A computer implemented method for performing fusion of 3D image data, which represent at least a part of a patient's body, with two 2D images of the patient's body with a known spatial relation between the viewing directions of the 2D images, comprising the steps of: —acquiring the 3D image data, —acquiring the two 2D images, —calculating two virtual images from the 3D image data, the two virtual images corresponding to the two 2D images, —classifying the two 2D images into a primary and a secondary image, —determining a primary alignment between the primary image and the corresponding virtual image such that they match, —calculating a spatial axis relative to the viewing directions of the two 2D images from the primary alignment and a predetermined point which is imaged in the virtual image which corresponds to the primary image, wherein the spatial axis is a line in space on which the predetermined point lies, and —performing fusion of the 3D image data with the two 2D images based on the calculated spatial axis in order to obtain a virtual position of the 3D image data in space.