Diagnostic ultrasound ( PDFDrive )

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APPENDIX
Ultrasound Artifacts: A Virtual Chapter
BEAM PROFILE–RELATED ARTIFACTS
Frequently echoes are seen within what should be an anechoic
structure. his can occur as a result of side lobe or grating lobe
artifacts in which information from the side of the image projects
centrally, or because of partial volume averaging (owing to the
thickness of the ultrasound beam (resolution in the Z plane).
Side Lobe and Grating Lobe Artifacts
Click here to see an explanatory video of side lobe artifact (Video
A.17).
FIG. A.39 The ultrasound beam is not a narrow straight line but has
a complex proile that varies depending on the type and shape of the
transducer. Although most of the energy generated by a transducer is
emitted in a beam along the central axis of the transducer (A), some
energy is also emitted at the periphery of the primary beam (B and C).
These are called “side lobes” (B) or “grating lobes” (C) and are lower
in intensity than the primary beam. Side lobes or grating lobes may
interact with strong relectors that lie outside of the scan plane and
produce artifacts that are displayed in the ultrasound image. 2 They are
more evident when the misplaced echoes overlap an expected anechoic
structure. (See Chapter 1, Fig. 1.28.)
FIG. A.40 Side or Grating Lobe 1. Transverse image of the gallbladder
reveals a bright internal echo (A) that suggests a band or septum within
the gallbladder. This is a side lobe artifact related to the presence of a
strong out-of-plane relector (B) medial to the gallbladder. The low-level
echoes in the dependent portion of the gallbladder (C) are also artifactual
and are caused by the same phenomenon. Side lobe and slice thickness
artifacts are of clinical importance because they may create the impression
of debris in luid-illed structures. 2 (See Chapter 1, Fig. 1.29.)