The development of PACS image databases has long been thought of as a major technological challenge, due to the amount of data to be managed. On the contrary, the authors think that despite major improvements in storage technology, new data management techniques must be proposed to make image databases medically useful in PACS environments. More precisely, image databases must contain not only images per se, but also the description of all objects used in medical imaging, in order to permit the remote processing, analysis, and interpretation of images. In several other papers, the authors explain why they adopted an object-oriented approach to model information in medical imaging. In this paper, the focus is on the inventory of objects manipulated in medical imaging from a qualitative viewpoint. For this purpose, a large number of representative imaging procedures were selected. The authors characterized how they are asked for by clinicians, realized in imaging departments, and consumed by requiring physicians and surgeons, in three French university hospitals. On the basis of this inventory, a set of image data -- i.e. of objects used in medical imaging -- was defined to show that this set must evolve with advances in medical imaging, and to point out that relational DBMS concepts cannot represent all image data.