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Freshly Baked Science

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X-Ray Vision

by Emily Smith

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9th July 2019

Have you ever wondered how doctors can take pictures of your bones? Or how security at the airport can see what you’ve got in your luggage? Chances are, you (or your bags) have had at least one X-ray in your life. But what actually are they and are they dangerous? Let’s take a look under the surface… 

 What are X-rays?

 X-rays are part of the electromagnetic spectrum – along with the light we see with, the radio waves we listen to music with, and the microwaves that transport texts to our friends within seconds. As the name suggests, electromagnetic waves travel around via variations in electric and magnetic fields. We might not see them, but they are all around us.

X-rays are at the top end of the spectrum due to their high frequency and short wavelength. This means that they’re more ‘bunched up’. Even though the waves travel at the same speed, you could fit about 500 waves of X-rays in the same space as one wave of visible light! 

How can they “see-through” things?

 We can’t see all our insides because visible light can’t travel through our bodies– we are opaque to light (which I’m sure we’re all quite glad about!). However, most parts of our bodies are not opaque to X-rays, so they can travel straight through us. 

X-ray images are formed by detecting the amount of X-rays that travel all the way through. They essentially show shadows of whatever is in the X-rays’ path. Bones are opaque, so most X-rays can’t travel through them. The air in our lungs is transparent, while fat and muscle are somewhere in between. Imagine the different amounts of light that would come through a window on a sunny day if it had a blackout blind, a thin curtain or nothing hanging on it.

Like the blackout blind, bones block lots of X-rays and produce a clear shadow. Other body parts show up more faintly because they block less of the X-rays from travelling through.

Like a clear window, a thin curtain and a blackout, the air, muscle and bones allow different amounts of X-rays to pass through them. Just to make it a little more confusing, the resulting shadows are typically inverted so the brightest white parts represent tissues that have blocked the X-rays the most (usually bones).

How do we make them?

 X-rays are produced deep inside atoms, which are made up of protons, neutrons and electrons. When an atom has too much energy, it can release that extra energy in the form of an X-ray as it relaxes back to its preferred chilled-out, low energy state. We can make this happen in an X-ray tube.

A wire is heated up until it releases electrons. These electrons are fired at a metal target, travelling at superspeed. When they smash into the target, they give the atoms inside the metal a big kick of extra energy. The atoms then throw their excess energy out as X-rays so that they can return to normal. The X-rays come out of a window in the tube as a beam.


Are they dangerous?

 X-rays are a type of ionising radiation which means they can cause harm to people. This type of radiation can change the makeup of cells and DNA, which increases the risk of them mutating and causing complications, including cancer. To minimise this risk, it is important to keep exposure to X-rays as low as possible. 

The risks associated with medical X-rays, or things like airport scanners, are small. In fact, due to the natural levels of radiation in the atmosphere, just getting on with normal life for about ten days would give you the same amount of radiation as a medical chest X-ray would!

Wherever there are X-rays, there are strict procedures in place to keep everyone safe. In a hospital, every X-ray is carefully considered and is only recommended if it will really help a patient get back to full health. Medical and scientific experts make sure that every scan is as safe and useful as possible. If you need an X-ray at the hospital, never be afraid to have it!  

What are they used for?

 X-rays can help doctors spot broken bones, diseases and infections. They are used to monitor how someone’s responding to a certain treatment, show surgeons where they need to operate, check for diseases in screening programmes and much more. 

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Normal chest x-ray in a 12-year-old boy. Source: https://radiopaedia.org/cases/normal-chest-x-ray-12-year-old-male-3?lang=us

CT scanners take lots of X-rays from a number of different angles, then combine them all to make a 3D X-ray picture. Looking in 3D gives improves visualisation and gives a better idea of positioning. In a traditional 2D X-ray, certain features could be hiding in the shadow of another bone or organ.

Fluoroscopy is like X-ray video; lots of very short X-rays are taken in quick succession and displayed live on a screen. This is used to guide doctors when they are inserting tubes, wires and pacemakers to make sure they are put in exactly the right location.

You will find X-rays in all sorts of places. They should be used with care, but they are amazingly useful, providing that valuable window into the things we wouldn’t normally be able to see inside…