Diagnostic ultrasound ( PDFDrive )

APPENDIX Ultrasound Artifacts: A Virtual Chapter
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A
B
FIG. A.46 Artifactual Lack of Flow. (A) Color Doppler image shows low in the portal vein. (B) When a color image is taken to assess the
common duct, no low is visible in the portal vein. Note the difference in overall gain in image B.
FIG. A.47 Color Direction. Shown in color is a portion of the portal
venous system. Note how the low direction appears to change in the
region of branching, but this is merely a result of the orientation of low
with respect to the mid transducer. Note the aliasing in the posterior
branch of the right portal vein. This is due to the curve of the vein and
change in Doppler angle. 19 (See Chapter 51, Fig. 51.22.)
FIG. A.48 Color Direction as Shown in Recanalized Umbilical
Vein. Flow on color Doppler will sometimes appear to change direction,
but the low needs to be assessed with respect to the transducer in
order to determine if it is in the appropriate direction or not. In this
example, transverse paramedian gray-scale and color Doppler sonograms
show left lobe of liver in a child with cirrhosis and portal hypertension. 19
The recanalized umbilical vein is always lowing in relatively the same
direction out of the liver, but at times, due to tortuosity, appears to
change low direction. Note that the low changes from red (toward the
transducer) to blue (away from the midpoint of the transducer), but at
each interface there is a black region where the Doppler angle is 90.
(See Chapter 51, Fig. 51.28.)