Ch 3c Wall Filters

Question 1

What does a wall filter do?

Answer 1

-Rejects frequencies below an adjustable value to eliminate clutter (which is high intensity, low frequency doppler shifted echoes)

-Rejects these strong echoes that would otherwise overwhelm the weaker echoes from blood

Question 2

What stuctures cause clutter?

Answer 2

-Heart or vessel wall
-Cardiac valve motion with pulsatile flow

Question 3

What sound does clutter produce?

Answer 3

Wall thump (produces a bright echo on PW)

Question 4

As the wall filter increases higher, what happens to the frequency echoes?

Answer 4

They are rejected

Question 5

What should we do to see the effects of the wall filter on PW + get used to the function?

Answer 5

-Increase the PW gain
-Adjust wall filter

Question 6

As the wall filter is increased, what could possibly be eliminated?

Answer 6

Slower flow (be careful not to overdo the wall filter by putting it too high)

Question 7

What happens if the wall filter is too high on PW?

Answer 7

-Diastolic evaluation can be negatively affected
-Ensure the wall filter is not masking the end diastolic flow + that we are not only seeing systolic flow

(slide image has high wall filter)

Question 8

If the bottom of the waveforms appear “flat” on PW doppler, what is happening?

Answer 8

May be rejecting diagnostic slower flow

Question 9

What does CD wall filter do + is it similar to spectral doppler wall filters?

Answer 9

-Removes slower flow + clutter from images
-Similar to spectral

Question 10

On the colour scale, the width of the black bar in the middle represents what in regards to wall filtering?

Answer 10

Indicates amount of filtering

(ensure it is not set too wide as this will cut out low flow)

Question 11

We must be cautious when increasing our CD wall filter, why?

Answer 11

We could end up removing useful low flow information if the wall filter is set too high

(ex imaging hepatic veins - we see red HV flow + we want to see slower blue flow in surrounding vessels on screen as well)

Question 12

Main take away is if the wall filter is too high, what happens?

Answer 12

Low flow/frequency information can be missing

Question 13

Which image would demonstrate a low wall filter: A vessel with CD aliasing OR a vessel perfectly filled in with CD?

Answer 13

Low WF: aliasing

(must increase the WF to remove clutter)