AQA GCSE Physics

Revision Notes

6.1.13 Ultrasound in Medical & Industrial Imaging

Higher Tier Only

Ultrasound in Medical & Industrial Imaging

  • When ultrasound reaches a boundary between two media, some of the waves are partially reflected
  • The remainder of the waves continue through the material and are transmitted
  • Ultrasound transducers are able to:
    • Emit ultrasound
    • Receive ultrasound
  • The time taken for the reflections to reach a detector can be used to determine how far away a boundary is
    • This is because ultrasound travels at different speeds through different media
  • This is by using the speed, distance, time equation

Speed distance equation, IGCSE & GCSE Physics revision notes

  • Where:
    • v = speed in metres per second (m/s)
    • s = distance in metres (m)
    • t = time in seconds (s)
  • This allows ultrasound waves to be used for both medical and industrial imaging

Ultrasound in Medicine

  • In medicine, ultrasound can be used:
    • To construct images of a foetus in the womb
    • To generate 2D images of organs and other internal structures (as long as they are not surrounded by bone)
    • As a medical treatment such as removing kidney stones
  • An ultrasound detector is made up of a transducer that produces and detects a beam of ultrasound waves into the body
  • The ultrasound 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 detector calculates the distance from the transducer to the tissue boundary
  • By taking a series of ultrasound measurements, sweeping across an area, the time measurements may be used to build up an image
  • Unlike many other medical imaging techniques, ultrasound is non-invasive and is believed to be harmless

Ultrasound Medical Imaging, downloadable IGCSE & GCSE Physics revision notes

Ultrasound can be used to construct an image of a foetus in the womb

Ultrasound in Industry

  • In industry, ultrasound can be used to:
    • Check for cracks inside metal objects
    • Generate images beneath surfaces
  • A crack in a metal block will cause some waves to reflect earlier than the rest, so will show up as pulses on an oscilloscope trace
    • Each pulse represents each time the wave crosses a boundary
  • The speed of the waves is constant, so measuring the time between emission and detection can allow the distance from the source to be calculated

Ultrasound Cracked Bolt, downloadable IGCSE & GCSE Physics revision notes

Ultrasound is partially reflected at boundaries, so in a bolt with no internal cracks, there should only be two pulses (at the start and end of the bolt)

Worked Example

WE Ultrasound Cracked Bolt, downloadable IGCSE & GCSE Physics revision notes

In the diagram above, a very high-frequency sound wave is used to check for internal cracks in a large steel bolt. The oscilloscope trace shows that the bolt does have an internal crack.

Each division on the oscilloscope represents a time of 0.000002 s. The speed of sound through steel is 6000 m/s.

Calculate the distance, in cm, from the head of the bolt to the internal crack.

Step 1: List the known quantities

    • Speed of ultrasound, v = 6000 m/s
    • Time taken, t = 5 × 0.000002 = 0.00001 s

Step 2: Write down the equation relating speed, distance and time

distance, d = v × t

Step 3: Calculate the distance

d = 6000 × 0.00001 = 0.06 m

Step 4: Convert the distance to cm

d = 6 cm

Author: Katie

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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