Abstract Body (Do not enter title and authors here): Background:
Abdominal aortic aneurysms (AAA) expand over time and increase the risk of fatal ruptures.
While large aortic diameter increases the risk of rupture, some AAA rupture at small diameters and some large aneurysms do not rupture. Therefore, identification of patients at increased risk of rapid AAA expansion and rupture is importance. To predict expansion, the isolated assessment of ¹⁸F-fluorodeoxyglucose (FDG) and sodium fluoride (NaF) uptake or calcification volume in aneurysms has been investigated with variability in results. We systematically evaluated whether ¹⁸F-FDG and ¹⁸F-NaF uptake were predictive of AAA expansion.

Methods:
Seventy-four (74) male Sprague–Dawley rat AAA models were imaged using positron emission tomography-computed tomography (PET-CT) with ¹⁸F-FDG and ¹⁸F-NaF at 1, 2, 4, 6, and 8 weeks after CaCl₂ or saline stimulation. In the 1-week cohort (n=25), the correlation between ¹⁸F-FDG or ¹⁸F-NaF uptake and pathological markers was investigated. In the time-course cohort (n=49), animals received either atorvastatin, losartan, aldactone, or risedronate to assess the effect of these drugs, and the relationship between aortic size and sequential ¹⁸F-FDG and ¹⁸F-NaF uptake or calcification volume was examined.

Results:
In the 1-week cohort, the maximum standard unit value of ¹⁸F-FDG and ¹⁸F-NaF uptake correlated with CD68-(r=0.82, p=0.0010) and von Kossa staining-positive areas (r=0.89, p<0.0001), respectively.
In the time-course cohort, ¹⁸F-FDG and ¹⁸F-NaF uptake changed in a time-dependent manner and drugs attenuated this uptake. Specifically, ¹⁸F-FDG showed high uptake at weeks 1 and 2, whereas a high ¹⁸F-NaF uptake was noted throughout the study period. Although drugs suppressed ¹⁸F-NaF and ¹⁸F-FDG uptake, only atorvastatin significantly reduced aortic enlargement. Risedronate decreased the calcification volume; however, the aorta was significantly enlarged.
The final aortic area correlated well with ¹⁸F-FDG and ¹⁸F-NaF uptake and calcification volume, especially at 1 and 2 weeks [¹⁸F-NaF(1week): r=0.61, ¹⁸F-FDG(2weeks): r=0.51, calcification volume(1week): r=0.59, p<0.0001]. Multiple linear regression analysis showed that the combination of these factors predicted the final aortic size, with ¹⁸F-NaF uptake at 1 week being the strongest predictor.

Conclusion:
The uptake of ¹⁸F-NaF and ¹⁸F-FDG and the calcification volume at appropriate times correlated with the development of AAAs, with ¹⁸F-NaF uptake being the strongest predictor.