F-18-FDG Uptake in uninfected aortic endovascular grafts

1601 Objectives: The aim of our investigation was to evaluate 18F-FDG accumulation in uninfected aortic endovascular grafts, and to track the changes in 18F-FDG uptake over time. Methods: The departmental database was searched to identify pts with aortic endovascular grafts who underwent serial 18F-FDG PET/CT imaging for oncologic indications. All pts were more than 6 months post aortic graft implantation and were asymptomatic with respect to the graft. The time interval of all scans for all pts was 1.5±1.2 yrs (range = 84 days - 5.4 yrs). Seventy-three 18F-FDG PET/CT scans performed on 22 pts (4 female; 18 male; age: 74±10 yrs; range: 63 - 90 yrs) were reviewed retrospectively by a single nuclear physician. SUVmax values were measured in the ascending thoracic aorta and were considered to represent 18F-FDG background (B). SUVmax values also were measured at 3 locations along the graft (G). Mean aortic G SUVmax values and G/B ratios were calculated. Differences in G /B ratio per pt were determined by the unpaired t-test. Significance of changes over time were determined by comparing B/G ratios at later time points compared to the initial time point, per pt. Results: There were a total of 73 18F-FDG PET/CT scans performed on the 22 pts: 10 pts had 2 scans, 5 pts had 3, 2 pts had 4, 2 pts had 5, 2 pts had 6 and 1 pt had 8 scans. Among all 22 pts at all time points, G ranged from 0.7-3.0 and B ranged from 1.0-3.2; G and B were statistically similar (1.80±0.44 versus 1.81±0.33, p = 0.85). Per pt, G was significantly lower than B in 10 scans of 5 pts (1.49±0.22 versus 1.82±0.39, p = 0.002), and G was significantly higher than B in 7 scans of 5 pts (2.42±0.27 versus 1.89±0.27, p = 0.009). Over time, statistically significant differences in G were found in 16% (12/73) of scans. Ten of the 22 pts (45%) had statistically significant differences between G and B values. G increased in 5/10 pts, starting with a mean SUVmax 0.77±0.89, which increased to SUVmax 1.99±0.50 (p = 0.01) over a mean time of 833± 644 days. G decreased in 5/10 pts, starting with a mean SUVmax 1.95±0.50, which decreased to SUVmax 1.54±0.56 (p = 0.01) over a mean time difference of 513±474 days. However, much of this apparent change was attributable to overall changes in 18F-FDG uptake per pt, insofar as G/B ratio changed only marginally over time and in only 3 pts, decreasing from 1.01±0.21 to 0.70±0.05 (p = 0.07). For all scans of all pts, G/B ratio = 1.00±0.22 (range: 0.57-1.84). Consequently, in our series of pts, the upper limit of G/B ratio for uninfected aortic endovascular grafts was 1.43. Conclusion: On a scan-by-scan basis, mean aortic endovascular graft uptake can appear to be higher or lower than background uptake. But intraindividual 18F-FDG G/B ratios for these grafts is relative stable over time.