A method for determining or updating a registration between a 3D image of a region of interest and a set of at least two 2D images of the same region of interest includes selecting at least one respective contour point in the 3D image for each 2D image. A 2D position of a respective depiction of each contour point is determined in the respective 2D image. At least one condition for the registration parameters that needs to be fulfilled is determined, for each contour point, to map the respective contour point to the respective 2D position in the respective 2D image. An updated set of registration parameters is determined by solving a set of equations or an optimization problem that depends on the conditions.