Describe how ultrasound is used to produce an image of structures inside the body.

AQA A-Level Physics (7408) — 3.10.4 Non-ionising Imaging · Describe · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

1. Ultrasound pulses are transmitted into the body using a transducer.
2. The pulses are partially reflected at boundaries between tissues of different acoustic impedance.
3. The reflected pulses (echoes) are detected by the same transducer.
4. The time taken for each echo to return is measured to calculate distance.
5. The time and intensity data from many echoes are processed to construct an image of internal structures.

Examiner tips

Use the exact terminology: "transducer", "acoustic impedance", "echoes".
Show the sequence of steps logically.
Mention that distance is calculated from time using speed of sound.
Include that intensity gives contrast in the image.

Common mistakes

Confusing ionising radiation with ultrasound.
Failing to mention the transducer as both source and detector.
Not recognising that distance is derived from time of flight.

Mark scheme (5 marks)

Ultrasound pulses are transmitted into the body
Ultrasound is partially reflected at boundaries between different tissues/media
The reflected pulses (echoes) are detected
The time taken for each echo to return is measured
The time (and intensity) data from multiple echoes is processed to build up an image

Key terms in this question

ultrasound