Week 4 - Lesson 1 Flashcards
Doppler shift
A change in frequency due to the Doppler effect
What is the formula for doppler shift? (without velocity)
Fd = Ft - Fr
- Fd = doppler shift
- Ft = transmitted frequency
- Fr = returning frequency
Which parameter profoundly affects the Doppler equation?
Angle of insonation
- cosine
What is the cosine of 0 deg?
1
What is the cosine of 30 deg?
0.8
What is the cosine of 60 deg?
0.5
What is the cosine of 90 deg?
0
What is the formula for doppler shift? (with velocity)
Fd = 2 x f x V x cos / c
- Fd = doppler shift
- f = frequency
- V = velocity
- cos = cosine
- c = speed of sound (1540 m/sec)
What are the 4 types of doppler?
- Continuous wave doppler
- Spectral doppler
- duplex - Spectral and colour doppler
- triplex - Power doppler
What does the angle correct need to be in spectral doppler? (2)
- 60 deg
2. Parallel to the walls of the vessel
Where do you want the waveform to be situated on the US?
2 fingers or 1/3rd width from the bottom and not cutting it off at the top
How does the angle affect the flow?
The direction of blood flow in relation to the transducer
- toward or away
When does 0 deg to the vessel only work?
With straight vessels
What happens if you alter angle correct?
You alter velocities
How does 60 deg or less help measure a vessel?
It helps to minimize errors
What is the ideal angle?
0
- but usually not possible
What happens if you use an angle greater than 60?
Great error in velocity
What happens if you use an angle greater than 90?
You will get a complete loss of flow
What does signal above the baseline indicate?
Flow towards the transducer
What does signal below the baseline indicate?
Flow away from the transducer
What should the sample volume size be?
As small as possible when in arterial flow
Why dont you want a larger sample volume?
Because a larger sample volume will depict an unclean signal
- lots of velocities
What adjusts the scale?
PRF
Doppler gain
Brightness of the signal
What happens if the spectral wall filter is too low?
Wall thump from arterial systole
What happens if the spectral wall filter is too high?
Eliminates the echoes within the waveform
- resulting in altered waveform
What causes aliasing?
If PRF is too low
- causes wrap around
How do you fix aliasing?
Increase the velocity
What happens if the colour flow is too low?
Only higher flow will be depicted
What happens if the colour flow is too high?
Only lower velocities will be depicted
Doppler characteristics (7)
- Baseline
- Sample volume
- gate - Scale
- Doppler gain
- Spectral wall filter
- Spectral aliasing
- Colour map
