Week 9 artifacts Flashcards
Axial artifact
RESOLUTION artifact
- unable to distinguish separate reflectors along the beam axis
- looks like a single structure, but it is actually 2 closely spaced objects
- to fix, try changing to transducer types to one with better res
Elevational artifact
RESOLUTION artifact
- unable to distinguish separate reflectors within the slice plane thickness
- looks like a single structure, but it is actually 2 closely spaced objects
- to fix, try changing to transducer types to one with better res
lateral artifact
RESOLUTION artifact
- unable to distinguish separate reflectors perpendicular to the beam
- looks like a single structure, but it is actually 2 closely spaced objects
- to fix, try changing to transducer types to one with better res
point spreading artifact
RESOLUTION artifact
- a small point in the far field is displayed as a line
- happens bc the beam widens in the far field and the distance btw scan lines increases
- to fix, try changing to transducer types to one with better res
beam width artifact
RESOLUTION artifact
- in general US
- occurs when beam is just wider than the object (cyst), and all echos (incl those outside the cyst) are drawn within the cyst
- hollow structures appear filled in (pseudo-sludge in gallbladder)
- to fix, try changing to transducer types to one with better res
speed error artifact
MACHINE AAUMPTION ERRORS artifact
- when c is not 1540 m/s and structures are drawn at incorrect depths
- if c>1540 = echos return sooner = structure displayed shallower than its true position
- looks like a line with a break in it, but actually the line is continuous
- try scanning from a new location
range ambiguity artifact
MACHINE AAUMPTION ERRORS artifact
- the echo from one pulse is so distant that it only returns to the probe after the next pulse is sent = machine assumes it is the echo from the second pulse and draws it shallower than it actually is.
- get “wrap around” similar to aliasing in Doppler
- to avoid, try to decr PRF or use a lower freq probe
(artifact is seen most often when high freq probes with high PRF)
grating lobes (side lobes) artifact
MACHINE AAUMPTION ERRORS artifact
- when a grating lobe hits a structure the machine assumes the echos came from the main beam and draws the structure in the wrong spot
- looks like a linear line in LA (actually came from posterior wall of the Ao)…. you know its not a pathology bc not seen in other views and colour flows over it.
- to fix, try scanning from a new window
Note:
grating lobes - from multielement transducers
side lobes - from single element transducer
ghosting artifact
REFRACTION artifact
- occurs when part of the beam refracts… the beam changes direction but the machine assumes it travelled along a straight line and echos came from its original path.
- looks like a duplicate image BESIDE the real structure
- eg. 2 AoV’s bc part of the beam hit a rib and refracted
- to fix, try scanning from a new window
edge artifact
REFRACTION artifact
- reflection and refraction of the beam at the edges of structures causes signal loss past the edges of structures.
- common near vessel walls = shadows are edge artifact, not vessels
- to fix, try scanning from a different window
Simple reverb artifact
REVERBERATION artifact
- there is a strong reflector perpendicular to the beam, so the signal bounces off the reflector then off the transducer and hit the reflector a second time
- looks like a line drawn at twice the depth of the actual structure
- Anterior wall of the Asc Ao in the correct spot plus an extra line at twice the depth
- to fix, try scanning from a diff window
Multi reverb artifact
REVERBERATION artifact
- 2 strong reflectors perpendicular to the beam. Sound waves reflect back and forth between them
- seen as a series of echogenic lines past the highly reflective structure
- eg. calcified AoV
- try scanning from a diff window
ring down artifact
REVERBERATION artifact
- sound waves get trapped and resonate inside a gas bubble that is the shape of an inverted tetrahedron (4 gas bubbles)
- looks like infinitely long vertical echogenic lines
eg. Cardiac - gunshot wound
eg. General - intestines
rem, air reflects sound vs fluid transmits sound well
comet tail artifact
REVERBERATION artifact
- sound waves get trapped and resonate within a highly reflective structure such as metal or calcium
- looks like long triangle with alternating light and dark banding below the metallic structure
- eg. mechanical valve
- try scanning from diff windows
multipath artifact
REVERBERATION artifact
- returning echo takes multiple paths back to transducer (it bounces off a structure at an angle, then hits strong reflector and bounces back to probe)
- looks like structure drawn deeper than it actually is
- try scanning from a diff window
mirror image artifact
REVERBERATION artifact
- occurs when there is a strong reflector near the structure of interest. Some sound waves hit the reflector and then the structure of interest and then bounce back to the transducer.
- looks like duplication of structure below the actual image
- try scanning from a diff window
eg. PLAX - pericardium can be strong reflector. See mirror image of MV (inverted AMVL)
enhancement artifact
ATTENUATION artifact
- occurs when small area of tissue has lower attenuation than the rest
- looks like part of the image is brighter
- in cardiac, adjust TCGs to get rid of this
- in general, can help identify a cyst from a solid structure (bc brighter posterior wall means fluid filled)
*opposite of shadowing
shadowing artifact
ATTENUATION artifact
- occurs when small area of tissue has higher attenuation than the rest
- looks like part of image is darker
- in cardiac, Ca build up on MV can make it hard to see past MV
- in general, helpful bc shadowing indicates stones (eg. gallstones - Ca)
*opposite of enhancement
focal banding artifact
ATTENUATION artifact
- caused by focal zone which bc slightly higher amplitude = brighter
- to fix, adjust TGCs
speckle artifact
ATTENUATION artifact
- caused by scattering of waves by small particles (rayleigh scatterers)
- looks like speckled image
- to fix:
1. Machine has coded excitation - digital codes in pulse helps the machine determine which pulse an echo belongs to
2. General US - averaging: - Temporal averaging - ave data from multiple frames
- Spatial compounding - scan from multiple angles and average
- Frequency compounding - ave frames produced with 2 diff frequencies
lung artifact
ATTENUATION artifact
- caused by large diff in attenuation coeff btw lung and tissue, therefore most of the beam reflects at the tissue/lung interface
- looks like grey fuzz, moving with breath
- to fix, get patient to breath in/out
spectral mirroring artifact
DOPPLER artifact
- artificial doppler signal is displayed in opposite direction of flow (flow above and below baseline)
caused by
- doppler angle close to 90
- gain too high or excessive transmit power
- superficial doppler with high freq probe
or caused by turbulent flow and NOT artifact
artificial spectral broadening
DOPPLER artifact
- widening of the spectral display
caused by
- gain too high
- large spl gate
- sampling too close to vessel wall
or caused by atherosclerosis (NOT artifact)
wall filter saturation artifact
DOPPLER artifact
- happens when strong reflectors saturate the wall filter, so machine picks up movement of tissue instead of blood
- in cardiac - valve clicks (opening and closing of a valve is seen as a spike)
aliasing artifact
DOPPLER artifact
- happens when velocity exceeds the Nyquist limit
- seen in colour and PW
twinkle artifact
DOPPLER artifact
- similar to comet tail
- seen in colour and power doppler as a vertical band of colour past a highly reflective structure such as calcium or metal
colour bleeding/blooming artifact
DOPPLER artifact
- when colour gain is too high and colour bleeds over into stationary objects
electronic interference artifact
DOPPLER artifact
- looks like lines parallel to baseline in spectral doppler
- happens in ICU when there is a lot of equipment and too much electricity in the air
- to fix, use an electrically isolated power supply (often not possible)
blurring artifact
3D/4D - AMPLIFICATION artifact
- caused by resolution artifacts in the elevational plane, which results in overamplification or thickening of structures
- looks like blurring of the edges of structures
- can’t fix bc in 4D, can only adjust axial and lat res, not elevational
*similar to beam width artifact in 2D
blooming artifact
3D/4D - AMPLIFICATION artifact
- similar to blurring, but specific to metal
- eg. blooming of pacemaker wire (over amplification makes it look thicker)
stitching artifact
3D/4D artifact
- happens when there is movement btw beats on a multi-beat acquisition = the beats won’t line up when the machine averages them
- looks like lines in image bc it didn’t stitch together well
Note: also happens if A-fib bc timing of beats doesn’t line up
