Lesson 23 (Part 4)

Question 1

What are 4 spectral limitations?

Answer 1

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

Question 2

How can you fix aliasing? (4)

Answer 2

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

Question 3

What does body habitus (depth) limit?

Answer 3

PRF

• higher PRF (superficial)
• lower PRF (deeper)

Question 4

What is occasionally used with doppler?

Answer 4

Continuous wave doppler

- CW

Question 5

How many transducer elements are there with CW doppler?

Answer 5

2

• one to send
• one to receive

Question 6

What is an oscillator?

Answer 6

A CW beam former

Question 7

What does an oscillator produce?

Answer 7

Continusous waves

Question 8

What is the sample volume in CW doppler?

Answer 8

Large overlapping areas

Question 9

What kind of probe is often used in CW doppler?

Answer 9

Pencil probe

Question 10

What is CW/PW doppler often built within?

Answer 10

The same system

- can toggle back and forth

Question 11

What can CW doppler not do?

Answer 11

Alias

Question 12

Why does CW doppler not produce alias?

Answer 12

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

Question 13

What is the benefit to CW doppler?

Answer 13

It can pick up very high maximum values without aliasing

Question 14

What are limitations of CW doppler?

Answer 14

Large sample volume

Question 15

What is the limitations of having a large sample size?

Answer 15

Can’t tell exactly where it’s coming from

- poor “range resolution”

Question 16

What type of doppler has excellent range resolution?

Answer 16

PW

- pulse wave

Question 17

What does an early gate mean for sample volume depth?

Answer 17

Shallow

Question 18

What is doppler signal power proportional to?

Answer 18

Cell concentration

Question 19

What does stenosis effect? (4)

Answer 19

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

Question 20

What kind of spectral trace is spectral broadening?

Answer 20

Vertical thickening

Question 21

What increases when stenosis is in progress? (3)

Answer 21

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

Question 22

What does flow reversal in diastole indicate?

Answer 22

High distal resistance

Question 23

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

Answer 23

To increase

Question 24

What gets increased if doppler angle gets increased?

Answer 24

Effect of angle error