Multiphase CT angiography in acute ischemic stroke
Multiphase CT angiography is an evolving imaging technique in acute ischemic stroke. The technique aims to quickly and reliably identify brain which is potentially salvageable with intervention. Brain tissue viability depends on many factors, with this technique assessing collateral leptomeningeal blood flow. Reliable identification of good versus bad collateral flow is essential to help guide patient selection for endovascular reperfusion .
On single-phase CT angiography (CTA), leptomeningeal collateral scoring systems are used to evaluate collateral flow,but can be inaccurate due to the absence of temporal resolution . Multi-phase CTA provides cerebral angiograms in three distinct phases (peak arterial, peak venous and late venous) after the injection of contrast material, allowing for time-resolved assessment.
The collateral blood flow is assessed by comparison of pial arterial filling in the ischemic area of the brain on CTA with that of similar arteries in the contralateral hemisphere. The advantage of multi-phase is that it can detect temporal delay in the filling of vessels in addition to the prominence and extent of vessels detectable with a single-phase technique. Some sites use a single delayed phase CTA.
Good collateral flow is associated with :
- better clinical outcomes
- less risk of hemorrhagic transformation
- a greater likelihood of successful recanalization
While the most appropriate imaging technique to guide intervention in acute ischemic stroke is not entirely clear at present (January 2017), CT perfusion studies are widely used in many centers. The advantages of multi-phase CTA when compared CT perfusion include:
- smaller radiation dose
- images which are easily obtained and interpreted without postprocessing
- reduction of the impact of patient motion on images
In addition, good inter-rater reliability and prediction of clinical outcome have been reported .
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