Background: Crohn disease (CD) is a chronic inflammatory bowel disease that can affect any part of the gastrointestinal tract from the oral cavity to the anal canal. It occurs in all ages and is a significant cause for morbidity in children. Interest in MRI evaluation of CD has increased because of the concern regarding cumulative radiation dose from contrast fluoroscopic studies and CT. Several reports have demonstrated MRI to be a useful technique for CD. Most of these studies were performed at 1.5-T field strength. Imaging at a higher field strength, with a greater signal-to-noise ratio, has the potential of reducing scan times and increasing the resolution. However, there is a concurrent increase in artefacts, and these can be pronounced with abdominal imaging at 3 T.
Objective: To determine the feasibility of 3-T MRI for CD in children and to assess the value of different sequences and the effect of artefacts that could potentially limit the role of bowel MR imaging at higher field strengths.
Materials and methods: A retrospective study of 46 children with biopsy-proven CD (ages 8-19 years, 53% boys) was performed. Sixty-eight consecutive MRI studies were performed on a 3-T scanner between 2005 and 2007; 42 of the abdomen (62%) and 26 of the pelvis/perineum (38%). Sorbitol was administered for the abdominal studies; orally for 36/42 (86%) studies and via a naso-jejunal (NJ) tube for 6/42 (14%) studies. For the abdomen, T2-W half-fourier acquisition single-shot turbo spin-echo (T2-W HASTE), true steady-state free precession (true FISP), pre-contrast and contrast-enhanced (CE) T1-volume interpolated gradient-echo (T1-W VIBE) and CE T1-W fast low-angle shot (T1-W FLASH) sequences were performed. For the perianal and pelvic assessment, fat-saturated T2-W turbo spin-echo (TSE), pre-contrast and CE T1-W FLASH or VIBE sequences were performed. The sequences were scored for diagnostic quality by two paediatric radiologists for visualisation of the bowel wall, whether normal or pathological and the visualization of extra intestinal manifestations. The effects of distension, susceptibility artefact and motion were assessed.
Results: Six (14%) abdominal MRI studies were normal. Thirty-six (86%) were abnormal with good correlation with endoscopic findings. The pelvic and perianal MRI studies were all abnormal (26/26, 100%) with good correlation with proctoscopy and examination under anaesthesia. All the sequences had high average scores (greater than or close to 3), except true FISP with a score of 2.4. The score was greatest in those who had NJ administration of sorbitol; however, satisfactory distension was also possible with oral administration of contrast. True FISP was the sequence most affected by a combination of suboptimal distension and artefact from colonic contents. With adequate distension, true FISP image quality improved remarkably. The overall score of this sequence was satisfactory in the absence of susceptibility and movement artefact.
Conclusion: With appropriate attention to technique, with optimal distension and control of movement, high-quality, 3-T assessment of the abdomen, pelvis and perineum is possible. All sequences used at 1.5 T can be used at 3 T, however true FISP was the most prone to artefact.