Chapter 1

Question 1

Aliasing

Answer 1

Artifact which appears when Doppler shift > 1/2 PRF (Pulse Repetition Frequency)

Question 2

FFT

Answer 2

Fast Fourier Transform - Mathematical way to process thousands of doppler frequency shifts into “bins” for visual analysis.

Question 3

Autocorrelation

Answer 3

Display of Doppler motion information by comparing change in frequency at various depths over time.

Question 4

Three factors affecting Doppler frequency shift.

Answer 4

1. Transmission frequency (f_t): The greater the f_t the greater the change in f.
2. Doppler angle: The smaller the angle, the greater the change in f.
3. Velocity of RBCs: The greater the velocity of RBCs, the greater the change in f.

Question 5

Continuous Wave Doppler

Answer 5

Two elements, one to transmit, one to receive.

Advantages:

• Detects flow of all vessels in beam
• Useful for obtaining systolic bp in lower arteries
• Will not create aliases

Disadvantages

• Not depth specific
• No image possible

Question 6

Pulsed Wave Doppler

Answer 6

One element is used to alteratively transmit and receive. (Transmits then “listens”.) May use an array of many elements.

Advantages:

• Depth specific
• Capable of creating images

Disadvantages

• Produces alias artifacts

Question 7

Quadrature Signal Processing

Answer 7

Phase information, provides information regarding the direction of movement of the RBCs.

Question 8

Conceptual Doppler Equation

Answer 8

Δf = f_r - f_t

RBCs moving away yields negative Δf

RBCs moving toward yields positive Δf

Question 9

How can aliasing be reduced?

Answer 9

• Lower the baseline
• Increase the scale or PRF
• Use lower frequency transducer
• Decrease sample volume depth
• Don’t time share