Free-Water-Eliminated (FWE)-SANDI for improving the accuracy of in vivo apparent soma and neurite imaging using high-gradient diffusion MRI

Motivation: Biophysical model of diffusion MRI has shown potential for capturing cellular characteristics and pathological conditions in gray matter but has limitations due to the partial volume effect around free water. Goal(s): To improve the current Soma and Neurite Density Imaging (SANDI) model by incorporating a free-water component that differentiates extracellular space from free water, providing accurate measurements of microstructural properties. Approach: We implemented the Free-Water-Eliminated (FWE)-SANDI model and validated its performance through noise propagation and in vivo high-gradient diffusion MRI data. Results: The FWE-SANDI shows consistently estimated soma density in line with standard SANDI while distinguishing between extracellular and free water components. Impact: The proposed Free-Water-Eliminated (FWE)-SANDI model reduces the partial volume effect from free water and improves the accuracy of non-invasive microstructural imaging in the brain gray matter, allowing ones to better study underlying mechanisms of cellular changes in neurodevelopment and neurodegeneration.