Lumen imaging in calcified coronary arteries using high-resolution Gd-enhanced color K-edge imaging with spectral photon-counting CT: a phantom study

Abstract Objective Conventional coronary computed tomography angiography (CCTA) lumen assessment is hampered by the similar attenuation of iodine and calcium. We assessed the lumen for Gd-enhanced CCTA on high-resolution color Gd K-edge imaging using a clinical spectral photon-counting computed tomography (SPCCT) prototype in an anthropomorphic phantom. Materials and methods A hollow cylindrical coronary artery phantom (10-mm outer diameter, 5-mm inner diameter) containing five cylindrical calcifications of different densities (75, 100, 200, 400, and 800 mg/cm 3 hydroxyapatite, deemed very low, low, medium, high, and very high, respectively) and equal size was scanned on a clinical SPCCT prototype using a clinical CCTA protocol. The artery model was filled with Gd mixed with saline to achieve 400 HU at 70 keV. The luminal area was compared with the physical area ( i.e ., 19.6 mm 2 ), and spectral results were compared to conventional acquisition. Results In the absence of calcification, physical lumen size was overestimated by 7% and 16% on color Gd K-edge and conventional images, respectively. In the presence of calcification, only color Gd K-edge images enabled the measurement of the lumen, i.e ., 22.25 ± 0.43 mm 2 , 22.85 ± 1.77 mm 2 , 14.63 ± 1.17 mm 2 , and 15.37 ± 0.78 for very low to very high calcium density, respectively. Largest underestimation (-26%) and overestimation (16%) were shown for the high- and low-density calcification in comparison to physical size, respectively. Conclusion Color Gd K-edge imaging with Gd-enhanced CCTA outperformed conventional imaging in assessing the coronary lumen in both noncalcified and calcified vessels, whilst accuracy depends on the presence and density of calcifications. Relevance statement In a phantom study, high-resolution color Gd K-edge imaging targeting Gd enabled accurate visualization of the coronary lumen in both calcified and noncalcified arteries, outperforming conventional CT angiography. In the presence of calcifications, only color Gd K-edge imaging provided objective lumen assessment, with accuracy influenced by calcium extent and density. Key Points Color Gd K-edge Gd-enhanced CCTA using SPCCT is feasible in a coronary artery phantom. Color Gd K-edge imaging improves lumen assessment in calcified vessels. Color Gd K-edge imaging potentially enhances diagnostic precision and treatment planning for patients with coronary artery disease. Graphical Abstract