Assessment of bone-implant interface image quality for in-vivo acetabular cup implants using photon-counting detector CT: Impact of tin pre-filtration.

Purpose: To assess the image quality of the bone-implant interface of acetabular cup implants using photon-counting detector (PCD) CT with and without tin pre-filtration in a clinical setting. Methods and materials: Twenty-four patients underwent PCD-CT imaging of their total hip replacement (THR). Twelve patients were scanned using 140 kVp and twelve patients using 140 kVp with tin pre-filtration (Sn140 kVp). All scans were acquired with a collimation of 120 × 0.2 mm. The acquired data was reconstructed with different slice thickness (0.2 mm - 0.6 mm) and kernel (Qr) strengths (56, 76, 89) with and without metal artifact reduction (iMAR). Two observers assessed the image quality of the bone-implant interface for the cup based on four image quality criteria. Bone contrast, contrast-to-noise ratio (CNR) of bone/fat and cortical sharpness was performed as quantitative measures. Results: Image quality was rated highest for 0.2 mm slice thickness and Qr89 kernel across all four criteria for both the 140 kVp and Sn140 kVp by both observers, with a slight preference for the Sn140kVp over the 140 kVp. In all cases and for all image criteria the 0.2 mm/Qr89 was preferred above the Qr76 and Qr56/iMAR for both the 140 kVp and Sn140 kVp by both observers. Quantitative measurements confirmed significantly improved bone contrast as well as cortical sharpness using 0.2 mm/Qr89. Tin pre-filtration did not affect the CNR at 0.2 mm/Qr89 but tended to decrease cortical sharpness. Conclusions: High resolution PCD-CT allows for in-vivo assessment of the bone-implant interface in patients with THR and is preferably acquired with tin pre-filtration.