Vascular Physics Flashcards
What is known as an increase in the “width” of the spectral waveform or “filling-in” of the normally clear area under the systolic peak?
Spectral broadening
What is the doppler shift equation?
Received frequency - transmitted frequency
What is the doppler shift equation with cosine?
DSF = (2x op freq) x velocity x cos / C (prop speed)
What is the doppler angle?
The angle between the US beam and the blood flow
As the doppler angle increases, what happens to the doppler shift?
Decreases
As doppler angle increases, what happens to the cosine?
Decreases
As cosine increases, what happens to the doppler shift?
Increases
What is the proper angle correction in vascular studies?
30-60 degrees
For vascular studies, you should not use angles greater than?
60 degrees
What is the Nyquist limit?
1/2 PRF - the maximum doppler shift before aliasing
PRF must exceed
2x the Nyquist limit
How do we eliminate aliasing?
- Increase PRF scale
- Decrease the doppler shift
- Use CW
How do we decrease the doppler shift?
- Decrease the frequency
- Increase doppler angle
What converts multiple frequency shifts into a spectral waveform?
Fast Fourier Transform
What is the filling in of the spectral window known as?
Spectral broadening
What does colour do to frame rate?
Decreases FR
What causes FLASH artifact?
Movement when using power doppler - very sensitive
What does a higher sweep speed do to the waveform?
Spreads it out
Where do we put the Focus?
At or just after the region of interest (ROI)
What change needs to be made when you see very dark red or very dark blue in a vessel? (slide 26)
Lower the PRF scale to see where the higher velocities are
If you are lacking flow in a vessel, what adjustment should be made?
- Decrease the scale FIRST
- Increase colour gains
What type of waveform will be shown with spectral doppler in an artery vs. a vein?
Artery = Pulsatile flow
Vein = Phasic flow
