d) Doppler scan

d) Doppler effect in ultrasound; speed of blood in the patient; Δf/f = (2vcosθ)/c for determining the speed v of blood

the doppler scanning process

• the transducer is placed over the blood vessel at an angle

• the transducer sends ultrasound pulses through the body

  • pulses reflected off tissues are received with the same frequency

  • pulses reflected off blood moving away from the transducer are received with a decreased frequency

  • pulses reflected off blood moving towards the transducer are received with increased frequency

• the computer displays a colour-coded image depending on the direction of blood

Δf = (2fvcosθ)/c

• Δf = change in ultrasound frequency (Hz)

• f = initial ultrasound frequency (Hz)

• v = speed of blood (ms^-1)

• θ = angle between the pulse and the skin (°)

• c = speed of ultrasound in blood (ms^-1)