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Diagnostic ultrasound ( PDFDrive )

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APPENDIX Ultrasound Artifacts: A Virtual Chapter

e15

Anisotropy

Anisotropy is an artifact caused by structures that are composed

of bundles of highly relective ibers running parallel to each

other, such as tendons and ligaments. If the sound beam hits

the tendon or ligament ibers perpendicular to their length, it

is relected directly back, resulting in an echogenic appearance.

But if the angle of insonation is not perpendicular to the tendon

ibers, the beam is relected away from the transducer, leading

to the generation of an image with artifactual hypoechogenicity

within the tendon.

Click here to see an explanatory video of anisotropy

(Video A.11).

Click here for video of real-time scanning of anisotropy at

supraspinatus insertion (Video A.12).

FIG. A.27 Anisotropy. The insertion of supraspinatus tendon artifactually

appears hypoechoic due to anisotropy.

FIG. A.28 Anisotropy. The peritrigonal region of the white matter

(ellipse) appears relatively echogenic, also called “peritrigonal blush.”

This anisotropic effect artifact occurs because in the trigone region,

the parallel white matter ibers run perpendicular to the incident sound

beam, causing increased relection. 14 The artifact is visible only in the

region of the trigone when the anterior fontanelle is used as a scanning

window.

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