Evaluating Changes in Coronary Artery Calcium: An Analytic Method That Accounts for Interscan Variability

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Abstract
OBJECTIVE. Coronary calcium measured by electron beam CT is associated with coronary disease and can be used to predict coronary disease events. Studies investigating changes in coronary calcium need to address interscan variability as it relates to the overall coronary calcium score in defining progression or regression of coronary calcium over time.SUBJECTS AND METHODS. Electron beam CT was performed on 1,074 participants. Coronary calcium volume scores were repeated 5 min apart. Interscan variability was examined using Bland-Altman plots and homogeneity tests. Transformations of the Box-Cox family (including power, roots, and logarithm) were applied to calcium volume scores. The transformation that stabilized the variation in calcium volume scores was applied to progression of calcium volume scores in 109 subjects with diabetes.RESULTS. The variability in calcium volume score increased as the level of coronary calcium increased (rho = 0.67, p < 0.001 for the relation between the absolute difference and...