Artifacts

Artifacts result from the changes to which the ultrasound beam is subjected when passing through biological tissues. On the other hand, artifacts can also be due to the operator's using faulty scanning technique.

Operators must have a deep knowledge of the different types of artifacts because these can represent not only problem with image interpretation, but also an important source of diagnostic information.

In fact, while some artifacts reduce the diagnostic power of the scan (reverberation, mirror effect, partial volume, doubling, empty tendon artifact), there are others that can be extremely helpful in the differential diagnosis (posterior acoustic enhancement, acoustic shadowing, comet tail, ring down and rain artifacts) [8,14].

Some artifacts can be avoided if the scan is performed in a proper way and the ultrasound equipment is properly set; others are caused by physical characteristics that cannot be changed but they must be understood in order to avoid diagnostic mistakes.

Posterior acoustic enhancement: an increase in echo intensity in tissues posterior to a fluid collection. It may not be detected when the fluid collection is small or spread over a large area (Fig. 1.7).

Acoustic shadowing: a weakening or absence of echoes posterior to a gas collection (high absorption of the beam), a bone surface (high reduction of the beam) or calcification (Fig. 1.8).

Acoustic shadowing artifact on an EFV US scan of the patella

Posterior acoustic enhancement artifact in a multiloculated cyst of Hoffa's fat pad

Lateral acoustic shadowing artifact (arrows) in a tenosynovitis of flexor tendons of a finger

Posterior acoustic enhancement artifact in a multiloculated cyst of Hoffa's fat pad

Lateral acoustic shadowing artifact (arrows) in a tenosynovitis of flexor tendons of a finger

Lateral acoustic shadowing: it occurs when the ultrasound beam is tangential to tissues with different acoustic impedance. The wider the impedance difference, the more visible is the artifact (Fig. 1.9).

Rain effect: a reverberation artifact due to the gain curve. This is an important sign because it occurs when soft tissue overlies a fluid collection. It appears as a band of low-to-medium echoes lying parallel to the transducer and apparently arising from the soft tissue and moving down through the fluid (Fig. 1.10 a,b).

Reverberation artifact: due to its appearance, this artifact is also referred to as "ring-down artifact" and "comet tail artifact". It is caused by the reflection of the ultrasound beam several times back and forth between two nearby interfaces. The multiple echoes thus created reach the transducer before the next pulse transmission and produce multiple copies of the anatomy. Reverberation artifacts are commonly seen at soft tissue-to-gas/bone/ metal interfaces (Fig. 1.11 a,b).

Mirror artifact: a duplication of the image occurring when the beam meets a highly-reflective interface causing reflection and reverberation phenomena.

Partial volume artifact: a noise that occurs when the ultrasound beam is wider than the scanned structure or the structure itself is just partially sectioned so that it is surrounded by tissues with different acoustic impedance. For example, if the beam sections a fluid collection that is narrower than the beam itself, a partial volume artifact will occur.

Fig. 1.10 a,b

a Rain effect artifact on the superficial layer of a multilocular Baker's cyst. b The artifact disappeared after the equipment was correctly set up a Rain effect artifact on the superficial layer of a multilocular Baker's cyst. b The artifact disappeared after the equipment was correctly set up

Reverberation artifacts on a distal ulnar epiphysis (a) and on a phalanx (b)

Reverberation artifacts on a distal ulnar epiphysis (a) and on a phalanx (b)

Duplication and triplication: occurs when the ultrasound beam crosses two tissues with different acoustic impedance. It appears as a duplication or a triplication of the image when the structure measures less than one centimeter and as a deformation, enlargement or interruption when the object is larger.

Empty tendon artifact: a tendon appears homogeneously hypoechoic without the normal fibril-lar echotexture (anisotropy) when using a sectional probe, because the progressive obliqueness of the beam highlights the anechoic appearance of the tendon. This artifact occurs when the ultrasound beam is not perpendicular to the tendon, on both longitudinal and axial scans, and can be avoided by tilting the beam almost perpendicular to the tendon (Fig. 1.12 a,b).

Fig. 1.12 a, b a Anisotropy artifact on a tendon: insertion of supraspinatus with hypoechoic appearance of the tendon caused by incorrect insonation angle. b After a little adjustment of the trans-ducer,the tendon appears normal

Fig. 1.12 a, b a Anisotropy artifact on a tendon: insertion of supraspinatus with hypoechoic appearance of the tendon caused by incorrect insonation angle. b After a little adjustment of the trans-ducer,the tendon appears normal

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  • Facino
    What is partial volume artifact in doppler?
    5 months ago

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