A Study to Evaluate the Role of Three-Dimensional Pseudo-Continuous Arterial Spin Labelling in Acute Ischemic Stroke.

Abstract

Introduction Magnetic resonance imaging (MRI) is well known to detect ischemic brain tissue and evaluate the tissue vulnerable to infarction. Diffusion-weighted imaging (DWI) has been a mainstay of stroke evaluation but has a few shortcomings, as it generally indicates only the core of ischemia and does not provide information regarding the tissue at risk or the ischemic penumbra surrounding the infarct. Perfusion imaging identifies brain tissue that has reduced blood flow as a potential target for reperfusion therapy. Arterial spin labelling (ASL) is a new non-invasive, non-contrast MRI perfusion sequence used to detect areas of hypoperfusion qualitatively and quantitatively and also identify the area at risk, i.e., the penumbra, in acute ischemic stroke. The most important component of the imaging is to determine the ischemic penumbra. One of the working definitions of penumbra is brain tissue that is ischemic but not yet infarcted and is at risk of further damage unless the flow is rapidly restored. Hence, perfusion-diffusion mismatch provides a realistic target for potential intervention. The aim of our study is to assess the role of ASLimaging in identifying the penumbra and providing insight into the management of acute ischemic stroke. Materials and methods Patients who presented with symptoms of acute ischemic stroke were included in the study, and an MRI stroke protocol comprising DWI, fluid-attenuated inversion recovery (FLAIR), ASL, and magnetic resonanceangiogram (MRA) sequences was done. Post-thrombolysis, a follow-up MRI was done using DWI, ASL, and MRA to see the restoration of perfusion in the ischemic penumbra. Three-dimensional pseudo-continuous ASL (in our study, ASL refers to pseudo-continuous ASL) is included in the stroke protocol in cases of acute ischemic stroke and assessed qualitatively. Results Our study included 43 patients (n = 43), of whom 39.5% (17 patients) belong to the age group of 51-60 years and 2.3% (one patient) are in the age group of 21-30 years. All 43 cases demonstrated DWI-FLAIR mismatch, suggestive of ischemic stroke within the window period, and all 43 cases showed DWI-ASL mismatch, suggestive of a large yet potentially salvageable peri-infarct ischemic penumbra. The most common territory involved was the middle cerebral artery (MCA), and the posterior cerebral artery (PCA) was the least commonly involved territory. We had one case involving the MCA-PCA watershed zone. Conclusion Arterial spin labelling is a novel, non-invasive, non-contrast MRI sequence with the capability to provide qualitative information regarding the salvageable ischemic penumbra, and timely management prevents the progression of the penumbra. The incorporation of ASL as part of the standard neuroimaging protocol aids in the management of acute stroke, giving insight into the prediction of outcome.