports. Furthermore, this data can be easily integrated with administrative data, insurance coverage and other, nonmedical information, depending on the user's needs.

Where DICOM fits in

As you know, as an ophthalmologist, you're heavily dependent on images, which you usually obtain via different instruments from different manufacturers. Again, before you can fully experience the benefits of IT advances in your practice, these instruments must be able to communicate with each other as well as with external reporting systems. DICOM is the standard that allows this to occur.

DICOM is the main international standard for the transmission of digital images. It was introduced in 1983 by a joint committee of the American College of Radiology and the National Electrical Manufacturers Association to foster closer cooperation between the imaging industry and the user community. The goal was to assure that digital images acquired on systems from different manufacturers could be freely exchanged. For example, a CT image acquired on a General Electric scanner could be displayed on a Siemens system.

Because many specialties besides radiology are heavy users of images, DICOM has expanded to include a variety of medical domains. DICOM groups have formed in mammography, ultrasound, and, of course, ophthalmology. (See "Developing the Standards".) Images used in ophthalmic practice include visible light (external, biomicroscopic, and fundus photography), angiographic, ultrasound, radiographic and many others.

To create a unified and accessible record, imaging machines will have to be DICOM-compliant. In addition to fostering efficiency, this protects the often large investment in imaging equipment that you make.

Putting it all together

As you can see, XML and DICOM are important standards driving developments in IT for ophthalmic practice. They offer freedom from proprietary IT systems and will allow seamless integration of devices into the medical data flow. These standards protect your investments by making a diverse set of machines interoperable. And, finally, they streamline the flow of medical information and make it accessible to the most important advance in computing in the last decade -- the World Wide Web. 

Dr. Michon is a member of the clinical faculty of the Department of Ophthalmology at Stanford University School of Medicine. He's also a researcher at the School's Section on Biomedical Informatics.