# Explain why ultrasound is used to image a developing fetus rather than X-rays.

> AQA A-Level Physics (7408) — 3.10.4 Non-ionising Imaging · Explain · 5 marks

## Mark scheme (5 marks)

1. Ultrasound is non-ionising (so does not damage cells / DNA / tissue)
2. X-rays are ionising radiation (which can damage cells / cause mutations / increase cancer risk)
3. Ultrasound is reflected at boundaries between tissues of different densities
4. The reflected pulses / echoes are detected and used to build up an image
5. Ultrasound can distinguish between soft tissues (whereas X-rays cannot / X-rays are only absorbed by denser materials such as bone)

## Key terms

- [ultrasound](https://www.gradenine.co.uk/glossary/ultrasound)

## Related

- [Revision notes for AQA A-Level Physics (7408)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-ultrasound-is-used-to-9fcf2363) · Published by Druglandscape Ltd.