Correlation between thoracic aorta 18F-natrium fluoride uptake and cardiovascular risk

Background and Aims: 18F Natrium Fluoride (NaF) has been proposed as a clinical tool to identify and quantify ongoing arterial calcification. Estimation of NaF uptake by vessel walls is feasible in the majority of large vessels; it is conversely more challenging within the coronary tree, given the small size of these vessels and the artifacts from cardiac movement. In CT-based studies, thoracic artery calcification has been linked to both coronary calcification and cardiovascular risk (CVR). Moreover, among thoracic segments, descending aorta has demonstrated the greatest correlation to CVR and to CV events. In this study, we evaluated NaF uptake in different segments of the thoracic aorta, its difference among CVR groups and its correlation with the absolute CVR value. Patients and Methods: 78 patients (44 females, mean age 63, range 44-83) underwent whole body NaF PET/CT, to detect intraosseous localization of breast or prostate cancer. CVR risk score was assessed with a modified version of the Framingham model, accounting BMI in lieu of cholesterol levels; patients were divided in three CVR categories: low (LR), medium (MR) and high risk (HR), who had a likelihood of 10-years CV events of <10%, 10-20% and >20%, respectively. NaF uptake was measured by manually drawing volumes of interest (VOI) on the ascending aorta, on the aortic arch, on the descending aorta and on the myocardium; average SUV measured within these VOI was normalized for blood-pool SUV, assessed in the inferior vena cava, to obtain target-to-background ratio (TBR). Values from the three aortic segments were then averaged to obtain an index of the whole thoracic aorta. Results: There was a significant difference in whole thoracic aorta ??? TBR between HR and LR (1.84±0.76 vs 1.07±0.3, p<0.001), but also between MR and HR-LR (1.4±0.4, p<0.02 and p<0.01, respectively). The most efficient CVR stratification was however observed in the descending aortic segment: significance of the TBR difference between HR vs LR, HR vs MR and MR vs LR was 0.0004, 0.008 and 0.01, respectively. Correlation between TBR and CVR was appreciable when the whole thoracic aorta was considered (R=0.67), but it peaked when correlating the descending thoracic segment (R=0.75), in comparison with the aortic arch and the ascending segment (R=0.55 and 0.53, respectively). Conclusions: Fluoride uptake within the thoracic aorta wall effectively depicts patients' risk class and closely correlates with cardiovascular risk. Among segments, descending thoracic aorta is the most effective in CVR determination.