Not all aortic segments are created equal: an exploratory analysis from a 18F-NaF PET-CT study

Abstract Introduction 18F-NaF-PET-CT (Positron emission tomography­ computed tomography with 18F­sodium fluoride) is able to identify active microcalcification, a marker of plaque instability. Differences in 18F-NaF uptake between the coronary, carotid and aortic territories have been described. Purpose We sought to further characterize regional variations in 18F-NaF uptake within the Aorta of a population with high cardiovascular (CV) risk. Methods We prospectively scanned individuals at high CV risk but no prior events with 18F-NaF-PET-CT. Aortic wall 18F-NaF uptake was quantified via tissue-to-background ratio (TBR), which was calculated by dividing the maximum standard uptake value in each region of interest by the baseline blood pool activity (measured in the atria). Results Thirty patients were included in this analysis. Mean age was 63.7 ± 9.5 years, 70.0% were male, most were diabetic and hypertensive (93.3%). Estimated 10-year CV event risk was 10.5% (6.5-15.5) according to SCORE2/SCORE-OP and 32.2 ± 18.6% according to the ASCVD equation. 18F-NaF uptake was significantly higher in the Abdominal Aorta compared with remaining aortic segments p0.001; Abdominal Aorta TBR: 1.84 (1.56-2.21); Descending Thoracic Aorta TBR: 1.63 (1.51-1.84); Aortic Arch TBR: 1.68 ± 0.25; Ascending Aorta TBR: 1.65 (1.43-1.78). No other significant regional differences were found. Males had higher Abdominal Aorta TBR (1.95 (1.68-2.62) vs. 1.56 (1.51-1.79), p = 0.014). Higher 18F-NaF uptake was positively correlated with the 10-year event risk estimated by the SCORE2/SCORE-OP and ASCVD systems (R=0.49/p=0.006 and R=0.43/p=0.017, respectively). There was no significant association between other baseline characteristics and Abdominal Aorta TBR. Conclusions In our cohort, the abdominal portion of the Aorta had significantly higher 18F-NaF activity than other segments. Abdominal Aorta TBR was more pronounced in males and was positively associated with greater predicted CV risk. Larger studies are required to validate these findings and determine the role of 18F-NaF-PET-CT in CV disease research and management.