1. A method for determining a position of a brain sulcus in the brain of a patient, the method comprising executing, on at least one processor of at least one computer, steps of: a) acquiring, at the at least one processor, patient image data describing a digital medical image of at least part of the brain, wherein the digital medical image is represented by a data set representing a curved surface which is defined in three dimensions; b) acquiring, at the at least one processor, atlas data describing an image-based model of the at least part of the brain; c) determining, by the at least one processor and based on the patient image data and the atlas data, mapping data describing a transformation between the patient image data and the atlas data, wherein the atlas data describes color values defining the image-based model and the patient image data describes color values defining the digital medical image, and wherein the mapping data is determined by comparing the color values of the atlas data to the color values of the patient image data, wherein each color value defining the digital medical image is associated with a type of anatomical tissue and each color value defining the image-based model is associated with information about a type of anatomical tissue; d) determining, by the at least one processor and based on the patient image data, the atlas data, and the mapping data, sulcus position data describing the position of the brain sulcus in the digital medical image, wherein the sulcus position data is determined in a projection of the digital medical image onto a planar surface which is defined in two dimensions; e) determining, based on the mapping data, the atlas data, and the patient image data, tissue type data describing at least one type of anatomical tissue described by the digital medical image and the position of the at least one type of anatomical tissue in the digital medical image; f) determining, based on the tissue type data, sulcus mask data describing a binary mask which can be applied to the digital medical image for masking it in order to differ, in the digital medical image, between the union of cortical grey brain matter and cortical cerebrospinal fluid on the one hand and white brain matter on the other hand; and g) filtering the sulcus position data by applying a two-dimensional filament detection filter to the sulcus position data to enhance image contrast of the sulcus.