N-acetyl-aspartate levels correlate with intra-axonal compartment parameters from diffusion MRI

Area of Science:

• Neuroimaging
• Biophysical Modeling
• White Matter Integrity

Background:

• Diffusion MRI and biophysical modeling offer compartment-specific white matter tract integrity (WMTI) metrics.
• Understanding these metrics' relationship with neurochemical concentrations is crucial for diagnosing brain injuries.

Purpose of the Study:

• To investigate the relationship between WMTI metrics derived from diffusion kurtosis imaging and neurochemical concentrations (NAA, Cr, Cho, mI) measured by proton MR spectroscopy ((1)H-MRS).
• To examine these relationships in patients with mild traumatic brain injury (MTBI).

Main Methods:

• Derived WMTI metrics (Daxon, De||, De┴, AWF, α) from diffusion kurtosis imaging.
• Measured global white matter neurochemical concentrations (NAA, Cr, Cho, mI) using (1)H-MRS in 25 MTBI patients.
• Analyzed correlations between WMTI metrics and neurochemical concentrations, including regional analysis.

Main Results:

• Found significant positive correlations between N-acetyl-aspartate (NAA) and intra-axonal diffusivity (Daxon), axonal water fraction (AWF), and tortuosity (α).
• Observed significant negative correlations between NAA and extra-axonal radial diffusivity (De┴).
• Identified correlations between Daxon and creatine (Cr), and between extra-axonal axial diffusivity (De||) and choline (Cho) and myo-inositol (mI).

Conclusions:

• Correlations between NAA and intra-axonal metrics, and between extra-axonal metrics and Cho/mI, support diffusion imaging's ability to differentiate axonal compartments.
• Findings align with MTBI pathophysiology, suggesting both intra-axonal injury and axonal damage/loss.
• Diffusion MRI and MR spectroscopy provide valuable insights into white matter changes post-MTBI.