Doppler

Question 1

How doppler derives the shift?

Answer 1

By comparing thw transmitted frequency with the received frequency

Question 2

When the rbcells are stationary, moving toward, and moving away from the probe , what happens to the doppler shift?

Answer 2

1. Stationary
2. Positive shift towards probe and therefore higher frequency
3. Negative shift away from probe, therefore lower frequency

Question 3

5 things that affect the magnitude of doppler shift include

Answer 3

The frequency of the transducer
2. Velocity of blood
3. Angle of U.S beam
4. Speed of sound
5. A factor of 2, which accounts for double doppler shift

Question 4

Why isn’t angle correct used in cardiac?

Answer 4

The direction of blood flow is difficult to determine in cardiac and blood flow is 3D.

Can use multiple windows or off axis imaging too align flow

Question 5

Optimal doppler frequency vs. 2d

Answer 5

Doppler = lower is optimal
2D= higher is optimal

Question 6

Information displayed on a doppler spectrum includes:

Answer 6

1. Velocity
   2.direction of flow
   3.timing of the signal
2. Intensity of the signal

Question 7

Advantage nd disadbantage of CW doppler

Answer 7

High velocities due to continuous sampling.

Poor range resolution- can’t tell exactly where sample from

Question 8

What is the nyquist limit?

Answer 8

The maximum doppler shift/velocity that can be unambiguously displayed by PW doppler.

Nyquist = PRF /2

Question 9

Aliasing occurs the the

Answer 9

Nyquist limit is exceeded

Question 10

How to avoid aliasing?

Answer 10

Lower frequency
Shift baseline
Decrease sample volume depth
High PRF
Change to CW