Figure 2.

Different oral contrast agents in MRI of the small intestine (SI). Double-negative contrast agents produce low-signal intensity of bowel lumen on both (a) T₁ and (b) T₂ weighted sequences. With these contrast agents the visualisation of the bowel's wall (w) is preferred to that of the lumen (l), emphasising the identification of parietal and extra-parietal findings such as oedema or fat stranding. With the use of positive contrast agents, the visualisation of bowel lumen is privileged on both (c) T₁ and (d) T₂ weighted sequences; the most significant limitation is represented by the fact that wall enhancement after intravenous Gd administration can be masked by the higher lumen signal on T₁ weighted sequences. Biphasic contrast agents produce an optimal contrast between lumen and walls on both (e) T₂ weighted (bright lumen and dark walls) and (f) T₁ weighted sequences (dark lumen and bright walls).