Diffusional anisotropy in cranial nerves with maturation: quantitative evaluation with diffusion MR imaging in rats.

Area of Science:

• Neuroscience
• Biophysics
• Medical Imaging

Background:

• Understanding nerve development is crucial for diagnosing neurological disorders.
• Diffusion Magnetic Resonance (MR) imaging offers insights into tissue microstructure.
• Myelination significantly impacts water diffusion in nerve fibers.

Purpose of the Study:

• To explore the relationship between diffusional anisotropy and anatomical changes during nerve development.
• To investigate the roles of myelination and fiber orientation in diffusion.
• To utilize quantitative diffusion MR imaging and electron microscopy in an animal model.

Main Methods:

• In vivo diffusion MR imaging measured transverse and longitudinal apparent diffusion coefficients (ADCs) in rat optic and trigeminal nerves (2-10 weeks old).
• Electron microscopy analyzed nerve sections at various developmental stages.
• Correlated diffusion changes with anatomical observations.

Main Results:

• Optic nerve ADC parallel to fibers increased with development and myelination, while perpendicular ADC remained constant, increasing diffusional anisotropy.
• Trigeminal nerves showed no significant ADC changes in either direction.
• Optic nerve axons transitioned from tortuous to straighter, parallel courses during maturation.

Conclusions:

• Maturation-related anatomical changes, specifically fiber straightening and increased parallelism, explain alterations in longitudinal ADC and diffusional anisotropy.
• These findings highlight the impact of nerve fiber architecture on diffusion metrics.