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Artifacts Flashcards

1
Q

What is an artifact?

A

Anything that does not correctly display the structures or functions that are imaged

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2
Q

Artifacts can be the result or related to what? (4)

A
  1. Manufacturing equipment
  2. Defective recording device (PAC)
  3. Improper operation of equipment
  4. Acoustic properties of tissues and propagation of sound waves
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3
Q

Artifacts occur because of what assumptions made about how sound propagates in tissue? (4)

A
  1. All tissues have the same acoustic velocity (1540m/s)- density/stiffness determine velocity
  2. The sound beams travel in a straight line
  3. Echo strength indicates organ echogenicity only
  4. The distance to each reflector equals the round trip time
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4
Q

What are the groups artifacts are categorized into? (4)

A
  1. No real- not representing actual interfaces
  2. Missing
  3. Improperly located
  4. Improper brightness, shape and size
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5
Q

What are the 2 most common groups artifacts are categorized into?

A
  1. The propagation group

2. The attenuation group

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6
Q

Is axial resolution artifact hurtful or helpful?

A

Hurtful

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7
Q

How does axial resolution hurtful?

A

When objects are less then 1/2 SPL apart in the axis of the beam - demonstrated as a single echo

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8
Q

How do you correct for the AR artifact?

A

Change SPL by increasing frequency

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9
Q

Is lateral resolution artifact hurtful or helpful?

A

Hurtful

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10
Q

What is lateral resolution artifact also known as?

A

Point spreading or image broadening

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11
Q

How does lateral resolution artifact appear?

A

Reflectors smeared across the screen in areas where the bean is wide

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12
Q

How can the lateral resolution artifact be exaggerated?

A

With increased gain or TGC

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13
Q

How do you correct for the lateral resolution artifact? (3)

A

Lower overall gain or TGC
Scan in the ZNL with properly adjusted focus
Use highest frequency possible

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14
Q

Why can lateral resolution artifact be hurtful?

A

Appears brighter and can cause us to misplace calibers

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15
Q

Is slice thickness artifact helpful or hurtful?

A

Hurtful

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16
Q

What is the slice thickness artifact sometimes referred to as?

A

Volume averaging

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17
Q

What artifact can account for filling in of anechoic structure with false debris?

A

Slice thickness artifact

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18
Q

Why does the slice thickness artifact happen?

A

Due to the assumption that all returning echos come back from the centre of the beam

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19
Q

What plane does slice thickness occur in?

A

Z axis

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20
Q

How do you correct for slice thickness artifact?

A

Reposition probe so that the narrowest portion of the z-axis is at the desired location

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21
Q

Is the acoustic speckle artifact hurtful or helpful?

A

Hurtful

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22
Q

What are non-specular reflectors?

A

Parenchyma

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23
Q

How does acoustic speckle artifact occur?

A

Several off axis reflections from scatter in parenchyma

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24
Q

How does constructive and destructive interference resulting from acoustic speckle artifact make the tissue appear?

A

Creates heterogeneous brightness- making liver look speckled (light and dark spots)- almost unhealthy

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25
Q

How do you correct the acoustic speckle artifact?

A

Persistance- smooths image by averaging out the frames to help homogenize the tissue brightness

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26
Q

Do acoustic speckle artifacts appear in the same spot twice?

A

No

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27
Q

Is the reverberation artifact hurtful or helpful?

A

Hurtful

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28
Q

What is reverberation?

A

The reflection of sound b/w the transducer and a strong interference

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29
Q

Where is the revelation artifact often seen?

A

Near probe surface or near fluid filled structures

Baby skull

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30
Q

What will reverberation artifact appear as?

A

Multiple equally spaced linear lines that get weaker with depth and look like rungs of a ladder

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31
Q

How do you correct for the reverberation artifact? (2)

A

Changing your window

Using harmonics

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32
Q

What is another type of reverberation?

A

Comet tail artifact

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33
Q

Is comet tail artifact hurtful or harmful?

A

Both

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34
Q

Describe comet tail artifact

A

Specifically a short range reverberation b/w 2 very closely spaced specular reflectors

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35
Q

What type of structures or materials can cause comet tail artifact?

A

Metal clips, metal pellets, biopsy needle, metal IUCD, thin layers of calcium, cholesterol crystals

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36
Q

How can the comet tail artifact be helpful?

A

To diagnose

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37
Q

Where is a comet tail the comet artifact commonly seen?

A

Gallbladder wall- calcium in walls

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38
Q

How do you fix for comet tail artifact?

A

Move windows

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39
Q

What is the third type of reverberation?

A

Ring down reverberation

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40
Q

How does the ring down artifact appear?

A

Similar to comet tail without the discrete echo and instead appears as a continuous stream of long echos

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41
Q

How long does the comet tail artifact last?

A

mm

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42
Q

What causes ring down reverberation?

A

Resonance phenomena associated with gas bubbles in which as vibrates and becomes a new round source

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43
Q

Is ring down reverberation hurtful or helpful?

A

Helpful

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44
Q

How does US associated with bubbles and gas vibrations?

A

Sound is a propagating mechanical wave causing bubbles to move therefore making their own source of sound

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45
Q

What is a mirror image artifact?

A

Duplication of an object due to an odd angled song reflector

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46
Q

How is a mirror image artifact produced?

A

When the machine assumes the beam travels in a straight line but the beam is reflected by a specular reflector towards the object and returned to the probe along the same path

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47
Q

What is an example of a specular reflector?

A

Diaphragm

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48
Q

Can you always correct for the mirror image artifact?

A

No

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49
Q

What is a multi path artifact the result of?

A

Assumption that the beam travels in a straight line

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50
Q

How do you correct for the multi path artifact?

A

Move probe more perpendicular to the structure of interest

51
Q

What is a refractive artifact?

A

Redirection of the beam when an interface is stuck at an angle both media have different velocities

52
Q

What are the different types of refractive artifacts? (4)

A
  1. Edge shadowing
  2. Refractive duplication
  3. Refractive malposition
  4. Refractive enhancement
53
Q

Why do we se edge shadows at curved reflectors?

A

Due to the beam changing direction with non-perpendicular incidence

54
Q

How to you correct for edge shadowing?

A

Change window to come at interface from a different angle

Apply compound CT

55
Q

What is another name for compound CT?

56
Q

How does compound CT reduce edge shadow?

A

Using multiple scan lines at different angles and takes all those frames and averages them together

57
Q

What can refractive duplication artifact do to the image?

A

Create a lateral duplication of the echo interface on wither side of its true location

58
Q

Is refractive duplication hurtful or helpful?

59
Q

Why does refractive duplication occur?

A

Refraction of beam across a strong interface- as the beam is swept the lines of sight are angled

60
Q

How do you correct for refractive duplication?

A

Get perpendicular to the structure of interest

Move away from the cause

61
Q

Where are some common places for refractive duplication to occur?

A

Aorta or Gestational sac

62
Q

What is refractive malposition?

A

Echo interface falsely allocated laterally from its true position- the echo is unlikely identified or hidden

63
Q

Is refractive malposition hurtful or helpful?

64
Q

What causes refractive malposition to occur?

A

Bending of the beam generating an echo falsely positioned along eh beam axis

65
Q

How do you correct for refractive malposition?

A

Get perpendicular to the structure

66
Q

What are side lobes?

A

Linear echoing bands or sheets in anechoic structures

67
Q

What causes side lobes?

A

Radial mode vibration

Echo that return from the weak side beams are placed along the axis of the main beam

68
Q

What kind of probe cause side lobes?

A

Single disc mechanical

69
Q

What corrects for side lobes? (2)

A

Insulator rings

TGC and gain manipulation

70
Q

What is responsible for grating lobes?

A

The length and width vibration of the array elements and crosstalk

71
Q

How are grating lobes corrected? (3)

A

Apodization
Sub dicing
Harmonics

72
Q

What accounts for propagation speed accounts?

A

Machines assumptions of the propagation speed

73
Q

What occurs when the propagation speed artifact is present?

A

Misallocation of reflectors proximal or distal to its actual location

74
Q

How do you correct for propagation speed artifact?

A

You can not

75
Q

Is the propagation speed artifact hurtful or helpful?

76
Q

How can the propagation speed artifact helpful?

A

Helps to characterize mass- fatty tissue within mass

77
Q

How can the propagation speed artifact harmful?

A

It can give a false location of echo

78
Q

What artifact causes echos to appear closer to the transducer then they actually are in 2D scanning?

A

Range ambiguity

79
Q

Is range ambiguity commonly encountered in doppler or 2D imaging?

80
Q

What causes range ambiguity to occur?

A

When a pulse is emitted before all echos from the previous pulse are received

PRF to high thereby exceeding its limit by the set depth

81
Q

How do you correct for range ambiguity?

A

Reduce the FR or PRF

82
Q

Why do you get a waveform trace when the SV is placed outside the vessel?

A

Since the PRF is so high the machine doesn’t know what depth is and gives a waveform

83
Q

What are the 4 attenuation artifacts?

A
  1. Shadowing
  2. Enhancement (lack of)
  3. Focal enhancement
  4. Edge shadowing
84
Q

What results in shadowing?

A

Lack of echo beneath a highly attenuating structure bc of absorption, reflection or scattering

85
Q

How do you see structures underneath the shadow?

A

Move windows

86
Q

Is shadowing hurtful or helpful?

87
Q

How can you increase shadowing to help diagnose?

A

Using a higher frequency (harmonics)- causes more attenuation and therefore shadowing
Adjusting focus to be at the source of the shadow
Reduce overall gain

88
Q

What causes compression of shadows?

A

Compound imaging

89
Q

What is enhancement seen as?

A

Posterior brightness to structures that attenuate less than surrounding structures (cyst or solid)

90
Q

What is an extremely rare occurrence when enhancement occurs?

A

Very homogeneous medium

91
Q

Is enhancement hurtful or harmful?

92
Q

Where is enhancement commonly seen?

A

By the bladder- so non attenuating- make everything bright

93
Q

What is focal enhancement?

A

False brightening to a particular area of the image at the level of the final zone

94
Q

What is focal enhancement also known as?

A

Focal banding

95
Q

Is focal enhancement hurtful or harmful?

96
Q

How do you fix focal enhancement?

97
Q

Where can focal enhancement be seen?

98
Q

What are some doppler artifact? (7)

A
  1. Aliasing
  2. Slice thickness
  3. Reverberating
  4. Mirror imaging
  5. Flash or Clutter
  6. Noise
  7. Refraction
99
Q

When does aliasing occur?

A

When RBCs exceed inquest limit

100
Q

How do you correct for aliasing?

A
  1. Increase PRF
  2. Move baseline
  3. Switch to CW
  4. Change angle of insinuation
  5. Decrease operating frequency
101
Q

How is aliasing helpful?

A

Identifying areas of higher velocity flows or turbulence to identify pathology

102
Q

Are RBCs specular or non specular reflectors?

A

Non-specular reflector

Reighlay scatter

103
Q

How is aliasing harmful?

A

Take away from actual velocities seen

104
Q

What is the beam width phenomenon? (Doppler slice thickness)

A

Multiple velocities seen within one envelope due to a large beam width

105
Q

What is doppler reverberation?

A

Similar to 2D appearance of reverberation- seen as buzzing or equidistant color lines

106
Q

What is twinkle artifact?

A

Form of doppler reverberation that helpful in aiding in diagnosing calculus

107
Q

What is the “color beard”

A

Reverberation b/w the front and back wall of the stone producing a mosaic of colour deep to the stone

108
Q

Is doppler mirror image harmful or helpful?

109
Q

What does the doppler mirror image artifact effect?

A

Color and spectral tracings

110
Q

What is doppler mirror image artifact caused by?

A

Spectral reflection:

Over gaining or having the angle of incidence to close to 90deg

111
Q

With color doppler a false vessel will appear deep or superficial to the real one?

A

Deep to the real one

112
Q

How does doppler flash or clutter appear?

A

Low level echos in color flow seen in the tissue as a result of tissue movement

113
Q

What are common motions within the body that case doppler flash or clutter?

A

Heart wall, valve or vessel wall motion

114
Q

What eliminates doppler flash or clutter artifact?

A

Filters present ina machine - artifact velocities lower then flowing blood

115
Q

What happens if the doppler flash or clutter filters are set to high in the machines?

A

Risk of eliminating real low flow information

116
Q

How does doppler noise occur?

A

Doppler gains set to high

117
Q

What occurs when doppler gains are set to high?

A

Color blossom outside vessel or appear in anechoic structures that have no flow

118
Q

What can occur in spectral when the overall gain is set to high?

A

Artificially increase the peak systolic velocities which can impact diagnosis

119
Q

What is the halo effect? What can this cause?

A

Over gaining the spectral trace

Can cause overestimation of velocity

120
Q

What are the artifacts related to malfunction of equipment? (4)

A
  1. Electronic interference
  2. Faulty software
  3. Faulty scan converter
  4. Faulty equipment
121
Q

What is electronic interference?

A

An echo pattern either of low/high intensity that can be regular/irregular (geometric/random)

122
Q

What causes electronic interference?

A

Radio frequency signals generated by other equipment that interfere with US wave

123
Q

What are some examples of faulty equipment?

A
  1. Malfunctioning crystal element(s)
  2. Cracked damping material
  3. Defective recording device
  4. Improper transducer shielding (electronic interference)

Physics (3 decks)

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