# Explain how an ultrasound scanner produces an image of the inside of a patient's body from the time taken for ultrasound pulses to return to the probe.

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

> An ultrasound probe is placed on a patient's skin with a layer of gel between the probe and the skin. The probe emits short pulses of ultrasound and detects the echoes that return.

## Mark scheme (5 marks)

1. Ultrasound pulses are reflected (at boundaries) between different tissues / media
2. The time taken for each echo to return to the probe is measured
3. The depth / distance of the boundary is calculated using the speed of ultrasound in the tissue and the time (depth = speed × time / 2 or equivalent statement that distance is proportional to time)
4. The gel / coupling medium prevents (ultrasound) reflection at the skin–air boundary / ensures ultrasound enters the body
5. Information from multiple echoes / reflections is processed (by a computer) to build up a two-dimensional image on a screen

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-an-ultrasound-scanner-produces-b50350e2) · Published by Druglandscape Ltd.