18FDG PET and ultrasound echolucency in carotid artery plaques.

Objectives: The objective was to evaluate inflammation in echolucent carotid artery plaques.

Background: Ultrasound echolucency of carotid artery plaques has been proven to differentiate patients at high risk of stroke. On the other hand, positron emission tomography (PET) of plaques with the use of [(18)F]-fluorodeoxyglucose (FDG) identifies highly inflamed plaques, and the combination of molecular imaging and morphology could improve identification of vulnerable plaques.

Methods: A total of 33 patients with cerebrovascular symptoms and carotid artery plaques were included prospectively for ultrasound and PET imaging. Plaque standardized gray scale medians (GSM) were measured in longitudinal ultrasound images to quantitate echolucency, and GSM values were compared with FDG PET uptake quantified by maximum standardized uptake values (SUV). Symptomatic plaques were compared with contralateral carotid artery plaques considered asymptomatic, and in 17 symptomatic patients, endarterectomized plaque specimens were analyzed for CD68 expression.

Results: There was a negative correlation between GSM and FDG SUV (r = -0.56, p < 0.01). Whereas echo-rich plaques tended to show low FDG uptake, echolucent plaques ranged from high to low inflammatory activity, as depicted with PET. Quantitative FDG SUV differentiated asymptomatic from symptomatic plaques, whereas GSM values did not. There was a positive correlation between CD68 expression and FDG uptake (r = 0.50, p = 0.04).

Conclusions: Our results substantiate previous findings of an association between plaque FDG uptake and inflammation. Echolucent plaques exhibit a wide range of inflammatory activity, whereas echorich plaques show little inflammation. FDG PET may be useful for further stratification of echolucent plaques being either active (vulnerable) or inactive.