CT perfusion (brain)

Last revised by Dr Yair Glick on 19 May 2021

CT perfusion of the brain is a dynamic, contrast-enhanced study utilized in patients with suspected stroke to differentiate salvageable ischemic brain tissue (i.e. penumbra) from damaged infarcted brain.

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

CT perfusion studies are performed in the context of patients presenting with acute neurological symptoms that may represent cerebral infarction or cerebral hemorrhage. It is often the last study in the code stroke CT pathway.

The purpose of this scan is to measure/observe contrast enhancement as it makes its way through the arterial and venous system, making this a 'functional scan'. The scan will calculate the enhancement (if any) over time.

Previous severe reactions to iodinated contrast.

  • patient position
    • supine with their arms by their side
    • the head is placed in a 'chin tuck position' with he chin tucked toward the chest (via a sponge behind) 
    • sponges can be placed on both sides to ensure that the head is straight
  • scout
    • base of the skull to the top of the vertex 
      • if this is part of the code stroke pathway the scout may be from the carina to the tip of the skull as a CT angiogram of the neck and head will be performed before or after
  • scan extent
    • most perfusion scans begin at the base of the pituitary fossa focusing on the basal ganglia and supra-ganglionic level with a shuttle range of around 10 cm
  • scan direction
    • this is a functional scan, the scan will 'shuttle' up and down as contrast is injected
  • scan duration
    • scan duration is often 45-60 seconds, but to be more precise, it takes as long as is required for the contrast to fully dissipate
  • contrast injection considerations
    • cannula size 
      • this exam requires an injection of contrast at a considerable rate (ranging from 6-8 mL/s); therefore, a large bore (at least 18 gauge) cannula is required
    • injection rate
      • 6-8 mL/s 
    • injection volumes
      • 35-40 mL of highly concentrated iodinated contrast (300-350 mg/cc) followed by 30-40 mL of saline chaser
  • scan delay
    • minimal scan delay 
  • perfusion scans focus on the pituitary fossa at the basal ganglia and supra-ganglionic level; however, patients with symptoms of cerebellar infarction will require an adjustment of the scan extent
  • thick slices are often used to minimize noise
  • two of the most important factors of this exam are patient positioning and a quality IV access
  • poor cardiac output can lead to inaccurate perfusion maps; performing the carotid angiogram before the perfusion is a good way to get an idea of cardiac output and decide whtether or not the scan duration needs to be adjusted

Post-processing

Post-processing methods differ, depending on the vendor of the machine; however, the primary focus of the post-processing will be the measure of: 

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Cases and figures

  • Case 1: normal head (CT perfusion)
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  • Case 2: MCA infarct (CT perfusion)
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