NaF-PET/CT as a measure of atherosclerotic calcification in the aorta

Objectives: To quantify the effects of obesity and high-calcium diet on aortic calcification, assessed by 1) NaF-PET/CT and 2) number of aortic calcium depositions on histological section. Methods: This study included 13 swine divided into 4 groups: 2 animals on normal-calorie / normal-calcium diet (control), 4 metabolic syndrome (obese) pigs on high-calorie / normal-calcium diet (MetS), 3 MetS pigs on high-calorie / high-calcium supplement diet (HS), and 4 MetS pigs on high-calorie / high-dairy calcium diet (HD). Each animal underwent whole-body PET/CT 120 min after NaF injection. After NaF-PET/CT analysis, the aorta of each high-fat diet pig was formalin-fixed and paraffin-embedded, and then cross-sections were cut and stained with hematoxylin, eosin stain, and Von Kossa stain. The number of calcium depositions within each microscopic image was averaged for each animal. OsiriX MD software v.10.0.2 was used for semi-quantification of NaF uptake from regions of interest (ROIs) manually drawn around the lumen of the thoracic aorta (Figure 1) and the coronary arteries. SUVmean and ROI volume were measured for each trans-axial slice. The tracer uptake in each slice was calculated by multiplying the slice SUVmean by the slice ROI volume. Avg SUVmean across all slices was used for statistical comparison. Results: Avg SUVmean of the aorta was observed to be lower in the controls (0.647) compared to MetS (0.848), HS (0.791), and HD animals (0.818); however, these trends were not significant (p>0.05). The number of aortic calcium depositions present on histology was significantly lower in MetS animals (1.67) compared to either HS (3.25, p<0.05) or HD (2.88, p<0.05) animals. Previous work in our lab has demonstrated that MetS animals demonstrated 2-fold greater coronary uptake of NaF compared to controls, and histology of coronary specimens revealed microcalcifications present in 36% of MetS pigs. Taken together, these data indicate that NaF-PET/CT shows utilities in the systemic effects of MetS. Conclusion Both MetS and high-calcium diet are associated with increased arterial calcification quantified by NaF-PET/CT. Our lab has previously demonstrated the feasibility of NaF-PET/CT in the quantification of atherogenesis. Blomberg et al. demonstrated that thoracic aorta NaF uptake is significantly associated with each subject’s corresponding Framingham Risk Score (p<0.001), but FDG uptake is not (p= 0.49). These data additionally support the utility of NaF-PET/CT atherosclerotic disease. Additional studies with greater numbers of animals should be performed to validate the use of the effect of high-calorie and high-calcium diets on aortic NaF uptake.

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