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. 2024 May;91(5):2126-2141.
doi: 10.1002/mrm.29975. Epub 2023 Dec 29.

Tensor-valued diffusion MRI of human acute stroke

Mi Zhou  1 , Robert Stobbe  1   2 , Filip Szczepankiewicz  3 , Matthew Budde  4 , Brian Buck  5 , Mahesh Kate  5 , Mar Lloret  5 , Paige Fairall  5 , Ken Butcher  6 , Ashfaq Shuaib  5 , Derek Emery  2 , Markus Nilsson  3 , Carl-Fredrik Westin  7 , Christian Beaulieu  1   2
Affiliations

Tensor-valued diffusion MRI of human acute stroke

Mi Zhou et al. Magn Reson Med. 2024 May.

Abstract

Purpose: Tensor-valued diffusion encoding can disentangle orientation dispersion and subvoxel anisotropy, potentially offering insight into microstructural changes after cerebral ischemia. The purpose was to evaluate tensor-valued diffusion MRI in human acute ischemic stroke, assess potential confounders from diffusion time dependencies, and compare to Monte Carlo diffusion simulations of axon beading.

Methods: Linear (LTE) and spherical (STE) b-tensor encoding with inherently different effective diffusion times were acquired in 21 acute ischemic stroke patients between 3 and 57 h post-onset at 3 T in 2.5 min. In an additional 10 patients, STE with 2 LTE yielding different effective diffusion times were acquired for comparison. Diffusional variance decomposition (DIVIDE) was used to estimate microscopic anisotropy (μFA), as well as anisotropic, isotropic, and total diffusional variance (MKA , MKI , MKT ). DIVIDE parameters, and diffusion tensor imaging (DTI)-derived mean diffusivity and fractional anisotropy (FA) were compared in lesion versus contralateral white matter. Monte Carlo diffusion simulations of various cylindrical geometries for all b-tensor protocols were used to interpret parameter measurements.

Results: MD was ˜40% lower in lesions for all LTE/STE protocols. The DIVIDE parameters varied with effective diffusion time: higher μFA and MKA in lesion versus contralateral white matter for STE with longer effective diffusion time LTE, whereas the shorter effective diffusion time LTE protocol yielded lower μFA and MKA in lesions. Both protocols, regardless of diffusion time, were consistent with simulations of greater beading amplitude and intracellular volume fraction.

Conclusion: DIVIDE parameters depend on diffusion time in acute stroke but consistently indicate neurite beading and larger intracellular volume fraction.

Keywords: Monte Carlo diffusion simulation; b-tensor; diffusion time; neurite beading; stroke; tensor-valued diffusion encoding.

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References

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