[18F]-Fluorodeoxyglucose PET/CT imaging as a marker of carotid plaque inflammation: Comparison to immunohistology and relationship to acuity of events

Background: [18F]-fluorodeoxyglucose ( ¹⁸ FDG) uptake imaged with positron emission tomography (PET) and computed tomography (CT) may serve as a biomarker of plaque inflammation. This study evaluated the relationship between carotid plaque ¹⁸ FDG uptake and a) intraplaque expression of macrophage and macrophage-like cellular CD68 immunohistology; b) intraplaque inflammatory burden using leukocyte-sensitive CD45 immunohistology; c) symptomatic patient presentation; d) time from last cerebrovascular event. Methods: 54 patients scheduled for carotid endarterectomy underwent ¹⁸ FDG PET/CT imaging. Maximum 18FDG uptake (SUV _max ) and tissue-to-blood ratio (TBR _max ) was measured for carotid plaques. Quantitative immunohistological analysis of macrophage-like cell expression (CD68) and leukocyte content (CD45) was performed. Results: ¹⁸ FDG uptake was related to CD68 macrophage expression (TBR _max : r = 0.51, p < 0.001), and total-plaque leukocyte CD45 expression (TBR _max : r = 0.632, p = 0.009, p < 0.001). ¹⁸ FDG TBR _max uptake in carotid plaque associated with patient symptoms was greater than asymptomatic plaque (3.58 ± 1.01 vs. 3.13 ± 1.10, p = 0.008). ¹⁸ FDG uptake differed between an acuity threshold of <90 days and >90 days (SUV _max :3.15 ± 0.87 vs. 2.52 ± 0.45, p = 0.015). Conclusions: In this CAIN cohort, ¹⁸ FDG uptake imaged with PET/CT serves a surrogate marker of intraplaque inflammatory macrophage, macrophage-like cell and leukocyte burden. 18FDG uptake is greater in plaque associated with patient symptoms and those with recent cerebrovascular events. Future studies are needed to relate ¹⁸ FDG uptake and disease progression.