Abstract
PURPOSE: To improve the evaluation of low-attenuation plaque (LAP) by using semiautomated software and to assess whether the use of a proposed automated function (LAP editor) that excludes voxels adjacent to the outer vessel wall improves the relationship between LAP and the presence and size of the lipid-rich component (LRC) verified at intravascular US. At coronary CT angiography, quantification of LAP can improve risk stratification. Plaque, defined as the area between the vessel and the lumen wall, is prone to partial volume effects from the surrounding pericoronary adipose tissue. MATERIALS AND METHODS: The percentage of LAP (%LAP), defined as the percentage of noncalcified plaque with an attenuation value lower than 30 HU (LAP/total plaque volume) at greater than or equal to 0 mm (%LAP(0)), greater than or equal to 0.1 mm (%LAP(0.1)), greater than or equal to 0.3 mm (%LAP(0.3)), greater than or equal to 0.5 mm (%LAP(0.5)), and greater than or equal to 0.7 mm (%LAP(0.7)) inward from the vessel wall boundaries, were quantified in 155 plaques in 90 patients who underwent coronary CT angiography before intravascular US. At intravascular US, the LRC was identified by using echo attenuation, and its size was measured by using the attenuation score (summed score/analysis length) based on the attenuation arc (1 = < 90°, 2 = 90° to < 180°, 3 = 180° to < 270°, 4 = 270°-360°) for every 1 mm. RESULTS: Use of LAP editing improved the ability for discriminating LRC (areas under receiver operating characteristic curve: 0.667 with %LAP(0), 0.713 with %LAP(0.1) [P < .001 for comparison with %LAP(0)]), 0.778 with %LAP(0.3) [P < .001], 0.825 with %LAP(0.5) [P < .001], 0.802 with %LAP(0.7) [P = .002]). %LAP(0.5) had the strongest correlation (r = 0.612, P < .001) with LRC size, whereas %LAP(0) resulted in the weakest correlation (r = 0.307; P < .001). CONCLUSION: Evaluation of LAP at coronary CT angiography can be significantly improved by excluding voxels that are adjacent to the vessel wall boundaries by 0.5 mm.Supplemental material is available for this article.© RSNA, 2019.