Artifacts Flashcards
1
Q
What is an artifact?
A
Anything that does not correctly display the structures or functions that are imaged
2
Q
Artifacts can be the result or related to what? (4)
A
- Manufacturing equipment
- Defective recording device (PAC)
- Improper operation of equipment
- Acoustic properties of tissues and propagation of sound waves
3
Q
Artifacts occur because of what assumptions made about how sound propagates in tissue? (4)
A
- All tissues have the same acoustic velocity (1540m/s)- density/stiffness determine velocity
- The sound beams travel in a straight line
- Echo strength indicates organ echogenicity only
- The distance to each reflector equals the round trip time
4
Q
What are the groups artifacts are categorized into? (4)
A
- No real- not representing actual interfaces
- Missing
- Improperly located
- Improper brightness, shape and size
5
Q
What are the 2 most common groups artifacts are categorized into?
A
- The propagation group
2. The attenuation group
6
Q
Is axial resolution artifact hurtful or helpful?
A
Hurtful
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
8
Q
How do you correct for the AR artifact?
A
Change SPL by increasing frequency
9
Q
Is lateral resolution artifact hurtful or helpful?
A
Hurtful
10
Q
What is lateral resolution artifact also known as?
A
Point spreading or image broadening
11
Q
How does lateral resolution artifact appear?
A
Reflectors smeared across the screen in areas where the bean is wide
12
Q
How can the lateral resolution artifact be exaggerated?
A
With increased gain or TGC
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
14
Q
Why can lateral resolution artifact be hurtful?
A
Appears brighter and can cause us to misplace calibers
15
Q
Is slice thickness artifact helpful or hurtful?
A
Hurtful
16
Q
What is the slice thickness artifact sometimes referred to as?
A
Volume averaging
17
Q
What artifact can account for filling in of anechoic structure with false debris?
A
Slice thickness artifact
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
19
Q
What plane does slice thickness occur in?
A
Z axis
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
21
Q
Is the acoustic speckle artifact hurtful or helpful?
A
Hurtful
22
Q
What are non-specular reflectors?
A
Parenchyma
23
Q
How does acoustic speckle artifact occur?
A
Several off axis reflections from scatter in parenchyma
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
25
How do you correct the acoustic speckle artifact?
Persistance- smooths image by averaging out the frames to help homogenize the tissue brightness
26
Do acoustic speckle artifacts appear in the same spot twice?
No
27
Is the reverberation artifact hurtful or helpful?
Hurtful
28
What is reverberation?
The reflection of sound b/w the transducer and a strong interference
29
Where is the revelation artifact often seen?
Near probe surface or near fluid filled structures
| Baby skull
30
What will reverberation artifact appear as?
Multiple equally spaced linear lines that get weaker with depth and look like rungs of a ladder
31
How do you correct for the reverberation artifact? (2)
Changing your window
| Using harmonics
32
What is another type of reverberation?
Comet tail artifact
33
Is comet tail artifact hurtful or harmful?
Both
34
Describe comet tail artifact
Specifically a short range reverberation b/w 2 very closely spaced specular reflectors
35
What type of structures or materials can cause comet tail artifact?
Metal clips, metal pellets, biopsy needle, metal IUCD, thin layers of calcium, cholesterol crystals
36
How can the comet tail artifact be helpful?
To diagnose
37
Where is a comet tail the comet artifact commonly seen?
Gallbladder wall- calcium in walls
38
How do you fix for comet tail artifact?
Move windows
39
What is the third type of reverberation?
Ring down reverberation
40
How does the ring down artifact appear?
Similar to comet tail without the discrete echo and instead appears as a continuous stream of long echos
41
How long does the comet tail artifact last?
mm
42
What causes ring down reverberation?
Resonance phenomena associated with gas bubbles in which as vibrates and becomes a new round source
43
Is ring down reverberation hurtful or helpful?
Helpful
44
How does US associated with bubbles and gas vibrations?
Sound is a propagating mechanical wave causing bubbles to move therefore making their own source of sound
45
What is a mirror image artifact?
Duplication of an object due to an odd angled song reflector
46
How is a mirror image artifact produced?
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
47
What is an example of a specular reflector?
Diaphragm
48
Can you always correct for the mirror image artifact?
No
49
What is a multi path artifact the result of?
Assumption that the beam travels in a straight line
50
How do you correct for the multi path artifact?
Move probe more perpendicular to the structure of interest
51
What is a refractive artifact?
Redirection of the beam when an interface is stuck at an angle both media have different velocities
52
What are the different types of refractive artifacts? (4)
1. Edge shadowing
2. Refractive duplication
3. Refractive malposition
4. Refractive enhancement
53
Why do we se edge shadows at curved reflectors?
Due to the beam changing direction with non-perpendicular incidence
54
How to you correct for edge shadowing?
Change window to come at interface from a different angle
| Apply compound CT
55
What is another name for compound CT?
Sono CT
56
How does compound CT reduce edge shadow?
Using multiple scan lines at different angles and takes all those frames and averages them together
57
What can refractive duplication artifact do to the image?
Create a lateral duplication of the echo interface on wither side of its true location
58
Is refractive duplication hurtful or helpful?
Hurtful
59
Why does refractive duplication occur?
Refraction of beam across a strong interface- as the beam is swept the lines of sight are angled
60
How do you correct for refractive duplication?
Get perpendicular to the structure of interest
| Move away from the cause
61
Where are some common places for refractive duplication to occur?
Aorta or Gestational sac
62
What is refractive malposition?
Echo interface falsely allocated laterally from its true position- the echo is unlikely identified or hidden
63
Is refractive malposition hurtful or helpful?
Hurtful
64
What causes refractive malposition to occur?
Bending of the beam generating an echo falsely positioned along eh beam axis
65
How do you correct for refractive malposition?
Get perpendicular to the structure
66
What are side lobes?
Linear echoing bands or sheets in anechoic structures
67
What causes side lobes?
Radial mode vibration
| Echo that return from the weak side beams are placed along the axis of the main beam
68
What kind of probe cause side lobes?
Single disc mechanical
69
What corrects for side lobes? (2)
Insulator rings
| TGC and gain manipulation
70
What is responsible for grating lobes?
The length and width vibration of the array elements and crosstalk
71
How are grating lobes corrected? (3)
Apodization
Sub dicing
Harmonics
72
What accounts for propagation speed accounts?
Machines assumptions of the propagation speed
73
What occurs when the propagation speed artifact is present?
Misallocation of reflectors proximal or distal to its actual location
74
How do you correct for propagation speed artifact?
You can not
75
Is the propagation speed artifact hurtful or helpful?
Both
76
How can the propagation speed artifact helpful?
Helps to characterize mass- fatty tissue within mass
77
How can the propagation speed artifact harmful?
It can give a false location of echo
78
What artifact causes echos to appear closer to the transducer then they actually are in 2D scanning?
Range ambiguity
79
Is range ambiguity commonly encountered in doppler or 2D imaging?
Doppler
80
What causes range ambiguity to occur?
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
How do you correct for range ambiguity?
Reduce the FR or PRF
82
Why do you get a waveform trace when the SV is placed outside the vessel?
Since the PRF is so high the machine doesn't know what depth is and gives a waveform
83
What are the 4 attenuation artifacts?
1. Shadowing
2. Enhancement (lack of)
3. Focal enhancement
4. Edge shadowing
84
What results in shadowing?
Lack of echo beneath a highly attenuating structure bc of absorption, reflection or scattering
85
How do you see structures underneath the shadow?
Move windows
86
Is shadowing hurtful or helpful?
Both
87
How can you increase shadowing to help diagnose?
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
What causes compression of shadows?
Compound imaging
89
What is enhancement seen as?
Posterior brightness to structures that attenuate less than surrounding structures (cyst or solid)
90
What is an extremely rare occurrence when enhancement occurs?
Very homogeneous medium
91
Is enhancement hurtful or harmful?
Both
92
Where is enhancement commonly seen?
By the bladder- so non attenuating- make everything bright
93
What is focal enhancement?
False brightening to a particular area of the image at the level of the final zone
94
What is focal enhancement also known as?
Focal banding
95
Is focal enhancement hurtful or harmful?
Hurtful
96
How do you fix focal enhancement?
TGC
97
Where can focal enhancement be seen?
Heart
98
What are some doppler artifact? (7)
1. Aliasing
2. Slice thickness
3. Reverberating
4. Mirror imaging
5. Flash or Clutter
6. Noise
7. Refraction
99
When does aliasing occur?
When RBCs exceed inquest limit
100
How do you correct for aliasing?
1. Increase PRF
2. Move baseline
3. Switch to CW
4. Change angle of insinuation
5. Decrease operating frequency
101
How is aliasing helpful?
Identifying areas of higher velocity flows or turbulence to identify pathology
102
Are RBCs specular or non specular reflectors?
Non-specular reflector
| Reighlay scatter
103
How is aliasing harmful?
Take away from actual velocities seen
104
What is the beam width phenomenon? (Doppler slice thickness)
Multiple velocities seen within one envelope due to a large beam width
105
What is doppler reverberation?
Similar to 2D appearance of reverberation- seen as buzzing or equidistant color lines
106
What is twinkle artifact?
Form of doppler reverberation that helpful in aiding in diagnosing calculus
107
What is the "color beard"
Reverberation b/w the front and back wall of the stone producing a mosaic of colour deep to the stone
108
Is doppler mirror image harmful or helpful?
Harmful
109
What does the doppler mirror image artifact effect?
Color and spectral tracings
110
What is doppler mirror image artifact caused by?
Spectral reflection:
| Over gaining or having the angle of incidence to close to 90deg
111
With color doppler a false vessel will appear deep or superficial to the real one?
Deep to the real one
112
How does doppler flash or clutter appear?
Low level echos in color flow seen in the tissue as a result of tissue movement
113
What are common motions within the body that case doppler flash or clutter?
Heart wall, valve or vessel wall motion
114
What eliminates doppler flash or clutter artifact?
Filters present ina machine - artifact velocities lower then flowing blood
115
What happens if the doppler flash or clutter filters are set to high in the machines?
Risk of eliminating real low flow information
116
How does doppler noise occur?
Doppler gains set to high
117
What occurs when doppler gains are set to high?
Color blossom outside vessel or appear in anechoic structures that have no flow
118
What can occur in spectral when the overall gain is set to high?
Artificially increase the peak systolic velocities which can impact diagnosis
119
What is the halo effect? What can this cause?
Over gaining the spectral trace
Can cause overestimation of velocity
120
What are the artifacts related to malfunction of equipment? (4)
1. Electronic interference
2. Faulty software
3. Faulty scan converter
4. Faulty equipment
121
What is electronic interference?
An echo pattern either of low/high intensity that can be regular/irregular (geometric/random)
122
What causes electronic interference?
Radio frequency signals generated by other equipment that interfere with US wave
123
What are some examples of faulty equipment?
1. Malfunctioning crystal element(s)
2. Cracked damping material
3. Defective recording device
4. Improper transducer shielding (electronic interference)
