Comparing different types of imaging


  • Different types of imaging tests have different risks and benefits.
  • Be informed about your medical imaging options, and talk to your health professional about any questions or concerns you may have.

The following table lists examples of how the different types of imaging (X-ray, CT scans, nuclear medical imaging, MRI and ultrasound) are used, including some advantages and disadvantages of each method.

Imaging type


Advantages & disadvantages

Plain X-ray

Uses X-rays to show images of bones, some tumours and other dense matter


  • Quick, non-invasive and painless
  • Can help diagnose various diseases and injuries, including broken bones, some cancers and infections 


Computed tomography (CT scans)

Uses multiple X-rays to produce cross-sectional layers that show detailed images inside the body, including bones, organs, tissues, and tumours


  • Quick and painless
  • Can help diagnose and guide treatment for a wider range of conditions than plain X-ray
  • Can detect or exclude the presence of more serious problems
  • Can be used to check if a previously treated disease has recurred 


  • Small increased risk of cancer in future from exposure to ionising radiation (X-rays). Risk is greater for children
  • Uses higher doses of radiation than plain X-ray, so the risks (while still small) are generally greater than for other imaging types
  • Injection of a contrast medium (dye) can cause kidney problems or result in allergic or injection-site reactions in some people
  • Some procedures require anaesthesia
Nuclear medicine imaging including positron-emission tomography (PET)

Involves injecting, inhaling or swallowing a radioactive 'tracer'. The gamma-rays emitted by this material are used by the scanner to show images of bones and organs


  • Usually painless
  • Can help diagnose, treat, or predict the outcome for a wide range of conditions
  • Unlike most other imaging types, can show how different parts of the body are working and can detect problems much earlier
  • Can check how far a cancer has spread and how well treatment is working


  • Involves exposure to ionising radiation (gamma-rays)
  • Radioactive material may cause allergic or injection-site reactions in some people
  • PET scanners cause some people to feel claustrophobic, which may mean sedation is required

Magnetic resonance imaging (MRI)

Uses magnetic fields and radio waves to show detailed images of organs, soft tissues, bones, ligaments and cartilage


  • Usually non-invasive and painless
  • Uses no ionising radiation
  • Can help diagnose and guide treatment for a wide range of conditions
  • Can provide similar information to CT in some types of investigations


  • Can be a lengthy and noisy procedure
  • Slight movement can ruin the image, requiring retesting
  • Can make some people feel claustrophobic
  • Sedation or anaesthesia may be required for young children or others who can't remain still
  • Injection of a contrast medium (dye) if needed can cause kidney problems or result in allergic or injection-site reactions in some people
  • Can't be undertaken in some situations (e.g. when a heart pacemaker is present)

Uses high-frequency sound waves to produce moving images onto a screen of the inside of the body, including organs, soft tissues, bones, and an unborn baby


  • Usually non-invasive, safe and relatively painless
  • Uses no ionising radiation
  • Does not usually require injection of a contrast medium (dye)
  • Can help diagnose a range of conditions in different parts of the body, such as the abdomen, pelvis, blood vessels, breast, kidneys, muscles, bones and joints
  • Can be used to check on the health of a baby during pregnancy


  • Quality and interpretation of the image highly depends on the skill of the person doing the scan
  • Other factors can affect image quality, including the presence of air and calcified areas in the body (e.g. bones, plaques and hardened arteries), and a person's body size
  • Use of a special probe (e.g. for the oesophagus, rectum or vagina) is required in some ultrasounds
  • Special preparations may be required before a procedure (e.g. fasting or a full bladder)

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