Resources/Protocols
Orbits
Imaging the optic nerve and globe in a bed of bright orbital fat. Fat suppression is the whole battle — without it the nerve and any inflammation disappear — and the sinuses next door make that suppression fail unless you plan for it.
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
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 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 — 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
Ranges, not commandments — field strength, coil and vendor 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 | Robust to 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.