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MIDS 139 (Core Exam) > Ch 13 2D B-Mode Artifacts > Flashcards

Ch 13 2D B-Mode Artifacts Flashcards

1
Q

What is an artifact?

A

Incorrect representations of anatomy or function

(either not real, missing, misplaced or of incorrect brightness/shape/size)

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2
Q

List propagation (wave movement) artifacts?

A

-Comet tail
-Grating lob
-Mirror image
-Range ambiguity
-Refraction
-Ring down
-Reverberation
-Slice thickness
-Speckle
-Speed error

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3
Q

List attenuation artifacts?

A

-Enhancement
-Focal enhancement
-Shadowing
-Refraction/Edge shadowing

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4
Q

List some causes of artifacts?

A

-Interactions with the sound + tissues
-Incorrect use of gains, TGCs or the PRF/scale
-Equipment degradation (such as damaged crystals or displays)

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5
Q

List 5 assumptions of the u/s system?

A

-That sound travels in a straight line
-That echoes return to the probe after a single reflection
-That echoes originate only from objects located on the beam axis
-That the amplitude of the returning echoes is directly related to the reflecting or scattering properties of those reflectors/scatters
-That the distance to the reflecting or scattering objects is directly proportional to the round trip travel time

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6
Q

What is slice thickness artifact?

A

-Echoes that occur in the 3rd dimension of the u/s beam
-Anechoic structures (such as cysts) appear “hazy” or partially filled in

(aka sectional thickness OR partial volume artifact)

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7
Q

How can we resolve slice thickness artifacts?

A

By using harmonic imaging

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8
Q

What are slice thickness artifacts caused by?

A

By poor elevational (3D slice thickness) resolution

(greater beam thickness causes artifactual echoes to be placed in front + behind the intended plane of imaging)

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9
Q

What is speckle noise artifact?

A

-Granular appearance of images that is due to interference of echoes from the distribution of scatterers in tissue
-Echoes can combine constructively or destructively
-May obstruct detection of low contrast objects

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10
Q

What types of resolution does speckle degrade?

A

Spatial + contrast resolution

(although it gives tissues their characteristic image texture)

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11
Q

How can we decrease speckle?

A

With speckle reduction imaging, such as compound imaging (this smooths tissues)

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12
Q

What will dead/damaged elements look like on our images?

A

-Dropout (black lines throughout image)
-Can occur anywhere along the array

(are weak or dead elements)

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13
Q

What is reverberation?

A

-Sound bouncing b/w a structure + the probe OR within a structure
-Equally spaced reflections of diminishing amplitude with increased imaging depth

(looks like horizontal lines going across image + blocking out the structure of interest)

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14
Q

What is a comet tail artifact?

A

-Closely spaced reverberations
-Has a banding appearance
-Progressively decreased amplitude + width with increasing depths

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15
Q

Comet tail is m/s seen with what 3 things?

A

-Metallic objects
-Calcifications
-Surgical clips

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16
Q

What is ring down artifact?

A

-Type of reverberation
-Arises from resonant vibrations within trapped air bubbles
-Aka dirty shadowing

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17
Q

Ring down is also known as what?

A

Dirty shadowing

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18
Q

Ring down can be useful in identifying what?

A

Abnormal foci of air

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19
Q

What is a mirror image artifact?

A

-Type of reverberation
-Duplication of a structure on the opposite side of a strong specular reflector

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20
Q

Mirror image artifacts are m/c where?

A

Around the pleura, pericardium + diaphragm

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21
Q

Mirror image artifacts break which assumption that the u/s machine has?

A

That sound travels in a straight line

22
Q

What is refraction artifact?

A

-Change in direction of the sound beam from 1 medium to the next
-Displaces structures laterally from their correct locations
-Aka ghosting

(slide image shows bending of u/s beam causing the AoV to be almost duplicated laterally from true AoV)

23
Q

What 2 things cause refraction artifact?

A

-Oblique angles
-Change in propagation speed b/w 2 boundaries

24
Q

Refraction is also known as what?

A

Ghosting artifact

25
Q

Refraction artifacts break which assumption that the u/s machine has?

A

That sound travels in a straight line + that sound travels at a consistent speed

26
Q

List common inducers of refraction?

A

-Costal cartilage
-Fascial structures
-Adipose tissue
-Pleural + pericardial surfaces

27
Q

How to fix refraction artifacts?

A

Alter probe angle + position

28
Q

What are grating lobe artifacts?

A

-Additional weaker beams emitted from the probe that propagate in different directions than the main beam
-It duplicates structures laterally to the true ones

29
Q

When do grating lobe artifacts occur?

A

When the grating lobes reflects off a strong reflector (such as bone or gas)

30
Q

List 5 ways we can reduce grating/side lobe artifacts?

A

-Apodization (m/c)
-Harmonic imaging
-Reducing overall gain
-Changing scan plane
-Repositioning pt

31
Q

What are speed error artifacts?

A

-Occurs when the speed of sound in soft tissue is faster/slower than the assumed 1540 m/s
-Displaces structures axially

Slower = places echoes deeper
Faster = places echoes closer

32
Q

Speed error artifacts break which assumption that the u/s machine has?

A

That the propagation speed of sound is constant

33
Q

What is the bayonet sign?

A

-Classic example of a speed error artifact
-This is when the needle appears broken (confirms that the needle is placed within the cyst/mass)

34
Q

What is range ambiguity artifact?

A

-Occurs when all echoes are NOT received before the next pulse is sent out/emitted
-Places structures much closer to the surface than they should be

35
Q

Range ambiguity artifacts break which assumption that the u/s machine has?

A

That for each pulse all echoes are received before the next pulse is emitted

36
Q

List 3 ways to reduce range ambiguity artifacts?

A

-Reduce PRF
-Reduce # of focal zones
-Increase imaging depth

37
Q

As sound travels through tissue, _____ decreases with increasing distance?

A

Amplitude

38
Q

What is attenuation mostly due to?

A

Absorption

(but is also contributed by reflection, scattering + divergence of sound beam)

39
Q

Attenuation artifacts break which assumption that the u/s machine has?

A

That the amplitude of the returning echoes is directly related to the reflecting or scattering properties of those reflectors/scatters

40
Q

What is posterior shadowing artifact?

A

-Weakening of echoes distal to a strongly attenuating or reflecting structure (or else from the edges of a refracting structure)

-Decreases brightness behind a strongly attenuating structure

41
Q

List 4 examples where we would see posterior shadowing?

A

-Bone
-Calcified plaque
-Stones
-Stiff breast lesions

42
Q

List 3 things posterior shadowing can help us identify?

A

-Common bile duct + kidney stones
-Calcific plaque
-Differentiation b/w mobile shadowing gallstones + non-mobile gallbladder polyps

43
Q

List 3 ways we can alter the appearance of posterior shadowing?

A

-By changing the focus (this will minimize slice thickness artifacts + maximize shadowing)

-By using spatial compounding (this will decrease + change shape of shadowing)

-By using higher operating frequencies + harmonic imaging (this will increase shadowing)

44
Q

What is refractive/edge shadowing artifact?

A

-Refractive artifact that occurs at the EDGE of a large curved boundary, with a different speed of sound than the other surrounding tissues

-Appears as hypoechoic parallel lines, distal to the edges of the structure

45
Q

Give 2 clinical examples of edge shadowing?

A

-Fetal skull
-Round cysts

(looks like 2 hypoechoic lines on either side of the structure)

46
Q

List 2 main factors that cause edge shadowing?

A

-Oblique angles
-Change in propagation speed b/w 2 boundaries

(exact same factors as refraction artifacts)

47
Q

What is posterior enhancement artifact?

A

-Occurs through fluid filled regions
-It is the strengthening of echoes distal to a weakly attenuating structure
-Increases brightness behind a weakly attenuating structure

(ex. a cyst will have this artifact)

48
Q

List 3 common examples where we would see posterior enhancement?

A

-Cystic structures
-Bladder
-Blood pool

49
Q

What is posterior enhancement helpful in distinguishing?

A

Cystic from solid structures

50
Q

What is focal enhancement?

A

-Aka focal banding
-It is brightening of echoes caused by increased intensity in the focal region (at + before the focus)

51
Q

What 2 things can alter the appearance of posterior enhancement?

A

-Spatial compounding (alters brightness + shape of enhancement)

-Harmonic imaging (will increase enhancement)

MIDS 139 (Core Exam) (16 decks)

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