In cardiac CT, it is the goal to acquire data for a full scan as fast as possible. For this reason, gantry rotation is increased further and further, such that the G-forces on the tube of the devices on the gantry become a limiting factor. Alternatively, the temporal resolution of scans can be doubled by mounting two complete tube-detector assemblies onto the gantry. However, this solution doubles the costs for the tube-detector assembly. According to the present invention it is proposed to modify one of the tube-detector assemblies such that one detector has a reduce size. Then, information from another detector is used to supplement scanning results from the detector with reduced size.