1. An image processing device for detecting line structures in an image data set, comprising: a model definition unit for defining a line model of a line structure to be detected, said line model comprising a number of voxels; and said line model configured to define a two-dimensional rectangular line model having a predetermined length and width, a calculation unit for calculating, per voxel of interest of said image data set, several correlation values of a correlation between said line model and an image area around said voxel of interest, said image area comprising a corresponding number of voxels as said line model, wherein for each of a number of different relative orientations of said line model with respect to said image area a respective correlation value is calculated, and wherein said calculation unit is configured to calculate, per pixel of interest of two-dimensional image data set, several correlation values of a correlation between said two-dimensional rectangular line model and a two-dimensional image area around said pixel of interest, and a determining unit for determining, per voxel of interest, the maximum correlation value from said calculated correlation values and the corresponding optimal orientation at which said maximum correlation value is obtained.