Low frequency oscillating gradient spin-echo sequences improve sensitivity to axon diameter: An experimental study in...

Area of Science:

• Neuroimaging
• Biophysics
• Medical Physics

Background:

• Accurate mapping of axon diameters is crucial for understanding nerve pathways and diagnosing neurological disorders.
• Conventional single diffusion encoding (SDE) spin echo sequences are widely used but have limitations.
• Oscillating gradient spin echo (OGSE) sequences show promise for improved diffusion MRI.

Purpose of the Study:

• To experimentally compare the performance of SDE and trapezoidal OGSE ActiveAx approaches for axon diameter mapping.
• To investigate the advantages of OGSE over SDE in realistic nerve tissue conditions.

Main Methods:

• Optimized SDE and OGSE ActiveAx protocols for rat peripheral nerve tissue.
• Utilized Monte Carlo simulations and a pre-clinical imaging experiment with excised rat sciatic nerve.
• Compared diffusion MRI estimates with post-scanning histology.

Main Results:

• OGSE ActiveAx provided higher accuracy and precision in axon diameter index estimation compared to SDE.
• OGSE estimates (4.2–6.5 μm) closely matched histology (4–5.8 μm), while SDE overestimated (5.2–8 μm).
• OGSE demonstrated greater robustness to reduced diffusion gradient directions.

Conclusions:

• Low-frequency OGSE sequences offer improved accuracy and precision for axon diameter mapping in viable nerve tissue.
• OGSE is a more robust technique than SDE for axon diameter estimation, especially in complex fiber orientations.
• These findings support the use of OGSE for enhanced neuroimaging applications.