2. *
*An ultrasound artifact is a structure in an image which
does not directly similiar with actual tissue being
scanned.
*Artifact assumes different forms including :
• Structures in the image that are not actually present
• Objects that should be represented but are missing from
the image.
• Structures which are misregistered on the image.
4. • This is the production of false echoes due to repeated
reflections between two interfaces with a high acoustic
impedance mismatch.
• The echo from the interface is received by the transducer
and displayed on the image.
• Some of the energy in the returned echo is reflected at the
transducer face, and return to the reflecting interface as if
it was a weak transmitted pulse, returning as a second
echo.
• As the time taken for the second echo to arrive is twice
that taken by the depth.
*
5. • This sequence of reflection and transmission can occur
many times, with the third echo taking three times as long
to return to the transducer and being displayed at three
times the depth, and so on.
• The reverberation echoes will be equally spaced because
the time for each additional echo is multiple of the time of
return of the first echo.
• These reverberation echoes will be strong because of the
high acoustic mismatch.
6. This artifact will be seen at the skin-transducer interface
and behind bowel gas.
Rectification:
• Increase the amount of gel used.
• Use a stand-off pad.
• Reduce the gain.
• Move the position of the transducer.
7.
8. • This appears as an area of low amplitude echoes behind an
area of strongly attenuating tissue.
• It is caused by severe attenuation of the beam at an
interface, resulting in very little sound being transmitted
beyond.
• The attenuation can be due to either absorption or
reflection of the sound waves, or a combination of the
two.
• Acoustic shadowing will occur at interfaces with large
acoustic mismatch such as:
Soft tissue and gas
Soft tissue and bone or calculus
*
9.
10.
11. • This artifact appears as a localized area of increased echo
amplitude behind an area of low attenuation.
• On a scan it will appears as an area of increased brightness,
and can commonly be seen distal to fluid-filled structures
such as the urinary bladder, GB or a cyst.
• The artifact arises due to the application of the time-gain
compensation(TGC) to areas of low attenuating structures
such as fluid.
• It is caused by the low level of attenuation of the beam as it
passes through fluid relative to the greater attenuation of
the beam in the adjacent more solid tissue.
*
12. • This artifact can often be an useful diagnostic aid,
particularly when scanning a soft-tissue mass or cyst
containing low level echoes.
• These echoes may often cause the structure to disappear
in the image as it blend into the surrounding echo pattern.
13. • A combination of refraction and reflection occurring at the
edges of rounded structures will result in edge shadowing
artifact.
• It arises due to refraction of the beam caused by both the
curvature of the rounded edges and difference in speed of
two materials.
• When the ultrasound beam reaches the rounded edge of a
structure, reflection will occur, with an angle of incidence
equal to the angle of reflection.
• The outer part of the beam will be totally reflected, but
the reminder of the beam passes through the rounded
structure and is refracted.
*
14. • This combination of reflection and refraction of the
beam at the edges of a rounded structure results in a
thin strip of tissue behind the edge not being insonated
and causes a shadow.
15. • This artifact can be demonstrated by scanning a point
reflector in a phantom, where the display will clearly
portray this as a line.
• During routine scanning, the artifact can be seen when
spurious echoes are displayed in an echo-free area.
• Correct positioning of the focal zone will help to reduce
this artifact.
• The focal zone is controlled by electronically narrowing
the beam
*
16.
17. • These occurs due to the thickness of the beam, and are
similar to beam width artifacts.
• These artifacts will typically be seen in transverse views of
the urinary bladder when structures adjacent to the slice
through the bladder being scanned will be incorporated
into the image.
• These echoes are then displayed as if they were arising
from within the bladder.
• Although the appearance of this artifact is similar to the
beam width artifact, the differentiating factors is that the
reflector causing the slice thickness artifact will not be
seen on the display.
*
18. • This artifact is a result of inherent characteristics of the
transducer, and apart from trying a different transducer,
cannot be eliminated.
19. • The energy within the ultrasound beam exists as several
side lobes radiating at a number of angles from a central
lobe.
• Echoes are generated by these side lobes in addition to
the main lobe, but all the returning echoes are assumed
by the transducer to have arisen from the central axis of
the main lobe.
• Side lobe echoes will therefore be misregistered in the
display.
• This artifact can often be seen in area such as the urinary
bladder and may also arise within a cyst.
*
20.
21. • These artifacts results in a mirror image of a structure
occurring in an ultrasound display.
• They arise due to specular reflection of the beam at a
large smooth interface.
• An area close to a specular reflector will be imaged twice,
once by the original ultrasound beam and once by the
beam after it has reflected off the specular reflector.
• Mirror image artifacts are most commonly seen where
there is a large acoustic mismatch, such as a fluid-air
interface.
*
22. • Typically this artifact can occur during the scanning of a
full bladder, when air in the rectum behind the bladder
act as specular reflector and mirror image of the
bladder is displayed posteriorly.
• It will then have the appearance of a large cyst behind
the bladder.
• It can also be seen when scanning the liver, and the
diaphragm act as a specular reflector.
23.
24. • This image is caused by refraction of the beam and may
occur in areas such as the rectus abdominis muscle on the
anterior abdominal wall.
• In the transverse plane the edges of the muscle act as a
lens and the ultrasound beam to be refracted and this
causes the single structure to be interrogated by two
separate refracted beams.
• Two sets of echoes will therefore be returned and these
will cause display of two structures in the image.
*
25. This results in, for example, two images of the transverse
aorta side by side in the abdomen.
26. • Incorrect use of the equipment controls can lead to artifact
appearing.
• Misuse of controls such as the gain or TGC can result in
echoes being recorded as too bright or too dark.
• Care must be taken when setting these controls, to ensure
an even brightness throughout the image.
• If the dynamic range control is incorrectly set, this can lead
to an image which has too much contrast, and result in the
loss of subtle echo information.
*
27. • Gain must be in medium level.
• Blurring of a moving image can occur if the frame rate is
too low or if the persistence is too high.
• It is important to ensure that the frame rate is capable of
recording a moving structure at the speed.
• Use of multiple focal zones can give rise to a prominent
banding effect within the image.
28.
29. *
• The refraction is the change of the sound direction on
passing from one medium to another.
• In ultrasound, refraction is due to sound velocity
mismatches combines with oblique angles of incidence,
most commonly with convex scanheads.
• When the ultrasound wave crosses at an oblique angle the
interface of two materials, through which the waves
propagate at different velocities, refraction occurs, caused
by bending of the wave beam.
• Refraction artifact cause spatial distortion and loss of
resolution in the image.
