Only diagnostically evaluable, unstented native coronary segments 1.5 mm in luminal diameter and exhibiting 25% stenosis on visual inspection of coronary computed tomographic angiography images were initially included, resulting in exclusion of 18 patients. One patient had a completely uninterpretable study due to inappropriate contrast timing. Of the 289 segments with 25% stenosis from the remaining 84 patients, 11 were incompletely visualized on invasive coronary angiography, leaving 278 such segments for analysis. Fifty <25% stenotic segments were also randomly selected as control segments.

All images are 0.6 mm in slice thickness and obtained by manipulation of oblique multiplanar reconstructions. Each example is shown with longitudinal view on top and short-axis view on bottom. Dotted orange circles outline short-axis location of the vessel in more stenotic segments. The darker vessel lumen appearance in the top grade 2 and grade 3 examples is due to windowing changes to reduce artifact from heavily calcified plaque. Coronary computed tomographic angiography (CCTA) readers assigned a grade between 0 and 5 for each segment by assessing plaque morphology in both longitudinal and short-axis views.

All images are 0.6 mm in slice thickness and obtained by manipulation of oblique multiplanar reconstructions. Visual grading of plaque calcification was obtained by consensus from the same coronary computed tomographic angiography readers who graded stenosis severity. Grade 1 = calcified plaque makes up less than one-third of total plaque; grade 2 = calcified plaque makes up one-third to two-thirds of total plaque; grade 3 = calcified plaque makes up greater than two-thirds of total plaque. Because of artifacts associated with dense calcification, stenoses of plaques with grade 2 or grade 3 calcification may be less accurately characterized on coronary computed tomographic angiography.

Coronary computed tomographic angiography (CCTA) images are on the left, and invasive coronary angiography (ICA) images are on the right. Computed tomography–based quantitative coronary analysis (CTQCA) was performed on the thinnest possible image slice by using a simplified formula based on the technique described by Reiber et al. (20) (see Methods section). This simplified formula may be useful for future investigations requiring routine stenosis calculation on CCTA. (A) Quantification of an intermediately stenotic noncalcified plaque in the midleft circumflex artery. (B) Quantification of a severely occlusive noncalcified plaque in the proximal left anterior descending artery. (C) Quantification of mild stenosis from a calcified plaque in the proximal left anterior descending artery.

Components of each bar total 100%. Each stepwise increase in coronary computed tomographic angiography (CCTA) grading is accompanied by an increase in frequency of higher grade stenoses on invasive coronary angiography–based stenosis quantification (IQCA) (p < 0.001). Frequency of IQCA grade 5 stenoses was higher in segments determined grade 4 by CCTA quantification (B) (21.7%) than by visual inspection (A) (5.8%, p = 0.016). A grading discrepancy of >1 between CCTA and IQCA occurred rarely. For example (A), only 1.9% visual CCTA grade 2 segments were grade 4 on IQCA, indicating that when maximal stenosis within a segment is determined at 25% to 49% on CCTA, 70% stenosis by IQCA can be excluded.

Overall Pearson r-coefficient is 0.82, indicating very good correlation (A). However, Bland-Altman analysis (B) showed CTQCA to have an average bias of +3.70, with 95% of the differences between invasive coronary angiography–based quantitative coronary analysis (IQCA) and CTQCA falling between –27.2 and 34.6, indicating high variability in CTQCA accuracy for individual lesions. SD = standard deviation; other abbreviations as in Figure 4.