Horizontal CT number profiles for the titanium (top row) and steel (bottom row) inserts at 70 keV (left), 110 keV (middle) and 140 keV (right). The known dimensions of the different materials within the inserts as well as the theoretical CT numbers of titanium, steel, polyoxymethylene and the surrounding Plastic Water materials are shown by the solid grey line for comparison. The images were acquired with Dual Source (DS) and fast kV-switching (FKS) DECT techniques, and the aforementioned combined by each vendor’s proprietary metal artefact reduction (MAR) algorithm (DS-MAR and FKS-MAR). Note that the theoretical CT number of steel at 70 keV is out of scale as the value is 34 287 HU.