7. Advanced Ultrasound Modes (Doppler)

Pulse Wave (PW) Doppler Mode

Pulse Wave (PW) Doppler allows you to measure the velocity of blood flow (at a single point). A unique aspect of Pulse Wave Doppler is that you can specify to the ultrasound machine exactly where you would like the machine to measure the velocity using the Sample Gate. It’s usually seen by two horizontal lines along your cursor. you can move your cursor and your sample gate and place it exactly where you want to measure your blood velocity.

See the example figures below:

Pulse Wave Doppler Sample Gate
Pulse Wave Doppler Towards Probe
Pulse Wave Doppler AWAY from Probe

The biggest limitation with Pulse Wave Doppler, however, is that there is a limit on the maximum speed you can detect. Anything past this limit (termed Nyquist Limit) will cause the signal to alias. In general, you do not want to use Pulse Wave Doppler for any applications that require measuring speed above 200cm/second.

This is why you can’t use this mode for very high-velocity applications such as severe regurgitation or stenosis of the heart valves. Here is an example of aliasing with pulse wave Doppler:

Ultrasound with Aliasing Artifact Nyquist Limit
Ultrasound Aliasing with Pulse Wave

Common applications of pulse wave Dopplers are to measure cardiac output (LVOT VTI) or diastolic dysfunction.

Here are the steps to properly use Pulse Wave Doppler after you acquire your 2D image:

  • PW Doppler Step 1: Push Pulse Wave Doppler Button to make PW Cursor line appear
  • PW Doppler Step 2: Place PW Sample Gate at Area of Interest
  • PW Doppler Step 3: Push PW button again to activate Pulse Wave Doppler Mode
  • PW Doppler Step 4: Adjust the PW Gain, Baseline, and Scale
  • PW Doppler Step 7: Adjust the Sweep Speed (how many seconds are shown on the X-axis, see video below for example)
  • PW Doppler Step 8: Push the Freeze Button
  • PW Doppler Step 9: Scroll to the desired image
  • PW Doppler Step 10: Push Measure Button
  • PW Doppler Step 11: Measure Area of Interest

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