Diffusion‐weighted signal from the genu ROI, averaged over the six voxels. Across each column and row, the signal pertains to one of the gradient strengths or pulse times δ used; in each subplot, the six shells shown in different colours are Δ‐specific, increasing in value (22, 40, 60, 80, 100, 120 ms) from top to bottom. Inside the legend, the b value is in s/mm2 units; here, the HARDI shells kept for testing are those marked with a star; the remaining shells comprise the training data. On the x‐axis is the cosine of the angle between the applied diffusion gradient vector G and the fibre direction n. Some models in this study omit data outliers; two such data points are shown in the bottom‐left subplot with vertical arrows — obviously each model has its own criteria for determining the outliers