X-rays are waves of electromagnetic radiation that are used to create images of organs and other structures inside the body. X-rays have a very short wavelength. As they penetrate the body, they are absorbed in different amounts by different body tissues. For example, bones are dense and absorb X-rays very well, but soft tissues (skin, fat, muscle) allow more X-rays to pass through. The result is an X-ray shadow on a film or fluorescent screen, where images of bones appear white, while shadows of soft tissues appear as various shades of gray.
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