GUIDE TO MR IMAGING OF THE FOOT &
ANKLE
SNeedell@BocaRadiology.com
www.bocaradiology.com
www.bocaradiology.com
For purposes of MR imaging, the foot is divided into two exams:
1. Ankle/Hindfoot/Midfoot (everything behind metatarsals)
2. Forefoot (metatarsals & toes)
MRIs for tendons & ligaments use "Ankle" protocol unless AOI is specifically in the forefoot.
"Foot" MRIs should be treated as Ankle/Hindfoot/Midfoot MRIs until proven otherwise.
Exceptions: For neuroma, mass, stress fracture,
or osteomyelitis in the forefoot- do a dedicated forefoot (metatarsals
and toes) exam.
• Plantar fibroma & LisFranc fractures- use forefoot protocol but center
over area of interest in the midfoot.
-only image one foot at a time
ANKLE/HINDFOOT/MIDFOOT PROTOCOL
Sagittal T1 & STIR
Axial T1 & fat sat T2 (or T2 without fat sat if low field)
Coronal fat sat T2 (or STIR)
-Ankle tendons and ligaments are best imaged with the foot plantar flexed 15-30°. So don't use the chimney in the coil. Position the calcaneus in the middle of the coil and the relaxed foot will fit comfortably in the coil at the correct degree of plantar flexion.
-Prescribe Sagittals off an axial scout at the level of the tibiotalar joint (see figure below). Angle slices through the long axis of the hindfoot by bisecting the Achilles tendon with the middle third of the anterior margin of the distal tibia:
-Inferiorly, axial sections through the ankle must include the fifth metatarsal base.
-Superiorly, axial images should include about 3 cm above the level of the ankle joint. If the exam is specifically to evaluate the Achilles tendon, make sure to add enough axial slices to include the Achilles myotendinous junction.
-Axial images can be angled slightly with the tibiotalar joint, but it's better to do straight axials than to oblique too much (see figure below).
FOREFOOT MRI
FOREFOOT MRI
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- Place patient prone to image forefoot whenever possible
- Forefoot images should be prescribed off the level of the MTP joints.
- Prescribe longitudinal and sagittal slices off a transverse scout.
- Look at the sagittal or longitudinal STIR images before you prescribe the transverse sections so that you can be sure you've covered all the pathology (bright signal on STIR = edema = pathology).
The longitudinal Rx should bisect the 2nd & 3rd metatarsal heads (see figures below):
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- Always mark region of concern with a Vitamin E tablet.
- Use small FOVs
Longitudinal T1 (1mm) & STIR (3/0.5mm)
Transverse T1 & STIR (4/1 mm)
Sagittal T1 & STIR (4/1 mm)
If the patient has had prior neuroma surgery then add a transverse post gad T1W (with fat sat if available)
Plantar fibroma & LisFranc fractures of midfoot
If the area of concern is isolated to the midfoot, such as plantar fibroma, then center the coil over the area of interest & use forefoot protocol.
MATRIX:
If you have enough signal, use 512 x 256 for T1W sequences. STIR & T2 fat sat can be 256x192.