Purpose To compare F-18-fluoro-2-deoxy-D-glucose (F-18 FDG) positron emission tomography/computed tomography (PET/CT) imaging at two different circulation times after injection of F-18 FDG in order to measure atherosclerosis in carotid arteries. Methods We assessed 12 patients with recent symptomatic plaques in the carotid arteries. F-18 FDG PET/CT carotid plaque imaging was performed for 20 min at 2 h after F-18 FDG injection in five patients and at 3 h in seven patients. We measured vessel wall uptake using the maximal standardized uptake value (SUV), and the mean and maximal blood target-to-background ratios (TBR) of the symptomatic carotid arteries. Blood pool activity (BPA) was measured as the mean SUV of the superior vena cava (SVC) and jugular vein of these 12 patients, and in 14 ageand gender-matched patients who underwent whole-body F-18 FDG PET/CT examinations 1 h after injection. Results F-18 FDG PET/CT revealed visible F-18 FDG uptake in all patients with symptomatic carotid plaques. Maximal SUV did not differ between groups evaluated at 2 h and 3 h ($2.62{pm}0.45$ vs $3.00{pm}0.85$, p=0.335). However, mean ($2.04{pm}0.22$ vs $3.54{pm}0.62$, p<0.05) and maximal ($1.65{pm}0.15$ vs $2.70{pm}0.42$, p<0.05) TBR values that were normalized to BPA in the SVC differ significantly. Conclusions Symptomatic carotid plaques are visualized for a relatively short period of imaging time on ${geq}1$-h PET/CT images. Quantitative parameters of atherosclerotic carotid arteries are preserved or even increased over time, whereas those of blood pools are decreased.