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chapter 20 optimizing doppler imaging

Terms in this set (17)

the angle between the direction of flow and the direction of sound beam is 90 degrees. no doppler shift is created
in image A why does vessel appear without color?
In images B and C the color box is steered. angle between flow and sound beam directions is different than 90 degrees, creating color.
what will make color appear in this vessel?
angle between direction of flow and sound beam is 90 degrees.

this image illustrates that a 90 degree angle between direction of sound and flow can be created with slanted vessels.
why is there no color in image A
steer the box
what will make color appear in this vessel?
color appears throughout the color box.
image was created by setting color gain to a level that is too high
color confetti
color gain set too low, sound beam and flow are not perpendicular, increase color doppler gain.
color gain is set too high.
decreasing the pulsed doppler gain.
gray scale noise appears when the pulsed doppler gain is set too high.
what alteration was responsible for the change in appearance from image B to A?
Aliasing
central flow stream is blue (toward transducer or right to left)
flow streams closer to the vessel wall are red ( away from transducer or left to right)

unlikely there is flow in different directions within a single vessel.
what artifact appears in image A
If the colors that touch each other (on image) go through the maps middle flow reversal is present. (A)

if the colors that touch each other (on image) go around the outside of the map aliasing is present. (B)
How can we distinguish bidirectional flow from aliasing with color flow doppler?
flow reversal, red black and blue are close to maps middle
is the blue area in this image aliasing or flow reversal?
most effective way to reduce aliasing on color flow image is to increase the velocity scale.
A is .07 m/s B is .55 m/s
how is aliasing reduced or eliminated on a color doppler image?
yes, increasing color doppler scale decreases sensitivity to slow flows.

The scale is increased from image A to B, it helps to reduce aliasing in the artery with high velocity, but now color is absent on the vein with low velocity because it is insensitive to slow flows at this scale setting.
does increasing the scale have any other effect on a color doppler image?

what effects occurred to image B?
increased wall filter to very high level.

color of vein has vanished and ghosting artifact vanished. high velocity flows are unchanged.
what adjustment did the sonographer perform to create image B?
increased wall filter

wall filter selectively eliminates low frequency doppler shifts near the baseline.
what adjustment did the sonographer perform to change the upper spectrum into lower spectrum?
increased wall filter

low frequency doppler shifts eliminated (veins)
what adjustment did the sonographer perform to create image B?
the scale is increased, aliasing is no longer present in the artery, vein no longer appears blue because as scale increases sensitivity to slow flow is reduced.

It is not wall filter because of the change in arterial flow, a wall filter will not alter the high velocity flows.
wall filter vs increasing scale
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