NEXI for the quantification of human gray matter microstructure on a clinical MRI scanner

Motivation: This study assesses the Neurite Exchange Imaging (NEXI) microstructure model in human cortex using clinical MRI data, addressing the model's clinical applicability. Goal(s): How meaningful, robust, and reproducible are microstructural properties in the human cortex estimated using the NEXI diffusion model on clinical data?Approach: Scan-rescan clinical data from six volunteers were collected and processed. NEXI was estimated and compared to expected cortical distributions and to the myelin water fraction distribution. Results: NEXI provided robust, biologically plausible results and maintained inter-subject sensitivity and intra-subject reproducibility. A significant correlation between exchange time and myelin water fraction supports the relationship between membrane permeability and myelination. Impact: We successfully estimate the Neurite Exchange Imaging (NEXI) model on clinical MRI data and report a strong correlation between the estimated exchange time, a proxy for membrane permeability, and the Myelin Water Fraction in the human cortex.