Reflection of Ultrasound (OCR A Level Physics)

Revision Note

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Katie M


Katie M



Reflection of Ultrasound

  • In an ultrasound scanner, the transducer sends out a beam of high-frequency sound waves into the body
  • The sound waves are reflected back to the transducer by boundaries between tissues in the path of the beam
    • For example, the boundary between fluid and soft tissue or tissue and bone

  • When these echoes hit the transducer, they generate electrical signals that are sent to the ultrasound scanner
    • Using the speed of sound and the time of each echo’s return, the scanner calculates the distance from the transducer to the tissue boundary
  • These distances can be used to generate two-dimensional images of tissues and organs

Medical Imaging, downloadable AS & A Level Physics revision notes

Using ultrasound to obtain information about an unborn child

  • The frequency of the ultrasound is important because:
    • The higher the frequency (or the shorter the wavelength) of the ultrasound, the higher the resolution of the image
    • This is desirable so that the finer detail and smaller structures can be distinguished
  • The ultrasound gives two main pieces of information about the boundary:
    • Depth: the time between transmission and receipt of the pulse (the time delay)
    • Nature: amount of transmitted intensity received (will vary depending on the type of tissue)

Worked example

Explain the main principles behind the use of ultrasound to obtain diagnostic information about internal body structures.


    • A pulse of ultrasound is emitted by the piezo-electric crystal
    • This is reflected from the boundaries between media
    • The reflected pulse is detected by the ultrasound transmitter
    • The signal is then processed and displayed on the screen for the healthcare worker to analyse and use for medical diagnosis
    • The intensity of the reflection gives information about the nature of the boundary
    • The time between transmission and receipt of the pulse (the time delay) gives information about the depth of the boundary

Exam Tip

6 mark exam questions about this topic are very common, make sure you practice writing about using and detecting ultrasounds in full, coherent sentences with correct spelling and grammar. Writing short or vague answers could lose you marks, as well as misspelling words!

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Katie M

Author: Katie M

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

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