Diagnostic ultrasound ( PDFDrive )

APPENDIX Ultrasound Artifacts: A Virtual Chapter
e3
ATTENUATION ERRORS
When the ultrasound beam encounters a focal lesion that attenuates
the sound to a greater or lesser extent than the surrounding
tissues, the intensity of the beam deep to the lesion will be either
weaker (shadowing) or stronger (increased through transmission)
than in the surrounding tissues.
Click here to see an explanatory video of attenuation-related
artifacts (Video A.2).
Shadowing
Shadowing results when there is a marked reduction in the
intensity of the ultrasound deep to a strong relector, attenuator,
or refractor. Clean dark shadows will be seen behind calciied
objects when the focal zone is at or just below the structure.
Click here to see an explanatory video of shadowing
(Video A.3).
Water 0.00
Blood
Fat
Soft tissue
(average)
Liver
Kidney
Muscle
(parallel)
Muscle
(transverse)
Bone
0.18
0.63
0.70
0.94
1.00
1.30
3.30
5.00
Air
10.00
0 2 4 6 8 10
Attenuation (dB/cm/MHz)
FIG. A.3 As sound passes through tissue, it loses energy through
the transfer of energy to tissue by heating, relection, and scattering.
Attenuation is determined by the insonating frequency and the nature
of the attenuating medium. Attenuation values for normal tissues show
considerable variation. Attenuation also increases in proportion to
insonating frequency, resulting in less penetration at higher frequencies. 2
(See Chapter 1, Fig. 1.9.)
FIG. A.4 Gallstone With Shadowing. Note the dark, well-deined
shadow. 3 (See Chapter 6, Fig. 6.39C.)