Purpose: To evaluate the relationship between atherosclerotic plaque inflammation, as assessed by FDG-positron emission tomography/computed tomography (FDG-PET/CT), and plaque morphology and composition, as assessed by magnetic resonance imaging (MRI), in the carotid and femoral arteries.
Materials and methods: Sixteen patients underwent FDG-PET/CT and MRI (T2-weighted (T2W) and proton density weighted (PDW)) of the carotid and femoral arteries. For every image slice, two observers determined the corresponding regions of the FDG-PET/CT and MRI image sets by matching CT and T2W axial images. Each plaque was then classified into one of three groups according to the CT appearance and T2W/PDW signal: (1) collagen, (2) lipid-necrotic core and (3) calcium. Arterial FDG uptake was measured for each plaque and normalized to vein FDG activity to produce a blood-normalized artery activity called the target to background ratio (TBR). The vessel wall thickness (VWT), the vessel wall area and the total vessel wall area were measured from the T2W MR images.
Results: The TBR value was higher in the lipid-necrotic core group compared to the collagen and calcium groups, (p<0.001). The lipid-necrotic core group demonstrated a significant TBR variation according to the median of the VWT (TBR=1.26+/-0.25 vs. 1.50+/-0.12). There was no correlation with other morphological MR parameters.
Conclusions: This study demonstrates the complementary value of non-invasive FDG-PET/CT and MR imaging for the evaluation of atherosclerotic plaque composition and activity. Lipid-rich plaques are more inflamed than either calcified or collagen-rich plaques.