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Flashcards in Week 10 Deck (29)
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1
Q

Define Range Ambiguity

A

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

2
Q

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

A

low, high, display

3
Q

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

A

high, increased gain

4
Q

What does demodulation do?

A

calculates the ƒ shift

5
Q

What does phase quadrature do?

A

determines positive or negative ƒ shifts

6
Q

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

A

frequent samples

7
Q

Another term for sampling frequency is what?

A

pulse repetition frequency

8
Q

what does PRF stand for?

A

pulse repetition frequency

9
Q

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

A

accurate

10
Q

The PRF for Doppler is usually what?

A

4,000 - 12,000 / sec

11
Q

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

A

Aliasing

12
Q

Aliasing is due to what?

A

too low PRF for the highest frequencies

13
Q

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

A

the Nyquist limit

14
Q

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

A

2x

15
Q

What are the 6 ways to eliminate Aliasing?

A
  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)
16
Q

High PRF mode is used to measure what?

A

high velocities

17
Q

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

A

higher, lower

18
Q

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

A

lower

19
Q

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

A

toward, positive

20
Q

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

A

lower, negative

21
Q

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

A

above, positive

22
Q

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

A

When the waveform is inverted

23
Q

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

A

The INVERTED notation

Negative numbers on the scale sample

24
Q

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

A

Head

25
Q

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

A

right

26
Q

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

A

downward

27
Q

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

A

away from the skin

28
Q

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

A

a. 6 kHz

29
Q

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?

A

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