Reflection of Ultrasound (OCR A Level Physics)

• 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

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)

ANSWER:

• • 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