Doppler Review Flashcards
Define Doppler method
A method for detecting the direction and velocity of moving red blood cells and tissue within the heart
What does Doppler echo include
Colour flow imaging
Spectral Doppler
What is kind of Doppler is used in colour flow imaging
Power Doppler
What types of Doppler are involved in spectral Doppler
Pulsed wave (PW)
Continuous wave Doppler (CW)
Tissue Doppler
What is the doppler principle measuring
Frequency shift
What is the doppler shift formula
Df = fd– f0
F0
Transmitted beam frequnecy
Fd
Received beam frequency
V
Velocity of blood flow
C
Sound speed in the medium
What is the doppler shift formula for blood flow
Df = 2 x f0 x V x cos f/ C
What is the purpose of doppler in echo
Detect areas of NORMAL and ABNORMAL flow
Assess systolic and diastolic function
Provide functional information
What are the areas of abnormal flow that doppler can detect
Valves: stenosis/regurg
Shunts
Differentiate between tissue and areas of blood flow
What is the functional information that doppler in echo provides
Flow velocity
Pressure gradient through valves
What are the advantages of PW doppler
Range specificity
Adjustment of sample volume size and position
Able to map velocities at any point in the heart
What are the disadvantages of PW doppler
Inability to measure high velocities (>2.0-2.5m/s) due to aliasing
Is limited by the speed of sound in tissue and PRF
What is the main limitation of PW doppler due to
The NyQuil limit
What is the Nyquist limit
Approximately 1/2 PRF
When does aliasing occur
If the nyquist limit is exceeded
What is doppler CW
2 crystal transducer
-one for transmitting, one for receiving
What is the main advantage of CW doppler
High velocity range
What is the main disadvantage for CW doppler
No range resolution
Why is there no range resolution in CW doppler
Only maximum velocity is measured along a scan line
Unable to be sure that a velocity is coming from a specific location- can only assume
What does TDI use the same principle as
Blood flow
What does TDI measure
Movement of myocardial tissue
tissue doppler signal if of what intensity
Greater
When the tissue doppler signal is compared to the blood flow signal, which velocity is lower
Tissue doppler (e prime, s prime)
What is the machine automatically able to change the settings on for TDI
Filters set to exclude high velocities
Filters set to exclude weak reflectors (blood)
What is the pros of tissue doppler
Easily reproducible
Provides systolic and diastolic information in one waveform
Can be preformed on TDS patients
Less volume (preload) dependant than MV inflow
What are the cons of tissue doppler
Angle dependant
E primes should be measured at end expiration
Filter settings can vary widely between vendors
Gain setting can be to low on certain machines
Velocities will be lower than myocardium in rest of LV due to
-prosthetic valves, MAC, mitral annular ring
What does the x axis represent on doppler signal display
Time in seconds
What does the y axis represent on the doppler signal display
Direction + velocity (m/sec or cm/s)
What does the z axis represent in doppler signal display
Brightness, strength of returning echo, # of cells at a particular velocity
What does a strong signal represent in doppler signal display
More cells moving at that velocity
What does a weak signal represent on doppler signal display
Less cells moving at that velocity
In spectral Doppler the velocity range is adjusted so what happens to the waveform
So that it occupies at least 50% of the available scale
What does blue represent in colour doppler
Flow away from the probe
What does red represent in colour doppler
Flow towards the probe
What does green indicate in colour doppler
Turbulence
What is colour doppler
A pulsed wave technique, subject to aliasing
What happens when the colour doppler aliases
The flow direction becomes ambiguous
In the heart how can the flow direction change
It can change within one structure during the cardiac cycle
What does flow direction add to cardiac scanning
A dynamic component
If we call flow “normal” in cardiac scanning what are we referring to
Directional flow during a particular portion of the cardiac cycle
Is colour doppler effected by the nyquist limit
Yes
What are the advantages of colour doppler
Sensitivity
Region of interest
Laminar vs turbulent flow
What are the disadvantages of colour doppler
Aliasing
Directional ambiguity
What does the Bernoulli equation outline
The relationship between velocity and pressure
As velocity of a moving fluid increases what what happens to the pressure within the fluid
Decreases
What does the drop in pressure create
A pressure difference between the region proximal to a narrowing and within the narrowing
What is the simplified Bernoulli equation
P1-P2=4V^2
When is the modified Bernoulli equation used
To assess maximum instantaneous and mean pressure gradients
What is the maximum gradient calculated from
The maximum velocity
How is the mean gradient calculated
By averaging the instantaneous gradients over the ejection period
Pressure gradient estimations can be underestimated by
Non-parallel sampling of blood flow
A 20 degree offset from flow direction = what
6% underestimation of blood flow velocity
When the offset degree is factored into the Bernoulli equation what will happen
The error will be much higher because the velocity is squared
If an arrhymia is present what must be measured for pressure gradient estimations
3-5 beats, they will than be averaged
What are other factors that will underestimate the pressure gradients
Significant flow acceleration
Viscous forces
Increased proximal velocities
Are prosthetic valves heavier than normal valves
Yes
What are the different types of viscous forces
Long, tubular stenosis
When a stenosis is >10mm in length
Eccentric wall jets
In a normal heart where there is no significant regurg or shunts, the SV through all 4 valves will be what
The same
The stroke volume through a regurgitant valve will be what than through a competent valve
Higher
The SV through a regurgitant valve will include what
The volume of the leak and the normal SV
What is the equation for SV
SV(rv)= SV(cv)+ RV
What is the equation for the regurgitant calculation
RF=RV/SV
What does the Dp/Dt measure
The rise (or fall) of pressure divided by the change in time How quickly the LV can generate pressure
What is the Dp/Dt most often used for
Assess LV global systolic function
When is Dp/Dt only done
When MR is present
