Abstract: An imaging method for radiologically guiding an instrument during medical interventions on an object is disclosed. First, a prior volumetric image of the object is provided, followed by periodically providing a current volumetric image on-the-fly during the intervention to an operator by measuring an undersampled set of projections of the object and reconstructing the current image based on changes between the prior volumetric image or an updated prior image and the undersampled set of projections. The method and corresponding system are used for radiologically guiding medical interventions on an object. The system includes a first image provider, an imaging apparatus for measuring undersampled sets of projections, and a processor. The processor communicates with the imaging apparatus for providing updated images on-the-fly during the intervention by reconstructing the updated image based on changes between the first image or an update of the first image and the undersampled sets of projections.