Chapter 19: Doppler Flashcards
What is the Doppler equation
2 x velocity of blood x transducer frequency x cos Ø
Divided by propagation speed
Doppler shift= reflected frequency - _________ frequency
Transmitted
What is demodulation
The process of extracting the low Doppler frequency from the transducers carrier frequency
Positive Doppler shift happens when RBCs move _____ the transducer
Towards
Negative Doppler shift happens when RBCs move _________ the transducer
Away from
Reflected frequency is ______ during positive Doppler shift
Higher
Doppler shift indicates: (velocity/speed)
Velocity
What is the difference between speed and velocity
Speed measures magnitude (50mph)
Velocity measures magnitude AND direction (50 mph to the south)
Doppler shift is directly related to _____ and _______
Velocity and frequency of transducer
Doppler shifts range from ___ to ____ Hz
20 to 20,000 Hz. Audible sound
Transducers used to perform clinical Doppler exams have a range of frequency of ____ to ___ MHz
2-10 MHz
The best measurement of blood flow is when the sound beam at what angle related to vessel
Parallel to blood flow ( 0 grados)
What is the phase quadrature (aka quadrature detection) in bidirectional Doppler
The component that differentiates between positive and negative frequency shifts, letting us know the direction of flow
A continuous wave transducer has how many crystals
- One receiving and one transmitting
The continuous wave transducer accurately measures very ____ velocities
High
What is the disadvantage of continuous wave
Range ambiguity. We can’t see so we don’t know exactly where it’s pointing at
Anatomical image + Doppler =
Duplex image
Duplex image can be achieved with what type of probe and why
Array probe. 2 crystals are receiving/ transmitting constantly to listen for velocities and the rest are creating an image
What is aliasing
When the peak velocities of a wave exceed the nyquist limit
The nyquist limit is ___ of the pulse repetition frequency
Half
What characteristics create more aliasing
High frequency transducers, faster blood velocity, deep gate (low PRF)
5 Steps to avoid/fix aliasing
Increase scale, decrease depth, use low frequency transducer, move baseline, switch to continuous wave
Grey shades of a spectrum are related to what two things
Amplitude of reflected signal, and number of RBCs creating reflection
Color flow Doppler reports what type of velocity
Average.
What are the two types of maps
Velocity mode and variance mode
The velocity mode map shows what
Direction and velocity
The variance mode map shows what
Direction, velocity and ALSO distinguishes laminar flow from turbulent flow
Doppler pockets are also known as
Ensembles
What are Doppler packets
When a group of pulses are sent to accurately measure velocities
Power Doppler is also known as _____ and it is non-directional dolor Doppler. Only identifies presence of movement
Color angio
What is ghosting artifact
When it “bleeds” outside the vein during COLOR Doppler
What is clutter artifact in Doppler
Low Doppler shifts from moving anatomy
What is used to eliminate ghosting and clutter artifacts
Wall filter
Crosstalk mirror image artifact is only seen in
Spectral Doppler
What is spectral analysis
Tool that breaks complex signals to identify velocities
What are the two methods of spectral analysis
Fast Fourier transform and autocorrelation
Which one is faster, autocorrelation or fast Fourier transform
Autocorrelation
The fast Fourier transform method process both pulsed and ______ wave
Continuous
