Fiber orientation-dependent white matter contrast in gradient echo MRI

Area of Science:

• Neuroimaging
• Biophysics
• Magnetic Resonance Imaging

Background:

• White matter (WM) MRI contrast is linked to nerve fiber orientation.
• Myelin is hypothesized as the primary source of this contrast.
• Accurate modeling is crucial for understanding WM contrast and tissue microstructure.

Purpose of the Study:

• To develop and validate a model for myelin's effect on NMR signal evolution in WM.
• To investigate the relationship between myelin sheath properties and gradient echo MRI contrast.
• To provide a framework for novel diagnostic tools in neuroimaging.

Main Methods:

• Simulations and in vivo experiments on human subjects at 7 Tesla.
• Modeling the myelin sheath as a hollow cylinder with anisotropic magnetic susceptibility.
• Employing a two-pool model accounting for water in the sheath with reduced T2 relaxation and spin density, including exchange.

Main Results:

• The proposed hollow cylinder model accurately characterizes WM signal magnitude and phase.
• The model incorporates anisotropic magnetic susceptibility of the myelin sheath.
• The two-pool model effectively describes water properties and exchange within the sheath.

Conclusions:

• The hollow cylinder model offers an accurate and simple framework for WM contrast analysis.
• This model facilitates understanding the impact of WM microstructure on MRI signals.
• The findings pave the way for exploiting WM microstructure effects in clinical MRI for diagnostics.