1. A method for reconstructing a 3D image from 2D X-ray images acquired with an X-ray imaging system, said method comprising the steps of: a) receiving a set of 2D X-ray images of a region of a patient with said X-ray imaging system, b) computing an initial 3D image within the coordinate system of the X-ray imaging system by using the complete set of 2D X-ray images with their respective projective geometry data; c) projecting said initial 3D image on each of said 2D X-ray images and adjusting the respective projective geometry data of said 2D X-ray images by registration of each 2D X-ray image with the projection of the initial 3D image using an image-to-image registration technique which determines an affine transform or a warping transform that displaces the four corners of each image independently; d) computing an updated 3D image using the complete set of 2D X-ray images with their respective adjusted projective geometry data.