FDG PET/CT in Crohn's disease: correlation of quantitative FDG PET/CT parameters with clinical and endoscopic surrogate markers of disease activity

Purpose The aim of this study was to determine the feasibility and potential clinical utility of assessment of Crohn's disease (CD) activity by F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT employing a new quantitative approach. Methods A total of 22 subjects (mean age 37) with CD who had undergone FDG PET/CT followed by ileocolonoscopy within 1 week were included in this analysis. The CD endoscopy index of severity (CDEIS) for various bowel segments was calculated. The CD activity index (CDAI) was evaluated, and fecal calprotectin was measured. On PET, regions with increased FDG uptake in large bowel were segmented with an adaptive contrast-oriented thresholding algorithm, and metabolically active volume (MAV), uncorrected mean standardized uptake value (SUVmean), partial volume-corrected SUVmean (PVC-SUVmean), SUVmax, uncorrected total lesion glycolysis (TLG = MAV x SUVmean), and PVC total lesion glycolysis (PVC-TLG = MAV x PVC-SUVmean) were measured. Global CD activity score (GCDAS) was calculated as the sum of PVC-TLG over all clinically significant FDG-avid regions in each subject. Correlations between regional PET quantification measures (SUVs, TLGs) and CDEIS were calculated. Correlations between the global PET quantification measure (GCDAS, global SUVs) with CDAI, fecal calprotectin, CDEIS, and CRP level were also calculated. Results SUVmax, PVC-SUVmean, and PVC-TLG significantly correlated with segment CDEIS subscores (r = 0.50, r = 0.69, and r = 0.31, respectively; p < 0.05). GCDAS significantly correlated with CDAI and fecal calprotectin (r = 0.64 and r = 0.51, respectively; p < 0.05). Conclusion By employing this new quantitative approach, we were able to calculate indices of regional and global CD activity, which correlated well with both clinical and pathological disease activity surrogate markers. This approach may be of clinical importance in measuring both global disease activity and treatment response in patients with CD.