The radiation question: CT, X-ray and the doses involved

Radiation is the worry that puts people off scans, so here is the picture.

First, not every scan involves it. Ultrasound and MRI use no ionising radiation at all, one using sound and the other magnets, which is part of why they are chosen for many questions. X-ray, CT and DEXA do use it, in very different amounts.

The way to think about dose is against the radiation we all receive from living, from the ground, the air and space, which adds up to a couple of millisieverts a year in the UK. A chest X-ray is a tiny fraction of that, a few days of background radiation. A DEXA scan is lower still. A CT scan is more, depending on the part of the body, ranging from a few months to a couple of years of background equivalent, and a low-dose CT, such as a calcium score or a lung screen, sits well below a standard CT.

The principle doctors work to is simple: use the lowest dose that answers the question, and only scan when the answer is worth having. For a one-off scan with a real purpose, the dose is small set against the benefit of a clear answer. The caution is about not scanning repeatedly without reason, which is why a scan is matched to a question rather than run on spec.

If radiation is on your mind, raise it. We will tell you the dose involved, whether a no-radiation option such as ultrasound or MRI would answer your question just as well, and let you decide.

Ready to start? Choose the check that fits your question and tell us a little about yourself. A doctor reviews it, arranges what you need, and explains what it means. Most of it is done online, with the clinic there if you would rather be seen.