Quantitative evaluation of carotid plaque composition by in vivo MRI

Objective - This study evaluates the ability of MRI to quantify all major carotid atherosclerotic plaque components in vivo. Methods and Results - Thirty-one subjects scheduled for carotid endarterectomy were imaged with a 1.5T scanner using time-of-flight -, T1-, proton density -, and T2-weighted images. A total of 214 MR imaging locations were matched to corresponding histology sections. For MRI and histology, area measurements of the major plaque components such as lipid-rich/necrotic core (LR/NC), calcification, loose matrix, and dense (fibrous) tissue were recorded as percentages of the total wall area. Intraclass correlation coefficients (ICCs) were computed to determine intrareader and inter-reader reproducibility. MRI measurements of plaque composition were statistically equivalent to those of histology for the LR/NC (23.7 versus 20.3%; P=0.1), loose matrix (5.1 versus 6.3%; P=0.1), and dense (fibrous) tissue (66.3% versus 64%; P=0.4). Calcification differed significantly when measured as a percentage of wall area (9.4 versus 5%; P<0.001). Intrareader and inter-reader reproducibility was good to excellent for all tissue components, with ICCs ranging from 0.73 to 0.95. Conclusions - MRI-based tissue quantification is accurate and reproducible. This application can be used in therapeutic clinical trials and in prospective longitudinal studies to examine carotid atherosclerotic plaque progression and regression.