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Updated: Aug 19, 2026
Multiple-mouse Neuroanatomical Magnetic Resonance Imaging
Published on: February 27, 2011
Experimental studies of g-ratio MRI in ex vivo mouse brain
Kathryn L West1, Nathaniel D Kelm1, Robert P Carson2
1Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, United States; Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, United States.
Abstract:
This study aimed to experimentally evaluate a previously proposed MRI method for mapping axonal g-ratio (ratio of axon diameters, measured to the inner and outer boundary of myelin). MRI and electron microscopy were used to study excised and fixed brains of control mice and three mouse models of abnormal white matter. The results showed that g-ratio measured with MRI correlated with histological measures of myelinated axon g-ratio, but with a bias that is likely due to the presence of non-myelinated axons. The results also pointed to cases where the MRI g-ratio model simplifies to be primarily a function of total myelin content.
Insights
This study validates an MRI method for mapping axonal g-ratio, finding it correlates with histology but is influenced by non-myelinated axons. The MRI method shows potential for assessing white matter integrity.
Area of Science:
- Neuroimaging
- Biophysics
- Histology
Background:
- Accurate measurement of axonal g-ratio is crucial for understanding white matter integrity.
- Existing methods for g-ratio mapping have limitations.
- A novel MRI-based method was previously proposed.
Purpose of the Study:
- To experimentally evaluate a proposed MRI method for mapping axonal g-ratio.
- To compare MRI-derived g-ratio with histological measures.
- To investigate the influence of non-myelinated axons and myelin content on MRI g-ratio.
Main Methods:
- Utilized magnetic resonance imaging (MRI) and electron microscopy.
- Studied excised and fixed brains from control mice and mouse models of abnormal white matter.
- Quantified axonal g-ratio using both MRI and histological techniques.
Main Results:
- MRI-measured g-ratio showed a significant correlation with histological g-ratio measures.
- A consistent bias was observed in MRI g-ratio, attributed to non-myelinated axons.
- The MRI g-ratio model was found to simplify to a function of total myelin content in certain conditions.
Conclusions:
- The evaluated MRI method provides a viable approach for mapping axonal g-ratio in vivo.
- The presence of non-myelinated axons necessitates careful interpretation of MRI-derived g-ratio.
- This MRI technique holds promise for non-invasive assessment of white matter pathologies.
