Carotid plaque classification: Defining the certainty with which plaque components can be differentiated

Multicontrast‐weighted MRI has the potential to become a powerful tool for assessment of atherosclerotic plaque. However, similarities in MR properties across plaque components limit the certainty with which these components can be differentiated. An understanding of MRI's underlying limitations in distinguishing atherosclerotic plaque components, and optimization of key parameters (including the set of components investigated and contrast weightings used) are required. In this study we analyzed endarterectomy specimens using multicontrast MRI and compared the results with matching histological findings to determine the probability of error, an unbiased measure of the underlying error caused by similarity in the spectral characteristics of components. The total error was >40% when five distinct components were investigated, but this was halved when components with similar functions and intensities were grouped together. When three contrast weightings were used to view plaque, diffusion‐weighted imaging (DWI) proved valuable for separating hemorrhage from necrotic core, and “hemorrhage + necrotic” from “loose connective tissue + fibrous tissue.” A two‐way interaction between contrast weightings and components demonstrated that the value of a contrast can be exploited or marginalized depending on the choice of contrast weightings used. Magn Reson Med 57:874–880, 2007. © 2007 Wiley‐Liss, Inc.