ULTRASOUND ARTIFACTS
Ultrasound artifacts are encountered daily in clinical practice and may be a source
of confusion on interpretation. Some artifacts arise secondary to improper scanning techniques
and may be avoidable. Other artifacts are generated by the physical limitations of the technique.
Recognition of artifacts is important, as they may be clues to tissue composition and aid in
diagnosis. The ability to recognize and correct potential ultrasound artifacts is important for
image-quality improvement and optimal patient care (Hindi, 2013).
1) MIRROR IMAGE ARTEFACTS
Mirror image artifact in sonography is seen when there is a highly reflective surface in
the path of the primary beam. It is produced by reflection of the ultrasound waves after they
propagate through a structure and encounter a strong, smooth interface acting as a mirror. The
waves bounce between the mirroring interface and the reflective object, and ultimately return to
the transducer. These signals are displayed as a ‘real' structure. However, because of the signal
delay in arriving back to the transducer, the image representation on the screen is deeper than the
real structure and located at a similar distance from the reflective structure (Ahn et.al, 2013).
Typically, the appearance of mirror images is duplicated structure equidistant from, but
deep to a strongly reflective interface (Hindi, 2013). It is hypoechoic, blurred, and distorted
compared to the image of the real structure, which has been attributed to the absorption and
refraction of the reflected ultrasound signals. Mirror artifacts have been reported in vascular,
abdominal, cardiac, and musculoskeletal ultrasound. Interestingly, a literature search showed that
only 2 cases of mirror images have been reported in obstetrics. Both were observed in early
pregnancy, and the diagnostic challenge was related to an abdominal ectopic/heterotopic
pregnancy.
Reducing this artifact by changing the position and angle of scanning to change the angel
of insonation of the primary ultrasound beam (Ahn et.al, 2013). Also, the use of higher frequency
transducers and a reduction in the energy output (gain), using multiple imaging windows may
eliminate the display of these false images. Avoiding these artifacts is important because a mirror
1
, image artifact may simulate an abnormal pathologic condition such as pseudo thickened bowel
wall or consolidated lung. (Baad et.al, 2017; Sandler et.al, 1987).
A B
Figure 1: examples of mirror image artifacts for (A): reflection of a liver lesion into the thorax.
(B): signals are reflected by the structure (fetal head), and by the reflective surface (posterior uterine
wall and bowel wall) arriving on time to the transducer. Some ultrasound signals bounce back and
forth between the head and the reflective surface finally arriving to the transducer. As they arrive later
than the original signals, they are represented as another structure behind the reflective surface.
2) RING DOWN ARTIFACTS
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. It appears as a solid streak or a series of parallel bands radiating away from
abdominal gas collections. 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 (Avruch, 1985). Spatial compounding should
2
Ultrasound artifacts are encountered daily in clinical practice and may be a source
of confusion on interpretation. Some artifacts arise secondary to improper scanning techniques
and may be avoidable. Other artifacts are generated by the physical limitations of the technique.
Recognition of artifacts is important, as they may be clues to tissue composition and aid in
diagnosis. The ability to recognize and correct potential ultrasound artifacts is important for
image-quality improvement and optimal patient care (Hindi, 2013).
1) MIRROR IMAGE ARTEFACTS
Mirror image artifact in sonography is seen when there is a highly reflective surface in
the path of the primary beam. It is produced by reflection of the ultrasound waves after they
propagate through a structure and encounter a strong, smooth interface acting as a mirror. The
waves bounce between the mirroring interface and the reflective object, and ultimately return to
the transducer. These signals are displayed as a ‘real' structure. However, because of the signal
delay in arriving back to the transducer, the image representation on the screen is deeper than the
real structure and located at a similar distance from the reflective structure (Ahn et.al, 2013).
Typically, the appearance of mirror images is duplicated structure equidistant from, but
deep to a strongly reflective interface (Hindi, 2013). It is hypoechoic, blurred, and distorted
compared to the image of the real structure, which has been attributed to the absorption and
refraction of the reflected ultrasound signals. Mirror artifacts have been reported in vascular,
abdominal, cardiac, and musculoskeletal ultrasound. Interestingly, a literature search showed that
only 2 cases of mirror images have been reported in obstetrics. Both were observed in early
pregnancy, and the diagnostic challenge was related to an abdominal ectopic/heterotopic
pregnancy.
Reducing this artifact by changing the position and angle of scanning to change the angel
of insonation of the primary ultrasound beam (Ahn et.al, 2013). Also, the use of higher frequency
transducers and a reduction in the energy output (gain), using multiple imaging windows may
eliminate the display of these false images. Avoiding these artifacts is important because a mirror
1
, image artifact may simulate an abnormal pathologic condition such as pseudo thickened bowel
wall or consolidated lung. (Baad et.al, 2017; Sandler et.al, 1987).
A B
Figure 1: examples of mirror image artifacts for (A): reflection of a liver lesion into the thorax.
(B): signals are reflected by the structure (fetal head), and by the reflective surface (posterior uterine
wall and bowel wall) arriving on time to the transducer. Some ultrasound signals bounce back and
forth between the head and the reflective surface finally arriving to the transducer. As they arrive later
than the original signals, they are represented as another structure behind the reflective surface.
2) RING DOWN ARTIFACTS
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. It appears as a solid streak or a series of parallel bands radiating away from
abdominal gas collections. 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 (Avruch, 1985). Spatial compounding should
2
