Colour Doppler

Question 1

what information do doppler instruments provide on blood flow? (4)

Answer 1

presence
speed
character
direction

Question 2

what are the three types of doppler displays

Answer 2

colour
spectral
audible

Question 3

what does colour doppler do/incorporate?

Answer 3

pulsed echo imaging + doppler shifted

Question 4

what does the colour doppler display on the screen

Answer 4

parallelogram because of steering (to get closer to zero)

Question 5

one pulse per scan line is colour doppler true or false

Answer 5

false. multiple pulses sent out (3-32***) per scan line in doppler colour. one pulse per scan line is in B-mode

Question 6

autocorrelation

Answer 6

determines mean and variance of the doppler shift signal, done in the signal processor

Question 7

ensemble length

Answer 7

number of pulses per scan line

Question 8

What is the ensemble length for colour doppler

Answer 8

3-32

Question 9

what happens when you increase ensemble length?

Answer 9

frame rate decreases

Question 10

what is the process that detects doppler shifts in colour doppler instruments

Answer 10

autocorrelation

Question 11

ensemble length needs to be higher for these conditions (3)

Answer 11

sensitivity
accuracy of speed calculation

this decreases temporal resolution however!

Question 12

4 parameters of the signal processor

Answer 12

direction*
velocity*
variance*
power/strength

*colour map helps to interpret

Question 13

what does power depend on

Answer 13

concentration of RBC
impedence (higher z mismatch, more reflection)
reflectors (specular vs scattering)

Question 14

changing the colour map does what

Answer 14

decreases temporal resolution

Question 15

colour map helps to interpret (3)

Answer 15

direction
velocity
variance

Question 16

invert

Answer 16

flips the colour map - top is positive shift

say if you want arteries to be red but direction is away

Question 17

baseline

Answer 17

can move BL up or down if you want more of one direction of flow

Question 18

PRF is proportionate to the

Answer 18

scale/velocity range

Question 19

what happens if your scale is set too high

Answer 19

slower flows go undetected

Question 20

aliasing happens when

Answer 20

PRF is set too low

Question 21

what is aliasing and what does it depend on

Answer 21

shows wrap around colour, depends on the nyquist limit which is 1/2 PRF

Question 22

if PRF = 16 KHz a doppler shift of anything over what would alias? how do you get rid of this artifact?

Answer 22

Anything over 8 KHz (nyquist limit 1/2 PRF) would alias

Increase PRF

Question 23

What happens once the instrument processes the doppler data?

Answer 23

it goes to the display

Question 24

what are the colour display parameters (3)

Answer 24

hue
saturation
luminance

Question 25

what colour is shown is what type of display parameter

Answer 25

hue

Question 26

brightness is what type of display parameter

Answer 26

luminance

Question 27

what is saturation

Answer 27

amount of a colour

Question 28

wall filter

Answer 28

gets rid of clutter, eliminates lower frequency doppler shift caused by tissue motion

Question 29

what happens if you increase PRF too much to get rid of aliasing?

Answer 29

echo misplacement

Question 30

true or false - you can use aliasing to your advantage in stenosis

Answer 30

true - highlights areas of highest velocity

Question 31

priority

Answer 31

greyscale vs colour threshold - echoes below cut off amplitude will show as colour. Stronger echoes will be grey scale

Question 32

in priority, echoes below cut-off amplitude will show as what? and echoes above cut-off amplitue will show as

Answer 32

below cut off amplitude = colour

above cut off amplitude = greyscale

Question 33

Limitations to colour doppler (5)

Answer 33

1. sonographer skill
2. body type
3. aliasing
4. Angle dependence
5. Tortuous vessels may look like flow reversal or aliasing

Question 34

power doppler displays

Answer 34

related to amplitude / concentration of RBC

Question 35

what is the only thing power doppler displays do?

Answer 35

only shows presence of flow

Question 36

advantages of power doppler (4)

Answer 36

independent of doppler shift 
independent of doppler angle
no aliasing (same as CW)
improved sensitivity (deeper penetration, smaller vessels, slower flows)

Question 37

disadvantages of power doppler

Answer 37

no directional information
no flow speed information
no flow character information