Multi-modality Imaging of Inflammation and Calcification within the Lower Limb Arterial Tree: A PET/CT Study

Abstract

Atherosclerosis is linked with both inflammatory and calcific processes occurring at the vessel wall. Novel imaging techniques (PET CT analysis) have been developed to assess such processes using 18F-sodium fluoride (18F-NaF – calcification) and 18F-fluorodeoxyglucose (18F-FDG – inflammation). Such imaging has been predominantly undertaken within the coronary and carotid circulation. This study is the first to prospectively validate PET CT analysis in peripheral arterial disease (PAD). 8 patients (16 legs; 5 men, median age 74.5 years) with intermittent claudication underwent PET CT analysis using the 18F-NaF and 18F-FDG tracers using standard protocols. For each scan, the lower limb arterial tree was examined from the aortic bifurcation to the ankle. The degree of arterial calcification (AC) was measured using the modified Agatston score. Atherosclerotic disease burden was analysed using Bollinger scoring method. Overall whole limb median (IQR) TBR levels for 18F NaF was 1.30 (0.98–1.74) and for 18F FDG was 1.42 (1.11–1.75). The median limb AC score was 1954.5 (1198–2216). Significant correlations were seen between FDG uptake and both NaF uptake and AC and there was an inverse relationship between NaF tracer uptake and AC (all p < 0.05). Increasing burden of atherosclerosis was associated with lower NaF uptake and a higher AC (p < 0.05). This study is the first to validate PET CT analysis in patients with PAD. It also starts to assess potential relationships between inflammation and calcification. Further studies are required to look at longer-term consequence of such findings with regard to atherosclerotic progression/development.