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MED 107- MEDICAL PHYSICS II > 80. ULTRASOUNDS: IMAGE ARTEFACTS > Flashcards

80. ULTRASOUNDS: IMAGE ARTEFACTS Flashcards

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1
Q
  1. What are the 5 Image Artefacts?
A
  1. Mirror Image
  2. Acoustic Shadows
    (Shadowing Artefacts)
  3. Acoustic Enhancement
    (Enhancement Artefacts)
  4. Reverberation
  5. Refraction
    (Edge artefacts)
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2
Q
  1. What are Artefacts?
A
  • they are ultrasound images
  • they do not represent anatomical structures
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3
Q
  1. How are Artefacts generated?
A
  • they are generated by ultrasounds interacting with
    structures within the body
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4
Q
  1. What are Shadowing Artefacts caused by?
A

THEY ARE CAUSED BY WHEN:
- an ultrasound encounters high-density structures

ALL OF THE ULTRASOUND CAN EITHER BE:
- absorbed by the surface of the structure
- or reflected from the surface of the structure

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5
Q
  1. How will the surface of the structure appear in Shadowing Artefacts?
A
  • they will appear as Hyperechoic (white)
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6
Q
  1. What structures appear as Anechoic (black) in Shadowing Artefacts?
A
  • bone
  • anechoic

THIS IS BECAUSE:
- there is no ultrasound available deep to these
structures

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7
Q
  1. What is the black area of Shadow Artefacts known as?
A
  • it is called the Shadow
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8
Q
  1. What do we use Shadowing artefacts for?
A
  • we use them for identifying a structure
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9
Q
  1. Provide an example where we would need to use Shadowing Artefacts?
A

WE COULD USE IT WHEN ANALYSING:
- gallstones and gallbladder polyps
- they can appear as similar protrusions from the
gallbladder wall

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10
Q
  1. How do we tell apart gallstones and gallbladder polyps?
A

ONLY GALLSTONES:
- produce a shadow deep to their image
- this is because of their high density

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11
Q
  1. How are shadowing artefacts a disadvantage?
A
  • they can obstruct the view of a deeper structure
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12
Q
  1. What kind of structures absorb the ultrasound?
A
  • dense structures
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13
Q
  1. When do we have Enhancement Artefacts?
A
  • when an Ultrasound passes through a low density
    structure
  • this structure is filled with fluid
  • it passes through this structure with very little
    attenuation

EXAMPLE:
- gallbladder
- fluid filled cyst

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14
Q
  1. What happens when the Ultrasound reaches the fluid filled structures in an Enhancement Artefact?
A
  • it will reach the deep tissues that surround the fluid
    filled structure
  • it will reach them with more energy

THIS MAKES THE FLUID FILLED STRUCTURE LOOK MORE ENHANCED:
- this means that they it looks more white
- it is more echogenic than the surrounding tissues

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15
Q
  1. What do we use Enhancement artefacts for?
A
  • we use them to distinguish between a fluid filled cyst
    and a tumour

BOTH OF THESE LOOK LIKE:
- circular structures within a solid organ

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16
Q
  1. What will the Fluid Filled cyst produce?
A
  • it will produce an enhancement artefact
17
Q
  1. What will the tumour produce?
A
  • it either won’t produce an enhancement artefact
  • or it will produce much less of an enhancement
    artefact
18
Q
  1. What can an enhancement artefact introduce?
A
  • it can introduce errors
19
Q
  1. What parts of the gallbladder are enhanced when we take an Ultrasound image of it?
A
  • the posterior wall is enhanced
  • it appears thicker than it actually is
20
Q
  1. When do we have a Mirror Image Artefact?
A
  • when an ultrasound encounters a high reflective
    curved surface
  • such as the diaphragm

PART OF THE REFLECTED ULTRASOUND TRAVELS:
- through the liver
- it then returns directly to the probe

HOWEVER:
- part of the ultrasound will follow a longer indirect
trajectory when it returns to the probe

21
Q
  1. What does the Ultrasound system interpret this longer indirect trajectory as in a Mirror Artefact?
A
  • it interprets it as a deeper structure
  • this results in a mirror image of the liver
  • this appears deeper than the diaphragm
22
Q
  1. What stops the formation of a mirror image of the liver?
A
  • the presence of a Pleural Effusion
  • there will be no mirror image of the liver
  • this liver is positioned near the anterior of the
    diaphragm
23
Q
  1. What is the disadvantage of the Mirror Artefact?
A

THE MIRROR IMAGE OF THE LIVER:
- can be misinterpreted as a more solid lung

24
Q
  1. When do we have a Reverberation Artefact?
A
  • when an ultrasound encounters two closely apposed
    reflective surfaces
  • the ultrasound will reverberate between the two
    surfaces
25
Q
  1. What is an example of two closely apposed reflective surfaces?
A
  • the Parietal and the Visceral Pleura
26
Q
  1. Define “Reverberate”?
A
  • this is when a sound wave is repeated several times as
    an echo
27
Q
  1. What do Reverberation Artefacts create?
A
  • they create parallel linear artefacts
  • these are at equidistance intervals on an image
28
Q
  1. What do we call Reverberation Artefacts that occur while imaging the lung?
A
  • they are called “A lines”
29
Q
  1. What is the significance of a presence of “Alines” on an ultrasound image of the chest?
A
  • they can be used in the assessment of a Patient with
    dyspnoea
30
Q
  1. When do we have a Refraction (edge) Artefact?
A
  • when an ultrasound encounters the edge of a fluid
    filled structure
  • this structure is curved

THE ULTRASOUND WAVES:
- are deflected from their path

31
Q
  1. What do Refraction (edge) artefacts result in?
A
  • they result in Anechoic artefacts
  • these are black
  • they project from the edge of the fluid filled structure
  • they extend into the far-field

MED 107- MEDICAL PHYSICS II (108 decks)

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