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Ultrasound Physics > Artifacts > Flashcards

Artifacts Flashcards

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1
Q

error in imaging

A

artifact

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2
Q

artifacts include reflections that are described as…

A

not real, not seen on image, incorrect shape/size/position/brightness

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3
Q

causes of artifacts

A

violation of assumption
equipment malfunction / poor design
the physics of ultrasound
operator error

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4
Q

portions of an image that are brighter than surrounding tissues, or tissues that appear brighter than normal

A

hyperechoic

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5
Q

portions of an image that are not as bright as surrounding tissues, or tissues that appear less bright than normal

A

hypoechoic

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6
Q

extreme form of hypoechoic, meaning entirely without echoes

black

A

anechoic

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7
Q

structures with equal echo brightness

A

isoechoic

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8
Q

a portion of tissue or an image that has similar echo characteristics throughout

A

hoomgenous

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9
Q

a portion of tissue or an image that has differing echo characteristics throughout

A

heterogeneous

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10
Q

6 assumptions used in imaging systems

A
  1. sound travels in a straight line
  2. sound travels directly to a reflector and back
  3. sound travels in soft tissue at exactly 1540 m/s
  4. reflections only arise from structures positioned in the beams main axis
  5. the imaging plane is very thin
  6. the strength of a reflection is related to the characteristics of the tissue creating the reflection
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11
Q

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 US beam

A

reverberation

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12
Q

characteristics of reverberation

A

appear in multiples
appear equally spaced
are located parallel to the sound beams main axis
are located at ever increasing depths

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13
Q

with reverberation, do shallow or deep echoes correspond to true anatomic structures

A

shallow - real

deep - artifact

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14
Q

reverberation with the spaces squeezed out
appears as a solid hyper echoic line directed downward
also known as ring down artifact

A

comet tail

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15
Q

how is comet tail artifact created

A

when closely spaced reverberations merge

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16
Q

do comet tails appear when reflecting surfaces are located in an area of high/low propagation speed

A

high speed (such as a mechanical heart valve)

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17
Q

comet tail can also arise from…

A

resonance of small gas bubbles

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18
Q

characteristics of a comet tail

A

appears as a single long hyper echoic echo (bright white line)
located parallel to the sound beams main axis

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19
Q

this type of artifact appears as hypo echoic or anechoic region extending downward from a highly attenuating structure
(they are the same color as the image background)

A

shadows

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20
Q

what causes shadowing

A

when too much attenuation occurs, deep reflectors do not appear on the image
(attenuation is higher in the tissue above the shadow than in the surrounding tissue)

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21
Q

characteristics of shadowing

A

hypo or anechoic
result of too much attenuation
located beneath the structure with abnormally high attenuation
prevents visualization of true anatomy on the scan

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22
Q

how is shadowing related to the speed of sound in a medium

A

UNRELATED

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23
Q

type of artifact that is a special form of shadowing that appears as a hypo echoic region extending down from the edge of a curved reflector

A

edge shadow

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24
Q

what happens during edge shadow artifact

A

the sound beam refracts (transmits with a bend) at the edge of a curved reflector, the beam diverges and results in a drop in intensity that causes edge shadowing

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25
Q

edge shadow is also called

A

shadowing by refraction

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26
Q

characteristics of edge shadow

A

hypo or anechoic
results when the beam spreads after striking a curved reflector
extends downward from the curved reflectors edge, parallel to the beam
prevents visualization of true anatomy on the scan

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27
Q

artifact that appears as a hyper echoic region beneath tissues with abnormally low attenuation

A

enhancement

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28
Q

enhancement artifact is the opposite of…

A

shadowing

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29
Q

how is enhancement artifact related to speed of sound

A

UNRELATED

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30
Q

characteristics of enhancement

A

hyper echoic
result of too little attenuation
located beneath a structure with abnormally low attenuation

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31
Q

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

32
Q

focal enhancement is also called

A

focal banding

33
Q

has the same appearance as an incorrect TGC setting

A

focal enhancement

34
Q

in focal enhancement, an entire horizontal region of tissue appears… hyper echoic/hypoechoic

A

hyper echoic

35
Q

characteristics of focal enhancement

A

hyper echoic side-to-side region

results from increased intensity at the focus

36
Q

this artifact is created when sound reflects off a strong reflector and is redirected toward a second structure
the redirection causes a replica of the structure to appear on the image

A

mirror image

37
Q

is mirror image artifact located more superficially or deeper than the real sttructure

A

deeper

38
Q

characteristics of mirror image

A

a second copy of a true reflector
appears deeper than the true reflector
the bright reflector/mirror lies on a straight line between the artifact and the transducer
true reflector and artifact are equal distances from the mirror

39
Q

this artifact is a mirror image artifact that appears on a spectral doppler display

A

crosstalk

40
Q

this artifact is created when a sound wave propagates through a medium at a speed other than that of soft tissue
(correct number of reflectors are displayed but at incorrect depths)

A

speed error

41
Q

propagation speed error are also called

A

range error artifact

42
Q

characteristics of speed error

A

correct number of reflectors at improper depth

appears as a step-off

43
Q

this artifact appears when sound energy is transmitted in a direction other than along the beams main axis

A

lobes

44
Q

lobe artifact degrades _____ resolution

A

lateral

45
Q

characteristics of lobe artifact

A

a second copy of the true reflector

the artifact and the true reflector are located side-by-side at the same depth

46
Q

other names for lobe artifact

A

side lobes

grating lobes

47
Q

lobes created by a single crystal transducer, such as a mechanical probe, are called

A

side lobes

48
Q

lobes created by array transducers are called

A

grating lobes

49
Q

how to reduce grating lobes

A

apodization - process of differential excitation

dividing each PZT element into small pieces (called subdicing)

50
Q

artifact that is created when a sound pulse changes direction during transmission

A

refraction

51
Q

refraction artifact degrades _____ resolution

A

lateral

52
Q

characteristics of refraction

A

second copy of reflector

copy is side-by-side or at the same depth as the true reflector

53
Q

what is slice thickness

A

the beam flares out like the bell of a trumpet, therefore reflections from structures above or below the assumed imaging plane may appear in the image

54
Q

slice thickness is also called

A

section thickness artifact

partial volume artifact

55
Q

slice thickness is related to the dimension of the beam that is parallel/perpendicular to the imaging plane

A

perpendicular

56
Q

_____ resolution is determined by slice thickness

A

elevational

57
Q

slice thickness is reduced by these transducers

A

1.5 array

58
Q

occurs when a pair of side-by-side reflectors are closer than the width of the sound beam
these reflectors are positioned perpendicular to the beam
two objects appear as one reflection on the image

A

lateral resolution artifact

59
Q

lateral resolution artifact is also called

A

point spread artifact (it can display a small reflector as a wide line)

60
Q

lateral resolution artifact is most likely to occur where the beam is wide/narrow

A

wide

61
Q

artifact that is created when a long pulse strikes two closely spaced structures and only one reflection appears on the image

A

axial resolution artifact

62
Q

transducers that create short/long pulses will minimize axial resolution artifact

A

short

63
Q

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

A

multipath

64
Q

artifact that occurs when a sound beam strikes a curved or oblique reflector and some of the reflected sound may be directed away from the transducer

A

curved and oblique reflectors

65
Q

characteristics of curved/oblique reflectors

A

absent on image
appear weak on image
appear different from other similar reflecting boundaries

66
Q

artifact with poor temporal resolution caused by low frame rates that results in less accurate positioning of moving reflectors

A

temporal resolution artifact

67
Q

image with low line density that exhibits less detail, and the spatial resolution is poor

A

spatial resolution artifact

68
Q

how does the systems display affect spatial resolution?

A

spatial resolution is affected by the number of horizontal scan lines per frame
(or pixel density for digital displays)

69
Q

occurs when a reflecting structure is located deeper than the imaging depth of the image. this reflector is placed at a shallow location on the image

A

range ambiguity artifact

70
Q

range ambiguity artifact can be eliminated by

A

increasing PRP

71
Q

appears as small amplitude echoes and results from many sources including electrical interference, signal processing, and spurious reflections
more likely to affect low level hypo echoic regions

A

noise

72
Q

appears as tissue texture, especially within the shallow parts of an ultrasound image
speckled grainy appearance that is not directly related to the actual biologic tissue

A

speckle

73
Q

why does acoustic speckle arise

A

constructive and destructive interference of small sound wavelets

74
Q

another form of noise

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

A

clutter

75
Q

reduces an images noise content

A

harmonic imaging

Ultrasound Physics (24 decks)

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