Chapter 21 Artifact Flashcards
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
causes of artifact (4)(VETO)
-Violation of assumptions
-Equipment malfunction or poor design
-Physics of ultrasound
-Operator error
Hyperechoic
tissues that appear brighter than normal
hypoechoic
tissues that appear less bright than normal
anechoic
an extreme form of hypoechoic meaning without echoes or echo free
isoechoic
tissue that has similar echo brightness
homogenous
tissue that has similar echo characteristics throughout
heterogenous
tissue that has differing echo characteristics throughout
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
when corrective measures are taken artifacts usually _______; if not, what should be considered?
vanish, instrument malfunction should be considered
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
Reverberation violates the assumption that
sound travels directly to a reflector and back
reverberations resemble
a ladder or venetian blinds
in reverberation the 1st two reflections are real, but the remaining deeper reflections are
repeats
comet tail is also known as
ring down artifact
comet tail is caused by
reverberations so close together that they merge and spaces between them are “squeezed” out
comet tail artifact violates the assumption that
sound travels directly to reflector and back
comet tail appears as a
solid hyperechoic line directed downward
comet tail is likely to occur in mediums with fast propagation speeds like
mechanical heart valves
comet tail can also arise from
resonating small structures like gas bubbles
Shadow artifact is
hypoechoic or anechoic region extending downward from a very strong attenuating medium (reflectors like bone, stones, prosthesis)
shadow artifact is caused by
sound cannot pass through the attenuating structure therefore we have no or little reflections off deeper structures
shadow artifact violates the assumption that
the intensity of reflection is related to the tissue creating the reflection
shadow artifact is unrelated to speed of sound, and related to the
attenuating proximal structure
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
- probe redirects and send subsequent beam
- probe places reflector as if it had come from the main beam
Intensity equation
I = P/cross sectional area
