Microvascular Measures of Perfusion in Stroke Recanalization

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ABSTRACT. The recanalization of brain following ischemic stroke is the best means of recovering brain. However, restoration of flow is often accompanied by brain injury and tissue death. A reliable depiction of restoration of flow together with salvageable brain is of clinical significance. Imaging with MRI offers diagnostically useful depictions of stroke injury from T2, DWI, and perfusion imaging. However, we need improved methods of perfusion in order to best map and differentiate flow from tissue status. The clinical hypothesis that reperfusion of brain is a process of restoration of flow in the time window of salvaging brain, and being able to depict both aspects of that reperfusion process are crucial to the hundreds of reperfusion procedures done daily worldwide. The overall goal of this new submission is to identify and improve cerebral blood flow (CBF) techniques from dynamic susceptibility contrast (DSC) perfusion-weighted MRI (PWI) methods that can depict both restoration of flow together with the microvascular status that would optimally compare with DWI to form a clinically useful DWI-PWI mismatch representing brain tissue-at-risk or salvageable brain. To do this, we will assess the value of mapping perfusion with a gradient- echo (GRE) and a spin-echo (SE) signal acquired together in a multi-shot, multi- echo, and DSC first-pass bolus contrast agent MRI technique. The perfusion maps will be compared with a gold-standard xenon CT (xeCT) value of CBF. We aim to show equivalence between GRE- and SE-DSC to the gold-standard in order to visualize vascular and microvascular status in 120 stroke patients having had recanalization procedures. We will obtain T1, T2, T2*, diffusion-weighted imaging (DWI), and bolus PWI in 120 patients presenting at 6-48 hours following reperfusion and obtain a second follow-up study at 30 days as a measure of tissue outcome together with clinical assessments. We believe successful attainment of these aims promises to markedly improve acute stroke care by validating a MRI-based perfusion methods sensitive to both vascular status and tissue microvascular status. This study will lead to better understanding of mapping flow and microvascular status in patients with severe cerebrovascular disease and greatly enhance the already significant diagnostic power of MRI in acute ischemic stroke by better mapping metabolic- perfusion mismatches after reperfusion.