Lecture 3 & 4 US Doppler Principles

Question 1

what is the doppler effect?

Answer 1

change in frequency due to motion

Question 2

what is a positive doppler shift?

Answer 2

when the source & receiver approach each other

Question 3

what is a negative doppler shift?

Answer 3

when source & receiver move away from each other

Question 4

what is the doppler shift equation?

Answer 4

doppler shift = reflected - incident f

Question 5

what is the cosine of 90 degrees?

Answer 5

0

Question 6

for vascular scanning, we want a (higher/lower) angle

Answer 6

lower

Question 7

to get a smaller angle for doppler, we want cosine to (increase/decrease)

Answer 7

increase

Question 8

why do we use Doppler in vascular imaging?

Answer 8

facilitates the exam by giving qualitative & quantitative data

Question 9

how many crystals are in continuous wave doppler?

Answer 9

2 crystals: 1 continuously sends & the other continuously receives

Question 10

advantage of CW?

Answer 10

able to track high velocities

Question 11

what is a disadvantage of CW?

Answer 11

range ambiguity

Question 12

what is an advantage of PW?

Answer 12

has range resolution

Question 13

what is a disadvantage of PW?

Answer 13

aliasing & limited ability to measure velocity

Question 14

5 ways to eliminate aliasing?

Answer 14

1. lower baseline
2. increase scale/PRF
3. lower frequency
4. shrink sample gate/sample volume
5. use CW

Question 15

aliasing occurs when the ___ is exceeded?

Answer 15

nyquist limit

Question 16

what is the nyquist limit?

Answer 16

1/2PRF

Question 17

what 3 things about flow does spectral analysis provide?

Answer 17

1. direction
2. flow type/pattern
3. velocity

Question 18

another name for spectral broadening?

Answer 18

spectral or sonic window filling

Question 19

laminar flow characteristics in regards to: velocity range & sonic window

Answer 19

narrow range of velocities
empty sonic window

Question 20

turbulent flow characteristics in regards to: velocity range, sonic window, envelope

Answer 20

broad range of velocities
spectral broadening
irregular envelope

Question 21

4 reasons for false window filling

Answer 21

1. doppler gain is too high
2. gate is too large
3. gate is too close to vessel wall
4. incorrect doppler angle

Question 22

4 other names for pulses per scan line?

Answer 22

1. packet size
2. ensemble length
3. color sensitivity
4. color quality

Question 23

what is packet size?

Answer 23

the number of pulses sent per line of color

Question 24

what is the normal amount of scan lines?

Answer 24

8-30

Question 25

increased line density leads to ___ color resolution and ___ frame rate

Answer 25

increased color resolution decreased frame rate

Question 26

what type of flow does green represent in variance maps?

Answer 26

disturbed or turbulent flow

Question 27

what is typically imaged when using a variance map?

Answer 27

cardiac imaging

Question 28

4 other names for color power doppler?

Answer 28

1. power doppler 2. color doppler energy 3. U/S angio 4. color power angio

Question 29

what is power doppler based on?

Answer 29

amplitude of RBC motion

Question 30

the power of power doppler shift relates to ___ of RBCs

Answer 30

concentration

Question 31

power doppler info is based on velocity of RBC. T/F?

Answer 31

false -- it's based on strength of RBCs

Question 32

4 advantages of power doppler

Answer 32

1. not angle dependent 2. no aliasing 3. increased sensitivity to flow 4. improved noise filtering