18F-FDG PET-MR enterography in predicting histological active disease using the Nancy index in ulcerative colitis: a randomized controlled trial

Purpose To evaluate the diagnostic performance of PET-MR enterography in detecting histological active inflammation in patients with ulcerative colitis and the impact of bowel purgation on diagnostic accuracies of PET-MR parameters. Methods Fifty patients were enrolled in this randomized controlled trial (clinicaltrials.gov [NCT03781284]). Forty patients were randomized in two study arms, in which bowel purgation was performed either before or after PET-MR enterography. All patients underwent ileocolonoscopy with mucosal biopsies after PET-MR within 24 h. Diagnostic performance of MR morphological parameters (MRmorph), diffusion-weighted imaging (DWI), and PET in detecting histological inflammation determined by the Nancy index was compared with each other and between study arms. Correlation between PET and histological inflammatory severity was calculated. Results In study arm without previous bowel purgation, SUVmax ratio of bowel segment (relative to SUVmax of the liver) facilitated the highest specificity and diagnostic accuracy compared with MRmorph and DWI. Bowel cleansing led to markedly increased metabolic activity of bowel segments, resulting in significantly reduced specificity of PET compared with study arm without purgation (0.808 vs. 0.966, p = 0.007, respectively). Inter-observer concordance for assessing MRmorph was clearly increased after bowel cleansing (Cohen's kappa, 0.847 vs. 0.665; p = 0.013, respectively), though diagnostic performance of MRmorph was not significantly improved. Our findings suggested that the change of metabolic status was mainly associated with the grade of neutrophil infiltrate and less dependent on chronic infiltrate. Conclusion PET-MR enterography was an excellent non-invasive diagnostic method in the assessment of histological active inflammation in ulcerative colitis without the need of previous bowel purgation.