Artifacts and Bioeffects

ARTIFACTS AND BIOEFFECTS
BY: ADEDEWE NUSIRAT ADEOLA
M.SC MEDICAL PHYSICS
UNIVERSITY OF LAGOS
5/23/2017ARTIFACTS AND BIOEFFECTS BY ADEDEWE NUSIRAT 1

WHAT ARE ARTIFACTS

DEFINITION
• Artifacts are errors in imaging
• These are modifications in the appearance of a displayed structure as a
result of certain changes in tissue characteristics in a patient.
• They are structure or feature in an ultrasound image that does not
correspond one on one to the actual object being scanned.

TYPES OF ARTIFACTS
• Artifacts are of various types. They can be:
• Artifacts associated with ultrasound beam characteristics.
• Artifacts associated with multiple echoes.
• Artifacts associated with velocity errors.
• Artifacts associated with attenuation errors

A TYPICAL ULTRASOUND IMAGE

• Artifacts are common occurrences in an ultrasound display, they are
often the result of the physical properties of ultrasound itself. Artifacts
assumes different forms:
• REVERBERATION
• ACOUSTIC SHADOWING
• ACOUSTIC ENHANCEMENT
• EDGE SHADOOWING
• BEAM WIDTH ARTIFACT
• SLICE THICKNESS ARTIFACT
• MIRROR IMAGE
• SIDE LOBE ARTIFACT
• DOUBLE IMAGE ARTIFACT
• REFRACTION ARTIFACT
• And many more

ARTIFACTS ASSOCIATED WITH ULTRASOUND BEAM
CHARACTERISTICS
• Transducers have a main beam axis along which the main beams are
transmitted parallel to the long axis of the transducer with an
additional off-axis beam called SIDE LOBES
• The side lobe beams may be reflected back from a strong reflector to
the transducer and sometimes detected
• The transducer cannot differentiate between the reflected beams
returning from the main beam and the those returning from the side
lobe, it considers any detected beam as originating from the main lobe.

• Side lobes are lower in amplitude than the main lobe
• In order to be detected by the transducer, they must be reflected by a
highly reflective structure.
• Side lobe artifact have the appearance of a hyperechoic object within an
anechoic of hypoechoic structure, such as a gall bladder, urinary
bladder.

Image showing side lobe artifact
• Side lobe
artifact (red
arrow) seen in
a mucinous
ovarian tumor

RECTIFICATION
• Adjusting the focal zone and placing the transducer
at the centre of object would reduce the side lobe
artifact

BEAM WIDTH ARTIFACT
• The origin is similar to side lobe artifact. The main ultrasound beam
exits the transducer at approximately the same width as the transducer,
then narrows as it approaches the focal zone and widens again distal to
the focal zone
• A highly reflective object located within the widened beam may
generate detectable echoes
• The transducer cannot differentiate between echoes, whether they
originate from a location within the widened beam or within the
narrow imaging plane.

• The transducer falsely interpretes object located in the widened beam
to be located within the narrow beam.
• They are recognized when structures that should be anechoic such as
bladder contains peripheral echoes.

• Caused due to the widening of the main beam after the
focal spot

RECTIFICATION
• Image quality may be improved by adjusting the focal zone to the level
of interest and by placing the transducer at the center of the object of
interest

ARTIFACTS ASSOCIATED WITH MULTIPLE ECHOES
• Ultrasound assumes that an echo returns to the transducer after a
single reflection and that the depth of an object is related to the time
for this round trip.
• The echo that returns to the transducer after a single reflection will be
displayed in the proper location
• In the presence of two parallel highly reflective surfaces, the echoes
generated from the ultrasound beam may be repeatedly reflected back
and forth before returning to the transducer for detection.

• The sequential echoes will take longer to return to the transducer, and
the ultrasound processor will erroneously place the delayed echoes at
an increased distance from the transducer.
• At imaging, this is seen as multiple equidistantly spaced linear
reflections and is referred to as REVERBERATION ARTIFACT.

Image showing reverberation artifact
• Transverse US
image
obtained over
a palpable
mass in a
neonate shows
reverberation
artifact.

Image showing reverberation artifact
• Reverberation artifact of the
lung occuring as ultrasound
waves bounce between the
transducer and the pleura. The
pleura is shown as a hyperdense
white line (black arrow). The
reverberation lines (white
arrows) represent repetition of
the pleural line. The distance
between these lines are equal

COMET TAIL
• Comet tail artifact is a form of reverberation.
• In this artifact, the two reflective interfaces and thus sequential
echoes are closely spaced. On the display, the sequential echoes may
be so close together that individual signals are not perceivable.
• In addition, the later echoes may have decreased amplitude secondary
to attenuation; this decreased amplitude is displayed as decreased
width.
• The result is an artifact caused by the principle of reverberation but
with a triangular, tapered shape. 5/23/2017ARTIFACTS AND BIOEFFECTS BY ADEDEWE NUSIRAT 19

Image showing comet tail artifact
• Longitudinal US image
of the gallbladder shows
comet tail artifact
(arrow) caused by
cholesterol crystals in
RokitanskyAschoff
sinuses

RING DOWN ARTIFACT
• Transmitted ultrasound causes resonant vibrations within fluid
trapped between a tetrahedron of air bubbles.
• These vibrations create continuous sound wave that is transmitted
back to the transducer.
• This phenomenon is displayed as a line or series of parallel bands
extending posterior to a gas collection

Image showing ring down artifact
• Left lateral decubitus US
image of the gallbladder
shows air and fluid in the
duodenum causing ring-down
artifact

ARTIFACTS ASSOCIATED WITH ATTENUATION
ERRORS
• When the US beam encounters a tissue that attenuates the sound to a
greater or lesser extent than in the surrounding tissue, the strength of
the beam distal to this structure will be either weaker or stronger than
in the surrounding field.
• Thus, when the US beam encounters a strongly attenuating or highly
reflective structure, the amplitude of the beam distal to this structure
is diminished.
• The echoes returning from structures beyond the highly attenuating
structure will also be diminished. The hypoechoic or anechoic band
occurring deep to a highly attenuating structure is called
SHADOWING.

Image showing acoustic shadowing
• Clean Shadowing (white
arrow) behind a large
gallstone and dirty
shadowing (black arrow)
from an adjacent loop of
bowel.

ACOUSTIC ENHANCEMENT
• Acoustic enhancement is a reciprocal of acoustic shadowing.
• Sound is less attenuated as it passes through a fluid filled structure
causing the image behind the fluid filled structure to appear brighter
than normal or hyperechoic
• It occurs if decreasing of the echo amplitude is not equal with
penetrating depth.
• The attenuation of the ultrasound wave in fluid is much lower as the
attenuation in other tissues, therefore tissues distal to fluid are
enhanced

Image showing acoustic enhancement

RECTIFICATION
• Increase the amount of gel used.
• Use a stand-off pad.
• Reduce the gain.
• Move the position of the transducer
• Acoustic enhancement can be adjusted by decreasing the time-gain
compensation on the console

REFRACTION ARTIFACT
• Refracted ultrasound waves are beams that have been deflected from
their original uniform path and occur as a result of the waves passing
through a medium with a different acoustic impedance.
• Refraction artifact cause spatial distortion and loss of resolution in the
image. In refraction artifact, echoes return from a structure that is
located along a path different than that of the returning beam.
• In other words, a structure that is anatomically located lateral to the
path of the returning beam is interpreted by the machine as being
located in the path of the returning beam. Refraction artifact may
cause structures to appear wider than they actually are or may cause an
apparent duplication of structures.

Image showing refraction artifact
• Transabdominal scan of
first-trimester pregnancy
with a single intrauterine
gestation. Refraction artifact
from the rectus abdominis
muscle causes appearance
of a duplicate yolk sac (red
arrow) adjacent to the
actual yolk sac (blue arrow).

•BIOEFFECTS

ULTRASOUND BIOEFFECT
• Ultrasound is a high frequency mechanical waves that are above the
human hearing range(>20,000 Hz).They are produced by converting
the electrical energy into mechanical energy.
• Biological effects of ultrasound are the potential biological
consequences due to the interaction between the ultrasound wave and
scanned tissues.

TYPES OF BIOEFFECT

THERMAL BIOEFFECT
• This is an ultrasound bioeffect that is related to the production of heat.
Sonic energy is absorbed and converted to heat.
• Whenever ultrasound energy is absorbed by a tissue the heat produced
depends on the intensity of the ultrasound, the time of exposure
and the absorption characteristic of the tissue.
• It is more likely to occur with endocavity probes where the probe is
enclosed within the body & can be almost stationary for several
minutes.

CAVITATION
• In this type of Bioeffect, ultrasound energy creates
mechanical forces that does not depend on thermal effect
such as CAVITATION
CAVITATION
This is the interaction of ultrasound waves with gas bubbles
causing rapid large changes in the bubble size
An increase in temperature and pressure within the bubble
causes mechanical stress in surrounding tissues

• Gas-containing structures (e.g., lungs, intestines) are
most susceptible to the effects of cavitation
• Cavitation may be transient (very rapid expansion
and violent collapse, could cause genetic damage)
and can be stable (bubbles oscillating with sound
beam cause mechanical damage and membrane
rupture)

• However, because of the relatively high viscosity of blood
and soft tissue, significant cavitation is unlikely and
cavitation has not been shown to occur with the ultrasound
exposure commonly used during a diagnostic examination
• Ultrasound has been considered safe, but a probability exists
of potential damage or injury with the use of diagnostic
ultrasound, based on some experimental observations

• A variety of other physical forces may also be produced by ultrasound
energy. Although each of these effects can be demonstrated in vitro.
• Potential bioeffect concerns of US raised in past includes: Autism, lung
hemorrhage, childhood cancer, abnormal hearing.
• No casual relationship yet between clinical applications of diagnostic
US and bioeffect on patient
• Both are potential for exposure

• There is no evidence that any of these physical
phenomena has a significant biological effect on
patients

CONCLUSION
• It is important for radiologist to be aware of the
bioeffects of ultrasound in ensuring that excellence
risk/benefit performance of diagnostic ultrasound is
preserved
• The ability of any examiner to recognize artifacts, use
them to their advantage is very important for image
quality development and for adequate patient care.
This is likely to have a major impact on the overall
diagnosis

REFERENCES
• Hindi A, Peterson C, Barr RG. Artifacts in diagnostic ultrasound; Reports in
Medical Imaging 2013:6 29-48
• Feldman MK, Katyal S, Blackwood MS. US artifacts. Radiographics.
2009;29(4):1179-1189.
• Taljanovic MS, Melville DM, Scalcione LR et al. Artifacts in Musculoskeletal
Ultrasonography; Semin Musculoskelet Radiol 2014;18:3-11
• Acobson JA. Fundamentals of Musculoskeletal Ultrasound. 2nd ed.
Philadelphia; PA: Elsevier Saunders; 2012
• Bushberg JT, Seibert JA, Leidholdt EM, Boone JM. The essential physics of
medical imaging. 2nd ed. # Philadelphia, Pa: Lippincott Williams & Wilkins,
2002; 469-553.#

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