Computed tomography optimization using a volumetric channelized Hotelling observer approach for energy integrating and photon-counting CT scanners

Purpose: To develop a volumetric channelized Hotelling observer (vCHO) for protocol optimization studies using an anthropomorphic phantom across different types of scanners, including energy integrating (EI-CT) and photon-counting (PC-CT) CT scanners and validate it against human observer results. Methods: The anthropomorphic abdominal phantom was scanned on a PCCT and EICT. The phantom consists of 5 anatomical landmarks and a cylindrical insert, containing low-contrast spheres (diameters 4, 6, and 8mm, 15 of each size) and a sizable signal-free background. The phantom was scanned on both systems with a wide range of CT parameters: tube voltage, dose, reconstruction settings, FOV, and slice thickness (more than 350 scans). An anthropomorphic vCHO was created to assess the targets detectability. A two-layer approach was used, where first the target locations were estimated using a CHO with Laguerre-Gauss channels, followed by an anthropomorphic CHO with volumetric difference-of-Gaussians channels to assess the percentage correctly detected spheres (PC). The threshold diameter (Dtr) at 62.5% PC was estimated via logistic regression, with lower Dtr representing better detectability and expressed in 'mm'. Results: For almost all settings the PCCT performs better than the EICT. For both scanners while keeping the rest of the settings, the performance increased with tube voltage. As expected, the performance increased with higher dose. Softer kernel yielded higher quality. For the EICT, FBP outperformed iterative reconstruction, while for the PCCT the IR strength did not result in statistically significant results (p>0.1). Smaller FOV enhanced and similarly narrower slice thickness improved performance. When the results were compared to the human observer readings the vCHO outperformed the humans under all conditions, but comparatively the same conclusions about the image quality can be drawn. The human observers are more sensitive to scanning parameters change, where the vCHO detects smaller change in Dtr for the same reading conditions. Conclusions: This study introduced an anthropomorphic vCHO for CT image quality assessment using an anthropomorphic phantom and the first vCHO tendencies for different parameters for an EICT and PCCT scanners.