Regional Homogeneity (ReHo) is a voxel-based measure of brain activity which evaluates the similarity or synchronization between the time series of a given voxel and its nearest neighbors.

This measure is based on the hypothesis that intrinsic brain activity is manifested by clusters of voxels rather than single voxels. Kendall’s coefficient of concordance (KCC) is used as an index to evaluate the similarity of the time series within a cluster of a given voxel and its nearest neighbors. ReHo requires no a priori definition of ROIs and can provide information about the local/regional activity of regions throughout the brain.