Carotid Plaque Characteristics Evaluation on DUS and MDCTA: Interobserver and Intermodality Agreement in a Single-Center Study

Background and Objectives: Carotid artery stenosis has traditionally guided therapeutic decision-making; however, plaque morphology and composition are increasingly recognized as more reliable indicators of cerebrovascular risk than luminal narrowing alone. As imaging strategies shift toward vulnerability-based assessment, reproducibility of plaque characterization becomes essential for consistent clinical decision-making. This study aimed to evaluate interobserver agreement in carotid plaque assessment using multidetector computed tomography angiography (MDCTA) and to assess intermodality agreement with duplex ultrasonography (DUS). Materials and Methods: In this single-center study (January–September 2022), 50 patients with ≥60% internal carotid artery stenosis diagnosed by DUS (NASCET criteria), the majority of whom were asymptomatic (90%), were included. MDCTA examinations were independently analyzed by two radiologists, while DUS examinations were evaluated by a third observer. Plaque composition (lipid, fibrous, calcified), surface characteristics (regular, irregular, ulcerated), degree of stenosis, and plaque length were assessed. CT plaque characterization was based on Hounsfield unit (HU) thresholds (<50 HU lipid; 50–120 HU fibrous; >120 HU calcified). Interobserver agreement and intermodality agreement were calculated using Cohen’s kappa coefficient. Results: Good interobserver agreement was observed between the two MDCTA readers (κ = 0.751). Intermodality agreement between MDCTA and DUS was moderate (κ = 0.624 and κ = 0.595). Although significant differences were identified in 3 of 16 HU measurement points, no significant differences were found in overall plaque composition classification between MDCTA observers. DUS yielded significantly higher stenosis values (p = 0.007 and p = 0.005) and greater plaque length measurements (p < 0.0005) compared with MDCTA. Significant differences were also observed in plaque surface assessment between modalities (p = 0.044 and p = 0.033). Conclusions: MDCTA demonstrates good interobserver reproducibility for carotid plaque characterization, while intermodality agreement between MDCTA and DUS is moderate. Minor attenuation measurement differences do not significantly affect plaque classification; however, systematic intermodality differences in stenosis grading, plaque surface evaluation, and plaque length measurement should be considered in clinical decision-making.