Diagnostic ultrasound ( PDFDrive )

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APPENDIX
Ultrasound Artifacts: A Virtual Chapter
A
B
FIG. A.60 Aliasing Due to Doppler Angle Theta Changes. (A) Velocity obtained in the distal internal carotid artery with angle theta of 60
degrees is higher than that obtained at 44 degrees (arrow). (B) However, the sample angle does not parallel the vessel wall at 60 degrees. Note
central color aliasing in the region of highest velocity (curved arrow). 6 (See Chapter 26, Fig. 26.16.)
FIG. A.61 Aliasing in Pseudoaneurysm. Note the swirling low in a pseudoaneurysm, resulting in a yin-yang appearance. 24 At the midline
border of red and blue, there is a black line where the Doppler angle is 90 degrees. Here the low is perpendicular to the sound beam, and so it
is not detected. At 3 and 9 o’clock positions, there is aliasing within the blue and red areas. Here the Doppler angle is zero degrees with the low
directly toward and away from the transducer, thus appearing with maximal velocity. As the velocity exceeds the selected 35-cm/sec Doppler
velocity range, aliasing results with artifactual opposite direction color signal. (See Chapter 27, Fig. 27.63.)
Click here to see the pseudoaneurysm video clip showing
even more dramatic aliasing in the femoral artery (Video A.21). 24
(See also Chapter 27, Video 27.5.)