1. A device for the three-dimensional reconstruction of flow conditions in a vascular system using two-dimensional projections of the vascular system during a contrast-medium injection, comprising; an imaging device for producing two-dimensional projection pictures of the vascular system taken from different directions; an injection device for controlled injection of a contrast medium into the vascular system; a control unit that is coupled to the imaging device and that is designed to drive the imaging device in accordance with the following steps: a) production of projection pictures taken from the same projection direction at a high picture-taking rate during inflow of the contrast medium after a contrast-medium injection; b) rotation of the imaging device around the vascular system and production of projection pictures taken from different directions while the vascular system is filled with the contrast medium; c) production of projection pictures from a fixed direction during drainage of the contrast medium from the vascular system.