1.1 Core Strengths

MRI is the primary cross-sectional imaging modality for the orbit whenever soft-tissue and neural detail — rather than bone detail alone — is the diagnostic priority. Its core strengths in this region are: superior soft-tissue contrast for distinguishing orbital fat, extraocular muscle, lacrimal gland, and the optic nerve-sheath complex from one another and from pathological tissue; direct multiplanar imaging without the beam-hardening artefact that limits CT near the orbital apex and cavernous sinus; and — critically for this anatomical region specifically — the complete absence of ionising radiation to the lens, relevant given the lens’s radiation sensitivity and the frequency with which orbital imaging is repeated for surveillance. MRI also directly visualises the optic nerve and optic chiasm, structures CT characterises poorly, and reliably distinguishes intraconal from extraconal disease — a distinction with direct surgical-approach implications.

1.2 Limitations and When Dedicated Child Protocols Are Required

This generic protocol establishes the universal orbital MRI backbone appropriate for any indication. It deliberately does not include the specific protocol modifications, semiotics, differential diagnosis, and reporting templates required for individual pathology categories — each of which has its own dedicated child page: orbital tumour and mass lesion, thyroid eye disease/Graves’ orbitopathy, optic neuropathy, globe and intraocular pathology, orbital trauma, orbital inflammatory/infectious disease, and orbital vascular lesions (see Section 11, Related Content, for links to whichever of these have been published). A request specifically naming one of these clinical scenarios should be directed to the relevant dedicated child page rather than relying on this generic protocol alone.

2.1 Standard Indications

The generic protocol is the correct starting point for every orbital MRI indication. Each indication also has, or will have, a dedicated child page documenting pathology-specific protocol modifications, semiotics, and reporting — full pathology-specific detail is deliberately not duplicated here.

Suspected orbital mass or tumour — a palpable, visible, or incidentally identified orbital mass, or proptosis of unclear cause. See the dedicated Orbital Tumour and Mass Lesion child page (where published) for lesion-specific imaging signatures and differential diagnosis.

Thyroid eye disease / Graves’ orbitopathy — proptosis, lid retraction, or diplopia in a patient with known or suspected thyroid dysfunction. See the dedicated Thyroid Eye Disease child page (where published) for extraocular muscle measurement convention and activity assessment.

Suspected optic neuropathy — acute or subacute visual loss with optic nerve dysfunction, whether demyelinating, compressive, or ischaemic in origin. See the dedicated Optic Neuropathy child page (where published) for dedicated nerve-specific sequence protocol.

Globe or intraocular pathology — suspected intraocular mass, retinal or choroidal detachment, or vitreous haemorrhage, particularly where ultrasound is technically limited or inconclusive. See the dedicated Globe and Intraocular Pathology child page (where published).

Orbital trauma — suspected orbital wall fracture, globe injury, retrobulbar haematoma, or (with the specific safety precautions detailed in Section 3.4) suspected non-metallic intraorbital foreign body. See the dedicated Orbital Trauma child page (where published).

Orbital inflammatory or infectious disease — suspected orbital cellulitis, abscess, or idiopathic orbital inflammation. See the dedicated Orbital Inflammatory/Infectious Disease child page (where published).

Orbital vascular lesion — suspected orbital varix, vascular malformation, or carotid-cavernous fistula. See the dedicated Orbital Vascular Lesions child page (where published).

Retrochiasmal or cortical visual field defect — homonymous hemianopia or quadrantanopia. Although the underlying lesion is almost always retrochiasmal (optic tract, optic radiations, or occipital cortex) rather than orbital, and the generic orbital sequence backbone in Section 4 is not the correct starting point for this indication, this presentation is grouped clinically within this Orbit / Visual Disorders cluster rather than split across the Brain and Cranial Nerves clusters, consistent with how neuro-ophthalmology is organised as a clinical discipline. See the dedicated Retrochiasmal / Cortical Visual Field Defects child page (where published) for the whole-brain-focused protocol this indication actually requires.

Ocular motor nerve palsy — diplopia or restricted eye movement from cranial nerve III, IV, or VI dysfunction, at any point along the nerve's course from brainstem nucleus to target muscle. See the dedicated Ocular Motor Nerve Palsy child page (where published) for the full-course protocol spanning brainstem, cavernous sinus, and orbital segments.

Visual hallucinations or colour perception disorder — structural visual phenomena (as opposed to psychiatric hallucination) or acquired colour vision loss, generally reflecting cortical (occipito-temporal) rather than orbital pathology. See the dedicated Visual Hallucinations and Colour Perception Disorders child page (where published).

2.2 Urgent Red Flags Requiring Expedited or Emergency Imaging

Sudden, severe visual loss; clinical suspicion of globe rupture; retrobulbar haematoma with signs of orbital compartment syndrome (severe pain, proptosis, relative afferent pupillary defect, elevated intraocular pressure); and orbital cellulitis with clinical signs of orbital apex or intracranial extension (ophthalmoplegia, reduced consciousness) are vision- and occasionally life-threatening presentations requiring same-day or emergency imaging, and in several of these scenarios (suspected globe rupture, active orbital compartment syndrome) urgent ophthalmological assessment alongside — and sometimes ahead of — imaging.

3.1 Patient Preparation

No specific dietary or medication preparation is required for standard orbital MRI beyond the site’s universal MRI preparation protocol. Patients should be counselled that they will be asked to keep their eyes still, and where possible closed, during acquisition, since even small eye movements degrade the high-resolution sequences this protocol depends on; sedation is occasionally considered in patients (particularly paediatric patients) genuinely unable to remain still, following institutional sedation policy.

3.2 Coil Selection

A dedicated head coil is standard; where available, additional local/surface coil elements specifically covering the orbits improve achievable spatial resolution for the small structures (optic nerve, extraocular muscles, lacrimal gland) this protocol is designed to characterise, at the cost of a smaller field of view that must still be balanced against the need for adequate coverage of both orbits for comparison.

3.3 Why the Orbit Is a Technically Demanding Region — the Underlying Physical Challenges

Three physical characteristics of the orbit, taken together, explain why a generic head or brain protocol is never an adequate substitute for a genuinely dedicated orbital protocol, and why fat-suppression and diffusion technique selection specifically (Sections 4.3 and 4.5) require more deliberate reasoning here than in most other anatomical regions:

• Small absolute structure size. The optic nerve is typically only 3-4 mm in diameter, the extraocular muscles only a few millimetres thick, and the lacrimal gland a comparatively small, flat structure — all considerably smaller than the voxel dimensions a routine brain protocol would use, demanding genuinely high in-plane resolution and thin slices (Section 4.6) rather than an incidental view salvaged from a larger acquisition.
• A uniquely challenging fat/water/air/bone interface geometry. The orbit packs abundant intraconal and extraconal fat immediately adjacent to muscle, nerve, and the globe itself, while sitting immediately anterior to the ethmoid and sphenoid sinuses and lateral/inferior to further paranasal air spaces — a combination of abundant fat (demanding reliable fat suppression for lesion conspicuity) and multiple nearby air-bone interfaces (a classic source of local B0 field inhomogeneity, as introduced generically in the companion Physics of MRI Artefacts child page) that together make fat-suppression technique selection a genuinely consequential decision in this region, not an interchangeable formality (Section 4.3).
• Motion from two independent sources. Beyond the whole-head motion relevant to any brain or head MRI, the orbit is additionally vulnerable to genuine eye movement (saccades, involuntary drift) even when the head itself is perfectly still — a source of motion degradation specific to this anatomical region, and specifically consequential for the longer-readout sequences (heavily T2-weighted 3D imaging, conventional DWI) discussed in Sections 4.2 and 4.5.

3.4 Screening for Intraorbital Metallic Foreign Body — a Safety Priority Specific to This Protocol

Unlike most other anatomical regions, a retained intraorbital metallic foreign body represents a genuine, well-documented risk of permanent, MRI-induced visual loss, established by a landmark 1986 sentinel case report in which a patient with an undetected ferromagnetic intraocular foreign body suffered unilateral blindness following an MR study performed for an unrelated indication. Every patient with a history of ocular trauma, particularly involving high-velocity metal fragments (grinding, hammering metal-on-metal, or similar mechanisms), metalwork occupational exposure, or any injury of unclear mechanism involving the face or eyes, should be specifically and directly questioned about this risk before scheduling, independent of the standard general MRI safety screening questionnaire — reliance on general safety screening alone has been specifically identified as an insufficient safeguard in this population. Where genuine risk factors are present and the history cannot definitively exclude a retained metallic foreign body, dedicated orbital plain radiography (the most widely validated and cost-effective screening approach) should be performed before MRI proceeds, per long-established practice in this specific clinical scenario, rather than proceeding directly to MRI on history alone.

4.1 Mandatory Core Sequences

4.2 Sequence-by-Sequence Technical Rationale

Sequence 1-2 — High-resolution fat-suppressed T2 (axial and coronal). This is the primary sequence for detecting and characterising most orbital soft-tissue pathology: T2 signal increase against a suppressed, otherwise-bright orbital fat background is the single most sensitive generic marker of oedema, inflammation, and many mass lesions in this region. Both planes are mandatory, not merely one supplemented by reformats, because the coronal plane specifically is what allows individual extraocular muscles and the optic nerve-sheath complex to be assessed in cross-section, while the axial plane better demonstrates the nerve’s course and any focal lesion’s craniocaudal and anteroposterior extent. Typical technical parameters at 1.5T/3T are a small (approximately 12-16 cm) dedicated orbital FOV, 2-3 mm slice thickness with minimal or no interslice gap given the small target structures, and the highest in-plane resolution the available SNR and acquisition-time budget allow — a genuinely different, more demanding resolution target than a routine brain T2 sequence.

Sequence 3 — Non-fat-suppressed T1 (axial). Acquired specifically without fat suppression, and specifically before contrast, this sequence serves two distinct purposes: baseline anatomical detail (orbital fat itself provides excellent natural intrinsic contrast against muscle, nerve, and lesion on a non-suppressed T1 sequence, which a fat-suppressed acquisition would deliberately remove), and — diagnostically important — detection of any lesion with intrinsic T1 hyperintensity (haemorrhage, melanin-containing lesion, or fat-containing lesion such as a dermoid) that would otherwise be difficult to distinguish from genuine post-contrast enhancement if only fat-suppressed sequences were reviewed.

Sequences 4-5 — Post-contrast fat-suppressed T1 (axial and coronal). Enhancement pattern is the primary discriminator for most orbital mass and inflammatory pathology, but orbital fat is itself T1-bright, meaning enhancing tissue against a non-suppressed fat background is frequently difficult to appreciate confidently — fat suppression on the post-contrast sequence is therefore not an optional refinement but a genuine prerequisite for reliably detecting and characterising enhancement in this specific anatomical region. The specific fat-suppression technique used for this sequence is a consequential technical decision in its own right, addressed in full in Section 4.3.

Sequence 6 — DWI with ADC map. Diffusion restriction supports the differential diagnosis of several orbital entities, but conventional single-shot EPI DWI performs genuinely poorly in the orbit for physical reasons specific to this region, discussed in depth in Section 4.5, which also documents the modern technical alternatives now preferred here.

Sequence 7 — Whole-brain T2/FLAIR extending through the chiasm. Because a meaningful proportion of orbital and optic nerve pathology (demyelinating disease, chiasmal or retrochiasmal compressive lesions, and perineural tumour spread intracranially) genuinely extends, or has its full clinical significance determined, by structures beyond the orbit itself, coverage that stops abruptly at the orbital apex is incomplete: this sequence deliberately extends coverage posteriorly through the optic chiasm and, where relevant, the optic tracts.

4.3 Fat-Suppression Technique Selection — A Full, Weighting-by-Weighting Rationale

Fat-suppression technique in the orbit is not a single, interchangeable choice applied uniformly across the whole protocol: the correct technique differs by weighting, and the reasoning behind each choice is worth making fully explicit, both because the orbit’s specific fat/air/bone geometry (Section 3.3) makes technique selection more consequential here than in many other regions, and because getting this wrong is a genuinely common, avoidable source of diagnostic-quality loss.

Pre-contrast T1 (Sequence 3): no fat suppression. As explained in Section 4.2, this sequence is deliberately left non-fat-suppressed, both to preserve the natural anatomical contrast fat provides and to allow confident identification of any lesion with genuine intrinsic T1 hyperintensity, which a fat-suppressed acquisition would obscure or, worse, could be misread as enhancement if only post-contrast fat-suppressed images were available for comparison.

Fat-suppressed T2 (Sequences 1-2): STIR vs spectral/chemical-shift-selective (CHESS/SPIR) vs Dixon. Three broad technique families are available for this weighting, and they are not interchangeable:

• STIR nulls fat based on its short T1 relaxation time, a mechanism that depends on B0 field strength but is inherently insensitive to B0 inhomogeneity — meaning STIR remains reliable even where local field homogeneity is genuinely compromised. Its major drawback is a lower intrinsic SNR than spectral techniques, and — because it nulls any tissue with a sufficiently short T1, not fat specifically by chemical identity — a genuine risk of also suppressing other short-T1 tissue.
• Spectral (CHESS) or hybrid spectral-inversion (SPIR/SPAIR) fat suppression targets the fat resonance frequency directly, offering higher SNR than STIR, but is directly, meaningfully degraded by local B0 inhomogeneity — precisely the vulnerability the orbit’s proximity to the ethmoid and sphenoid sinuses (Section 3.3) makes genuinely relevant here.
• Dixon-based (chemical-shift-encoded) fat suppression computes separate water-only and fat-only images from multiple echoes rather than attempting to suppress fat signal directly during acquisition — a mechanism inherently more robust to B0 inhomogeneity than spectral techniques, while typically preserving higher SNR than STIR.

A direct comparative study across head and neck MRI found multipoint Dixon technique produced better image quality and more uniform fat suppression, at a shorter scan time, than both STIR and spectral presaturation with inversion recovery for gadolinium-enhanced T1-weighted imaging specifically. An orbit-specific comparative study in thyroid eye disease similarly found that Dixon-T2WI at 3T outperformed conventional fat-suppression imaging. Taken together, this evidence base supports Dixon-based fat suppression, where available, as the preferred default technique for fat-suppressed T2 imaging in this specific anatomical region, with STIR retained specifically as the fallback for situations of genuinely severe local field inhomogeneity or where Dixon acquisition is not locally available.

Post-contrast fat-suppressed T1 (Sequences 4-5): spectral/Dixon only — STIR is contraindicated. This is the one fat-suppression decision in this protocol with a genuinely absolute, rather than comparative, answer: STIR must never be used after gadolinium administration. Because STIR’s fat-nulling mechanism depends on T1 alone, and gadolinium enhancement works specifically by shortening the T1 of enhancing tissue, genuinely enhancing tissue can fall into, or near, the same short-T1 range STIR is designed to null — meaning STIR can directly suppress the very enhancement the sequence is intended to demonstrate. Post-contrast fat suppression in this protocol therefore always uses either spectral/SPIR or Dixon-based technique, with Dixon preferred as the default where locally available.

4.4 3D Heavily T2-Weighted Sequences for the Optic Nerve-Sheath Complex

A 3D heavily T2-weighted sequence (CISS/DRIVE/FIESTA-C-family) may be added specifically where detailed optic nerve-sheath anatomy is required beyond what Sequences 1-2 provide. Because this sequence family is inherently sensitive to CSF pulsation and, given its typically longer acquisition time, to eye-movement motion, it benefits specifically from the patient-coaching approach discussed in Section 8.1.

4.5 DWI Technique — Why Conventional Single-Shot EPI Under-Performs in the Orbit, and What Replaces It

Conventional single-shot echo-planar imaging (ss-EPI) performs genuinely poorly in the orbit for reasons directly traceable to the region-specific physical challenges introduced in Section 3.3. Its long readout duration makes it inherently prone to susceptibility-related geometric distortion and signal loss precisely at the air-bone-tissue interfaces the orbit is full of, while the optic nerve’s small diameter relative to ss-EPI’s typically coarse spatial resolution compounds the problem with genuine partial-volume effects.

Two modern technical alternatives directly address this:

• Readout-segmented EPI (rs-EPI, commercially RESOLVE and similarly-named vendor implementations) divides k-space acquisition into multiple shorter-readout segments, directly shortening echo spacing and substantially reducing susceptibility-related distortion, at the cost of a longer overall acquisition.
• Reduced field-of-view (rFOV, “zoomed” or “inner volume”) DWI restricts the excited and encoded volume specifically to the orbit rather than the whole head, directly enabling higher spatial resolution for the same acquisition time.

A direct comparative study of these techniques for optic nerve DWI found reduced-FOV DWI showed image-quality improvement over conventional single-shot EPI for a matched acquisition time, while readout-segmented EPI showed overall superior image quality at the cost of a substantially (approximately 47%) longer scan time. Where either technique is locally available, one should be preferred over conventional ss-EPI DWI for orbital and optic nerve imaging specifically.

4.6 Field of View and Resolution Considerations

Because the orbit contains multiple small, closely apposed structures that dedicated child protocols depend on characterising in detail, a genuinely small, dedicated field of view is essential. As a practical reference point, a dedicated orbital FOV in the range of 12-16 cm, combined with 2-3 mm slice thickness and minimal interslice gap, is a reasonable starting point for Sequences 1-5 at both 1.5T and 3T.

4.7 Contrast Strategy

Gadolinium contrast is mandatory for suspected mass lesion, inflammatory/infectious disease, and most optic neuropathy presentations. Standard macrocyclic GBCA dosing applies, per site-wide policy documented on the Contrast Media in MRI master page.

4.8 Conditional and Advanced Sequences — Additional Notes

MR angiography or venography is added specifically where a vascular lesion is suspected. Extended coverage into the paranasal sinuses or brain more broadly is added where the clinical question specifically requires it.

5.1 Motion and Eye-Movement Artefact Management

Clear pre-scan patient coaching, specifically to fix gaze on a single point or keep the eyes gently closed throughout acquisition, measurably improves image quality, particularly for the longer-readout sequences discussed in Sections 4.4-4.5.

5.2 Managing Susceptibility Artefact Near the Sinuses and Orbital Apex

Careful shimming specifically over the orbital volume, and preference for Dixon-based or, as a fallback, STIR fat suppression over spectral/CHESS/SPIR technique specifically in this region (Section 4.3), are the primary practical mitigation strategies.

5.3 Balancing Resolution, SNR, and Acquisition Time

Parallel imaging acceleration is frequently used specifically to help achieve adequately thin slices and fine in-plane resolution within a tolerable scan time for this anatomically demanding region.

6.1 Compartment-Based Localisation

A structured, compartment-based approach — intraconal vs extraconal vs conal vs lacrimal gland vs globe/intraocular — is the standard first step in generating an orbital differential diagnosis.

7.1 Structured Reporting Template

Laterality: unilateral vs bilateral involvement. Compartment: intraconal / extraconal / conal / lacrimal / globe. Lesion or finding description: location, size, signal characteristics, enhancement pattern. Optic nerve-sheath complex: explicitly assessed. Extraocular muscles: explicitly assessed. Bony orbital walls: explicitly assessed. Comparison with prior imaging: stable/progressed/new.

7.2 Mandatory Reporting Elements

Every orbital MRI report should explicitly comment on the optic nerve-sheath complex and extraocular muscles, even when the primary clinical question concerns a different structure.

8.1 Sequence Order and Patient Comfort

Briefing the patient clearly before the table moves into the bore measurably improves compliance, particularly before the longer-readout sequences in Sections 4.4-4.5.

8.2 Coil and Positioning Considerations

Confirm genuinely symmetric, centred positioning of both orbits before beginning acquisition.

8.3 Common Avoidable Errors

Using an incidental orbital view salvaged from a larger brain FOV; using STIR fat suppression on a post-contrast sequence (an absolute error, not a quality trade-off); defaulting to conventional single-shot EPI DWI without considering the alternatives in Section 4.5; omitting explicit optic nerve/muscle assessment; and proceeding directly to MRI without foreign-body screening in a relevant trauma history.

11.1 Evidence Gaps

• Optimal intraorbital metallic foreign body screening strategy remains genuinely debated (Section 3.4).
• Optimal balance between spatial resolution and acquisition time is not fully standardised.
• Direct head-to-head comparative evidence for Dixon vs STIR specifically in the orbit remains more limited than for the wider head and neck region; current orbit-specific evidence focuses substantially on thyroid eye disease.
• Readout-segmented vs reduced-FOV DWI trade-off has not been extensively validated across orbital pathology types beyond optic neuritis specifically.

A. Guidelines / Consensus / Society Recommendations

C. Important Prospective / Original Studies

E. Landmark Historical References