Computers in Biology and Medicine 36 (2006) 768 – 788 www.intl.elsevierhealth.com/journals/cobm Computation of semantic similarity within an ontology of breast pathology to assist inter-observer consensus Olivier Steichen a , Christel Daniel - Le Bozec a, b, ∗ , Maxime Thieu a , Eric Zapletal a, b , Marie-Christine Jaulent a a INSERM U729, F-75006, Paris, France b Medical Informatics Department, Georges Pompidou Hospital, Paris, France Received 5 April 2005; accepted 5 April 2005 Abstract Computer-assisted consensus in medical imaging involves automatic comparison of morphological abnormalities observed by physicians in images. We built an ontology of morphological abnormalities in breast pathology to assist inter-observer consensus. Concepts of morphological abnormalities extracted from existing terminologies, published grading systems and medical reports were organized in an taxonomic hierarchy and furthermore linked by the relation “is a diagnostic criterion of” according to diagnostic meaning. We implemented position-based, content-based and mixed semantic similarity measures between concepts in this ontology and compared the results with experts’ judgment. The position-based similarity measure using both taxonomic and non-taxonomic relations performed as well as the other measures and was used for automatic comparison of morphological abnormalities within the IDEM computer-assisted consensus platform.  2005 Elsevier Ltd. All rights reserved. Keywords: Multimedia knowledge representation; Ontology; Semantic similarity; Similarity measures; Computer-assisted consensus; Breast pathology 1. Introduction Pathologists describe specimens to provide relevant diagnostic and prognostic information to guide patient care. Many studies have shown that intra- and inter-pathologist variability is large and therefore ∗ Corresponding author. INSERM U729, Université Paris Descartes, Faculté de médecine, 15 rue de l’école de médecine 75006 Paris, France. Tel.: +33 1 42 34 69 86; fax: +33 1 53 10 92 01. E-mail address: christel-lebozec@spim.jussieu.fr (C.D.-L. Bozec). 0010-4825/$ - see front matter  2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.compbiomed.2005.04.014