Factors affecting the appearance  


The image on the left is "unenhanced" (no x-ray dye was given). Note that the kidneys, liver, pancreas, spleen and blood vessels all appear nearly the same shade of gray. The image on the right is "enhanced" (obtained after intravenous contrast was administered). Note that each organ is a lighter shade of gray than on the unenhanced image, and each now differs from each other in its subtle shade of gray. This results from differences in the amount of x-ray dye that each organ absorbs; the more absorbed, the lighter the shade of gray. The kidneys absorb the most dye and so appear the lightest. Also note that you can see blood vessels in the liver, since they contain a higher concentration of the dye than the adjacent liver parenchyma. Also note the splenic vein, which sits immediately posterior to the pancreas, is now seen discretely apart from it.