Perfusion CT and acute stroke imaging: Foundations, applications, and literature review

Donahue, J., & Wintermark, M. (2015). Perfusion CT and acute stroke imaging: foundations, applications, and literature review. Journal of neuroradiology, 42(1), 21–29. https://doi.org/10.1016/j.neurad.2014.11.003

Multimodal CT features prominently in the rapidly evolving field of acute stroke triage, with perfusion CT applications at the forefront of many clinical research efforts. Perfusion CT offers a time sensitive and widely practicable assessment of cerebral hemodynamics and parenchymal viability that is key in acute stroke management. The following article reviews perfusion CT foundations and technical considerations while highlighting recent modality advances and frontline clinical applications. Ischemic penumbra and other prognostic imaging biomarkers are discussed in the context of results of recent clinical trials (MR-RESCUE, IMS III, Tenecteplase, etc.), with an emphasis on evidence based image guided stroke triage.

Determining ischemic penumbra and infarct core
Perfusion CT maps characterize tissue viability by reflecting changes in parenchymal autoregulatory mechanisms that follow an acute ischemic insult. As illustrated in Fig. 1 and summarized in Fig. 2, the decreased perfusion pressure that accompanies all ischemic cerebrovascular events causes an increase in MTT. Initially following arterial occlusion, reactive vasodilation and collateral flow recruitment attempts to normalize parenchymal blood flow (CBF) and results in an overall increase in ischemic territory CBV. Increased CBV is a hallmark of ischemic penumbra, and is observed if collateral circulation is robust enough to maintain compensatory neurobiochemical mechanisms. When such mechanisms are overwhelmed by prolonged or severe ischemia, the CBV and CBF will decline below viability thresholds and precipitate irreversible tissue damage, resulting in the infarct core.