CT Protocol For The Orbit | Beginners Tips

bySagar Srivastava - 0
CT Protocol For The Orbit | Beginners Tips
CT Protocols- Beginners Tips

Protocol for the Orbit

Indications
  • Detections
  • Exclusion or follow up of the orbital space-occupying lesions including tumors, abscesses, etc,
  • and other inflammatory or infiltrative pathologies, trauma, etc.
  • Assessment of intra and extraconal compartments.
Patient Positioning
  • Prone with Head First, with extended neck and chin resting on the chin rest to scan in the Coronal Plane, or
  • Supine with Head First to scan in the Axial Plane.
Topogram Position/Landmark
Lateral
  • 2-3 cm anterior to the forehead in the prone position.
  • Midforehead in the supine position.
Mode of Scanning
Helical

Scan Orientation
1. Posterior to anterior in the prone position.
2. Craniocaudal in the supine position.

_Start Location
  • Level of the anterior margin of the foramen magnum in the prone position.
  • Just above the orbital plates.
_End Location
  • Tip of the nose in the prone position
  • The floor of the orbit in the supine position.
Gantry Tilt
  • As many degrees as required to make the scanning plane perpendicular to the bony palate in the prone position.
  • No tilt in the supine position.
Field of View
Always includes the cavernous sinuses including the anterior ventral part of the brainstem.

Contrast Administration
Intravenous

Volume of Contrast
60-80 mL.

Rate of Injection of Contrast
2-3 mL/sec.

Scan Delay
30-40 sec.

Slice Interval in Reconstruction
1-3 mm.

Reconstruction Algorithm/Kernel
Medium smooth for soft tissues, sharp for the bony orbits.

3D-Reconstructions
MPR, MIP

Comments

  • The neck should be extended as far as possible to minimize gantry tilt.
  • Instruct the patient to close the eyes and maintain in the neutral position without movement during the period of scanning.
  • Sagittal images should be in the plane parallel to the long axis of the orbit.
Criteria of Good Image Quality
  • Symmetric position with the orbital plates overlapping with each other.
  • Absence of the motion artefacts.
  • Absence of beam hardening.
  • Optimal opacification of the cavernous sinuses.
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