Lesson 22 (Part 3) Flashcards
What does aliasing show?
Wrap around colour
- top of the graph gets cut off
What does aliasing depend on?
Nyquist limit
What is the Nyquist limit?
1/2 PRF
When are you more likely to get alias?
At higher velocities
- eg) 8kHz PRF and fD over 4 kHz would alias
What should doppler shift be in order to not alias?
lower than the nyquist limit
- lower than 1/2 the PRF
When will aliasing often show?
Within a stenosis if PRF is set too low
How can we use aliasing for good? (2)
- Can adjust the PRF for the normal flow
- Areas of stenosis will show aliasing
- highlights areas of highest velocity
How does gain benefit us in colour doppler?
We can amplify the returning echo voltages
- similar with 2D gain
What do we want the gain to demonstrate in colour doppler?
Wall to wall filling
- within the vessel
What is priority also known as?
Echo-Write Priority
What will echoes below the colour cut off amplitude be shown as?
Colour
- anything above will be apart of the grey scale
What do stronger echoes show as in priority?
Grayscale
What happens if you decrease priority?
You will see less colour
What happens if you increase priority?
You will see more colour
Wall filter
Any movement in the tissues will produce Doppler shifts