ARRS 2022 Abstracts

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E1781. CT Perfusion in Stroke Using Conventional and Rapid Automated Software: A Survival Guide for Residents and Emergency Room Radiologists
Authors
  1. Heta Ladumor; University of Arkansas for Medical Sciences
  2. Sanaz Ameli; University of Arkansas for Medical Sciences
  3. Surjith Vattoth; University of Arkansas for Medical Sciences
Background
CT perfusion (CTP) is increasingly used as part of the routine evaluation in acute ischemic stroke. Conventional vendor-provided CTP software differentiates between core infarct vs ischemic penumbra using the tiebreaker of critically reduced cerebral blood volume (CBV) values within brain regions showing abnormally elevated time parameters like mean transit time (MTT). On the other hand, Rapid automated CTP software (iSchemaView, Inc.) differentiates between core infarct vs ischemic penumbra using the tiebreaker of critically reduced cerebral blood flow (CBF) values within brain regions showing abnormally elevated time to maximum (Tmax). CBV thresholds can also be used in Rapid as seen in conventional vendor software, but Rapid was developed based on results from studies using critically low CBF thresholds, which correlates well with the real tiebreaker of CBV < 2 mL/100 g with cytotoxic edema/infarction. Rapid software is more precise and accurate in comparison to conventional software, especially in early and fully recanalized patients. Another advantage of the Rapid CTP software is its use of a delay-insensitive deconvolution algorithm, which corrects any delay in the arrival of the contrast agent.

Educational Goals / Teaching Points
The goals of this exhibit are to review technical principles and patterns of CTP imaging in stroke; compare conventional and Rapid-generated CTP maps; and discuss important thresholds and criteria for reperfusion therapy in Rapid CTP.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Conventional CTP maps can be generated using the deconvolution method or maximum slope method, and Rapid CTP maps are generated using the deconvolution method. The deconvolution method generates CBV, CBF, MTT, Tmax, time to drain (TTD), time to start (TTS), and flow extraction product. The maximum slope method generates CBV, CBF, TTS, and time to peak (TTP). The correct interpretation of CTP imaging depends on two main values, Tmax and CBF. A Tmax of > 6 seconds represents the volume of the ischemic penumbra and infarcted core. CBF < 30% is the standard threshold to determine infarcted core volume. However, in the case of presentation during the golden hour, a CBF < 20% is used so that the salvageable brain tissue is not over-called as an infarcted core. The best correlation with DWI MRI is seen with CBF < 38%, but this occasionally overcalls the infarcted core volume. Other important values to know are the hypoperfusion index (> 0.5 is associated with poor outcome) and CBV index (> 0.7 is associated with better outcome).

Conclusion
Both conventional and Rapid CTP automatically provide quantifiable and color-coded perfusion maps. This guide provides a practical and simplified approach to navigating these CTP programs and details the important threshold values needed for interpretation.