What is the recommended order for an eye X-ray (radiograph) prior to a Magnetic Resonance Imaging (MRI) scan?

Orbital X-ray Prior to MRI: Screening Protocol for Metallic Foreign Bodies

CT of the orbits without IV contrast must be performed prior to MRI when there is any concern for metallic foreign bodies to prevent potentially fatal complications.1

Screening Protocol for Metallic Foreign Bodies Before MRI

When to Obtain Orbital X-ray/CT Prior to MRI

• Orbital radiographs or CT scans should be obtained before MRI for any patient with:
  • Known history of metallic foreign body in the eye or orbit 2
  • Occupational exposure to potential metallic ocular injury (welders, grinders, metalworkers) 2
  • History of orbital trauma with possibility of retained metallic fragments 1
  • Educational or recreational exposure to kinetic metal fragments 2

Imaging Modality Selection

• CT is superior to MRI for foreign body assessment and should be the first-line imaging modality when screening for metallic foreign bodies 1
• CT provides excellent spatial resolution and is advantageous due to:
  • Short scanning time (reducing motion artifacts) 3
  • Superior visualization of foreign bodies 1
  • Natural contrast between bone, soft tissues, air, and fat 3

Safety Considerations

• MRI is contraindicated if metallic foreign bodies are present due to potential movement of ferromagnetic objects in the magnetic field, which could cause severe tissue damage 1
• Even small metallic fragments (as small as 3×1 mm) can be dangerous in an MRI scanner 2
• In a study of 2,626 patients undergoing orbital radiographic screening, 0.65% had evidence of intraorbital metallic foreign bodies, with one patient having no known history of injury 2

After Confirming Absence of Metallic Foreign Bodies

MRI Protocol for Orbital Imaging

• MRI of the orbits without and with contrast is preferred for evaluating:
  • Soft tissue pathology within and around the orbit 1
  • Optic nerve pathology 1
  • Intraocular masses 1
  • Disease within the globe and orbit 1

CT vs. MRI for Orbital Pathology

• CT and MRI are complementary for orbital imaging 3
• CT is preferred for:
  • Acute trauma assessment 1
  • Orbital fractures 1
  • Bone erosion evaluation 1
  • Calcification detection 1
• MRI is preferred for:
  • Soft tissue characterization 4
  • Evaluation of optic neuritis 1
  • Assessment of intraocular masses 1
  • Evaluation of optic pathway tumors 1

Common Pitfalls and Caveats

• Relying solely on patient history can miss metallic foreign bodies, as demonstrated by the case of a welder with no recalled injury who had a metallic foreign body detected on screening 2
• Skipping orbital screening before MRI in high-risk populations can lead to potentially fatal complications 1
• Using inappropriate imaging modality for specific conditions (e.g., using MRI first for trauma or suspected foreign body) 1
• Inadequate communication between ophthalmologist and radiologist can result in suboptimal diagnostic yield 5

By following this systematic approach to orbital imaging before MRI, clinicians can ensure patient safety while obtaining the most diagnostically valuable information for patient care.