A method of improving the volume reconstruction in navigationally guided operations is provided. In certain implementations, a phantom which contains X-ray positive marks and marks detectable by a position detection system in a fixed spatial relation to each other is positioned in the region of the volume being investigated on the subject. For the volume reconstruction, a series of 2D X-ray projection images can be created, each of them containing, alongside the structures of the subject being examined, the images of the X-ray positive marks of the phantom as image information. Each 2D data set is transformed by a familiar method, in which, for example, the mechanical deviations of a real-world C-arm type X-ray diagnostic machine are identified by a kinematic model and are corrected. The transformed 2D data can be used for the volume reconstruction, and the volume model with the position information of the X-ray positive marks is relayed to a navigation system.