Doppler

What is the “Doppler shift”. It boils down to the change in the frequency sent from the machine to the frequency of the returned echo. The difference is the shift.

If the operating frequency is 5 MHz and the returned echo is 4 MHz then the doppler shift is -1 MHz.

The Doppler effect in tissue may be expressed as an equation (shown below). The Doppler shift (Fd) of ultrasound will depend on both the transmitted frequency (Fo) and the velocity (v) of the moving blood. This returned frequency is also called the “frequency shift” and is highly dependent upon the angle between the beam of ultrasound transmitted from the transducer and the moving red blood cells. The propagation speed of sound in tissue is constant (c) and is an important part of the Doppler equation.

  • Fd = 2 Fo v / c
  • Fd is the Doppler shift
  • Fo is the original frequency
  • v is the velocity of target
  • c is the propagation speed of interrogating beam through soft tissue

Example: 2 (5MHz) (120 cm/s) / 1540 m/s

120 cm/s = 1.2 m/s (this converts centimeters into meters)

2 x 5MHz = 10 MHz

1.2 m/s x 10MHz = 12MHz

/ 1540 = 0.0078MHz (this is the doppler shift)

 


Doppler

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Question 1
What is the doppler shift?
A
The difference between the original pulse frequency and the returned pulse frequency.
B
The change between the original pulse frequency and the transducer pulse frequency.
C
The difference between the original pulse velocity and the returned pulse velocity.
D
The difference between the original pulse propagation speed and the returned propagation speed.
Question 2
Which equation is used to find the doppler shift?
A
Fd = 2 Fi v / c
B
Fd = Fr – Fi
C
Fd = 2 Fi c / v
D
v = c ( fi / fo + 1)
Question 2 Explanation: 
Fd = Fr – Fi will show the shift, but only if you know the original frequency and returned frequency.
Question 3
The best angle to have the source of the originating signal is what?
A
0, 180 degrees
B
45 degrees
C
30, 60 degrees
D
90 degrees
Question 3 Explanation: 
0 or 180 is preferred as you are able to detect close to 100% of the doppler shift. Because the nature of Ultrasound and having to penetrate from an off angle, 30 - 60 degrees is the second best location.
Question 4
In the doppler equation Fd = 2 Fo v / c what does Fd stand for?
A
The Doppler shift
B
The original frequency
C
The velocity of target
D
The propagation speed of interrogating beam through soft tissue
Question 5
In the doppler equation Fd = 2 Fo v / c what does Fo stand for?
A
The original frequency
B
The velocity of target
C
The Doppler shift
D
The propagation speed of interrogating beam through soft tissue
Question 6
In the doppler equation Fd = 2 Fo v / c what does v stand for?
A
The velocity of target
B
The original frequency
C
The Doppler shift
D
The propagation speed of interrogating beam through soft tissue
Question 7
In the doppler equation Fd = 2 Fo v / c what does c stand for?
A
The propagation speed of interrogating beam through soft tissue
B
The Doppler shift
C
The velocity of target
D
The original frequency
Question 8
In the image below, is the returned frequency higher or lower than the original frequency?Carotid Ultrasound Flow Practice Question
A
Higher
B
Lower
C
The same
D
Color in an Ultrasound is unrelated to frequency.
Question 8 Explanation: 
This image illustrates how doppler is used to determine direction. Remember the example of the waves emitting from a car horn. If the object is moving towards the listener then the waves are compressed and it creates a higher frequency. So the red color on the color scale displays objects moving towards the transducer. Therefore the frequency has to be higher in the echo that returned.
Question 9
The propagation speed that we input into the doppler equation is dependent on what?
A
The medium
B
The frequency of the beam
C
The source
D
The velocity of the interrogated object
Question 10
What will the doppler shift be if you are 90 degrees to the reflector?
A
0
B
1
C
100
D
Unable to determine
Question 11
The propagation speed that we use in the doppler equation is what?
A
1,540 m/s - The speed of sound in soft tissue.
B
1,570 m/s - The speed of sound in blood.
C
4,080 m/s - The speed of sound in bone.
D
330 m/s - The speed of sound in gas.
Question 11 Explanation: 
You could almost think that the propagation speed in blood would be a factor but the beam spends most of the time in soft tissue.
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I am the founder and lead Instructor here at ExamRefresh.com. I strive to help those that are entering the field of Ultrasound to be the best that they can be. Ultrasound is my passion.

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Comments

  1. This is really great i take my spi on sept 28 IM SO NERVOUS

  2. Maryam Khan says:

    Good job!
    Thanks

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