Objectives: Transmural involvement in Crohn’s disease (CD) might precede fistula formation which may warrant a change in medical management. Indian ink artifact (also known as black boundary artifact) shows a signal drop-out in voxels that contain water and fat. Thus, this artifact appears as a smooth black line on the outer border of normal bowel walls. Inflammatory changes in the bowel wall or the mesentery may cause this smooth line to become blurred or irregular. We aimed to assess the change in appearance of the Indian ink artifact in the True Fast Imaging with Steady-State Free Precession (TrueFISP) sequence and to correlate it with other inflammatory markers.
Material and Methods: This ancillary study utilized 41 MRE’s of 31 children (average age 12.5 ±2.88, 21 (51%) males) with CD performed as part of the larger prospective ImageKids study in which children with CD, underwent MRE and ileocolonoscopy as part of clinical care. Inclusion criteria for this study were: 1. Disease limited to the terminal ileum 2. The MRE included TrueFISP sequences. The TrueFISP sequences were reviewed and evaluated for the distortion of the Indian ink artifact. Findings were compared with the endoscopic score (Simple Endoscopic Score for Crohn`s Disease (SES-CD)), CRP and calprotectin levels.
Results: Nine of the 41 examinations (22%) had marked irregularity of the Indian ink artifact, 20 (48.8%) had mild irregularity, and 12 (29.2%) had normal appearance. All constructs of disease severity showed a significant gradient across the three groups: mean segment length was 16.3±12.4cm vs. 13±8.7 cm vs. 3.2±3.2 cm, respectively (p=0.001; Kruskal Wallis test). Edema of the mesentery was noted in 9 examinations (100%), vs. 13 (61%) vs. 3 (25%), respectively (p=0.002; Fisher’s exact test). Enhancement of the mesentery was noted in 9 examinations (100%), vs. 12 (57%) vs. 2 (16%), respectively (p=0.0001). Median CRP values were 8.8 (IQR 6.95-25.6) vs. 4.1 (1.0-16.7) vs. 0.2 (0.2-0.5); respectively (p=0.0001). Finally, median fecal calprotectin levels were 813 (IQR 487-1728) vs. 327 (81-892), vs. 57 (10-77), respectively (p=0.004).
Conclusion: In our study, distortion of the Indian ink artifact was associated with both radiologic and laboratory markers of inflammation. Further studies are required to validate our findings and their utility in follow-up during treatment and differentiating inflammation from fibrosis.
