Medical imaging using radiation

Radiation is often used in medical imaging, to allow doctors to take a picture of the inside of your body. Two main kinds of medical imaging use radiation: x-ray imaging and nuclear medicine.

X-ray imaging

X-rays are a kind of radiation that can travel through your body. Your doctor can use x-rays to take a picture or video of the inside of your body.

Some parts of your body absorb more x-rays, and they show up as light areas on the picture. Parts that don’t absorb x-rays show up as dark areas. For example, bones are very good at absorbing x-rays. They show up as light areas. So x-rays are ideal for diagnosing broken bones.

Examples of x-ray imaging

  • X-ray – still x-ray image
  • Mammogram – x-ray of the breast
  • Bone density test – x-ray of the bones
  • Fluoroscopy – video taken with x-rays
  • CT scan (computed tomography scan) – 3D x-ray image. The CT scanner takes x-rays of many ‘slices’ of your body. These slices are added together to make the 3D image

Nuclear medicine

In scans using nuclear medicine, you’re injected with a radioactive substance. This collects in certain parts of your body – for example, cancerous cells or your bones.

The radioactive substance releases gamma rays. A special ‘gamma camera’ can take a picture of the gamma rays. This lets your doctor see where the radiation is in your body. So if you’re having a scan for cancer, the doctor can see where the cancerous cells are.

Sometimes doctors may use nuclear medicine and x-rays together. This gives them a picture of your body’s structure overlaid with the gamma ray image.

Examples of nuclear medicine imaging

  • PET scan (positron emission tomography scan) – scan for cancer, brain disease or heart disease
  • Bone scan – scan for changes in the bones

Safety of radiation in medical imaging

The type of radiation used in medical imaging can cause cancer. But it is used in very low doses, so the risks are very low.

For example:

  • a chest x-ray is equal to a few days’ worth of natural radiation (what you receive naturally from the soil and the environment)
  • a CT scan is equal to a few years’ worth of natural radiation. Even this is only a tiny increase to your chance of getting cancer.

Your doctor will decide whether or not the benefits of an x-ray or scan outweigh the risks. They will also ensure that you aren't exposed to any more radiation than necessary for your diagnosis.

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