Ultrasound (OCR A Level Physics)

Revision Note

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Katie M


Katie M




  • Ultrasound is defined as:

Sound waves with a frequency above the human hearing range of 20 000 Hz

  • Ultrasound is, therefore, a longitudinal wave

Range of human hearing

Ultrasound is above 20 kHz, although in medical applications the frequencies can be up to the MHz range

A-Scan & B-Scan

  • There are two types of ultrasound techniques that are used to obtain diagnostic information:
    • A-Scan, or amplitude scan
    • B-Scan, or brightness scan


  • An A-scan, or amplitude scan, uses a single transducer to emit a signal and then later receive the reflected signal back
  • It is defined as:

A one-dimensional ultrasound scan used to determine the distance or depth of an internal structure

  • This is achieved by:
    • Measuring the time delay between generating and receiving the signal
    • Using the speed of sound in the media to calculate the distance travelled by the signal
  • This type of scan is used for:
    • Determining distances from the ultrasound device to the point of reflection (usually the boundary between two media)
    • For example, the length of an eye needs to be determined in planning surgeries or assessing the presence of abnormalities, such as tumours
  • This type of scan gives measurements only and does not produce an image


  • A B-scan, or brightness scan, is a more complex scan that produces a 2D or 3D image of internal structures in the body
  • It is defined as:

An ultrasound scan used to build up a two or three-dimensional image of an internal structure using a number of sensors or one sensor in different positions

  • This is achieved by:
    • Using pulsed ultrasound waves in different positions to produce several measurements of time intervals between generating and receiving pulses
    • Moving the transducer over the patient’s skin, or using several transducers, to produce a series of A-scans that are combined to form an image
  • This type of scan is used for:
    • Creating images of internal structures for diagnostic purposes
    • For example, bones, muscles and organs or checking on the progress of an unborn child
  • To achieve the clearest images:
    • Pulsed ultrasound waves are used to allow time for the reflected waves to be received and not interfere with transmitted waves
    • Smaller wavelengths are used to give more detailed images as they will allow the sound waves to diffract around finer points of detail on the internal structure being studied

Exam Tip

Make sure you can summarise the key differences between A-scans and B-scans:


  • A-scan = one direction
  • B-scan = many directions / angles

End result:

  • A-scan = measurement of distance
  • B-scan = 2D or 3D image

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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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