Large lipid core (extended into arterial lumen) and high density of macrophages (associated with 18F-fluorodeoxyglucose "18F-FDG" uptake) in atherosclerotic plaque were shown to be an overt feature of plaque rupture. Nineteen participants were imaged with computed tomography (CT) and positron emission tomography (PET) with 18F-FDG in a dynamic mode. The mean lumen density in Hounsfield unit (HU) was measured per region of interest (ROI) on CT images and classified as non-calcified and calcified classifications. Calcified group was divided into partially calcified and calcified groups. Metabolic rate of glucose (MRG) was computed per ROI on PET dynamic images using modified 2-tissue compartmental model that is independent of partial volume effect. Data is clustered using Automatic Hierarchical K-means algorithm (AKH) with silhouette-coefficient. Arterial segments of 1180 ROIs for Aorta and iliac arteries were classified as non-calcified and calcified segments and clustered using AHK with respect to the mean of intravascular attenuation (in HU). There was a statistical difference in MRG corresponded to low intravascular attenuation cluster compared to higher intravascular attenuation clusters (P<0.05), but not within higher clusters (P>0.05), for both non-calcified and calcified classes. In partially calcified segments, same pattern was observed as the low intravascular attenuation cluster was accompanied with significant metabolic activity but not for calcified segments. Low intravascular attenuation is associated with high MRG measured on 18F-FDG PET images, which may reflect the instability of atherosclerotic plaque. Partially calcified plaque is metabolically active compared to calcified plaque.
Keywords: 18F-FDG; Atherosclerosis; CT; PET; lumen density; metabolic activity.
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