The human body has many different tissue types because different tissues absorb X rays to different degrees. Each tissue type appear different on an X ray. Most obviously bone can be distinguished from any other sort of tissue, which is why X rays are often using to find the location of a bone break. Some tissues absorb X rays to almost the same degree, and it is difficult to distinguish them on X rays. To improve the contrast between tissue type, we can use 'contrast media'. A contrast media is a substance like iodine or barium, which is a good absorber of X rays.A patient may drink or eat something containing a measure of contrast media,or have an injection into the area to be X ray-ed. The contrast media is absorbed preferentially by different parts of the body, which them show up darker on X rays. This is especially useful when imaging the digestive system.