Diffusion distinguishes between axonal loss and demyelination in brain white matter

axonal geometry used for the MC simulations showing the intraaxonal space (red), extra-axonal space (blue) and myelin (green). Neurodegeneration is modeled by increasing axonal loss (left to right), and/or demyelination (top to bottom). (b) The simulated tortuosity as a function of the AWF. The full lines represent contours for constant axon number and varying gratio, while the dashed lines represent constant g-ratio and varying axon number. (c) The average values and standard error ellipses for the tortuosity and AWF (corrected for age) in two clinical applications (left: MS, right AD) overlaid on Fig. 1(b). (a)