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

47 Ankle and Foot 2247 47
ankle tendons and is also useful for the ankle ligaments
and syndesmosis.
Oblique axial slices (see Fig. 47-52C) are set up off the
same straight sagittal reference image as previously but are
oriented parallel to the long axis of the metatarsals. This is
our primary plane for imaging the tarsal bones, and the
slices should include all of the tarsals from the back of the
calcaneus through the metatarsal bases.
There are at least three ways to orient slices in the
coronal plane. Least commonly used is the straight coronal
plane (see Fig. 47-52D). These slices are set up off a sagittal
reference image, are oriented roughly perpendicular to the
plantar aponeurosis, and are used primarily when evaluating
the plantar fascia.
Oblique coronal slices (see Fig. 47-52E) are used much
more often then straight coronal slices and are set up off
the same sagittal reference slice as previously. The oblique
coronal slices are oriented perpendicular to the posterior
facet of the subtalar joint. (See Fig. 47-7 to review the
anatomy of the posterior facet of the subtalar joint.) This
is a good secondary plane to evaluate the tendons and
tarsals, and the slices should include all of the hindfoot
and midfoot.
Mortise coronal slices (see Fig. 47-52F) are set up off
a straight axial reference image taken through the top of
the talar dome. This axial reference image can be either an
axial scout image or one of the straight axial slices from a
preceding acquisition. The slices are aligned parallel to a
line drawn between the medial and lateral malleoli. This
is one of the primary planes used for imaging osteochondral
lesions of the talus (OLTs), and it is also good for
looking at the malleoli and the ankle ligaments.
Mortise sagittal slices (see Fig. 47-52G) are set up off
the same straight axial reference image as previously, and
the slices are oriented perpendicular to the mortise coronal
slices. This, rather than the straight sagittal plane, is the
survey plane we use for OLTs.
With regard to the forefoot, we have found that there
is come confusion among technologists as to the coronal
and axial planes, and to avoid potential ambiguity we refer
to the short-axis and long-axis planes relative to the metatarsals.
Short-axis images are obtained off a straight sagittal
reference image and are oriented perpendicular to the long
axis of the metatarsals (see Fig. 47-52H). This yields a series
of short-axis slices that cut transversely through the metatarsals
and phalanges, an example of which is shown in
Figure 47-52I. This is a good plane to evaluate for bone
marrow edema in the forefoot.
Long-axis images are obtained off a short-axis reference
image through the metatarsals and are oriented to
include all five, or at least four, metatarsals on individual
slices (see Fig. 47-52I). This is the best way to obtain a
side-by-side comparison of the metatarsals and is used
when evaluating for stress fractures or osteomyelitis.
Figure 47-52. The standard imaging planes we use for MRI of the foot and ankle. The white lines represent the orientation, but not the actual
number or spacing, of the slices. A, Straight sagittal slices are set up off an axial scout image and are oriented parallel to the long axis of the foot.
(Using a cushioned foot holder, as in Figs. 47-49 and 47-50, helps keep the foot in place relative to the scanner.) This is our survey plane, and it is
the first plane acquired in all of our ankle and foot MRI protocols. Most of the other imaging planes are acquired relative to a straight sagittal
reference image. B, Straight axial slices are set up off a straight sagittal reference image, either a sagittal scout image or one of the midsagittal
slices acquired in A. The straight axial slices should be roughly perpendicular to the long axis of the tibia and, if the ankle is held in the neutral
position, will be roughly parallel to the bottom of the foot. The slices should begin well proximal to the level of the malleoli and extend distal to
the calcaneus. This is our primary plane for imaging the ankle tendons. C, Oblique axial slices are set up off the same straight sagittal reference
image as in B and are oriented parallel to the long axis of the metatarsals. This is our primary plane for imaging the tarsal bones, and the slices
should include all of the tarsals from the back of the calcaneus through the metatarsal bases. (Although the field of view can be enlarged to
include the metatarsals and phalanges in their entirety, we prefer to use the short-axis and long-axis planes delineated in H and I when the
clinical question involves the forefoot.) D, Straight coronal slices, set up off a sagittal reference image, are used primarily when evaluating the
plantar fascia and should be oriented roughly perpendicular to the plantar aponeurosis. E, Oblique coronal slices are used much more often then
straight coronal slices and are set up off the same sagittal reference slice as in B. The oblique coronal slices are oriented perpendicular to the
posterior facet of the subtalar joint. (Refer to Fig. 47-7 to review the anatomy of the posterior facet of the subtalar joint.) This is a good secondary
plane to evaluate the tendons and tarsals, and the slices should include all of the hindfoot and midfoot. F, Mortise coronal slices are set up off a
straight axial reference image taken through the top of the talar dome. This axial reference image can be either an axial scout image or one of the
straight axial slices acquired in B. The slices are aligned parallel to a line drawn between the medial and lateral malleoli. This is one of the
primary planes used for imaging osteochondral lesions of the talus (OLT), and it is also good for looking at the malleoli and the ankle ligaments.
G, Mortise sagittal slices are set up off the same straight axial reference image as in F, and the slices are oriented perpendicular to the mortise
coronal slices. This is the survey plane for OLT. (The marker [m] indicates the site of maximal tenderness.) With regard to the forefoot, we prefer
to refer to the short-axis and long-axis planes, rather than coronal or axial, to avoid ambiguity. H, Short-axis images are obtained off a straight
sagittal reference image and are oriented perpendicular to the long axis of the metatarsals. A short-axis image through the metatarsals is shown in
I. I, Long-axis images are obtained off a short-axis reference image through the metatarsals and are oriented to try to include all five, or at least
four, metatarsals on individual slices. This is the best way to obtain a side-by-side comparison of the metatarsals and is used when evaluating for
stress fractures or osteomyelitis.
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