(Radiographics. 2000;20:287-293.)
© RSNA, 2000
Potential Use of Extensible Markup Language for Radiology Reporting: A Tutorial1
Cun Wang, PhD and
Charles E. Kahn, Jr, MD
1 From the Office of Clinical Informatics, Medical College of Wisconsin, 9200 W Wisconsin Ave, Milwaukee, WI 53226-3522. Recipient of a Certificate of Merit award for an infoRAD exhibit at the 1998 RSNA scientific assembly. Received April 13, 1999; revision requested July 6 and final revision received September 20; accepted October 1. Supported in part by The Whitaker Foundation. Address reprint requests to C.E.K.
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Abstract
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One of the main goals of radiology is to communicate imaging information to aid in patient management. Information standards can facilitate communication and help realize this goal. Extensible Markup Language (XML) is a new information transmission standard that was developed to meet the growing need for robust, large-scale World Wide Web applications. XML notation provides a compact document representation scheme that allows radiology reports to be transmitted over the Web as universally understandable, self-defining documents. XML documents can include a report-specific document type definition (DTD) that defines the allowable data fields and values. XML may also be used to generate data entry forms for radiology reporting and help physicians improve the efficiency of the reporting process. XML documents can be used to store reporting results directly, thus allowing pertinent data to be shared on the Web. An XML-based approach can allow users to link information to entities outside the information systems of a given institution. XML-based methods and applications have the potential to promote development of robust radiology reporting systems and integration with broader, enterprise-wide information systems.
Index Terms: Computers • Internet • Radiology and radiologists
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Introduction
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A central goal of the practice of radiology is to communicate imaging information to aid in making decisions regarding patient care. This information goes not only to physicians but also to a growing number of automated systems that assist clinicians in delivering care. Such systems archive, retrieve, and present patient-oriented information; mediate between information sources and users; and integrate patient-specific information and general medical knowledge. Information standards allow information systems from different vendors, at different sites, and on different platforms to communicate with one another.
The explosive growth of the World Wide Web demonstrates the power of a simple standard—Hypertext Markup Language (HTML)—to promote interaction among information systems. HTML is a language for transmitting multimedia hypertext documents (1). HTML-based documents have been used to capture and display radiology results (2,3).
Despite its simplicity and ubiquity, HTML has several limitations. It allows only a single, fixed type of document. Users cannot specify their own tags or attributes to parameterize or otherwise semantically qualify their data. HTML does not support the specification of deep structures needed to represent database schemas or object-oriented data for structural validity (4). Extensions to HTML often result in incompatibilities among vendors (5).
HTML is based on Standard Generalized Markup Language (SGML), an international standard for document interchange endorsed by the International Standards Organization (ISO 8879:1986) that has been used in industrial, governmental, and academic applications for 13 years (6). Unfortunately, the complexity of SGML makes it ill-suited for use on the Web. Extensible Markup Language (XML), which is also based on SGML, was created to bring the power of SGML to the Web. In this article, we introduce the general features of XML, describe the use of XML for radiology report information, and analyze the potential of XML-based systems for radiology results reporting.
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What Is XML?
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XML is a proper subset of SGML and preserves its key features— extensibility, structure, and data-checking—to create robust, large-scale Web applications (4,7). XML has been adopted by the World Wide Web Consortium (5,8) and has received support from major software vendors such as Microsoft (Redmond, Wash), Sun Microsystems (Mountain View, Calif), Netscape Communications (Mountain View, Calif), Adobe Systems (San Jose, Calif), and International Business Machines (IBM) (Armonk, NY) (9). It is also being incorporated into health information standards such as Health Level Seven (HL7) (10,11).
As with SGML, XML allows authors to define the structure of documents to represent database schemas or object-oriented hierarchies. XML omits the more complex and less-used parts of SGML such as the SGML declaration and tag minimization (12). Because XML is a subset of SGML, existing SGML "parsers" and tools can be applied to XML documents. The use of XML is particularly attractive in light of the ability to incorporate distributed software modules (eg, Java applets) that embed powerful data manipulation capabilities into Web clients (4). XML documents can serve as the objects upon which such distributed software components operate (13).
The structure of an XML document can be defined in a Document Type Definition (DTD) included within the document or referenced from an external source. Simply stated, a DTD defines the elements contained in the document and the relationships among the elements. The content of the document (document instance) follows the DTD. In a sense, the DTD specifies a grammar for the documents to which it applies.
The DTD specifies the names of the allowable elements in the document, how often a given element may appear, and the order in which the elements appear. An element consists of an opening tag (eg, <NAME>), specific contents, and a closing tag (</NAME>). For "empty" elements that contain no other elements, the closing tag can be omitted by including a forward-slash character at the end of the opening tag (eg, <ITEM/>). Elements can be nested to arbitrary depth. Attributes that further describe the element can appear within the angle brackets of the opening tag.
Figure 1 shows how an author can incorporate the definition of data elements within the document itself.
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Figure 1. Incorporation of the definition of data elements within an XML document. In this document, programs that can be used to interpret XML (parsers) have specified the patient's name (John Harrison) and identification number (5021029413) within the <Name> and <PID> elements, respectively.
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Structured Reporting
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Diagnostic imaging information can be used for population-based health policy decisions, and it is becoming increasingly important for radiologists to provide information that can be aggregated locally, regionally, and nationally for outcomes analysis. The desire to analyze outcomes and other measures across institutions has led to the development of standardized reporting lexicons such as the Breast Imaging Reporting and Data System (14,15) and the Fleischner Society's thoracic imaging vocabulary (16,17). These vocabularies can form the basis for structured reporting applications.
Unlike conventional "free-text" reports, structured reports incorporate a standardized set of concepts in a predefined format. A practical goal of structured reporting applications is to capture most of the information in structured format and allow free-text comments as needed. The major advantages of this approach include reduced transcription costs and turn-around times, increased report completeness, greater usefulness of cases for teaching and research, and improved quality assurance, utilization review, and health services research efforts. Efforts to apply structured reporting to radiology date from the 1960s and have included the UltraSTAR (Ultrasound Structured Attribute Reporting) system at the Brigham and Women's Hospital (18) and the chest radiography reporting system at Johns Hopkins Medical Institutions (19).
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XML in Radiology Structured Reporting
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Report Definition
XML documents can include a report-specific DTD that defines the allowable data fields and values; the resulting report is both portable and self-defining (20,21). Thus, the DTD explicitly describes the structure of a report and the relationships of the incorporated concepts to each other and to other medical concepts. An alternative to reporting with predefined structured formats is to try to impose structure onto the report after the fact. For example, the MedLEE system provides a tool for parsing natural-language reports that encodes the parsed report into XML (22). Natural-language processing may inform model building, but algorithms that would replace manual modeling have not yet been discovered (23). An ongoing challenge is the development of formalisms and tools to help build appropriate models such as DTDs to represent the content of radiology reports. Such DTDs could include a conventional set of modifiers (eg, degree of certainty, chronicity, change from previous examination) for each reporting concept.
Data Entry
Because XML is created for use on the Web directly, it may also be used to generate data entry forms for radiology reporting. XML parsers and some programs may generate specific data entry forms according to user definitions. These forms are very important in radiology structured reporting systems. A well-defined data entry form can help physicians improve the efficiency of the reporting process. To generate these data entry forms, different report templates are necessary to record different findings for a variety of examinations and diseases. XML-based report templates can be easily and effectively mapped to Web browsers through XML parsers or some specific programs. For example, binary (yes/no) reporting elements can be rendered as form objects (eg, checkboxes), and physicians can enter information about a specific patient by simply clicking on these form objects.
Structured Platform-Independent Data Entry and Reporting, or SPIDER, is a developmental system for radiology reporting that can accommodate a wide variety of structured reporting applications (2). It was initially developed for use with HTML and has since been generalized for use with SGML and XML (20). With SPIDER, hierarchically organized reporting concepts are represented as familiar graphical objects such as text windows, checkboxes, and radio buttons in Web data entry forms. Each reporting concept may be a single data element, a collection of data elements (GROUP), or a block of repeated data elements (REPEAT). Three types of data items—binary, numeric, and textual—can be defined. Binary items are indicated by the <BIN> tag and have a Boolean value of either 1 (true) or 0 (false). Numeric items (<NUM>) allow entry of uni- or multidimensional numeric values. Textual items (<TXT>) allow entry of one or more lines of narrative text data. Figure 2 shows a report definition for aortic US that is written in SPIDER's Data-entry and Reporting Markup Language (3). Figure 3 shows a report data entry form for aortic US generated with the SPIDER system.
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Figure 2. Report definition for aortic ultrasound (US) written in Data-entry and Reporting Markup Language. The Concept Identifier (CID) attributes refer to the unique identifier of the concept in the UMLS Metathesaurus. Concept relationship (CREL) attributes indicate the relationship between the reporting concept and that in the external vocabulary; for example, LT indicates that the concept in the report is narrower in scope than the externally referenced concept.
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Report Generation
XML documents can be used to store reporting results directly, thus allowing pertinent data to be shared on the Web. SPIDER can be used to create an XML document with a report-specific DTD and document instance. The DTD defines a given reporting application (eg, aortic US) and can be reused for all similar reports. The document instance encodes the values entered for a specific individual. Figures 4 and 5 show the DTD and the document instance generated with the SPIDER system in structured reporting for aortic US. The elements and their contents, such as the element Aorta–Ultrasound and its four sub-elements—Clinical–Information, Aorta, Common–Iliac–Arteries, and Comments—are defined in the DTD.
Vocabulary and Data Linking
One potential advantage of an XML-based approach is the ability to link information to entities outside the information systems of a given institution. For example, SPIDER allows reporting concepts to be linked to external vocabularies such as the National Library of Medicine's Unified Medical Language System (UMLS) Metathesaurus. UMLS allows concepts to be communicated across disparate sources of biomedical information such as bibliographic databases, diagnostic coding schemes, and other medical vocabularies (24,25). Even if a reporting domain does not have a standardized vocabulary, the reporting terms can be mapped to the UMLS to allow interchange with other information systems.
In addition, reporting applications in SPIDER can specify that certain input fields receive data directly from a local or remote computer system. For example, a radiology report could incorporate specific laboratory test results for a given patient by querying the laboratory information system for results of the patient's most recent serum creatinine test. The World Wide Web Consortium is developing an XML Linking Language and is specifying constructs that can be inserted into XML resources to further describe links between objects (26).
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Discussion
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XML offers a number of advantages for radiology reporting. Although XML is a relatively new standard, it derives a strong foundation from prior work with SGML and can take advantage of SGML-based reporting platforms. The newest generation of Web browsers (eg, Microsoft Internet Explorer 5.0, Netscape Communicator 5.0) will be able to interpret XML documents. Many database management systems are moving rapidly to support XML (27). The use of XML affords opportunities to link radiology reporting information with relational or object-oriented databases.
XML has close relationships with other interchange protocols for radiology and health care data. The Digital Imaging and Communications in Medicine (DICOM) standard specifies a nonproprietary data interchange protocol, digital image format, and file structure for biomedical images and image-related information (28). DICOM includes a proposed standard for structured reporting and has a syntax that can readily be expressed in SGML (29). Efforts are underway to use XML as the document interchange protocol for the HL7 standard. As a result, HL7 will use XML as a format for structured reporting as well. Users can select XML, DICOM, HL7, and so on to transfer patient data to other systems or institutions according to the requirements of a particular implementation (29).
Distributed object computing protocols such as CORBA (Common Object Request Broker Architecture) or DCOM (Distributed Component Object Model) allow fast, flexible implementation of Web-based software systems. Client-side software components such as Java applets and "ActiveX" objects can readily be incorporated into Web documents and can add functionality to Web browsers. XML can facilitate communication among such distributed software objects and can play an important role in the exchange of data between client and server software components. For example, a Web-based applet could allow a user to drag a patient's folder icon from the Web application of a hospital to the internal database application of a home health care agency to transfer information into that database (4).
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Conclusions
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XML notation provides a compact document representation scheme that allows radiology reports to be transmitted over the Web as universally understandable, self-defining documents. XML is poised to play an important role in many aspects of radiology reporting. It can be used to build robust radiology reporting systems and integrate them with broader, enterprise-wide information systems.
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Footnotes
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Abbreviations: DICOM = Digital Imaging and Communications in Medicine
HL7 = Health Level Seven
HTML = Hypertext Markup Language
SGML = Standard Generalized Markup Language
SPIDER = Structured Platform-Independent Data Entry and Reporting
UMLS = Unified Medical Language System
XML = Extensible Markup Language
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Top
Abstract
Introduction
