Abstract WMP14: Increased Diffusion Heterogeneity After Acute Ischemic Stroke is Associated With Salvageable Tissue

Abstract

Background: Diffusion kurtosis MRI (DKI) may be more sensitive to microstructural changes in acute ischemic stroke (AIS), compared to diffusion weighted MRI (DWI). We investigated differences in diffusion kurtosis metrics related to time and tissue outcome. Methods: DKI from AIS patients enrolled in a prospective serial MRI study were analyzed (N=18). Mean kurtosis (MK), axial kurtosis (AK), radial kurtosis (RK), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD) and fractional anisotropy (FA) maps were calculated. Follow-up (FU) FLAIR infarct volumes were defined as “final.” Abnormal perfusion was defined as tissue with Tmax values greater than 6 seconds. All maps were co-registered to one another. DWI and DKI were compared (nonparametric Spearman’s correlation analysis) in the following regions: Core (abnormal acute DWI and FU), Growth (normal acute DWI, abnormal FU), and Salvaged (normal acute DWI, abnormal acute perfusion, normal FU). Results: Patient characteristics were: mean±SD age 66±10 years, median [IQR] admission NIHSS score 6 [3-11], time-to-acute MRI 6.2±2.1 h, time-to-FU MRI 3.0±1.3 days, acute DWI lesion 4.9 [0.8-21.1] cm3 and FU lesion 12.9 [1.8-54.7] cm3. Significant correlations were found between time-to-MRI and diffusivity and kurtosis metrics, but differed depending on tissue outcome (Table). Discussion: The significant inverse correlation between FA and RK and time-to-MRI in salvaged tissue suggests renormalization of transient ischemia-induced increases in FA and RK tissue with otherwise preserved cytoarchitecture. One possible mechanism underlying this could be that hyperacute ischemia-induced cellular swelling increases tortuosity of water diffusion paths, imposing direction-dependent restrictions upon diffusion. Coupled with changes in DWI, DKI may provide further insight into tissue evolution after AIS and therefore improve identification of potentially salvageable tissue.