MR imaging of the small bowel – technique and current applications

Increased importance has been placed on evaluating small bowel disease to guide management in often chronic conditions such as Crohn’s disease. Imaging of the small bowel has always played a key role in diagnosis and decision making. Traditionally, fluoroscopic studies such as barium follow through and small bowel enteroclysis have been used. More recently, the gold standard of evaluating the small bowel has moved towards cross sectional modalities with computed tomography (CT) and magnetic resonance (MR) imaging. MR has the properties to make it well suited for small bowel imaging. It has the ability to show good mucosal detail, transmural inflammation, extra-luminal changes and fistula formation. These qualities outperform barium techniques and provide important clinical distinction between active, inflammatory and chronic disease. The major limitation to a complete shift to MR imaging is lack of access to scanner facilities, time and radiological expertise. This is gradually improving and indeed many centres employ cross sectional imaging as their first line of investigation. Two MR techniques are currently used – MR enteroclysis and MR enterography. In enteroclysis, enteric contrast material is administered through a nasoenteric tube which is normally inserted under fluoroscopic guidance, whereas in enterography, contrast material is administered orally. The use of oral contrast medium is associated with better patient tolerance and compliance, and avoids the radiation and staffing required for fluoroscopic nasojejunal tube placement, although there is evidence that enteroclysis allows slightly better bowel wall distension. At the authors’ centre, enterography is the preferred technique.