Assessment of Inflammation in Non-calcified Artery Plaques with Dynamic 18F-FDG-PET/CT: CT Alone, Does-It Detect the Vulnerable Plaque?

Background: The goal of this work was to measure artery inflammation in aged volunteers with atherosclerosis using computed tomography (CT) and positron emission tomography (PET) with 18F-FDG. The artery plaques are composed of lipid rich fibrous tissue and foamy macrophages and are the most vulnerable for detachment. Such plaques can be differentiated by their density with CT imaging. Methods: A healthy artery (NAR) was considered with no plaque on a CT images and with density between 51 and 130 Hounsfield Units (HU). A non-calcified plaque (NCP) and a calcified plaque (CP) were respectively identified as having a density ≤ 50 HU and >130 HU. In the calcified arteries, the calcification area divided by the artery area (RCA) and the calcification score (ACS) were classified with Hierarchical K-means algorithm into 4 clusters and were correlated with the metabolic rate of 18F-FDG (MRG). Results: we found MRG statistically higher in NCP in comparison to NAR and CP in subjects without medication (P < 0.05). In subjects under-medication, NCP values were found the lowest. MRG of NCP in non-medication subjects was statistically significantly different from CP with small area but not from CP with large areas (P = 0.40). In under-medication subjects, no statistical differences were found between NCP and CP independently of plaque area and density. Conclusion: Since the low-density plaque was reported as the vulnerable plaque, based on the present work, this latter can be simply identified on CT images with intensity between 30 HU and 50 HU.