Heart rate sensitivity of virtual non-contrast calcium scores derived from photon counting detector CT data: a...

To assess the reliability of virtual non-contrast (VNC) derived coronary artery calcium quantities in relation to heart rate and the VNC algorithm used compared to reference true non-contrast (TNC), considering several clinically established acquisition modes.

An ad hoc built coronary phantom containing four calcified lesions and an iodinated lumen was scanned using three cardiac acquisition modes three times within an anthropomorphic cardiac motion phantom simulating different heart rates (0, 60, 80, 100 bpm) and reconstructed with a conventional (VNC_conv) and a calcium-sensitive (VNC_pc) VNC algorithm. TNC reference was scanned at 0 bpm with non-iodinated lumen. Calcium scores were assessed in terms of number of lesions detected, Agatston and volume scores and global noise was measured. Paired t-test and Wilcoxon test were performed to test measurements for significant difference.

For both VNC algorithms used, calcium levels or noise were not significantly affected by heart rate. Measurements on VNC_pc reconstructions best reproduced TNC results, but with increased variability (Agatston scores at 0 bpm for TNC, VNC_conv, and VNC_pc were 47.1 ± 1.1, 6.7 ± 2.8 (p < 0.001), and 45.3 ± 7.6 (p > 0.05), respectively). VNC reconstructions showed lower noise levels compared to TNC, especially for VNC_pc (noise_heart on TNC, VNC_conv and VNC_pc at 0 bpm was 5.0 ± 0.4, 4.5 ± 0.2, 4.2 ± 0.2).

No significant heart rate dependence of VNC-based calcium scores was observed in an intra-reconstruction comparison. VNC_pc reproduces TNC scores better than VNC_conv without significant differences and decreased noise, however, with an increasing average deviation with rising heart rates. VNC-based CACS should be used with caution as the measures show higher variability compared to reference TNC and therefore hold the potential of incorrect risk categorization.