An X-ray imaging apparatus (XI) including an X-ray source (XS) with a cathode (C) and an anode (A). The source (XS) is to generate an X-radiation beam (XB). An X-ray detector (XD) detects the X-radiation after interaction with an imaged object (OB). The beam (XB) has different spectra on its anode side (AS) and cathode side (CS) caused by the heel effect when the X-ray source (XS) is in operation. -ray imaging apparatus (XI) has a heel-effect-harnessing (HH) mechanism configured to cause a pixel (PX) of the detector (XD) to be alternately exposed to both, the anode side (AS) and the cathode side (CS) of the beam (XB).