The good news is that all of the principles of Pulse Wave Doppler also apply to Tissue Doppler. In fact, Tissue Doppler is just another form of Pulse Wave Doppler that allows you to measure the much slower speeds of tissue/muscle movement (from 1cm/s – 20cm/s) compared to Pulse Wave Doppler that measures the much faster speed of blood (30cm/s – 200cm/s).
Accessing the Tissue Doppler function will vary by machine but usually just involves pushing a knob/button labeled “TDI” (Tissue Doppler Imaging) while you are in the Pulse Wave Doppler mode.
Here are the steps to using Tissue Doppler Imaging:
Continuous Wave Doppler is very similar to pulse wave Doppler except it does not alias and can detect very high velocities (greater than 1000cm/second). So Continuous Wave Doppler is the optimal choice for measuring high-velocity applications such as valvular stenosis and regurgitation.
Unlike Pulse Wave Doppler which has a sampling gate to measure a single point along your cursor, Continuous Wave Doppler measures all points along your cursor. Therefore what you will see will be the maximum velocity of flow detected along the cursor line. This is a pro and a con. It is a pro because you don’t have aliasing and can detect high velocities, but it is a con because you don’t know exactly where that velocity is coming from on the cursor. Also if there are two velocities along the cursor line, you won’t be able to differentiate the lower velocity compared to the higher velocity signal, since the high-velocity signal will mask the low-velocity one.
The steps to performing continuous wave Doppler are the similar to Pulse wave Doppler except where you put the sample gate does not matter. It will measure velocities across the entire cursor line.
Steps to performing Continuous Wave Doppler:
CW Doppler Step 1: Push Continuous Wave Doppler Button to make CW Cursor line appear
CW Doppler Step 2: Place CW Cursor at Area of Interest (where you put the sample gate doesn’t matter)
CW Doppler Step 3: Push CW button again to activate Continuous Wave Doppler Mode
CW Doppler Step 4: Adjust the CW Gain, Baseline, and Scale
CW Doppler Step 7: Adjust the Sweep Speed (if needed)
CW Doppler Step 8: Push the Freeze Button
CW Doppler Step 9: Scroll to the desired image
CW Doppler Step 10: Push Measure Button
CW Doppler Step 11: Measure Area of Interest
Here is an example of measuring tricuspid regurgitation (TR) using continuous wave Doppler. Notice how CW Doppler can measure the high velocity of this TR jet (344cm/s).
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:
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:
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)
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 flow/motion 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:
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. So you can’t tell if the flow is going towards or away from the probe given that it has only one color. It is more sensitive than color Doppler and is used to detect low flow states such as venous flow in the thyroid or testicles.
The most common Doppler mode you will use is color Doppler. This mode allows you to see the movement of blood 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.
All Doppler signals (regardless of which Doppler mode you are using) are calculated using the Doppler Shift Equation. 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 speed 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.
(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 technique for any Doppler mode is to make sure that the movement/speed 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.
Besides B-mode and M-mode you will have other advanced ultrasound Modes that involve “Doppler.” Here is an image of all the available ultrasound modes:
Initially, these Doppler modes may seem confusing but in reality, all Doppler settings are simply meant to detect speed going either Towards or Away from your probe. Understanding this is the first step to mastering ultrasound Doppler.