Ch 2 Doppler

Question 1

What is the doppler effect?

Answer 1

Change in frequency due to motion of a sound source, receiver or reflector

Question 2

List factors that the doppler effect depends on?

Answer 2

-Relative motion of reflector/source
-Motion direction
-Velocity of moving objects
-Angle b/w direction of wave propagation + motion direction of reflector
-Transmitting frequency
-Propagation speed of sound in a medium (assumes 1540 m/s in soft tissue)

Question 3

Flow moving to the right is what kind of doppler shift?

Answer 3

Positive shift, results in a positive number

(motion of reflector is traveling towards probe)

Question 4

Flow moving to the left is what kind of doppler shift?

Answer 4

Negative shift, results in a negative number

(motion of reflector is traveling away from probe)

Question 5

What is a doppler shift?

Answer 5

Change in frequency of returning echoes with respect to the emitted frequency

Question 6

What is doppler shift proportional to?

Answer 6

-Blood flow speed
-Operating frequency

Question 7

List what the variables mean in the doppler shift equation: DS = Fr-Ft

Answer 7

Frequency change (DS) = Received frequency (Fr) - Transmitted frequency (Ft)

(ex 8MHz - 10MHz = -2MHz, a negative shift)

Question 8

At which angle will we receive the most accurate doppler shift?

Answer 8

Either 0 or 180 degrees to a vessel
(avoid 90 degrees)

Question 9

What is the only thing the doppler equation tell us?

Answer 9

Only indicates if relative motion is moving directly towards or away from the probe

Question 10

List what each variable means in the complete doppler equation: F (DS) = 2 Fo V (cos) / c

Answer 10

F: doppler shifted frequency
Fo: operating frequency
V: velocity of moving reflectors (RBCs)
C: speed of sound in soft tissue (1540 m/s)
2: round trip travel time
Cos: doppler angle of incidence or angle correct

Question 11

What angle is doppler dependent on + what is this angle called?

Answer 11

-Angle b/w direction of blood flow + direction of sound propagation
-Known as the insonification/insonation angle

Question 12

What is the insonation angle?

Answer 12

Angle b/w direction of blood flow + direction of sound propagation

Question 13

If doppler angle increases, the doppler shift frequency will increase or decrease?

Answer 13

Decrease (they are inverse of each other)

Question 14

The doppler shift depends on what?

Answer 14

The cosine of the doppler angle

(see chart in slides - as the doppler angle increases, the cosine decreases and gets less accurate)

Question 15

Flow speed measurements incorporate/require what?

Answer 15

Proper doppler angle correction

Question 16

Cosine 1.0 is accurate or not?

Answer 16

100% accurate

Question 17

If we are not getting any color flow in a vessel, what should we do with our probe?

Answer 17

Heel/toe it to try and create an angle under 60 degrees

Question 18

Are cosine + doppler inverse of each other?

Answer 18

Yes

Question 19

What doppler angle should we ALWAYS stay under?

Answer 19

Under 60 degrees (50% cosine) b/c it is more accurate

Question 20

What should we do if we cant get a doppler angle of 60 degrees?

Answer 20

Go lower, never higher b/c way less accurate

Question 21

A doppler angle of 30 degrees has a cosine of 0.87, what is this telling us?

Answer 21

That only 87% of the true shift is detected

Question 22

A doppler angle of 90 degrees has a cosine of 0, what is this telling us?

Answer 22

No motion towards or away from probe, therefore no doppler effect!!

(Never have an angle over 60 degrees)

Question 23

Perpendicular angles (90 degrees) create no doppler shift, how does this affect our CD display?

Answer 23

Poor/no color shown on screen b/c it is referencing nothing

(best to have parallel angle of 0 or 180 degrees)

Question 24

What can we do as sonographers if we can’t align our doppler beam to be parallel to a vessel?

Answer 24

-Use angle correct on machine
-Line up the doppler arrow so it is parallel with vessel flow