Rectal staging is necessary for the preoperative assessment of intra- and extramural tumor infiltration or the decision for adjuvant radio-chemotherapy.
One indication of
MRI with luminal
contrast enhancement is small bowel enteroclysis after duodenal intubation for visualization of inflammatory bowel wall thickening and other complications.
"Double contrast" enhancement of the bowel lumen is the administration of plain water or water with methylcellulose along with heavily
T2 weighted sequences or
contrast enhanced
T1 weighted sequences.
Several
oral contrast agents have been used for small bowel MRI: Mannitol, metamucil, locust bean gum, and PEG. All provide sufficient bowel distension and
homogeneity, but suffer from side effects such as diarrhea. The volume of PEG or mannitol administered must be not too large in order to achieve the best compromise between distension and acceptance by the patient.
MR colonography with positive bowel lumen enhancement
requires higher concentrations of
paramagnetic agents compared to the
available dedicated enteral
contrast agents, IV compounds are used to dope water enemas for this purpose.
Some investigators advocate negative bowel enhancement
with
Contrast Agents to suppress high signal bowel content in
MRCP (
Magnetic resonance cholangiopancreaticography ).
The use of a mixture of metamucil and 20 ml of
gadolinium chelate provides good
homogeneity and good tolerance without diarrhea.
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