CDA stands for Clinical Document Architecture (previously also known as PRA -Patient Record Architecture, which is part of the HL7 standard) and is expected to incorporate references to DICOM objects such as images. Diagnostic report applications are mostly encoded and exchanged in the HL7 domain and it is because of this that a mapping of DICOM to HL7, especially version 3 (which uses XML for encoding) and into the clinical document architecture (CDA) of HL7 is very appropriate.

XML (Extensible Markup Language) is a popular emerging standard encoding technology, and is considered by many to be suitable for distribution of all kinds of information in a client-server environment. XML deals with presentation; it is merely an encoding scheme, it conveys syntax, but no intrinsic semantics. The encoding function provided by XML can be compared with the tag/length/value structure of a DICOM data element. If two communicating applications do not share the same semantic XML tag definition, no interchange interoperability exists, despite the fact that the tag may be humanly readable.

HL7 is migrating to XML encoding (starting with version 3.0) to provide for a more powerful mechanism for encoding messages than the existing ASCII. SR (Structured Report) objects encoded in DICOM can be translated into XML (and vice versa) within the context of a specific implementation for e.g. an Ultrasound OB/GYN report or a cardiology procedure log. HL7 structured documents (SD) can be referred to in DICOM instances, using the DICOM standard SOP Class/Instance paradigm and attributes. The Object Identifier (OID) of the Hierarchical (Message) Definition of the HL7 document class is used as the SOP Class UID for DICOM reference purposes. The SOP Instance UID contains the HL7 Instance Identifier (II). A UID is assigned for use within the DICOM Data Set that is mapped to the native Instance HL7 Identifier. In support of clinical reports encoded in both SR and CDA formats, the SR object has a reference to its equivalent CDA document CDA is designed to support professional society recommendations, national clinical practice guidelines, standardized data sets, etc.

From the perspective of CDA, the ASTM CCR is a standardized data set that can be used to constrain CDA specifically for summary documents. The resulting specification, known as the Continuity of Care Document (CCD), is being developed as a collaborative effort between ASTM and HL7.