Ultra-high resolution photon-counting CT with tin prefiltration for bone-metal interface visualization

Purpose: To investigate the metal artifact suppression potential of combining tin prefiltration and virtual monoenergetic imaging (VMI) for osseous microarchitecture depiction in ultra-high-resolution (UHR) photon-counting CT (PCCT) of the lower extremity.Method: Derived from tin-filtered UHR scans at 140 kVp, polychromatic datasets (T3D) and VMI reconstructions at 70, 110, 150, and 190 keV were compared in 117 patients with lower extremity metal implants (53 female; 62.1 +/- 18.0 years). Three implant groups were investigated (total arthroplasty [n = 48], osteosynthetic material [n = 43], and external fixation [n = 26]). Image quality was assessed with regions of interest placed in the most pronounced artifacts and adjacent soft tissue, measuring the respective attenuation. Additionally, artifact extent, bone-metal interface interpretability and overall image quality were independently evaluated by three radiologists.Results: Artifact reduction was superior with increasing keV level of VMI. While T3D was superior to VMI70keV (p >= 0.117), artifacts were more severe in T3D than in VMI >= 110 keV (all p <= 0.036). Image noise was highest for VMI70keV (all p < 0.001) and lowest for VMI110keV with comparable results for VMI110keV - VMI190keV. Subjective image quality regarding artifacts was superior for VMI >= 110 keV (all p <= 0.042) and comparable for VMI110keV - VMI190keV. Bone-metal interface interpretability was superior for VMI110keV (all p <= 0.001), while T3D, VMI150keV and VMI190keV were comparable. Overall image quality was deemed best for VMI110keV and VMI150keV. Interreader reliability was good in all cases (ICC >= 0.833).Conclusions: Tin-filtered UHR-PCCT scans of the lower extremity combined with VMI reconstructions allow for efficient artifact reduction in the vicinity of bone-metal interfaces.

Automated summary

This study investigated the potential of tin prefiltration and virtual monoenergetic imaging (VMI) in suppressing metal artifacts in high-resolution CT images of the lower extremities. The results showed that VMI reconstructions had better artifact reduction compared to T3D. VMI110keV had the least image noise. In terms of image quality, interpretability of bone-metal interface, and overall image quality, VMI110keV performed the best.