Doppler Shift Flashcards
The process of extracting the low Doppler frequency from the transducer’s carrier frequency is called:
Demodulation
What doppler shift range can we detect between?
20 Hz to 20,000Hz or -20 Hz to -20,000Hz
(based on direction of the reflector)
What is the doppler equation?
What is speed equation?
distance/time (cm per second -cm/s)
What is phase quadrature or quadrature detection?
Analyze the doppler signal to determine the direction flow is in relation to the transducer
How many crystal does a CW doppler require?
2 crystals
[one to transmit ultrasonic energy and one to receive reflection for RBC (constantly)]
Sample Volume
What are the disadvantage of using CW Doppler?
- Range Ambiguity
- Lack TGC(time gain compensation) for display
What are the advantage of using CW Doppler?
- Accurately detect high velocity
- No aliasing
Range Ambiguity
an erroneous mapping of returning echoes into a composite picture
*correct this artifact by decreasing the pulse repetition frequency (PRF)*
What is duplex imaging?
When the machine is creating an anatomical image and doppler.
What is triplex imaging?
When a machine is creating a 2D image, color, and spectral tracing.
How many crystal does a PW doppler require?
1 PZT crystal
What are the disadvantage of using PW Doppler?
- Cannot detect high velocity
- Aliasing
What are the advantage of using PW Doppler?
- Range resolution
- Sample gate
What is the fast fourier transform?
technique used to understand the doppler shift information returning to the machine and create the spectral waveform.
Shows direction and velocity
Velocity Mode
As moving away from the baseline (black line) the velocity are higher (light green and light blue) whereas closer to the baseline will have lower velocities (dark blue and red).
`Mode that show speed, direction, and types of flows (laminar and turbulent)
Variance Mode
