Relative motion between the sound source and the receiver creates a …
Frequency change
Does frequency change when the distance between the sound source and receiver remains constant?
No
What is the Doppler principle used for?
To measure RBC velocities
The process of extracting the low Doppler frequency from the transducer’s carrier frequency is called
Demodulation
What is the term that describes a low frequency that “rides” on top of the much higher transducer frequency?
Doppler shift
What way are RBC’s traveling when the Doppler shift is positive?
Toward the transducer
What are the equations for Doppler shift?
Doppler shift = reflected frequency - transmitted frequency
Doppler shift = (2 x velocity of blood x transducer frequency x cos θ) / (propagation speed)
T/F Frequency for Doppler shifts range from 2MHz-10 MHz (transducer frequencies)
FALSE. Doppler shifts range from 20-20,000 MHz (audible sound)
During a Doppler examination, a sound with a frequency of 5,000,000 Hz is transmitted from the transducer and reflects off of moving RBC. The frequency of the reflected signal is 5,003,000 Hz. What is the Doppler shift? Is it positive or negative? Which way is the blood traveling?
- Doppler shift: 3,000
- Positive because reflected sound is higher than transmitted
- Towards the transducer
How is a Doppler shift created?
When transmitted sound waves strike moving RBC’s
If the reflected frequency is higher what is the Doppler shift?
Positive
If the reflected frequency is lower what is the Doppler shift?
Negative
If the reflected frequency is higher what direction is the blood flow traveling?
Toward transducer
If the reflected frequency is lower what direction is the blood flow traveling?
Away from transducer
Doppler frequencies indicate which of the following:
A. Speed
B. Velocity
C. Speed and velocity
D. Just a magnitude
B. Velocity
Doppler frequencies indicate velocity, NOT speed
Speed is:
A. Magnitude and direction
B. Purely magnitude
C. Purely direction
D. None
B. Purely magnitude
Velocity is:
A. Magnitude and direction
B. Purely magnitude
C. Purely direction
D. None
A. Magnitude and direction
Doppler frequencies indicate:
A. The distance that a RBC moves in 1 second
B. Swiftness of a fluid moving one location to another
C. The number of particular events that occur in a specific duration of time
D. The time it takes a wave to vibrate a single cycle
B. Swiftness of a fluid moving one location to another
-definition of velocity
How is Doppler shifts related to velocity?
Directly related to
A Doppler study is performed and the Doppler shift is 8kHz when the bloods velocity is 2 m/s. If the bloods velocity slows 1 m/s, what will the Doppler shift be reduced to?
4 kHz
When velocity is halved, the Doppler shift is halved
How many doppler shifts occur during an ultrasound exam? And when?
2
- When the sound waves hit the moving blood cells
- Transducers reception of the sound wave from the moving rbc
The x-axis of a Doppler spectrum represents
Time
The y-axis of a Doppler spectrum represents
Doppler shift or velocity
An ultrasound system uses the frequency information and the Doppler equation to calculate and display…
Velocity of blood
