The influence of axonal beading and undulation on axonal diameter mapping

Area of Science:

• Neuroimaging
• Biophysics
• Cellular Biology

Background:

• Diffusion MRI is used to estimate axonal diameter, a key microstructural parameter.
• Axons are typically modeled as simple cylinders, but real axons exhibit complex shapes.
• Non-cylindrical features like caliber variation and undulation are present in human axons.

Approach:

• Simulated diffusion MRI signals in realistic axonal models derived from electron microscopy.
• Quantified the impact of caliber variations and undulations on axon diameter estimation.
• Investigated the influence of tunable features on diffusion signal.

Key Points:

• Caliber variations lead to under-estimation of axon diameter.
• Axonal undulations result in over-estimation of axon diameter.
• Biases in diameter estimation can reach up to 100%.

Conclusions:

• Deviations from cylindrical axonal models significantly confound diffusion MRI-based diameter mapping.
• Axon diameter alterations in pathological conditions (e.g., TBI, ischemia) may be misinterpreted due to these shape effects.
• Accurate interpretation of microstructural changes requires accounting for axonal morphology.