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Ultrasound Physics > Ch 21: Artifacts > Flashcards

Ch 21: Artifacts Flashcards

1
Q

Artifacts result from:

  1. violations of __
  2. __ malfunction
  3. __ of ultrasound
  4. operator __
A

assumptions
equipment
physics
error

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2
Q

Assumption #1: Sound travels in…

A

in a straight line.

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3
Q

Assumption #2: Sound travels directly…

A

to a reflector and back.

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4
Q

Assumption #3: Sound travels in soft tissue…

A

at exactly 1540 m/s.

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5
Q

Assumption #4: Reflections arise only from…

A

structures positioned in the beam’s main axis.

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6
Q

Assumption #5: The imaging plane is…

A

very thin.

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7
Q

Assumption #6: The strength of a reflection is related to…

A

the characteristics of the tissue creating the reflection.

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8
Q

These appear on the display as multiple equally spaced echoes caused by the bouncing of the sound wave between two strong reflectors positioned parallel to the u/s beam.

A

reverberation

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9
Q

Reverb violates which assumption?

A

2 (sound travels directly to the reflector and back)

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10
Q

This artifact appears in multiples, equally spaced, and are located parallel to the sound beam’s main axis, at ever-increasing depths.

A

reverberation

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11
Q

This appears as a solid hyperechoic line directed downward.

A

comet tail aka ring down

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12
Q

This artifact is created when closely spaced reverberations merge.

A

comet tail

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13
Q

Comet tail violates which assumption?

A

2 (sound travels directly to the reflector and back)

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14
Q

Two characteristics of comet tail?

A
  1. a single long hyperechoic echo

2. located parallel to the beams main axis

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15
Q

This appears as a hypoechoic or anechoic region extending downward from a highly attenuating structure.

A

shadow

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16
Q

Shadows are the same color as the…

A

image background.

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17
Q

Shadows appear when the __ in the tissue above the shadow than in the surrounding tissue.

A

attenuation is higher

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18
Q

Shadowing violates which assumption?

A

6 (reflection strength is related to the tissue creating the reflections)

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19
Q

This artifact is located beneath the structure with abnormally high attenuation and prevents visualization of true anatomy on the scan.

A

shadowing

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20
Q

T/F? Shadowing is unrelated to the speed of sound in a medium.

A

true

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21
Q

This is a special form of shadowing that appears as a hypoechoic region extending down from the edge of a curved reflector.

A

edge shadow aka shadowing by refraction

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22
Q

Edge shadowing violates which assumption?

A

6 (reflection strength is related to the tissue creating the reflections)

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23
Q

This appears as a hyperechoic region beneath tissues with abnormally low attenuation.

A

enhancement

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24
Q

Enhancement violates which assumption?

A

6 (reflection strength is related to the tissue creating the reflections)

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25
Q

This artifact is the opposite of shadowing.

A

enhancement

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26
Q

T/F? Enhancement artifact is entirely unrelated to the speed at which sound travels in a medium.

A

true

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27
Q

This is a special form of enhancement in which a side-to-side region of an image appears brighter than tissues at other depths.

A

focal enhancement aka focal banding

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28
Q

Focal enhancement violates which assumption?

A

6 (reflection strength is related to the tissue creating the reflections)

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29
Q

This is created when sound reflects off a strong reflector and is redirected toward a second structure.

A

mirror image

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30
Q

The ‘mirror image’ is located (deeper/shallower) than the real structure.

31
Q

Mirror image violates which assumption?

A

1 (sound travels in a straight line) and #2 (sound travels directly to the reflector and back)

32
Q

The mirroring structure lies __ between the artifact and the transducer.

A

on a straight line

33
Q

This is a mirror image artifact that appears on a spectral Doppler display.

34
Q

This is created when a sound wave propagates through a medium at a speed other than that of soft tissue.

A

speed error aka range error artifact

35
Q

When the medium’s speed is __ than soft tissue, the reflector appears deeper than it really is.

36
Q

When the medium’s speed is __ than soft tissue, the reflector appears shallower than it really is.

37
Q

Speed error violates which assumption?

A

3 (sound travels at 1540 m/s in soft tissue)

38
Q

Speed errors appear as a…

A

step-off, as if structures are ‘split’ or ‘cut’.

39
Q

This appears when sound energy is transmitted in a direction other than along the beam’s main axis.

A

lobe artifact

40
Q

Lobe artifacts __ lateral resolution.

41
Q

Lobe artifacts degrade __ resolution.

42
Q

Lobe artifact violates which assumption?

A

2 (sound travels directly to the reflector and back)

43
Q

The lobe artifact and the true reflector are located __ at the __.

A

side-by-side, same depth

44
Q

Lobes created by a single crystal transducer are called…

A

side lobes.

45
Q

Lobes created by array transducer are called…

A

grating lobes.

46
Q

This process reduces grating lobes by dividing each PZT element into small pieces.

47
Q

This process reduces grating lobes by exiting the element with different voltages.

A

apodization

48
Q

This is created when a sound pulse changes direction during transmission.

A

refraction

49
Q

Refraction violates which assumption?

A

1 (sound travels in a straight line)

50
Q

The refraction artifact and the true reflector are located __ at the __.

A

side-by-side, same depth

51
Q

This artifact occurs when a sound wave strikes a boundary obliquely and the media on either side of the boundary have different speeds.

A

refraction

52
Q

Slice thickness is also known as…

A

section thickness or partial volume.

53
Q

This is related to the dimension of the beam that is perpendicular to the imaging plane.

A

slice thickness

54
Q

This is determined by the thickness of the imaging plane.

A

elevational resolution

55
Q

Slice thickness artifact violates which assumption?

A

5 (the imaging plane is very thin)

56
Q

Slice thickness is reduced with…

A

1.5 D array transducers

57
Q

This occurs when a pair of side-by-side reflectors are closer than the width of the sound beam.

A

lateral resolution artifact aka point spread

58
Q

T/F? Lateral resolution artifact is least likely to occur at th focus.

59
Q

This is created when a long pulse strikes two closely spaced structures, where one is in front of the other.

A

axial resolution artifact

60
Q

Transducers that create __ minimize axial resolution artifact.

A

short pulses (high frequency, less ringing)

61
Q

This is created when sound pulses glance off a second structure on the way to or from the primary reflector.

A

multipath artifact

62
Q

This is a subtle artifact tat often cannot be explicitly identified on the image.

63
Q

Multipath violates which assumption?

A

2 (sound travels directly to the reflector and back)

64
Q

What kind of reflectors direct reflected sound away from the transducer?

A

curved or oblique reflectors

65
Q

Spatial resolution is affected by the number of…

A

horizontal scan lines per frame.

66
Q

This occurs when a reflecting structure is located deeper than the imaging depth of the image.

A

range ambiguity artifact

67
Q

Range ambiguity artifact is eliminated by increasing the…

68
Q

This appears as small amplitude echoes and results from many sources, including electrical interference, signal processing and spurious reflections.

69
Q

This is noise resulting from the constructive and destructive interference of small sound wavelets.

70
Q

This is an effective tool to reduce speckle.

A

spatial compounding

71
Q

This is the presence of false echo signals arising from locations outside of the main sound beam.

72
Q

Name three examples of clutter.

A

side lobes, grating lobes, and section thickness

73
Q

This reduces an image’s noise content.

A

harmonic imaging

Ultrasound Physics (23 decks)

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