X-rays explained: what they're used for and how they work

The X-ray has been around since 1895, and it’s still the scan you’re most likely to have. There’s a good reason it has lasted: it’s fast, cheap, widely available and answers a huge range of questions with a tiny amount of radiation.

How an X-ray works

An X-ray machine sends a small, controlled beam of radiation through the body onto a detector on the other side.^[1] Different tissues absorb different amounts:^[2]

• Bone is dense and absorbs a lot, so little reaches the detector — it shows up white.
• Soft tissue (muscle, organs) absorbs less — shades of grey.
• Air (in the lungs) absorbs almost none — black.
• Metal absorbs the most — bright white.

It’s these differences that create the picture. Importantly, an X-ray is only present while the machine is switched on, like a light bulb — having an X-ray doesn’t make you radioactive, and no radiation stays in your body afterwards.^[2]

What X-rays are used for

X-rays are at their best with bone and the chest:^[1]

• Fractures and bone problems — the first-line test for a suspected broken bone, and useful for arthritis and bone infections
• The chest — pneumonia, fluid, heart size, and lung problems
• Dental — decay, roots, and impacted teeth
• Foreign objects — a swallowed coin, or glass in a wound
• Joints — alignment, dislocations and wear

What X-rays aren’t good at

Because soft tissues all look similar shades of grey, X-rays are poor at showing soft-tissue detail.^[1] For a torn ligament, an organ problem or a subtle brain issue, you’d need ultrasound, CT or MRI instead. That’s why an X-ray sometimes comes back “normal” even though there’s a real problem — it just isn’t the right tool for that tissue.

The radiation: very small

X-rays use a very low dose. A chest X-ray is only about 0.02 mSv — roughly two to three days of the natural background radiation we all receive anyway.^[3] Dental and limb X-rays are lower still. There are no short-term effects, and the benefit of the information easily outweighs the tiny theoretical risk. (See our guide to X-ray risks.)

What to expect

There’s usually no preparation. You’ll remove metal and jewellery over the area (and may change into a gown), and the radiographer positions you and asks you to stay still — for a chest X-ray, to take a breath and hold it.^[2] The image takes a moment, there’s no aftercare, and you can leave straight away. Tell staff if you are, or might be, pregnant.

Getting results and cost in Australia

A radiologist interprets the X-ray and reports to your referring doctor. In Australia, plain X-rays are inexpensive and often bulk billed, so many people pay nothing — it’s worth asking the clinic when you book.^[4]

Frequently asked questions

Do X-rays hurt?

No — an X-ray is completely painless. You just need to stay still for a moment while the image is taken.^[2]

Why did my X-ray come back normal when I’m still in pain?

X-rays are excellent for bone but poor at soft tissue. If your problem involves muscle, ligament or an organ, an X-ray can look normal — your doctor may then order an ultrasound, CT or MRI.^[1]

Is the radiation from an X-ray dangerous?

The dose is very small (a chest X-ray is a few days of natural background radiation) with no short-term effects. The benefit almost always outweighs the tiny risk.^[3]