Orbits protocol (MRI)

Orbits protocol is an MRI protocol comprising a group of MRI sequences as a useful approach to routinely assess the orbits and their related conditions.

Note: This article is intended to outline some general principles of protocol design. The specifics will vary depending on MRI hardware and software, radiologist's and referrer's preference, institutional protocols, patient factors (e.g. allergy) and time constraints.

Sequences

A standard screening protocol might look like:

• T1-weighted
  • plane: axial with FOV for the orbits and coronal (from chiasm through the orbits)
  • sequence: fast-spin echo (T1 FSE)
  • purpose: anatomical overview
• T2-weighted (fat-saturated)
  • plane: axial
  • sequence:  fat-saturated T2 FSE
  • purpose: highlight inflammatory changes
• STIR / T2-weighted Dixon
  • plane: coronal (from chiasm through the orbits)
  • sequence:  STIR or T2WI Dixon
  • purpose: highlight inflammatory changes
• postcontrast sequences (fat-saturated)
  • plane: axial with FOV for the orbits and coronal (from chiasm through the orbits)
  • sequence: postcontrast fat-saturated fast-spin echo (T1 FSE). 
    • Gadolinium-based contrast agents (GBCAs) for CNS :
      • gadoterate meglumine (Dotarem®)
      • gadobutrol (Gadavist®)
      • gadopentetate dimeglumine (Magnevist®)
      • gadobenate dimeglumine (MultiHance®)
      • gadodiamide (Omniscan®)
      • gadoversetamide (OptiMARK®)
      • gadoteridol (ProHance®)
    • all these GBCAs are approved by FDA at identical administered total doses of 0.1mmol/kg body weight
  • purpose:  given the relatively large amount of fat in the orbits, its suppression is essential when assessing abnormal enhancement in the  characterization of tumors or inflammatory/infective change 
• diffusion-weighted imaging (DWI)
  • plane: axial
  • sequence: DWI: B=0, B=1000 and ADC 
  • purpose: multiple possible purposes (from the identification of ischemic stroke to the assessment of active demyelination)