Variability in the measurement of minimum fibrous cap thickness and reproducibility of fibroatheroma classification by optical coherence tomography using manual versus semiautomatic assessment

Aims: The minimum fibrous cap thickness (FCT) is considered a major criterion of coronary plaque vulnerability according to autopsy studies. We aimed to assess the reproducibility in the measurement of the optical coherence tomography (OCT)-detected minimum FCT and the agreement in the classification of thin-cap fibroatheroma (TCFA), by a software-based semi-automatic method compared with the manual method. Methods and results: A total of 50 frames with fibroatheromas (FA) were randomly selected from the Integrated Biomarker Imaging Study-4 (IBIS-4). Two experienced OCT analysts independently measured the minimum FCT at two different time points, manually and by three different semi-automatic softwarebased algorithms, based on the assessment of light intensity along the axial scan line. A TCFA was defined as an FA with minimum FCT <65 μm. The inter-and intra-observer reproducibility of the manual measurement of the minimum FCT was moderate with an intra-class correlation coefficient (ICC) of 0.71 and 0.79, respectively. The corresponding ICCs by either one of the three semi-automatic algorithms were 0.99. When categorising FA according to the minimum FCT based on the manual assessment, the inter-and intraobserver agreement was poor (κ=0.23) and moderate (κ=0.50), respectively. In contrast, the semi-automatic assessment showed perfect agreement for both inter-and intra-observer assessments (κ=0.90-1.00 and 1.00, respectively). Conclusions: While semi-automatic assessment of FCT and TCFA classification was associated with excellent reproducibility and agreement, manual measurements were associated with a moderate reproducibility and agreement in the quantification of FCT and classification of TCFA.