Optimal virtual monoenergetic energy level of dual-layer spectral CT angiography for coronary stenosis quantification in patients with calcified coronary plaques: a prospective study

To investigate the optimal virtual monoenergetic energy level of dual-Layer spectral CT angiography for coronary stenosis quantification in patients with calcified coronary plaques. 42 patients with clinical suspicion of coronary atherosclerosis who were underwent coronary CT angiography (CCTA) using dual-layer spectral CT and completed invasive coronary angiography (CAG) within four weeks were prospectively included. The conventional 120 KVp images and virtual monoenergetic images (VMIs, 40 ~ 190 keV at 30 keV intervals) were reconstructed at the optimal phase on a dedicated post-processing workstation. Differences in image quality and vascular stenosis measurements were compared among and within multiple groups. One-way analysis of variance (ANOVA) was used for comparing objective image quality indicators, followed by post-hoc testing with Tukey’s Honestly Significant Difference test (Tukey-HSD) method for pairwise comparisons. The Friedman test was used for subjective image quality scores. Inter-observer agreement between two radiologists was assessed using Cohen’s weighted kappa test (kappa ≥ 0.75: excellent agreement; 0.4 < kappa < 0.75: good agreement; kappa ≤ 0.4: poor agreement). Bland-Altman analysis was used to evaluate the agreement of stenosis measurements between conventional CCTA, various VMIs, and invasive CAG. A total of 42 patients were included. Bland-Altman analysis showed no significant difference between stenosis rates measured on 100 keV VMIs and the gold-standard CAG ( P = 0.726, P > 0.05), indicating excellent consistency. The bias rate of 100 keV VMIs was only approximately 0.1%, representing an average accuracy improvement of 10.2% compared with the 10.3% bias rate of 120KVp images ( P < 0.01). Significant differences in image quality were observed between conventional 120KVp images and all VMI groups (all P < 0.01). The 100 keV VMIs achieved the highest subjective scores (4.81 ± 0.40) in diagnostic confidence, image artifacts, and vascular visualization ( P < 0.01). Cohen’s weighted kappa values between the two observers were all above 0.75, indicating excellent consistency ( P < 0.01). Compared with invasive CAG as reference standard, 100 keV VMIs from spectral-CT achieve favourable luminal visualization and improved agreement for coronary stenosis quantification in the setting of calcified coronary plaques.