Improved coronary calcification quantification using photon-counting-detector CT: an ex vivo study in cadaveric specimens

Abstract

Objectives: To compare the accuracy of coronary calcium quantification of cadaveric specimens imaged from a photon-counting detector (PCD)-CT and an energy-integrating detector (EID)-CT.

Methods: Excised coronary specimens were scanned on a PCD-CT scanner, using both the PCD and EID subsystems. The scanning and reconstruction parameters for EID-CT and PCD-CT were matched: 120 kV, 9.3-9.4 mGy CTDI_vol, and a quantitative kernel (D50). PCD-CT images were also reconstructed using a sharper kernel (D60). Scanning the same specimens using micro-CT served as a reference standard for calcified volumes. Calcifications were segmented with a half-maximum thresholding technique. Segmented calcified volume differences were analyzed using the Friedman test and post hoc pairwise Wilcoxon signed rank test with the Bonferroni correction. Image noise measurements were compared between EID-CT and PCD-CT with a repeated-measures ANOVA test and post hoc pairwise comparison with the Bonferroni correction. A p < 0.05 was considered statistically significant.

Results: The volume measurements in 12/13 calcifications followed a similar trend: EID-D50 > PCD-D50 > PCD-D60 > micro-CT. The median calcified volumes in EID-D50, PCD-D50, PCD-D60, and micro-CT were 22.1 (IQR 10.2-64.8), 21.0 (IQR 9.0-56.5), 18.2 (IQR 8.3-49.3), and 14.6 (IQR 5.1-42.4) mm³, respectively (p < 0.05 for all pairwise comparisons). The average image noise in EID-D50, PCD-D50, and PCD-D60 was 60.4 (± 3.5), 56.0 (± 4.2), and 113.6 (± 8.5) HU, respectively (p < 0.01 for all pairwise comparisons).

Conclusion: The PCT-CT system quantified coronary calcifications more accurately than EID-CT, and a sharp PCD-CT kernel further improved the accuracy. The PCD-CT images exhibited lower noise than the EID-CT images.

Key points: • High spatial resolution offered by PCD-CT reduces partial volume averaging and consequently leads to better morphological depiction of coronary calcifications. • Improved quantitative accuracy for coronary calcification volumes could be achieved using high-resolution PCD-CT compared to conventional EID-CT. • PCD-CT images exhibit lower image noise than conventional EID-CT at matched radiation dose and reconstruction kernel.

Keywords: Artifacts; Cadaver; Coronary artery disease; X-ray tomography.

Fig.1

Five calcification types with different morphological features, reconstructed using PCD-D50 data. Each magnified image is 50 × 50 voxels (11.7 mm × 11.7 mm). The window level/width was adjusted to clearly visualize the morphological features in each calcification. a A calcification with an irregular border. b A ring-shaped calcification. c A discontinuous calcification with irregular border. d A discontinuous calcification with a smooth border. e A continuous, oval-shaped calcification

Fig. 2

The volume of each calcification measured on EID-D50, PCD-D50, and PCD-D60 expressed as a percentage of the micro-CT volume. The volume in 12 of the 13 total calcifications followed a similar trend: EID-D50 > PCD-D50 > PCD-D60 > micro-CT

Fig. 3

A smooth border, continuous, oval-shaped calcification with the half-maximum thresholds (HMT) overlaid (EID-CT, PCD-CT display window level/width: 2128/458 HU). a EID-D50: HMT in green, 62 voxels. b PCD-D50: HMT in red, 55 voxels. c PCD-D60: HMT in blue, 48 voxels. d Corresponding micro-CT image

Fig. 4

Summary statistics with boxplots showing the calcified volume measurements (mm³) for EID-D50, PCD-D50, PCD-D60, and micro-CT, respectively. Inside each box, the horizontal line indicates the median, while the bottom and top edges indicate the 25th and 75th percentiles, respectively. The whiskers indicate variability outside the quartiles. Below the boxplots are the corresponding volume measurements depicted (mm³). The volume of the largest calcification in EID-D50, PCD-D50, and PCD-D60 was 225.7, 196.4, and 165.0 mm³, respectively. These three outliers’ value is shown as the numerical maximum volume measurements (mm³) and indicated with an asterisk (below the boxplots) but are not depicted in the graph

Fig. 5

Bland-Altman plots according to the Harrell and Davis method, using quantiles of the original values. The mean difference is indicated with a dotted green line and the 95 % limits of agreement are shown in gray. a PCD-D60 in relation to micro-CT: mean difference 15.1 and 95% limits of agreement − 32.4 to 62.7. b PCD-D50 in relation to micro-CT: mean difference 20.8 and 95 % limits of agreement −41.9 to 83.6. c EID-D50 in relation to micro-CT: mean difference 26.6 and 95% limits of agreement − 52.4 to 105.5. HD quantiles indicate Harrell and Davis quantiles

Fig. 6

A smooth border, continuous calcification with a ring-like shape, with the half-maximum thresholds (HMT) overlaid. Compound calcium blooming artifacts present at both the inner and outer boundaries induced an incremental volume discrepancy between EID-CT, PCD-CT, and micro-CT measurements (EID-CT, PCD-CT display window level/width: 1735/466 HU). a EID-D50: HMT in green, 249 voxels. b PCD-D50: HMT in red, 197 voxels. c PCD-D60: HMT in blue, 137 voxels. d Corresponding micro-CT image