209 quiz (wk9) Flashcards
Color Doppler superimposes Doppler shift information onto a 2D image with color. The color represents ____ of flow.
direction
color Doppler reports
average/mean velocity
color Doppler imaging is a pulsed-wave device, and is therefore bounded by the same limitations such as _____
aliasing
What are 3 components of color?
hue: the perceived color, lowest (red) yo highest (violet)
saturation: shade of the original color, “saturated” = pure hue & white = less hue i.e. red = very saturated, and pink = less saturated
brightness (luminance/intensity): from dull to brilliant
color information obtained at many points on the scan lines within the gate. what is this called?
ensemble length
or
packet size
the greater the ensemble length, the better to detect slow flow and the more accurate the mean velocity. what is the effect on frame rate?
color Doppler with large gates cause a significant decrease in the frame rate (frame rate killer!)
When ensemble length increases…
flow sensitivity _____ & frame rate _____
increases, decreases
*ensemble length = pocket size = the number of pulses per scan line
What is color persistence?
also called: smoothing
It averages frames of color information (let color linger longer to fill the color in the vessel)
*good for slow flow and poor color filling
*for echo, color persistence should be 0 due to rapid movement/flow of blood
color Doppler instruments use ______ to process signal information
auto-correlation
what are the characteristics of autocorrelation?
- faster technique than FFT but not as accurate as FFT
- not as detailed
- no information on peak velocities
what information does autocorrelation provide?
- mean velocities
- direction of flow (positive or negative shift)
- variance
what does power Doppler do?
identifies amplitude of Doppler shift (*NOT speed or direction)
power Doppler also known as:
- CDE (color Doppler energy)
- power angio
- amplitude Doppler
what are the pros of power Doppler?
- very sensitive: good to detect slow flow & small vessels
- nearly independent of beam angle
what are the cons of power Doppler?
due to its sensitivity, adversely affected by motion = flash artifact
what does affect power Doppler signal?
the density/concentration of RBCs determines the amplitude
more RBCs = increased amplitude = brighter the image
Power Doppler does not detect _____
It detects only ________
- velocity or flow direction
- presence and strength of the shift
what is FFT?
fast fourier transform
what does FFT do?
a mathematical process to display various velocities of RBCs traveling through vessels as a graph of velocities over time. spectral analysis allow us to identify the individual components that make up the returned signal, and FFT rapidly transforms a function into components we can identify
Doppler Artifacts - noise resulting from wall or organ motion - eliminated by wall filters (high pass filter) what is it?
clutter
which direction does the blood flow?
right to left
what does this image indicate?
stenosis
color Doppler aliases when Doppler shift exceeds _____ *same as spectral Doppler
1/2 PRF
*color aliasing at high PRF settings can be used to pinpoint potential areas of stenosis
what is wrong with this image?
improper color box steering
Doppler Artifacts
Mirror image occurs with spectral and color Doppler and can be caused by _______ or _______
too-high Doppler gain
angle too close to 90 degree
Doppler Artifacts
motion artifacts seen with power Doppler (CDE: color Doppler energy)
what is it?
flash artifact
the artifact was created by the fetus’s movement (image on left) & the artifact disappeared when the movement of the fetus stopped (image on right)
Doppler Artifacts
what kind of artifact is this?
color bruit
- a stenosis, AV fistula, or pseudoaneurysm can cause a “thrill” or tissue vibration due to high velocity - this tissue motion is picked up by color Doppler
- color bruit is potential valuable clue to occult pathology
- The color bruit or tissue vibration artifact is a type of color Doppler ultrasound artifact which results in color signal overflowing to the perivascular tissues most often caused by stenosis, AV fistulas, or shunts. Thus, this artifact is useful by pinpointing areas of potentially pathological blood flow.
Doppler Artifacts
color that extends beyond the vessel walls
What kind of artifact is it?
How do you correct them?
color bleeding (blooming/blossoming)
corrected by using appropriate color gain
Fix this image
- increase gain
- decrease gain
- increase scale
- decrease scale
3: increase scale
*notice: aliasing
when you see aliasing, increase the scale!
Fix this image
- change steer
- decrease gain
- increase scale
- decrease scale
1: change steer
*no Doppler shift at 90 degree angle
Fix the image
- increase gain
- decrease gain
- increase scale
- decrease scale
2: decrease gain
*notice: color bleeding outside the vessel
Fix this image
- increase PRF
- increase gain
- decrease wall filter
- change steer
3: decrease wall filter
*notice: wall filter is too high, therefore missing diastolic information
Fix this image
- increase scale
- decrease scale
- decrease wall filter
- decrease gain
1: increase scale
*notice: aliasing, PRF is to low causing aliasing, therefore increase the scale
Fix this image
- increase frequency
- decrease scale
- decrease wall filter
- decrease gain
4: decrease gain
*notice: the spectral gain is too high = risk of over measuring
Doppler Analysis
FFT vs autocorrelation
FFT: slow but accurate, used for spectral Doppler (PW & CW)
autocorrelation: fast but not as accurate, used for color Doppler
Tissue Doppler Imaging
blood flow is low amplitude, high-velocity signal, whereas wall motion is ____ amplitude and ____ velocity signal
high, low
Tissue Doppler Imaging
Instead of using a high-pass filter to filter out high-amplitude wall motion, TDI uses a _____ to filter out the _______ RBCs signals
low-pass filter
low-amplitude
*note: still limited by 90 degree limitation
Artifacts
The u/s machine makes some basic assumptions about the medium the sound traveling though. What are those assumptions?
- sound beams travel in a straight line
- reflections that are produced lie in the path of the beam
- sound travels at exactly 1540m/s
- sound travels directly to the reflector and back
- echo intensity corresponds to reflector’s scattering strength
- imaging plane is very thin
- echoes are derived from the most recent pulse
Types of Artifacts
4 types of attenuation artifacts?
- shadowing
- edge shadowing
- enhancement
- focal enhancement
Types of Artifacts
9 types of propagation artifacts?
- resolution - axial, lateral, slice thickness
- speckle
- reverberation - comet-tail, ring-down
- mirror image
- refraction
- speed error
- range ambiguity
- multipath
- lobe artifacts
Propagation Artifacts
longer u/s beam (SPL) hits two closely spaced structures (anterior-posterior) and creates one reflection
What type of artifact?
axial resolution
Propagation Artifacts
Wider u/s beam hits two closely spaced adjacent structures and creates one reflection
what type of artifact is this?
lateral resolution
Propagation Artifacts
“step-ladder” appearance
what type of artifact is this?
reverberation
- appears as multiple, equally spaced reflections on an image
- caused by sound bouncing back and forth between two strong reflectors and then returning to the TDR
- comet-tail & ring-down artifacts are the forms of reverberation artifacts
Propagation Artifacts
- form of reverberation
- closely spaced parallel echoes - appears as solid white line, unlike reverb
- caused by surgical clips, etc
What type of artifact is this?
comet tail
called “twinkle artifact” in color
Propagation Artifacts
- caused by vibration of air or very small metal objects
- looks like a comet tail
- most common cause is foci of air
- potential useful artifact because it indicates air e.g. abscess or pneumobilia
what type of artifact is this?
ring-down
Propagation Artifacts
- violates assumption that beam directly to reflector and back
- occurs when beam is reflected off one structure and bounces off additional structures before returning to the TDR
- causes primary reflector to appear deeper due to delayed time of returning echo
- causes improper brightness due to weakened reflection
What type of artifact is this?
multipath artifact
Propagation Artifacts
- sound beam bounces off of a strong reflectors, such as the diaphragm, and reflects the sound toward another reflector
- causes an image of the original reflector to be displayed at the wrong location on the display
- duplicate object always appear deeper than the original object (true reflector and reflected image are equal distance from each other)
Whet type of artifact is this?
mirror image artifact
Propagation Artifacts
- beam strikes a boundary at oblique incidence
- there is a difference in propagation speeds between the two media
- may distort location, size and shape
- caused when reflectors to appear at a different location on the display than the actual anatomic location
- reflection can be duplicated or triplicated and they are displayed side-by-side or at the same depth
What type of artifact is this?
refraction artifact/ghost image
*image above: refraction from rectus muscles cause duplication of aorta
*image below: the aorta on the right is ghost image
Propagation Artifacts
- caused by refraction
- beam hits a curved specular reflector (such as the GB) and is sent off in another direction
- the area that the beam was supposed to image is represented by a shadow
- reduced with spatial compounding
What type of artifact is this?
edge shadowing (a form of refraction artifact)
Propagation Artifacts
Speed error artifact
- violates assumption that the sound travels at speed of 1540 m/s
- if the actual propagation speed is > 1540 m/s (echoes arrive sooner), it will be displayed _____
- if the actual propagation speed is < 1540 m/s (echoes arrive later), it will be displayed _____ from the TDR
too close
too far away
what is range equation?
depth (mm) = propagation speed ( c ) x ½ x time of flight
Propagation Artifacts
- acoustic energy emitted in a different direction than the primary beam
- violates assumption that reflections occur along main beam axis
- reflectors can appear in the wrong place or multiple locations
- weaker lobes may pick up strong reflectors outside main beam axis
- duplication artifacts appears lateral to true reflector at the same depth
What type of artifact is this?
lobe artifacts
2 types of lobe artifacts and how they are created?
- side lobes - created by single crystal/element TDR (mechanical)
- grating lobes - created by array TDRs (*not common with advanced electronics due to apodization, which alters the voltages sent to individual elements
Grating lobes can be reduced by…..
- subdicing: slicing an element into small sub-elements, wired so they act together as a single element
- apodization: elements receive different voltages when excited (higher voltage in the middle, lower voltage at outermost element)
- tissue harmonics:
What type of artifact is this?
revebration/mirror image
*be careful not to mistaken this artifacts with blood clots or thrombus
Resolution & Propagation Artifacts
- assume the beam is razor thin, but it is not
- the beam may travel through adjacent solid and cystic areas, causing the cyst to appear to have internal echoes
- aka: elevation resolution
What type of artifact is this?
slice thickness/section-thickness artifact
what type of artifact is this?
slice thickness/section-thickness artifact
*note: the image below is the transverse plane of the same image above. notice that echo within the vessel is gone, which means the echoes in the image above is artifact caused by the elevation
Attenuation Artifact
- beam travels through an area of high attenuation i.e. gallstone, bone, ribcage
- acoustic energy is greatly diminished
- insufficient energy is available to return to TDR
what type of artifact is this?
shadowing
Attenuation Artifacts
- occurs when sound travels through a medium with a lower attenuation rate than the surrounding tissue
- reflectors distal to the weak attenuation appear brighter
what type of artifact is this?
enhancement
*note: solid masses may also have enhancement i.e. breast cancer
Attenuation Artifacts
- region of increased brightness due to the higher intensities in the focal zone
what type of artifact is this?
focal banding
How do you fix focal banding?
TGC
Misc. Artifacts
- tendons and sometimes muscles turn black if not 90 degree
- relates to specular reflectors within tissue
what type of attenuation is this?
anisotropy
*Anisotropy in ultrasound examination is an angle-generated artifact. It is produced in tissue that contains multiple, parallel linear sound interfaces (e.g., tendons, ligaments) that lead to the preferential reflection of the beam in one direction.
Misc. Artifacts
- low level echoes filling in cystic structures
- sue to inadequately shielded nearby electronic devices
- arc-like or vertical bands
what type of artifact is this?
electronic noise
*there’s nothing you can do about it
Propagation Artifact
- from of noise
- results from interference from small amplitude waves due to scattering
- granular appearance mostly near TDR
- no one-to-one correspondence between reflectors and mage brightness
what type of artifact is this?
speckle
what type of artifact is this?
comet tail
what type of artifact is this?
multiartifact
what type of artifact is this?
refraction/ghost image artifact
what type of artifact is this?
reverberation artifact
what type of artifact is this?
reverberation
what type of artifact is this?
mirror image
what type of artifact is this?
reverberation
*apparent pedunculated mass in the apex of the ventricle caused by reverberation artifact
*if there’s motion with reverberation artifact, the motion of the artifact will be in the same direction as the motion of the actual structure
what type of artifact is this?
clutter artifact
*in PSAX view of the PV and PA
what type of artifact is this?
ring down artifact
*caused by air in the biliary system
what type of artifact is this?
ring down artifact caused by air at the boundary of the diaphragm and lung
what type of artifact is this?
TEE image of comet tail artifact (asterisks) created by the two discs from a bileaflet St Jude mechanical prosthetic MV
what type of artifact is this?
intracrdiac echocardiography image taken during surgery to place Amplatzer septal occluder device showing reverberation (comet tail) artifact emanating from the catheter
what type of artifact is this?
prosthetic AoV with evident color Doppler twinkle artifact (comet tail) emanating from the metal of the valve
what type of artifact is this?
spurious second aortic valve root caused by grating lobe artifact
what type of artifact is this?
speed error artifact
*since the propagation velocity is faster in the tissue than in the fluid of the cyst, the needle appears as if broken
what type of artifact is this?
image showing mirror of a calcification in liver from the diaphragm
what type of artifact is this?
transverse image of normal liver demonstrating mirror artifact (arrow) of the IVC across the diaphragm
what type of artifact is this?
large mirror artifact reflected across the trachea
what type of artifact is this?
mirror artifact with lines indicating u/s path which creates the mirror of the anterior MV leaflet
what type of artifact is this?
“pseudo MR” as a result of mirror artifact; color Doppler image illustrating mirror artifact from a mechanical prosthetic MV resulting in LVOT flow presenting as “pseudo MR” flow in the LA
what type of artifact is this?
transverse image of a gallbladder with acoustic shadowing from a gallstone
what type of artifact is this?
image of the liver and right kidney with acoustic shadowing caused by the ribs
*note: how the shadow widens with depth as beams fan out in curvilinear image
what type of artifact is this?
shadowing and enhancement of the femoral artery
Doppler Waveform Classification
triphasic
Doppler Waveform Classification
biphasic
Doppler Waveform Classification
sharp monophasic
Doppler Waveform Classification
monophasic
Doppler Waveform Classification
triphasic waveform
Doppler Waveform Classification
biphasic waveform
Doppler Waveform Classification
monophasic waveform
Doppler Waveform Classification
poor monophasic waveform
Doppler Waveform Classification
biphasic waveform
Doppler Waveform Classification
monophasic
Doppler Waveform Classification
reduced biphaisc
Doppler Waveform Classification
monophasic
Doppler Waveform Classification
triphasic
