Basics of Spectral Echo Flashcards
Blood Flow Characteristics are based on:
- Type of vessel
- Size of vessel
- Resistance to flow
- Disease process which will make the vessel more narrow
- Phase of the cardiac cycle
What is rate of flow (flow rate) determined by?
Change in pressure between two areas and resistance to flow
What is the flow resistance influenced by?
- Length
- Viscosity
- Radius of a tube
(8 x L x viscosity/radius)
Poiseuilles law?
The relationship between pressure difference, flow rate, and resistance
Examples of types of plug flow?
Entrance to vessels or flow due to crossing valves
- RVOT and LVOT
- TV and MV
Examples of parabolic flow?
Occurs in long and straight vessels
- Peripheral vessels in cardiovascular system
In a curved vessel with skewed flow, where are velocities highest and lowest?
Highest on the outside of the curve
Lowest on the inside of the curve
In a U shaped vessel with skewed flow, where are the velocities the highest?
On the inside of the curve on the ASCENDING portion
On the outside of the curve on the DESCENDING portion
What type of flow occurs in a stenosis or bifurcation?
Disturbed flow
What type of flows are seen in a bifurcation of disturbed flow?
- Laminar flow on the straight portions of the vessel
- Slower, circular flow on the inside of the bifurcation branches
What is the term used for the slower, circular flow seen on the inner side of bifurcation branches?
Eddy flow
What are examples of turbulent flow?
- Stenosis
- Regurgitation
- Septal defects
What law explains “flow before a stenosis and after a stenosis must be equal” ?
Continuity principle
What formula explains change in pressure and velocity at a stenosis?
4(v)^2
As flow increases through a stenosis, what happens to the pressure?
There is an increase in pressure DROP
What is volumetric flow rate?
Velocity of flow x cross section area of a vessel
When Cos = 1, what is the doppler shift?
It is at 90 degrees = perpendicular and NO FLOW
What is on the ‘x’ and ‘y’ axis in spectral doppler?
x = time: adjusted via sweep speed
y = velocity
Brightness and density of the spectral doppler signal equals?
Higher intensity and velocity and increased amplitude
In what application can spectral broadening be seen?
Pulsed wave doppler
What application is useful in detecting velocities at specific locations?
Pulsed wave doppler
What does a higher PRF mean in terms of number of samples?
More samples being generated with a higher PRF
How many samples does pulse wave need per cycle to prevent aliasing?
2
What is nyquist limit?
Maximum doppler shift to avoid aliasing = 1/2 PRF
Why is CW doppler a benefit?
It does not cause aliasing and can visualize high velocities
How can you tell PW from CW?
PW has a spectral window and CW does not
What is a disadvantage of CW?
Since it samples along the entire cursor line, it is tough to tell what depth the signal is coming from.
AMBIGUITY
What probe has the best CW doppler signals?
Pedoff probe
What are pedoff probes most often used for?
Stenosis - most commonly aortic
As velocity increases, what happens to pressure?
Decreases
What type of imaging records myocardial velocities?
TDI
What is TDI used to determine?
LV diastolic dysfunction/function
RV systolic function
If you image a higher velocity, what should you do to your baseline to accommodate the higher velocities?
Increase to accommodate visualizing higher velocities
How much of the screen should a waveform take up?
2/3
For faster heart rates, how do you adjust sweep speed?
Increased sweep speed to spread out waveform
What would cause an increase in signal:noise ratio?
Increasing sample gate
What is an optimal sample gate?
3mm
What should you do to the wall filter in slower flow?
Decrease it to capture the slower flow
What do wall filters eliminate?
High intensity, low-velocity signals (clutter)
