Week 9 Flashcards
(24 cards)
If you change transducers from an 8 MHz to a 4 MHz, how will the waveform be affected?
a. increase in amplitude
b. decrease in amplitude
b. decrease in amplitude
If the blood flow increases, the Doppler shift _______.
increases
Doppler waveforms show changes in _________ _________ over time. When velocities change, _________ change.
Frequency shifts, f-shifts
You should steer the Doppler beam toward the _________ point of the vessel. Why?
lowest, this will yield in better Doppler angles and therefore better waveforms
If the vessel is more vertical than horizontal, you should steer the beam ________.
vertically
When measuring velocities, you should use the _________ sample volume size to avoid what?
smallest, other vessels and slower flow along the wall
A large SV will cause what? Why?
Spectral broadening, because slower velocities from along the wall will fill in the spectral window
When is a time you should use a large SV?
When searching for a small flow in an occlusion
You should place the sample volume at the _______ point of velocity. This is especially true in a _________.
highest, stenosis
Velocities will __________ on the outside of a curve.
increase
In the presence of a calcification, how should you measure the velocity directly underneath it?
You should steer the sv under the plaque from both ends
What would result from overgain in your waveform?
overestimation of velocity
What is it called when your Doppler scale is set too low and a portion of the waveform appears as artifact on the opposite side?
Aliasing
Flow _________ the beam is above the baseline.
toward
Flow __________ the beam is below the baseline.
away from
Doppler angle = the angle between the _________ _________ and ___________ ____________.
Doppler Beam and flow direction
What is the best way to find a 60º angle?
- Beam steer in the direction of the artery
- Set the angle correct to 60º
- 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.
State the 10 steps for the best order to get a velocity measurement using doppler controls
- Get long view on axis
- Steer the Doppler beam same way as vessel
- Place Sample volume small and center stream
- Adjust gain to see and hear
- Invert if needed
- Set Scale correctly
- Set Baseline correctly
8 Overgain and then reduce to avoid speckles outside the waveform - Set angle cursor to 60º and adjust beam steer parallel to walls
- Adjust “fine steer” or heel and toe to make cursor parallel to flow
What is the advantage of CW Doppler?
Large focal zone (sample volume)
What is the disadvantage of CW Doppler?
Hear everything in the Doppler beam’s path
In a zero-crossing detector, the device counts the number of times the echo wave does what?
crosses the zero line
When are wall filters typically needed?
In abdominal vasculature
The brighter the dot on a waveform, the ________ RBCs there are.
more
Adjusting the output power up on the transducer does what?
increases the amplitude of the transmitted beam, and increases the amplitude of the echoes received
