Doppler Mode

Doppler assess a frequency change in the returning ultrasound signal. If a signal impacts a moving object; it returns to the transducer at a different frequency.

Movement towards the transducer INCREASES the frequency of the return signal
Movement away from the transducer DECREASES the frequency of the return signal
The amount of Doppler shift is related to the velocity of movement (higher velocity flow; more Doppler shift)
In “regular” Doppler, the moving object is blood flowing. However, in tissue Doppler Imaging the moving object is the tissue itself

Pulsed Wave Doppler (PWD) (Figure 1)

Pulsed signal allows listening at a specific point. However, it will alias at high flows (Figure 2)
A grey value (white to black) is assigned to the Doppler shift
Along a Time (sec) X-axis vs. Distance (cm, or m) Y-axis to display velocity (cm/sec)
X-axis is called the baseline
Used to assess stroke volume and hepatic and portal venous flow (Figure 1)

Continuous Wave Doppler (CWD) (Figure 3)

One crystal continuously sends and another on one receives the signal
It listens along the entire cursor, not a specific spot, and it does not alias.
It measures high flow jets
A grey value (white to black) is assigned to the Doppler shift
Displayed on distance vs time axis
Used to assess for elevated systolic pulmonary artery pressure, and to grade/assess aortic stenosis (Figure 3)

Color Flow Doppler (CFD) and Duplex Doppler (Figure 4)

Type of pulsed wave Doppler (will alias at high flows)
A color value is assigned to positive and negative Doppler shift
The CFD is overlaid onto a 2D image to create Duplex Doppler
Used to identify location of normal blood flow, identify pathologic blood flow (i.e. ventricular septal defect), and assess valvular function

Tissue Doppler Imaging (TDI) (Figure 5)

Type of pulsed wave Doppler
Measures tissue movement
Most commonly the left ventricle at the mitral annulus
Used to asses diastolic function

Tip

In color Doppler, by convention flow towards the transducer is red, flow away is blue. This is not related to arterial or venous flow

Figures

Figure 1 - Pulsed Wave Doppler

Figure 2 - Aliasing at high flows

Figure 3 - Continuous Wave Doppler

Figure 4 - Color Flow Doppler

Figure 5 - Tissue Doppler

References

Chan, Vincent, and Anahi Perlas. “Basics of ultrasound imaging.” Atlas of ultrasound-guided procedures in interventional pain management. Springer, New York, NY, 2011. 13-19.