Objectives: To elucidate the relation between the echolucent plaque on carotid ultrasound and acute inflammation on F-18 FDG carotid PET/CT Methods: Thirty two patients (M:F ratio =19:13, mean age=62 짹 13 years) who underwent carotid ultrasound were divided into two groups—echolucent plaque (n=22), calcified (n=10). All of the patients underwent F-18 FDG carotid PET/CT. The mean standardized uptake values (SUV), namely target to background ratio (TBR) on 180 min delayed F-18 FDG carotid PET/CT images were compared with serum level of secretory phospholipase A2(sPLA2, Cayman Chemical co., Ann Arbor, MI, USA) in terms of the presence of carotid plaque on carotid US. Results: 180 min TBR of carotid arterial wall at echolucent plaque, calcified plaque were 1.40짹0.05, 1.23짹0.03 in both carotid artery. TBR of carotid arterial walls for echolucent plaque were significantly larger than TBR for calcified plaque at the both side of carotid artery (p<0.05)(Fig). sPLA2 levels in echolucent was larger than in calcified plaque but did not reach the statistical significance.(1.12짹1.29 vs 1.04짹1.32 ng/ml, p=0.07) Conclusions: Our results show that F-18 FDG carotid PET/CT can depict metabolically active echolucent carotid plaques. Furthermore secretory phospholipase A2 need to be inverstigated for surrogates of atherosclerotic plaque