Evidence for microscopic kurtosis in neural tissue revealed by Correlation Tensor MRI

Abstract

Purpose: The impact of microscopic diffusional kurtosis ($\mu K$) - arising from restricted diffusion and/or structural disorder - remains a controversial issue in contemporary diffusion MRI (dMRI). Recently, Correlation Tensor MRI (CTI) was introduced to disentangle the sources contributing to diffusional kurtosis, without relying on a-priori assumptions. Here, we aimed to investigate $\mu K$ in in vivo rat brains and assess its impact on state-of-the-art methods ignoring $\mu K$. Methods: CTI harnesses double diffusion encoding (DDE) experiments, which were here improved for speed and minimal bias using four different sets of acquisition parameters. The robustness of CTI estimates from the improved protocol is assessed in simulations. The in vivo CTI acquisitions were performed in healthy rat brains using a 9.4T pre-clinical scanner equipped with a cryogenic coil, and targeted the estimation of $\mu K$, anisotropic kurtosis, and isotropic kurtosis. Results: The improved CTI acquisition scheme substantially reduces scan time and importantly, also minimizes higher-order-term biases, thus enabling robust $\mu K$ estimation, alongside Kaniso and Kiso metrics. Our CTI experiments revealed positive $\mu K$ both in white and grey matter of the rat brain in vivo; $\mu K$ is the dominant kurtosis source in healthy grey matter tissue. The non-negligible $\mu K$ substantially biases prior state-of-the-art analyses of Kiso and Kaniso. Conclusion: Correlation Tensor MRI offers a more accurate and robust characterization of kurtosis sources than its predecessors. $\mu K$ is non-negligible in vivo in healthy white and grey matter tissues and could be an important biomarker for future studies. Our findings thus have both theoretical and practical implications for future experiments.

arXiv comment64 pages (34 pages main text + 17 pages supporting information + 13 pages references), 9 main figures (+ 6 supporting figures), 1 main table (+ 2 supporting tables)

References in corpus (12)

• Rotationally-invariant mapping of scalar and orientational metrics of neuronal microstructure with diffusion MRI
• In vivo observation and biophysical interpretation of time-dependent diffusion in human cortical gray matter
• Whole-brain diffusional variance decomposition (DIVIDE): Demonstration of technical feasibility at clinical MRI systems
• A time-dependent diffusion MRI signature of axon caliber variations and beading
• Microscopic anisotropy misestimation in spherical-mean single diffusion encoding MRI
• Correlation Tensor Magnetic Resonance Imaging
• Effects of nongaussian diffusion on "isotropic diffusion measurements'': an ex-vivo microimaging and simulation study
• Accurate estimation of microscopic diffusion anisotropy and its time dependence in the mouse brain
• Double diffusion encoding and applications for biomedical imaging
• ConFiG: Contextual Fibre Growth to generate realistic axonal packing for diffusion MRI simulation
• Evidence for microscopic kurtosis in neural tissue revealed by Correlation Tensor MRI
• Validation and noise robustness assessment of microscopic anisotropy estimation with clinically feasible double diffusion encoding MRI

Cited by in corpus (1)

• Evidence for microscopic kurtosis in neural tissue revealed by Correlation Tensor MRI