Development of applications which use these 3-D images poses technical challenges above and beyond the reconstruction and display of the images themselves.   In particular, users need a symbolic – word based – tool in order to access images of entities which are not displayed on the computer screen. In this paper we address the challenge of how to construct a system for navigating 3-D anatomical images that is both computationally tractable and useful in the context of medical education.

     We are building a system for navigating 3-D anatomical images associated with anatomical concepts linked together by a semantic ontology, a set of concepts linked by meaningful, formally-defined relations.  In what follows, we describe a prototype ‘curriculum-driven ontology’developed specifically for use as a study tool  in conjunction with the interactive pelvis lesson designed by the second author of this paper [3] for use in the clinical anatomy course required of all first-year medical students at Columbia University.

     A sample screen for the prototype curriculum ontology appears in Figure 1. The prototype can be viewed at http://cds.cpmc.columbia.edu/vesalius/kb/index.html readers should be aware that it is a work in progress.

     In the left-hand window is an image of the urethra, reconstructed from the Visible Human Dataset; this image can be rotated 360 degrees.   In the right-hand window is the ‘concept space’ for the urethra, a fragment of the ontology displaying anatomical entities which are related it in anatomically significant ways.   The concept label is highlighted in the blue rectangle.  A fragment of the ontology which shows those entities most closely related to the pelvis are also shown, with lines and arrows indicating different kinds of relations.   The straight lines indicate a taxonomic (or classificational) relationship.  The urethra is one of the pelvic viscera (viscus[pelvis]), as are the bladder, rectum, prostate, vas deferens, and seminal vesicle.  The urethra is also a component of the pelvic urinary system (urinary system[pelvis]), along with the bladder and ureters; the ‘component’ relation is  indicated by the lines with circles at each end.

     Clicking on the label for another entity brings up an image of the entity and its concept space.  For example, clicking on urinary system[pelvis], brings up an image of the pelvic urinary system—i.e., the urethra, bladder and ureters in their normal position relative to each other-- and  of the fragment of the ontology which shows entities related to pelvic urinary system . Each of the component entities listed can be viewed individually.

     Students can use the study application to view the anatomical images that the professor talked about in class, and put them together and take them apart.  The significance of the anatomical image is reinforced by the simultaneous view of the ontology, which emphasizes the anatomical entity’s relations to other entities.

     The tool described in this paper is part of the Vesalius Project of the Columbia University Division of Health Sciences. [2], in this volume, describes some of the imaging techniques under development for use in this project. Ultimately, the 3-D anatomical images and the anatomical ontology will reside in a knowledge base that is part of an application-independent mechanism linking  a wide spectrum of curriculum applications[5].  We plan to use the ontology as the basis for  a system to  navigate the large collection of electronic anatomical images  needed for these applications; ultimately we hope to provide a complete ‘body map’ of the human anatomy. [6], also in this volume, presents an overview of the Vesalius Project.