In vivo cortical microstructure mapping using high-gradient diffusion MRI accounting for intercompartmental water...

Area of Science:

• Neuroimaging
• Biophysics
• Medical Physics

Background:

• Diffusion MRI is crucial for mapping cortical microstructure.
• Existing Soma And Neurite Density Imaging (SANDI) models do not account for water exchange, limiting accuracy in gray matter.
• Understanding water exchange is vital for precise microstructural property estimation.

Purpose of the Study:

• To systematically evaluate an extended SANDI model (in vivo SANDIX) that incorporates water exchange effects for in vivo human cortical microstructural mapping.
• To assess the model's sensitivity to various microstructural parameters and water exchange times.
• To validate the model's performance on in vivo diffusion MRI data.

Main Methods:

• Developed the in vivo SANDIX model, extending SANDI to include water exchange via the anisotropic Kärger model.
• Conducted Monte Carlo simulations to test model sensitivity to radii, compartment fractions, and exchange times.
• Applied the in vivo SANDIX model to diffusion MRI data from 13 healthy adults acquired on a 3-Tesla Connectome MRI scanner.

Main Results:

• The in vivo SANDIX model successfully accounts for water exchange, providing accurate intra-soma and intra-neurite signal fractions without parameter time-dependence.
• Simulation results demonstrated model sensitivity and highlighted the need for cautious interpretation of measured water exchange times.
• In vivo application revealed distinct water exchange times between gray and white matter, consistent with anatomical characteristics.

Conclusions:

• The SANDIX approach, using high-gradient diffusion MRI, enables effective in vivo cortical microstructure mapping by evaluating water exchange effects.
• This advanced model offers a more accurate description of in vivo cortical microstructure.
• The findings enhance data interpretation for future neurobiological studies.