Diagnostic ultrasound ( PDFDrive )

CHAPTER 12 The Retroperitoneum 449
A
B
C
D
FIG. 12.20 Descending Thoracic Aortic Coarctation. (A) and (B) Renal duplex ultrasound of a 15-year-old football lineman presenting with
hypertension. Waveforms from the right and left renal arteries. Waveforms bilaterally have low velocity, low resistance, and a rounded peak, all
indications of a poststenotic waveform. No renal artery stenosis was seen. Waveforms suggested a more proximal aortic stenosis and are what
might be expected with thoracic coarctation. (C) Axial computed tomography (CT) scan shows a severely narrowed thoracic aorta. (D) 3D CT
reconstruction shows severe narrowing of the descending thoracic aorta.
Color Doppler sonography is usually necessary for visualization
of the entire extrarenal portion of the artery. In rare cases,
however, the right renal artery can be seen better without color
Doppler, using the liver as a window. Color Doppler sometimes
makes the site of stenosis obvious because of a color bruit or
increased diastolic velocity, causing a portion of the artery to
remain illed with color throughout the cardiac cycle. At our
facility, we typically set the color scale relatively low to increase
our ability to see the artery. he entire length of the artery oten
is more readily seen with this setting.
We set the wall ilter to the lowest setting allowed by the
manufacturer. If the renal artery is not well seen, color gain is
increased. he very highest color sensitivity is achieved by
increasing gain to the point where color artifact starts to ill the
image and then slightly backing of the gain to remove the artifact.
When necessary, power output is increased to aid visualization.
We set the ensemble packet size (this setting is controlled in
varying ways on diferent machines) to the highest size possible
to increase sensitivity of low detection. Maintaining an adequate
frame rate (>10 frames/sec) is important. We keep the frame
rate adequate by making the color window as narrow as reasonably
possible. We also decrease the line density of the image and the
sector width of the transducer. Our pictures of the renal artery
oten are not “pretty” because of the aliasing and the high color
gain. Our goal, however, is to see the artery. With these settings,
we can see the entire extrarenal portion of the artery in almost
all patients, regardless of size.
We generally use a 5-1 curvilinear transducer. With thin
patients, interrogation from the anterior midline is likely to be
successful. At our facility, however, the lank approach is most