Chapter 21 Artifact Flashcards by Anna Waskowski

artifact is

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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causes of artifact (4)(VETO)

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

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Hyperechoic

tissues that appear brighter than normal

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hypoechoic

tissues that appear less bright than normal

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anechoic

an extreme form of hypoechoic meaning without echoes or echo free

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isoechoic

tissue that has similar echo brightness

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homogenous

tissue that has similar echo characteristics throughout

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heterogenous

tissue that has differing echo characteristics throughout

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

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

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

vanish, instrument malfunction should be considered

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Reverberation is caused by

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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Reverberation violates the assumption that

sound travels directly to a reflector and back

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reverberations resemble

a ladder or venetian blinds

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

repeats

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comet tail is also known as

ring down artifact

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comet tail is caused by

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

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comet tail artifact violates the assumption that

sound travels directly to reflector and back

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comet tail appears as a

solid hyperechoic line directed downward

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

mechanical heart valves

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comet tail can also arise from

resonating small structures like gas bubbles

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Shadow artifact is

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

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shadow artifact is caused by

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

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shadow artifact violates the assumption that

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

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

attenuating proximal structure

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edge shadow artifact is

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

edge shadow is caused by

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

edge shadowing is also called

shadowing by refraction

edge shadowing violates the assumption that

the strength of a reflection is related to tissue characteristics

enhancement artifact appears as

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

enhancement occurs when

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

enhancement is the opposite of

shadowing

enhancement violates assumption that

the strength of a reflection is related to tissue characteristics

focal enhancement is

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

focal enhancement is also called

focal banding

focal banding/ enhancement is most prominent at

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

focal enhancement appears like an

overgained TGC

focal enhancement violates the assumption that

the strength of a reflection is related to tissue characteristics

Mirror image occurs when

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

Mirror reflector images shows

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

mirror image artifact violates the assumption that

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

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

real, artifact

cross talk artifact results from

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

cross talk is

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

to eliminate cross talk

get as parallel to flow as possible

speed error artifact occurs when

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

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

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

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

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

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

step up or step down

speed error is also known as

range error

speed error violates the assumption that

sound travels at 1540 m/s

array probes may have

grating lobe artifact -- if not in harmonics

mechanical probes may have

side lobe artifact

very strong reflectors in a side beam can be

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

with lobe artifact which resolution degrades

lateral

grating lobes can be reduced through

apodization and subdicing

refraction occurs when

a sound pulse changes direction during transmission

refraction occurs when

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

refraction causes a reflector to appear

twice, side by side at same depth

refraction occurs when

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

refraction violates the assumption that

sound travels in a straight line

2 types of refraction

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

Intensity equation

I = P/cross sectional area