Page 42 - Feline diagnostic imaging

References 35
make‐up of the reflective surface. Unfortunately, informa- evaluating the liver at the lung–diaphragm junction, the liver
tion deep to the reflective surface is lost. This artifact is most may appear to be within the thoracic cavity [1, 5]. Mirror
notable with urinary calculi, renal mineralization, or gas image artifacts are produced by rounded, strongly reflective
within the gastrointestinal (GI) tract. interfaces that cause part of the beam to be reflected back
Distal enhancement or acoustic enhancement (Figure 3.7b) into the organ (liver in this example). The ultrasound
is the exact opposite of acoustic shadowing. This is an appar- machine assumes the sound travels in a straight line and does
ent increase in amplitude of returning echoes that lie beyond not account for the reflected portion. As a result, the echo
weakly attenuating reflectors [3, 5, 11]. This would be most return time is increased, resulting in misplacement of the
commonly seen beneath fluid‐filled objects such as the uri- echo locations [4]. This artifact can be problematic when try-
nary bladder, gallbladder, or cystic structures in parenchymal ing to use ultrasound for diaphragmatic hernias.
organs. It is often useful in helping to determine if a very Slice thickness artifacts (Figure 3.7e) occur if the beam is
hypoechoic or anechoic structure is fluid or solid in partially within a weakly attenuating structure and a
character. strongly reflective structure because the echoes will be
Reverberation artifact occurs when a highly reflective averaged [3, 5]. This is typically seen in the gallbladder or
surface is encountered resulting in reflection of the sound urinary bladder, resulting in the appearance of material
wave multiple times between the transducer and the inter- referred to as pseudo‐sludge. The surface of pseudo‐sludge
face and appears as multiple hyperechoic foci that occur at is usually curved and that of real sludge is usually flat [3].
regular intervals [1, 5, 6, 11]. This can occur internally with Edge shadowing (Figure 3.7f) occurs at the margins of
the lung surface during thoracic imaging or with gas in the rounded structures due to refraction or bending of the ultra-
GI tract or may be seen when there is poor transducer cou- sound beam as it encounters the rounded edge, leading to a
pling with the skin. The distance between the hyperechoic void of echoes at the edge of the round reflector [12]. This is
foci will be symmetric and equal to the distance between commonly seen adjacent to the gallbladder, kidney, trans-
the transducer and the reflective surface. verse images of the small intestine, and urinary bladder.
Comet tail artifacts (Figure 3.7c) are a type of reverbera-
tion artifact. These are called ring down artifacts. With
comet tail artifacts, the reflective interfaces are close 3.9 Summary
together, resulting in reverberation of the sound. This
causes a thinly spaced or tapering triangular hyperechoic Ultrasound is an exciting diagnostic tool that has made
band to develop at the reflective interface [5, 11]. This arti- much progress in recent years. As the quality of the image
fact is seen at the pleural surface of an irregular lung or produced by current ultrasound machines has improved
with gas bubbles in the GI tract. dramatically, the price of this technology has come down.
Mirror image artifact (Figure 3.7d) will result in errors in This makes this modality an affordable and invaluable
interpreting the location of an organ. For example, when diagnostic tool.

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