COMMON B-MODE ARTIFACTS

• Anisotropy• Acoustic shadowing• Reverberation• Refractile shadowing• Enhanced through-transmission

ANISOTROPY: TRANSDUCER NOT PERPENDICULAR

Anisotropy is a sonographic artifact, especially relevant in tendons that occurs when the ultrasound beam does not insonate perpendicular to the tendon

TransverseHumerus Humerus

Biceps tendon bright Biceps tendon dark

ANISOTROPY: OBJECT NOT PERPENDICULAR

The probe should be maintained parallel to the tendon. In the event that the object (region of interest) is not perpendicular to the transducer , non uniform pressure can be applied –in this case, pressing down slightly harder at the heel end will ensure that the tendon is perpendicular.

Longitudinal HumerusHumerus

Biceps tendon bright Biceps tendon dark

Heel endToe end

ACOUSTIC SHADOWING

Acoustic shadowing below a dense calcification. As no significant sound is passing underneath the calcification and returning to the transducer, a black ‘shadow’ (S) is observed.

Calcification

S

REVERBERATION (COMET TAIL OR RING DOWN ARTIFACT)

This occurs when there are two very reflective surfaces which are closing spaced as are seen in needles or other metal work. This imae shows a knee being aspirated from the right side. A reverberation artifact is seen below the needle.

Reverberation

REFRACTILE SHADOWING

This is particularly seen with tendons (T). It occurs because the US beam is hitting a structure of a different acoustic impedance at an oblique angle. In this case, the hypo-echoic areas (arrows) should not be mistaken for tenosynovitis.

T

ENHANCED THROUGH-TRANSMISSION

This occurs when there is over-compensation of returning echoes as the sound waves have passed through the liquid filled structure e.g. cyst (C) more quickly than expected. As a result, the area below appears more echogenic (arrows) than usual.

C