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What are X-rays?

Updated on August 20, 2014
Wilhelm Conrad Roentgen
Wilhelm Conrad Roentgen | Source


You wouldn't know it, but X-rays are all around us! They come from both naturally occurring and man-made sources. And since the discovery of X-rays by Wilhelm Conrad Roentgen in 1895, they have been an important part of our lives – primarily because of their use in medical X-ray imaging.

But what is an X-ray?

X-rays are part of the same 'spectrum' as visible light, but because they are at the far end of this electro-magnetic spectrum they have very different properties than the light our eyes detect.

Because we can't see X-rays, we're often unaware of their presence all around us — but they are around us, everyday, and they come from a number of sources.

So where do X-rays come from?

X-rays are used to produce medical images and scans — but where do they come from? The biggest source is nature like rocks and space. Very hot bodies, such as stars and our sun, produce X-rays as part of their reactions but luckily nearly all of these are absorbed by our atmosphere. Man-made X-rays are produced in specialised equipment for medical, industrial, and scientific uses.

More X-rays pass through skin and muscle than through bones
More X-rays pass through skin and muscle than through bones | Source
A lot more X-rays pass through air-filled structures (like lungs) which consequently 'blackens' the film more
A lot more X-rays pass through air-filled structures (like lungs) which consequently 'blackens' the film more

And how can X-rays see through stuff

The energy/wavelength of X-rays allow them to pass through some things and not through others. This comes down to chemical make-up, and it's this characteristic that allows us to create medical images. The human body is made up of a large variety of very different tissues — from hard teeth and dense bone to soft things like the lungs and bowel — and they all absorb X-rays differently!

How does this 'stuff' affect X-rays

Bone contains plenty of hard, dense calcium which is the reason it supports our weight. It's also the reason it absorbs more X-rays.

Skin, muscle, and other 'soft' tissues in our body are far less dense and contain less X-ray absorbing molecules. Because of this, far more X-rays pass through the skin and muscle than through the bones.

The most important part of making sense of these X-rays is to create an image from them. And because the amount of X-rays making it all of the way through the body depends on how 'dense' that bit of body is, an X-ray image is simply a shadow cast by our body tissues!

White areas are produced through less X-rays reaching the film or digital plate
White areas are produced through less X-rays reaching the film or digital plate

What can X-rays show us?

Diagnostic images can be used to:

  • See breaks in bones, or other indications (such as fluid) that suggests a break
  • Identify dental problems in teeth before they are visible
  • visualise the 'soft tissues' of the body to diagnose tumours and other problems
  • Assist surgeons and doctors to perform procedures using the smallest cuts (key-hole surgery)
  • Allow orthopaedic surgeons to accurately insert pins and screws into broken bones
  • Identify gall stones and renal stones (in the kidneys) that can cause pain

Therapeutic uses in medicine

Radiation therapy (or radiotherapy) uses focused beams of X-rays to reduce the size of tumours. In a lot of cases they can be destroyed altogether. This procedure can be complemented by chemotherapy — the use of strong medication to attack tumours from within.

Radiotherapy uses X-ray energies far greater than the ones we use to make images. To complete a course of radiotherapy it will often require many individual treatments.

X-Ray image of a spinning pulsar creating an X-ray nebula spanning 150 light years
X-Ray image of a spinning pulsar creating an X-ray nebula spanning 150 light years | Source

Other uses of X-rays

Naturally occurring cosmic X-rays can be used to analyse the substance of the universe and can show us information that isn't visible to our eyes. Some objects such as stars and black holes give out X-rays which we see using special telescopes. Because X-rays were produced by the Big-Bang, vast amounts of information has been gathered to help scientists understand what happened at the beginning of the universe.

Scientists also use the properties of man-made X-rays to analyse the composition of chemical substances. X-rays have a smaller wavelength than light which allows them to image even smaller structures than 'optical' microscopes.

Man-made X-rays can be used to detect weaknesses in metal structures. When a minute crack occurs in metal it can often be because of stresses within the metal itself. This type of damage is impossible to see with the naked eye, but because X-rays can 'see' different densities, cracks and stresses can be seen before it's too late. This saves time and money, and even lives, by finding where future problems might occur in places like high rise buildings and oil rigs.


Our invisible world

X-rays can 'see' so much more than the naked eye. From broken bones, tumours, and defects in metal, to the atoms and molecules they're made from. With the great technological leaps being made today, other things might soon be used instead of X-rays — but until then, they continue to play a key role in our lives.


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    • Mark S Waterhouse profile imageAUTHOR

      Mark S Waterhouse 

      4 years ago from Christchurch, NZ.

      Thanks Candice. Yep, X-ray imaging is an easy tool for a clinician to ask for. They're quick, easy, and cheap (which is probably an important factor).

      Good point about the conditions and imaging. You wouldn't use, for example, MRI to look for a broken bone - you'd use an X-ray based modality because of how they interact with the body. Similarly, you wouldn't use CT of or X-rays to identify a suspected brain abnormality, you'd use MRI.

      My wife performs and reports Ultrasound scans, so has a great insight into their use. I think as Ultrasound technology has improved, it's provided quicker, cheaper, and safer investigations for a variety of new conditions/symptoms.

      Thanks Candice for the comment.

    • profile image

      Candice Harding 

      4 years ago

      Very interesting hub. I have to admit, I had never even thought about being interested in medical imaging until my mom went back to school to become an MRI technologist. It's fascinating to compare types of imaging and their uses. When she first started telling me about MRI technology I wondered why it hadn't already replaced x-rays, but x-ray is still more accessible. You're never going to find an MRI machine in an after hours clinic, for example. And there are conditions that are only visible using specific kinds of imaging.

      Candice Harding


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