2. What is an Artifact?
Artifact is used to describe any part of an
image that does not accurately represent the
anatomic structures present within the subject
being evaluated.
3. In ultrasonography (US), artifacts may cause
structures to appear in an image that are not
present anatomically or a structure that is
present anatomically may be missing from the
image. US artifacts may also show structures
as present but incorrect in location, size, or
brightness.
4. US is prone to numerous imaging artifacts,
and these are commonly encountered in
clinical practice. Artifacts have the potential
to interfere with image interpretation.
Ultrasound display equipment relies on
physical assumptions to assign the location
and intensity of each received echo.
7. Acoustic enhancement
Acoustic enhancement, also called posterior
enhancement or enhanced through
transmission, refers to the increased echoes
deep to structures that transmit sound
exceptionally well.
8. This is characteristic of fluid filled structures such
as cysts, the urinary bladder and the gallbladder.
The fluid only attenuates the sound less than the
surrounding tissue. The time gain-compensation
(TGC) overcompensates through the fluid-filled
structure causing deeper tissues to be brighter.
Simply it is seen as increased echogenicity
(whiteness) posterior to cystic area. The presence
of acoustic enhancement aids in the identification
of cystic masses but some solid masses,
especially lymphoma, may also show acoustic
enhancement posteriorly.
9. ACOUSTIC SHADOWING
Acoustic shadowing on an ultrasound image is
characterized by a signal void behind structures
that strongly absorb or reflect ultrasonic waves.
This happens most frequently with solid
structures, as sound conducts most rapidly in
areas where molecules are closely packed, such
as in bone or stones.
10. ANISOTROPY
Anisotropy is an artifact encountered in
ultrasound, notably in muscles and tendons
during a musculoskeletal ultrasound. In
musculoskeletal applications, the artifact may
prompt an incorrect diagnosis of tendon tear.
11. When the ultrasound beam is incident on a
fibrillar structure as a tendon or a ligament, the
organized fibrils may reflect a majority of the
insonating sound beam in a direction away
from the transducer. When this occurs, the
transducer does not receive the returning echo
and assumes that the insonated area should be
hypoechoic.
12. This anisotropic effect is dependent on the
angle of the insonating beam. The maximum
return echo occurs when the ultrasound beam
is perpendicular to the tendon. Decreasing the
insonating angle on a normal tendon will cause
it to change from brightly hyperechoic (the
actual echo from tightly bound tendon fibers)
to darkly hypoechoic. If the angle is then
increased, the tendon will again appear
hyperechoic.
13. If the artifact causes a normal tendon to appear
hypoechoic, it may falsely lead to a diagnosis of
tendinosis or tear.
In some situations, anisotropy may be useful in
diagnosis. If a tendon is surrounded by other
brightly hyperechoic structures (e.g. fat), then
altering the angle of the transducer will cause
the tendon to become hypoechoic,
differentiating it from the other structures.
14. Beamwidthartifact
Ultrasound beam width artifact occurs when a
reflective object located beyond the widened
ultrasound beam, after the focal zone, creates
false detectable echoes that are displayed as
overlapping the structure of interest.
15. To understand this artifact, it is important to remember
that the ultrasound beam is not uniform with depth, the
main beam leaves the transducer with the same width as
it, then narrows as it approaches the focal zone and
widens again distal to this zone.
Usually, it occurs when scanning an anechoic structure
and some peripheral echoes are identified, i.e. Gas
bubbles in the duodenum simulating small gallstones and
peripheric echoes in the bladder.
It is possible to avoid this artifact adjusting the focal zone
to the depth level of interest and by placing the
transducer at the center of the object being studied.
16. BLOOMING ARTIFACT
Blooming or color bleed artifact occurs when the
color signal indicating blood flow extends
beyond its true boundaries, spreading into
adjacent regions with no actual flow.
This artifact mainly affects the portion of the
image distal to the vessel and the transducers. It
is somewhat similar to its MRI namesake as both
phenomena denote something that seemingly
appears larger than its true physical limits.
17. Blooming occurs because the spatial
resolution of color Doppler is lower than
greyscale ultrasound . It can be exaggerated by
inappropriately high color gain. It is important
to be aware of as it may obscure partial
occlusions such as thrombi resulting in
misdiagnosis . It can be avoided by lowering
the color gain until the bleed of signal outside
of the vessel disappears.
18. COMET-TAIL ARTIFACT
The comet-tail artifact is a grey-scale
ultrasound finding seen when small calcific /
crystalline / highly reflective objects are
interrogated and is believed to be a special
form of reverberation artifact.
It is similar to the color comet-tail
artifact and is seen in similar situations,
although is in general less sensitive than the
latter.
19. Small renal or ureteric calculi
Small common bile duct stones
Adenomyomatosis of the gallbladder
Pancreatic calcifications of chronic pancreatitis
Testicular microlithiasis (sometimes)
Thyroid colloid nodules
Identification of foreign bodies
Surgical clips
Catheter tips
Debris / glass / metal
20. Electrical interference artifact
Electrical interference artifact is an ultrasound
artifact usually caused by the ultrasound
machine being too close to the unshielded
electrical equipment. The disturbance appears
as arc-like moving bands in the ultrasound
image.
21. While the presence of electrical
equipment (e.g. unshielded ventilators) near
the ultrasound machine may cause this artifact
because of external electronic signals, the
artifact can also occur when the ultrasound
probe malfunctions.
22. Mirror image artifact
Mirror image artifact in sonography is seen
when there is a highly reflective surface
(e.g. diaphragm) in the path of the primary
beam.
The primary beam reflects from such a surface
(e.g. diaphragm) but instead of directly being
received by the transducer, it encounters
another structure (e.g. a nodular lesion) in its
path and is reflected back to the highly reflective
surface (e.g. diaphragm). It then again reflects
back towards the transducer.
23. The ultrasound machine makes a false
assumption that the returning echo has been
reflected once and hence the delayed echoes
are judged as if being returned from a deeper
structure, thus giving a mirror artifact on the
other side of the reflective surface.
It is a friendly artifact that allows the
sonographer to exclude pleural effusion by the
reflection of the liver image through the
diaphragm.
24. Examples:
reflection of a liver lesion into the thorax (the
commonest example)
reflection of abdominal ascites mimicking pleural
effusion
duplication of gestational sac (either ghost twin or
heterotopic pregnancy)
duplication of the uterus
To avoid this artifact, change the position and angle of
scanning to change the angel of insonation of the
primary ultrasound beam.
25. Multipathartifact
A multipath artifact is an ultrasound beam
artifact in which the primary beam reflects off
anatomy at an angle, resulting in a portion of
the beam returning to the transducer, whilst
another portion takes a longer duration as it
reflects a second structure. This phenomenon
results in a propagation path error in which the
transducer will interpret a structured to be
deeper than it is.
26. REVERBERATION ARTIFACT
Reverberation artifact occurs when
an ultrasound beam encounters two strong
parallel reflectors.
When the ultrasound beam reflects back and
forth between the reflectors
("reverberates"), the ultrasound transducer
interprets the sound waves returning as
deeper structures since it took longer for the
wave to return to the transducer.
27. Reverberation artifacts can be improved by
changing the angle of insonation so that
reverberation between strong parallel reflectors
cannot occur.
Comet-tail artifact is a specific type of
reverberation artifact. This results a short train
of reverberations from an echogenic focus which
has strong parallel reflectors within it (e.g.
Cholesterol crystals in Adenomyomatosis).
28. Ring down artifact
Ring down artifact is a special type
of resonance artifact. Its appearance is similar
to the ladder-like reverberation of comet-tail
artifact, but it is produced by a completely
different mechanism.
29. The artifact is only associated with gas bubbles, and
occurs when an ultrasound pulse encounters a "horn" or
"bugle" shaped fluid collection that is trapped between an
inverted tetrahedron of 4 bubbles (3 on top and 1 nestled
deep to them) The trapped fluid resonates, emitting a
continuous signal back to the transducer. Whereas the
transducer pulse is broad spectrum, the returning signal
consists of one or more discrete (resonant) frequencies.
"Beats" between these frequencies produce the variable
appearance of the ring down. There is no "reverberation"
( i.e. multiple reflectances).
This artifact can be eliminated by angling the ultrasound
probe.
30. SIDE LOBE ARTIFACT
Side lobe artifacts occur where side lobes
reflect sound from strong reflector that is
outside of the central beam, and where the
echoes are displayed as if they originated from
within the central beam.
31. Ultrasound transducer crystals expand and contract
to produce primary ultrasound beams in the direction
of the expansion and contraction. Secondary beams
also occur because the crystals also expand and
contract radially. These radial beams are called side
lobe beams. Side lobe beams are low-intensity beams
that surround the central beam.
Side lobe artifacts are echogenic, linear or curvilinear
artifacts. Strong reflectors include bowel gas adjacent
to the gallbladder or urinary bladder.
32. SPECKLE ARTIFACT
Speckle artifact may be encountered in
ultrasound. It is caused by the scattering of
waves from the surface of small structures
within a certain tissue. The artifact produces a
textured appearance.
33. Twinkling artifact
Twinkling artifact is the result of intrinsic
machine noise seen with color Doppler
ultrasound. It occurs as a focus of alternating
colors on Doppler signal behind a reflective
object (such as calculi), which gives the
appearance of turbulent blood flow . It appears
with or without an associated color comet-tail
artifact .
34. Twinkling artifact is more sensitive for detection
of small stones (e.g. urolithiasis, cholelithiasis)
than is acoustic shadowing. It is most
pronounced when the reflecting surface is rough
and highly dependent on machine setting:
when the focal zone is located below a rough
reflecting surface, the twinkling artifact
becomes more obvious than when it is above it
increased pulse repetition frequency facilitates
better visualization of the artifact .
