Comparison of Iterative Metal Artifact Reduction Presets In Ultra-high-resolution Photon-counting CT Angiography of Patients with Total Knee Endoprosthesis

Rationale and Objectives Ultra-high-resolution (UHR) photon-counting CT angiography (PCCTA) has become the reference standard for non-invasive assessment of peripheral artery disease. In the presence of total knee endoprosthesis, however, metal artifacts hamper visualization of the popliteal vasculature. This study investigated the effect of the different iterative metal artifact reduction (IMAR) settings in patients with knee joint replacement. Materials and Methods Twenty-five patients with knee arthroplasty (74.0 ± 8.5 years; 12 women) undergoing lower extremity UHR-PCCTA between August 2024 and August 2025 were included, yielding 31 lower extremities for analysis. Each dataset was reconstructed without IMAR and with the seven available IMAR presets ("Extremity", "Hip", "Pacemaker", "Lung coils", "Shoulder", "Dental", and "Neuro coils"). Objective image quality was assessed by region-of-interest measurements in the most pronounced hyperdense and hypodense artifacts. Subjective image quality was evaluated by seven radiologists using a forced-choice pairwise comparison tool, totaling 6076 pairwise comparisons. Results Compared with non-IMAR datasets (median 4300.1 HU) and the other six IMAR presets (3117.9 – 3377.1 HU), application of IMAR Dental resulted in the strongest reduction of hyperdense artifacts (932.5 HU; all p <0.001). Similarly, IMAR Dental (−97.5 HU) provided superior reduction of hypodense artifacts versus datasets reconstructed with the other IMAR presets (−567.9 – −1523.3 HU) and without IMAR (−3319.7 HU; all p ≤0.022). Image noise was comparable across all reconstructions (median 10.6 – 11.3 HU; all p >0.05). Subjective evaluation of popliteal artery assessability favored IMAR Dental with the highest preference probability in pairwise comparison to the other IMAR and non-IMAR data (0.92, 95% confidence interval 0.90–0.93). Conclusion Despite its misleading name, IMAR Dental provides the strongest reduction of metal artifacts in UHR-PCCTA of the leg, allowing for the best assessability of the popliteal vasculature in patients with total knee endoprosthesis.