Lesson 23 (Part 4) Flashcards Preview

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Flashcards in Lesson 23 (Part 4) Deck (24)
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1

What are 4 spectral limitations?

1. Sonographer skills
2. Movement
3. Range gated to a specific depth
4. Aliasing

2

How can you fix aliasing? (4)

1. Adjust the baseline
2. Lower the operational frequency (fD)
3. Increase your Doppler angle
- lowers all Doppler shifts
- slightly incorrect values though
4. Increase the PRF
- increases the Nyquist limit
- allows for higher Doppler shifts/velocities

3

What does body habitus (depth) limit?

PRF
- higher PRF (superficial)
- lower PRF (deeper)

4

What is occasionally used with doppler?

Continuous wave doppler
- CW

5

How many transducer elements are there with CW doppler?

2
- one to send
- one to receive

6

What is an oscillator?

A CW beam former

7

What does an oscillator produce?

Continusous waves

8

What is the sample volume in CW doppler?

Large overlapping areas

9

What kind of probe is often used in CW doppler?

Pencil probe

10

What is CW/PW doppler often built within?

The same system
- can toggle back and forth

11

What can CW doppler not do?

Alias

12

Why does CW doppler not produce alias?

Aliasing happens because the shift is more than the Nyquist limit. The Nyquist limit = ½ PRF and there is no PRF in CW
- no pulses

13

What is the benefit to CW doppler?

It can pick up very high maximum values without aliasing

14

What are limitations of CW doppler?

Large sample volume

15

What is the limitations of having a large sample size?

Can’t tell exactly where it’s coming from
- poor “range resolution”

16

What type of doppler has excellent range resolution?

PW
- pulse wave

17

What does an early gate mean for sample volume depth?

Shallow

18

What is doppler signal power proportional to?

Cell concentration

19

What does stenosis effect? (4)

1. Peak systolic flow speed
2. End diastolic flow speed
3. Spectral broadening
4. Windows

20

What kind of spectral trace is spectral broadening?

Vertical thickening

21

What increases when stenosis is in progress? (3)

1. Systolic doppler shift
2. Diastolic doppler shift
3. Spectral broadening

22

What does flow reversal in diastole indicate?

High distal resistance

23

What does decreased distal resistance normally cause end-diastolic flow to do?

To increase

24

What gets increased if doppler angle gets increased?

Effect of angle error