Week 10

Question 1

Define Range Ambiguity

Answer 1

the location of the flow cannot be determined due to no image

Question 2

A wall filter filters out _________ ƒ’s, and leaves ________ƒ’s from ________ on the display.

Answer 2

low, high, display

Question 3

______ velocities with spectral broadening often need ____________ ____________ to see waveforms.

Answer 3

high, increased gain

Question 4

What does demodulation do?

Answer 4

calculates the ƒ shift

Question 5

What does phase quadrature do?

Answer 5

determines positive or negative ƒ shifts

Question 6

PW doppler uses ________ ________ of the returning sound waves rather than continuously monitoring

Answer 6

frequent samples

Question 7

Another term for sampling frequency is what?

Answer 7

pulse repetition frequency

Question 8

what does PRF stand for?

Answer 8

pulse repetition frequency

Question 9

In Doppler, the more frequently the returning echo wave is sampled, the more __________ the display.

Answer 9

accurate

Question 10

The PRF for Doppler is usually what?

Answer 10

4,000 - 12,000 / sec

Question 11

The result of less than two samples per cycle is what?

Answer 11

Aliasing

Question 12

Aliasing is due to what?

Answer 12

too low PRF for the highest frequencies

Question 13

The PRF that will give you less than 2 samples per cycle is what?

Answer 13

the Nyquist limit

Question 14

You usually want the PRF to be at least ______ the highest f shift or PSV

Answer 14

2x

Question 15

What are the 6 ways to eliminate Aliasing?

Answer 15

1. Increase scale (increases PRF)
2. Decrease baseline
3. Use a lower frequency transducer
4. Find a higher angle (always <60º)
5. Change to a CW Doppler (No velocity)
6. Use high PRF mode (possible range ambiguity)

Question 16

High PRF mode is used to measure what?

Answer 16

high velocities

Question 17

Lower ƒ transducers are better to detect _________ velocities due to __________ ƒ shifts.

Answer 17

higher, lower

Question 18

Because of the Doppler equation: a __________ transducer yields lower ƒ shifts

Answer 18

lower

Question 19

If blood flows __________ the Doppler beam it creates a higher frequency. ( ________ shift)

Answer 19

toward, positive

Question 20

If blood flows away from the Doppler beam it creates a ________ frequency ( _______ shift)

Answer 20

lower, negative

Question 21

Flow toward the Doppler beam is displayed _______ the baseline or ________.

Answer 21

above, positive

Question 22

When is the flow toward the beam displayed below the baseline?

Answer 22

When the waveform is inverted

Question 23

What two things tell you whether the waveform has been inverted or not?

Answer 23

The INVERTED notation

Negative numbers on the scale sample

Question 24

Flow going toward the left side of the screen is always going toward the _______.

Answer 24

Head

Question 25

Flow going towards the feet will always be going to the ______ side of the screen.

Answer 25

right

Question 26

If a Doppler Beam is steered vertically, flow away from the beam is in the ________ direction.

Answer 26

downward

Question 27

If flow is going downward, it is going _________ the skin.

Answer 27

away from the skin

Question 28

If a peak Doppler frequency shift for an echo is 6 kHz, at which of the following PRF’s will aliasing occur?

a. 6 kHz
b. 12 kHz
c. 18 kHz
d. 24 kHz

Answer 28

a. 6 kHz

Question 29

For a given Doppler signal, the Doppler angle is 0º and the highest Doppler shift is 6 kHz. The PRF is 9 kHz. Will aliasing occur?

Answer 29

Yes. 6 x 2 = 12. the PRF is 9. 9<12.