Now some learners may feel like the “other doppler modes” such as Pulse wave, Continuous wave, and Tissue Doppler are very advanced settings. However, the same principles of color Doppler apply to these other Doppler modes as well. The ultrasound probe is just detecting flow or motion either TOWARDS or AWAY from it. If it is towards the probe there will be a positive deflection and if it is away from the probe there will be a negative deflection.
Here is an illustration that sums up the those Doppler modes:
The most common Doppler mode you will use is color Doppler. This mode allows you to see the movement of blood movement in arteries and veins with blue and red patterns on the ultrasound screen.
A common question that comes up with color Doppler is: What do the colors on ultrasound mean? The answer is: RED means there is flow TOWARDS the ultrasound probe and BLUE means that there is flow AWAY from the ultrasound probe. It is a misconception that red is arterial and blue is venous. It actually just depends on the direction blood is flowing relative to the angle of your ultrasound beam.
An easy way to remember this is to use the BART mnemonic: Blue AWAY, Red TOWARDS.
Ultrasound Color Doppler Principles using BART (Blue Away, Red Towards)
There is a mode similar to color Doppler that you may encounter called Power Doppler. This mode does not show up as red or blue on the screen but only uses a single yellow color signifying the amplitude of flow. It is more sensitive than color Doppler and is used to detect low flow states such as venous flow in the thyroid or testicles.
Doppler Shift = (2 x Velocity of blood x transducer frequency x cos θ)/ Propagation speed
*θ = Angle of Insonation (angle of incidence between the ultrasound beam and the direction of flow)
So the Doppler shift is mainly related to TWO things:
The Velocity of the blood cells
The Angle of Insonation
Below is a figure detailing how the Doppler Shift is used and how the angle of insonation is extremely important in what the transducer will detect as the amount of flow/movement. For any type of Doppler you want the flow/movement to be going directly towards your probe (zero degrees) as you move more towards a 90 degree angle there will be no flow detected by the ultrasound machine.
Doppler Shift Equation
(Note: I’m using the velocity of blood as the example here. But the same principles apply if you are measuring muscle movement using tissue doppler.
So the most important thing you can do to improve your Doppler technique for any mode is to make sure that the movement of whatever you are measuring is parallel to your ultrasound probe as much as possible (zero degrees). Anything above 25-30 degrees will significantly underestimate your measurements. And if you are perpendicular, the cosine of 90 degrees = 0 and the ultrasound Doppler will read no flow or movement.
One of the most used modes with ultrasound is Doppler. Initially, Doppler may seem confusing with all of the different Doppler modes available to you (color Doppler, power Doppler, pulse wave Doppler, continuous wave Doppler, and tissue Doppler).
But if you just think of Doppler signals as detecting the speed of movement either Towards or Away from your probe you can derive all of the different Doppler ultrasound modes.
The Doppler Effect (or Doppler Shift) is used to evaluate movement either towards or away from the ultrasound probe/transducer. The most common Doppler ultrasound application we think of is detecting movement of blood, but we can also use Doppler on ultrasound to evaluate tissue and muscle movement.
