Carotid Plaque Positron Emission Tomography Imaging and Cerebral Ischemic Disease

Background and Purpose— The clinical utility of positron emission tomography (PET) imaging in evaluating carotid artery plaque vulnerability remains unclear. Two tracers of recent interest for carotid plaque imaging are 18 F-fluorodeoxyglucose ( 18 F-FDG) and 18 F-sodium fluoride ( 18 F-NaF). We performed a systematic review and meta-analysis evaluating the association between carotid artery 18 F-FDG or 18 F-NaF uptake and recent or future cerebral ischemic events. Methods— A systematic review of Ovid MEDLINE, Ovid EMBASE, and the Cochrane library was conducted from inception to December 2017 for articles evaluating PET tracer uptake in recently symptomatic versus asymptomatic carotid arteries, and articles evaluating carotid uptake in relation to future ischemic events. Cerebral ischemic events were defined as ipsilateral strokes, transient ischemic attacks, or amaurosis fugax. We quantitatively pooled studies by a random-effects model when 3 or more studies were amenable for analysis. We assessed the standardized mean difference between tracer uptake in the symptomatic versus asymptomatic carotid artery using Cohen’s d metric. Results— After screening 4144 unique articles, 13 prospective cohort studies assessing carotid artery 18 F-FDG uptake in patients with recent cerebral ischemia were eligible for review. Eleven cohorts of 290 subjects scanned with 18 F-FDG were eligible for meta-analysis. We found that carotid arteries ipsilateral to recent ischemic events had significantly higher 18 F-FDG uptake than asymptomatic arteries (Cohen’s d =0.492; CI=0.130–0.855; P =0.008) as well as significant heterogeneity (Cochran’s Q =31.5; P =0.0005; I 2 =68.3%). Meta-regression was not performed due to the limited number of studies in the analysis. Only 2 studies investigating 18 F-NaF PET imaging, and another 2 articles investigating ischemic event recurrence were found. Conclusions— Recent ipsilateral cerebral ischemia may be associated with increased carotid 18 F-FDG uptake on PET imaging regardless of degree of carotid stenosis, although significant heterogeneity was found, and these results should be interpreted with caution. Emerging evidence suggests a similar association may be present with 18 F-NaF plaque uptake. More studies are warranted to provide definitive conclusions on the utility of 18 F-FDG or 18 F-NaF in carotid plaque evaluation before investigating carotid PET as a diagnostic tool for cerebral ischemic events.