Angiography For The Circle Of Willis | CT Protocols

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CT protocol- Circle of Willis

Indications

• Suspected incidental intracranial aneurysm 
• Subarachnoid aneurysm 
• Arterial occlusion 
• Arteriovenous malformation, etc. 

Patient Positioning
Supine with Headfirst, with Arms beside the trunk. 

Topogram Position/Landmark
Lateral; level of the vertex. 

Mode of Scanning
Helical. 

Scan Orientation
Caudocranial

• Starting Location-Level of the occipital squame. 
• End Location-To the expected upper limit of the region of interest. 

Gantry Tilt
Nil. 

Field of View
Just including the region of interest.

Contrast Administration
Intravenous. 

The volume of Contrast
100-150 mL. 

Rate of Injection of Contrast
4-5 mL/sec. 

Scan Delay
20-25 sec. 

Slice Thickness in Reconstruction
1.0-1.5 mm. 

Slice Interval in Reconstruction
0.5-0.75 mm. 

Reconstruction Algorithm/Kernel
Smooth. 

3D-Reconstructions

• MPR
• MIP
• VRT
• SSD 

Comments

• The use of a headrest is recommended for head positioning. 
• The use of the bolus tracking method for determining the optimal scan delay is preferred. 
• A noncontrast scan in sequential mode should precede the angiography protocol as it will give the baseline scans, will determine the region of interest, and also are useful for subtraction images.
• There should be no motion between the noncontrast and contrast scans besides using the same technical parameters if subtraction images are desired.