Sunday, August 29, 2010

X-ray: What's the big picture?

One of the most common and well-known procedures in diagnostic imaging is the X-ray. Though it was one of the first medical imaging technologies to make its stay in the field (1896), several billion medical and dental x-ray examinations are still made every year worldwide. It is an incredibly useful technology used for many things all the way from diagnosing broken bones to the positioning of cancers inside the body in preparation for treatment (often with more X-rays!).

Before we continue, a brief point of clarification should be made. The term "X-ray" is often used as a shorthand reference to "X-ray image" (as in the paragraph above). Depending on the context, X-ray may also refer to the actual rays used to produce X-ray images or to treat/cure disease. You can think of these rays just like you would rays of visible light. Different objects cast different shadows when placed in front of a light source. Opaque objects (like a brick) will block all of the light casting a strong shadow behind it whereas translucent objects (like a thin mesh or thin fabric) will allow some light to pass through them casting a more faint shadow. Transparent objects (like clear plastic or even air) allow nearly all light to pass through them leaving no detectable shadow. Objects placed in front of an X-ray beam will behave in a similar manner. Opaque objects (like thick lead) block nearly all X-rays. Translucent objects (like human flesh and cancer) stop some of the X-rays and allow some to pass through. Translucent objects (like air and many other gases) permit almost all X-rays to pass through them undisturbed.

This is the basic idea behind the X-ray image. You shine an X-ray beam on a person and take a photograph of the shadows that get cast by different objects inside the body. This makes X-ray imaging a great alternative to cutting people open just to see what's inside! And in fact, this is the drive behind medical imaging as a whole: to get a non-invasive look at objects inside the human body so that doctors can have more information from which to draw more accurate conclusions regarding patient diagnosis.

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