Ankle and Foot 47 - Department of Radiology - University of ...

47 Ankle and Foot 2241 47
Figure 47-44. Importance of weight-bearing view.
A, Non–weight-bearing lateral view, obtained
portably. On this image, the long axis of the talus
(dashed white line) is parallel to the long axis of the
first metatarsal (dashed black line), suggesting normal
alignment. B, Same patient as in A, obtained upright at
a follow-up clinic visit 3 months later. On this weightbearing
lateral view, the long axis of the talus (solid
white line) is now angled downward relative to the
first metatarsal (solid black line). This indicates that
the patient has a nonrigid flat-foot deformity (pes
planus), demonstrable only with weight bearing.
A
B
A
B
C
Figure 47-45. A, The patient is positioned supine on the CT table
with her legs straight, feet together, toes pointing to the ceiling.
B, Example of a foot holder we built to help keep patients’ feet
centered in the CT scanner in neutral position. C, In lieu of a
dedicated foot holder, we have used a box.
metal, including it in the scanning field-of-view (FOV)
does not cause excessive streak artifacts and does not
increase the radiation exposure to organs in the torso.
Securing the patient’s feet to a dedicated holder (Fig.
47-45B) or to a box (Fig. 47-45C) helps to hold the feet in
neutral position and to prevent motion during the scan.
Scout views are obtained in both the AP and lateral
projections (Fig. 47-46). The scanning FOV should be
set wide enough to include both the right and left lateral
malleoli; for most patients this is less than 25 cm. The
coverage should begin superior to both syndesmoses
and extend below the calcanei. In cases of pilon fractures,
which are comminuted fractures involving the plafond,
coverage is extended superiorly to include more of the
distal tibia. We typically scan using 120 kVp at less than
200 mA.
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9/9/2008 5:34:22 PM