A method for extracting a geometric parameter from a cardiac tomography data set. The method includes providing a cardiac tomography data set and a region of interest, computing an approximative model of a surface of interest, computing a plurality of normal vectors associated with a respective surface coordinate from the approximative model of the surface of interest, computing a plurality of biopsy data sets, each biopsy data set being oriented along a respective normal vector from the plurality of normal vectors, computing an exact model of the surface of interest from the plurality of biopsy data sets, and computing the geometric parameter on a basis of the exact model of the surface of interest.