Variability of FDG-liver uptake in patients with treated large vessel vasculitis

Objectives To assess disease activity of large vessel vasculitis FDG-liver uptake has been proposed as visual and quantitative reference for arterial wall uptake. Aim of this study was to examine the variability of liver uptake in pts. with treated and untreated large vessel vasculitis.

Methods 82 PET/CTs from 27 pts. were analyzed. Ten pts. were studied before and during therapy, in 17 pts. a total of 62 scans was obtained under therapy with glucocorticoids. PET was acquired 60 min. following iv injection of 350 MBq FDG. Variability of average-SUV of the liver (LSUV) was determined by spherical 3D ROIs (diameter: 2 or 4 cm) in one (1xROI) or three (3xROI) localisations and between scans (before and during or exclusively during treatment). For statistical comparison of LSUV the Wilcoxon-test was applied.

Results Variability of LSUV using 2cm-3xROIs (mean 10%, median 9%, range 1-34%) was significantly higher compared to 4cm-3xROIs (mean 7% median 5% range 1-36%; p<0.001). In two consecutive scans under therapy mean variability of LSUV was 13% (2cm-1xROI: median 9%, range 0-70%), 13% (2cm-3xROI: median 9%, range 0-69%), 14% (4cm-1xROI: median 9%, range 0-69%) or 14% (4cm-3xROI: median 9% range 0-78%; differences not significant). A variability of more than 30% was observed in 12% (2 cm-1xROIs), 8% (2cm-3xROI), 9% (4 cm-1xROI) or 8% (4cm-3xROI) of the patients. No significant difference was found between LSUVs before and under therapy (2cm-1xROI: 2,41+/-0,52 vs. 2,37+/-0,25; 2cm-3xROI: 2,86+/-0,56 vs. 3,17+/-0,46; 4cm-1xROI: 2,37+/-0,41; vs. 2,36+/- 0,25; 4cm-3xROI: 2,97+/-0,66 vs. 3,32+/-0,58).

Conclusions Variability of liver uptake in consecutive FDG-PET/CT scans under therapy was up to 78% (>30% in 8-12% of pts.), and in a single scan up to 36%. These findings should be considered when visual or quantitative vessel-to liver-scores are used for diagnosis of large vessel vasculitis. By use of 3 3D-ROIs or a single large 3D-ROI variability of liver uptake can be reduced considerably