Figure 2. Delineating fiber covariance networks with orthogonal projective NMF.

opNMF yields a probabilistic parcellation such that each fixel receives a loading score onto each of the 14 networks quantifying the extent to which the fixel belongs to each network. Here, the probabilistic parcellation was converted into discrete covariance network definitions for display by labeling each fixel according to its highest loading. The coloring of fixels is based on the red-green-blue (RGB) convention, which encodes the left-right, anterior-posterior, and inferior-superior directions, respectively. The networks identified include commissural bundles (1, 6, and 7), cerebellar white matter (11, 12, and 13), association bundles (5, 9, 10, 14, and 2), and projection bundles (2, 3, 4, and 8). Network 2 is included both in the association and projection networks because it encompasses the fornix and the cingulum (hippocampus). Network 10 refers to the parietal portion of the superior longitudinal fasciculus (SLF). CC, corpus callosum; CST, corticospinal tract.