The Nasal And Paranasal Sinus Region | CT Protocols

The Nasal And Paranasal Sinus | CT Protocols
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CT protocol for Nasal and Paranasal Sinus

Indications
  • Trauma to the face
  • Inflammatory 
  • Granulo- matous and infiltrative diseases and their complications
  • Preoperative staging of tumors and postoperative follow-up.
Patient Positioning 
  • For direct Coronal scanning-Prone with Headfirst, with Arms beside the trunk, the neck is hyperextended or Supine with Headfirst, with Arms beside the trunk and the neck hanging over the edge of the table. 
  • For axial scanning-Supine with Headfirst (resting on the headrest), with arms beside the trunk (preferred it the coronal position cannot be maintained by the patient).  
Topogram Position/Landmark
  • Lateral. 
  • For Coronal scanning-2-3 cm anterior to the tip of the nose.
  • For axial scanning-Level of the vertex. 
Mode of Scanning
Helical.

Scan Orientation
  • Posterior to anterior in Coronal scanning;
  • Caudocranial in axial scanning.

Starting Location
  • For Coronal scanning-Level of the clivus. 
  • For Axial scanning-Level of the hard palate. 

End Location
  • For Coronal scanning-Anterior part of the nasal cavity anterior to the frontal sinuses. 
  • For Axial scanning-cephalic limit of the frontal sinuses. 
Gantry Tilt
  • As many degrees as required making the scanning plane. 
  • For Coronal scanning-Parallel to the face or perpendicular to the hard palate.
  • For Axial scanning-Parallel to the hard palate. 
Field of View
Include the cavernous sinuses as well.

Contrast Administration
Intravenous (in cases of mass lesions (inflammatory or tumoral). 

The volume of Contrast
60-100 mL. 

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

Scan Delay
30-40 sec. 

Slice Thickness in Reconstruction
1.0-1.5 mm. 

Slice Interval in Reconstruction
0.5-0.75 mm. 

Reconstruction Algorithm/Kernel
Medium smooth for the soft tissues and sharp kernel for the bones. 

3D-Reconstructions
  • MPR
  • MIP 
  • Virtual Endoscopy. 

Comments   

  • The use of a headrest and chin rest is recommended for positioning. 
  • Ba┼čeline non-contrast scans can be taken in the sequential mode but with the same slice thickness.
  • Ensure that the patient does not move in between the non-contrast and contrast-enhanced scans. 
  • Remove all the dentures and nasal ornaments that can produce artefacts.
  • Axial scanning is preferred if there are multiple dental fillings to avoid artefacts arising from them. 
  • As there is a natural contrast between the bone and air, mA can be reduced whenever possible to minimize radiation exposure to the eye lens. 
  • Axial and Coronal images are the mainstay for the diagnosis. Oblique sagittal MPR are prepared in the plane of the osteomeatal unit complex separately on either side.
Criteria of Good Image Quality
  • Symmetric position with the orbital plates overlapping with each other.
  • Absence of the motion artefacts.
  • Absence of beam hardening.

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