The invention relates to simulating 2D X-ray images from 3D CT data. A user can access a repository of CT data of a patient's anatomy 2 by using a computer network system. The CT data has been obtained by a CT scanning of the patient 1. Firstly, the user retrieves the CT image data 3 and a 3D image is generated 4. Secondly, the user may orient the CT image in any orientation desirable with respect to a virtual X-ray source and a virtual image plane. And thirdly, a 2D X-ray image is simulated 6 from the chosen viewpoint and shown to the user.