Chapter 20: Optimizing Doppler Flashcards
How to reduce aliasing?
increase PRF (scale)
decreasing scale (PRF) increases what?
sensitivity to slower flow
at what angle is a normal incidence
90°
what happens with a normal incidence?
cannot determine direction of flow (no doppler)
how to fix normal incidence
angle vessel or steer color box
if color doppler gain is too low what happens to the vessel?
vessel doesn’t fill completely
what happens when color doppler gain is too low?
the vessel overflows (bleeds)
what is it called when colors on the map touch but are separated by a black line?
flow reversal (bidirectional flow)
what is it called when colors touch each other going around the map (mixing colors)
aliasing
characteristics of a low wall filter
cluster can appear in waveform and low velocity’s are shown
when lowering the PRF you are producing a lower or higher nyquist limit?
lower
increasing PRF increases what?
scale& numbers on scale
increasing PRF makes more or less sensitivity to slower flow?
less
increasing PRF may eliminate what?
clutter (noise)
increasing PRF causes waveform to _ in size?
decrease
Decreasing PRF causes a decrease in?
scale and numbers on scale
Decreasing PRF causes _ sensitivities to slower flow
more
when decreasing PRF there is more or less clutter?
more
decreasing PRF waveform _ in size
increases
decreasing PRF has more or less of a chance of aliasing?
more
