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Diffusion Tensor Magnetic Resonance Imaging in the Analysis of Neurodegenerative Diseases
Published on: July 28, 2013
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Mapping mean axon diameter and axonal volume fraction by MRI using temporal diffusion spectroscopy.
Junzhong Xu1, Hua Li2, Kevin D Harkins3
1Institute of Imaging Science, Vanderbilt University, Nashville, TN 37232, USA; Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN 37232, USA; Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37232, USA.
Neuroimage
|September 17, 2014
Summary
This study introduces oscillating gradient spin echo (OGSE) MRI to accurately measure mean axon diameter and intra-axonal volume fraction, improving sensitivity to small axons for neurodegenerative disease research.
Area of Science:
- Neuroimaging
- Biophysics
- Quantitative MRI
Background:
- Mean axon diameter and intra-axonal volume fraction are clinically relevant for understanding nerve conduction velocity and neurodegenerative diseases.
- Conventional diffusion-weighted MRI using pulsed gradient spin echo (PGSE) has limitations in accurately assessing small axons (<2μm) due to long diffusion times, often overestimating mean axon diameter.
Purpose of the Study:
- To develop and validate a non-invasive MRI method for quantifying nerve morphology, specifically mean axon diameter and intra-axonal volume fraction.
- To enhance sensitivity to small axons, which are affected in various neurodegenerative conditions.
Main Methods:
- Utilized oscillating gradient spin echo (OGSE) diffusion sequences with variable frequency gradients and short effective diffusion times (1-5ms) in rat spinal white matter tracts.
- Incorporated frequency-dependent diffusion rates to model non-Gaussian diffusion in the extra-axonal space, validated by histology-based simulations.
- Analyzed OGSE data to derive mean axon diameters and intra-axonal volume fractions.
Main Results:
- The OGSE method successfully derived mean axon diameters ranging from approximately 1.27μm to 5.54μm in rat spinal white matter.
- The derived values showed good agreement with histology, demonstrating high sensitivity to small axon diameters (<2.5μm).
- This contrasts with previous PGSE methods that showed lower sensitivity and potential overestimation of smaller axon diameters.
Conclusions:
- The oscillating gradient spin echo (OGSE) method provides a robust framework for non-invasively quantifying nerve morphology with improved sensitivity to small axons.
- This technique holds significant potential for clinical applications in diagnosing and monitoring neurodegenerative diseases that affect specific axon populations.
