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Is water diffusion restricted in human brain white matter? An echo-planar NMR imaging study
D Le Bihan1, R Turner, P Douek
1Diagnostic Radiology Department, Warren G. Magnuson Clinical Center, National Institutes of Health, Bethesda, MD.
Neuroreport
|July 1, 1993
Summary
Water diffusion in brain white matter is not restricted by myelin sheaths. Our findings suggest water can move across these fibers, challenging previous models of restricted diffusion.
Area of Science:
- Neuroimaging
- Biophysics
- Cellular Biology
Background:
- Water diffusion in brain white matter exhibits significant anisotropy, influenced by myelin fiber orientation.
- A prevailing hypothesis suggests myelin sheaths act as impenetrable barriers, restricting water diffusion transversely to axons.
Purpose of the Study:
- To investigate the role of myelin sheaths in restricting water diffusion in the human brain.
- To test the hypothesis of impenetrable myelin barriers using diffusion time-dependent measurements.
Main Methods:
- Utilized an ultra-fast nuclear magnetic resonance imaging (MRI) technique.
- Acquired in vivo, non-invasive imaging data from the human brain.
- Analyzed the dependence of the diffusion coefficient on diffusion time.
Main Results:
- The observed diffusion coefficient's dependence on diffusion time did not support the model of water restriction by impenetrable barriers.
- Evidence suggests that water can diffuse across myelin fibers at a measurable rate.
- Challenged the long-held assumption of myelin acting as a complete barrier to transverse water movement.
Conclusions:
- Myelin sheaths do not completely restrict water diffusion in brain white matter.
- Water movement across myelin fibers occurs at a measurable rate, implying a more dynamic exchange than previously modeled.
- These findings necessitate a revision of current models explaining water diffusion anisotropy in white matter.