 Let's close your eyes and picture an x-ray image. You have likely pictured something like this, whichever part of the body you've pictured, it was an image with your bones. This is possible because x-rays cannot pass through your bones. This property is known as radio opacity. It is possible to get an x-ray image of your gastrointestinal tract, primarily your stomach and intestines, but we must somehow block x-rays from passing through the soft muscle and tissues. In this had to take an x-ray of your gastrointestinal tract, you would have had to ingest a barium meal. It appears to be a white chocolatey liquid, but is in fact a suspension of barium sulfate, which is an insoluble white solid. A suspension is a mixture of an insoluble solid and a liquid. Since the two components are not in the same phase, a suspension is a heterogeneous mixture. Think about it as sand in water. Sand is obviously insoluble in water. If we let the stand, the sand particles settle at the bottom. If you've ever taken medication where the instructions say shake before using, it was likely a suspension. The same scenario occurs. The medication, which is an insoluble solid, settles at the bottom of the container. Shaking ensures that all the solids are interspersed evenly throughout the liquid before consumption. The same must be done for a barium meal. Most barium compounds are highly toxic. However, the ingested barium meal can safely pass through your body without being absorbed. The barium meal is a bit like a worm crawling through the soil. The worm, like the barium meal, is not absorbed by the soil and passes through intact. When it comes out of the soil, the worm is still a worm. Since the barium sulfate is highly insoluble, it is not absorbed by your body. If you've ever had to consume it, you will find that it has a very chalky taste and it's very thick and dense. Sometimes, flavoring agents are added to mask this chalky taste. As it passes through your gastrointestinal tract, it mimics the density of your bones. Since x-rays cannot pass through, an image can be produced. Therefore, this barium sulfate compound is radio opaque because it prevents x-rays from passing through them. In medical terms, it is a contrast agent because it improves the visibility of certain parts of your body. In this case, your gastrointestinal tract. Another contrast agent used is an iodine-based dye injected through blood vessels to obtain an angiogram. An angiogram is an image of your blood vessels at certain parts of your body. So to recap, it is possible to obtain an x-ray image of your gastrointestinal tract by consuming a barium meal, which is a suspension of barium sulfate in water. It lines your gastrointestinal tract and prevents x-rays from passing through. Since barium sulfate is highly insoluble, it passes through your system safely.