Lesson 23 (Part 4) Flashcards
What are 4 spectral limitations?
- Sonographer skills
- Movement
- Range gated to a specific depth
- Aliasing
How can you fix aliasing? (4)
- Adjust the baseline
- Lower the operational frequency (fD)
- Increase your Doppler angle
- lowers all Doppler shifts
- slightly incorrect values though - Increase the PRF
- increases the Nyquist limit
- allows for higher Doppler shifts/velocities
What does body habitus (depth) limit?
PRF
- higher PRF (superficial)
- lower PRF (deeper)
What is occasionally used with doppler?
Continuous wave doppler
- CW
How many transducer elements are there with CW doppler?
2
- one to send
- one to receive
What is an oscillator?
A CW beam former
What does an oscillator produce?
Continusous waves
What is the sample volume in CW doppler?
Large overlapping areas
What kind of probe is often used in CW doppler?
Pencil probe
What is CW/PW doppler often built within?
The same system
- can toggle back and forth
What can CW doppler not do?
Alias
Why does CW doppler not produce alias?
Aliasing happens because the shift is more than the Nyquist limit. The Nyquist limit = ½ PRF and there is no PRF in CW
- no pulses
What is the benefit to CW doppler?
It can pick up very high maximum values without aliasing
What are limitations of CW doppler?
Large sample volume
What is the limitations of having a large sample size?
Can’t tell exactly where it’s coming from
- poor “range resolution”
What type of doppler has excellent range resolution?
PW
- pulse wave
What does an early gate mean for sample volume depth?
Shallow
What is doppler signal power proportional to?
Cell concentration
What does stenosis effect? (4)
- Peak systolic flow speed
- End diastolic flow speed
- Spectral broadening
- Windows
What kind of spectral trace is spectral broadening?
Vertical thickening
What increases when stenosis is in progress? (3)
- Systolic doppler shift
- Diastolic doppler shift
- Spectral broadening
What does flow reversal in diastole indicate?
High distal resistance
What does decreased distal resistance normally cause end-diastolic flow to do?
To increase
What gets increased if doppler angle gets increased?
Effect of angle error
