High tissue matrix metalloproteinase (MMP) activity has been associated with advanced atherosclerosis and plaque rupture. 18F-FDG uptake has been reported to detect inflammation. This investigation examined the vascular 18F-FDG uptake by PET/CT and its correlation with circulating MMP-1 levels. METHODS: We examined 25 consecutive patients with significant carotid stenosis and 22 healthy control subjects using 18F-FDG PET/CT. The leukocyte counts, C-reactive protein (CRP), and MMP-1 were measured. RESULTS: 18F-FDG arterial uptake, as well as calcifications, was significantly higher in extensive distributions in patients with established carotid stenosis. However, their distribution was not consistently overlapping. The values of circulating MMP-1 and leukocyte counts were significantly higher in patients with carotid stenosis (all P 2.0) in target lesions had higher baseline and poststenting MMP-1 levels (all P