Imaging giant cell arteritis and Aortitis in contrast enhanced 18F-FDG PET/CT: Which imaging score correlates best with laboratory inflammation markers?

Purpose: To define the most appropriate imaging parameters in combined Fluorodeoxyglucose (FDG) PET/CT reflecting the inflammatory burden in large vessel vasculitis.

Methods: Two readers retrospectively graded disease extent and activity in 17 LVV patients using visual and quantitative scores in FDG PET and contrast enhanced CT. Visual PET scores were assessed corresponding to FDG-uptake vs. liver uptake (score 0-3). CT visual scoring referred to the affected vessel extent (score 1-5). Quantitative PET scores relied on normalized SUV ratios. For quantitative CT evaluation vessel wall thickness was correlated with FDG- uptake. Imaging scores were correlated with Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP). Intraclass correlation coefficients (ICC) were measured for interreader reliability.

Results: Visual PET scores showed stronger correlation with CRP (ρ 0.640, 0.541 for reader I and II, respectively) than with ESR levels (ρ 0.477, 0.447). Quantitative PET showed strongest correlation with CRP using liver as reference tissue. Visual CT scores did neither correlate with ESR nor with CRP levels (ESR: ρ 0.085, 0.294 with p 0.743, 0.252; CRP: ρ 0.322, 0.395 with p 0.208, 0.116). Quantitative CT evaluation correlated with ESR levels in one reader (ρ 0.505, -0.026), however no correlation between quantitative CT measures and quantitative PET scores was found. Best ICC between readers was 0.994 for highest SUV_avg vessel/highest SUV_avg liver.

Conclusions: Visual and quantitative PET scores were superior to CT scores with best ICC and strongest correlations between quantitative PET score and inflammation markers especially when using vessel to liver ratios.