CT orbits (protocol)

Last revised by Henry Knipe on 8 Jul 2023

CT orbits (computed tomography of the orbits) involves the visualization of bony and soft tissue structures of the orbits. This examination is most commonly performed as a non-contrast scan or reconstructed from other examinations such as a CT head/face. Contrast-enhanced scans are utilized depending on clinical indications, initial assessment, and the radiologist's consultation 1.

Note: This article is a general guideline for CT imaging of the orbits.

A standard CT orbits protocol might follow as such:

A CT orbit exam aims to evaluate the following pathologies 2:

  • congenital/pediatric orbital anomalies

  • orbital trauma including fractures, penetrating or blunt trauma

  • orbital inflammations or infections

  • orbital neoplasms

  • orbital mass or lesions

CT is considered the optimal form of imaging for evaluating orbital pathologies in a trauma setting 3. The purpose of a non-contrast orbit CT predominantly includes the evaluation of bony structures for fractures and any blunt or penetrating trauma. Contrast-enhanced CT examinations are generally requested to better evaluate soft tissue structures in emergency imaging and in the circumstance the patient is unable to obtain a magnetic resonance imaging (MRI) orbits which is generally preferred 1.

  • patient preparation

    • remove all radiopaque jewelry and dental prosthetics

  • patient position

    • head first

    • supine with arms by their side

  • scout

    • anterior-posterior and lateral

    • C2 to vertex

  • scan extent

    • hard palate to frontal sinus

  • scan direction

    • caudocranial

  • scan geometry

    • slice thickness: 0.6 mm

    • slice increment: 0.6 mm

  • respiration

    • suspended

  • contrast medium

  • scan delay

    • contrast-enhanced CT: scan 70 - 80 seconds post injection

  • multiplanar reconstructions

    • 2 mm axial, coronal and sagittal bone reformats

    • 3 mm axial, coronal and sagittal soft reformats

Although conventional multi-slice CT imaging is the preferred imaging method for visualizing orbits, dose optimization can be achieved through the use of cone beam computed tomography 4.  The tube current (mA) used in cone beam computed tomography is significantly lower in comparison to conventional CT 5. However, this can compromise image quality as there are fewer x-ray photons and thus contributing to greater noise and less contrast in the resultant image 5.

  • two scouts (anterior-posterior and lateral) for accurate dose modulation

  • utilize the head holder for optimal position of the patient's head to reduce the dose delivered to the patient

  • derive multiplanar reconstructions of the orbits through a CT head/face to avoid scanning the patient again

  • access to multiplanar reconstructions facilitate surgical planning 4

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