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X-ray - Introduction

NHS Choices Medical Reference

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An X-ray is a safe and painless procedure that's

often used to produce images of the inside of the body.

It's a very effective way of looking at fracturedbones, such as a broken arm or wrist.

X-rays can also be used to examine organs and identify problems. For example, an X-ray can highlight a lung infection, such as pneumonia.

X-rays are also often used by surgeons during therapeutic procedures, such as a coronary angioplasty, to help guide equipment to the area being treated.

Read more about when X-rays are used.

How X-rays work

X-rays are a type of radiation. They're similar sources of energy to light. However, light has a much lower frequency than X-rays and is absorbed by your skin. X-rays have a higher frequency and pass through the human body.

As X-rays pass through the body, energy particles (called photons) are absorbed at different rates. This pattern shows up on the X-ray images.

The parts of your body made up of dense material, such as bone, show up as clear white areas on an X-ray image. The softer parts, such as your heart and lungs, show up as darker areas.

Having an X-ray

X-rays are carried out by radiographers who are healthcare professionals trained to use imaging technology, including X-ray machines, computerised tomography (CT) scanners and ultrasound scanners.

During an X-ray, you'll be asked to lie on a table or stand against a flat surface so that the part of your body being examined is positioned between the X-ray machine and a photographic plate.

The X-ray will last for a fraction of a second. As the X-rays hit the photographic plate, the plate will capture a snapshot of the image.

The image will then be transferred to a computer so that it can be studied on a screen and, if necessary, printed out.

Read more about how an X-ray is taken.


Exposure to high levels of radiation can be very harmful. However, the X-rays used for medical purposes are safe because the dose of radiation is very small.

The strength of radiation in relation to long-term risk is measured using units called millisieverts (mSv). Some examples of typical exposures are:

  • chest X-ray - 0.02 mSv
  • a year's worth of medical tests - 0.4 mSv
  • average annual exposure to natural radiation - 2.2 mSv

In the UK, 20 mSv is the maximum that someone who works with radiation is allowed to be exposed to in any given year. Most workers receive considerably less than this.

Read more about the risks of X-rays.

Medical Review: October 29, 2013
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