Abstract 17612: Is Glucose Corrected [18f]-fluorodeoxyglucose Uptake in Human Carotid Plaque Associated with the Extent of Inflammation on Immunohistology? A Sub-Study of the Canadian Atherosclerosis Imaging Network (CAIN)

Abstract

Background ‘Vulnerable’ plaque has increased density of macrophages that require high-levels of energy for phagocytic activity. The uptake of radiolabelled glucose or [18F]-fluorodeoxyglucose (FDG) imaged with positron emission tomography (PET) and computed tomography (CT) may serve as a surrogate marker of inflammatory activity within plaque. Variance in glucose homeostasis exists amongst patients, thus FDG uptake corrected to patient blood glucose levels may be necessary [[Unable to Display Character: –]] albeit not routinely performed. We hypothesized that glucose corrected FDG uptake (CG-FDG) is associated with intraplaque inflammatory burden using macrophage-specific CD68 immunohistology.

Methods Thirty-one patients (66±10 years, 25 male) scheduled for carotid endarterectomy were prospectively recruited. Patients underwent PET and CT angiography. Maximum CG-FDG was measured at the left and right internal carotid arteries and normalized to blood, resulting in a glucose corrected tissue to blood ratio (TBR). Excised plaque was fixed, sectioned and immunostained for CD68. CD68 expression was analyzed with whole-slide digitized images.

Results Of 31 patients, immunohistology was performed in 22 patients and 1 patient required a 2^nd endarterectomy due to bilateral disease. Maximum CG-FDG uptake correlated with macrophage expression assessed by CD68 staining (r=0.589, p=0.003) (Fig. 1). Patients were divided into symptomatic (n=50 plaques, 25 patients) and asymptomatic (n=12 plaques, 6 patients) groups. CG-FDG uptake was greater in the symptomatic group (3.5±1.3 TBR vs. 2.7±0.9 TBR, p=0.04). CG-FDG uptake did not vary between diabetic and non-diabetic plaques (3.3±0.8 TBR n=10 diabetic vs. 3.4±1.3 TBR n=52 non-diabetic, p=0.8).

Conclusion CG-FDG uptake in carotid vasculature is related to inflammatory burden within plaque. CG-FDG may serve as a surrogate marker of high-risk inflamed plaque and may enable early identification of patients at risk.