The present invention proposes an apparatus and method for characterizing a tissue in a first region of a subject. The apparatus comprises a receiving unit (210) for receiving ultrasound data of the tissue in the first region and ultrasound data of a predetermined target reference tissue of said subject; a deriving unit (220) for deriving a subject-specific model of the target reference tissue on the basis of the ultrasound data of the target reference tissue; and a characterizing unit (230) for determining a match between tissue in the first region and the target reference tissue on the basis of the subject-specific model and ultrasound data of the tissue in the first region. Unlike conventional tissue characterization based on a large cohort of patient data, the proposed subject-specific model is personalized for the specific subject without any generalization, resulting in higher sensitivity and/or accuracy. Preferably, the subject-specific model of the target reference tissue is derived on the basis of both the ultrasound data of the target reference tissue and the ultrasound data of a background reference tissue of a different type than the target reference tissue.