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.