Lesson 22 (Part 1) Flashcards
What is the speed of blood flow?
110cm/s
What are characters of blood flow? (2)
- Laminar
2. Turbulent
What are 3 types of Doppler displays?
- Colour
- Spectral
- Audible
What does colour doppler demonstrate for blood flow?
- Presence
- Speed
- Character
- Direction
What is a benefit for colour doppler compared to spectral doppler?
It asses a very large area at a time
What is another name for colour doppler?
Duplex scanning
Why is duplex scanning also another name for colour doppler?
Because the colour portion is on top of a grey scale
- 2 parts
How is colour doppler steered?
Through phasing
What is the end goal of phasing? (2)
- To get closer to 0 deg
- To avoid 90 deg
- if vessels are parallel to the surface
What is the formula for doppler shift?
fD = fR- fT fD = doppler shift fR = frequency received fT = frequency transmitted
When does doppler shift occur?
If the returning echoes have a different frequency than from the emitted ones
What does a positive doppler shift indicate?
Flow is going towards the transducer
What does a negative doppler shift indicate?
Flow is going away from the transducer
What kind of pulses are sent out during colour doppler?
Multiple pulses are sent out per scan line
What does a signal processor detect for colour doppler? (4)
- Direction
- Mean velocity
- Variance
- Power
How is colour doppler created? (4)
- Bean former
- Signal processor
- Image processor
- Display
What does direction do for colour doppler?
Tells us if it flowing towards the transducer (+) or away from the transducer (-)
What does the mean velocity tell us with colour doppler?
The average velocity of the blood in an area is calculated and displayed
What does the variance tell us with colour doppler?
The ‘variety’ within the blood flow / standard deviation
What is power related to in colour doppler?
Amplitude
- strength/intensity of the echo
What does power depend on?
- Reflectors
- specular vs scattering - Impedance
- Concentration of RBCs
What does it mean in colour doppler if you have a higher impedance mismatch?
There is more reflection
What does it mean in colour doppler if the concentration of RBCs is high?
More reflection
How many pulses are sent out per scan line in colour doppler?
3-32
- usually 10-20
Ensemble length
Is the number of pulses per scan line
Are more pulses per scan line good or bad?
Good
Why are more pulses per scan line good?
- Accuracy for speed calculation
- Better sensitivity
- can detect weaker echoes better
What happens to temporal resolution with increasing pulses for scan line?
It gets worse
- the most functions the machine has to do the worse the temporal resolution gets
