Introduction: Positron emission tomography (PET) with 18F-fluorodeoxyglucose ([18F]FDG) can be used to detect atherosclerotic plaque inflammation. The degree of [18F]FDG uptake in different stages of coronary atherosclerosis remains largely unknown. Thus, we studied the amount of [18F]FDG uptake and feasibility of its in vivo quantification by combination of PET and computed tomography angiography (CTA) in a pig model of atherosclerosis.

Methods: In order to induce coronary atherosclerosis, diabetes was caused by streptozotocin injections in farm pigs (n=10). After 6 months on high-fat diet, pigs underwent dual gated cardiac PET and CTA to measure [18F]FDG uptake in the proximal segments of coronary arteries as maximal target to background ratio (TBR = [18F]FDG uptake normalized to blood pool). Proximal coronary segments (n=33) were harvested for ex vivo measurement of radioactivity and for histology and measurement of tracer uptake into the vessel wall by autoradiography (ARG).

Results: The pigs were hyperglycemic (12.3±4.7 mmol/L) and hypercholesterolemic (12.7±5.1 mmol/L) at the end of the study. The coronary arteries showed intimal thickening (n=16 segments) and atheroma (n=10 segments). Compared with the normal vessel wall, ARG showed 1.7±0.7 times higher accumulation of [18F]FDG in intimal thickening and 4.1±2.3 in atheroma (p=0.004 and p=0.003, respectively). Ex vivo mean vessel to blood ratio of segments with atheroma was higher than non-atherosclerotic segments (2.6±1.2 vs. 1.3±0.7, p=0.04). In vivo PET imaging showed the highest TBR of 2.7. However, maximal TBR was not significantly different in segments without atherosclerosis (1.1±0.5) and either intimal thickening (1.2±0.4, p=1.0) or atheroma (1.6±0.6, p=0.4) and no correlation was seen between the segmental TBR measured by in vivo PET-CT and [18F]FDG uptake measured by either biodistribution or autoradiography.

Conclusions: We found increased [18F]FDG uptake in atherosclerotic lesions. However, quantification of [18F]FDG uptake in these relatively small and early stage atherosclerotic lesions by dual gated PET and CTA was not feasible. Further studies are needed to clarify feasibility of this approach in more advanced and highly inflamed atherosclerotic coronary plaques.