A Noninvasive Imaging Approach to Assess Plaque Severity: The Carotid Atherosclerosis Score

ROC curve analyses for the classification of IPH (A) and FCR (C) in the training set by maximum percentage LRNC. Adjacent to each ROC curve is a cumulative prevalence plot for IPH (B) and FCR (D) versus maximum percentage LRNC. The cumulative prevalence plots clearly depict changes in slope (arrows) for both IPH (B) and FCR (D), which were subsequently used to construct the CAS. E, ROC curve analysis for prediction of the presence of LRNC in the training set by maximum wall thickness, maximum total vessel area, and maximum NWI. F, In the cumulative prevalence plot for LRNC by maximum wall thickness, LRNC was absent in lesions with a maximum wall thickness <2 mm.

Flow diagram of CAS. Subjects with a maximum wall thickness >2 mm require additional evaluation. Further categorization of lesions can be determined by the size of the maximum percentage LRNC. Examples of matched cross-sectional images from 3 contrast weightings (TOF, T1WI, and CE-T1WI) for each category are provided. Images corresponding to CAS 1 (maximum wall thickness <2 mm) are from the left common carotid artery of a 69-year-old man imaged at MSU. The plaque in the CAS 2 (maximum percentage LRNC, ≤20%) example is from the right internal carotid artery of a 63-year-old man imaged at UW. There is a small LRNC (arrow) present on postcontrast imaging. Of note, there are also flow artifacts visible in the lumen—common artifacts in images distal to the bifurcation. The lesion in CAS 3 (maximum percentage LRNC, >20% and ≤40%) is from the left common carotid artery of a 65-year-old man imaged at AH. A noticeable LRNC (arrows) is present in both the anterior and posterior arterial wall. An example of a large LRNC (arrow) without IPH in the left common carotid artery of a 64-year-old man imaged at PLA is shown for CAS 4 (maximum percentage LRNC, >40%). Arrowheads indicate the outer wall boundary; asterisk, the lumen.

Prevalence of key features in the carotid artery is shown for each MR imaging location relative to the bifurcation. Distance from the bifurcation (0) is labeled on the x-axis, where positive and negative integers represent locations within the internal and common carotid arteries, respectively.