Fig. 10.

(a) Signal contribution of extra-axonal space calculated from Monte Carlo simulations of parallel cylinders with a Gamma distribution of radii corresponding to the spinal cord ROI values. The signal is the average over the 12 gradient directions used for computing TDR₁₂. The contributions are shown for the different waveforms (left to right), as well as for different b-values and maximum gradient strengths (markers). The largest differences observed for b = 8 ms/μm² do not exceed 0.03 for the simulated substrates. The dotted line represents 0.01 signal difference. b) Optimised TDR (12 gradient directions, optimised waveforms) as a function of axon diameter for different protocols, when particles in the MC simulation are distributed either uniformly (‘x’) or just inside the cylinders (‘□’). c) Optimised intra-axonal TDR (12 gradient directions, optimised waveforms) as a function of axon diameter for dispersed cylinders following a Watson distribution with different concentration parameters κ = {1, 6, 100}. The TDR values overlap for the different κ values. c) Comparison of optimised TDR for the data acquired with b = 20 ms/ μm² and 8 ms/ μm² for the two gradient strengths.