Everything you need to know about scans and radiation

Key takeaways

• Some medical scans use a small amount of ionising radiation to diagnose certain problems and conditions
• Radiation is measured in 'millisieverts' or mSv
• A return transatlantic flight exposes us to around 0.1 mSv (equivalent to five chest X-rays).
• We absorb around 2.2 mSv annually from natural background radiation (equivalent to 110 chest X-rays)
• Radiographers are legally exposed to up to 20 mSv a year
• A mammogram produces around 0.6 mSv (equivalent to 12 return transatlantic flights)
• It takes approximately 1000 mSv to induce acute radiation sickness

Which scans give off radiation?

X-rays

X-rays are among the most common imaging scans that use ionizing radiation. They’re typically used to diagnose fractures, infections, and lung conditions.

CT scans

CT stands for computed tomography. This type of scan provides detailed cross-sectional images of the body and uses more radiation than a standard X-ray.

They’re valuable for diagnosing complex conditions in areas like the brain, chest, and abdomen.

Mammograms

Mammograms are used in breast cancer screening and involve low-dose X-ray radiation to create images of breast tissue.

What about MRI scans?

MRI scans do not use any radiation. Instead, they use a large magnet and radio waves to give medical professionals a detailed inside view of the body.

There are no known health risks associated with having an MRI scan.

How much?

A CT scan

A CT scan produces around 7 mSv, or around the same amount of radiation as you'd expect to absorb if you spent a year in Cornwall, where the sun exposure and radioactive rocks pump up the levels of 'natural background radiation' (even this amount isn't considered dangerous).

An X-ray

To get an idea of how much radiation is in an X-ray, take a look below:

• Chest X-ray: -0.1 mSv, or about 10 days of natural background radiation
• Dental X-ray: -0.005 mSv, or less than a day's background radiation
• Spine X-ray: -1.5 mSv, or about 6 months of background radiation
• Abdominal X-ray: -0.7 mSv, or about 3 months of background radiation

A mammogram

A mammogram produces around 0.6 mSv, or the same amount of radiation as a dozen flights across the Atlantic.

I'm worried before my scan

If the word 'radiation' sounds scary, it's because we've come to associate it with incredibly negative news stories, illness, and even death. It's a word we never associate with positive outcomes, even though medical scans can help diagnose conditions and even save your life.

The reality is that the amount of radiation in a medical scan is tiny compared with the amount you'd need to absorb to harm, hurt, or kill you.

How much radiation can harm us?

It takes a dose of around 1,000 mSv absorbed over a short period of time to induce acute radiation sickness. Heavier exposure of up to 10,000 mSv can result in cell and neurological damage, and even death. But you'd only find this amount after a catastrophic event.

Astronauts can easily be exposed to over 150 mSv annually, which is the same as 20 CT scans, 250 mammograms, or 7,500 chest X-rays. A mammogram on the other hand, only produces around 0.6 mSv.

So while radiation is very bad for you at extreme levels, the amount needed for medical scans is relatively safe and you won't be referred for tests unless there's a medical need.

Learn more about radiation in medical scans

To learn more and to get a visual representation of how different scans use radiation, take a look at the video below:

Figures provided by the Radiological Protection Centre.

Last updated Friday 8 November 2024

First published on Friday 16 September 2016