Diagnostic imaging is the umbrella term for the tests that let doctors see inside the body without surgery — including X-ray, CT, ultrasound, MRI and nuclear medicine. Each works differently: some use radiation (X-ray, CT, nuclear medicine), while ultrasound and MRI use none. Together they help diagnose disease and injury, guide treatment, and monitor how conditions change.
Key takeaways
- Diagnostic imaging is the umbrella term for scans that see inside the body.
- Main types: X-ray, CT, ultrasound, MRI and nuclear medicine.
- Some use radiation; ultrasound and MRI use none.
- It's used to diagnose, guide treatment and monitor conditions.
“Diagnostic imaging” (also called medical imaging) is the umbrella term for the tests that let doctors see inside the body — without surgery.[1]
The main types
Each type of imaging works on a different principle:[2]
- X-ray — uses a small amount of radiation; great for bones and chests.
- CT — uses X-rays and a computer to build detailed cross-sectional images.
- Ultrasound — uses sound waves (no radiation); used in pregnancy, the abdomen and blood vessels.
- MRI — uses magnets and radio waves (no radiation); excellent for soft tissues like the brain, joints and spine.
- Nuclear medicine (including PET) — uses a tiny radioactive tracer to show how organs are working.
A key distinction: X-ray, CT and nuclear medicine use ionising radiation, while ultrasound and MRI use none — which is why the radiation-free options are often preferred for children and in pregnancy.[2]
What it’s used for
Diagnostic imaging helps doctors:[1]
- diagnose disease and injury;
- guide treatment (such as planning surgery, or steering a needle during a procedure);
- monitor how a known condition is changing over time.
Structure vs function
Another helpful way to group imaging: most scans show structure (what something looks like — X-ray, CT, ultrasound, MRI), while nuclear medicine shows function (how an organ is working). Sometimes they’re combined, as in PET-CT.[2]
Frequently asked questions
Is diagnostic imaging the same as radiology?
They’re closely linked: diagnostic imaging refers to the scans themselves, while radiology is the medical specialty that performs and interprets them. In everyday use the terms overlap.[1]
Do all scans use radiation?
No — X-ray, CT and nuclear medicine use radiation, but ultrasound and MRI use none. That’s why the radiation-free options are often chosen for children and in pregnancy.[2]
Is diagnostic imaging different from interventional radiology?
Yes — diagnostic imaging is about seeing to make a diagnosis; interventional radiology uses imaging to guide treatments (like draining a collection or placing a stent) through tiny incisions.[1]
Sources
- healthdirect (Australia) — Diagnostic imaging — www.healthdirect.gov.au/diagnostic-imaging
- RANZCR / InsideRadiology — Radiation risk of medical imaging — www.insideradiology.com.au/radiation-risk/
