Radiographic Densities & Colors
In radiographic images, only five radio-densities show:
Of these five materials, air has the lowest specific gravity (weight) and metal has the highest. Therefore, the thicker (higher weight) a tissue is, the whiter it will appear in radiographs.
Since the lungs have mostly air, they will look almost black.
Since the liver is mainly composed of water, it will appear gray.
Since the bones contain minerals, they will show almost white.
Materials of equal density in contact with each other will not contrast each other. For instance, unless contrast agents are used, arteries and veins won't show in radiographs. That's because they have water density, just like the water that makes up most of the body.
Materials of different density in contact with each other will contrast each other. Examples include:
Water (gray) against mineral (white)
Air (black) against water (gray)
Metal (white) against water (gray)
Water and fat have very similar specific gravities, so the contrast between them is minimal. Fat appears slightly darker than water because it weighs less. The specific gravity of water is 1, while that of fat is 0.9.
In summary, we can expect to see a grayscale ranging from black to white in radiographic images. However, we will only notice the body parts that can be contrasted with their surroundings due to having different densities.