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.
