The root mean square error (RMSE) of the CT numbers obtained from scans with titanium (left) or steel (right) inserts, as a function of virtual photon energy level for the central positions 1–4 (top row) and the peripheral positions 5–17 (bottom row) (as defined in Figure 1). 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). Corresponding data from images with PMMA inserts are included for comparison.