Lesson 23 (Part 2) Flashcards
What factors affect magnitude in spectral doppler? (2)
- Speed of blood flow
- eg. within a stenosis - Doppler angle
What is the magnitude within a stenosis?
Faster
Doppler angle
Between the scan line and the blood flow
What can doppler flow affect?
The calculated Doppler velocity
What does a larger doppler angle mean? (2)
- Smaller doppler shift
- Slower velocity calculated
- without angle correct
What factors affect amplitude? (4)
- Brightness
- intensity of the returning echo - Concentration of the RBCs
- Reflectors
- Impedance
What are the special controls for spectral doppler? (4)
- Gate size/sample volume
- Gain
- Spectral invert
- Baseline
What does gate size/sample volume affect?
Range of resolution
Range of resolution
Knowing exactly where the signal is coming from
What is the opposite of range resolution?
Range ambiguity
What does gain do in spectral doppler?
Amplifies the incoming echoes’ voltage
Where are arteries normally compared to the baseline in spectral doppler?
Above the baseline
- positive signals
Where are veins normally compared to the baseline in spectral doppler?
Below the baseline
- negative signals
Can you move baseline?
Yes
What does wall filters do in spectral doppler? (2)
- Cuts off slower flows
2. Gets rid of clutter
What is considered to cause clutter? (2)
- Tissue motion
2. Valves
What can PRF affect?
Scale
- which velocities we can display
What happens if we decreases the PRF too much?
It will cause aliasing
- wrap around
What happens if we increase the PRF too much?
It will produce a poor signal
- wasted space
What does increasing the PRF try and show?
Faster flow speeds
What happens to the doppler shift when ingle correction increases?
It decreases
What is velocity calculated from?
From doppler shift
What does correcting the angle do?
Brings the calculated speed back up to its true value
What can spectral doppler be converted to?
An audible signal
What do higher frequencies have?
Higher pitches
What do lower frequencies have?
Lower pitches
Wy can we hear spectral doppler?
Because they are in kHz
- this is in audible range
What can audible signals do?
Be turned up or down
- volume
What can we do at areas of higher volumes/speeds?
Listen
- we can hear them
