In Vivo Tensor‐Valued Diffusion Magnetic Resonance Imaging Reveals Isotropic‐Anisotropic Kurtosis Mismatch in a Rat Middle Cerebral Artery Occlusion Stroke Model

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Abstract
Background: Tensor‐valued diffusion magnetic resonance imaging enables the separation of total kurtosis into isotropic and anisotropic components, offering improved specificity over conventional diffusion kurtosis imaging. In this study, we introduce a novel framework for detecting anisotropic‐isotropic kurtosis mismatch and evaluate its relevance in experimental ischemic stroke. Methods: Tensor‐valued diffusion magnetic resonance imaging was performed in a rat model of middle cerebral artery occlusion. Metrics, including anisotropic mean kurtosis and isotropic mean kurtosis, were quantified to assess microstructural tissue heterogeneity. Histologic validation was conducted using coregistered tissue sections. Results: We observed significant mismatches between mean diffusivity, mean kurtosis, as well as specifically in anisotropic mean kurtosis and isotropic mean kurtosis in ischemic regions. Notably, anisotropic mean kurtosis and isotropic mean kurtosis exhibited statistically significant alterations compared with contralateral regions. Moreover, these metrics strongly correlated with pathologic findings. The observed mismatch highlighted microstructurally distinct subregions within the lesion. Conclusions: This study establishes an in vivo framework for characterizing anisotropic‐isotropic kurtosis mismatch in an experimental stroke model. By quantifying the isotropic mean kurtosis/anisotropic mean kurtosis mismatch, tensor‐valued diffusion magnetic resonance imaging provides a more specific mechanistic characterization of diffusion heterogeneity than conventional diffusion tensor imaging and diffusion kurtosis imaging metrics, supporting its use as a preclinical tool for investigating microstructural alterations in ischemic brain tissue.

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