To observe a catheter advancing in a vessel system, a 3D model of the vessel system is reconstructed with the help of differently oriented X-ray projections generated by a C-arm system during the injection of a contrast agent. Moreover, the voltage recovery device reduces the overall transmission losses in a utility power system. The hub is mounted on, or pivots on, the base and supports the blade units. The hollow chamber can fill with molten metal to form a core that aids in orienting the body in a narrow end downward position. In one embodiment at least 4 optical surfaces are provided that are arranged in at least one volume which is optically conjugate with the volume of the refractive optical element.