Diffusional kurtosis time dependence and the water exchange rate for the multi‐compartment Kärger model

Jensen, Jens H.

doi:10.1002/mrm.29926

Cited by 3 publications

References 30 publications

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Investigating exchange, structural disorder, and restriction in gray matter via water and metabolites diffusivity and kurtosis time-dependence

Mougel,

Valette,

Palombo

2024

Imaging Neuroscience

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Water diffusion-weighted MRI is a very powerful tool for probing tissue microstructure, but disentangling the contribution of compartment-specific structural disorder from cellular restriction and inter-compartment exchange remains an open challenge. In this work we use diffusion-weighted MR spectroscopy (dMRS) of water and metabolite as a function of diffusion time in vivo in mouse gray matter to shed light on: i) which of these concomitant mechanisms (structural disorder, restriction and exchange) dominates the MR measurements and ii) with which specific signature. We report the diffusion time-dependence of water with excellent SNR conditions as provided by dMRS, up to a very long diffusion time (500 ms). Water kurtosis decreases with increasing diffusion time, showing the concomitant influence of both structural disorder and exchange. However, despite the excellent experimental conditions, we were not able to clearly identify the nature of the structural disorder (i.e. 1D versus 2D/3D short-range disorder). Measurements of purely intracellular metabolites diffusion time-dependence (up to 500 ms) show opposite behavior to water, with metabolites kurtosis increasing as a function of diffusion time. We show that this is a signature of diffusion restricted in the intracellular space, from which cellular microstructural features such as soma’s and cell projections’ size can be estimated. Finally, by comparing water and metabolite diffusion time dependencies, we attempt to disentangle the effect of intra/extracellular exchange and structural disorder of the extracellular space (both impacting water diffusion only). Our results suggest a relatively short intra/extracellular exchange time (~1-50 ms) and short-range disorder (still unclear if 1D or 2D/3D) most likely coming from the extracellular compartment. This work provides novel insights to help interpret water diffusion-time dependent measurements in terms of the underlying microstructure of gray matter and suggests that diffusion-time dependent measurements of intracellular metabolites may offer a new way to quantify microstructural restrictions in gray matter.

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Investigating exchange, structural disorder, and restriction in gray matter via water and metabolites diffusivity and kurtosis time-dependence

Mougel,

Valette,

Palombo

2024

Imaging Neuroscience

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Time-dependent diffusion magnetic resonance imaging: measurement, modeling, and applications

Ba,

Kang,

2024

J. Zhejiang Univ. Sci. A

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The interplay between exchange and microscopic kurtosis as measured by diffusion MRI with double diffusion encoding: Theory and simulations

Chakwizira,

Szczepankiewicz,

Nilsson

2024

Preprint

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Double diffusion encoding (DDE) makes diffusion MRI sensitive to a wide range of microstructural features, and the acquired data can be analysed using different approaches. Correlation tensor imaging (CTI) uses DDE to resolve three components of the diffusional kurtosis: isotropic, anisotropic, and microscopic. The microscopic kurtosis is estimated from the contrast between single diffusion encoding (SDE) and parallel DDE signals at the same b-value. Another approach is multi-Gaussian exchange (MGE), which employs DDE to measure exchange. Sensitivity to exchange is obtained by contrasting SDE and DDE signals at the same b-value. CTI and MGE exploit the same signal contrast to quantify microscopic kurtosis and exchange, and this study investigates the interplay between these two quantities. We perform Monte-Carlo simulations in different geometries with varying levels of exchange and study the behaviour of the parameters from CTI and MGE. We conclude that microscopic kurtosis from CTI is sensitive to the exchange rate. In an attempt to separate microscopic kurtosis from exchange, we propose a heuristic signal representation referred to as µMGE (MGE incorporating microscopic kurtosis) that accounts for both effects, by exploiting the distinct signatures of exchange and microscopic kurtosis with varying mixing time: exchange causes a dependence of the signal on mixing time while microscopic kurtosis does not. We find that applying µMGE to data acquired with multiple mixing times for both parallel and orthogonal DDE allows estimation of exchange as well as all three sources of kurtosis.

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Diffusional kurtosis time dependence and the water exchange rate for the multi‐compartment Kärger model

Cited by 3 publications

References 30 publications

Investigating exchange, structural disorder, and restriction in gray matter via water and metabolites diffusivity and kurtosis time-dependence

Investigating exchange, structural disorder, and restriction in gray matter via water and metabolites diffusivity and kurtosis time-dependence

Time-dependent diffusion magnetic resonance imaging: measurement, modeling, and applications

The interplay between exchange and microscopic kurtosis as measured by diffusion MRI with double diffusion encoding: Theory and simulations

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