Doppler Instrumentation Flashcards
What is the change in frequency when there is motion between the source and receiver, or motion of a reflector.
the Doppler Effect
you can hear the doppler effect with a car horn http://www.wfu.edu/physics/demolabs/demos/3/3b/3B40xx.html
What creates the doppler shift in medical sonography?
What is the shift used to do?
blood
identify blood flow
determine direction
measure the velocity
What presentaiton of doppler shift is shown in each of these images?
What other form of doppler shift is there that would not be dislplayed as an image?
from top to bottom
Spectral – DS vs. time
Color Doppler – average Doppler Shift on 2D image
Power Doppler – amplitude of Doppler Shift on 2D image
Audible – Doppler shift frequency as a pitch that you can hear
What type of flow will reflect a higher frequency, + Doppler shift? Where is it in relation to the baseline? What color is it? What is it’s opposite lower frequency - doppler shift?
Flow towards the Td, above the baseline, RED
Flow away from the Td, below the baseline, BLUE
How does Laminar or “normal” blood flow work?
Parallel layers of flow at different velocities
Fastest in middle, slowest on sides
What is Doppler Shift Frequency affected by? (3)
How does laminar flow affect this?
Velocity of reflector (blood)
Transmitted frequency
Angle between source and reflector
Laminar flow causes multiple DS frequencies b/c different velocities of flow
What is Doppler shift Amplitude affected by? (3)
if RBCs are low, what is apmplitude?
Strength of the DS
Reflectors are RBC
Number of RBC moving a given speed will determine the amplitude of DS
Less RBC = lower amplitude DS
This is an eg of DS frequencies processed into a waveform.
what demonstrates frequency, time and amplitude on this waveform?
Y axis DS frequency – Converted to velocity if angle corrected
X axis is time
Amplitude of DS is displayed by waveform brightness
what happen to frequency on a waveform w/ angle correction?
it’s convered to veolocity
What
Identifies all different DS frequencies – Width of spectrum
Displays them as different DS frequencies - Vertical axis
Displays them as different amplitudes - Brightness
?
spectral analyzer
What is a zero crossing detector?
averages all Doppler shifts together into one waveform.
–If sampling artery and vein simultaneously the waveform will be a complex combination of them
What demonstrates + and – DS averaged into one waveform
zero crossing detector
What’s the difference b/t a zero crossing detector and a spectrum analzer?
zerocrossing - inexpensive. physiologic testing equip
spectrum analyzer = expensive duplex US equip
What display shows
directoin, DS frequency, time, amplitude and frequency spectrum?
spectral doppler display
What demonstrates a range of DS frequencies detected due to laminar flow as the “vertical width” of waveform?
What is another name for it?
frequency spectrum
spectral width
below it is demonsrated by the red arrows
What instrumentation is used w/ spectral doppler?
Angle/steering
Direction - Invert
Gain
Baseline
Scale (PRF) - Aliasing, Nyquist limit, HPF
what do you need to remember about angle steering?
you want to achieve more parallel angle to vessel (away from perpendicular)
which hAS A better steer?
Rt image. lt is perpendicular rt is at 45 degrees
Whats the differences b/t the waves of the lt and rt?
the lt are away from the Td and below baseline per usual
the rt are away from the Td but above the baseline b/c they have been inverted
how do you get the best gain?
Turn gain up until there is too much, then turn down just until background noise goes away
what key is used to increase the PRF?
scale key
what acquires Doppler information from a specific depth based on arrive time of the reflections.
What relationship does this have with aliasing?
PW Range Gating
artifact which occurs when the rate of pulsing (pulse repetition frequency, PRF) is not high enough to detect a large Doppler shift.
What is the nyquist limit?
what relationsihp does it have with PRF?
maximum Doppler shift which can be detected w/o aliasing.
Nyquist limit = 1/2 PRF
what can you say about this PRF?
it’s too slow – so it’s aliasing.
the bleow is correct.
what are the baseline and scale keys used for?
to display the waveform as big as possible without aliasing
What will you see if the scale (PRF) is too high?
too low?
what do you need to remember?
no flow (waveform to small) if set too high
aliasing if set too low
Must be set for the range of velocities you’re sampling but want waveform to be as big as possible w/o aliasing.
what happens when DS exceeds nyquist limit?
what can you do to fix this?
aliasing
shift baseline and increase PRF (scale)
What does a high PRF (scale) allow you to do? How?
Can you do this with color doppler?
sample high velocities which would normally cause aliasing.
The PRF is increased to a point which causes range (depth) ambiguity, therefore “ghost gates” appear.
The instrument does not know from what depth reflections are coming.
Not possible with color Doppler.
HPRF
HPRF
if you turn on spectral doppler and get nothing what can you do?
check doppler angle
turn gain up
change scale (1st look for slow flow - must increase if looking at tight stenosis w/ fast flow)
the same princlies w/ reagards to: angle, gain, PRF/scale, and filter apply to ___ as well as to spectral doppler.
What’s the differencE?
color
the image is created using DS info and displays it in 2D
what does narrowing your smaple volume size do?
improves spaial and temporal resolution
_____ will have Color Doppler displays the average DS frequency (velocity) and
No information about frequency spectrum as we get with spectral Doppler
autocorrelation
which way is the blood flowing?
lt - away from Td
rt - toward the Td
in these eg of doppler shift frequency what colors represent low to high DS and are they + or - ?
what type of flow does this demonstrate?
Red to Yellow: +, low DS to high DS
Blue to light blud: -, low DS to high DS
Yellow is higher velocity flow in the middle of the vessel. Darker red is slower flow on the edges of the vessel.
Normal laminar flow.
whats wrong w/ this steer?
too perpendicular
should be more parallel like this
what’s wrong w/ this steer?
wrong way – should be the other direction, this is more perpendicular
what direction is this flow?
Flow toward transducer b/c displayed in red. White arrow demonstrates the flow direction, coming toward green beam arrow.
what direction is this flow?
Flow away from transducer b/c displayed in blue. White arrow demonstrates the flow direction, moving away from green beam arrow.
what do you have to remember when determining what directon the flow is?
always look at map (lt side)
this map has been inverted so Towards is blue Away is red
what happens w/ tranverse angles
why can’t you measure velocity in transverse?
If exactly transverse to vessel you will get basically no flow in CDI b/c 90 degrees.
Slight angles up or down will produce + or – DS
If using power will get some flow at 90 because more sensitive
don’t know the angle
which way is the blood in the ivc and aorta flowing?
top away - ivc
bottom toward - aorta
what can turning down the gain in 2D help?
helps the color disply better
*Color will be placed in anechoic structures artifactually before placed in other areas of the image
what the dif in these images?
lt scale too high - set at ,92 m/s
rt scale well adjust .34 m/s (fills vessel walls)
whats the difference b/t these 2 images?
lt scale too low – Aliasing is displayed by color wrap around from yellow to green. Green in the middle of the vessel is the highest velocity which should be yellow but is aliasing to green
rt - Increasing the PRF (scale) eliminates the aliasing. Now the vessel is red and slightly yellow in the middle where fasted flow is located.
when you see aliasing inside the vessel walls what do you want to do with the scale?
increase it.
rt - .13 m/s, flow goes from blue to green to yellow to red. The yellow and red are aliasing.
lt - .53 m/s. Now flow is light blue in the center where it is fastest, dark blue on the edge where it is slowest.
what does this image show?
True reversal of flow Note the black separation between the red and blue, also there is no high velocity yellow or light blue.
what does power display differntly than color?
how?
what are some aka’s of power?
Displays the amplitude of the DS, not the DS frequency
Displays the power of the DS that are detected in each gate, rather than displaying Doppler shift itself. The displayed data is related to the # of RBCs moving within the sample volume. Not related to the velocity.
Powerflow Doppler
Doppler energy
Color energy
Color amplitude
Color angio
whats the main difference b/t CDI and Power Doppler?
CDI displays the frequency of the DS as a shade of color
Power Doppler displays the amplitude of the DS as a color
In power there is a higher amplitude when there are ______ RBC’s not due to the _____ of RBC’s
more, velocity
Angle is ____ in power allowing for ____ demonstration of flow. ___ does however need to be detected.
not as criitical. better. DS.
can and should be steered like color tho - the better the angle the better the power doppler display
which scale is high and which is low?
lt high, rt low
Lowering the scale make the instrument more sensitive to low velocity flow – Just like color Doppler imaging
what is Caused by
Receiver overload from high gain setting.
Doppler angle of 90 degrees.
Bifurcation of vessel.
?
Doppler Artifacts
Spectral Doppler waveform mirror image artifact.
what does the sample gate reciee at birfurcation?
what does this cause?
flow from 2 sm vessels at the save time. flow is opposite direction in the vessels
mirror image
what is this?
color mirror image (mirror image of IVC is cirles)
rt photo improved w/ change in Td angle but some mirror still there
what happens to create color mirror image?
Pleura acts as the “mirror” US bounces in the SC, take time and mirror image is displayed deeper Straight arrow is true vessel. Curved arrow is the mirror image artifact.
color mrror image w/ spectral mirror
