Spectral Doppler Displays Flashcards
spectral doppler aka
pulsed wave
how many scan lines in spectral doppler
firing along a single scan line (versus colour doppler which fires 3-32 pulses per scan line, 10-20)
how many cycles per pulse in doppler
5-30 cycles per pulse
pulsed wave doppler systems provide the ability to ___
select depth from which doppler info is received (CW cannot do this)
range gating
ability to select info from a specific depth along beam
what does range gating enable (2)
depth sensitivity and a small sample volume
sample volume
specific area being assessed “gate”
what is an effective sample length? sample width?
sample length = 1/2 SPL + gate length
sample width = beam width
spectral doppler detects (4) of blood flow
same as colour : presence speed character direction
spectral doppler allows for quantification of blood flow- true or false
true
what is on the x and y axis of spectral doppler
x - time
y - doppler shift or velocity
bidirectional doppler what and where
detects positive and negative shifts IN THE doppler-shift detector/ quadrature phase detector
what is fast fourier transform and WHERE
within spectrum analyzer
Determines frequency spectrum
Determines each doppler shift frequency (x) and its strength (y)
converts voltage over time to amplitude over frequency
each point of a spectral waveform shows (3)
direction (+/-)
magnitude (how fast)
amplitude (brightness)
what factors affect direction? (2)
coming away/towards transducer
direction of steering
what factors affect magnitude? (2)
speed of blood flow (e.g. within stenosis) doppler angle (larger angle, smaller cosine, smaller Doppler shift, larger calculated velocity)
Without angle correct, it is a slower calculated velocity -therefore UNDERESTIMATES velocity with a 0 angle
what factors affect amplitude? (3)
intensity of returning echo
- concentration of RBCs
- reflectors
- impedences
gate size/sample volume affects
range resolution
what is the opposite of range resolution
range ambuiguity
gain
amplification of incoming echoes voltages
invert
arteries + above BL,
veins - below BL
if you want more positive signals, do what?
move baseline down
wall filter
gets rid of clutter, cuts off slower/low frequency flows
what affects the scale?
PRF
increase PRF and what happens to the scale
increases
if you decrease PRF too much what happens
aliasing
what happens if you increase PRF too much?
shows faster flow speeds but can produce a poor signal because of wasted space
if you don’t correct the angle, will the speed be underestimated or or over estimated?
underestimated because increasing the angle:
increases the speed
decreases doppler shift
true/false - arteries are phasic and lower velocity wave form
FALSE thats veins
arteries are pulsatile and higher velocity waveform
high resistance flow seen in
external carotid artery
extremities
low resistance flow seen in
internal carotid artery, common carotid artery, blood hungry organs
factors that characterize a stenosis (4)
- decreased area increased velocity
- turbulence (if surpassed reynolds number)
- potential for aliasing
- spectral broadening
what is spectral broadening
caused by turbulent flow where theres a greater variation in the velocities, causing vertical thickening of the spectral trace
narrowing of window
spectral broadening can be produced artificially (3)
increased gain
increased sample size
beam spreading with wide aperture arrays
what waveforms suggest a proximal stenosis (2)
upstream, pre-stenosis
tardus parvus waveform
monophasic waveform
tardus parvus waveform
pre-stenosis waveform that is very slow and rounded
what may suggest a distal stenosis?
increased resistance
if the ICA waveform (recall low resistance) looks like the ECA wavefirm (recall high resistance) what can this suggest?
distal stenosis
quantitative index
acceleration time
what does quantatative index show
tardus parvus
spectral limitations (5)
- sonographer skill
- body type
- aliasing
- movement
- range gated to specific depth
how can you fix aliasing (4)
- adjust baseline
- lower operational frequency
- increase doppler angle
- increase PRF
spectral doppler is continuous wave and pulsed wave
true
what is the sample volume like in CW
LARGE overlapping sample volume (due to two transducer elements)
what is the limitation to CW
range ambiguity (poor range resolution) PW has great range resolution
benefit to CW
CW cannot alias because there’s no PRF in CW
can pickup very high max values without aliasing
what type of doppler shows perfusion?
power
what type of doppler shows quantitative?
spectral
what type of doppler shows global
doppler shift and doppler power
Without angle correct, will calculated velocity be higher or lower?
Lower
Cos0 = 1 Cos60 = 0.5
Increasing the angle puts a fraction in the denominator of the velocity equation, increasing the calculated value
