Medical Radiation--X rays are a form of radiant energy like light or radio waves. Just like light and radio waves, they can pass easily through some things and are absorbed by others. In the human body, some tissues are better at absorbing the radiation than others. The images made by x-ray beams come from these differences. Bone stops x rays efficiently, making them look white in an image; air, like in the lungs, does not absorb radiation much at all, and looks black in the image. Sometimes the images are still, like pictures from a camera, and sometimes they show movement, like a video camera.