What is another term for Doppler shift?
Doppler frequency.
What changes when there is relative motion between the sound source and the receiver?
The frequency changes
What happens when the distance between the sound source and the receiver do not move closer or farther apart?
The frequency remains constant
What is the process of extracting the low Doppler frequency from the transducer’s carrier frequency?
Demodulation
What is the equation for a Doppler shift
Doppler shift = reflected frequency - transmitted frequency
What happens when transmitted sound waves strike red blood cells that are moving through the body?
A Doppler shift
When blood moves toward the transducer, is the Doppler shift positive or negative? Does this mean the reflected frequency is higher or lower than the transmitted?
The Doppler shift is positive when blood moves toward the transducer. This means that the reflected frequency is higher than the transmitted frequency.
When blood moves away from the transducer, is the Doppler shift positive or negative? Does this mean the reflected frequency is higher or lower than the transmitted?
The Doppler shift is negative when blood moves away from the transducer. This means that the reflected frequency is lower than the transmitted frequency.
Do Doppler frequencies indicate velocity, speed, or both? Why?
Velocity. Speed is a magnitude meaning it is distance/time whereas velocity has a magnitude and direction so its distance/time in a specific direction.
What is the relationship between the velocity of blood and a Doppler shift
They are directly related. Faster velocities have greater frequency.
How many doppler shifts usually occur?
- First when the beam hits the blood cells and second when the transducer receives the sound wave
What unit is the doppler shift measured in? How does the computer display this information?
The frequency difference is measured in Hz but the computer displays the velocity in m/s.
What is the relationship between the frequency and a Doppler shift
they are directly related.
Why do we measure velocity at 60 degrees?
The most accurate meaurement will occur when the beam is parallel with the vessel because the entire velocity will be accounted for. Other angels of the sound beam in relation to the flow will not have accurate velocity.
How does the angle between the direction of flow and direction of sound relate to the doppler shift?
The doppler shift is directly related to the cosin of this angle
What is the equation for measured velocity in a vessel?
measured velocity = true velocity x cos θ
What does a positive doppler shift indicate?
flow toward the transducer.
How many crystals are needed for continuous wave doppler?
2
What is the biggest advantage of continuous wave doppler?
Continuous wave can accurately measure btoh very high and very low velocities.
What are the biggest disadvantages of continuous wave doppler? Why?
range ambiguity (signals from all blood cells overlap) and lack of TGCs (blood cells deeper in the body might not be as accurately interpreted)
What is duplex imaging
Simultaneous doppler and anatomic imaging.
What is a dedicated continuous wave transducer? How is the PZT shaped?
a simple transducer that does not produce images but can transmit sound and receive it by using two semicircular crystals.
Do dedicated continuous wave transducers use backing material to dampen the pulse? What affect does this have on the bandwidth/Qfactor/sensitivity.
They do not have backing material. A non-dampened pulse results in narrower bandwidth, high Qfactor, and higher sensitivity.
Why does aliasing occur?
When the velocity is too high for the scale
