A computed tomography (CT) imaging apparatus includes an X-ray source to emit X-rays a plurality of photon-counting detectors (PCDs) arranged in a circular ring between the X-ray source and a CT detector and processing circuitry to cause the X-ray source and the CT detector to perform a helical scan of an object to obtain projection data extract, from the obtained projection data, a plurality of sets of projection data corresponding to a plurality of X-ray tube positions of the helical scan and combine the plurality of sets of extracted projection data to obtain a scanogram.
