Chapter 18: Carotid Duplex Flashcards
over estimating of the disease process (thinking theres a stenosis) can be from
cardiac output (faster flow on young people)
tortuous vessel
compensatory flow
inappropriate doppler angle
under estimation of the disease process
jet of accelerated flow missed
long smooth plaque formation
stenosis are area of dilation (carotid bulb)
inappropriate doppler angle
patient positioning
supine
neck slightly hyperextended
head turned slightly
what is used to Carotid imaging
spectral analysis
continous wave doppler
pulsed doppler
continous wave doppler
two piezo-electric crystals (one constantly sending and one receiving)
no range resolution
fixed sample size
pulsed doppler
crystals send then receive
high range resolution
variable sample size
well defined spectrum
color doppler
color displays average frequencies and direction
pulsed doppler eval multiple sample sites
slower scan rates
hypoechoic and homogeneous level echoes
low level echoes of similar appearance
fatty streaks
found in person of all ages
homogenous echoes
low to medium level echoes of similar appearance
fibrous plaque
echoic and heterogenous echoes
all levels of echoes
complex plaque of intraplaque hemorrhage
hyperechoic echoes
bright reflective echoes
shadowing from calcium deposits
suface characteristics
smooth
slightly irregular
grossly irregular
a stenosis should be visible from
at least two projections
occluded artery
varying echogenicity but vessel completely filled
vessel motion: horizontally or piston like
ICA doppler signals
high pitched and continous compared to ECA
waveform has rapid upstroke and down stroke with high diastolic component
ECA doppler signals
pulsatile, similar to peripheral vessels
rapid upstroke and down stroke with low flow in disatole
temporal tap technique
tapping STA you will see vibration in ECA waveforms
CCA doppler signals
similar to both ICA and ECA
Stenosis doppler signal
high pitched sound and waveform with higher velocity spectral broadening (representing turbulence) loss of spectral window (represents loss of laminar flow)
distal to stenosis doppler
distrubed flow patterns
turbulent, bidirectional, dampened and monophasic
when high resistant flow patterns in ICA, consider
disease at carotid siphon ( S shaped part of ICA)
diminished CCA velocities bilaterally may indicate
poor cardiac output or stroke volume
diminished velocities unilaterally suggest
proximal disease of innominate or CCA
Normal PSV
<125 cm/sec
Less than 50% stenosis
PSV <125cm/sec
50-79% stenosis
PSV >125cm/sec
EDV <140 cm/sec
80-99% stenosis
PSV >125cm/sec
EDV >140cm/sec
NASCET criteria > / = 70% stenosis
ICA/CCA ratio >/= 4.0
highest ICA divided by Mid CCA
Occlusion signals
CCA may have low or absent diastolic component
collaterals (ECA high diastolic flow)
Absent ICA signal or pre-occlusive thump
absent signal may indicate occlusion but what can never be ruled out
a very significant stenosis
alaising is
misrepresenttation of high doppler signal due to limitations of equipment being used
PRF is too low
maximum frequency is
1/2 PRF
nyquist limit
flow greater than 1/2 PRF cannot be displayed
waveform has a flat crew cut appearance
methods of increasing the PRF/Nyquist limit
decrease baseline increase doppler scale change transducer frequency change angle of insonation decrease depth use CW doppler
mirror imaging (crosstalk)
doppler shifts above and below baseline
display duplicate spectrum
artifact from strong reflectors or too much gain
Helical flow occurs when
flow moves into a wider portion of the vessel (bulb) doppler shifts above and below baseline spectral waveforms different doppler angle constantly changing flow is not laminar spectral broadening is present
Intraoperative monitoring is used to
identify defects secondary to surgery and/or areas of platelet aggregation
eval wall irregulatirty
intraoperative monitoring technique
12MHz sterile sleeve containing gel wound filled with sterile saline areas of flow disturbance identified gray scale imaging for wall defects
