Higher reliability of 18F-FDG target background ratio compared to standardized uptake value in vulnerable carotid plaque detection: a pilot study

To evaluate the role of [18F]-fluorodeoxyglucose positron emission tomography/computer tomography [18F-FDG PET/CT] comparing target background ratio (TBR) and standardized uptake value (SUV) with the histopathological inflammatory status of the carotid plaques. Vulnerable carotid plaques are the primary cause of acute cerebrovascular events. 18F-FDG PET/CT represents a morpho-functional technique able to identify the highly inflamed and most vulnerable carotid plaques. Several literature studies experimented this new method to identify vascular inflammation, but few have effectively compared PET/CT results with plaque histological data and no studies had directly compared TBR to SUV. Thirty-two consecutive patients (20 men and 12 women, mean age 74 +/- A 8 years) undergoing carotid endarterectomy were enrolled and studied with carotid 18F-FDG PET/CT. Maximum and mean SUV and TBR were used to quantify 18F-FDG uptake while surgical specimens were analyzed by optical microscopy to identify inflamed carotid plaques, with evaluation of macrophages infiltration by mean of immunohistochemistry. On the basis of the presence of inflammation at the histological analysis, we divided population in two groups: group A (n = 12) patients with inflamed carotid plaques and group B (n = 20) patients with non-inflamed ones, then crossed and evaluated the histological data with 18F-FDG PET/CT findings. SUV max and SUV mean values resulted higher in group A (respectively, 2.14 +/- A 0.77 and 1.99 +/- A 0.68) than in group B (respectively, 1.79 +/- A 0.37 and 1.64 +/- A 0.34) without reaching a statistical significance (p = ns). TBR max and TBR mean values resulted higher in group A (respectively, 1.42 +/- A 0.32 and 1.34 +/- A 0.26) than in group B (respectively, 1.16 +/- A 0.19 and 1.03 +/- A 0.20) with a statistically significant differences between the two groups and carotid inflammation (respectively, p < 0.01 and p < 0.001). TBR (max and mean values) is a more reliable parameter than SUV in identifying inflamed plaques. Although limited by the small population analyzed, our results suggest the important role of 18F-FDG PET/CT, using TBR, in identification of high-risk carotid atherosclerotic plaques.