1. A method for providing a live 3D image of a body lumen, comprising the steps of: determining the 3D shape of a flexible surgical tool in the body lumen using optical shape sensing; taking an x-ray image of the body lumen, at least one of said body lumen and said surgical tool being radiopaque; segmenting a 2D projection of the tool in the x-ray image; and calculating a pose recovery matrix using the determined 3D shape and the segmented 2D projection.