Basics of Doppler Ultrasound
Doppler ultrasonography (DUS) is used to identify the blood flow, quantify it as well as evaluate the flow pattern. In Nephrology practice, it is mainly used in the assessment of arteriovenous dialysis access, focused cardiac ultrasound and assessment of venous congestion.
- You get maximum Doppler shift (better detection of flow) when the angle between the ultrasound beam and the blood flow is 0 degrees (parallel).
- In color Doppler, blue indicates that the flow is away from the transducer and red indicates flow towards the transducer (BART).
- The spectral waveform is displayed above the baseline if the flow is towards the transducer (analogous to red in color Doppler) and below the baseline if the flow is away from the transducer (blue in color Doppler)
- Pulsed-wave Doppler should be used when determining the flow/velocity from a particular location/depth is important (e.g. a vessel or location such as LV outflow tract), while continuous wave Doppler is used when the velocity is more important than the exact location (e.g. peak flow across a cardiac valve).
- Aliasing occurs with pulsed-wave but not continuous wave Doppler.