Accuracy and reproducibility of automated, standardized coronary transluminal attenuation gradient measurements

Abstract

Coronary computed tomography angiography (CCTA) contrast opacification gradients, or transluminal attenuation gradients (TAG) offer incremental value to predict functionally significant lesions. This study introduces and evaluates an automated gradients software package that can potentially supplant current, labor-intensive manual TAG calculation methods. All 60 major coronary arteries in 20 patients who underwent a clinically indicated single heart beat 320 × 0.5 mm detector row CCTA were retrospectively evaluated by two readers using a previously validated manual measurement approach and two additional readers who used the new automated gradient software. Accuracy of the automated method against the manual measurements, considered the reference standard, was assessed via linear regression and Bland-Altman analyses. Inter- and intra-observer reproducibility and factors that can affect accuracy or reproducibility of both manual and automated TAG measurements, including CAD severity and iterative reconstruction, were also assessed. Analysis time was reduced by 68% when compared to manual TAG measurement. There was excellent correlation between automated TAG and the reference standard manual TAG. Bland-Altman analyses indicated low mean differences (1 HU/cm) and narrower inter- and intra-observer limits of agreement for automated compared to manual measurements (25 and 36% reduction with automated software, respectively). Among patient and technical factors assessed, none affected agreement of manual and automated TAG measurement. Automated 320 × 0.5 mm detector row gradient software reduces computation time by 68% with high accuracy and reproducibility.

Figure 1

(A) Snapshot of the software performing automated TAG calculations in an LAD with obstructive (>70%) calcified plaque proximally. User manually defines segment of interest from left main ostium to a 2 mm² distal landmark (white arrows), with access to centerline editing in curved MPR and luminal contour editing in cross-sectional images. (B) Methodology for manual TAG calculations in the same artery. User performs manual measurement of the luminal intensity in ROIs placed within the lumen beginning at the ostium every 5 mm along the length of the coronary artery, and statistical analysis software is used to perform the linear regression. Accuracy of the two techniques as defined by (C) Bland-Altman plot and (D) linear regression plot.

Figure 2

Inter-observer agreement of automated and manual TAG: (A) Bland-Altman plots for automated and (B) manual TAG; (C) Linear regression analysis for automated and (D) manual TAG.

Figure 3

Reproducibility of automated and manual TAG: (A, C) Bland-Altman plots for reader 1 and 2 using automated, and (E,G) for reader 3 and 4 using manual TAG methods. (B,D) Linear regression plots for reader 1 and 2 using automated, and (F,H) for reader 1 and 2 using manual TAG methods.