Doppler Review Flashcards
What does Doppler tell the sonographer (6)
presence of flow
direction of flow
quality of flow
velocity of RBCs
resistance/pulsatility
timing
what is doppler
change in frequency of a sound wave in a moving source
when RBCs are moving toward the transducer the received frequency will be _____ than the transmitted frequency (______/_____ shift)
higher
antegrade/positive shift
when RBCs are moving away from the transducer the received frequency will be _____ than the transmitted frequency (______/_____ shift)
less
retrograde/negative shift
doppler shift basic calculation
Δf = f(received) - f(transmitted)
doppler shift formula (not basic)
Δf = (2fo x v x cosO)/C
doppler shift formula but for velocity
v= (Δf x C)/(2fo x cosO)
if the operating f or RBC velocity increases = doppler shift ____
increases
if the angle of insonation increases = doppler shift _____
decreases
doppler shift frequencies calculated by ______ (____)
fast Fourier transform (FFT)
autocorrelation is the technique that analyzes _____ in a scan line
pulses
autocorrelation determines the ___ and ____ of the blood flow
sign
mean velocity
colour doppler uses many pulses to obtain the mean velocity = reduction in ___ = effects the ____ resolution
PRF
temporal
Venous flow 4 characteristics
spontaneous (sometimes further from the heart isn’t ex. distal fem/pop)
unidirectional (for the most part)
respirophasic
augmentable (not every vein)
what is the most under utilized control in Doppler
gain
what does gain overcome
the attenuation of small RBCs and scatter
if gain is too low =
too high=
poor visualization of spectral trace/colour fill
vs
creates artifacts
scale (PRF) AKA
velocity range
scale too low =
scale too high=
aliasing
vs
spectral trace too small, difficult to see low velocity shifts in colour
how much space is above/below baseline for venous flow
arterial?
1/4 above
3/4 below
arterial = opposite
for most studies, the colour baseline will not be adjusted. what is the exception
echo
do we angle correct for venous flow? why/why not
no as velocities are not important (they range so much)
what do we do with the box angle in venous studies
woo hoo it
gate size should be how big compared to vessel
1/3 size of the vessel
gate size too big =
too small =
spectral broadening
vs
difficult to interrogate the true middle of the vessel
what does the wall filter do
eliminates low-frequency noise
what does priority do
it can give more emphasis to the colour when overwriting the grayscale
priority high =
low=
more colour
vs
grayscale shows instead of colour
doppler noise/blooming
doppler gains too high
colour: blossoms out of the vessel or appears in an anechoic structure that has no flow
spectral: artificially increase PSV
doppler flash/clutter
appears as low level echoes in the colour flow seen in the tissue as a result of movement like the heart wall, valve, or vessel wall motion
aliasing occurs when the _____ is exceeded
nyquist limit
the Nyquist limit is what
1/2 PRF
1/2 PRF usually falls between
5-30 kHz
correcting for aliasing (5)
move baseline
increase PRF
increase doppler angle
lower operating frequency
change to continuous wave
what to corrections for aliasing can we actually do
move baseline
increase PRF
doppler mirror image (spectral and colour: caused by and looks like)
spectral: flow on both sides of baseline caused by over gain or angle too close to 90
colour: false vessel appears deep to real one due to a deeper strong specular reflector
power doppler is where what is measured
power or intensity of signal is measured rather than doppler shift
power doppler is based on
density of RBCs not speed
what is power doppler used for
assess small vessel, tissue perfusion, and slow flow
does power doppler have aliasing
no
what is less dependent on angle, doppler or power doppler
power
