Resources/Protocols
Routine ankle
A complex hinge where the question is almost always the lateral ligaments or the Achilles — and one wrong angle makes a ligament vanish or fake a tear. Precision positioning, starting with a dorsiflexed foot, is the whole game.
When this study is used
- Ankle sprain, chronic instability or suspected ligament tear (ATFL/CFL).
- Achilles tendinopathy or rupture.
- Osteochondral defect or tarsal-tunnel symptoms.
Patient & coil positioning
- Feet-first supine in a dedicated ankle coil, medial malleolus centred.
- Dorsiflex the foot to 90° (toes to the ceiling) against a wedge — this pulls the ATFL taut into a straight line and takes tendons out of the 55° magic-angle orientation.
- Strap the dorsum of the foot; even a wiggled toe blurs the whole ankle.
Localizer
Three-plane localizer. Sagittal from ~10 cm up the distal tibia to the plantar skin; axial showing both malleoli.
Sequence planning
Each sequence below lists how the slice group is positioned — the reference line it follows, its coverage, and why it earns its place in the protocol. Plan against the localizer, not by eye.
Axial T1 + PD fat-sat
AxialPlanning — Angle parallel to the tibial plafond (the flat tibio-talar joint line) — never a straight axial. This single angle catches the ATFL and CFL in one slice. Distal tibia to calcaneus.
Why — Lateral ligaments as dark bands (T1 anatomy, PD FS for oedema of an acute tear).
Coronal PD fat-sat
CoronalPlanning — Parallel to the tibial shaft vertically and to the malleoli horizontally. Posterior talus to navicular.
Why — Talar-dome cartilage (osteochondral defect) and the mortise.
Sagittal STIR / PD fat-sat
SagittalPlanning — Parallel to the long axis of the tibia; malleolus to malleolus.
Why — Full-length Achilles — oedema (tendinopathy) or a gap (rupture).
3D GRE fat-sat (if indicated)
3D / reformattedPlanning — Isotropic volume over the joint.
Why — High-resolution cartilage mapping and loose bodies.
Representative parameters
Ranges, not commandments — field strength, coil and vendor move the numbers. What must not move is understanding why each sits where it does.
| Sequence | Field | Matrix / FOV | Notes |
|---|---|---|---|
| T1 axial | 1.5–3 T | 320 / 12–14 cm | Ligament anatomy |
| PD fat-sat | 1.5–3 T | 320–384 / 12–14 cm | Acute tear oedema |
| STIR sagittal | 1.5–3 T | 256–320 / 14–16 cm | Achilles full length |
| 3D GRE FS | 1.5–3 T | isotropic 0.5 mm | Cartilage, loose bodies |
Artifacts & how to fix them
| Artifact | Typical cause | Mitigation |
|---|---|---|
| Magic angle | Relaxed foot puts tendons at 55° | Dorsiflex to 90°; confirm on T2 (long TE) |
| Fat-sat failure in the heel | Curved heel, air interface | Re-shim on the calcaneus/talus; STIR; plantar sat band |
| Toe-motion blur | Involuntary movement | Strap the dorsum; raise NEX |
| Metal blooming | Screws/plates | High bandwidth; spin echo over GRE |
What am I looking at?
You are not reporting the study, but recognising pathology helps you keep it in the field of view and know when to add a sequence or contrast. How the common findings read on the console:
| Finding | Sequence to check | How it reads |
|---|---|---|
| ATFL tear | Axial T1 | The dark fibula-to-talus band wavy, thickened or missing |
| Achilles rupture | Sagittal STIR | A bright fluid gap in the dark tendon |
| Osteochondral defect | Coronal PD FS | A 'pothole' break in the grey talar-dome cartilage |
Review checklist
- Foot dorsiflexed to 90° — ligaments taut, no magic angle.
- Axial angled to the plafond so ATFL and CFL appear together.
- Achilles shown full length on the sagittal.
- Fat suppression uniform over the curved heel.
Mistakes that cost repeats
- A relaxed, plantarflexed foot faking a tendon tear via the magic angle.
- A straight axial that misses the lateral ligaments.
- Fat-sat failing in the heel and hiding oedema.
- Toe motion blurring the whole study.
Common questions
- Why dorsiflex the foot to 90° for an ankle MRI?
- Two reasons. It pulls the anterior talofibular ligament taut so it images as a straight, assessable band, and it moves the tendons out of the 55° orientation to the magnetic field that causes magic-angle brightening — a common mimic of a tear.
- Why angle the axial to the tibial plafond?
- Angling parallel to the flat tibio-talar joint line captures both the ATFL and the calcaneofibular ligament in the same slice. A straight axial block cuts across them and can make a normal ligament look torn.
- What is the magic-angle artefact?
- When a tendon lies at about 55° to the main magnetic field, it brightens on short-TE sequences (T1/PD) and can mimic tendinopathy or a tear. Checking the T2 sequence — where the brightening fades if it's an artefact — settles it.
Try it in ScanFlo: Scan the ankle plantarflexed, then dorsiflexed to 90°, and watch the ATFL and the tendons change. The taut ligament and the vanished magic-angle signal are exactly why the 90° rule is non-negotiable.