What is the natural history of 18F-FDG uptake in arterial atheroma on PET/CT? Implications for imaging the vulnerable plaque

Purpose: Increased uptake of 18F-fluorodeoxyglucose (18F-FDG) in atherosclerotic plaque on Positron Emission Tomography (PET), predicts vulnerability. Recent studies have shown that the PET signal is reproducible over a 2-week period and as a result drug trials are underway. However, the natural history of these lesions is unknown. The aim of this study is determine the natural history of increased vascular wall uptake of 18F-fluorodeoxyglucose (18F-FDG).

Methods: Following institutional ethics committee approval, we retrospectively examined PET/CT images of patients from our Institution that had at least 4 examinations in the last 5 years. This represented 205 studies in total, from 50 patients (29 men, 21 women, mean age 49.4+/-12.1 years, mean 5.1+/-1.7 studies/patient). The mean follow-up was 27.2+/-11.8 months. The carotids and the aorta were evaluated for increased 18F-FDG uptake with a maximum Standardized Uptake Value (SUVmax)>2.5, and >3.0, and calcification. Plots of SUVmax and Hounsfield units (HU) were made versus time.

Results: The initial prevalence of increased focal arterial 18F-FDG uptake was 17/50 patients and of arterial calcification 19/50. 132 sites of 18F-FDG uptake in total were observed longitudinally. 18F-FDG vascular uptake did not persist with time. There was no correlation between 18F-FDG uptake and HU. No calcifications developed at sites of focal increased 18F-FDG uptake.

Conclusions: Arterial lesions with increased 18F-FDG uptake represent transient phenomena. This data is important for the interpretation of findings of clinical trials using arterial 18F-FDG uptake as an imaging biomarker to monitor pharmacological intervention.