T2* Mapping to characterize intestinal fibrosis in crohn's disease

Background: Assessing bowel fibrosis in patients with Crohn's disease (CD) has important therapeutic implications.

Purpose: To determine the utility of T2* mapping versus that of contrast enhanced (CE) imaging in grading intestinal fibrosis in patients with CD using surgical pathology as the reference standard.

Study type: Prospective.

Specimens: 102 specimens from 27 patients with CD.

Field strength/sequence: 3.0T; T2WI; T1WI; T2*WI.

Assessment: The T2*WI values of the bowel wall targeted for resection were measured by two radiologists by drawing regions of interest on the thickened bowel wall. The resected bowel specimens with pathological fibrosis and type I collagen were classified into four severity grades (0-3) by a pathologist using a semi-quantitative scoring system.

Statistical tests: The differences in the T2*WI values among the different histological grades were analyzed using one-way analysis of variance or the Kruskal-Wallis test, and their correlations were analyzed. The ability of the T2*WI values to discriminate between various degrees of fibrosis was assessed using a receiver operating characteristic (ROC) curve.

Results: Significant differences were observed in the T2* values of mild (23.56 ± 1.60 ms), moderate (16.19 ± 0.55 ms), and severe (13.59 ± 0.53 ms) fibrosis types (F = 35.84; P < 0.001). T2* values were moderately associated with histological fibrosis (r = -0.627; P < 0.001) and type I collagen scores (r = -0.588; P < 0.001). T2* values were highly accurate, with an area under the ROC curve (AUC) of 0.951 (P < 0.001) for differentiating moderate-to-severe fibrosis from nonfibrosis and mild fibrosis, followed by an AUC of 0.508 for the percentage of enhancement gain (P = 0.908). A threshold T2* value of 18.06 ms was recommended for diagnosing moderate-to-severe fibrosis with 94.7% sensitivity and 78.3% specificity.

Data conclusion: MRI T2* mapping outperforms CE parameters in distinction of various degrees of bowel fibrosis in CD.

Level of evidence: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018.