This article originates from the need to introduce semantic aspects in the retrieval procedures in Medical Information Systems. Our working database records documents which gather various type of information : medical images (X-rays, MRI, tomography...), data on the patient's civil and clinic identity, and examination report. A retrieval process should answer to queries involving both explicit alphanumeric data from the document and information that is carried by the images. We propose a data model that allows content-based retrieval for the images. The image is viewed as pairs of iso-semantic regions and signals in respect with an anatomic and a pathological model. A graphical interface is also provided for the users to index the images and formulate the queries.