Neurite orientation dispersion and density imaging of mouse brain microstructure

Area of Science:

• Neuroimaging
• Biophysics
• Computational Neuroscience

Background:

• Advanced biophysical models like neurite orientation dispersion and density imaging (NODDI) assess brain microstructure.
• Previous NODDI applications in fixed mouse brains were limited by long scan times.
• High-resolution NODDI data from mouse brains were previously unattainable due to acquisition time constraints.

Purpose of the Study:

• To reduce scan time for high-resolution diffusion MRI enabling ex vivo NODDI in mouse brains.
• To establish optimal acquisition parameters for ex vivo NODDI experiments.
• To validate NODDI metrics against histochemical analyses and assess sensitivity to microstructural changes.

Main Methods:

• Modified a 3D diffusion-weighted spin-echo pulse sequence for multi-shell and undersampling acquisition.
• Acquired an 8-shell diffusion dataset at 50 µm isotropic resolution with 384 directions.
• Derived NODDI metrics (NDI, ODI) and compared them with histochemical staining (myelin, neuronal density) and a demyelination model.

Main Results:

• Successfully acquired high-resolution NODDI data in reduced scan times.
• Demonstrated good agreement between NODDI metrics (NDI, ODI) and histochemical measures.
• Showcased NDI's sensitivity to microstructural changes in the corpus callosum using the cuprizone model.
• Identified a three-shell acquisition strategy with at least 64 directions as essential for ex vivo NODDI.

Conclusions:

• Optimized diffusion MRI protocols enable routine high-resolution ex vivo NODDI in mouse brains.
• NODDI provides valuable insights into brain microstructure, correlating with histological findings.
• This method is promising for characterizing brain microstructure in mouse models of neurological disorders.