Brain age from white matter fiber orientation: 3.54-year mean error across 692 people, and predictions rotate with the input
Brain age prediction no longer relies only on diffusion tensor scalar metrics: white matter fiber orientation distributions (WM-FODs) enter directly as spherical harmonic coefficients, processed by an SE(3) equivariant CNN that preserves their transformation properties under rotation. On 692 participants aged 36-90 from the Human Connectome Project Aging dataset, this combined framework outperformed the evaluated DTI-based models and conventional CNNs; averaging five cross-validation models gave a mean absolute error of 3.54 years and a Pearson correlation of 0.958. The advantage depended on combining WM-FODs with equivariant processing, and accuracy was highest at maximum spherical harmonic order Lmax = 2.