Carotid Doppler Flashcards
Duplex:Two functions:
- Image for anatomy 2. Doppler for physiology
DOPPLER: What does∆f due to motion do?
Bounce ultrasound off the moving RBCs, look for different frequency in backscattered echoesproportionate to velocity of RBCs.
Define Pulse wave Doppler:
Send a pulse, wait for returnso you know how far it went.
Range-gating vs. continuous wave
continuous wave—no gate:you get everything along the beam
Define Gate or sample volume:
specific depth along beamfor sampling flow. Usually adjust fairly small for center-stream flow.
PW Doppler vs. CW Doppler:
PW has a sample volume (gate): scanner pays attention only to that one portion of the Doppler beam, ignoring the rest. CW gives you everything along the beam.
Can you change the size of the gate?
You can change the size of the gate, though it’s usually best to leave it fairly small for precise evaluation.
What to do with the returning shifted frequencies?
Spectral analysis
What is Spectral analysis?
Give a pixel to each separate shifted frequency.Pixel is brighter or darker depending on strength of echo at that frequency.
X axis:
time
Y axis:
frequency shift (velocity)
Z axis:
pixel brightness– echo strength for that frequency
Bright pixel:
lots of blood moving at that speed.
Dark pixel:
not much blood moving at that speed.
On the doppler controls what does the Scale do?
Make waveform take most of the display without going off the top.
On the doppler controls what does the Baseline do?
Lower the baseline if necessary to give the waveform more room. (Probably no reverse flow for carotid)
On the doppler controls what does the Spectral invert do?
To put waveform above baseline
The convention for vascular work is to
put antegrade flow above the baseline—use the “invert” controlif necessary.
On the doppler controls what does the Gain:
amplification of return echoes—Doppler pixels in this case.
What do you not want to do with the gain and why?
Don’t overgain.Tacky, and leads to falsely-high velocity measurements.
What does a 0° angle give?
gives themaximum possible frequency shift
When is a 0° angle used?
during echo
Doppler angle relative to flow: 90° angle
is the worst
Why is the 90° angle the worst?
cosine is 0, and 0 times anything is 0, so no frequency shift
The Apical view has valve flow almost directly toward the beam or away from the beam at what angle?
0° (flow is parallel to the Doppler beam)
What do we standardize at for duplex work?
50-60°
Why is the standard for duplex work at 50-60° ?
Consistancy Not because it’s more accurate,but because it’s moreconsistent.
How do you know what the angle is?
Assume flow direction is parallel to arterial walls. And be sure you are oriented correctly (feet to right).
VERY IMPORTANT: What do you need to do with the ANGLE-CORRECT CURSOR?
Adjust cursor to be parallel with arterial walls.
Why do you need to create a good angle?
Create a good anglefor Doppler assessmentand velocity measurement.
Who creates the angle?
YOU do
How do you make the walls parallel with the angle correct cursor?
Rock the beam to level out the artery.
What if a level artery gives you a 70° angle when you line up the angle-correct cursor with the wall?
First set the angle-correct cursor so that it reads 60°, even though it is now not parallel with the walls. Then rock the beam a bit more to make the artery go downhill to the left, giving you a true 60° angle relative to flow.
If you Steer beam to right, which way is flow going? towards the beam or away from the beam?
flow is toward the beam.
If you Steer beam to left, which way is flow going? towards the beam or away from the beam?
flow is away from the beam.
What does the ICA profuse?
the brain
What does the ECA profuse?
the face and scalp
What does the CCA supply?
both ICA and ECA
What is the flow character in the branches?
Flow character will be different in different branches
What is the ICA flow:
low-resistance character —> lots of diastolic flow
What is the ECA flow:
somewhat higher-resistance character —> less diastolic flow, sharper
What is the CCA flow:
elements of both ICA and ECA, since it supplies both
What is the Normal flow character in arteries:
LAMINAR(orderly, concentric layers)Narrow range of velocitiesSystolic window
What are you looking for Before freezing the imagefor measurement?
- Are the waveforms clear? 2. Are the walls clear? 3. Is the angle-correct cursor lined up with the walls?
After freezing:
Double-check the angle correction.The ends of the cursor should be equidistant from the walls(i.e., parallel).
Mainstream velocity criteria PSV > 125 cm/sec = EDV > 100 cm/sec = EDV > 140 cm/sec =
> 50% > 70% > 80%
Basic generic protocol
- Transverse up and down 2. Sagittal up and down 3. Doppler at proximal and distal ICA, CCA, ECA
What does an abnormal ICA doppler look like?
Here is a normal one
60-70% stenosis
>80% stenosis
normal ICA waveform
Normal ECA waveform
Normal CCA waveform
Imagine a perpendicular to the beam direction.
If the flow direction is above that perpendicular, flow is more toward the beam than away.
If flow direction is below the perpendicular,then flow is more away than toward.
If the flow direction is above that perpendicular, flow is more toward the beam than away.
If flow direction is below the perpendicular, then flow is more away than toward.
