Measurement of Plaque Characteristics Using Coronary Computed Tomography Angiography: Achieving High Interobserver Performance.

Background: Coronary computed tomography angiography (CCTA) is used to assess plaque characteristics, remodelling, and progression and regression. Few papers address standard operating procedures that ensure achievement of high interobserver reproducibility. Moreover, assessment of coronary artery bypass grafts has not been reported.

Methods: A training set of images was created of native coronary segments, spanning the full range of atheromatous disease from normal to severe, excluding totally occluded segments, and including segments with or without calcification (n = 24) and completely normal-appearing bypass grafts (n = 16). Three observers used a validated software program during a training phase to establish standard operating procedures and then to achieve high intraobserver performance based on Pearson's correlation coefficient. Subsequently, interobserver variability for the laboratory as a whole was determined with a focus on measures of plaque volume, low- attenuation plaque (LAP), mixed plaque (MP), and calcified plaque (CP).

Results: We found no substantive differences in analytical issues between grafts and native vessels and emphasize the aggregated data. The range of mean total plaque percent was approximately 55% of total vessel volume with maximal interobserver mean absolute differences of 2% or less. Percent of LAP, MP, and CP demonstrated interobserver standard errors of 1% to 2% and interobserver mean absolute differences of 0% to 1%. Pearson's correlations were all highly significant and ranged from 0.969 to 0.999.

Conclusions: CCTA provides a rich diversity of measures of atherosclerosis in coronary and bypass segments that are highly reproducible with experience and adherence to standard operating procedures.