Week 9 artifacts

Question 1

Axial artifact

Answer 1

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

Question 2

Elevational artifact

Answer 2

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

Question 3

lateral artifact

Answer 3

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

Question 4

point spreading artifact

Answer 4

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

Question 5

beam width artifact

Answer 5

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

Question 6

speed error artifact

Answer 6

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

Question 7

range ambiguity artifact

Answer 7

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)

Question 8

grating lobes (side lobes) artifact

Answer 8

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

Question 9

ghosting artifact

Answer 9

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

Question 10

edge artifact

Answer 10

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

Question 11

Simple reverb artifact

Answer 11

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

Question 12

Multi reverb artifact

Answer 12

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

Question 13

ring down artifact

Answer 13

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

Question 14

comet tail artifact

Answer 14

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

Question 15

multipath artifact

Answer 15

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

Question 16

mirror image artifact

Answer 16

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)

Question 17

enhancement artifact

Answer 17

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

Question 18

shadowing artifact

Answer 18

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

Question 19

focal banding artifact

Answer 19

ATTENUATION artifact

• caused by focal zone which bc slightly higher amplitude = brighter
• to fix, adjust TGCs

Question 20

speckle artifact

Answer 20

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

Question 21

lung artifact

Answer 21

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

Question 22

spectral mirroring artifact

Answer 22

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

Question 23

artificial spectral broadening

Answer 23

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)

Question 24

wall filter saturation artifact

Answer 24

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)

Question 25

aliasing artifact

Answer 25

DOPPLER artifact - happens when velocity exceeds the Nyquist limit - seen in colour and PW

Question 26

twinkle artifact

Answer 26

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

Question 26

colour bleeding/blooming artifact

Answer 26

DOPPLER artifact - when colour gain is too high and colour bleeds over into stationary objects

Question 27

electronic interference artifact

Answer 27

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)

Question 28

blurring artifact

Answer 28

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

Question 29

blooming artifact

Answer 29

3D/4D - AMPLIFICATION artifact - similar to blurring, but specific to metal - eg. blooming of pacemaker wire (over amplification makes it look thicker)

Question 30

stitching artifact

Answer 30

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