Types of
oral contrast agents with positive signal enhancement:
Ideal
oral contrast agents are immiscible with water, biologically inert, have a low
viscosity and surface tension. Oral positive
contrast agents may improve the separation of bowel loops, the detection of polyps in colon
MRI or the assessment of inflammatory bowel in the small intestine.
Several positive
oral contrast agents are available and they are safe to use, for example
gadolinium solution,
ferric ammonium citrate, different oil emulsions and pediatric formula.
Unfavorably motion artifacts caused by respiration and peristalsis may be increased in
MR imaging. In addition, the signal of the positive
contrast medium may decrease caused by dilution in
gastrointestinal (GI) secretions. With the use of
contrast agents that are immiscible with water, no dilution and accompanying signal loss occur even when the
contrast agent is in
contact with the intraluminal contents of the GI tract.
Another disadvantage may be residual substances in the bowel, resembling masses when enclosed by bright signal. In addition, positive
contrast agents may have a similar signal as bright masses, which make their (e.g. lipoma) detection difficult.
See also
Gastrointestinal Paramagnetic Contrast Agents,
Combination Oral Contrast Agents,
Gastrointestinal Diamagnetic Contrast Agents.
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