Investigating microstructural changes between in vivo and perfused ex vivo marmoset brains using oscillating gradient...

Area of Science:

• Neuroscience
• Biophysics
• Medical Imaging

Background:

• Ex vivo models are crucial for studying brain microstructure.
• Perfusion fixation is a common method for preserving brain tissue.
• Understanding fixation-induced changes is vital for accurate interpretation of ex vivo data.

Purpose of the Study:

• To investigate microstructural alterations in brain tissue caused by perfusion fixation.
• To assess the impact of these changes on the application of ex vivo models to in vivo microstructure.
• To utilize advanced diffusion MRI techniques for this investigation.

Main Methods:

• Employed oscillating gradient spin echo (OGSE) and b-tensor encoding diffusion MRI on marmoset brains (in vivo and ex vivo).
• OGSE was used to shorten effective diffusion times.
• b-tensor encoding differentiated isotropic and anisotropic kurtosis; Monte Carlo simulations estimated microstructural changes.

Main Results:

• Perfusion fixation induced significant changes (~50%-60%) in kurtosis frequency dispersion, anisotropic, and isotropic kurtosis.
• Structural MRI revealed an average volume reduction of ~10% post-fixation.
• Monte Carlo simulations suggested extracellular fluid loss, axon beading, and increased dot compartment signal fraction as likely causes.

Conclusions:

• Perfusion fixation causes substantial microstructural alterations detectable by advanced MRI.
• These changes, likely due to fluid loss and axon changes, impact the validity of ex vivo models for in vivo microstructure.
• Exercise caution when extrapolating ex vivo findings to in vivo brain tissue.