Neutral intraluminal contrast:
® Contrast agents that have an intermediate density (10-30 HU). They are used with increasing frequency.
® With IV contrast, they provide very good display of the bowel wall and thus better visualization of the enhancing bowel wall is obtained.
® The most widely used neutral oral contrast agent is water. it is inexpensive and universally available and well tolerated but water alone is not an ideal contrast agent, because it is absorbed early in the gastrointestinal system and is not available in the mid and distal section of the small bowel so it does not always result in optimal distention of the distal small bowel. The administration of agents such as Glucagon may improve distension but is not routinely done.

® To overcome early absorption of water as a neutral contrast agent, additives that increase the osmolarity of the water are used without changing the contrast characteristics. Mannitol or other long- chain sugars can be used. The adverse effects of these additives are nausea and diarrhea.

® A newly introduced neutral oral contrast agent (VoLumen) is used which is based in oral barium sulfate solutions containing all the additives but with only 0.1 % of barium sulfate. With such a low concentration of barium it has no possible contrast effect in MDCT and even though containing barium, it is considered a neutral contrast agent. Compared with water or meglumine diatrizoate, this contrast agent creates for better distension and the display of the bowel wall is very clear compared with these intraluminal contrast agents.
® Milk has been used by some groups in order to distend the small bowel in patients undergoing CT angiography. Whole milk has a CT density similar to water, but has a slower small bowel transit time and should therefore result in better distention of the bowel.
Source: This was lifted from a PDF slide show: MDCT as a Diagnostic Tool in Evaluating Small Bowel Disorders.