Week 4 - Lesson 2 Flashcards
What must be understood before inverting the colour on a vessel?
The correct direction of flow
- try to have arteries in red
- try to veins in blue
What does the colour red indicate on colour doppler?
Flow towards the transducer
What does the colour blue indicate on colour doppler?
Flow away from the transducer
What does a colour doppler image with an oversized box result in? (2)
- Decreased frame rate
2. Poor resolution of colour within the vessel
What does an appropriate sized colour box demonstrate? (2)
- Increase frame rate
2. Improved colour image quality
How does wasted space in the far field affect the resolution?
Due to increased pulse transit time
- slower PRF
What could wasted space in the far field produce?
Aliasing of colour flow
What influences frame rate?
PRF
What happens if you increase PRF?
You increase frame rate
What kind of relationship does PRF and frame rate have?
Proportional
When do you use steering in a colour box?
When the vessel is parallel or slightly angled
What happens to the sensitivity of the transducer when steering is applied?
It decreases
When do you use a straight colour box?
When vessels are steeply angled
Which way do you steer the colour box?
So that it is parallel to the flow
- not angled in the opposite direction
What do you have to do if you invert the colour doppler?
You need to do the same with spectral doppler
How do you steer a colour box in bifurcation?
You may need to angle the colour box twice to delineate each branch with the most clarity as the vessels usually are not parallel
What do you want in your first bifurcation picture?
You want to optimize the posterior vessel
What do you want in your second bifurcation picture?
You want to optimize the anterior vessel
What kind of settings do carotid arteries have?
High velocity ranges
- due to higher arterial flow
What kind of scale do you need for venous flow?
Lower scale
- because venous flow is much slower in nature
When will colour aliasing occur?
If a venous setting is used to visualize arterial flow
What do higher numbers in colour doppler represent?
Brighter colours
What do lower numbers in colour doppler represent?
Lower colours
What is the normal flow for the portal vein?
20-30 cm/s
What is the flow of the portal vein when there is pathology?
Slower than 20-30 cm/s
Why can a vessel appear occluded?
If the scale of a vessel is incorrect
- especially in veins
What happens if the colour scale is set too high?
The venous echoes will not be represented
- due to slower flow
What does the velocity of the inner portion of a tricky vessel be?
Moves slower
What does the velocity of the outer portion of a tricky vessel be?
Moves faster
