A method for modelling a composition of an object of interest comprises segmenting object of interest image data provided by computer tomography image data resulting in a plurality of image segments. A determined Hounsfield density value is then extracted from the object of interest image data for each image segment. A component ratio of at least two component classes is defined for the object of interest, the at least two component classes having different component Hounsfield density values. At least one component class is assigned to each image segment based on the corresponding determined Hounsfield density value resulting in simulated image segments comprising the component Hounsfield density values. The simulated image segments define simulated image data of the object of interest, where a ratio of the assigned component classes corresponds to the component ratio. A deviation between the simulated image data and the object of interest image data is then determined.