Orbits MRI protocol
Imaging the optic nerve and globe in a bed of bright orbital fat. Everything rides on fat suppression. Without it the nerve and any inflammation disappear, and the sinuses next door make that suppression fail unless you plan for it.
By the ScanFlo Editorial Team · Updated
In this section · Protocols
When this study is used
- Optic neuritis or unexplained visual loss.
- Orbital mass, proptosis or thyroid eye disease.
- Suspected optic-nerve glioma or meningioma.
Patient & coil positioning
- Head-first supine in a head coil, eyes closed and still; instruct the patient to fix gaze straight ahead to reduce eye motion.
- Centre on the glabella; immobilise firmly.
- High-channel coil for the resolution small structures need.
Localizer
Three-plane localizer. The dedicated sequences use thin slices and a small FOV over the orbits.
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 T2 fat-sat
AxialPlanning: Parallel to the optic nerve (slightly oblique to the hard palate) on the sagittal, so the tortuous nerve is 'unravelled' along its length. Both orbits.
Why: Optic-nerve signal and orbital contents against suppressed fat.
Coronal STIR
CoronalPlanning: Perpendicular to the optic nerve.
Why: Uniform fat suppression immune to sinus field-inhomogeneity. It is the reliable oedema detector here.
Axial/coronal/sagittal T1 + contrast fat-sat
Multi-planePlanning: Matched thin slices post-gadolinium.
Why: Enhancing optic neuritis or an orbital lesion.
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 | Slice | Notes |
|---|---|---|
| T2 fat-sat axial | ≤3 mm | Along the optic-nerve axis |
| STIR coronal | ≤3 mm | Tolerates sinus inhomogeneity |
| T1 +C fat-sat | ≤3 mm | Enhancement, three planes |
Artifacts & how to fix them
| Artifact | Typical cause | Mitigation |
|---|---|---|
| Black holes (susceptibility) | Air–tissue interface at the sinuses | Use STIR (frequency-independent); smaller voxels |
| Failed spectral fat-sat | Off-resonance near the orbits | STIR instead of spectral fat-sat |
| Eye-motion blur | Roving gaze | Fix gaze straight ahead; eyes closed and still |
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 |
|---|---|---|
| Optic neuritis | Coronal STIR / T2 FS | Swollen, bright optic nerve against dark suppressed fat |
| Optic-nerve glioma / meningioma | T1 +C fat-sat | Enhancing, thickened nerve or sheath |
| Thyroid eye disease | Coronal | Enlarged extraocular muscle bellies sparing the tendons |
Review checklist
- Axials 'unravel' the optic nerve along its length.
- STIR used where spectral fat-sat would fail near the sinuses.
- Post-contrast in three planes for a suspected lesion.
- Eye motion controlled with a fixed forward gaze.
Mistakes that cost repeats
- Spectral fat-sat failing near the sinuses and hiding the nerve.
- Nerve not profiled along its axis, so its length isn't shown.
- Eye motion blurring the thin slices.
- Susceptibility black-holes over pathology on gradient-echo sequences.
Common questions
- Why is fat suppression critical in orbit imaging?
- Orbital fat is bright on both T1 and T2. Without suppression it drowns out the optic nerve and any inflammation, so fat-suppressed sequences (often STIR) are essential to see the nerve at all.
- Why prefer STIR over spectral fat-sat in the orbits?
- The air-filled sinuses beside the orbit distort the local magnetic field, which makes frequency-based spectral fat-sat fail patchily. STIR suppresses fat by inversion time rather than frequency, so it stays uniform in that 'messy' environment.
- How are the axial slices angled for the optic nerve?
- Parallel to the optic nerve (slightly oblique to the hard palate), so the naturally tortuous nerve is straightened out and its full length is shown in fewer slices.
Try it in ScanFlo: Run a spectral fat-sat T2 and a STIR through the orbits and compare the suppression near the sinuses. STIR stays uniform where the spectral sequence breaks up. That is why it is the orbit workhorse. See ScanFlo MRI →