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Ultrasound Physics II > Chapter 21 Artifact > Flashcards

Chapter 21 Artifact Flashcards

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1
Q

artifact is

A

an error in imaging and includes reflections that are:
not real
not seen in the image
not of correct size or shape
not of correct brightness

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2
Q

causes of artifact (4)(VETO)

A

-Violation of assumptions
-Equipment malfunction or poor design
-Physics of ultrasound
-Operator error

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3
Q

Hyperechoic

A

tissues that appear brighter than normal

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4
Q

hypoechoic

A

tissues that appear less bright than normal

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5
Q

anechoic

A

an extreme form of hypoechoic meaning without echoes or echo free

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6
Q

isoechoic

A

tissue that has similar echo brightness

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7
Q

homogenous

A

tissue that has similar echo characteristics throughout

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8
Q

heterogenous

A

tissue that has differing echo characteristics throughout

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9
Q

The ultrasound relies on 6 imaging assumptions — most artifacts are explained by identifying which assumptions are violated, name the 6 assumptions-

A
  1. Sound travels in a straight line
  2. Sound travels directly to the reflector and back to the probe
  3. sound travels in soft tissue at exactly 1540 m/s
  4. Reflections arise only from structures positioned in the beam’s main axis
  5. The imaging plane is very thin
  6. The strength of reflection is related to the characteristics of tissue creating the reflection
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10
Q

when corrective measures are taken artifacts usually _______; if not, what should be considered?

A

vanish, instrument malfunction should be considered

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11
Q

Reverberation is caused by

A

the sound wave bouncing back and forth between a strong reflector and the prober or two strong reflectors positioned parallel to the beam

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12
Q

Reverberation violates the assumption that

A

sound travels directly to a reflector and back

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13
Q

reverberations resemble

A

a ladder or venetian blinds

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14
Q

in reverberation the 1st two reflections are real, but the remaining deeper reflections are

A

repeats

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15
Q

comet tail is also known as

A

ring down artifact

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16
Q

comet tail is caused by

A

reverberations so close together that they merge and spaces between them are “squeezed” out

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17
Q

comet tail artifact violates the assumption that

A

sound travels directly to reflector and back

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18
Q

comet tail appears as a

A

solid hyperechoic line directed downward

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19
Q

comet tail is likely to occur in mediums with fast propagation speeds like

A

mechanical heart valves

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20
Q

comet tail can also arise from

A

resonating small structures like gas bubbles

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21
Q

Shadow artifact is

A

hypoechoic or anechoic region extending downward from a very strong attenuating medium (reflectors like bone, stones, prosthesis)

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22
Q

shadow artifact is caused by

A

sound cannot pass through the attenuating structure therefore we have no or little reflections off deeper structures

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23
Q

shadow artifact violates the assumption that

A

the intensity of reflection is related to the tissue creating the reflection

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24
Q

shadow artifact is unrelated to speed of sound, and related to the

A

attenuating proximal structure

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25
Q

edge shadow artifact is

A

a specific form of shadowing that appears as a long hypoechoic region along the edge of a curved reflector

26
Q

edge shadow is caused by

A

soundbeam refracts at the edges, causing an inadequate forward beam intensity to reflect off of deeper structures

27
Q

edge shadowing is also called

A

shadowing by refraction

28
Q

edge shadowing violates the assumption that

A

the strength of a reflection is related to tissue characteristics

29
Q

enhancement artifact appears as

A

a hyperechoic region beneath tissues with abnormally low antuation (cystic or fluid filled structures)

30
Q

enhancement occurs when

A

the beam does not attenuate through proximal structures, making distal structures echo bright

31
Q

enhancement is the opposite of

A

shadowing

32
Q

enhancement violates assumption that

A

the strength of a reflection is related to tissue characteristics

33
Q

focal enhancement is

A

a special form of enhancement in which a side-to-side or horizontal region of an image is hyperechoic or brighter

34
Q

focal enhancement is also called

A

focal banding

35
Q

focal banding/ enhancement is most prominent at

A

the focus, because stronger intensity is experienced in a narrow beam

36
Q

focal enhancement appears like an

A

overgained TGC

37
Q

focal enhancement violates the assumption that

A

the strength of a reflection is related to tissue characteristics

38
Q

Mirror image occurs when

A

the first beam reflects off of the true reflector and is placed on the image, then the probe redirects and sends subsequent beam that reflects off of a strong reflector, hits true reflector and returns to probe – probe places reflector as if it had come from the main sound beam

39
Q

Mirror reflector images shows

A

mirror like reflector or line with real reflector on one side shallower and the false replica on other side deeper

40
Q

mirror image artifact violates the assumption that

A

sound travels in a straight line and that sound travels directly to reflector and back

41
Q

in mirror image artifact the shallower vessel is _____ and the deeper vessel is ______

A

real, artifact

42
Q

cross talk artifact results from

A

Doppler receiver gain too high or near 90 degree angle with flow at the focus

43
Q

cross talk is

A

a special form of mirror image artifact that appears on the Doppler display

44
Q

to eliminate cross talk

A

get as parallel to flow as possible

45
Q

speed error artifact occurs when

A

sound travels through a medium at a speed other than that of soft tissue
***reflector is placed at incorrect depth

46
Q

with speed error artifact, if prop speed is faster than soft tissue –

A

reflector will be displayed shallower than its true location (short GRT)

47
Q

w/speed error artifact, if prop speed is slower than soft tissue –

A

reflector will be displayed deeper than its true location (longer GRT)

48
Q

(speed error artifact)
with a continuous horizontal structure, part of the structure may appear to

A

step up or step down

49
Q

speed error is also known as

A

range error

50
Q

speed error violates the assumption that

A

sound travels at 1540 m/s

51
Q

array probes may have

A

grating lobe artifact – if not in harmonics

52
Q

mechanical probes may have

A

side lobe artifact

53
Q

very strong reflectors in a side beam can be

A

inaccurately placed in the main bean — making the reflector appear twice side by side at same depth

54
Q

with lobe artifact which resolution degrades

A

lateral

55
Q

grating lobes can be reduced through

A

apodization and subdicing

56
Q

refraction occurs when

A

a sound pulse changes direction during transmission

57
Q

refraction occurs when

A

sound hits boundary at oblique incidence and prop speeds differ on either side of boundary

58
Q

refraction causes a reflector to appear

A

twice, side by side at same depth

59
Q

refraction occurs when

A

subsequent beam refracts, sees the true reflector and returns to the probe

60
Q

refraction violates the assumption that

A

sound travels in a straight line

61
Q

2 types of refraction

A
  1. probe redirects and send subsequent beam
  2. probe places reflector as if it had come from the main beam
62
Q

Intensity equation

A

I = P/cross sectional area

Ultrasound Physics II (2 decks)

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