Ch 14 Doppler Artifacts

Question 1

If the scale (PRF) is set at 10 kHz, what doppler shift would violate the nyquist limit?

Answer 1

> 5 kHz

(must be 1/2 the PRF/scale for no aliasing to occur)

Question 2

The highest doppler shifted frequency (nyquist limit) is 3000 kHz, at what value should we set our PRF to avoid aliasing?

Answer 2

> 6000 kHz

(nyquist limit must be 2x the PRF/scale to avoid aliasing)

Question 3

How can we eliminate aliasing with CD?

Answer 3

-Increase scale/PRF
-Adjust angle of the CD box
-Shift baseline

Question 4

How can CD aliasing be a helpful artifact?

Answer 4

When assessing regurg + stenosis in cardiac valves

Question 5

What is a mirror image artifact?

Answer 5

Duplication of a vessel or doppler shift on the opposite side of a strong reflector

(ex. the diaphragm)

Question 6

What is the risk with mirror image artifacts?

Answer 6

-Could misinterpret as an additional vessel with similar CD characteristics (is actually just a duplication of a vessel)

-Mirror vessel will demonstrate color + spectral flow

Question 7

Mirror image artifact is also known as what?

Answer 7

Ghost artifact

Question 8

What causes mirror image artifacts?

Answer 8

-From strong specular reflectors
-Caused by reverberation

Question 9

Explain how mirror image artifacts appears on spectral doppler?

Answer 9

-The doppler spectrum appears on the opposite side of the baseline, when flow is truly unidirectional (moving in 1 direction only)

-Known as “cross talk”

Question 10

What causes cross-talk (mirror image in spectral doppler)?

Answer 10

-High doppler gains
-Doppler angles close to 90 degrees

Question 11

What is flash artifact?

Answer 11

-Aka clutter
-Sudden burst of CD
-Is an extension of color beyond the region of blood flow

Question 12

What is flash artifact caused by?

Answer 12

Tissue or probe motion

Question 13

How can we eliminate flash artifact?

Answer 13

By altering our color wall filters

Question 14

What is noise artifact in CD?

Answer 14

-Aka CD bleeding
-It mimics flow in hypoechoic or anechoic regions

Question 15

What is CD noise due to?

Answer 15

High overall CD gains

Question 16

How can we eliminate noise with CD?

Answer 16

Turn down CD gains

Question 17

What is shadowing in CD due to?

Answer 17

Weakening or elimination of doppler shifted echoes beyond a shadowing object

(similar to 2D B-Mode shadowing)

Question 18

Give 3 examples of things that can cause CD shadowing?

Answer 18

-Calcified plaque
-Bone
-Prosthetic valves

Question 19

Explain the multiple angle artifact with CD?

Answer 19

-Doppler angles in CD are assumed to be 0 degrees
-When the insonification angle is 90 degrees there will be CD drop out
-Changes in color are indicative of the insonification angle

(<90 = + doppler shift, >90 = - doppler shift)