Fig. 2.

Measures of diffusion are differentially related. A. Average Spearman’s correlations between diffusion metrics in white matter. The top triangle depicts correlations derived from multi-shell DTI fitting, and the bottom triangle reflects correlations derived from single-shell fits. In the corresponding sampling schemes, the distance of each dot from the center of the sphere represents the b-value of a single volume, and the angle represents its b-vector. B. Average correlations between single and multi-shell DTI metrics. FA = fractional anisotropy, MD = mean diffusivity, AD = axial diffusivity, RD = radial diffusivity, ICVF = intracellular volume fraction, ODI = orientation dispersion index, ISOVF = isotropic volume fraction, RTOP = return-to-origin probability, RTAP = return-to-axis probability, RTPP = return-to-plane probability.