Colour Doppler Flashcards
what information do doppler instruments provide on blood flow? (4)
presence
speed
character
direction
what are the three types of doppler displays
colour
spectral
audible
what does colour doppler do/incorporate?
pulsed echo imaging + doppler shifted
what does the colour doppler display on the screen
parallelogram because of steering (to get closer to zero)
one pulse per scan line is colour doppler true or false
false. multiple pulses sent out (3-32***) per scan line in doppler colour. one pulse per scan line is in B-mode
autocorrelation
determines mean and variance of the doppler shift signal, done in the signal processor
ensemble length
number of pulses per scan line
What is the ensemble length for colour doppler
3-32
what happens when you increase ensemble length?
frame rate decreases
what is the process that detects doppler shifts in colour doppler instruments
autocorrelation
ensemble length needs to be higher for these conditions (3)
sensitivity
accuracy of speed calculation
this decreases temporal resolution however!
4 parameters of the signal processor
direction*
velocity*
variance*
power/strength
*colour map helps to interpret
what does power depend on
concentration of RBC
impedence (higher z mismatch, more reflection)
reflectors (specular vs scattering)
changing the colour map does what
decreases temporal resolution
colour map helps to interpret (3)
direction
velocity
variance
invert
flips the colour map - top is positive shift
say if you want arteries to be red but direction is away
baseline
can move BL up or down if you want more of one direction of flow
PRF is proportionate to the
scale/velocity range
what happens if your scale is set too high
slower flows go undetected
aliasing happens when
PRF is set too low
what is aliasing and what does it depend on
shows wrap around colour, depends on the nyquist limit which is 1/2 PRF
if PRF = 16 KHz a doppler shift of anything over what would alias? how do you get rid of this artifact?
Anything over 8 KHz (nyquist limit 1/2 PRF) would alias
Increase PRF
What happens once the instrument processes the doppler data?
it goes to the display
what are the colour display parameters (3)
hue
saturation
luminance
what colour is shown is what type of display parameter
hue
brightness is what type of display parameter
luminance
what is saturation
amount of a colour
wall filter
gets rid of clutter, eliminates lower frequency doppler shift caused by tissue motion
what happens if you increase PRF too much to get rid of aliasing?
echo misplacement
true or false - you can use aliasing to your advantage in stenosis
true - highlights areas of highest velocity
priority
greyscale vs colour threshold - echoes below cut off amplitude will show as colour. Stronger echoes will be grey scale
in priority, echoes below cut-off amplitude will show as what? and echoes above cut-off amplitue will show as
below cut off amplitude = colour
above cut off amplitude = greyscale
Limitations to colour doppler (5)
- sonographer skill
- body type
- aliasing
- Angle dependence
- Tortuous vessels may look like flow reversal or aliasing
power doppler displays
related to amplitude / concentration of RBC
what is the only thing power doppler displays do?
only shows presence of flow
advantages of power doppler (4)
independent of doppler shift independent of doppler angle no aliasing (same as CW) improved sensitivity (deeper penetration, smaller vessels, slower flows)
disadvantages of power doppler
no directional information
no flow speed information
no flow character information
