CT of abdomen is superior at visualizing the liver, spleen, pancreas and other internal organs. CT of abdomen can be performed with or without contrast of which there are two forms: oral contrast, which you drink to fill the stomach, small bowel and colon, and IV contrast, which is injected through and IV, used to highlight internal organs like the liver, spleen, pancreas and kidneys.
The use of contrast in abdomen CT depends on the need, the symptoms and if you are able to have it. Some abdomen scans can be performed with oral only; some with IV only and some with both oral and IV contrast are often necessary. CT of abdomen , especially in trauma situations like a car accident, is performed with IV contrast in order to visualize internal organs for tear or assess injury. Visualization of the pancreas is best seen using CT with IV and oral contrast to evaluate the extent of conditions such as pancreatitis, pancreatic cysts and lesions or tumors of the pancreas. Drinking oral contrast outlines the head of the pancreas as the stomach empties itself in a "C-shaped" loop around the pancreatic head.
When the colon or small bowel needs to be visualized, you would need to drink oral contrast in order to see the loops of small intestine more distinctly. It serves as a white contrasted background and allows the bowel to stand out against the other abdominal structures when the loops of bowel are filled with it.
It usually takes about 2 hours for oral contrast to reach the end of the colon after it’s consumed. The standard preparation is two 450ml bottles, about a pint each; the first bottle 2 hours before the scan and the second bottle 1 hour before the scan. This waiting time gives the oral contrast time to evenly coat and distribute itself throughout the small bowel and colon.