Abstract 2422: Calcification within the Advanced Human Carotid Atherosclerotic Plaque is Associated with Intraplaque Hemorrhage: A Magnetic Resonance Imaging and Histology Investigation
Purpose: There is a lack of consensus regarding the significance of calcification in the atherosclerotic carotid plaque. While some studies suggest calcification is a stabilizing factor, others have associated it with intraplaque hemorrhage (IPH) - an indicator of plaque vulnerability. Since magnetic resonance imaging (MRI) has been proven to accurately identify the lipid-rich necrotic core (LRNC) and IPH of the carotid lesion, we sought to determine if carotid MRI can accurately detect and quantify calcification. We then tested the hypothesis that the location of calcification relative to the LRNC is an important determinant for the presence of IPH.
Methods: 24 subjects scheduled for carotid endarterectomy were imaged with high-resolution, multi-contrast carotid MRI (T1-weighted, proton density, T2-weighted, and 3D time of flight) at 1.5T. The LRNC, IPH and calcification were identified with previously established MRI criteria. Types of calcification were defined based on location as Type I: adjacent to LRNC; Type II: separate from LRNC; and Type III: calcification without LRNC or IPH present. Agreement between MRI and matched histology sections for presence of calcification was assessed using Cohen’s Kappa. Area measurements were compared using Pearson’s correlation, and comparison of calcification type and presence of IPH was assessed using Chi-square analysis.
Results: Of the 187 matched cross-sections, there was a strong agreement between MRI and histology for identifying calcification (Kappa =0.77), with a specificity and sensitivity of 93% and 85%, respectively. MRI area measurements of calcification strongly correlated with histology (r=0.93; p<0.001). Of 135 locations with calcification identified on MRI, 90 (67%) were Type I, 20 (15%) Type II, and 25 (18%) Type III. The presence of IPH occurred significantly more often with the presence of Type I than Type II (78% vs. 20%, respectively; p<0.001).
Conclusions: High-resolution MRI can accurately identify calcification in the carotid plaque and determine its association with the LRNC and IPH. Our findings indicate that the location of calcification with respect to the LRNC may play a significant role in the development of IPH and plaque destabilization.