Fig 7.

In vivo model for myelinated axonal diameter. (A) A simplified model of myelinated axon diameter under assumption of an approximation of constant myelin sheath thickness (t_m ~ 0.09 m). (B) The estimated microstructure g-ratio $\left(={\text{d}}_{\text{a}}/\left({\text{d}}_{\text{a}}+2{\text{t}}_{\text{m}}\right)\right)$, where d_a is the axon diameter, and its mean value is 0.69 m (pointed by the red arrow) in the human CC (Aboitiz et al. 1992b; Liewald et al. 2014)). (C) The estimated myelin water fraction ($\text{MWF}=\frac{\pi }{4}\left(1-{\text{g-ratio}}^2\right)$ or $\frac{\pi }{4}\left(1-\left({\text{d}}_{\text{a}}/{\left({\text{d}}_{\text{a}}+2{\text{t}}_{\text{m}}\right)}^2\right)\right)$ as a function of axon diameter. (D) The estimated relation between T₁ and MWF (T₁ = 0.291/MWF +0.05).