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Artifacts Flashcards

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
edge shadow is also called
shadowing by refraction
26
characteristics of edge shadow
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
27
artifact that appears as a hyper echoic region beneath tissues with abnormally low attenuation
enhancement
28
enhancement artifact is the opposite of...
shadowing
29
how is enhancement artifact related to speed of sound
UNRELATED
30
characteristics of enhancement
hyper echoic result of too little attenuation located beneath a structure with abnormally low attenuation
31
a special form of enhancement in which a side-to-side region of an image appears brighter than tissues at other depths
focal enhancement
32
focal enhancement is also called
focal banding
33
has the same appearance as an incorrect TGC setting
focal enhancement
34
in focal enhancement, an entire horizontal region of tissue appears... hyper echoic/hypoechoic
hyper echoic
35
characteristics of focal enhancement
hyper echoic side-to-side region | results from increased intensity at the focus
36
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
mirror image
37
is mirror image artifact located more superficially or deeper than the real sttructure
deeper
38
characteristics of mirror image
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
this artifact is a mirror image artifact that appears on a spectral doppler display
crosstalk
40
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)
speed error
41
propagation speed error are also called
range error artifact
42
characteristics of speed error
correct number of reflectors at improper depth | appears as a step-off
43
this artifact appears when sound energy is transmitted in a direction other than along the beams main axis
lobes
44
lobe artifact degrades _____ resolution
lateral
45
characteristics of lobe artifact
a second copy of the true reflector | the artifact and the true reflector are located side-by-side at the same depth
46
other names for lobe artifact
side lobes | grating lobes
47
lobes created by a single crystal transducer, such as a mechanical probe, are called
side lobes
48
lobes created by array transducers are called
grating lobes
49
how to reduce grating lobes
apodization - process of differential excitation | dividing each PZT element into small pieces (called subdicing)
50
artifact that is created when a sound pulse changes direction during transmission
refraction
51
refraction artifact degrades _____ resolution
lateral
52
characteristics of refraction
second copy of reflector | copy is side-by-side or at the same depth as the true reflector
53
what is slice thickness
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
slice thickness is also called
section thickness artifact | partial volume artifact
55
slice thickness is related to the dimension of the beam that is parallel/perpendicular to the imaging plane
perpendicular
56
_____ resolution is determined by slice thickness
elevational
57
slice thickness is reduced by these transducers
1.5 array
58
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
lateral resolution artifact
59
lateral resolution artifact is also called
point spread artifact (it can display a small reflector as a wide line)
60
lateral resolution artifact is most likely to occur where the beam is wide/narrow
wide
61
artifact that is created when a long pulse strikes two closely spaced structures and only one reflection appears on the image
axial resolution artifact
62
transducers that create short/long pulses will minimize axial resolution artifact
short
63
artifact that is created when sound pulses glance off a second structure on the way to or from the primary reflector
multipath
64
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
curved and oblique reflectors
65
characteristics of curved/oblique reflectors
absent on image appear weak on image appear different from other similar reflecting boundaries
66
artifact with poor temporal resolution caused by low frame rates that results in less accurate positioning of moving reflectors
temporal resolution artifact
67
image with low line density that exhibits less detail, and the spatial resolution is poor
spatial resolution artifact
68
how does the systems display affect spatial resolution?
spatial resolution is affected by the number of horizontal scan lines per frame (or pixel density for digital displays)
69
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
range ambiguity artifact
70
range ambiguity artifact can be eliminated by
increasing PRP
71
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
noise
72
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
speckle
73
why does acoustic speckle arise
constructive and destructive interference of small sound wavelets
74
another form of noise | the presence of false echo signals arising from locations outside of the main sound beam
clutter
75
reduces an images noise content
harmonic imaging

Ultrasound Physics (24 decks)

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