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Image artifact in Ultrasound
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DR.SHAMIM RIMAMBBS,DMU,FCGP
M.PHILRADIOLOGY & IMAGING
BSMMU.
Figure : Diagram of an ultrasound beam. The main ultrasound beam narrows as it approaches the focal zone and then diverges. Grating lobes and side lobes are forms of off-axis energy
Figure : Diagram of an ultrasound beam. The main ultrasound beam narrows as it approaches the focal zone and then diverges. Grating lobes and side lobes are forms of off-axis energy
US Beam US Beam
ARTIFACTS
An image artifact is any image attribute, which is not present in the original imaged
object. An image artifact is sometime the result of an improper operation of the imager,
and in other times a consequence of natural processes or properties of the human
body.
Artifacts in diagnostic ultrasound are a reflection or an echo, which appears on the display and represents the real anatomical structure not correctly.
An artifact can be a false, multiple or misleading information introduced by the imaging system or by interaction of ultrasound with the adjacent tissue.
Artifacts in ultrasound can be classified as to their source like e.g.:
Physiologic (motion, different sound velocities, acoustical impedances of tissue);
Hardware (dimension of the ultrasound beam and the transducer array);
Imaging technique (B-mode, Spectral Doppler , color-Doppler, 3D ultrasound).
Image artifacts can occur in each medical ultrasound. Then an interpretation of the image is complicated and can eliminate the structural information of objects looking for.
Technique-dependent artifacts: Noise
Noise caused by excess gain
Resolving noise caused by excess gain- Decrease overall gain
An undesirable background interference or disturbance that affects image quality.
The noise is commonly characterized by the standard deviation of signal intensity in
the image of a uniform object (phantom) in the absence of artifacts.
Overall increase in echogenicity.
Low signal
Low signal caused by inappropriate transducer selection or low gain settings
Resolving low gain artifacts:
- Increase overall gain
- Increase far gain
- Apply more acoustic coupling gel
ARTIFACTS ASSOCIATED WITH ATTENUATION ERRORS
Shadowing
Shadowing Increased through transmission
Shadowing
Caused by sound striking a strong reflective interface example;
areas behind ribs or gall stones
Shadowing corrective technique:
- Scan around object causing shadowing
Shadowing corrective technique:
- Scan around object causing shadowing
Shadowing.(a) Diagram shows the ultrasound beam encountering a strongly
attenuating material. The echoes received from points distal to this material are
significantly lower in intensity than echoes received from a similar
depth. (b)Longitudinal US image of the gallbladder shows shadowing (arrow)
posterior to echogenic gallstones.
Shadowing.(a) Diagram shows the ultrasound beam encountering a strongly
attenuating material. The echoes received from points distal to this material are
significantly lower in intensity than echoes received from a similar
depth. (b)Longitudinal US image of the gallbladder shows shadowing (arrow)
posterior to echogenic gallstones.
Enhancement
Caused by sound travelling through fluid-filled structures without attenuation (example: area
behind cysts, area behind gallbladder)
Enhancement corrective technique:- Reduce overall gain- Decrease far gain
Enhancement corrective technique:- Reduce overall gain- Decrease far gain
Enhancement artifacts occur if decreasing of the echo amplitude is not equal
with penetration depth caused by inhomogeneous tissue layers and fluids like
cysts or air-filled regions.
The enhanement artifacts appears as a hyperintense (hyperechoic) signal. The
attenuation of the ultrasound wave in fluids is much lower as the attenuation in
other tissues, therefore tissues distal to fluid are enhanced.
Artificial enhancement may also be found distal to a homogeneous solid tumor
surrounded by adipose tissue, due to the comparatively high attenuation in fat
Enhancement artifacts occur if decreasing of the echo amplitude is not equal
with penetration depth caused by inhomogeneous tissue layers and fluids like
cysts or air-filled regions.
The enhanement artifacts appears as a hyperintense (hyperechoic) signal. The
attenuation of the ultrasound wave in fluids is much lower as the attenuation in
other tissues, therefore tissues distal to fluid are enhanced.
Artificial enhancement may also be found distal to a homogeneous solid tumor
surrounded by adipose tissue, due to the comparatively high attenuation in fat
Enhancement artifacts
Figure: Increased through transmission. (a)Diagram shows the ultrasound beam encountering a
focal weakly attenuating material. The echoes received from points distal to this material are
higher in intensity than echoes received from a similar depth in the imaging
plane. (b)Transverse US image of the liver shows hypoechoic and weakly attenuating hepatic
cysts. The hepatic parenchyma distal to the cysts is falsely displayed as increased in intensity
(arrow) secondary to increased through-transmission artifact.
Figure: Increased through transmission. (a)Diagram shows the ultrasound beam encountering a
focal weakly attenuating material. The echoes received from points distal to this material are
higher in intensity than echoes received from a similar depth in the imaging
plane. (b)Transverse US image of the liver shows hypoechoic and weakly attenuating hepatic
cysts. The hepatic parenchyma distal to the cysts is falsely displayed as increased in intensity
(arrow) secondary to increased through-transmission artifact.
Reverberation
Caused by sound interfacing with two structures of markedly differing acoustic properties;
example: inadequate amount of gel, obstructing bowel gas
Reverberation corrective technique:- Change angle of transducer- Apply more gel- Rotate patient
Reverberation corrective technique:- Change angle of transducer- Apply more gel- Rotate patient
Reverberation occurs when sound encounters two highly reflective layers. The sound
is bounced back and forth between the two layers before traveling back. The probe
will detect a prolonged traveling time and assume a longer traveling distance and
display additional ‘reverberated’ images in a deeper tissue layer
Reverberation occurs when sound encounters two highly reflective layers. The sound
is bounced back and forth between the two layers before traveling back. The probe
will detect a prolonged traveling time and assume a longer traveling distance and
display additional ‘reverberated’ images in a deeper tissue layer
Reverberation
Figure. Reverberation artifact. (a) Diagram shows ultrasound echoes
being repeatedly reflected between two highly reflective
interfaces. (b) The display shows multiple equally spaced signals
extending into the deep field.
Figure. Reverberation artifact. (a) Diagram shows ultrasound echoes
being repeatedly reflected between two highly reflective
interfaces. (b) The display shows multiple equally spaced signals
extending into the deep field.
Transverse US image obtained over a palpable mass in a neonate shows reverberation
artifact (arrow).
Longitudinal US image of the gallbladder shows comet tail artifact (arrow) caused by
cholesterol crystals in Rokitansky-Aschoff sinuses. This finding is diagnostic of
adenomyomatosis. Shadowing gallstones are also identified.
Transverse US image obtained over a palpable mass in a neonate shows reverberation
artifact (arrow).
Longitudinal US image of the gallbladder shows comet tail artifact (arrow) caused by
cholesterol crystals in Rokitansky-Aschoff sinuses. This finding is diagnostic of
adenomyomatosis. Shadowing gallstones are also identified.
Mirror Image Artifacts
If a structure is located close to a highly reflective interface (such as the diaphragm),
it is detected and displayed in its normal position. However, the strong reflector
causes additional sound waves to bend towards the neighboring anatomy, from
where they are bounced back towards the strong reflector and return to the
transducer. These sound waves have a longer travel time and are perceived as an
additional anatomic structure. The image is duplicated on the other side of the strong
reflector .
Figure . Mirror image artifact. (a) In this diagram, the gray arrows represent the expected reflective path of the ultrasound beam. These echoes are displayed properly. The black arrows show an alternative path of the primary ultrasound beam. In this path, the primary ultrasound beam encounters the deeper reflective interface first. (b) The echoes from the deeper reflective interface take longer to return to the transducer and are misplaced on the display. (c) Longitudinal US image obtained at the level of the right hepatic lobe shows an echogenic lesion in the right hepatic lobe (cursors) and a duplicated echogenic lesion (arrow) equidistant from the diaphragm overlying the expected location of lung parenchyma.
Figure . Mirror image artifact. (a) In this diagram, the gray arrows represent the expected reflective path of the ultrasound beam. These echoes are displayed properly. The black arrows show an alternative path of the primary ultrasound beam. In this path, the primary ultrasound beam encounters the deeper reflective interface first. (b) The echoes from the deeper reflective interface take longer to return to the transducer and are misplaced on the display. (c) Longitudinal US image obtained at the level of the right hepatic lobe shows an echogenic lesion in the right hepatic lobe (cursors) and a duplicated echogenic lesion (arrow) equidistant from the diaphragm overlying the expected location of lung parenchyma.
Mirror Image Artifacts
Comet Tail artifacts
A comet tail artifact is similar to reverberation. It is produced by the front and back of a very
strong reflector (air bubble, BB gun pellet, suture) , createsa dense echogenic line extending
through the image.
The reverberations are spaced very narrowly and blend into a small band.
A comet tail artifact is similar to reverberation. It is produced by the front and back of a very
strong reflector (air bubble, BB gun pellet, suture) , createsa dense echogenic line extending
through the image.
The reverberations are spaced very narrowly and blend into a small band.
Ring Down Artifacts
The artifact is caused by a resonance phenomenon from a collection of gas bubbles. A
continuous emission of sound occurs from the ‘resonating’ structure causing a long and
uninterrupted echo. It appears very similar to the comet tail artifact
Diagram shows the main ultrasound beam encountering a ring of bubbles with fluid trapped centrally. Vibrations from the pocket of fluid cause a continuous source of sound energy that is transmitted back to the transducer for detection. The display shows a bright reflector with an echogenic line extending posteriorly. Left lateral decubitus US image of the gallbladder shows air and fluid in the duodenum causing ring-down artifact (arrow).
Figure : Ring-down artifact. (a) Diagram shows the main ultrasound beam encountering a ring of bubbles with fluid trapped centrally. (b) Vibrations from the pocket of fluid cause a continuous source of sound energy that is transmitted back to the transducer for detection. (c) The display shows a bright reflector with an echogenic line extending posteriorly.
Figure : Ring-down artifact. (a) Diagram shows the main ultrasound beam encountering a ring of bubbles with fluid trapped centrally. (b) Vibrations from the pocket of fluid cause a continuous source of sound energy that is transmitted back to the transducer for detection. (c) The display shows a bright reflector with an echogenic line extending posteriorly.
Side Lobe Artifacts
This artifact is caused by low energy ‘side lobes’ of the main ultrasound beam. When an
echo from such a side lobe beam becomes strong enough and returns to the receiver, it is
‘assigned’ to the main beam and displayed at a false location. Side-lobe artifacts are
usually seen in hypoechoic or echo-free structures and appear as bright
Lobe Artifacts
Side lobes and grating lobes are sound waves that are created peripheral to the
main beam
Are lower energy, so generally are lost to attenuation
Provide distracting echoes when misinterpreted as being from the main beam
Side lobes are multiple beams of low-amplitude ultrasound energy that project radially from the
main beam axis .
Side lobe energy is generated from the radial expansion of piezoelectric crystals and is seen
primarily in linear-array transducers
Strong reflectors present in the path of these low-energy, off-axis beams may create echoes
detectable by the transducer.
These echoes will be displayed as having originated from within the main beam in the side lobe
artifact . As with beam width artifact, this phenomenon is most likely to be recognized as
extraneous echoes present within an expected anechoic structure such as the bladder
Side lobesSide lobes
Refraction artifact.
Refraction Artifact.
A change in velocity of the ultrasound beam as it travels through two adjacent tissues
with different density and elastic properties may produce a refraction artifact.
In refraction, nonperpendicular incident ultrasound energy encounters an interface
between two materials with different speeds of sound. When this occurs, the incident
ultrasound beam changes direction.
The degree of this change in direction is dependent on both the angle of the incident
ultrasound beam and the difference in velocity between the two media.
The ultrasound display assumes that the beam travels in a straight line and thus misplaces
the returning echoes to the side of their true location .
In clinical imaging, this artifact may be recognized in pelvic structures deep to the junction
of the rectus muscles and midline fat.
Refraction artifact may cause structures to appear wider than they actually are or may
cause an apparent duplication of structures
Figure: Refraction artifact. (a) Diagram shows the refraction or change in direction of the
obliquely angled incident ultrasound beam as it travels between two adjacent tissues with
different sound propagation velocities (C1and C2). The incident ultrasound beam with
refraction encounters two structures. (b)The object in the path of the refracted portion of
the beam is misplaced because the processor assumes a straight path of the beam.
Figure: Refraction artifact. (a) Diagram shows the refraction or change in direction of the
obliquely angled incident ultrasound beam as it travels between two adjacent tissues with
different sound propagation velocities (C1and C2). The incident ultrasound beam with
refraction encounters two structures. (b)The object in the path of the refracted portion of
the beam is misplaced because the processor assumes a straight path of the beam.
Figure: Refraction artifactFigure: Refraction artifact
Edge Shadowing
The lateral edge shadow is a thin acoustic shadow that appears behind edges
of cystic structures. Sound waves encountering a cystic wall or a curved
surface at a tangential angle are scattered and refracted, leading to energy
loss and the formation of a shadow.
Figure . Side lobe artifact. (a) Diagram shows multiple beams of off-axis side lobe ultrasound
energy encountering an object (black circle). (b) The display assumes that the echoes
returning from this off-axis object came from the main beam and misplaces and duplicates the
structure.
ARTIFACTS ASSOCIATED WITH VELOCITY ERRORS
Speed Displacement Artifact
Refraction Artifact.
Speed Displacement Artifact
When sound travels through material with a velocity significantly slower than the
assumed 1540 m/sec, the returning echo will take longer to return to the
transducer.
The image processor assumes that the length of time for a single round trip of an
echo is related only to the distance traveled by the echo.
The echoes are thus displayed deeper on the image than they really are . This is
referred to as the speed displacement artifact; in clinical imaging, it is often
recognized when the ultrasound beam encounters an area of focal fat.
When sound travels through material with a velocity significantly slower than the
assumed 1540 m/sec, the returning echo will take longer to return to the
transducer.
The image processor assumes that the length of time for a single round trip of an
echo is related only to the distance traveled by the echo.
The echoes are thus displayed deeper on the image than they really are . This is
referred to as the speed displacement artifact; in clinical imaging, it is often
recognized when the ultrasound beam encounters an area of focal fat.
Figure. Speed displacement artifact. (a)In this diagram, the gray arrows represent the expected reflected
path of the ultrasound beam. The echoes returning from the posterior wall of the depicted structure will
be displayed properly. The black arrows represent the path of an ultrasound beam that encounters an
area of focal fat. The dashed lines indicate that the sound beam travels slower in the focal fat than in the
surrounding tissue. (b) Because the round trip of this echo is longer than expected, the posterior wall is
displaced deeper on the display. (c, d) Transverse US image of the liver (c) and close-up detail
image (d) show that the interface between the liver and the diaphragm (arrow in c) is discontinuous and
focally displaced (arrows in d). This appearance may be explained by areas of focal fat within the liver.
Figure. Speed displacement artifact. (a)In this diagram, the gray arrows represent the expected reflected
path of the ultrasound beam. The echoes returning from the posterior wall of the depicted structure will
be displayed properly. The black arrows represent the path of an ultrasound beam that encounters an
area of focal fat. The dashed lines indicate that the sound beam travels slower in the focal fat than in the
surrounding tissue. (b) Because the round trip of this echo is longer than expected, the posterior wall is
displaced deeper on the display. (c, d) Transverse US image of the liver (c) and close-up detail
image (d) show that the interface between the liver and the diaphragm (arrow in c) is discontinuous and
focally displaced (arrows in d). This appearance may be explained by areas of focal fat within the liver.
Slice Thickness
Remember that the image is a two dimension representation of a volume of tissue, not
a true two dimensional plane
Results in false echoes, especially in anechoic structures
Thick slices result in an inability to see objects substantially smaller than beamThickness
This is also referred to as elevational resolution
Generally not controllable by the user
Generally the poorest resolution in the system.
Remember that the image is a two dimension representation of a volume of tissue, not
a true two dimensional plane
Results in false echoes, especially in anechoic structures
Thick slices result in an inability to see objects substantially smaller than beamThickness
This is also referred to as elevational resolution
Generally not controllable by the user
Generally the poorest resolution in the system.
Slice Thickness Artifacts
When the interface between a fluid-filled & soft tissue is acutely angled, the beam, which is relatively wide (2-3mm), may strike both tissue & fluid simultaneously.
Low-level artifactual echoes will be displayed within the fluid.
When the interface between a fluid-filled & soft tissue is acutely angled, the beam, which is relatively wide (2-3mm), may strike both tissue & fluid simultaneously.
Low-level artifactual echoes will be displayed within the fluid.
TGC Banding
Occurs when the user has not appropriately adjusted the TGC curve
Aliasing
Occurs only in Doppler imaging
If the pulse repetition frequency is set at too fast a speed, signals return to
transducer after the transmission of next signal.
With color flow, this artifact induces specks of color at the opposite end of the
color spectrum from the rest of the color related to high-velocity areas.
If the velocity exceeds the range, it will be depicted as going the other direction
Occurs only in Doppler imaging
If the pulse repetition frequency is set at too fast a speed, signals return to
transducer after the transmission of next signal.
With color flow, this artifact induces specks of color at the opposite end of the
color spectrum from the rest of the color related to high-velocity areas.
If the velocity exceeds the range, it will be depicted as going the other direction
Aliasing of color doppler imaging and artefacts of color. Color image shows regions of aliased flow (yellow arrows).
Aliasing of color doppler imaging and artefacts of color. Color image shows regions of aliased flow (yellow arrows).
Reduce color gain and increase
pulse repetition frequency.
Reduce color gain and increase
pulse repetition frequency.
Aliasing
Figure (a,b): Example of aliasing and correction of the aliasing. (a) Waveforms with
aliasing, with abrupt termination of the peak systolic and display this peaks bellow the
baseleineSonogram clear without aliasing. (b) Correction: increased the pulse
repetition frequency and adjust baseline (move down)
Figure (a,b): Example of aliasing and correction of the aliasing. (a) Waveforms with
aliasing, with abrupt termination of the peak systolic and display this peaks bellow the
baseleineSonogram clear without aliasing. (b) Correction: increased the pulse
repetition frequency and adjust baseline (move down)
Can control aliasing by increasing PRF or changing baseline
It’s important to correct in pulse Doppler so accurate measurements can be made
It’s important to correct in color Doppler because it is easily mistaken for turbulence
Can control aliasing by increasing PRF or changing baseline
It’s important to correct in pulse Doppler so accurate measurements can be made
It’s important to correct in color Doppler because it is easily mistaken for turbulence
Aliasing
Poor Angle For Color
As with pulsed Doppler, the best visualization of a vessel is a with the transducer at an
angle of less than 600 to the vessel.
If a 900 angle is used. Flow within vessels will be poorly seen.
As with pulsed Doppler, the best visualization of a vessel is a with the transducer at an
angle of less than 600 to the vessel.
If a 900 angle is used. Flow within vessels will be poorly seen.
Figure : Effect of high vessel/beam angles. (a) and (b) A scan of fetal aortic flow is undertaken at a high
beam/vessel angle. Beam/flow angles should be kept to to 60° or less. A hudge discrepancy is observed
when use unapropiate angles > 60°. If absolute velocities are to be measured, beam/flow angles should
be kept to 60° or less.
Figure : Effect of high vessel/beam angles. (a) and (b) A scan of fetal aortic flow is undertaken at a high
beam/vessel angle. Beam/flow angles should be kept to to 60° or less. A hudge discrepancy is observed
when use unapropiate angles > 60°. If absolute velocities are to be measured, beam/flow angles should
be kept to 60° or less.
ADVERSE BIOLOGICAL EFFECTS OF ULTRASOUND ON BODY TISSUES
There are several known effects of ultrasound on tissues, but at the low doses used in
diagnostic imaging these are not thought to create any adverse effect. At higher therapeutic
doses the effects are used to influence tissues.
There are several known effects of ultrasound on tissues, but at the low doses used in
diagnostic imaging these are not thought to create any adverse effect. At higher therapeutic
doses the effects are used to influence tissues.
The various effects of ultrasound can be categorised into three main types : The various effects of ultrasound can be categorised into three main types :
Mechanical - no adverse effect on cell structure or chromosomes have been reported Mechanical - no adverse effect on cell structure or chromosomes have been reported
Vibration of tissues
Forms small cavities in fluids during "suction" phase which disperse during the
"pressure" phase
This phenomenon is called cavitation in gas-free fluids, and pseudocavitation in
fluids containing gas
Vibration associated with high intensities of ultrasound result in heat production
Vibration of tissues
Forms small cavities in fluids during "suction" phase which disperse during the
"pressure" phase
This phenomenon is called cavitation in gas-free fluids, and pseudocavitation in
fluids containing gas
Vibration associated with high intensities of ultrasound result in heat production
ADVERSE BIOLOGICAL EFFECTS OF ULTRASOUND ON BODY TISSUES
Heat Heat
At usual frequencies and intensities the heat produced by ultrasound is dispersed by
the local blood circulation
High intensity ultrasound is used to induce local hyperthermia for therapeutic purposes
At usual frequencies and intensities the heat produced by ultrasound is dispersed by
the local blood circulation
High intensity ultrasound is used to induce local hyperthermia for therapeutic purposes
Chemical Chemical
Depolymerisation - experimentally ultrasound can breakdown polysaccharides and
polypeptides including DNA. These effects have not been reported to occur in vivo
following diagnostic ultrasound procedures.
Oxidation
Reduction
Depolymerisation - experimentally ultrasound can breakdown polysaccharides and
polypeptides including DNA. These effects have not been reported to occur in vivo
following diagnostic ultrasound procedures.
Oxidation
Reduction
ADVERSE BIOLOGICAL EFFECTS OF ULTRASOUND ON BODY TISSUES
High intensity, high frequency ultrasound has been shown to result in adverse effects
including :
High intensity, high frequency ultrasound has been shown to result in adverse effects
including :
Tissue necrosis
Chromosomal damage
Genetic mutations
Teratogenic changes
Tissue necrosis
Chromosomal damage
Genetic mutations
Teratogenic changes
So far these adverse effects have not been reported following diagnostic
ultrasonography but safety limits to minimise potential risks have been set as follows
So far these adverse effects have not been reported following diagnostic
ultrasonography but safety limits to minimise potential risks have been set as follows
Intensities over 100mW/cm2 (spatial peak/temporal average) should only be applied
for a few seconds/minutes.
For human use 10 mW/cm2 is approved for commercial 2-D ultrasound.
Intensities over 100mW/cm2 (spatial peak/temporal average) should only be applied
for a few seconds/minutes.
For human use 10 mW/cm2 is approved for commercial 2-D ultrasound.