MRI, CT, X-ray, ultrasound, PET: how they differ
Each scan sends a different kind of energy through the body and shows something different. Here is what each one shows, whether there is radiation and how long it takes.
| Scan | How it works | Shows best | Radiation | Time in the room | |
|---|---|---|---|---|---|
| Ultrasound | Sound waves bounce back from organs | Abdomen, thyroid, heart, pregnancy, vessels | None | 10–30 min | How to prepare → |
| X-ray | One flat X-ray picture, like a shadow | Bones, lungs, teeth | Low | 5–10 min | How to prepare → |
| CT | Many X-ray pictures in a circle, built into slices | Bones, lungs, bleeding, injuries — fast | Medium | 5–15 min | How to prepare → |
| MRI | A strong magnet and radio waves | Brain, spinal cord, joints, soft tissue | None | 15–40 min | How to prepare → |
| PET-CT | A small dose of a tracer shows which areas use more energy | Searching for and staging tumours | Higher | 2–3 hours with the wait | How to prepare → |
Where each scan sits
Which scan you need is decided by your doctor. This page only explains the difference.