Artifacts Flashcards
what is an artifact
anything that does not correctly display the structures of functions that are imaged
what are the 4 things artifacts can be related to
malfunctioning equipment
defective recording device
improper operation of equipment
acoustic properties of tissues and propagation of sound waves
4 assumptions about how sound propagates in tissue that can create artifacts
all tissues have same acoustic velocity (1540 m/s)
the sound beam always travels in a straight line
echo strength indicates organ echogenicity only
the distance to each reflector equals the round trip time
artifacts can be in the 4 following categories
not real
missing
improper location
improper brightness shape or size
ultimately artifacts belong to 2 groups
the propagation group
the attenuation group
axial resolution and artifacts
objects less tan 1/2 SPL in the axis of the beam are demonstrated as a single echo
lateral resoltuion has an artifact called
point spreading
point spreading
reflectors appear smeared across the screen in areas where the beam is wide
point spreading can be accenuated with increased ____ or ___
gain or TGC
how to correct for point spreading
lower overall gain or TGC and scan in the near zone with a properly adjusted focus
point spreading AKA
image broadening
point spreading is a beam ____ artifact
width
point spreading happens when an echo is ____ than the width of the beam
smaller
point spreading helpful or hurtful
hurtful especially in anechoic structures (simple cysts looks complex)
slice thickness referred to as ____
volume averaging
how to help slice thickness artifact
repositioning the probe so that the narrowest portion of the Z axis is at the desired location
slice thickness is same as lat resolution but __
in the Z axis
acosutic speckle is the result of several off axis reflections from ______ in the parenchyma
scatter reflection
cause of acoustic speckle
constructive and destructive interference occurs and creates heterogeneous brightness
what helps acoustic speckle
persistence is the controls that average out the frames to help homogenize the tissue brightness
acoustic speckle helpful/hurtful
hurtful
when do you not use persistance
echo/ob as we don’t want to average out motion
rverberation is the reflection of sound between the ____ and a _____
transducer
strong interface
reverberation is often seen _____ or ____
near the probe surface
in fluid filled structures
what will reverberation appear as
multiple equally spaces linear lines that get weaker with depth and look like rungs of a ladder
how to fix reverbation
changing window and using harmonics
reverberation is when the beam bounces back and forth between the ___ and ___ until it ___
transducer and reflector
attenuates
what is another type of reverberation artifact
Comet trail
comet trail is specifically a ____ range reverberation between _____
short
2 very closely spaces specular reflectors
ex of things that can cause comet trail
metal clips (staples)/pallets/IUCD, biopsy needle, thing layers of calcium, cholesterol crystals
is comet trail helpful or hurtful
can be helpful by helping to diagnose
is regular reverb helpful or hurtful
hurtful
3 types of reverb
regular
comet tail
ring down
comet tail
short-range reverb between 2 very close specular reflectors (ex metal clips, biopsy needle, IUCD, thing layers of calcium, cholesterol crystals)
is comet tail useful or hurtful
can be useful to help diagnose (ex. cholesterol crystals)
ring down artifact appears as
appears a continuous stream of long echoes
ring down helpful or hurtful
can be helpful for the diagnosis
what can produce ring down artifact
gas
mirror image is a result of duplication of an object due to _______
an odd angled strong reflector
what is an example of something that causes a mirror image
diaphragm
explain how mirror image occurs
beam bounces off strong reflector = different angle -> machine assumes line can only be straight and puts the mirror image along the beam line -> original real echo shows in proper space from other beams
can you correct for mirror image
not usually
is mirror image hurtful or helpful
mostly hurtful but can indicate healthy lung
T/F mirror image is more hurtful with 2D than doppler
F, more hurtful with Doppler
multipath artifacts is a result of the assumption that ___
the beam travels in a straight line (like mirror image)
multipath artifacts is when
beam takes several off-axis vectors before returning to probe resulting in the incorrect location of echoes due to assumption that beam only travels in a straight line
can you be tested on an image for multipath artifacts
no cause how do we know an echo is in the wrong location without sweeping ourselves
how to correct for multipath artifacts
get more perpendicular to the structure of interest
4 refractive artifacts
edge shadowing
refractive duplication
refractive malposition
refractive enhancement
refractive artifacts refers to the redirection of the beam when an interface is struck at an angle and both media have different ____
velocities
edge shadow
shadows seen at the edges of strong curved reflectors because the beam changes direction with non-perpendicular incidence
how to correct for edge shadowing
changing window to come at the interface from a different angle
edge shadowing hurtful or helpful
hurtful as shadow can block stuff
helpful as it can help us see isoechoic/not well defined masses
refractive duplication creates the appearance of ______ of the echo interface on _____
lateral duplication
either side of its true location
what can act as an acoustic lens to create the refractive duplication artifact
rectus abdominus
how to correct refractive duplication
get perpendicular to structure of interest and move away from the cause (change the angle)
what would son can most likely show as an example image for refractive duplication
2x aorta
what is a common refractive duplication that isnt the aorta
2x GS = think its twins
refractive malposition is where echo interference is falsely allocated _____ from its true position and in reality, the echo is ____ identified or hidden
laterally
unlikely
how to correct for refractive malposition
Get perpendicular to the structure
side lobes are seen as _____ or ____ in anechoic structures
linear echogenic bands
sheets
how to correct for side lobes in single disc probe
insulator rings with TGC/gain
side lobes hurtful or helpful
hurtful
grating lobes corrected by
apodization and sub dicing
harmonics (but we dont know why yet)
propagation speed error is due to
the machines assumption of propagation speed accounts for this artifact
propagation speed error results in
misallocation of reflectors proximal or distal to its actual location
propagation speed error commonly occurs deep to ___
fat
how to correct for propagation speed error
you cant
sound gets slower = echoes appear _____
further away
propagation speed error can be seen as the diaphragm _____ deep to ___
breaking
fat (liver cirrhosis, lipoma, etc)
T/F range ambiguity is common in 2D
false, more common in Doppler
range ambiguity occurs when a pulse is ____
emitted before all echoes from the previous pulse are received
(PRF is too high and is exceeding its limit set by depth)
how to correct for range ambiguity
reduce the frame rate or PRF
range ambiguity can look like on a vessel spectral
can get a spectral trace even when SV isn’t placed in vessel (if more than one vessel you don’t know which one you’re sampling)
4 attenuation artifacts
shadowing
enhancement
focal enhancement
edge shadowing
shadowing results in ______ due to what 3 things
lack of echoes beneath a highly attenuating structure
due to absorption reflection scattering of sound
how to fix shadowing
move to different window
in most cases we try to _____ the shadowing to help with diagnoses
increase
how to increase shadowing
higher frequency (including harmonics)
adjust focus to be at source of shadow
reduce overall gain
enhancement artifact is seen as ____due to ____
posterior brightness
structures that attenuate less than surrounding structures
an extremely rare occurrence is when a very _______ causes enhancement
homogenous medium
can enhancement help with a diagnosis
yes
focal enhancement artifact is a
false brightening to a particular area of the image at the level of the focal zone
focal enhancement AKA
focal banding
focal enhancement occurs because the _____ of sound is highest at focus
intensity
how to fix focal enhacement
TGCs
7 Doppler artifacts
aliasing
slice thickness
reverberation
mirror imaging
flash/clutter
noise
refraction
how can aliasing be helpful
identifies areas of higher velocity flows or turbulence to help diagnose
when velocities are bigger than ____, aliasing occurs
1/2 PRF
is aliasing helpful in spectral
no, can’t measure anymore
is aliasing in colour helpul
yes can tell where high velocities are
2 ways to correct fo aliasing on spectral
move baseline
increase scale (PRF)
doppler slice thickness artificat
velocities from multiple flows are seen within one flow envelope because of the beam width phenomenon
how does doppler slice thickness artifact appear on US
“bartery” artery in background of vein
or in echo, you get 2 flow profiles
doppler reverberation artifact has a similar appearance to what
reverb on 2D
what does doppler reverb look like
buzzing or equidistant colour lines
what doppler reverb is helpful in diagnosing and why
twinkle artifact
reverb artifact between the front and back walls of the stone will produce a mosaic of colour deep into the stone
doppler mirror image affects only colour doppler T/F
F it affects both spectral and colour
spectral mirror appearance and cause
doppler flow on both sides of the baseline and is caused by over-gaining or having the angle of incidence too close to 90
with colour doppler mirror what appears
a false vessel appears deep to real one
can you sample in a false vessel colour
yes but its not technically right
doppler flash/clutter
low level echoes in the colour flow seen in the tissue as a result of tissue movement like the heart wall, valve, or vessel wall motion
how to eliminate doppler flash/clutter
filters within the machine to help eliminate this motion as their velocities are usually lower than the flowing blood
what is a pitfall to wall filter
if it is too high then there is a risk of eliminating real flow info
reject
vs
wall filter
2D
vs
doppler (also specifically for wall motion)
stenosis can cause vibration of wall = ____ (artifact) = ______ (what is it called)
doppler flash/clutter
bruit
doppler noise (due to/causes in colour)
occurs when doppler gains are too high causing colour to appear outside vessel or appear in anechoic structures with no flow
doppler noise in spectral does what
over gain can artificially increase the PSV which can impact the diagnoses
doppler noise in spectral can cause _____ effect
halo
T/F cysts can appear to have flow if doppler gain too high (what artifact)
T
doppler noise
electronic interference is what
echo pattern either of high or low intensity that can be regular or irregular (geometric/random)
electronic interference due to
usually radio f signals generated by other equipment that interfere with US wave
electronic interference known as
the 60 Hz bandwidth artifact
what faulty equipment can cause artifacts (4)
malfunctioning crystal elements
cracked damping material
defective recording device
improper transducer shielding
