All data sets were evaluated by image postprocessing software (Fa. TeraRecon GmbH, Frankfurt, Germany). The volume artefact of the metal implant was segmented to adjusted HU-based intervals and volumetrically calculated with this software.

The range of HU densities for dark and bright artefacts were defined by appreciating values for background noise on images with an expected maximum of heterogeneity (40 keV, 80 kVp), which were measured to −200 to 310, mean 17 HU respectively –200 to 330, mean 28 HU. Therefore, the values outside these ranges were attributed to bright and dark streak artefacts. (Fig. 2D).

CT images of metal implants show metal artefact reduction with increasing energies 40 keV (A), 100 keV (B) and 190 keV (C). The grade of artefact reduction is similar with chrome-cobalt (2) and stainless steel (3) but increased with titanium (1). The transversal reconstructions (190 keV) on mid-stem level illustrate alloy-dependent dark and bright streak artefacts (D). The density of reference pellet 1 (left upper corner) is decreasing with rising energy.

The artefact size was measured volumetrically by semiautomatic region of interest (ROI) selection. The range of density was chosen between –1042 HU to –200 HU for the dark artefacts and 400 HU to 2500 HU for the bright artefacts. The volume of the prosthesis was subtracted from the value of bright artefacts to isolate the volume artefact value.

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