Diagnostic ultrasound ( PDFDrive )

CHAPTER 51 The Pediatric Liver and Spleen 1749
A1
A2
B
FIG. 51.18 Biliary Rhabdomyosarcoma in 3-Year-Old
Child. (A1) and (A2) Transverse and longitudinal sonograms of
porta hepatis in child with intermittent jaundice and abdominal
pain show an intraductal mass enlarging the common bile duct
between the cursors. (B) Coronal T1-weighted magnetic resonance
image demonstrating the intraductal mass (arrow) and secondary
biliary ductal dilation.
ultrasound coupled to a spectral or color Doppler display are
discussed in Chapter 1.
Most of the abdominal vessels studied in children have a low
low velocity. herefore the wall ilter should be as low as possible,
preferably at 50 Hz or less. he pulse repetition frequency should
be as low as possible for the same reason, unless there is
aliasing.
here are great advantages to color mapping (Video 51.7)
because entire segments of vessels are seen at a glance (e.g.,
portosystemic collateral veins in portal hypertension or stenoses
of vessels). When examining small vessels in children, motion
may produce lashes or dots of color artifact. Pulsed Doppler
sampling of such doubtful signals distinguishes these artifacts
from low signals. Because of their small body size and ready
access to the Doppler beam, children are particularly suited to
color, power, and pulsed Doppler abdominal examinations.
New Doppler techniques that are more sensitive to low-velocity
low, which was previously obscured by noise or “signal clutter,”
have the potential to reveal isoechoic lesions in the liver, including
metastases. Superb microvascular imaging shows third- and
fourth-order branches of the portal veins 56 (Fig. 51.21, Video
51.8, Video 51.9). SMI takes the same returning ultrasound signal
and declutters the information to depict very-low-velocity low.
Intravenous Doppler contrast agents, various formulations of
microbubbles, are now approved by the U.S. Food and Drug
Administration (FDA) for cardiac and liver use in the United