Week 5 Quiz

• The process of extracting the low Doppler frequency from the transducer's carrier frequency is demodulation.
• What is the Doppler shift equation ?

  Doppler shift = reflected frequency - transmitted frequency
• What is the difference between speed and velocity ?

  Velocity is a vector; speed is purely magnitude
• What is the longer Doppler shift equation ?

  Doppler shift = (2 x velocity of blood x transducer frequency x cos0) / propagation speed
• Doppler shift is directly related to the velocity.
• The faster the velocity, the greater the Doppler frequency.
• Why is there a 2 in the Doppler equation ?

  The 2 represents the fact that there are actually two Doppler shifts during a clinical ultrasound
• If the Doppler shift is measured with units of frequency, how do ultrasound systems report blood velocity ?

  They actually measure the frequency difference between the received and transmitted sound waves
• What does the x axis of a Doppler spectrum represent ?

  Time
• What does the y axis of a Doppler spectrum represent ?

  Velocity
• Doppler shift is directly related to the frequency of the transmitted sound.
• When the blood cells are moving parallel to the sound beam, the velocity measurement is 100% accurate.
• Measured velocity = true velocity x cos0
• What are the 3 standard Doppler modalities ?

  CW Doppler, PW Doppler, Colour Doppler
• What are the three axes to a spectral Doppler ?

  Time, Frequency shift, Amplitude
• PW has good range resolution while CW has no range resolution.
• Which suffers from aliasing, PW or CW ?

  PW
• Aliasing occurs when the Nyquist criterion is violated.
• When the Doppler shift is greater than half the PRF, aliasing on the spectrum occurs.
• What is the difference between doppler aliasing and display aliasing ?

  Display aliasing can be unwrapped by shifting the baseline, doppler aliasing is true aliasing
• The presence of a spectral window indicates the presence of laminar flow.
• In order to get a clean spectral window, the gate should be placed in the center of the vessel.
• Doppler shift is directly related to velocity.
• As the frequency increases, the Doppler shift will increase.
• Since the Doppler shift results from a change of wavelength, two factors that also affect the Doppler equation are:

  frequency and propagation velocity
• As the propagation velocity increases, the Doppler shift decreases
• What is the simplified form of the Doppler equation not accounting for the angular correction ?


  f(dop) = (2 x fo x v) / c
• If the flow is directly toward the transducer then the resulting Doppler shift is positive.
• If the flow is directly away from the transducer, the resulting Doppler shift is negative.
• If the angle between flow direction and the steered Doppler line is 90 degrees, then there is no frequency shift
• Arterial waveforms should be pulsatile in nature.
• Where can you find low resistance waveforms in the body ?

  This kind of flow is seen in all areas of the cardiac cycle (ICA and Renal Artery)
• Where can you find high resistance waveforms in the body ?

  Lower extremity arteries, ECA, and SMA