An ontology for PACS integration

Abstract

An ontology describes a set of classes and the relationships among them. We explored the use of an ontology to integrate picture archiving and communication systems (PACS) with other information systems in the clinical enterprise. We created an ontological model of thoracic radiology that contained knowledge of anatomy, imaging procedures, and performed procedure steps. We explored the use of the model in two use cases: (1) to determine examination completeness and (2) to identify reference (comparison) images obtained in the same imaging projection. The model incorporated a total of 138 classes, including radiology orderables, procedures, procedure steps, imaging modalities, patient positions, and imaging planes. Radiological knowledge was encoded as relationships among these classes. The ontology successfully met the information requirements of the two use-case scenarios. Ontologies can represent radiological and clinical knowledge to integrate PACS with the clinical enterprise and to support the radiology interpretation process.

Fig 1

Top-most classes in ontology of radiology procedure information. A screen capture of the ontology in the Protégé ontology editor is shown. The top-most class, Radiology Information Model Entity, subsumes all other classes, which have an “is–a” relationship to their parents. The ontology is shown as a tree as demonstrated in this figure, with child classes shown indented and below the parent classes.

Fig 2

Ontology frame for the Chest PA radiology procedure step. This class has many attributes, specifying the information that describes details of this procedure step, such as the acquisition method, imaging plane, radiographic position, and page in Merrill's Atlas where the details of this procedure step are described.

Fig 3

Using the ontology of radiology procedures to determine whether all necessary images have been acquired for a study to be interpreted at the PACS workstation. This information is identified as follows: (A) look up the exam orderable (“CXR”), (B) determine the requested procedures needed to fulfill that orderable (“Chest PA and Left Lateral”), and finally (C) identify the images that are acquired in that requested procedure (“Chest PA” and “Chest Left Lateral”). The radiologist can also determine that images to be interpreted on the PACS workstation actually meet the technical requirement of the exam that was ordered by looking at the detailed specification of the procedure steps associated with those images (D; also see Fig. 2).

Fig 4

Using the ontology of radiology procedure information to find images from a patient taken in the same imaging plane. The classes in the Radiology Imaging Procedure Step hierarchy (Fig. 1) can be searched for those procedures that are acquired in the frontal plane (Chest PA Step, Chest AP Step, and CT Chest Scout AP; left side of the figure). Images in the PACS archive belong to particular series that correspond to these procedure classes in the ontology; accordingly, the chest PA, chest AP, and CT chest scout series could be retrieved by the PACS system. Thus, the ontology contains the information needed to inform the PACS manager which series to retrieve that contain frontal images of the chest (right side of figure).