1. A system for determining an effective cross-sectional area of a tubular cardiovascular structure to enable assessment of blood flow through the tubular, cardiovascular structure, the system comprising: an image interface for obtaining a three-dimensional image of the tubular cardiovascular structure; a segmentation subsystem for segmenting the three-dimensional image to obtain a segmentation of a lumen inside the tubular cardiovascular structure; an analysis subsystem configured for i) determining a centerline of the tubular cardiovascular structure, the centerline representing an assumed direction of blood flow through the lumen, ii) using the segmentation of the lumen, determining an apparent flow aperture of the tubular cardiovascular structure in a direction of the centerline; and iii) determining the effective cross-sectional area of the tubular cardiovascular structure based on the apparent flow aperture; wherein the segmentation subsystem is configured for obtaining the segmentation of the lumen of the tubular cardiovascular structure by applying a deformable model to the three-dimensional image, the deformable model comprising a representation of the lumen of the type of tubular cardiovascular structure, said applying comprising fitting the deformable model to image data of the three-dimensional image to obtain a fitted model representing the segmentation of the lumen; wherein the deformable model represents a plurality of anatomical landmarks, and wherein the analysis subsystem is configured for determining the centerline of the tubular cardiovascular structure based on positions of the plurality of the anatomical landmarks in the fitted model.