Nowadays, biomedical images of the human body are an invaluable source of information that clinicians can use in order to make a correct and final diagnosis. Their use is widespread in almost every branch of medicine. In some cases, computer-aided diagnosis (CAD) tools have received approval for being used without any human intervention and validation, like, for example, in breast cancer detection relying on X-rays mammograms. In this paper we present a framework for building CAD tools based on the well-known software design patterns and an implementation of the first modules of a CAD tool for computed tomography (CT) colonography.