What are the parts of a doppler waveform creation?
- Doppler beam
- Sample volume
- Angle cursor sets doppler angle.
Doppler waveforms shows changes in ______ ______ over time.
What happens when velocities change?
Frequency shift change.
How must your vessel be?
-Must be on axis. (open at each end)
How is flow seen when the vessel is on axis?
Flow direction is typically parallel to the walls.
if SV is moved along a vessel while you can, what may you need to do?
You may need to change steer directions as vessel changes direction up or down.
Why do you want to ster the doppler beam towards the lowest point of the vessel?
It yields better doppler angles so better waveforms.
True or False:
Beam steer affects waveform.
When is vertical beam steer not a good option?
Vertical beam steer is not good if nearly perpendicular to flow.
When is a vertical beam steer a good option?
Vertical beam steer is good if the vessel is already angled.
When measuring velocities, why should you use the smallest sv?
To avoid other vessels and flow along the wall.
What do larger sv demonstrate?
It shows all velocities across a vessel, including slower velocities along the wall.
Large SV causes spectral broadening, filling in the spectral “window”
When should you use a large SV?
When searching for flow in a near occlusion, to find a small channel of flow.
What does a sample volume affect?
Where should you place the sample volume?
Place sample volume center stream rather than along walls where velocities are lower and flow direction changes are more likely.
Where should you place the sample volume in a stenosis?
Place SV at the highest point of velocity (proximal to distal).
Where do flow disturbances occur?
Around a curve.
Where do velocities naturally increase?
On the outside of the curve.
What often occurs on the inside of the curve?
FLow seperation, with reversed flow.
How must you steer the sv under a calcification area?
- Steer sv under clacified plaque from each end.
- Use multiple windows to get around the shadow.
- AP Lateral
Describe the echoes from RBC’s?
Echoes are so small that they must be amplified.
What is loudness attached to?
What does gain do?
It affects brightness of each echo in waveform.
How should you increase the spectral gain?
Turn spectral gain up until echoes appear outside waveform, then turn down until they disappear for correct gain.
What does an overgain result in?
Overestimating velocity slightly.
It also results in a mirror wave “crosstalk”
What does an undergain result in?
It may underestimate velocity or make you think the vessel is occluded when its not.
How should the scale be set?
Scale should be set so th dopple waveform fills most of the size of the entire scale.
Why do you not want the scale to be too high?
It may hide information at the lower levels.
A scale too low will cause an artifact called?
How should the baseline be between arteries and veins?
Arteries: Keep baseline low.
Veins: Keep baseline high
but…leave enough room to display reversed flow.
Flow ______ is above the baseline.
towards the beam. (positive shift)
Flow _____ is below the baseline.
Away from the beam. (negative shift)
What is an exception to the flow and their relation with the baseline?
How is normal arterial flow shown?
How is retrograde arterial flow shown?
Below the baseline.
How is normal venous flow seen?
Below the baseline.
How is venous reflux seen?
Above the baseline.
When should you invert?
Invert as needed to demonstrate a normal or abnormal flow direction. This will assist the intrepreter in noting abnormal flow.
What is the doppler angle?
Angle between the doppler beam and flow direction.
How do we indicate the flow direction?
We assume flow is parallel to he walls and set the angle cursor parallel to the vessel walls.
What will happen If you change the angle correct?
It will not change the doppler waveform, but it will change the velocity measurement.
What will happen if you do not set the angle cursor parallel to the walls (or flow)?
The velocity you report will be inaccurate.
What doppler angle is appropriate?
Must use a doppler angle that is 60° or less.
Why must the doppler be 60° or less?
Because the cosine of the angle in the doppler equation is not linear, so a small error in setting the angle results in a big difference in velocity at angles higher than 60°
How to find a 60° angle?
- Beam steer in the direction of the artery.
- Set the angle correct to 60°
- Use “fine steer”, heel and toe probe, and/or find a location in the area of interest where the angle correct is parallel to the walls/flow.
Even though you should avoid measuring vleocities on a curve, if you must measure velocities on a curve, what should you do?
Set the middle of the angle cursor parallel to the walls.
How do you measure PSV?
Measure highest peak in area of interest unless the patient has arrhythmias, then use most common peak level.
How do you measure EDV?
Measure at the END of diastole. (just before systolic upstroke)
What is the best order to use doppler controls for velocity measurements?
- Get long view on axis.
- Steer the Doppler beam same way as vessel.
- Place sample volume small and center stream.
- If you don’t hear and see waveform, gain up.
- Invert if needed so normal artery flow is above baseline.
- Set scale so waveform takes up most of the full scale.
- Change baseline if needed to set scale further. Keep low, but leave room for reversed flow below it.
- Turn gain up then down to avoid speckles outside waveform.
- Set angle cursor to 60 degrees and adjust beam steer to make it parallel to walls. You may need to steer it another direction to achieve 60 degrees.
- If adjusting fine beam steer doesn’t help, heel and toe vessel to make cursor parallel to flow.