Assessment Of Inflammation In Atherosclerosis: Relationship Between~18F-FDG-PET And DCE-MRI

Background and Purpose: Inflammation plays an important role in both thepathogenesis and prognosis of atherosclerotic plaques.18F-fluorodeoxyglucose positronemission tomography (18F-FDG-PET) and dynamic contrast–enhanced magneticresonance imaging (DCE-MRI) have been proposed to quantitatively assess plaqueinflammation. We sought to investigate their relationship by performing dual imagingon the same individual.Methods: Forty-one patients (34men; aged65±12years) with a total of68carotidplaques (thickness≥2mm on ultrasound;20symptomatic) had carotid plaqueinflammation assessed by both18F-FDG-PET/CT and DCE-MRI within two weeks.Plaque inflammation was quantified as target-to-background ratio (TBR) on PET/CT,and transfer constant (Ktrans) on DCE-MRI, which are commonly used measurementsthat probe intraplaque macrophages and neovessels, respectively. Spearman’scorrelation coefficient (r) was used to evaluate their correlations under different clinicalconditions.Results: Overall, the correlation between TBR and Ktranswas only marginal in thewhole study sample (r=0.22, p=0.068). The two variables correlated with each other inthe symptomatic plaques (r=0.59, p=0.006), but were independent in the asymptomaticplaques (r=0.07, p=0.625; p=0.033for difference in r). Neither TBR nor Ktranswassignificantly higher in the symptomatic plaques, but both showed inverse relationshipswith time since last cerebrovascular ischemic event (r=-0.94and-0.69for TBR andKtrans, respectively).Conclusion: The correlation between18F-FDG-PET and DCE-MRI measurementsvaried with clinical conditions, pointing to a complex interplay between macrophagesand neovessels under different pathophysiological conditions. The moderatecorrelation shown only in symptomatic plaques indicates the presence of acute plaque inflammation with increased metabolic activity and cytokine production byinflammatory cells.