Imaging for Crohn disease: use of 3-T MRI in a paediatric setting.

This study was carried out to review our experience with 3-T MRI in the assessment of Crohn disease in a paediatric population. Twenty-four patients with biopsy proven Crohn disease identified on the radiology information system underwent abdominal MRI, with or without pelvic MRI. Twenty-eight studies were carried out on a 3-T scanner at a tertiary paediatric hospital. Eight of 24 of these (30%) had a gastrointestinal barium study, 2 of 24 (8%) a CT and 9 of 24 (38%) an abdominal ultrasound. The different MRI sequences were rated for observation of the bowel wall and abnormalities (0-5). The findings were correlated to relevant findings on endoscopy, examination under anaesthesia (EUA) and where available surgery, barium studies, CT and ultrasound. In this study, the colon was involved in 5 of 28 (18%), small bowel in 7 of 28 (25%), terminal ileum in 5 of 28 (18%). All the perineal studies (9 of 9) showed abnormalities. Sinus tracts or fistulas were identified in 7 of 28 (25%) studies. The mean rating of the different MRI sequences in showing bowel wall and changes of Crohn disease was T2 TSE 3.6, T2 half fourier aquisition single shot turbo spin echo (HASTE) with a long TE 3.6, T2 HASTE with short TE 3.4, true fast imaging with steady state precession (FISP) 2.7, T1 4.1 and Post-contrast T1 4.3. The T2 HASTE sequences with thinner slices improved observation. Detection of superficial abnormalities was similar on the 3D VIBE images and on the post-contrast T1 spin-echo (SE) sequences. In five of nine (56%) of those that had ultrasound, both studies were abnormal, with incomplete correlation of the abnormalities. Computed tomography and MRI were abnormal in two of two (100%) patients with good correlation of the abnormalities in one; in the other there was a minimal discrepancy in the estimation of the length of involved bowel. In 7 of 11 (64%) the barium study was abnormal. Good correlation to MRI findings was found in five of seven (71%) of patients. In two of seven (29%) both studies were abnormal, with incomplete correlation of the abnormalities. Barium underestimated the length of involved segment in these patients with inflammatory ileal thickening and ulceration. Notably, in both studies compression was limited because of patient discomfort and the involved segments obscured by overlap. Abdominal and pelvic MRI at 3 T is a useful imaging technique for evaluation of Crohn disease in the children. The extent of bowel wall involvement and extra-intestinal complications, such as abscesses and fistulas can be accurately assessed non-invasively, without the use of ionizing radiation or sedation.