Background: Metal artifacts in computed tomography (CT) can be reduced with high energy virtual monoenergetic images (VMI) and iterative metal artifact reduction (IMAR) algorithms. At high VMI energies, however, iodinated contrast media show decreased attenuation. High atomic number (high-Z) contrast media potentially preserve vessel contrast near metal implants even at high VMI energies. Hence, the purpose of this study was to assess the effect of high-Z contrast media on vessel visualization near metal implants in photon-counting detector (PCD)-CT across VMI energies, with and without IMAR and for different metal types. Methods: A pelvis phantom containing titanium or steel inserts and contrast media inserts including iodine, bismuth, holmium, or tungsten was scanned using photon-counting detector computed tomography (PCD-CT). VMI (40-190 keV, 1 keV steps) were reconstructed with and without IMAR. Three predefined regions of interest (ROI) were placed in the background (background noise, standard deviation of HU), in the contrast media inserts (vessel attenuation, mean HU), and between the metal and contrast inserts (metal artifacts, defined as standard deviation of HU). An artifact-adjusted contrast-to-noise ratio (CNR) was calculated using background noise, vessel attenuation and metal artifacts, and averaged across three VMI energy ranges: 40-90, 90-140, and 140-190 keV. Peak CNR was the maximum value across all VMI energies. Wilcoxon rank sum tests with Benjamini-Hochberg correction were applied. Conclusions: High-Z contrast media provide superior vessel contrast compared to iodine near metal implants in PCD-CT, both at low VMI energy with holmium and at high VMI energy with tungsten and bismuth, where metal artifacts are additionally reduced. Under metal artifact conditions, vessel contrast can be further improved by applying IMAR.
Klambauer et al. (Sun,) studied this question.