Impact of slice thickness on CACS calculation with virtual non-contrast in photon-counting CT

This study aims to investigate the feasibility of coronary artery calcium scoring (CACS) calculating from PureCalcium virtual non-iodine algorithm on photon-counting detector CT (PCD-CT) and the potential impact of different section thickness, level of virtual monoenergetic images (VMIs), and quantum iterative reconstruction (QIR) on the accuracy of CACS quantification.

A total of 123 patients who underwent coronary CT angiography on PCD-CT with a separate true non-contrast CACS (CACS_TNC) scan were prospectively included. Agatston scores were calculated from the PureCalcium algorithm (CACS_PC) using a section thickness of 3 mm-1.5 mm, different VMI (55-75 kilo-electron volt (keV)) and QIR (strength 1,4) levels, respectively. CACS_TNC at 70 keV and QIR 2 were used as reference standards. Differences in CACS of different reconstructions section thicknesses, various keV levels, and QIR strength were compared using the Wilcoxon rank sum test with Bonferroni correction. The intraclass correlation coefficients (ICCs) and Bland-Altman analysis were conducted to assessed the agreement. The agreement of plaque burden groups (based on CACS) at different reconstruction parameters was evaluated using weighted Cohen kappa.

At all investigated section thickness, VMI, and QIR levels, the CACS_PC were strongly correlated with CACS_TNC (ICC: 0.94-0.98, P < 0.001 for all). There were no statistical differences in CACS between CACS_PC at 3 mm section thickness, 60/65 keV (QIR1/4), and at 1.5 mm section thickness with 55 keV (QIR1/4), compared with CACS_TNC. The smallest CACS bias was observed at a 1.5 mm section thickness, 55 keV, QIR 1, with mean bias of 2.4; LoA (IQR: -182.7, 187.4). CACS_PC correctly identified 105 of 123 participants (85.4%) into the corresponding plaque burden group using CACS_TNC as the referent standard (excellent agreement, κ = 0.904).

CACS derived from the PureCalcium algorithm with optimized reconstruction parameters shows excellent correlation with true non-contrast scans derived values. Thus, it is may possible to use the PureCalcium virtual non-iodine algorithm to replace the true non-contrast scans for CACS quantification, without additional radiation dose exposure.