Exploring the contribution of gray matter microstructure to R1 contrast via multi-compartment diffusion modelling in...

Area of Science:

• Neuroimaging
• Biophysics
• Structural MRI

Background:

• The Soma And Neurite Density Imaging (SANDI) model improves MRI sensitivity to gray matter (GM) microstructural complexity.
• Longitudinal relaxation rate R1 (1/T1) is a key MRI parameter sensitive to tissue properties.
• Understanding the relationship between diffusion metrics and R1 is crucial for advanced neuroimaging.

Purpose of the Study:

• To investigate if diffusion metrics from the SANDI model contribute to R1 contrast in brain tissue.
• To explore the relationship between SANDI-derived metrics and R1 in both gray matter (GM) and white matter (WM).

Main Methods:

• Twenty healthy volunteers underwent diffusion-weighted imaging and R1 mapping using MP2RAGE at 3 Tesla.
• Diffusion metrics analyzed included intra-neurite signal fraction (fneurite), intra-soma signal fraction (fsoma), extra-neurite fraction (fextra), soma radii (Rsoma), and intra-neurite and extra-neurite diffusivities (Din and De).
• Spatial and cross-subject correlations between R1 and SANDI metrics were calculated for GM and WM.

Main Results:

• In GM, R1 showed moderate negative correlations with soma-related metrics (fsoma, Rsoma), indicating GM microstructure influences R1.
• In WM, R1 exhibited moderate to strong positive correlations with intra-neurite metrics (Din, fneurite), linked to myelinated axons.
• These findings suggest both WM and GM microstructural characteristics contribute to R1 contrast.

Conclusions:

• Microstructural features of brain tissue, including myelination, significantly contribute to R1 contrast.
• The study enhances the understanding of relaxation differences across brain parenchyma using the SANDI model.
• Future research should examine these relationships in clinical populations with demyelination and neurodegeneration.