X-rays and light are identical forms of energy known as electromagnetic radiation. Electromagnetic radiation is formed of photons with a certain energy. The only difference between x-rays and, say, blue light, is that x-rays have a higher energy, and therefore a shorter wavelength, than blue light. In fact, radio waves, microwaves (inside your microwave), light, and x-rays are all part of the electromagnetic spectrum. The figure above shows how the wavelengths of different types of electromagnetic radiation compare with objects like houses and molecules.

The high energy and short wavelength of x-rays makes them extremely useful at looking through dense objects. Just like visible light can be used to look through objects like glass, x-rays can be used to look inside more dense objects like skin, muscle, bones and even inside cargo. For example, airport baggage scanners can easily look inside your bags to screen for dangerous items (just like in the figure on the right). Of course, we could just open our bags at the airport and take everything out for inspection but this takes fifteen minutes while looking through it takes fifteen seconds!

Using x-rays to peer inside your luggage…

…and inside a cargo truck.

We even have cargo scanners that can look inside a shipping container without having to go through it manually. The lower of the two figures on the left shows an x-ray image of a car inside a truck.

X-rays are even more useful at looking inside things that can’t be easily or safely opened. This happens regularly in industry in areas of work where the internal structure of materials needs to be monitored for safety reasons. For example, in the field of industrial radiography x-rays are used to inspect internal damage to critical components or to analyse the behaviour of intricate objects in extreme environments.

An aircraft fatigue crack identified in an x-ray scan.

Shockwaves generated inside a high-pressure fuel injector.

In the medical industry, x-rays are extremely good at revealing internal information and therefore accurate diagnoses. At some point in their life, most people will have had an x-ray image taken as part of a medical diagnosis. By far the most common type of x-ray image is a simple two-dimensional image of either teeth (to look for decay) or bones (to look for a fractures).

Using x-rays to look for tooth-decay…

…and bone fractures.

We have seen that x-rays are useful in a variety of fields. Some of these are,

• Medical x-ray imaging
• Cargo screening & security screening
• Industrial radiography & non-destructive testing

A fractured jaw.

While all of the images we have seen above were two-dimensional, sometimes it’s useful to generate full three-dimensional reconstructions of objects. This happens regularly in hospitals, where doctors may need a 3D image of an injury in order to make an accurate diagnosis or plan a delicate operation. Scans which can be used to reconstruct 3D objects are often referred to as CT Scans (Computed Tomography Scans) or CAT Scans (Computer-Axial Tomography Scans).

To learn more about 3D imaging, and how we can generate 3D models from 2D projections, click “next”.

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