PHY- Doppler Flashcards
define Doppler effect
change in frequency caused by the motion of a source, reflector or receiver
examples of doppler affect? (4)
- weather forecasting
- police radar
- door openers
- burgler alarms
Define dopper shift and give examples
- quantification of the change in frquency
getting closer, frequency ↑ (positive shift)
getting farther, frequency ↓ (negative shift)
Doppler 4 steps?
- Transducer sends a pulse to moving object
- transducer receives the new frequency and calculates doppler shift doppler shift
- doppler shift depends on the objects velocity
- machine calculated speed based on doppler shift
what does the doppler shift depend on?
- Objects velocity
- cosine of doppler angle
if the angle of interrogation is non-zero what will occur?
Lesser dopper shift with occur
why do we incorporate cos 0 to dopper shift?
to compensate for the lesser shift
What is doppler angle?
the angle of incident beam to the direction of blood flow
cosine 0, 30, 60, 90 degrees?
cos 0= 1
cos 30= 0.87
cos 60= 0.5
cos 90= 0
to achieve an angle close to zero the sonographer must?
- heel-toe
- phase (steer)
define doppler ultrasound characteristics (4)
presence, speed, character and direction of blood flow
what are the 3 characteristics of doppler ultrasound display?
- colour
- spectral
- audible
what information are we getiing from colour doppler (4)
- presence
- speed
- character
- direction
how is doppler shift detected?
- beam former sends digitized voltages to signal processor
- signal processor detect dopper shifted echoes using autocorrelation
what detects shifted echos and using what?
- signal processor detects doppler shifted echos using autocorrelation
define autocorrelation
mathematical technique that determines mean and variance of doppler shift signal
what 4 things does autocorrelation determine?
- mean of doppler shift signal
- variance of doppler shift signal
- power
- sign
how many pulses are sent out per scan line?
3-32
pros and cons of multiple pulses being sent out per scan line
pros: increased accuracy and sensitivity (picking out weaker echoes/shifts)
cons: decreased frame rate
what does autocorrelation calculate and display? (4)
- average velocity
- distribution of velocities
- strength of echoes
sign -/+
what is power? what is it related to?
- the intensity of an echo
- related to the amplitude
what does power depend on? (3)
- reflectors
- impedance
- concentration of RBC’s
more relection =
more reflection, more echo
higher delta z =
more echo
higher concentration of RBC’s =
more reflectors, more echo
what does power doppler use?
ONLY uses the power/strength of doppler shifts
pros of power doppler?
- increased sensitivity
- no angle dependence
- no aliasing
cons of power doppler? (4)
- no direction
- no flow sleed
- no flow character info
- cannot detect a stenosis
3 colour display parameters?
- hue
- saturation
3, luminance
what is saturation?
richness of colour
what is luminance?
brightness of colour
9 colour controls?
- box
- colour map
- colour invert
- baseline
- PRF
- gain
- wall filter
- ensemble length
- priority
baseline AKA?
zero point
to show more positive flows what should you do to the baseline?
move it down
changing PRF will change our?
scale
what does lowering the PRF do?
- allows to pick up slower flow
- increases chance of aliasing
aliasing depends on?
Nyquist limit
pros of aliasing?
can highlight the fastest speeds within a stenosis
where in the instrument does gain occur?
amplifiers of beam former
what is wall filter?
cutting off slower flows/tissue motion
ensemble length AKA?
packet size
what is ensemble length?
number of pulses used for each colour scan line
priority AKA?
threshold
what is priority?
- echos below cut-off amplitude will show colour
- stronger echoes show as grayscale
if priority iof set too low what occurs?
- noise or artifacts within the vessel are displayed with little colour
if priority of set too high what occurs?
fills the vessel with colour
- when there is a low signal-to-noise ratio
4 colour limitaitons?
- angle dependence
- low FR
- lack of spectral info
- sonographer skill
what is duplex scanning?
- doppler = gray scale imaging
- Transducer does one at a time
- simultaneous does exist but decreased FR- rapidly switches between the two
In practice, approximately _____ pulses are required to obtain one line of color Doppler information?
10
Lack of color in a vessel with blood flow may be attributable to ______ (3)
- low colour gain
- high wall filter setting
- low priority setting
Increasing ensemble length ____ color sensitivity and accuracy and ________ FR
- improves, decreases
What color control helps with clutter?
wall filter
Color map baselines are always represented by what color?
black
steering the color window to the right or left changes _____? (2)
- doppler shift
- doppler angle
In a single frame, color can be different ( red and blue) in a vessel because of ____? (4)
- Vessel curvature
- Sector format
- Helical flow
- Diastolic flow reversal
Doppler power imaging indicates the _______ of flow
presence
what info are we getting from spectral doppler? (4)
- presence
- direction
- character
- speed
Pulse generates pulses _____ cycles long
what determines doppler shift accurately?
longer pulse
spectral doppler characteristics? (3)
- pulser
- detector
- spectrum analyzer
the detector is part of what element?
signal processor
function of detector?
- echo voltages are amplified
- doppler shifts determined by comparing to pulser frequency
2 things that contribute to the detecor?
- mixer (fR+ fT) and (fR-fT)
2. filter (gets rid of sum)
function of spectrum analyzer?
generates doppler shift spectral displays using fast Fourier transform
the spectrum analyzer generates doppler shift spectral displays using?
fast fourier transform
what is fast fourier transform?
mathematical technique for spectral doppler
** remember autocorrelation is the mathematical tequnique for colour doppler
The amplitude or power of each Doppler shift is shown as?
brightness
dark spots on spectral display means that doppler shift is?
very weak or nonexistant
what is range gating?
ability to take motion information from a specific depth
gate amplifier is found in?
beam former
the gate amplifier takes samples from? (2)
- specific sample volume (gate)
2. specific depth
what is gate width?
wb
- At the sample volume depth
when to use longer gate- gate length?
when searching for a vessel or flow location
when to use a shorter gate- gate length?
for spectral analysis and evaluation
a shorter gate improves?
the quality of the spectral display
What is spectral broadening? when is it seen? what does it cause?
- vertical thickening of the spectral trace
- seen with wider range of velocities
- causes narrowing of window
reasons for spectral broadening?
- disturbed or turbulent flow
what is artificial spectral broadening?
- excessive doppler gain
- excessive sample volume length
8 spectral controls?
- gate size/ sample volume
- gain
- spectral invert
- baseline
- PRF
- wall filter
- angle correct
- audio
with gain there is potential for?
- amplifications of echos
- potential for noise and spectral broadening
increasing angle, decreases?
- doppler frequency
- velocity
- makes it seem lower than it is
audio- higher frequency =
higher pitch
what is CW doppler?
- 2 transducer elements- one to send, one to receive
- very small probe
- sample volume is large in overlapping area
beacuse sample volume is large with CW doppler what occurs?
- poor range resolution and ability to determine depth of reflectors
T or F CW doppler can alias?
- False
- no PRF in CW
If angle correction is set at 60 degrees but should be zero degrees, the display indicates a flow speed of 100 cm/s
The correct flow speed is _____ cm/s.
50
If angle correction is set at 0 degrees but should be 60 degrees, the display indicates a flow speed of 100 cm/s
The correct flow speed is _____ cm/s.
200
If a 5-kHz Doppler shift corresponds to 100 m/s, a 2.5-kHz shift corresponds to ____ m/s
50
Which of the following is increased if Doppler angle is increased?
a. Aliasing
b. Doppler shift
c. Effect of angle error
d. b and c
e. None of the above
effect of angle error
Color-Doppler frame rates are ______ gray-scale rates
less than
Decreased distal resistance normally causes end diastolic flow to ________.
increase
Flow reversal in diastole indicates ______.
high distal resistance
T or F With angle correct incorporated, higher flow speed always produces a higher Doppler shift on spectral display.
true
Higher operating frequency produces a higher Doppler shift on spectral display. T or F
true
Does higher freq transducer overestimate velocity?
no
As stenosis progresses, which of the following increases?
a. Lumen diameter
b. Systolic Doppler shift
c. Diastolic Doppler shift
d. Spectral broadening
e. more than one of the above
e. (b,c,d)
Disturbed flow produces narrower spectrum?
false
T or F- Turbulent flow produces a narrower spectrum?
false
If all the cells in a vessel were moving at the same constant speed, the spectral trace would be _____________.
a. thin horizontal line
b. thick horizontal line
c. as in descending aorta
d. tardus parvus
e. depends on velocity
thin horizontal line
stenosis effect?
Peak systolic flow speed End diastolic flow speed Spectral broadening Window Envelope
T or F: Doppler ultrasound provides information about flow conditions only at the site of measurement.
False
Doppler signal power (or amplitude) is proportional to _______.
cell concentration
Compared with Doppler-shift imaging, Doppler-power imaging is _______.
More sensitive
Angle independent
Aliasing free
Speed independent
Doppler-power imaging indicates (with color) the _____ of the flow.
presence
