Can we detect the effect of spines and leaflets on the diffusion of brain intracellular metabolites? - Archive ouverte HAL Access content directly
Journal Articles NeuroImage Year : 2018

## Can we detect the effect of spines and leaflets on the diffusion of brain intracellular metabolites?

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Marco Palombo
• Function : Correspondent author
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Julien Valette
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#### Abstract

Prior models used to clarify which aspects of tissue microstructure mostly affect intracellular diffusion and corresponding diffusion-weighted magnetic resonance (DW-MR) signal have focused on relatively simple geometrical descriptions of the cellular microenvironment (spheres, randomly oriented cylinders, etc…), neglecting finer morphological details which may have an important role. Some types of neurons present high density of spines; and astrocytes and macroglial cells processes present leaflets, which may all impact the diffusion process. Here, we use Monte-Carlo simulations of many particles diffusing in cylindrical compartments with secondary structures mimicking spines and leaflets of neuronal and glial cell fibers, to investigate to what extent the diffusion-weighted signal of intracellular molecules is sensitive to spines/leaflets density and length. In order to study the specificity of DW-MR signal to these kinds of secondary structures, beading-like geometry is simulated as "control" deviation from smooth cylinder too. Results suggest that: a) the estimated intracellular tortuosity increases as spines/leaflets density or length (beading amplitude) increase; b) the tortuosity limit is reached for diffusion time t$_d$ > 200 ms for metabolites and t$_d$ > 70 ms for water molecules, suggesting that the effects of these finer morphological details are negligible at t$_d$ longer than these threshold values; c) fiber diameter is overestimated, while intracellular diffusivity is underestimated, when simple geometrical models based on hollow smooth cylinders are used; d) apparent surface-to-volume, S/V, ratio estimated by linear fit of high frequency OG data appears to be an excellent estimation of the actual S/V ratio, even in the presence of secondary structures, and it increases as spines and leaflets density or length increase (while decreasing as beadings amplitude increases). Comparison between numerical simulations and multi-modal metabolites DW-MRS experiments $in\ vivo$ in mouse brain shows that these fine structures may affect the DW-MRS signal and the derived diffusion metrics consistently with their expected density and geometrical features. This work suggests that finer structures of cell morphology have non-negligible effects on intracellular molecules' diffusion that may be measured by using multimodal DW-MRS approaches, stimulating future developments and applications.

#### Domains

Life Sciences [q-bio] Bioengineering Imaging

### Dates and versions

cea-02155338 , version 1 (13-06-2019)

### Identifiers

• HAL Id : cea-02155338 , version 1
• DOI :

### Cite

Marco Palombo, Clémence Ligneul, Edwin Hernandez-Garzon, Julien Valette. Can we detect the effect of spines and leaflets on the diffusion of brain intracellular metabolites?. NeuroImage, 2018, 182, pp.283-293. ⟨10.1016/j.neuroimage.2017.05.003⟩. ⟨cea-02155338⟩

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