Background: Colonoscopy is the gold standard for evaluating mucosal inflammation of ulcerative colitis (UC), but it is an invasive procedure with risks. Integrated positron emission tomography (PET)/magnetic resonance (MR) has the potential to be a non-invasive and sensitive tool for the evaluation of disease extent and activity in UC patients. The aim of this study was to explore the utility of PET/MR in patients with UC in clinical remission.
Methods: This prospective study was approved by the institutional review board of the hospital, and informed consent was obtained. Between November 2015 and September 2016, 19 patients with UC in clinical remission were enrolled. These patients received PET/MR and subsequent colonoscopy with biopsy. Laboratory biomarkers, including serum high sensitivity C-reactive protein (hs-CRP) and fecal calprotectin (FC), were also obtained. The findings of colonoscopy were graded using the Mayo score, and the PET activity grade were determined depending upon the maximum standardized uptake value (SUVmax) ratio of the colon segment to liver.
Results: Seventeen of 19 patients (89%) showed increased metabolism of colon on PET/MR.
On colonoscopy, nine of the patients had moderate to severe disease (Mayo score ≥2), six had mild disease (Mayo score =1), and four had inactive disease (Mayo score =0). The Mayo score showed significant correlation with the Nancy histological index (Spearman's ρ=0.547, p=0.015). There were significant higher PET scores in patients with moderate to severe disease (Mayo score ≥2) than patients with mild or inactive disease (p=0.025). In per-segment analysis, PET activity was seen in 38 of 95 (40%) colon segments, and the sensitivity and specificity for identifying moderate to severe disease were 0.67 and 0.64. In per-patient analysis, the area under the receiver operating characteristic curve (AUC) of hs-CRP, FC, and PET/MR were 0.589, 0.722, and 0.778, respectively. Using a combined index of FC and PET score, a higher AUC (0.850) can be achieved.
Conclusions: PET/MR is a promising non-invasive tool for evaluating subclinical inflammation in patients with UC in clinical remission.