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 settles it: if it's an artefact, the brightening fades there.

Ankle MRI protocol

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. Get the positioning precise, starting with a dorsiflexed foot.

By the ScanFlo Editorial Team · Updated 12 October 2026

In this section · Protocols

Protocols/Musculoskeletal

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

For each sequence below you get the reference line the slice group follows, how much it covers, and why the sequence is in the protocol at all. Plan against the localizer, not by eye.

Axial T1 + PD fat-sat

Axial

Planning: 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

Coronal

Planning: 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

Sagittal

Planning: 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 / reformatted

Planning: Isotropic volume over the joint.

Why: High-resolution cartilage mapping and loose bodies.

Representative parameters

Treat these as ranges. Field strength, coil and vendor all 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 settles it: if it's an artefact, the brightening fades there.

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. See ScanFlo MRI →

← All musculoskeletal studies

← Shoulder MRI protocol Hip MRI protocol (FAI and labrum) →