To assess the diagnostic value of magnetization transfer MRI (MTI) for bowel inflammation and fibrosis in humans with Crohn disease (CD).

From July 2014 through April 2017, 31 patients with a confirmed diagnosis of CD were prospectively recruited from the First Affiliated Hospital of Sun Yat-Sen University. They were scheduled for elective surgery due to bowel obstruction and other complications, and underwent preoperative MR enterography (MRE) and MTI within 15 days of surgery. All cases had available intestinal specimens identified on MRE and resected bowel segments for region-by-region matching. All patients underwent breath-hold conventional MRE and MTI examinations, and then the magnetization transfer ratios (MTRs) of pathological bowel segments were measured. Using region-by-region correlation between MTI and surgical specimen, the bowel segments were resected to stain with HE for evaluating bowel inflammation, Masson for bowel fibrosis, and type Ⅰ collagen staining for the deposition of type Ⅰ collagen within the bowel walls. The histologic sections from the most severe areas were scored as 0 (normal), 1 (mild), 2 (moderate) and 3 (severe). The correlations between MTR and histologic scores were analyzed by using Spearman rank correlation or partial correlation. The differences in MTR among different grades of bowel fibrosis were analyzed by one-way ANOVA. The efficacy of MTR for predicting bowel fibrosis was evaluated by receiver operating characteristic curves analysis. The difference in MTRs between purely inflammatory bowel walls and mixed fibrotic and inflammatory bowel walls was analyzed by Student's t test.

Sixty-two resected bowel specimens from 31 patients including 9 purely inflammatory bowel walls and 53 mixed fibrotic and inflammatory bowel walls were obtained in this study. There were significant differences in MTR among non-fibrotic [ (21.45±2.65) %], mildly [ (30.88±6.14) %], moderately [ (35.14±4.31) %] and severely [ (35.14±4.31) %] fibrotic walls (F=38.397, P<0.01). MTRs strongly correlated with fibrosis scores (r=0.681, P<0.01). High accuracy of MTRs was shown (curve under area=0.905, P<0.01) for differentiating moderately-severely fibrotic from non-fibrotic and mildly fibrotic bowel walls. Using MTR of 31.50% as a cutoff value, the sensitivity and specificity were 93.6% and 80.0%, respectively. The MTRs of purely inflammatory bowel walls [ (21.45±2.65) %] were significantly higher than that of mixed fibrotic and inflammatory [ (36.28±5.21) %] bowel walls (t=-13.052,P<0.01). MTRs correlated with the scores of type Ⅰ collagen (r=0.325, P=0.044) but did not correlate with inflammation scores (r=-0.024, P=0.857).

MTI enables quantitative evaluation of bowel fibrosis in patients with CD and can be used to differentiate purely inflammatory CD from mixed fibrotic and inflammatory CD.

Crohn disease; Magnetization transfer imaging; Fibrosis; Inflammation