How a Chest X-ray Works

X-RAYS are a form of invisible light discovered in 1895 by Wilhelm Rontgen. Although you can't see xrays with your naked eye, it can be picked up on photographic film. An X-ray works a lot like shining a flashlight through the palm of your hand. If you look on the other side in a dark room, you can clearly see the outlines of your bones from the soft tissues of your hand. An xray machine works like the flashlight and the image of your body is captured on special photographic film on the other side (Kodak and other camera companies make the film).

Although you may think of an X-ray as a picture of bones, that's only half the picture. A trained observer can also appreciate air spaces like the lung (which looks black) and fluid (which looks white but not quite as intense as the white of bone). In the chest xray pictures below you can see the black areas on both sides of a normal pair of lungs filled with air, and a lung that's filled with fluid.

A Normal Chest X-ray	Fluid in the Lung (Left)

Doctors learn to read xrays by memorizing what a normal xray looks like and comparing this mental image to the xray in front of them. After seeing many, reading an X-ray becomes as second nature as reading a newspaper.

A single X-ray exposure is equivalent to about 3 days of natural cosmic radiation exposure in the outdoors.

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