Investigating gray matter microstructure via multi-compartment diffusion model and cortical myelination in healthy brains

Motivation: The SANDI (Soma-And-Neurite-Density-Imaging) diffusion model enhances diffusion metrics sensitivity to gray matter (GM) complexity. However, their relationship with R1, a known index of cortical myelination, remains unknown. Goal(s): Investigate the association between SANDI metrics and cortical myelination in healthy subjects. Approach: Voxel-wise, regional and cross-subject correlations between SANDI metrics and R1 values were examined in GM and white matter. Results: GM signal fraction of neurons and their estimated radius show a spatial, negative correlation with R1, indicating that less myelinated areas, known to perform higher aerobic glycolysis, present larger neurons. This aligns with our recent finding that oxygen consumption rises with neuron radius. Impact: This study enhances the understanding of gray matter microstructure by revealing the relationship between metrics from advanced three-compartment diffusion model (Soma-And-Neurite-Density Imaging) and cortical myelination (R1). These insights may inform future research on brain development and pathology.