The main components of a multimodality medical image interpretation system (MMIIS) are: (1) a user interface, (2) an image database, storing image objects along with their description, (3) expert systems (ES) in various medical imaging domains and particularly in image processing (IP), and (4) an IP actor, toolbox of standard IP procedures. To implement such a system, we are building two prototypes: one with an object-oriented (OO) expert system and one with a classical logical expert system. In these two different approaches, we have to model the medical imaging objects and represent them. Both approaches use an OO data model even if its implementation is different in: (1) the characteristics of each ES, in managing knowledge and inferences (uncertainty, non-monotonicity, backward and forward chaining, meta- knowledge), (2) the environment to implement the different experts and to activate IP procedures, and (3) the communication means between the experts and the other components. In the OO approach, an ES based on smalltalk is used, and in the conventional one an adhoc Prolog ES was built. Our goal is to compare their advantages and disadvantages in implementing a MMIIS.