![]() Distention of the rectum with ultrasound gel aids in visualization of the primary tumor, and is generally less useful in staging extramural tumor extension. Rectal cancer staging generally requires high spatial resolution 2D fast spin echo (FSE) images in three planes for adequate tumor delineation and staging. Effective MRE examinations require adequate distention of bowel, achieved by ingestion of an oral contrast agent (VoLumen ®), reduction of peristalsis via intravenous and/or subcutaneous injection of an antiperistaltic agent ( glucagon), and time-efficient protocols, typically incorporating fast T2-weighted sequences such as balanced steady-state free precession (b-SSFP) and single-shot fast spin echo (SSFSE), and dynamic gadolinium-enhanced 3D spoiled gradient recalled (SPGR) acquisitions in coronal and axial planes. MRE protocols are primarily designed to optimize assessment of small bowel in the setting of inflammatory bowel disease fortunately, these protocols frequently improve visualization of the large bowel as well. This pictorial essay briefly discusses methods for optimizing bowel imaging with MRI and illustrates the MRI appearance of a variety of unusual lesions involving or related specifically to the large bowel. MRI for inflammatory bowel disease and rectal cancer staging represents some of the most rapidly growing segments of our body MRI practice, and the increasing volumes (and increasing scrutiny of bowel) have led to the detection of several unusual lesions involving the lower gastrointestinal (GI) tract. MRI allows superior soft tissue characterization in comparison to CT and ultrasonography, and does not require ionizing radiation. ![]() Dedicated MR colonography remains a rare application, most often performed in research settings as an alternative to screening CT colonography. Increasing use of MR enterography (MRE) for evaluating inflammatory bowel disease, while primarily being performed for detection and characterization of small bowel disease, also allows assessment of the colon. MRI, for example, has found clinical utility in staging of rectal carcinoma, with clear advantages over endoscopic, sonographic, or clinical staging. Depending on the indication and area of interest, advantages of each of these modalities vary. Imaging of the large bowel has traditionally relied on fluoroscopic techniques however, cross-sectional modalities including computed tomography (CT), magnetic resonance imaging (MRI), ultrasonography, and positron emission tomography-CT (PET-CT) have become commonplace since the mid 1990s.
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