X-rays are one means of looking indirectly at internal organs. Just what are X-rays? They are a form of electromagnetic radiation. Other electromagnetic rays include ordinary light, infra red, ultraviolet, radio and TV waves. These are all forms of energy which can travel through space in straight lines but differ in wavelength and frequency.

Light is the one that is most familiar to us, simply because light is the only one that the human eye can detect. To help you understand how an X-ray picture is produced, we can use an example involving a form of electromagnetic radiation that we all understand—light. Imagine a light shining through a stained glass window onto a white wall. On that wall you can see a ‘picture’ of the window. The picture is formed because light gets through some parts of the window more easily than others. No light gets through the frame or the lead separating the pieces of coloured glass. Some light gets through the glass but the amount depends on the strength of the light and the thickness and colour of the glass. The detail we get in our indirect ‘picture’ depends on these factors. Exactly the same sort of process is involved in getting an X-ray picture. The X-ray machine sends out X-rays like a source of light. The X-rays get through some parts of our body more easily than others. Because we can’t see X-rays with our eyes, instead of a white wall on the other side we need an X-ray plate. The X-rays react with the special coating on the X-ray plate to form a ‘picture’ which we can see. X-rays travel most easily through air and least easily through very solid things like metal and bone. Just as we can use a stronger light to get more detail, so we can adjust the machine to send out ‘stronger’ X-rays if we need more detail.

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