Reducing Metal Artifacts in Clinical Photon Counting Detector Computed Tomography-A Phantom Study of an Exemplary Total Hip Arthroplasty

Objective: To examine how different photon-counting detector (PCD) CT scanning and reconstruction methods affect the volume of metal artifacts and image quality for a hip prosthesis phantom.

Methods: A titanium and cobalt-chromium-molybdenum-alloy total hip prosthesis phantom was scanned using a clinical PCD-CT with a constant tube potential (140 kV) and Computed-Tomography-Dose- Index (7 mGy). Different scan settings were used: with/without tin-filter (Sn), with/without ultra-high resolution (UHR), both individually and combined, resulting in four modes: Quantumplus (Standard), UHR Quantumplus (HighRes), QuantumSn (Standard-Tin) and UHR QuantumSn (HighRes-Tin). Reconstructions included virtual monoenergetic images (VMI) spanning 40-190 keV and polychromatic images, with/without iterative metal artifact reduction (MAR). Artifact volumes rendered in a 3D-printing software were quantified in milliliters (ml), and image quality was evaluated using a Likert score.

Results: Polychromatic reconstruction: Tin-filter reduced artifact volumes (298 (Standard-Tin) vs. 347 ml (Standard) and 310 (HighRes-Tin) vs. 360 ml (HighRes)). The smallest artifact volume was measured in HighRes MAR (150 ml). VMI reconstruction: The smallest artifact volume was measured in Standard 130 keV (150 ml) and HighRes 130 keV (164 ml) and in Standard-Tin 120 keV (169 ml) and HighRes-Tin 120 keV (172 ml). MAR further reduced the artifact volumes to 130 ml (Standard 150 keV MAR) and 140 ml (HighRes 160 keV MAR). Image quality was rated best for Standard 65 keV MAR, polychromatic HighRes MAR, Standard 100 keV MAR, polychromatic Standard-tin MAR, HighRes-tin 100 keV and polychromatic HighRes-tin.

Conclusion: Combining tin-filter, UHR and MAR in VMI or polychromatic images achieve the strongest artifact reduction.