A process for the positioning of the focus of a magnetic nanoparticles leading to a destination and / or on the destination, of a magnet system with at least one magnet generated magnetic gradient field, which magnet system with an x-ray device is or will be registered, wherein by means of the x-ray apparatus, at least a three-dimensional, the destination location pointing image data set is received, the position of the destination manually and / or automatically in the image data set or a derived from the image data set is determined, and automatically, taking into account of the registration of the focus is positioned so that it coincides with the position of the destination.
