Endovascular therapy (ET) is typically not considered for patients with large baseline ischemic cores (irreversibly injured tissue). Computed tomographic perfusion (CTP) imaging may identify a subset of patients with large ischemic cores who remain at risk for significant infarct expansion and thus could still benefit from reperfusion to reduce their degree of disability 1).
DC improves cerebral hemodynamics in patients with malignant middle cerebral artery infarction, and the level of improvement is related to outcome. However, some patients did not seem to experience any additional hemodynamic benefit, suggesting that perfusion CT may play a role as a prognostic tool in patients undergoing DC after ischemic stroke 2).
Whole-brain CT Perfusion (CTP) on Day 3 after aneurysmal subarachnoid hemorrhage (aSAH) allows early and reliable identification of patients at risk for delayed ischemic neurological deficits (DIND) and tissue at risk for delayed cerebral infarction (DCI). Additional CTP investigations, guided by Transcranial Doppler sonography (TCD)-measured blood flow velocity (BFV) increase or persisting coma, do not contribute to information gain 3).
The method by which perfusion to an organ measured by CT is still a relatively new concept, although the original framework and principles were concretely laid out as early as 1980 by Leon Axel at University of California San Francisco.
It is most commonly carried out for neuroimaging using dynamic sequential scanning of a pre-selected region of the brain during the injection of a bolus of iodinated contrast material as it travels through the vasculature. Various mathematical models can then be used to process the raw temporal data to ascertain quantitative information such as rate of cerebral blood flow (CBF) following an ischemic stroke or aneurysmal subarachnoid hemorrhage. Practical CT perfusion as performed on modern CT scanners was first described by Ken Miles, Mike Hayball and Adrian Dixon from Cambridge UK and subsequently developed by many individuals including Matthias Koenig and Ernst Klotz in Germany, and later by Max Wintermark in Switzerland and Ting-Yim Lee in Ontario, Canada.
Tracer delay-sensitive perfusion algorithms in CT perfusion (CTP) result in an overestimation of the extent of ischemia in thromboembolic stroke. In diagnosing delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (aSAH), delayed arrival of contrast due to vasospasm may also overestimate the extent of ischemia.
The increase in perfusion that was observed might partially be responsible for improved clinical outcome following decompressive craniectomy for major stroke. The predictive value of perfusion CT on outcome needs to be evaluated in larger trials 4).